Raport de Cercetare 1.1

ISSN 1302 - 1672

Supplement to Volume 8 (2005)

Journal of the Balkan Geophysical Society Volume editors:

Dr. Radu G. Dimitriu, Dr. Amuliu Proca, Dr. Dumitru Ioane

CONTENTS1: Keyote Address KN - 01

Earthquake Seismology, Exploration Seismology and Engineering Seismology: How Sweet It Is - Listening to the Earth by Oz Yilmaz

Seismic Acquisition and Procession O1 - 01 O1 - 02 O1 - 03 O1 - 04

Prestack Scalar Reverse-Time Depth Migration of Three-Dimensional Elastic Seismic Data by Robert Sun, George A. McMechan, Chen-Shao Lee Time-Shift Wave-Equation Imaging by Paul Sava, Sergey Fomel A Grid-Enabled System for 3-D Seismic Imaging by Dimitri Bevc, Iulian Musat, Mihai Popovici, Sergio E. Zarantonello A Pragmatic View of Land Multiple Attenuation Technology by Panos Kelamis

Environmental, Engineering and Archaeo-Geophysics O2 - 01 O2 - 02 O2 - 03 O2 - 04 O2 - 05 O2 - 06 O2 - 07

Environmental Geophysics - Challenges for the Future by Snezana Komatina-Petrovic Geoelectrical Investigation of Dams in Georgia – CIS by Antonio Bratus, Elvio Del Negro, Daniel Nieto Yabar Outlook on the Possibility for Slope Stability Evaluation According to Petrophysical Data by Alfred Frasheri Uncertainty and Ambiguity of Measurements in Wide Area Networks of Sensing Devices Measuring Geophysical Parameters by John Sarivougioukas, George Sideris, Pavlos Sotiropulos, James Baker Development of a Non-Destructive Pulse Neutron Multiple Detector Tool by George Sideris, Pavlos Sotiropoulos, Kalevi Rasilainen, Klaus Buckup, James Baker, Robert J. De Meijer Magnetic Susceptibility as a Proxy for Heavy Metals in Urban Areas From Romania by C.G. Panaiotu, L. Dumitrescu, C.E. Panaiotu, E. Bilal Numerically Modeling the Unthinkable: When Reactor Core Melt Meets Groundwater by Ioan Vlad

Regional Geophysics and Geotectonics O3 - 01 O3 - 02

1

Geophysical Data on Structure of the Albanides by Salvatore Bushati Intramoesian Fault on Bulgarian Territory: Available Geophysical Data by Stefan Shanov, Antoaneta Boycova, Asen Mitev

Note: Press yellow buttons to open corresponding PDF files.

O3 - 03

O3 - 04 O3 - 05 O3 - 06

Rational geophysical strategy of buried active faults delineation and monitoring: Russian Platform and Romanian Carpathians Examples by V.G. Budanov, D. Zugravescu, C.S. Sava, Lucian Besutiu, V.I. Leontiev, V.B. Dubovskoy Investigation of Distribution of Volcanic Vents in Cappadocia Using Magnetic Method by Aydin Buyuksarac, Muzaffer Ozgu Arisoy, Ozcan Bektas, Abdullah Ates Influence of Evaporites Deposits on the Overthrusting Model of External Albanides Based on Seismic Data by Stavri Dhima, Ilia Gjermani, Shaqir Nazaj Birth, development and closure of the Dacian Basin (Upper Neogene, Romania) by Dan Jipa, Radu Olteanu

Seismic Acquisition and Processing O4 - 01 O4 - 02 O4 - 03 O4 - 04 O4 - 05

Riemannian Wavefield Extrapolation of Seismic Data by Jeffrey Shragge, Paul Sava, Guojian Shan, Biondo Biondi, Sergey Fomel Azimuth Moveout (AMO) for Land Data Regularization and Interpolation by Alexander Mihai Popovici, Sean Crawley, Dimitri Bevc, Dan Negut Microseismic Sounding Method - Experimental Background - Cases of Application by A.V. Gorbaticov, A.V. Kalinina, J. Arnoso, A.L. Odintsov, I.V. Getmanov Which Depth Imaging Method Should You Use? A Roadmap In The Maze of 3-D Depth Imaging by D. Bevc, B. Biondi Land Seismic Data Analysis – A review by Oz Yilmaz

Environmental, Engineering and Archaeo-Geophysics O5 - 01 O5 - 02 O5 - 03 O5 - 04

O5 - 05 O5 - 06 O5 - 07

Investigation of the Roman Defence Wall by Using Multi-Electrode Resistivity System by Mehmet Emin Candansayar Recent Applications of Archeological Prospection in Greece by Gregory N. Tsokas, Panagiotis I. Tsourlos, George Vargemezis, Alexandros Stampolidis MASW Measurements for Seismic Site Effect Evaluation by L. Hermann, A.I. Kanli, A. Pinar, Zs. Pronay, P. Tildy, E. Toros Local Site Effects on Structural Damages in a Residence of Gölcük Town During the August 17, 1999 Kocaeli Eartquake : A Case Study by Metin Asci, Ferhat Ozcep, Nuray Alpaslan, Turker Yas, Tahir Serkan Irmak, Ergin Ulutas, Ismail Talih Guven, Berna Tunc, Taciser Cetinol, Deniz Caka, Suleyman Tunc, Serif Baris, M.Firat Ozer On the Use of Microtremor Data for Microzonation in Buyucekmece (Istanbul), Turkey by Savas Karabulut, Ilhan Osmansahin A Quality Classification of Building Stones from P-wave Velocity and its Application to Stone Cutting with Gang Saw by S. Kahraman, U. Ulker The Contribution of Geological - Geophysical Methods to Determine the Water-Bearing Capacity of the Neogene Deposits of the Ballsh Sincline by Mihail Gjoka, Xhemil Buzi, Majlinda Mece, Arqile Piperi, Xhuljeta Hila

Regional Geophysics and Geotectonics O6 - 01 O6 - 02

Relationships Between Tectonic Elements and Crustal Reflectivity-A Case From Moesian Platform by J. Matresu, V. Raileanu, C. Dinu Considerations on the SE Extent of the Tornquist-Teisseyre Zone on the Romanian Territory by L. Besutiu, L.A. Atanasiu, A. Damian, M. Horomnea, L. Zlagnean

O6 - 03

Seismic Evidence for Salt- and Volcanism-Related Tectonics in the Eastern Transylvanian Basin by Alexandru Szakacs, Csaba Krezsek

O6 - 04

Crustal Structure and Phanerozoic (Pre-Black Sea Opening) Orogenic Processes on and Near the Southern Margin of Baltica: A EUROPROBE Overview by Randell Stephenson

Seismic Acquisition and Procession O7 - 01 O7 - 02 O7 - 03 O7 - 04 O7 - 05 O7 - 06

Application of Seismic Trace Interpolation to a Land Seismic Reflection Dataset by I. Panea, G.G. Drijkoningen, R. Stephenson, V. Mocanu Wave-Equation Depth Imaging in an Integrated Regional Framework by Alexander Mihai Popovici, Sean Crawley, Fusheng Yang, Michael Davidson, Mark Leander, Ken Mohn Application of High Resolution Seismic Surveys in Shallow Fresh Water by Luca Baradello, Francesco Fanzutti, Daniel Yabar Nieto Seismic Data Acquisition in Urban and Industrial Zones by Slobodan Z. Stanic, Katarina Z. Djordjevic, Zivko M. Pavlovic, Kosta V. Negovan Seismic Data Contribution in the Ionian Zone Limestone Structure Detection Under Kruja Zone Orogen in Tirana Area) by Vilson Silo, Daut Yzeiraj, Gentiana Merkaj, Shpresa Silo Which Multiple Removal Method Is Better? by Navid Amini

Gravity, Magnetics and Geomagnetism O8 - 01 O8 - 02 O8 - 03 O8 - 04 O8 - 05

The Airborne Geomagnetic Map of Romania: A New Look by Viorel Cristian Sprinceana, Lucian Besutiu The Use of Magnetic Data in Mapping Cretaceous Strata of the Alberta Foothills, Canada by Cristian I. Abaco, D.C. Lawton Complex Attributes Analysis of the Bouguer Gravity of Greece by Hamza Reci, Gregory N. Tsokas, Constantinos B. Papazachos, Alexandros Stampolidis, Dimitrios Papagiotopoulos Block Rotations and Curie Point Depth of the Marmara Sea NW Turkey Inferred From Aeromagnetic Data by Abdullah Ates, Funda Bilim Two and Three Dimensional Crustal Structure of the Eastern Pontides (NE Turkey) by Nafiz Maden, Kenan Gelisli, Osman Bektas, Yener Eyuboglu

Plate Tectonics Kinematics and Geodynamics O9 - 01 O9 - 02 O9 - 03 O9 - 04

Geological and Geophysical Paradoxes of the Mid-Atlantic Ridge Structure: Some Doubts Related to the Main Tenets of Plate Tectonics by Vladimir G. Budanov Recent Dynamics of East Romanian Fault Zones Produced by 3C Micro Seismic Screenings by Andrey B. Beklemishev, Vladimir G. Budanov, Lucian Besutiu, Constantin S. Sava CERGOP2/Environment Project - Three Dimensional Plate Kinematics in Romania by Tiberiu Rus, Lucian Besutiu, Gabriel Stanescu, Ion Stoian, Ion Buse Ten Years of GPS Observations in Romania Distinguished Lecture by B.A.C. Ambrosius, A.G.A. van der Hoeven, V. Mocanu, L. Munteanu, W. Spakman, G. Schmitt

Electrical, Electromagnetics and GPR O10 - 01

Faults Mapping Using Electrical Resistivity Tomography (E.R.T.) by Ilie Oancea, Alexandru Petrescu

O10 - 02 O10 - 03 O10 - 04 O10 - 05 O10 - 06

Hybrid Genetic Algorithms Derived from The Evolution Theories by Ahmet T. Basokur, Irfan Akca, Nedal W.A. Siyam 2-D Lamarckian Inversion of Resistivity Data by Irfan Akca, Ahmet T. Basokur DC Resistivity Map of Hungary, Based on the National Geoelectric Database by Laszlo Sores, Janos Kiss Resistivity Arrays in the Detection of Buried Bodies by G. Apostolopoulos, C. Orfanos, G. Amolochitis, K. Leontarakis, S. Stamataki GPR in a Single Borehole for Determining Complex Geological Structures by Dieter Eisenburger, V. Gundelach

Gravity, Magnetics and Geomagnetism O11 - 01 O11 - 02 O11 - 03 O11 - 04 O11 - 05

2D Modeling on the Base of Subsurface Gravity Measurements by Ivana Vasilievic Evaluation of Different Receiver Orientations and Receiver Separations in Magnetic Gradiometer Method by M. Ozgu Arisoy, Emin U. Ulugererli Interpretation of Potential Field Data Based on the Field and Enhanced Magnitude by Arben Lulo Non-Tidal Gravity Changes across Major Lithosphere Boundaries on the Romanian Territory by L. Besutiu, L. Zlagnean, M. Horomnea The Secular Variation of the Geomagnetic Field in Romania in the Time Interval 1980 - 2004 by C. Demetrescu, M. Ene, V. Dobrica

Global Changes and Marine Geosciences O12 - 01 O12 - 02 O12 - 03 O12 - 04 O12 - 05 O12 - 06

Variability of the Temperature-Dependent Susceptibility of Loess-Paleosol Deposits from Romania by C.G. Panaiotu, V. Hoffmann, M. Popa, C. Necula Ground Surface Temperature Variations in the Last 200 Years in Romania, from Inversion of Borehole Temperature Data by C. Demetrescu, M Tumanian, V. Dobrica, C. Boroneant Interaction of Petroleum Deposits to Atmosphere in Formation of Tornadoes by Shuji Mori Harvesting the Gas Hydrates in the Black Sea: Technology and Economics by Constantin Cranganu, Boyko Nitzov Multibeam Backscatter Seabed Classification by X. Monteys, D. Inamdar Altimeter Range Determination and Applications Using a Transponder by E. Cristea, W. Hausleitner, P. Pesec

Remote Sensing and Satellite Imagery O13 - 01 O13 - 02 O13 - 03

Satellite Remote Sensing and GPS Data for Seismic Hazard Analysis in Vrancea Area by Maria Zoran, Doru Mateciuc Recognition of Iron-Containing Ore Minerals and Rocks Using Remotely Sensed Data by D. Borisova, H. Nikolov, M. Danov, R. Kancheva Tectonic Alignments Analysis in Oas-Gutai Mts. Area (NW Romania) by Remote Sensing and Geophysical Methods by Dorin Dordea, Viorel Cristian Sprinceana, Anca Dobrescu

Seismic Modelling and Interpretation O14 - 01

The 3D Seismic Performance for the Thin Reservoir Evaluation in the Moesian Platform (Bilciuresti Area) by Mihai Tanasa, Constantin Manea, Marin Cismaru

O14 - 02 O14 - 03 O14 - 04 O14 - 05 O14 - 06

Do Seismic Attributes Reduce Exploration Risk in the Carpathian Foredeep, Northern Romania? by John Donato, Laurentiu Ionescu Advancing 3D Seismic Interpretation Methods for Unconventional Fractured Gas Reservoirs by James J. Reeves 3D Seismic Integrated Interpretation. The Oligocene of Tutana-Zarnesti Area – Getic Depression by Mirela Vasiliu, Eugenia Nicolae, Irina Cinca A Crustal Structure Model from the North Dobrogea Through the Vrancea Region to the Western Transylvania by V. Raileanu, F. Hauser, W. Fielitz, C. Dinu, A. Bala, M. Landes, C. Prodehi Tomography and Non-Linear Inversion in the Southeast Carpathians by R.B. Raykova, G.F. Panza

Seismology and Earthquakes O15 - 01 O15 - 02 O15 - 03 O15 - 04 O15 - 05 O15 - 06

The Use of P- And S-Wave Pulses to Identify Seismic Wave Attenuation in South Eastern Carpathians Area by M. Popa, E. Popescu, A.O. Placinta, M. Radulian, B. Grecu, G.F. Panza Preliminary Results of Shear Waves Splitting at Romanian Broad-Band Network by Marian Ivan, Mihaela Popa, Daniela Ghica Vrancea Intermediate-Depth Earthquakes in Romania - Seismicity and Mechanisms by Nobuo Hurukawa, Mihaela Popa, Mircea Radulian Temporal Variation Profiles of Seismicity along Seismotectonic Zones in Greece by Ioannis Baskoutas, George Papadopoulos, Theodora Rontoyanni, George Sideris 3D P-Wave Structure Beneath Sultandagi Afyon, Turkey From Local Earthquake Tomography by Aysun Nilay Dinc, Abdulah Karaman Stochastic Modelling of the Relaxation Process After the M=9.0, Sumatra Earthquake of December 26, 2004; Preliminary Analysis by D. K. Gospodinov, V. Karakostas, R. Papadimitriou

Borehole Geophysics and Physical Properties of Rocks O16 - 01 O16 - 02 O16 - 03 O16 - 04 O16 - 05

A Study Regarding the Relationships Between Dynamic Parameters and Drillability Index of Some Rocks by Rasit Altindag, Zuheyr Kamaci, Ali Etiz, Nazmi Sengun Bayesian Rock-Physics Inversion for Fracture Characterization by Diana Sava, Gary Mavko Determination of Water Saturation for Anisotropic Formations by I. Malureanu Using Artificial Neural Networks to Predict Abnormal Pressures in the Anadarko Basin, Oklahoma by Constantin Cranganu Dominante Rates of Natural Radioelements as an Indicator of Concentracion and Precious Elements and Polymetals by Anastas Dodona

Heat Flow and Geothermal Resources O17 - 01 O17 - 02

Calculation of Heat Flow and Pn Velocity Values of West Anotalia Using Curie Point Depth Values by Metin Mihci, Aydin Buyuksarac, Ozcan Bektas, Abdullah Ates Exploration of a Low-Temperature Hydrothermal System Using Geophysical Methods in Anzer Glacial Valley, İkizdere, Rize, Turkey by Abdulah Karaman, Aysun Nilay Dinc

O17 - 03

O17 - 04

Time Dependent Thermal State of the Litosphere in the Foreland of the Eastern Carpathians Bend. Insights from New Geothermal Measurements and Modelling Results by C. Demetrescu, H. Wilhelm, M. Tumanian, A. Damian, V. Dobrica, M. Ene The Type Curves With Skin and Wellbore Storage Effect for Analyzing Interference Test by Tom Age Jelmert, Afar A. Mbai

Seismic Modelling and Interpretation O18 - 01 O18 - 02 O18 - 03

O18 - 04

O18 - 05

S-Wave Coda Q Estimates for the Regions of Fethiye-Burdur, Büyükmenderes and Antalya Golf-Akşehir in SW Turkey by Sakir Sahin, Murat Erduran, Omer Alptekin, Ozcan Cakir, Timur Tezel Structural Characteristics, Seismic Facies and Depositional Framework of Eocene Deposits, in Central Romanian Black Sea Offshore by Corneliu Dinu, Dorina Tambrea, Adriana Raileanu Incoherent Acoustic Response of Visco-Plastic Salt Intrusions as Being Diagnostic for Abnormal Fluid Pressure Regimes in the Cilicia-Adana Basin, NE - Mediterranean Sea by Mustafa Toker, Vedat Ediger The Orientation of the Nonlinear Stress-Strain Relations to Acoustic Parameters and Elastic Modulus for Irreversible Plastic Strain Field in the Cilicia-Adana Basin, NE - Mediterranean Sea by Mustafa Toker, Vedat Ediger Analytic Solution to NMO-Velocity Surface in TI Media With an Arbitrary Symmetry Axis by Jianzhong Zhang, Chen Yao, Chongtao Hao, Minggang Cai

Seismology and Earthquakes O19 - 01

O19 - 02 O19 - 03 O19 - 04

Empirical Attenuation Relationship of PGA Based on 17 August 1999 Kocaeli and 12 November 1999 Duzce Earthquakes Data by Ergin Ulutas, Tahir Serkan Irmak, Ismail Talih Guven, Berna Tunc, Taciser Cetinol, Deniz Caka, Nuray Alpaslan, Suleyman Tunc, Metin Asci, Serif Baris, Mithat Firat Ozer Estimates of Stress Directions by Inversion of Earthquake Fault Plane Solutions From North Anatolian Fault Zone to North Anatolian Through by Nihan Sezgin, Ali Pinar Potassium Magnetics Technology for Earthquake Research by Ivan Hrvoic Predictability and Unpredictability of Large Earthquakes, and the Prediction of Vrancea Earthquakes by George Purcaru

Exploration Case Histories and Risk Management O20 - 01 O20 - 02 O20 - 03 O20 - 04 O20 - 05

The Pre-Salt Prospectivity of the Central Transylvanian Basin - A Key to the Last UnDrilled Play in Romania ? by R. Grunwald, U. Schulz Reservoir Optimization of the Southern License Area of Priobskoye Field, Western Siberia, Russia by Tatyana Kruchkova, Vadim Savostikov, Nik Kalita, Hector Ruiz, Edgar Carvajal African Platform - Albania Thrust Belt Relationship and Hydrocarbon Prospects Trends by Engjell Prenjasi, Stavri Dhima, Shaqir Nazaj, Frederik Qyrana Role of Geophysics in the New Strategy of the Ministry of Environment and Water Management by Sulfina Barbu, Nicolae Heredea The Legal Framework that Controls the Exploration Activities in Romania. Results of the Operating Petroleum Agreements and New Opportunities by M. German, N. Pandele, P. Cristian, P. Aurel

O20 - 06

Risk Management For Competitive E&P by N. Pandele, G. Duta, D. Caminschi, A. Sauciuc, M. Zamfirescu, D. Popescu, A. Dragomir, C. Popa

Seismic Acquisition and Processing P1 – 01 P1 – 02 P1 – 03 P1 – 04

Seismic Registration of the Plio- Quaternary Deposits by Spiro Bonjako, Ilia Fili, Marjeta Bonjako, Luan Hasanaj Algorithms for Numerical Evaluation of Spectra in Microseismic by Virgil Bardan, Dorel Zugravescu, Laurentiu Asimopolos Possibilities of Application Comparative Analysis Seismic Migration in 2D Seismic Data Processing by Slobodan Z. Stanic, Ratko Ruzic, Ljiljana Zoric, Zorica Vitas-Dokic Wavelet Decomposition as a Tool for Seismic Random Noise Removal by Hosein Hashemi, Navid Amini

Engineering, Environmental and Archaeo-Geophysics P2 – 01 P2 – 02 P2 – 03 P2 – 04 P2 – 05 P2 – 06 P2 – 07 P2 – 08 P2 – 09

The Water-Saturated Rock Searching and Mapping by Geoelectric Methods by S.P. Levashov, N.A. Yakymchuk, I.N. Korchagin, Yu.M. Pyschaniy, Yu.N. Yakymchuk Use of Geoelectric Methods for the Geological-Engineering Conditions Estimation within the Bridge Construction Sites by S.P. Levashov, N.A. Yakymchuk, I.N. Korchagin, E.P. Ivanchenko, N.G. Dravert Using Geophysical Methods to Identify Alteration Zones in an Abandoned Mining Site by J. Carvalho, E. Ramalho, S. Barbosa Determination of Karst and Water-Bearing Levels with Geophysical Methods in Jonike Zone by Sami Nenaj, Hamza Reci, Violeta Azizaj, Halil Hallaci Spectral Analysis of Acceleration Records for Blasts in Yalincak Town of Trabzon by Yusuf Bayrak, Hakan Karsli, Serkan Ozturk, Dilan Tunc Geophysical Methods for the Study of the Interaction Between the Retainine Wall and the Unstable Ground by V. Ciszkowski, L. Bogateanu, G. Popescu, G. Ticu, M. Ciuperceanu Georadar Method to Monitoring Railway Infrastructure by V. Ciszkowski, P.Curcaneanu, E. Oltean, L. Bogateanu, G. Ticu, M. Ciuperceanu Implementation of Geophysics in Contaminant Hydrogeology by Snezana Komatina-Petrovic Seismic Acoustic Research on Identification of Archeological Sites in Submersible Zones by Sorin Anghel, Gabriel Ion

Regional Geophysics and Geotectonics P3 – 01 P3 – 02 P3 – 03 P3 – 04 P3 – 05

Stratigraphic Interpretation of Depositional Sequences at the Aegean Sea Exit of Canakkale Strait by Bedri Alpar Upper Crustal Structure of The Vrancea Zone and Focsani Basin From Seismic Velocity Modelling and Potential Field Data by A. Bocin, R. Stephenson, A. Tryggvason, F. Hauser, V. Mocanu, L. Matenco Subhorizontal Fabric of the Transylvanian Lithosphere from The DRACULA I Profile by Melvin A. Fillerup, James H. Knapp, Camelia C. Knapp Geodinamic Evolution of the Eastern Carpathians - Black Sea Region by Ion Morosanu Synoptic Aero Magnetic and Gravity Maps Implementation of The Oas - Gutai - Tibles Mountains (Romania) by Viorel Cristian Sprinceana, Adrian Popescu, Cristina Petrescu, Steluta Prisecaru, Mihai Nedelcu, Vlad Zorilescu, Mircea Albaiu

P3 – 06 P3 – 07 P3 – 08 P3 – 09 P3 – 10

Tectonic Controls on The Coal Formation in the Ptolemaida Basin (North Of Greece) by Daniela Mitru, Constantin Pene Study of the Salt Mechanism in the Transylvanian Basin by Constantin Pene, Octavian Coltoi The Microfabric of the Crystalline Rocks from Badeanca Valley, Leaota Mts, Romania by Ema Bobocioiu Caracas, Denisa Jianu, Gheorghe C. Popescu Almas-Stanija: Epithermal Mineralizations Interrelated with an Underlying Porphyry Copper System (Southern Apuseni Mountains, Romania) by Tiberius Popa, Silvia Popa The Response of the Intraplate Mesozoic Basins at the Southern Margin of the European Plate to the Compressional Event in the Northern Tethys at the Triassic – Jurassic Transition by J. Swidrowska, M. Hakenberg, A. Seghedi, B. Poluchtovich, I. Vishniakov

Geomagnetism, Palaeomagnetism and Magnetostratigraphy P4 – 01 P4 – 02 P4 – 03 P4 – 04 P4 – 05 P4 – 06 P4 – 07

An Analysis of the Geomagnetic Storm in Local Coordinates and Time by B. Srebrov, I. Cholakov Magnetic Properties of the Typical Ukraine Soils. Results of the Investigations by Anatoliy Sukhorada, Aleksandr Menshov Magnetostratigraphy of the Upper Sedimentary Stratum near Hole DSDP-159 (Pacific Ocean) by M.I. Malakhov, G.Yu. Malakhova, E.I. Vedernikov Magnetic Rheologic Model of the Late Paleomagnetic Record in Deep-Sea Sediment by M.I. Malakhov, Ya.L. Solyanikov, D.M. Malakhov Evolution of the Geomagnetic Field in the South-East Europe at Different Epochs by L.A. Atanasiu, D. Zugravescu, M. Mandea, M. Roharik The Romanian Network of Geomagnetic Repeat Stations. Results of the 2003-2004 Survey by C. Demetrescu, M. Ene, A. Soare, V. Dobrica, G. Cucu, M. Tumanian A Comparison Between Local and Global Models of the Geomagnetic Reference Field for the Romanian Territory by Viorel Cristian Sprinceana, Mihai Nedelcu

Seismic Modelling and Interpretation P5 – 01 P5 – 02 P5 – 03 P5 – 04 P5 – 05 P5 – 06 P5 – 07 P5 – 08 P5 – 09

Regional Deep Petrovelocity Modeling of the Crust according to the Data of PTExperiments by Valery A. Korchin, Peter A. Burtnyi, Elena E. Karnaukhova Application of Advance Imaging Technique to Multi-Channel Shallow Seismic Reflection Data by Zakir Kanbur Fault Geometry of Tekirdag Basin, Marmara Sea, Turkey by Seismic Imaging Technique by Zakir Kanbur Examination of Seismic Data and Attributes by Imaging Techniques by Zekeriya Korkmaz, Hakan Karsli Geological Construction of the Selenica - Ramica Area Based on the Seismic Data Interpretation by Kristofor Jano, Vlashi Nakuci, Agim Mesonjesi, Ermira Jano, Marjeta Nakuci Direct Hydrocarbon Indicators by Mihai Tanasa The Evidence of New Structures in Dumre Region Explained by the GeologicalGeophysical Data by Luftar Bandilli, Sonila Marku, Majlinda Mece, Kristaq Jano Petroleum System’s Hydrocarbon Prospect in Romanian Sedimentary Basin by R. Negulescu, M. Axente, N. Ivanoiu Presence of Carbonatic Structures under Throw of Kruja Zone Based on The Seismic New Data in Elbasani Region by Piro Dorre, Vilson Silo, Lili Thomai

P5 – 10 P5 – 11

Integration of Advanced Multifocusing Seismics with Potential Data Analysis: Heletz Oil Field (Central Israel) Example by Alex Berkovitch, Israel Binkin, Lev Eppelbaum, Nathan Scharff, Emil Guberman Construction 3d Structural Model of an Oil Prospect Based on Seismic and Well Log Data by Ho Trong Long, Bui T.T. Huyen, Keisuke Ushijima.

Gravity and Magnetics P6 – 01 P6 – 02 P6 – 03 P6 – 04 P6 – 05

Analysis of Aeromagnetic Anomalies Related by Baklan Granite in S of Muratdagı, W Turkey by Erdinc Oksum, M. Nuri Dolmaz, Ali Etiz, Selman Aydogan, Ibrahim Aydin New Results of the Analysis of the Alcala De Ebro (Zaragoza, Spain) Gravity Anomaly with Point Sources by Zh. Zhelev, T. Petrova, F. Montesinos, R. Vieira, A. Camacho Some Results of Magnetic Regional Survey, Carried Out in Rehova-Erseka Area by Petrika Kosho, Shpresa Dema, Suzana Ballushi, Mimoza Papaqako. Geophysical Investigations During the 13th Bulgarian Antarctic Expedition 2005 by N. Krastev, N. Dimov, Petar Stavrev, V. Stanchev, R. Raditchev, M. Georgiev, D. Jordanova Considerations on the Geologic Signification of the Low Gravity Anomaly Teius – Turda – Puini – Dej by Justin Andrei, Ligia Narcisa Atanasiu, Paul Cristea

Electrical, Electromagnetics and GPR P7 – 01 P7 – 02 P7 – 03 P7 – 04 P7 – 05 P7 – 06 P7 – 07

Geoelectrical Models of Quaternary Depositions in Lowland of Adriatic Sea, Albania by Piro Leka & Fatbardha Vincani Resistivity Responses of Different Arrays for Sphere Model Using Image and FEM Methods by Sedat Yilmaz Express-Technology of Geoelectric and Seismic - Acoustic Investigations in Ecology, Geophysics And Civil Engineering) by S.P. Levashov, N.A. Yakymchuk, I.N Korchagin, Yu.M Pyschaniy The Use of Geophysical Methods in the Investigation of Subsurface Waters in Albania by Llesh Lleshi, Violeta Azizaj, Hamza Reci, Suzana Ballushi, Shpresa Dema An Approach to Interpretation of Tilt Angle Values by Using Edge Detection Techniques by Emre Timur CSAMT and VES Explorations in Salihli (Manisa) Geothermal Field by Sinem Temimhan, Emre Timur, Coskun Sari, Ergin Ulutas, Mustafa Ergun The Results Comparison Obtained Through the Electrometric and Georadar Method within the Studies Regarding the Pollution Degree of the Underground with Oil Products by Adrian Diaconu, Victor Ciszkowski, Luminita Danciu

Global Changes and Marine Geosciences P8 – 01 P8 – 02 P8 – 03

Geoelectric Investigations of Crustal Inhomogeneities at the Antarctic Peninsula Area by S.P. Levashov, N.A. Yakymchuk, I.N. Korchagin, V.D. Solovyov, Yu.M. Pyschaniy Statistical Modelling of Extreme Precipitation in the Czech Republic using a Regional Approach by Jan Kysely, Jan Picek A Bidimensional Mathematical Model of Coastal Morphology Produced Under Waves Actions by Constantin Bondar

Remote Sensing and Satellite Imagery P9 – 01 P9 – 02 P9 – 03

Variation of The Sf. Gheorghe River Effluent Plume using Remote Sensing, Danube Delta-Black Sea by Cornel Olariu, Gheorghe V. Ungureanu, Adrian Stanica Geophysical Analysis of Rupture Fabric in Jastrebac Mountain by M. Marjanovic, M. Cvetkovic A Field Wlan for Agro-Meteorological Data Collection by G. Georgiev, D. Petkov, H. Nokolov

GIS, Databases and Digital Mapping P10 – 01 P10 – 02 P10 – 03

Gravity Network of Serbia - History and New Measurements by Oleg Odalovic, Miroslav Starcevic Geoinformatization of Geophysical Data for Management of Natural Resources In Region of Tirana-Durres-Kabaje, Albania by Fatbardha Vincani, Piro Leka Digital Petroleum Databank as a Powerful Tool for Future Need's Prediction of Oil Companies (Experiences and Solutions) by Navid Amini, Hosein Hashemi

Seismology and Earthquakes P11 – 01 P11 – 02 P11 – 03 P11 – 04 P11 – 05 P11 – 06 P11 – 07 P11 – 08 P11 – 09 P11 – 10 P11 – 11

Statistical Analysis of the Aftershock Sequences that Occurred in Turkey During 19952004 by Serkan Ozturk, Yusuf Bayrak Mechanical Coupling of Mantle Seismicity and Crustal-Scale Faults in the SE Carpathian Foreland by Dana Mucuta, Camelia C. Knapp Iran Earthquakes and the Crustal Structure Inferred from Rayleigh Waves Observed in Turkey by Timur Tezel, Murat Erduran, Ozcan Cakir, Omer Alptekin Characteristics of the Focal Mechanism of the Earthquakes in Romania by Andrei Bala, Mircea Radulian, Emilia Popescu, Cristoforos Benetatos Local Seismic Effects as Resulted from a Seismic Experiment in Romania by Victor Raileanu, Andrei Bala, Bogdan Grecu GPS And DEMETER/ICE Space Observations: Case Study of Adriatic Seismic Events by E. Cristea, M.Y. Boudjada, K. Schwingenschuh, J.J. Berthelier, M. Vellante, P. Nenovski Empirical Evaluation of Site Effects in Romania by Means Of H/V Spectral Ratios by B. Grecu, M. Radulian, M. Popa, K-P. Bonjer, A. Bala, V. Raileanu Geological Influence of the 1940 and the 1977 Vrancea Earthquakes in Northern Bulgaria by Margarita Matova 3D Velocity Structure of the 2003 Bam Earthquake Area (SE Iran): Existence of a Shallow Brittle Layer and Its Relation to the Heavy Damages by Hossein Sadeghi, S.M.Fatemi Aghda, Sadaomi Suzuki, Takeshi Nakamura Contribution to the Estimation of Seismic Hazard in Banat Region (Romania) by Traian Moldoveanu Seismotectonics of the Foreland of the Romanian Carpathians Characterization of Seismic Sources and Insights on Seismic Hazard Analysis by C. Dinu, T. Moldoveanu, V. Diaconescu, L. Matenco

Borehole Geophysics and Reservoir Investigation P12 – 01 P12 – 02

Stress Field Orientation in the Transylvanian Basin Inferred from Borehole Measurements by Dorel Zugravescu, Gabriela Polonic, Victor Negoita The Contributon of Geophysical Methods to Formation Evaluation of Frakulla Gas Field by Aleksander Gjika, Xhemil Buzi, Jovan Sota, Ilir Varf, Drita Buzi

P12 – 03 P12 – 04

A Multi-Azimuth VSP Experiment for Fracture Orientation Detection in HMD Field Algeria by Farid Chegrouche, Foudil Babaia The Possibilities of Clay Minerals Nature Identification by Geophysical Logs by Mihaela Liana Negut, Aurelian Negut

Physical Properties of Rocks P13 – 01 P13 – 02 P13 – 03 P13 – 04

Electrical Characteristics of Gneisses From Gold-Productive and Nonproductive Strata by Sergiy Shepel Thermobaric Variations of the Magnetic Characteristics of Some Mineral Formations by Boris Ya. Savenko, Valery A. Korchin, Alexander S. Nekh Gama-Ray Spectrometry Rock in Albania by Anastas Dodona, Artan Tashko Physical Properties of the Upper Sedimentary Rocks in Bucharest Metropolitan Area by Andrei Bala, Victor Raileanu, Ion Zihan, Bogdan Grecu, Viorica Ciugudean

Exploration Case Histories and Risk Management P14 – 01 P14 – 02 P14 – 03 P14 – 04 P14 – 05 P14 – 06 P14 – 07

Geoelectric Investigation in Gas-Promising Areas in the Dnieper-Donetsk Depression by S.P. Levashov, N.A. Yakymchuk, I.N. Korchagin, I.G. Zazekalo, A.I. Soroka Geoelectric Methods Application for the Hydrocarbon Deposits Searching and Exploring on the Western Kazakhstan Oilfields by S.P. Levashov, N.A. Yakymchuk, I.N. Korchagin, K.M. Taskynbaev. Using Old Oil-Industry Seismic Reflection Data for Seismic Hazard Studies by J. Carvalho, L. Torres, J. Simoes, J. Cabral, L. Mendez-Victor Petrophysical Evaluation of Laslau Mare Gas Field Using Logging Behind Casing and Tubing by Frank Thomson, Rick Baggot Evaluation of the Oil and Gas Accumulation in the Moesian Platform (Romania) by Constantin Pene, Bogdan Niculescu, Rodica Negulescu, Victor Rosu The Hydrocarbon Potential of Western Greece - Past E&P Results and Future Possibilities by H. Dobrova, U Schmitz, A. Zelilidis Hydrocarbon Discoveries in Western Poland – “Future” in the Permian? by Helena Dobrova, Piotr Gawenda, Etienne Kolly

Heat Flow and Geothermal Resources P15 – 01 P15 – 02 P15 – 03 P15 – 04

Methane and Fluid Venting in Northern Black Sea: Relation to Geothermal Situation by R. I. Kutas The Derivation of the Natural Gas Plums on the Black Sea Floor by E.F.Shnykov, V.I. Starostenko, V.P. Kobolev Curie Point Depths of the Moesian Platform from Geomagnetic Data Interpretation by P. Trifonova, Zheljo Petkov Zhelev, T. Petrova The Evaluation of Thermal Waters with Complex Geophysical Method of Elbasan-Ishem Area by Violeta Azizaj, Hamza Reci, Sami Nenaj, Petrika Kosho, Safet Dogjani

EAGE Short Course SC - 01

Two Decades of Evolution of Hardrock Seismic Imaging Methods Applied to Nuclear Waste Disposal in Finland by Calin Cosma

KEYNOTE ADDRESS

KN - 01

Earthquake Seismology, Exploration Seismology and Engineering Seismology: How Sweet It is --- Listening to the Earth Oz Yilmaz GeoTomo LLC, SUA

Summary The seismic method has three applications with different requirements for band-width and depth-width: (1) Earthquake seismology with a bandwidth up to 10 Hz and a depth of interest down to 100 km, (2) Exploration seismology with a bandwidth up to 100 Hz and a depth of interest down to 10 km, and (3) Engineering seismology with a bandwidth up to 1000 Hz and a depth of interest down to 1 km. Each of the three categories of seismology makes use of a specific wave type: (1) In earthquake seismology, dispersion of surface waves is used to delineate velocity-depth models for the oceanic and continental crusts. (2) In exploration seismology, reflected and diffracted waves are used to derive an image of the subsurface. (3) In engineering seismology, refracted waves are used to derive a velocity-depth model for the near-surface. For a specific category of seismology, the associated wave type is considered signal, while other wave types are considered noise. For instance, surface waves are essential for earthquake seismology, while they are treated as coherent linear noise in exploration seismology --- ground roll in land seismic exploration and guided waves in marine seismic exploration. I shall present a case study for each of the three categories of seismology: (1) Earthquake seismology case study: A seismic microzonation to determine soil amplification and liquefaction probability within a municipal area; (2) Engineering seismology case study: A site characterization survey to determine P- and S-wave velocities, and delineate geometry of layers within the soil column; (3) Exploration seismology case study: A large-offset sesimic survey to image complex structures in thrust belts. Earthquake Seismology Case Study The August 1999 earthquake with 7.4 magnitude caused a severe damage within the municipality of Izmit, 170 km East of Istanbul. A survey of the damaged buildings was made by the municipal authorities shortly after the earthquake. The Municipal Government decided to conduct a pilot seismic zonation project to determine whether the cause of the damage was poor construction materials and methods or weak soil conditions. In this project, we investigated the soil conditions with two objectives in mind: (1) to estimate the seismic model of the soil column at each district so as to determine the geotechnical earthquake engineering parameters, and (2) to map active faults within the municipal area. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 3

KEYNOTE ADDRESS

We determined the seismic model of the soil column on a district basis within the Municipality of Izmit. Specifically, we conducted refraction seismic survey at 16 locations and estimated the P- and S-wave velocity-depth profiles down to a depth of 30 m. We then combined the seismic velocities with the geotechnical borehole information about the pedology and lithology of the soil column and determined the geotechnical earnthquake engineering parameters for each district. Specifically, we computed the soil amplification and its effective depth range, design spectrum periods TA-TB, and liquefaction probability and depth range. By applying a nonlinear traveltime tomography (Zhang and Toksoz, 1998) to the firstarrival times picked from the three shot records, we estimated a near-surface P-wave velocitydepth model along the receiver spread at each of the 16 locations. By applying smoothing during the inversion and lateral averaging after the inversion, we then obtained a P-wave velocity-depth profile representative of each location (Figure 1). Next, we identified the off-end shot record with the most pronounced dispersive surfacewave pattern and performed plane-wave decomposition to transform the data from offset-time to phase-velocity versus frequency domain. A dispersion curve associated with the fundamental mode of Rayleigh-type surface waves was picked in the transform domain based on the maximum-energy criterion and inverted to estimate the S-wave velocity as a function of depth as shown in Figure 1 (Park et al., 1999; Xia et al., 1999). The velocity estimation from surface seismic data represents a lateral average over the receiver spread length in contrast with the velocity estimation from borehole seismic measurements which are influenced by localized lithologic anomalies and borehole conditions.

Figure 1. Earthquake seismology case study: The P-wave velocity-depth (left) and the S-wave velocity-depth (right) profiles down to 30-m depth.

To determine the geotechnical earthquake engineering parameters, we began with an SH accelerogram associated with the August 1999 earthquake recorded at a rock site within the municipal area. Given the seismogram at the rock site, we extrapolated it through the soil column knowing the S-wave velocity-depth profile and the geotechnical borehole information to model the seismogram at the soil site corresponding to the 16 district locations. For each district, we computed the maximum acceleration as a function of depth (Schnabel et al., 1972; Kramer, 1996), and determined the soil amplification factor at the ground level and the depth range for which amplification is significant. Next, we computed the design spectra --- response of buildings with a range of natural periods to the modeled ground motion at the soil site and the actual ground motion at the rock 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

4

KEYNOTE ADDRESS

site (Kramer, 1996). The building structure is defined as a spring system with a single-degree of freedom. From the design spectra, we determined the design spectrum periods TA and TB. We extended the relationship between the S-wave velocity and maximum acceleration (Stokoe, 1988) to account for water saturation in the soil column. Provided certain soil conditions are also met, the liquefaction process occurs when the medium becomes fully saturated, in which case the P-wave velocity increases while the S-wave velocity is unchaged (Yilmaz, 2001). By correlating the Vp/Vs ratio with the maximum ground acceleration and the Swave velocity, all as a function of depth, we determined the liquefaction probability or earthquake-induced settlement and its depth range of occurrence at each of the 16 sites. In this analysis, we also took into account the fines content information from the geotechnical borehole data. The geotechnical earthquake engineering parameters estimated for the districts of the Izmit Municipality indicate that the cause of the severe damage by the August 1999 earthquake is primarily soil amplification in addition to liquefaction at certain localities. In most districts of the municipality, the soil conditions are such that soil remediation would be very costly. Therefore, use of timber and steel, rather than heavy concrete, for construction material would reduce the structural mass of the buildings and provide safer habitation for the municipal residents. In addition to geotechnical characterization of the soil column at each district, we also conducted shallow reflection seismic surveys at 10 locations within the municipal area along line traverses with an average length of 450 m primarily in the EW direction and derived seismic images down to a depth of 100 m. In contrast with a comprehensive processing sequence applied to reflection seismic data used in exploration for oil and gas fields (Yilmaz, 2001), shallow reflection seismic data usually require a simple processing sequence (Steeples and Miller, 1990) that includes application of a bandpass filter and AGC. Aside from deriving a seismic section that represents the subsurface image down a depth of 100 m, we also estimated the near-surface P-wave velocity-depth model, again using the nonlinear traveltime tomography, for each of the 10 line traverses. From the interpretation of the seismic sections, we delineated several faults most of which reach the surface and cause significant lateral velocity variations within the near-surface as verified by the first-arrival tomography solution for P-wave velocity-depth models along the line traverses. The fault patterns observed on the seismic sections are oblique to the North Anatolian right-lateral strike-slip fault system with EW orientation in the area. Such fault patterns, combined with the strike-slip fault system, are often associated with pull-apart tectonism. Therefore, the Izmit area, which is the eastern tip of the Marmara Basin, is a transition zone from the dominant strike-slip regime along the North Anatolian Fault System to the pull-apart tectonic regime of the Marmara Basin. Engineering Seismology Case Study We present a unified workflow for analysis of shallow seismic data to estimate a nearsurface model defined by layer geometries within the soil column, and the P- and S wave velocities of the layers themselves. In the unified workflow for engineering seismology presented here, we make use of all three wave types --- reflected, refracted, and surface waves: (1) Apply a simple conventional processing sequence to obtain a CMP stack associated with the reflected waves. (2) Perform inversion of traveltimes associated with the refracted waves to estimate a near-surface P-wave velocity-depth model and use it to delineate the geometry of the layers within the soil column and the geometry of the soilbedrock interface. (3) Perform inversion of the Rayleigh waves to derive an S-wave velocity profile in depth. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 5

KEYNOTE ADDRESS

A site investigation for determination of the seismic parameters of the soil column based on the unified workflow outlined above led to the discovery of a buried lake deposits (Figure 2) near the shores of the Marmara Sea, west of Istanbul. The shallow reflection seismic data were acquired with common-spread recording geometry using a 48-channel seismic recording system with 10-Hz geophones and an explosive source that uses a pipe-gun placed in a 30-cm hole. Both the receiver and shot station intervals are 2-m. A total of more than 2,000 m reflection profiling was conducted along three line traverses over the survey area (Figure 2).

Figure 2. Engineering seismology case study: The seismic section (top) derived from the analysis of reflected waves and the P-wave velocity-depth model (bottom)derived from the analysis of refracted waves. Horizon A defines the boundary between the top soil and the lake deposits, whereas horizon B defines the boundary between the soil-bedrock interface.

Figure 3. Engineering seismology case study: (a) Surface waves in a field record from a refraction profile (K09) after inside and outside mute to remove refracted and reflected waves; (b) the dispersion curve for the Rayleigh fundamental mode interpreted from the phase velocity spectrum; (c) the S-wave velocity-depth profile estimated from the inversion of the dispersion curve.

4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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KEYNOTE ADDRESS

Additionally, at 14 locations with 60-m spacing, refraction profiling was conducted using a 48-channel cable with 4.5- Hz geophones at 2-m interval. Shot records were acquired with shot stations at two ends of the receiver cable and at the center of the cable. While the first breaks from all three shots were used to estimate the P-wave velocity-depth profile at the location, an off-end was used to estimate S-wave velocity-depth proifle from the surface waves (Figure 3). The S-wave velocity-depth profiles were then used to generate depth contour maps for the S-wave velocity field over the survey area (Figure 4). The low-velocity trend coincides with the geometry of the lake deposits.

Figure 4. Engineering seismology case study: The S-wave velocity-depth contours over the site. The contours correspond to the maximum depths associated with 600 m/s (top) and 700 m/s (bottom) S-wave velocities.

Exploration Seismology Case Study Turkish Petroleum Corp. conducted a multichannel large-offset 2-D seismic survey near the town of Ergani, Southeast Turkey, in October, 2004. The objective is to image the complex, imbricate target structures in the Southeast Thrust Belt. The data were acquired using a commonspread recording geometry whereby the receiver spread was fixed for all shots. A total of 960 receiver groups was placed along a 23,975-m line traverse in the NNW-SSE dominant structural dip direction at a 25-m interval. A total of 145 shots was fired at a 250-m interval along the line traverse, beginning at a location outside the spread and 6 km away from the first receiver group in the SSE end of the line. The distance between the first and last shot locations is 35,975 m. Shown in Figure 5 is a portion of one of the large-offset shot gathers from the Ergani Line 201. Note that at small offsets the field record is overwhelmed by Rayleigh waves (ground roll) with backscattering, and essentially is void of reflection energy. When the same field record is examined at far offsets beyond the conventional spread length, note the abundance of supercritical reflections at large offsets. These reflections have been known to early researchers in exploration seismology (Richards, 1960). Land seismic data acquisition with conventional spread length (3,000 m) and conventional processing in midpointoffset coordinates may fail to image complex imbricate structures associated with overthrust tectonics. Irregular topography associated with a rugged terrain, complexity of the near-surface that includes high velocity layers and outcrops with significant lateral velocity variations, complexity of the overburden caused by allocthonous rocks, and the Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 7

KEYNOTE ADDRESS

complexity of the target imbricate structures themselves, all pose challenges to exploration in thrust belts. We analyzed the Ergani large-offset data for earth modeling and imaging in depth. By a nonlinear first arrival traveltime tomography, a velocity-depth model was estimated for the nearsurface. Then, a subsurface velocity-depth model was estimated based on rms velocities derived from prestack time migration of shot gathers. Finally, prestack depth migration of shot gathers from a floating datum that is a close representation of the topography was performed to generate the subsurface image in depth.

Figure 5. Exploration seismology case study: A portion of a field record from the large-offset Ergani seismic survey with offset range 1,750-25,500 m. Note the abundance of reflections at large offsets and the predominance of the ground-roll energy at near offsets.

Figure 6 shows the image from poststack time migration of the data from Line 221 recorded with conventional spread length (less than 3,000 m) along the same line traverse as that of the large-offset seismic line 201. The data analysis was done using a conventional processing workflow. Note the absence of any coherent signal in this section. It would not matter if the imaging was performed before or after stack, in time or in depth --- the primary cause of this poor image is that the shot records from the vintage line 221 contain weak reflection signal overwhelmed by strong surface waves within the conventional spread length that corresponds to the subcritical region of wave propagation. In contrast, in prestack migration of the data from Line 201, we made use of the supercritical reflections recorded at large offsets. Another major difference in the data analysis of the two seismic lines is that we migrated the large-offset data from a floating datum, not from a flat datum as in the case of the conventional data. The shotdomain analysis of the data from the large-offset Ergani seismic survey based on commonspread recording geometry has indeed unraveled the imbricate structures that can lead to significant discoveries in the Southeast Thrust Belt.


8

KEYNOTE ADDRESS

Figure 6. Exploration seismology case study: Top: Poststack time migration of the data from Line 221 recorded with common-midpoint geometry and conventional spread length (less than 3,000 m) along the same line traverse as the large-offset seismic line 201. The data analysis was done using a conventional processing workflow. Bottom: Prestack depth migration of the largeoffset data recorded with common-spread geometry. The length of this section spans the full extent of the receiver spread (24 km) down to 5 km. The section is posted with respect to a seismic reference datum of –1,300 m. A 6-30 Hz bandpass filter has been applied to both sections.

Acknowledgements Murat Eser, Anatolian Geophysical, was in charge of the field work for the earthquake and engineering seismology case studies. Mehmet Berilgen, Yildiz Technical University, performed the spectral analysis for the earthquake seismology case study. Alaattin Pince, Ahmet Aytunur, Aziz Elibuyuk, Serdar Uygun, Taner Onaran, and Ahmet Faruk Oner, Turkish Petroleum Corp., formed the project team for the exploration seismology case study. Thanks are due to the Izmit Municipality for granting the permission to present the earthquake seimology case study, to Opet Petroleum Products and Distribution Company for granting the permission to present the engineering seismology case study, and to Turkish Petroleum Corp. for granting the permissin to present the exploration seismology case study. References Kramer, S. L., 1996, Geotechnical Earthquake Engineering, p. 273, Prentice-Hall, New Jersey. Park, C. B., Miller, R. D., and Xia, J., 1999, Multichannel analysis of surface waves: Geophysics, 64, 800-808. Richards, T. C., 1960, Wide-angle reflections and their application to finding limestone structures in the Foothills of Western Canada: Geophysics, 25, 385-407. Schnabel, P. B., Lysmer, P. B., and Seed, H. B., 1972, SHAKE: A computer program for earthquake response analysis of horizontally layered sites, in Report EERC 72- 12, Earthquake Engineering Research Center, University of California, Berkeley. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 9

KEYNOTE ADDRESS

Steeples, D. W. and Miller, R. D., 1990, Seismic reflection methods applied to engineering, environmental, and groundwater problems: in Geotechnical and environmental geophysics, Ward, S. H., ed., Soc. of Expl. Geophys., Tulsa, OK, 1-30. Stokoe, K. H., Rosset, J. M., Bierschwale, J. G., and Aouad, M., 1988, Liquefaction potential of sands from shear-wave velocity, in Proceedings, 9th World Conference on Earthquake Engineering, Tokyo, vol. 3, pp. 213-218. Xia, J., Miller, R. D., and Park, C. B., 1999, Estimation of near-surface shear-wave velocity by inversion of Rayleigh waves: Geophysics, 64, 691-700. Yilmaz, O., 2001, Seismic data analysis --- processing, inversion, and interpretation of seismic data: Soc. of Expl. Geophys., Tulsa, OK. Zhang, J. and Toksoz, M. N., 1998, Nonlinear refraction traveltime tomography: Geophysics, 63, 1726-1737.


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SEISMIC ACQUISITION & PROCESSING

Prestack Scalar Reverse-Time Depth Migration of ThreeDimensional Elastic Seismic Data

O1 - 01

1

Robert Sun1,2, George A. McMechan2, Chen-Shao Lee1 Department of Earth Sciences, National Chengkung University, 1 Tahsueh Rd. Tainan, Taiwan 701 2 Center for Lithospheric Studies, University of Texas at Dallas, Richardson, Texas 75083, USA

Summary We migrate the reflected P- and S-waves in a prestack threedimensional (3-D), three-component (3-C) elastic seismic data volume generated with a P-wave source in a three-dimensional model, using two independent 3-D scalar reverse-time depth migrations. P- and P-S-converted waves are extracted by divergence (a scalar) and curl (a threecomponent vector) calculations during shallow downward extrapolation of the elastic seismic data recorded at the earth’s surface. The P-wave travel time from the source to each point is used as the imaging time at that point for migrations of both the reflected P- and P-S-converted waves. The divergence (the extracted P-waves) is reverse-time extrapolated and imaged with a 3D P-velocity model. The curl (the extracted S-waves) is first converted into a scalar S-wavefield, then reverse-time extrapolated in a 3-D S-velocity model and imaged with the same travel time imaging condition used for the P-wave. Introduction Migration of 3-D elastic seismic data has been implemented by Chang and McMechan (1994) using 3-C synthetic data. In that algorithm, the coupled reflected P- and S-waves are imaged simultaneously by extrapolation of the multicomponent wavefields in a 3-D elastic model, using the 3-D elastic wave equation; therefore the images of the reflected P- and S-waves are spatially concurrent rather than separated. An algorithm to separate the P- and S-waves in 3-D, 3-C elastic seismic data using divergence and curl calculations has been developed by Sun et al. (2004). The algorithm described below is a combination of the 3-D P-S wave separation and the 3-D migration. The input data are the 3-D, 3-C displacements of the elastic seismic waves recorded at the earth’s surface. The P- and S-waves in the 3-D elastic seismic data are first downward extrapolated to a shallow datum where divergence (a scalar) and curl (a three-component vector) are calculated to represent separated P- and S-waves, respectively. 3-D scalar reverse-time depth migration is then applied to the separated P- and S-waves to obtain independent P- and S-images. Extracting P- and S-waves at a decomposition depth The 3-D elastic wave equation is: ∂2U = (α 2 − β 2 )∇(∇ ⋅ U ) + β 2 ∇ 2 U , 2 ∂t Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 11

(1)

SEISMIC ACQUISITION AND PROCESSING

where t is time, U = [u, v, w] is the displacement vector, and α and β are the P- and S-velocities, respectively. The input prestack elastic seismic data contain only reflected P- and P-S-converted waves; direct arrivals and surface waves are removed in preprocessing. A vertically homogeneous 3-D elastic model is prepared. The prestack 3-D, 3-C elastic seismic data are downward extrapolated, using finite-difference solution of (1), to some decomposition depth z1, which is here chosen to be z1 = 0.1 km. The divergence Φ(x, y, z, t) of the wavefield (representing P-waves only) and the curl Θ(x, y, z, t) of the wavefield (representing S-waves only) are calculated and extracted at the decomposition depth z1. During reverse-time extrapolation, the divergence is extracted as a 3-D, one-component seismogram and the curl is extracted as a 3-D, 3-C seismogram, over the entire horizontal slice at the decomposition depth z1. Transforming an S-wave into a scalar function The S-waves reflected at a single point from adjacent sources may have reversed polarity and so stack destructively. To solve this problem, we transform the curl, extracted at the decomposition depth, into a one-component scalar S-wavefield seismogram using the method illustrated here. A P-wave from a source propagates radially outward from the source, so its ray path is in a vertical plane passing through the source (the radial-vertical plane), or is deviated from it when the velocity model is laterally heterogeneous. The P- and S-waves reflected from such an incident P-wave will also have ray paths roughly in the radial-vertical plane, if they eventually emerge at the earth’s surface. The curl of the reflected S-wave displacement is therefore roughly perpendicular to this radial-vertical plane. Consequently, we construct the amplitude of the scalar S-wavefield Θ(x, y, z, t) in the following way: (1) its absolute value equals that of the curl: |Θ(x, y, z, t)| = |Θ(x, y, z, t)|, and its sign is positive if the curl rotates approximately counterclockwise relative to the source, and is negative if the curl rotates approximately clockwise relative to the source, if the curl is not in the radialvertical plane and, (2) it is 0 if the curl is in the radial-vertical plane. The source (zero offset) point is a nodal point (with zero curl) because the S-wave has zero reflection coefficient, therefore the scalar S-wavefield at the source is set to zero. Imaging separated 3-D P- and Swaves Two 3-D velocity models, one with the P-velocity α and the other with the S-velocity β, are prepared. When P-wave sources are used, the imaging time at each grid point for both reflected P- and P-S-converted waves is the oneway P-wave traveltime from the source. Figure 1. (a) A 3-D laterally inhomogeneous model. S1 through S9 denote the source locations. X and Y denote locations of the slices along which the seismograms and migrated images are presented. (b) Profile on the vertical slice along line X, and (c) on the vertical slice along line Y. In (b) and (c), the numbers outside the parentheses denote P-velocities, and the numbers in the parentheses denote S-velocities (in km/s).


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The P-wave data are reverse-time extrapolated into the P-velocity model using the 3-D scalar wave equation ⎛ ∂ 2Q ∂ 2Q ∂ 2Q ⎞ ∂ 2Q ⎟, = c 2 ⎜⎜ 2 + + 2 ∂t ∂y 2 ∂z 2 ⎟⎠ ⎝ ∂x

(2)

with Q equal to the P-wave amplitude (the divergence Φ) and c set to the local P-wave velocity α. During reverse-time extrapolation, the P-image at each point is extracted as the P-wave amplitude at the imaging time of that point. The scalar S-wavefield is reverse-time extrapolated into the S-velocity model, again with the scalar wave equation (2), with Q equal to the scalar Swavefield Θ and c equal to the S-velocity β. During reverse-time extrapolation, the S-image at each point is extracted as the scalar S-wavefield amplitude at the imaging time of that point.

Figure 2. The 3-D, 3-C synthetic elastic seismic data, after removing the surface waves and muting the direct arrivals, generated for the model in Figure 1. (a) x-component, (b) y-component and (c) z-component along line X of Figure 1; (d) xcomponent, (e) y-component and (f) zcomponent along line Y of Figure 1.

Figure 3. (a) The divergence (P-waves) and the (b) scalar S-wavefield beneath line X, and (c) the divergence (P-waves) and (d) the scalar S-wavefield beneath line Y, extracted at the decomposition depth z1 = 0.1 km in the elastic model during downward extrapolation of the 3-D, 3-C elastic data in Figure 2.

Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 13

SEISMIC ACQUISITION AND PROCESSING

A 3-D laterally inhomogeneous example The migration algorithm is tested using a 3-D laterally inhomogeneous elastic model containing one convex and one concave reflector, with 9 sources located near the surface (Figure 1). Figure 2 shows the synthetic elastic seismic data generated for a P-wave source at (x, y, z) = (1.0, 0.4, 0.14) km (S2 in Figure 1) and with absorbing boundaries on all faces except the top. In Figure 2, the direct arrivals have been muted and the surface waves have been removed. Divergence (P-waves) and curl (S-waves) are extracted at the depth z1 = 0.1 km. The curl is transformed into the scalar S-wavefield. Figure 3 shows the divergence seismogram and the scalar S-wavefield seismogram for source S2. Figure 4 shows the stacks over the images from sources S1 through S9. Both the separated P- and S-waves provide correct image locations for the reflectors, with only minor artifacts. The amplitude of the image varies from place to place because of the limited number of sources; the amplitudes of the reflected waves from each source are angle-dependent, and they are imaged only if they are received in the limited recording aperture.

Figure 4. The migrated (a) P- and (b) Simages on the vertical slice along line X, and (c) P- and (d) S-images on the vertical slice along line Y, stacked from the images of sources S1 through S9. The S-images are weighted by a factor of 0.5. Compare with Figure 1.

Discussion and Conclusions We first separate the P- and S-waves in the prestack elastic seismic data, and then apply scalar reverse-time depth migration to the separated P- and S-waves independently to obtain 3-D P- and S-images. The S-image is a scalar function rather than a vector function. We demonstrate that prestack migrated 3-D P- and S-images can be stacked with constructive interference. From Snell’s law, an incident P-wave at a reflector will have different P- and S-wave reflection angles, since the P- and S-velocities are different. The reflected P- and S-waves received at the same surface location have come from different reflection points even if the reflector is a plane, and will therefore be imaged at different points on the reflector. Using the Pand S-waves separated from 3-D elastic seismic data therefore provides information about different locations on a reflector. References Chang, W. F., McMechan, G. A., 1994, 3-D elastic prestack reverse-time depth migration: Geophysics, 59, 597-609. Sun, R., McMechan, G. A., Hsiao, H. H., Chow, J., 2004, Separating P- and S-waves in prestack 3D elastic seismograms using divergence and curl: Geophysics, 69, 286-297.


14


O1 - 02

TIME-SHIFT WAVE-EQUATION IMAGING

Paul Sava, Sergey Fomel Bureau of Economic Geology, The University of Texas at Austin, Austin, TX 78758, USA

Summary We derive a new generalized imaging condition based on time shifts between source and receiver wavefields. This imaging condition contrasts with other imaging techniques requiring space shifts between the two wavefields. This imaging condition is applicable to both Kirchhoff and wave-equation migrations. The transformation allows us to generate common-image gathers presented as function of either time-shift or pseudo-angle at every location in space. Inaccurate migration velocity is revealed by common-image gathers with non-flat events. Introduction A key challenge for imaging in complex areas is accurate determination of a velocity model that describes with sufficient precision wave propagation in the area under investigation. Migration velocity analysis is based on image accuracy indicators that are optimized when data are correctly imaged. A common procedure for velocity analysis is based on alignment of images created with multi-offset data. An optimal choice of image analysis can be done in the angle domain which is free of some of the complicated artifacts present in offset gathers in complex areas (Stolk and Symes, 2002). Migration velocity analysis after migration by wavefield extrapolation requires image decomposition function of scattering angles relative to reflector normals. Several methods have been proposed for such decompositions (de Bruin et al., 1990; Prucha et al., 1999; Mosher and Foster, 2000; Rickett and Sava, 2002; Sava and Fomel, 2003; Soubaras, 2003; Biondi and Symes, 2004). These procedures require decomposition of extrapolated wavefields in components that are related to the reflection angle. A key component of such image decompositions is the imaging condition. A careful implementation of this imaging condition preserves all information necessary to decompose images in their angle-dependent components. The challenge is not only to use these angledependent images for velocity or amplitude analysis, but also to construct them cheaply, reliably and with direct access to velocity information. This paper presents a different form of imaging condition. The key idea of this new imaging condition is to use time-shifts instead of space-shifts between wavefields computed from sources and receivers. This imaging concept is applicable to both Kirchhoff migration and migration by wavefield extrapolation. We present a brief theoretical analysis of this new imaging condition, followed by examples illustrating the main features of this new technique. Imaging condition in wave-equation migration No shift imaging condition A traditional imaging condition for shot-record migration, also known as U D imaging condition (Claerbout, 1985), consists of time cross-correlation at every image location between the source and receiver wavefields, followed by image extraction at zero time: Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 15


u(m, t ) = us (m, t ) ∗ ur (m, t ) (1) (2) R (m ) = u(m, t = 0 ) . Here, m=[mx,my,mz] is a vector describing the locations of image points, us(m,t) and ur(m,t) are source and receiver wavefields respectively, and R(m) denotes the migrated image. The symbol ∗ denotes cross-correlation in time. Space-shift imaging condition Another generalized imaging condition (Sava and Fomel, 2005) estimates image reflectivity using the expressions: u(m, h, t ) = us (m − h, t ) ∗ ur (m + h, t ) (3) (4) R (m, h) = u(m, h, t = 0 ) . Here, h = [hx,hy,hz] is a vector describing the local source-receiver separation in the image space. Special cases of this imaging condition were presented by (Rickett and Sava, 2002) for horizontal space-shift, and by (Biondi and Symes, 2004) for vertical space-shift. Angle-domain common-image gathers can be obtained by a simple slant-stack operation on migrated images R (m, h) ⇒ R (m, tan θ ) , where tan θ is the dimensionless slant-stack parameter. Time-shift imaging condition Another possible imaging condition involves cross-correlation of the source and receiver wavefields in time, as opposed to space: u(m,τ , t ) = us (m, t − τ ) ∗ ur (m, t + τ ) (5) (6) R (m,τ ) = u(m,τ , t = 0 ) . Here, τ is a time shift between the source and receiver wavefields prior to imaging. This imaging condition can be implemented in the Fourier domain using the expression R (m,τ ) = Us (m, ω ) Ur (m, ω ) e 2iωτ , (7) which simply involves a phase-shift applied to the wavefields prior to summation over frequency w for imaging at zero time. The over-line represents a complex conjugate applied on the receiver wavefield Ur in the Fourier domain. Pseudo angle-domain common-image gathers can be obtained by a simple slant-stack operation on migrated images: R (m, h) ⇒ R (m,ν ) , where ν is the slant-stack parameter with velocity units.

Figure 1 An image is formed when the Kirchoff stacking curve (dashed line) touches the true reflection response. Left: the case of under-migration; right: over-migration.

Moveout analysis We can use the Kirchhoff formulation to analyze the moveout behavior for time-shift imaging condition in the simplest case of a flat reflector in a constant-velocity medium. Let s0 and z0 represent the true slowness and reflector depth, and s and z stand for the corresponding quantities used in migration. An image is formed when the Kirchoff stacking curve 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

16


() touches the true reflection response t (hˆ ) = 2s z + hˆ (Figure 1). Eliminating hˆ from the conditions t (hˆ ) = t (hˆ ) and t (hˆ ) = t (hˆ ), we find that the reflection response maps into two t hˆ = 2s z 2 + hˆ 2 + 2τ 0

'

0

0

2 0

2

' 0

images in the {z, τ} space. The first image is a straight line z s +τ z(τ ) = 0 0 , s and the second image is a segment of the second-order curve

z(τ ) = z02 +

τ2 s 2 − s02

(8)

.

(9)

Applying a slant-stack transformation with z = z1 + ντ turns line (8) into a point {z0s0/s,1/s} in the {z, ν} space, while curve (9) turns into the curve

(

)

z1 (υ ) = z0 1 + υ 2 s02 − s 2 .

(10)

The curvature of the z1(ν) curve at ν=0 is a clear indicator of the migration velocity errors. By contrast, the moveout shape z(h) appearing in wave-equation migration with the lateralshift imaging condition is (Bartana et al., 2005) z1 (h ) = s0

z02 h2 . + s 2 s 2 − s 02

(11)

After the slant transformation z= z1+h tanθ, the moveout curve (11) turns into the curve z z1 (θ ) = 0 s02 + tan 2 θ s02 − s 2 , (12) s which is applicable for velocity analysis. Curves of shape (10) and (12) are plotted on top of the experimental moveouts in Figures 4 and 5, respectively.

(

)

Figure 2 Common-image gathers for time-shift imaging.

Figure 3 Common-image gathers for space-shift imaging.

Example We exemplify the method with a simple flat reflector in a constant velocity medium. The synthetic data are imaged using shot-record wavefield extrapolation migration. Figures 2 and 3 show common-offset gathers for three different migration slownesses s, one of which is equal to the modeling slowness s0. For the time-offset CIGs imaged with correct slowness, Figure 2, the energy is distributed along a line with a slope equal to the local velocity at the reflector position, but it spreads around this region when the slowness is wrong. Slant-stacking produces the images Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 17


in Figure 4. For the space-shift CIGs imaged with correct slowness, Figure 3, the energy is focused at zero offset, but it spreads in a region of offsets when the slowness is wrong. Slantstacking produces the images in Figure 5.

Figure 4 Common-image gathers after slant-stack in time-offset. ν is the slant-stack parameter in the {m, τ} space. The vertical line indicates the migration velocity.

Figure 5 Common-image gathers after slant-stack in space-offset. Tanθ is the slant-stack parameter in the {m,h} space.

Conclusions We introduce a new imaging condition based on time-shifts between source and receiver wavefields. This method is applicable to both Kirchhoff and wave-equation migration and produces common-image gathers that indicate velocity errors. In wave-equation imaging, timeshift imaging is more efficient than space-shift imaging, since it only involves a phase shift applied prior to the usual imaging cross-correlation. More research is needed to investigate how this new information can be used for velocity and amplitude analysis. References Bartana, A., Kosloff, D., and Ravve, I., 2005, On angle-domain common-image gathers by wavefield continuation methods: Geophysics, submitted. Biondi, B., and Symes, W. W., 2004, Angle-domain common-image gathers for migration velocity analysis by wavefield-continuation imaging: Geophysics, 69, 1283.1298. de Bruin, C. G. M., Wapenaar, C. P. A., and Berkhout, A. J., 1990, Angle-dependent reflectivity by means of prestack migration: Geophysics, 55, 1223.1234. Claerbout, J. F., 1985, Imaging the Earth's Interior: Blackwell Scientific Publications. Mosher, C., and Foster, D., 2000, Common angle imaging conditions for prestack depth migration in 70th Ann. Internat. Mtg. Soc. of Expl. Geophys., 830.833. Prucha, M., Biondi, B., and Symes, W., 1999, Angle-domain common image gathers by wave-equation migration in 69th Ann. Internat. Mtg. Soc. of Expl. Geophys., 824.827. Rickett, J. E., and Sava, P. C., 2002, Offset and angle-domain common image-point gathers for shot profile migration: Geophysics, 67, 883.889. Sava, P., and Fomel, S., 2005, Coordinate-independent angle-gathers for wave equation migration in 75th Ann. Internat. Mtg. Soc. of Expl. Geophys. Sava, P. C., and Fomel, S., 2003, Angle-domain common-image gathers by wavefield continuation methods: Geophysics, 68, 1065.1074. Soubaras, R., 2003, Angle gathers for shot-record migration by local harmonic decomposition in 73rd Ann. Internat. Mtg. Soc. of Expl. Geophys., 889.892. Stolk, C., and Symes, W., 2002, Artifacts in Kirchhoff common image gathers in 72nd Ann. Internat. Mtg. Soc. of Expl. Geophys., 1129.1132.


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O1 - 03

A GRID-ENABLED SYSTEM FOR 3-D SEISMIC IMAGING Dimitri Bevc, Iulian Musat, Mihai Popovici, Sergio E. Zarantonello 3DGeo Development Inc., Suite 401, 4633 Old Ironsides Drive, Santa Clara, CA 95054, USA

Summary One way to meet the increasing computational demands of the seismic imaging industry is by seamlessly enabling access to compute on demand capability. Grid computing, by leveraging the Globus Toolkit (Foster & Kesselman, 1997) middleware, provides a framework where remote computational resources can be accessed whenever and wherever needed. The objective of this paper is to give an overview of a Grid-enabled environment for seismic imaging developed by 3DGeo. This system addresses the demand for advanced seismic imaging applications in the oil and gas industry, and the ensuing need of computational and data resources to run these applications flexibly and efficiently. 3DGeo has developed INSP (Bevc & Popovici, 2003), a proprietary Java based Internet infrastructure for remote collaborative seismic processing and seismic imaging, and a suite of advanced 3-D imaging applications that can be accessed, executed, and monitored with the INSP system. The conversion of INSP to a Gridenabled system, providing flexible and secure access to advanced imaging applications and to the resources to run these applications as needed, is a fundamental step in the seismic imaging industry. Advanced compute intensive imaging, enabled by the Grid, will allow the industry to much more effectively meet the imaging challenges presented by the increasingly complicated geological regimes we are exploring today. Introduction Seismic imaging methods are usually classified as methods based on the Kirchhoff integral equation and methods that operate directly with the wave equation. Wave-equation methods are further classified as shot-receiver (e.g. common azimuth and narrow azimuth methods) and shotprofile methods. To put the computational challenge in perspective, in Table 1 we compare the estimated runtimes of hypothetical imaging projects for Deep Gulf of Mexico 3-D marine surveys on a 128-CPU cluster of 2.4 GHz Pentium® 4 processors delivering a sustained performance of 900 Mflops/CPU. Size of data

Runtime in days

Blocks

Gbytes

Kirchoff

Narrow azimuth

Shot profile

10

620

3

31

184

100

6,200

111

1,100

6,640

500

30,700

996

9,960

59,800 (164 yrs !)

Table 1 The computational challenge: Gulf of Mexico 3-D marine surveys.



The generally computationally more intensive wave-equation methods give better accuracy than Kirchhoff migration, underscoring the need for more compute resources deliverable through the Grid. Overview of PSDM We use PSDM as an example to illustrate design issues that were addressed for Grid deployment. Prestack Depth Migration (PSDM) is 3DGeo's implementation of the threedimensional Kirchhoff depth migration. PSDM approximately solves the wave equation with a boundary integral method. In a computational setting we express the integral as a sum: where Ar and As are determined by the transport equation, and tr and ts are either found by raytracing or by solving the eikonal equation. We note that the sums for the different points of the image can be calculated independently from each other. The process of building an exact image is iterative, with successive improvements made to the velocity field and can be extremely demanding in terms of human and computational resources. Parallelization of PSDM on a cluster PSDM presents different parallelization issues in cluster and Grid environments. 3DGeo's implementation of Kirchhoff migration was designed to achieve maximum efficiency on a cluster of interconnected multiprocessor computers. The input data is distributed among the computational nodes, while the output image is divided into processing blocks that are distributed over parallel processors on each node. At the end, the results from each node are gathered to build the final image. Figure 1 illustrates the PSDM MPI architecture. We chose the Open MP1 standard for the implementation of the shared-memory parallelization on each multiprocessor node.

Figure 1 Parallelization of PSDM on a cluster (left) and on multiple clusters (right)

PSDM on the Grid Tests and benchmarking of PSDM on various cluster architectures and configurations shows that in a typical run the I/O operations associated with the input data distribution account for a small fraction of the total processing time. This encouraged us to use, in a first phase, the same architecture for distributing a PSDM job across multiple clusters, interconnected in a computational grid, as shown on the right side of in Figure 1. Using the Globus Toolkit (Foster & Kesselman, 1997) we built such a Grid, interconnecting two of 3DGeo's processing centers (Santa Clara, California, and Houston, Texas) and a Linux cluster at the San Diego 1

Hhttp://www.openmp.org/H


20


Supercomputing Center. The result was a Grid-enabled MPI implementation built on top of MPICH and Globus API. Demonstration on the Virtual Computer The SDSC cluster was configured to support the seismic imaging software and was connected to 3DGeo's distributed monitoring Grid. The connection to the monitoring grid was performed by the Ganglia Resource Monitoring tool. Ganglia2 is an Open Source application, originally developed by the Berkeley Millenium. Ganglia gives a view of resource utilization, and includes graphs showing the evolution in time of machine load, memory usage, number of processes, etc. It was thus possible to inspect from a single site the load of the machines geographically distributed in Santa Clara CA, San Diego CA and Houston TX. The final step was to incorporate the Grid-enabled applications such as PSDM within the INSP framework. Tying Grid resources together with INSP INSP (Bevc et al., 2002) is a collaborative environment, developed by 3DGeo for building and launching workflows of computationally intensive parallel and distributed jobs, visualizing data on client workstations, and monitoring jobs. Figure 2 demonstrates some of the INSP functionality. It shows a screen shot of the INSP Explorer interface. Through this interface, for example, tree structures for four servers in a 3DGeo operational Grid can be shown: Santa Clara, CA. (3DGeo Services), San Diego, CA (SDSC cluster), Houston, TX (3DGeo Houston Processing Center), and Terabyte3 (a Houston-based provider of computational resources to the oil and gas industry).

Figure 2 INSP Explorer is the Internet-based GUI for remote processing services.

Conclusions Large 3-D seismic imaging projects typically involve input data sets of 10 to 15 terabytes in size. With current technologies, it can take six to nine months of computer time to generate an image. By leveraging Grid resources effectively through our technology we expect this turn-around time to decrease by at least a factor of 10 and also make it practical to apply more accurate - but computationally more expensive imaging algorithms on multiterabyte data sets. In summary, A Grid environment for seismic imaging signifies a quantum leap over current methods in terms of efficiency and capability. Landmark and Schlumberger Information Systems through their association with IBM in the Deep Computing initiative, and GXT technologies, are all presently 2 3

Hhttp://ganglia.sourceforge.net/H Hhttp://www.terabyte.com/H



deploying Grid-enabled products for the oil and gas industry. We believe these Grid environments are not as optimally designed and deployed for 3-D seismic imaging as they could be, and that their functionalities overlap at most minimally with the Grid technologies presented in this paper. Ultimately, the goal of Grid Computing is to provide compute resources on demand, and enable the purchase of compute power over the internet as seamlessly as electricity is purchased over electrical grids today.

Figure 3 In today's operational scenario data are physically transported between the steps of acquisition, data processing, data storage, and the end user (oil company). The fully-enabled Grid scenario allows greater access to resources (data, computers, personnel), reduces turn around time, and ultimately shortens the time to making a drilling decision. In the fully-enabled Grid scenario, all components of the process become Grid nodes.

Seismic imaging is an application area where Grid computing holds great promise. Today’s operational environment, shown in the left panel of Figure 3, involves many inefficiencies that are seamlessly resolved in a Grid environment. A large imaging project today can easily require one to two years to complete. In a fully-optimized Grid operational environment, shown on the panel on the right, the time to complete the same project can be reduced to one half-year. These advantages are compelling, thus motivating 3DGeo’s efforts to be at the forefront of bringing the Grid to the energy exploration industry. Acknowledgement This work was supported in part by NASA. We take this opportunity to thank Tom Hinke, of NASA and Kevin Walsh of SDSC for their insight and support. References Bevc, D., Popovici, M., Biondi, B., 2002, Will Internet processing be the new paradigm for depth migration interpretation and visualization ?, First Break, vol. 20, no. 3. Bevc, D., Popovici, A.M., 2003, Integrated Internet collaboration, The Leading Edge, vol. 22, pp. 54-57. Foster, I., Kesselman, C., 1997, Globus: A Metacomputing Infrastructure Toolkit, in the International Journal of Supercomputing Applications and High Performance Computing, vol. 11, issue 2, pp. 115-128.


22


O1 - 04

A PRAGMATIC VIEW OF LAND MULTIPLE ATTENUATION TECHNOLOGY Panos G. Kelamis Saudi Aramco

Panos G. Kelamis obtained a B.Sc. (Hon.) in Physics from the University of Athens, Greece (1977), a M.Sc. and D.I.C. in Geophysics from the Imperial College of the University of London (1978), and a Ph.D. in Geophysics from the University of Alberta (1982). He worked with the Research & Development group of Western Geophysical in Houston, and for Dome Petroleum in Calgary, before joining Saudi Aramco in Dhahran. Within Saudi Aramco, Panos held various technical and supervisory positions in Geophysical Research, Processing, and Technical Services Divisions. His research efforts were focused primarily on imaging, signal processing, and reservoir geophysics. He was instrumental in the application and development of advanced multiple elimination techniques on land data. Currently, he is the Chief Geophysicist of Geophysical Technical Services of the Exploration Technical Services Department in Saudi Aramco. Panos is an active member of SEG, EAGE, and DGS. He has served the SEG in various capacities including, representative of the Africa & Middle East region and organizer and cochair of several technical workshops and meetings (1995 First Balkan Geophysical Conference in Athens, Greece; 1996 First Winter Symposium of EAGE on Reservoir Geophysics in Venice, Italy; 2001 SEG workshop on Velocity-Independent Imaging for Complex Structures, in San Antonio, TX; 2003 SEG/EAGE summer workshop on Processing and Imaging of seismic data using explicit or implicit velocity model information in Trieste, Italy; 2004 EAGE research workshop on Seismic Acquisition Technology in Rhodes, Greece; and 2005 SEG Land Seismic Forum in Bahrain). He served five years as an Associate Editor of GEOPHYSICS and he is currently serving in the editorial boards of the Journal of Seismic Exploration and the Journal of Geophysics & Engineering. Panos is also on the advisory board of the industry-sponsored DELPHI consortium at Delft University of Technology in The Netherlands. He has received the Best Paper Award for a paper presented at the CSEG in 1992 and Honorable Mention for papers presented at the SEG meetings in 1990, 1995 and 1999.



The identification and subsequent suppression of multiple energy are among the most challenging issues in seismic data processing. Recent advances in the arena of multiple elimination technology, firmly rooted to the acoustic wave equation, have resulted in algorithms that are successfully applied to marine datasets. On land, and especially in the desert terrains of the Arabian Peninsula, the application of multiple elimination technology is not always straightforward and requires innovative thinking and approaches. The presence of a complex near-surface in contrast to the simple free-surface of a marine environment and the low signal-tonoise ratio, combined with coupling and acquisition problems, are key characteristics of land seismic which deteriorate the performance of multiple elimination techniques.

This talk presents a series of practical strategies that target the attenuation of surface and internal multiples in the land environment. These strategies can be applied prestack, in shot and common mid-point gathers, and/or in stacked data. They include conventional statistical and frequency-wavenumber schemes, least-squares and high-resolution model-based algorithms, and data-driven, wave-theoretical approaches which require no knowledge of the subsurface. These techniques reflect the evolution of multiple elimination methods over the last 25 years. The physical principles of each methodology are discussed in detail but special emphasis is given to viable solutions that add value to the seismic data. A plethora of land datasets from the world’s largest onshore oil fields in Saudi Arabia is used to demonstrate the effectiveness as well as the limitations of each strategy. It is expected that these practical strategies will serve as a foundation for future developments in multiple attenuation technology onshore.


24

ENVIRONMENTAL, ENGINEERING & ARCHAEO-GEOPHYSICS

O2 - 01

ENVIRONMENTAL GEOPHYSICS – CHALLENGES FOR THE FUTURE Snezana Komatina-Petrovic Geophysical Institute, Nis-Naftagas Serbia and Montenegro

Summary Environmental geophysics is new discipline of applied geophysics, based on methods of mining and engineering geophysics and directed to near-surface exploration. The following problems are solved: waste disposal, groundwater protection against contamination, contamination in agriculture, exploration in archaeology and preserving cultural heritage, vibrations and noise monitoring, investigations related to problems of engineering geology, snow and ice exploration, etc. In the paper, problems to which attention of geophysicists in the future should be directed to are discussed, as well as the question if geophysical methods are environment-friendly.

Introduction In contrast to various ways of exploration applied to solve problems to protect the environment against different contaminants, geophysical methods are completely non-destructive and non-invasive, offering 3D view of the study area. Further, the reason why geophysics is famous as »green technology« is the fact that personnel performing investigations in the field is much more safe in comparison to the drilling crew (when toxic gas or liquids emmission is possible, but also other types of damages). As cost-efficient, geophysical methods are highly reccommended in the mentioned domain. Challenges to environmental geophysicists for the future are treated in the following text.

Future challenges For the future, skills and geophysical methods development (including data acquisition, processing and interpretation) has to be directed to solving of the following problems: soil and groundwater contamination, engineering geology and geotechnics, contamination in mining, exploration in regions under specific conditions (sea, snow, ice), locating paleo river beds, glacial and proglacial sediments, ecohazards and urban planning, exploration in archaeology and historical monuments, forensic investigations, UXO detection, underground CO2 sequestration, climate changes, etc. (Table 1). Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 25


As wide range of problems solved by environmental geophysics is based on quantitative analysis of processes existent within the rock/fluid system, numerical methods and modeling should be developed in the future. Modeling has to include conditions and skills of different disciplines: geosciences, chemistry, physics, mathematics, etc. So, the next step is expected to be more realistic modeling, based on analysis of appropriate problem, under real conditions and for defined geological structure of the study area. For example, in order to create a model of some landfill, geological structure of the terrain has to be defined, and from that stage, various contaminants, as artificial objects, to be distinguished. To obtain view on hydrogeological characteristics or homogeneity of the study area, as well as for monitoring natural attenuation of contamination in time- and space-domain, field experiments are highly reccommended. Geophysical methods have very important role in solving hydrogeological problems, particularly in contaminant hydrogeology (Komatina-Petrovic S., 2005a). Known as useful in timely detection of contamination, and, therefore, in contaminant transport outlining, future role of geophysics is in monitoring of remediation process. For successful remediation monitoring, combined application of various disciplines is understood – geophysics, hydrogeology, engineering geology, microbiology, chemistry, etc. As a »must do« challenge for geophysicists in the future is more serious research in domain of influence of natural and artificial (geo) physical fields on health of plants, animals and human beings – if Medical Geology (Komatina M., 2004) attracts attention of scientists from all over the world, why not to introduce just new geophysical dicpline – Medical Geophysics (Komatina-Petrovic S., 2005)?

Problem to be solved Air/gas emission quality monitoring Noise/vibrations monitoring, induced quakes control Geological mapping in urban areas Forensic/criminologic investigations Lithological and geological structure, depth to bedrock or groundwater level

Multidisciplinary approach Contamination chemistry, fluid dynamics, gas radiometry/emanometry Seismic monitoring, seismic signal processing Sophisticated geophysical methods,remote sensing, geological mapping Sophisticated geophysical methods, medical/engineering ultrasonic investigations, toxicology Geotechnics, Sophisticated geophysical methods

Sophisticated geophysical methods, civil engineering, archaeology, history Soil/rocks physical characteristics Geology, geophysics, hydrogeology, hydrogeochemistry Roads/bridges, railways, tunnels, channels, Geophysics, geotechnics, hydrogeochemistry, microbiology, pipelines and cables detection and quality toxicology Groundwater distribution, quality and Hydrogeology, hydrogeochemistry, toxicology, microbiology, management fluid transport modeling, regulations in domain of ecology Sophisticated geophysical methods, chemistry, fluid flow Groundwater contamination modeling, regulations in domain of ecology Leakage from landfills Toxicology, medical statistics, geochemistry, geophysics LNAPL transport detection and monitoring Geophysics, civil engineering, toxicology Public health: geochemical, factors, medical Volcanology, seismology, matematical modeling, Sophisticated geophysical methods, civil engineering, geography – GIS, fluid factors dynamics Stratigraphy, paleobiology, volcanology, matematical modeling, Safe disposal of toxic waste fluid dynamics, geophysics, geography – GIS, atmosphere physics Landslides, volcanic eruptions, earthquake forecasting, amelioration Sea level variations, global heating, catastrophic floods Cavities, caverns, mining shafts, soil sinking

Table 1 Solving problems related to protection of the environment on the basis of multidisciplinar approach (Meju, 2002).


26


Conclusions Environmental geophysics is dealing with wide range of problems, including not only changes at local level (fluid/rock system), but also global changes (climate changes), caused by natural processes and anthropogenic activity. That is why safety, health and quality are new standards within planning, monitoring and education, making a turnpoint in environmental geophysics. In order to preserve the environment and cultural heritage, the main task in solving any ecological problem is to put legal standards related to geophysics into effect. One of the most important goals and challenges of environmental geophysics is to overcome a gap between geophysicists, hydrogeologists, engineering geologists, civil engineers, land-use planners and all other experts using this discipline for near-surface exploration. Or, more simple – to make atmosphere in which geophysics will be widely accepted as a »geologist's tool kit« in solving problems refferring to protection of the environment.

References Komatina M., 2004. MEDICAL GEOLOGY. Effects of geological environments on human health. Developments in Earth & Environmental Sciences, Elsevier, 490 p. Komatina-Petrovic S., 2005a. Detecting groundwater pollution and monitoring by geophysical methods. Foundation Andrejevic, Beograd, 150 p (in Serbian). Komatina-Petrovic S., 2005. Environmental Geophysics. Geophysics and environmental protection. DIT NIS-Naftagas, Novi Sad, 350 p (in Serbian). Meju M., 2002. Environmental geophysics: Conceptual models, challenges and the way forward. The Leading Edge, Vol.21, No.5, 460-464.



O2 - 02

GEOELECTRICAL INVESTIGATION OF DAMS IN GEORGIA - CIS Antonio Bratus, Elvio Del Negro, Daniel Nieto Yabar Istituto Nazionale di Oceanografia e di Geofisica Sperimentale – OGS, 34010 Sgonico (TS) Italy

Summary This is a case history about a collaboration project between Italy and Georgia in the investigation and monitoring of dams in Georgia. The topic of this abstract is the results of a geoelectrical survey. Two dams, having different technical features, were investigated. Although there were many difficulties for the data acquisition, the results are very interesting. Introduction This project is an initiative co-financed by the Ministry of Foreign Trade of the Italian Republic (Italian Law 212-1999). Istituto Nazionale di Oceanografia e di Geofisica Sperimentale is one of the partner of the project, other partner are both Italian and Georgian. This is a pilot project having the aim of demonstrating the use of modern geophysical methods for the investigations of hydroelectric structures and basins in Georgia. Georgian partners participate in all steps of the project. Technology transfer was obtained by technical stages and training in Italy. The sites test Two dams having different features were investigated. Topic of the first step of the geoelectrical survey was the detection of voids in the rock mass, such as caves or jointed area, in the nearness of the high pressure tunnel of the Enguri dam. The Enguri dam is one of the biggest concrete arc-dam of the world.

Figure 1 The stars indicate the location of the dams, on the left side is indicated the position of the Enguri dam, on the right side the Zhinvali one.


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It has many problems because of geological features of the rocks of the area, in fact the presence of jointed limestone causes many leakages of water both from the basin and from the high pressure tunnel. The second step consists in the investigation of the structure of an earth dam. For this reason the Zhinvali dam, close to the capital Tbilisi, was investigated.

Figure 2 Geoelectrical line position in the Zhinvali survey

Data acquisition All data were acquired using a multielectrodic system and a resistivimeter Syscal R2 of the Iris Instruments. Resistivity and chargeability data were collected. All the cables and the electrodes were manufactured by the Georgian partner. The Enguri data were acquired inside tunnels, a particular mixing of mortar and salt water was used to couple the electrodes to the wall of the tunnels. This solution allows low values for the ground resistance and let the electrode to be positioned in critical situation. A short electrode spacing array was used in the Enguri dam but many problems on the data quality occur because of the presence of ferroconcrete in the tunnel structure. Where ferroconcrete structure wasn’t present the data quality were really good. The Zhinvali dam data acquisition was easier then the Enguri situation, because the survey was carried on the surface of the ground dam. Seven lines, having electrode spacing from 5 to 12 m, were acquired. The maximum investigation depth was 70 m (Figure 2).

Figure 3 On the left side, apparent resistivity pseudosection , calculated resistivity pseudosection and resistivity model of a line acquired in a tunnel of the Enguri dam, having no ferroconcrete structure. On the right side the synthetic model and the apparent resistivity pseudosection derived from the synthetic model. Note the two high resistivity bodies inside the rock mass and the concrete structure of the tunnel.



Results The RES2DINVsoftware was used for the tomographic inversion of the data; synthetic models were created by using the RES2DMOD software. In the Enguri dam, data have good quality in the tunnel where ferroconcrete structure wasn’t present. In this situation it is possible to define the position of some void area in the rock mass and define the thickness of the concrete. (Figure 3). In the Zhinvali dam the aim was to detect leakages from the basin and to know something else about the dam structure, such as the presence of clay level and the position of the different material on the structure of the dam.

Figure 4 3D presentation of the Zhinvali resistivity models: in the rectangle an example of the chargeability model is presented

The figure 4 illustrates the 3D resistivity models of the dam; as an example is presented the chargeability model of the line zh_07_03. The analysis of the chargeability model allows the definition of the clay levels, in fact, low resistivity values and chargeability values such as 13 msec indicate the presence of clay levels; otherwise low resistivity and chargeability values define saturated deposits inside the structure of the dam. By interpreting the geoelectrical data it is possible to describe a sort of clay wall just under the top of the dam, this structure was created to impermeabilize the basin and it is described in the plan of the dam. On the structure of the dam is possible to describe the position and the size of the deposits, high resistivity values mean deposits having more gravel inside. In the middle of 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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the dam structure, at a depth of about 45 m from the dam surface, a low resistivity volume, with no chargeability, defines water saturated sediments. An important low resitivity body is detected by the line which investigate the bottom of the dam: it locates the high pressure pipe of the dam. Conclusions The great importance of this project is the transfer of new methodologies to developing countries. Because of this, data were acquired also in condition where it is clear that geoelectric survey wouldn’t give good results. This to avoid the future acquisition of data having no significance. A training period for the Georgian scientist was held at OGS in September 2002, then data were acquired in the Enguri dam in December 2002 and in Zhinvali dam in July 2003. There was a close collaboration between Georgian and Italian partners. Georgian partners participate actively to the project despite the critical economical and political situation of their country. Great importance has the results of the geoelectrical acquisition in the Zhinvali dam, using this methods it is possible to investigate with great detail the structure of the dam, without having big cost for the survey, this, in countries such as Georgia, is really an important factor. Acknowledgment The author thanks Mauro Piccolo of the Eurekos s.r.l. and Ivan Noniev of the Centre for Diagnostic and Monitoring of Construction CMDC (Tbilisi - Georgia) for their cooperation and support during this project. References Abashidze, V., 2001, Geophysical Monitoring of Geodynamical Processes in Region of Enguri High Dam, Publishing House Metsniereba, Tbilisi. Loke, M.H., Barker, R.D., 1996, Rapid lest-square inversion of apparent resistivity pseudosections by a quasi-Newton method., Geophysical Prospecting, 44, pp. 131-152.



O2 - 03

OUTLOOK ON THE POSSIBILITY FOR SLOPE STABILITY EVALUATION ACCORDING TO PETROPHYSICAL DATA Alfred Frasheri Faculty of Geology and Mining, Polytechnic University of Tirana, Albania

Results of the geophysical data for in-situ evaluation of the physical-mechanical properties of the rocks in the unstable slopes in Albania are presented. Albania represents a mountainous country with complicated geology. There are unstable mountain and hill slopes. Developing of new landslides or re-activation of the old ones is mainly due to construction works. Special constructions, such as hydrotechnical works, civil, industrial, urban and rural constructions and constructions in the infrastructure, particularly during last years, as well as destroyed equilibrium in ecological systems through deforestation etc., all these events have contributed to landslide development. Landslides are located in the deluvial deposits, and in the altered-bedrock. The slipping bodies of some landslides have very big volume, more 50 than million cubic meters. Hydrotechnical works in Albania are generally constructed in conditions of rugged terrain and in geological formations in which the land sliding phenomena are often present. There are observed active landslides in the lakeshores of hydroelectric power plants, which represent a great geological risk. Buildings have been destroyed in some villages and some people died in ruins. This phenomenon has been more evidently activated when hydrotechnical works started to be used. During the exploitation period of more than 25 years, the huge hydrotechnical works influenced the physical-mechanical properties in the shore area and caused a series of landslides. One of the typical landslides was developed at lakeshore of the Vau Dejes Lake of Hydropower Plant in Northwestern Albania. The yearly movements of water level at Vau Dejes Lake caused a big landslide at eolated, weathered and destroyed serpentine rocks. Geophysical methodology for in-situ testing Integrated geological-geophysical engineering and geodetic observations have been carried out for slope stability studies and monitoring of the active landslides in Albania. In-situ geophysical investigation and monitoring have been programmed in three phases: 1. Surface integrated geological-geophysical survey and installation of geodetic markers. 2. Drilling of shallow boreholes, cross-hole seismic survey and well logging. 3. Periodical geophysical and geodetic observations in boreholes and on the ground surface. The basic method was the high frequency refraction seismic. Geophone setting in the survey line had distances from 0.5-43 meters, according to the object size and the required seismic depth investigation. The longitudinal and shear waves were recorded through the time intercept method. The natural seismic-acoustic activity inside and outside of slipping body has 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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been observed for a continuous time of 5 seconds. Creating the seismic waves is performed by mechanical shock. A seismic 12-channel station ECHO-2 of Canadian Company SCINTREX was used for recording the seismic signals. The processing of records is made by the company’s software package. The longitudinal waves velocity Vp, the shear waves velocity Vs and the layer thickness were calculated from the field data. The depth of the seismic investigation was about 25-27 m. Electrical Schlumberger soundings and profiling have been performed to investigate and to monitor landslides. Electrical soundings were performed by the Schlumberger array, with spacing up to AB/2 = 500 m, which allowed to reach a survey depth of 120-150 m. Resistivity profiling was performed by multiple Schlumberger arrays with two investigation depths, relating to the required depth of investigation for each object. Together with the geophysical methods mentioned above, the micro-magnetic and microgravity surveys were also applied in some landslides. The hole-hole seismic tomography of longitudinal and shear waves, the gamma-gamma density logging, neutron-gamma logging, electrical logging, acoustic logging and inclinometers have been applied in boreholes. Samples of soil and rocks from the studied area were analyzed in the laboratory for determination of their physical-mechanical properties and for further petrological studies of thin sections. The study of the shape and structure of the slipping body, estimation of physicalmechanical properties of the slipping body and of the bedrock, and evaluation of the level of the landslide natural seismic-acoustic activity were carried out using the results based on the interpretation of geophysical surveys. Physical-mechanical properties of rocks in the landslide area have documented their important role in relation to the slipping body mapping, study of slope stability and dynamics of the landslide’s development. RAGAMI LANDSLIDE VAU DEJES LAKE August, 1996

m 170

150

0

20

W

40m

ES.5 130

ES.4

2.5m

110

ES.3 ES.2

90

E 70

Legend Topographic marker Seismic boundary

ES.1

Geoelecric boundary Diluvium, upper part of slipping body, resistvity 60-400 Ohmm, Vp=140-170 m/sec, Vs=160 m/sec Altered serpentinite of slipping body, resistivity 10-40 Ohmm, Vp=540-1900 m/sec, Vs=230-170 m/sec

50

Altered serpentinite of slipping body, resistivity 60-150 Ohmm, Vp=2750 m/sec, Vs=600 m/sec Serpentinite, bedrock, resistivity 180-970 Ohmm, Vp=1750-3700 m/sec, Vs=970 m/sec

Figure 1 Engineering integrated geophysical section of the Ragami landslide.

Analysis of results Ragami landslide is located in the shores of the Vau Dejes Lake. It is developed in the ophiolitic formation represented by serpentinized rocks. The slipping body represents a big mass of serpentinite, which is eolated, destroyed and covered by a thin layer of deluvium. According to the geological survey in 1992, the landslide did not exist. Landslide has been significantly developed during the last ten years. Slipping body increased in the extent and in the volume substantially during this period. The front part of the slipping body is located along the shores of the lake. This part has the shape of a scarp about 2 -3 m high, and represents a destroyed, schistose serpentinite, partly in a form of mylonite. Three failures in different superficial levels can be observed in this landslide: Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 33


• • •

The first one 35 - 45 m from the shore, with a horizontal dislocation of about 2 m. The second one about 70 - 90 m from the shore, with a vertical jump of about 2 m. The third one about 115 - 130 m from the shore. This is the newest level and has the lowest amplitude.

The integrated engineering geophysical section of the slipping body is presented in Figure 1. Two main sliding plains separate this body. The rock material of plains is broken up. The first plain is at depths of 5 - 7 m, while the second one reaches depth up to 22 m. The lowest part of the second plain touches the lake under the water level. In this way, the sliding body has a block-type character. The physical-mechanical properties of the slipping body are lower than those of the basement rocks, not touched by the sliding phenomena. The micro movements in the slipping body are very intensive and have a wide frequency band, while outside the body no movement activity is observed. Physical-mechanical properties of rocks in the area of Ragami Landslide are presented in Tables 1 and 2. Layer Number

Thickness, in meters

Resistivity in Ohmm

Density, in g/cm3

Wave Velocity, in m/sec Vp Vs

Lithology

SLIPPING BODY 1

0.7

76.4

1.34

210

160

Deluvium

2

4.0

29.5

1.61

540

230

Breaking serpentinite

3

6.5

2.45

3700

680

Water-bearing serpentinite,

4

17.4

46.5

1500

485

2.56

BED ROCKS 3500

Breaking serpentinite 1920

Serpentinite

Table 1 Physical properties in landslide’s area

Layer Number

Poisson’s Ratio

Dynamic Modulus of Elasticity, Eds in *105 kg/cm2

Rigidity Modulus G, in *105 kg/cm2

SLIPPING BODY 0.00140 0.00420 0.00868 0.03630

1 2

0.35 0.39

0.00370 0.02413

3

0.48

0.56586

0.19167

0.26325

0.09608

4

Volume Compression, σ, in *105 kg/cm2

Rock state

Soft rocks Destroyed, shattered rocks

3.26503

Cleavages and fissured rocks Destroyed, shattered rocks

1.91408

Compact rocks

BED ROCKS 0.29

2.46271

0.96199

Table 2 Mechanical properties in landslide’s area

As documented in Tables 1 and 2, four layers with different physical-mechanical properties create the slipping body. First layer represents the deluvial cover. Layers 2 and 4 are represented by destroyed-shattered serpentinite. The third layer in between is characterized by 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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low electrical resistivity and low shear waves velocity. It corresponds to the water saturated cleavages and fissures in the serpentinite. The dynamics of slope movement is also reflected in the natural seismic-acoustic activity. The micro-movements in the slipping body are very intensive and have a wide frequency band. No movement activity is observed outside the slipping body (Figure 2).

Outside of slipping body

Inside of slipping body

Figure 2 Natural seismic-acoustic activity in the Ragami landslide area

Conclusions 1. Thick and high volume slipping bodies represent the Ragami active landslide in the shore area of the Vau Dejes Lake. 2. The extent of the landslide and the position of sliding plans were precisely fixed using the integrated geophysical survey. 3. The block-like character of the sliding bodies brings to the conclusion that the block of these bodies cannot fall down immediately in any kind of velocity. 4. Geophysical-engineering studies have a triple character: a) to study the soil of the landslide area, b) evaluation of in-situ physical-mechanical properties of soils and rocks and c) in-situ monitoring of landslide phenomena. Acknowledgments The authors thank for the generous cooperation to our colleagues Ass. Prof. Dr. Ludvig Kapllani, Dr. Foto Dhima, Eng. Burhan Çanga and Dipl. Eng. Entel Xinxo from Faculty of Geology and Mining, especially for collaboration during the field surveys and in-situ interpretation of geophysical investigations. Thanks also to Ministry of Public Economy and Privatization and Faculty of Geology and Mining for the good conditions created for the performing of the geophysical field investigations in the hydrotechnical works. We thank to the Institute of Informatics and Applied Mathematics, particularly to Prof. Dr. Neki Frasheri for good scientific collaboration in the processing and analysis of geophysical data, and to the Institute of Study and Projecting of Hydrotechnical Works. References Frasheri A., Kapllani L., Nishani P., Çanga B., Xinxo E, 1999, Project for in-situ investigation of the hydrotechnical works during the construction and exploitation. Faculty of Geology and Mining. Polytechnic University of Tirana. Research and Developing National Program: Geology, Exploitation and Mineral Processing, 1995-1998 years.



O2 - 04

UNCERTAINTY AND AMBIGUITY OF MEASUREMENTS IN WIDE AREA NETWORKS OF SENSING DEVICES MEASURING GEOPHYSICAL PARAMETERS John Sarivougioukas1, George Sideris2, Pavlos Sotiropoulos2, James Baker3 1 General Hospital of Athens, G. Gennimatas, 154 Mesogeion Avenue, Athens 11527, Greece 2 TerraMentor e.e.i.g., Serifou 23, Holargos 155 62, Attikis, Greece 3 Selor e.e.i.g. Saffierstraat 101c, 1074 GP Amsterdam, The Netherlands

Summary The study of the geophysical phenomena requires a plethora of evident and discrete data to draw conclusions. The examination of data obliges sometimes to focus either on local observations or to investigate the trends based on processed information of wider areas demanding for the installation of a large number of sensors with versatile quality characteristics retrieving many and different, in nature, information simultaneously. The diffusion of sensors into the environment, forming networks of spread acquisitions, offers the opportunity to examine either particular geographical regions or larger areas zooming in and out of each area according to each of the examinations’ needs. Since the conclusions rely on actual measurements performed by numerous data acquisition systems, monitoring and logging data, it is expected to deal with issues such as ambiguity and uncertainty. The presented work claims that the application of a network of sensing devices each measuring a number of geophysical and chemical parameters provide the necessary and sufficient means to obtain control over both, ambiguity and uncertainty. Introduction The development and evolution of data acquisition systems along with technology offers opportunities in measuring geophysical parameters. Specifically, the development of sensing devices that achieve simultaneous measurements of a number of parameters have been exploited and obtained. Hence, the employment of suitable hardware and software sets is a necessity allowing automated procedures for the recording of each parameter’s values. Since most of the data acquisition systems are installed in rural areas where there is available no kind of infrastructure regarding electric power and wired communications while the weather have to be considered due to the negative influences on the system’s efficiency. Proper computing apparatus allows the simultaneous reading of a number of geophysical sensors whose data may either be processed locally by the employed computer software or transmitted to a central station for further examination. The geophysical sensors along with the accompanying computer hardware has the capability to remain unattended for long periods of time due to both solar power and wireless communications availability too. Computing stations have the capability to be connected to a number of sensing systems in star network’s topology. Augmenting the network’s span, adding more central stations each supervising a number of data acquisition systems and allowing the interconnection among the central stations, a grid of central stations is 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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formed. Hierarchical structures of central stations creating trees of computer interconnected centers provide the capability to obtain the total set of all measured data of a wide area in a root central computer station. Motivation and Related Work We have written this paper in order to show the difficulties that we are facing when we try to monitor, in continuous mode, geophysical and chemical parameters to follow the regulations arriving from the implementation of the water directive 2000/60 for establishing a framework for Community action in the field of water policy which all the E.U. member states have to follow since the 1st of January 2005. From the work that we have accomplished so far it seems that a lot of work remains to be done and to overcome a lot of difficulties in order to implement all the details that the water directive needs for its materialization. Our goal is to try to measure in a network of more than ten (10) geophysical sensors, simultaneously, fifteen geophysical and chemical parameters that a lot of polluted areas in the world needs. It is an attempt which a small number of companies, so far, around the world are trying to achieve although they are facing a lot of difficulties. Wide Area Networks of Sensing Devices The geophysical examination of a wide geographical area requires a large number of observing stations in order to collect information about physical or chemical parameters which is accumulated at a central computing station. Properly prepared computing stations return their processed and raw data to computing stations of a higher level, ending up with a hierarchical model of a tree whose nodes are computing stations and the leaves are sensing devices. Considering the facts that each sensing device measures a number of parameters and the option that not all of the sensing devices measure the same set of parameters, we arrive at the conclusion that the interconnected sensors form sub-networks each characterized by the measuring set of parameters. Interconnecting sensing devices measuring multiple parameters into a star network topology and then connecting the corresponding central nodes of each star in another star network topology a hierarchical network is developed. At a central computing center, firstly, processing is performing on preliminary statistics showing average values, the minima and maxima of values, and standard deviations. Secondly, the processing includes the application of certain filters on the series of the collected data. Next, examining the correlations among the participating parameters a number of geophysical rules apply that provide the development of context related to the observation of a geographical area with a context to be created by the underlying software. In order to turn the contents of the context into safe conclusions both ambiguity and uncertainty have to be identified, quantified and then, taken off from the obtained values. Introduction of Ambiguity and Uncertainty into Measurements Processing a set of data obtained from the interconnected sensing devices concerning a number of simultaneous geophysical parameters includes the application and correlation of scientific and logic rules. In addition, in the processing procedure there may be control points that assure the correctness of the applied methods and the completeness of the used data. When the obtained data values cancel the validity of the employed rules or introduce fuzziness at any processing level, ambiguity ensures its presence. Similarly, when the values of the collected data show limited utilization then uncertainty takes its place into the measurements. Identifying the observed ambiguity a rule structure acting as a controlling object is required to verify the parameters that cause doubts in the decisions providing properly quantified evidences. The acquisition of data from the remotely installed sensing devices and the consequent examination of the obtained data applying mathematical filters translated into proper software computer programs reveal the occasional participation of uncertainty. The identification of the existence and participation of external factors affecting the data validity is not an easy task to Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 37


perform since at each of the sensing devices’ installations there exist local environmental peculiarities. Increasing the number of installed sensors and decreasing the placing distances, it offers the opportunity to obtain denser data and at the same time to acquire evidences about the opportunistic occurrences of uncertainty. The quality of the received data from the spread in the fields sensing devices is realized at the point of information processing. In the cases where the obtained processing results have acceptable or specious forms, the included ambiguity is not obvious and the applied for control mathematical mechanisms can hardly reveal the existence of it. In other words, ambiguity along with the pre-included in the collected data uncertainty always takes place in the data processing and it remains to the processing policies and strategies either to ignore or to identify, to estimate, and finally, to exclude them from the processing procedures. Context Awareness controlling Ambiguity and Uncertainty Spreading sensing devices, each measuring a number of geophysical parameters, physical and chemical, each transmitting the measured magnitudes at computing centers, it provides the ability to create geophysical computer models supplied with data directly from the remotely installed sensors. The computer models consist of mathematical models that have the capability to pass information to other models of wider use. The estimated kind and level of results obtained for a supervised area have to be translated in other forms in order to be understood by the local community or to be converted in other forms, in order to be usable by other informative systems, e.g. by the agricultural surveillance system. Hence, the data obtained by the sensing devices allow the creation of a polymorphic model since the reading values of the observable parameters give the opportunity to examine various aspects of cases using combinations of them. The computer software adapts itself to the context of the received measurements performing the corresponding data processing allowing it the characterization of a context-aware application of modular internal structure permitting the activation of the corresponding software module. The sensing devices supply the computer software with data to decide the activation of the appropriate module depending on the nature of the received data. The appropriate software module performs the predefined processing to issue the designed results, which have to be processed by another software module to examine the obtained quality where two parts are distinguished. First, ambiguity is searched on the obtained results trying to identify overstepping results from the acceptable and quantified set of limits, and the logic conflicts caused by the obtained results. Second, the degree of uncertainty is investigated in the set of used data applying control algorithms that indicate the appropriateness of the processed information. For example, an increase in temperature has to be followed by an increase in conductivity otherwise an investigation has to be started to reveal the causes of ambiguity. The intelligent adaptation of the computer software on the nature of the set of the received data is necessary and critical for two reasons. First, the employed software always applies complete control procedures on the received measurements in order to expose the participation of ambiguity. Second, the decisions on the level of the observed ambiguity is performed in a fuzzy manner that it is followed by the investigation on the degree of data’s uncertainty whenever it is required otherwise the processed information is considered as acceptable, even if some level of uncertainty is included. The critical aspect of the software’s intelligent behavior is related to the consequences related to the announcement of the processed information. An alarm may have disastrous results if it proved to be false and likewise if it proved to be true based on faulty data without informing on time the interested business community. Conclusions and Further Work Computer software automating both the phase of measurements’ processing and the phase of the results’ presentation too, actually brings closer the geophysical community’s efforts to the society’s needs. Context-aware computing structures assisting geophysics, it may be distinguished into active and passive. According to active context-aware software, a sequence of 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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actions performed on the users behalf assisting in the decision making processes announcing the obtained solutions. On the other hand, the employment of intelligent software systems that interact with the geophysicist to draw adequate conclusions is considered less productive and time consuming. However, the ability of tracing from the obtained results to the raw data collected, may expose the influence and permits the investigation of the causes of uncertainty and the consequent results of ambiguity. Some of the measured parameters are more vulnerable than others that appear to be less sensitive in the presence of uncertainty while the limits of sensitivity of each parameter are not clearly defined. Hence, fuzzy logic principles find another place of application but the execution of the required geophysical model demand the availability of flexible tools to simulate the physical processes. The application of colored Petri nets assists in the direction of developing a realistic picture of the real world based on collected measurements, with the colored token to represent the measuring parameters, with the results to correspond to the network’s states, and the transitional conditions correspond to external events. The development of computer software applications implementing the fuzzy logic’s membership functions for both uncertainty and ambiguity and then simulating the obtained results on colored Petri nets, it remains to be investigated to get geophysics into the forthcoming ubiquitous computing era. References Context-Aware Applications Survey, Mari Korkea-aho, 2000. Refer to applications based on Infrastructures deploying maps developed up to year 2000. Towards a Better Understanding of Context and Context-Awareness, Anind K. Dey and Gregory D. Abowd, Georgia Tech. Aspects and definitions of Context and Context-Awareness and related Infrastructures. The Context Toolkit: Aiding the Development of Context-Aware Applications, Anind K. Dey and Gregory D. Abowd, Georgia Tech. Abstraction of Infrastructure employed. Software Design Issues for Ubiquitous Computing, Gregory D. Abowd, Georgia Tech. Geochemistry of natural and contaminated surface waters in fissured bed rocks of the Lake Karachai area, Southern Urals, Russia. Solodov, I.N., Zotov, A.V., Khoteev, A.D., Mukhamed-Galeev, A.D., Tagirov A.B, and Apps J.A. (1998). Applied Geochemistry. Vol.13, No.8, pp.921-939. Charting Past, Present and Future Research in Ubiquitous Computing, Gregory D. Abowd and Elizabeth Mynatt, Georgia Tech, ACM 2000. Analysis of Resolutions of Predictive Models for Antropogenic Changes in the Chemical Composition of Groundwaters and Their Optimum Geochemical Content. Krainov S.S., Ryzhenko B.N. // Geochem. Intern. 2000, V.38(7), pp. 629-639



O2 - 05

A NON-DESTRUCTIVE PULSE NEUTRON MULTIPLE DETECTOR TOOL FOR USE IN ENVIRONMENTAL, HYDROCARBON AND MINERAL EXPLORATION WORK

George Sideris1, Pavlos Sotiropoulos1, Nikos Arvanitidis2, Alekos Dimitriadis2, Gabriel Gaal3, Kalevi Rasilainen3, Klaus Buckup4, James Baker5, Nikolaj Galunov5, Robert J. De Meijer6 1 TerraMentor E.E.I.G., Sarantaporou 8 & Str. Tompra, Ag. Paraskevi 15342, Greece 2 Institute of Geology and Mineral Exploration, Regional Division of Central Macedonia, Fragkon 1, 546 26 Thessaloniki, Greece 3 Geological Survey of Finland, Finland 4 DBM - Dr. Buckup Hohenwarther Str. 2 39126 Magdeburg, Germany 5 Selor e.e.i.g. Saffierstraat 101c 1074 GP Amsterdam, The Netherlands 6 Kernfysisch Versneller Insituut, Rijksuniversiteit, Groningen Zernikelaan 25, 9747 AA Groningen, The Netherlands

In the framework of the Specific Programme: “Promoting Competitive and Sustainable Growth” a detection system was designed and developed in order to provide an added value service beyond standard devices. In the hydrocarbon industry it will be possible for the first time to detect in a pulse regime, two types of radiation emissions using a single device. This means that any saturation of hydrocarbons can be detected, irrespective of the degree of formation water mineralisation, which is a major limitation on currently available neutron-gamma tools, where the formation water has a low mineralisation. When dealing with environmental problems, site evaluation, the essential first step before site remediation, requires a detailed knowledge of the contribution and distribution of potential pollutants. The Pulse Neutron Detector Tool (PNDT) can be used to quantitative data from observation wells and sites, enabling the 3D modelling of pollution plumes and spills. The project had the following quantifiable aims: • To develop for the first time a new Pulse Neutron emitter/detector system based on simultaneous parameter registration in one measuring cycle, giving quantifiable information on hydrocarbon saturation, metal and trace element concentrations including Hg, Ni, Cd, Se, Be, B, as well Fe, Cu and other elements; • To develop an all-purpose device with application in both logging and monitoring; • To develop communication and control software, which will be responsible for the operational status of the device; • To develop interpretation software that will allow rapid, in situ, data processing resulting in on site presentation of quantified concentration values, and appropriate presentation of quantified concentration values using a GIS either on-site or centrally via a mobile link; • The core of a pulse neutron system consists of an emitting tube and the corresponding detecting system. Emitting tube The high sensitivity of the neutron distribution in response to chemical elements and components is theoretically known, but there are problems limiting the application of the neutron technique under real conditions. Few attempts have been made in the past to make the neutron methods more widely applicable to environmental and exploration problems. Conditions in the nature such as water, rock, wet or dry soil, etc., each require a special approach, based on different physical principles. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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This means that the transmitters and receivers should in each case be different. This problem may be avoided by using the Pulse neutron technique, with only one reaction Deuterium/Tritium, delivering neutrons with energy of 14 MeV. Using such fixed conditions any process may be related to this energy and the neutron flux of the source. The best possible results for practical applications will require a high energy, for a high neutron flux, which for physical sources of practical sizes may reach 108 neutrons per second. With this type of neutron emission used in detection, different types of neutron reaction with the medium can be expected: • fast neutrons • epithermal neutrons • thermal neutrons • Gamma-emission produced by neutron reaction kHz. replenisher thermal cathode cathode anode

accelerating electrode target Gap (path) Cathode-replenisher Cathode-thermal cathode Cathode-anode Cathode-accelerating electrode Cathode-target Target-accelerating electrode

Resistance 4,0 Ohm 1,25 Ohm >5*108Ohm >1*109Ohm >1 *109Ohm >1 *109Ohm

Capacity, Farads 2*10-13 1s) and short periods (T5.8)

Discussion and conclusion In this paper we report a possible geodynamic variation occurred beneath Hellenic island arc around the time associated with significant earthquake activity. Previous mentioned variation caused simultaneous temporal variations in seismic b-values; energy released and log N distribution, which is reflected on their temporal profiles. It seems that the changes in the time and space observation of the seismic field, reflects on the seismogenic process. Thus it has been shown that some parameters are useful for earthquake preparation process interpretation and depends mainly on the stress condition that manifest in different areas, like a fault zone system which are controlled by the plate motions in the Aegean and surroundings. Seismicity distribution rate, temporal variation of energy released in term of seismic quiescence and temporal variation of b-value distribution shows a special behaviour before and after the occurrence of some strong earthquakes. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 321

SEISMOLOGY & EARTHQUAKES

The fact that the time decrease of b-value after a period of an increasing phase may implies an increase in the stress level in the crust. In most of the cases, during the decreasing phase and when b-value drops under 1σ confidence limit, a significant strong seismic is observed. As it is well known the use of b-value can be affected by many factors, which can cause different estimates of observed b-values. One of the most common factors is the change in network operating parameters and station density. As it has been shown in previous studies, (Papadopoulos et al., 2003; Baskoutas et al., 2004), applied approach help to overcome difficulties imposed from the use of row earthquake catalogs, at least on the qualitative character of the temporal variations trend. References Baskoutas I, Georg. Papadopoulos, G. Panopoulou, 2004, Long temporal variation of seismic parameters for seismic patterns identification in Greece. Bulletin of Geological Society of Greece. Proc. of the 10th Inter. Con. Thessaloniki, April 2004. (In press). Carter, J. A., E. Berg, 1981, Relative stress variations as determined by b-values from earthquakes in Circum-Pacific subduction zones, Tectonophysics, 76, 257– 271. Imoto, M., 1991, Changes in the magnitude-frequency b-value prior to large (M _ 6.0) earthquakes in Japan, Tectonophysics, 193, 311 –325. Kisslinger C., Mc Donald, C., J. R. Bowman, 1985, Precursory Time-space Patterns of Seismicity and their Relation to Fault Processes in the Central Aleutian Islands Seismic Zone, Abstracts, 23rd. General Assembly of IASPEI /, p. 32. Lyon Caen H., R. Armijo, J. Drakopoulos, I. Baskoutas, N. Delibasis, R. Gaulon, V. Kouskouna, J. Latoussakis, K. Makropoulos, P. Papadimitriou, D. Papanastasiou, G. Pedotti, 1988, The 1986 Kalamata (South Peloponnesus) Earthquake: Detailed Study of a Normal Fault, Evidences for East-West Extension in the Hellenic Arc. J. Geophys. Res., Vol. 93, No B12, 14967-15000. Mogi, K., 1962, Magnitude-frequency relation for elastic shocks accompanying fractures of various materials and some related problems in earthquakes, Bull. Earthq. Res. Inst., 40, 831–853. Papadopoulos, G., Baskoutas I., G. Stavrakakis., 2003, Tools for theFast Estimation of Expected Big Earthquake in predefined seismic prone areas. 1th International Workshop on Earthquake Prediction. Athens, November 2003. Papazachos, Β. C., Papadimitriou, Ε. Ε., Kiratzi, Α. Α., Papazachos, C. Β. and Louvari, Ε. Κ., 1998, Fault plane solutions in the Aegean Sea and the surrounding area and their tectonic implication, 801. di Geof. Teor. ed Applic. Papazachos, C. B. and Papazachos, B. C., 2001, "Precursory accelerated Benioff strain in the Aegean area". Ann. di Geofisica, 44, pp 460-474. Press, F., and C. Allen, 1995, Patterns of seismic release in the southern California region, J. Geophys. Res., 100, 6421–6430. Romanowicz, B., 1993, Spatiotemporal patterns in the energy release of great earthquakes, Science, 260, 1923– 1926. Scholz C.H., The frequency-magnitude relation of microfracturing in rocks and its relation to earthquakes. // Bull, seismol. Soc. Amer. 1968a, v.58, # 1, pp.399-415. Smirnov V.B., Baskoutas I., Zavyalov A. D., Papadopoulos G., P. Sotiropoulos, 2004, Spacetime magnitude cutoff evolution of Greece GI NOA earhtquake earthquake catalog for 1964-2003. XXIX General Assembly of the European Seismological Commission, Potzdam September 12-17, 2004. Wang, J. H., 1988, b-values of shallow earthquakes in Taiwan, Bull. Seismol. Soc. Am., 78, 1243–1254. Wyss, M., 1973, Towards a physical understanding of the earthquake frequency distribution, J. R. Astron. Soc., 31, 341– 359. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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3D P-WAVE VELOCITY STRUCTURE BENEATH SULTANDAĞI, AFYON, TURKEY, FROM LOCAL EARTHQUAKE TOMOGRAPHY Aysun Nilay Dinç and Abdullah Karaman Department of Geophysics, Istanbul Technical University, Maslak 34469, Istanbul, Turkey

Summary Sultandağı fault in Afyon, Turkey, remains within a transition zone between the extentional tectonic regime in the west and Central Anatolia Ova Province. The Sultandağı fault had been silent until October 1, 1995 earthquake with a magnitude of ML= 5.9. This earthquake was followed by two more devastating earthquakes on Februrary 3, 2002 with magnitudes of Mw=6.5 and Mw=5.8. These last earthquakes inflicted damage in buildings causing moderate human casulty. This study utilizes local earthquake tomography to process the aftershocks of the last two earthquakes, and presents a detailed 3-D P-wave velocity structure of the region. The tomographic images of the structure to a depth of 14 km suggest that a prominent anomalous low velocity zone dips beneath Sultandağ metamorphics as identified with high a velocity. Tests with various block sizes confirm such anomalous low velocity zone that may be the geophysical evidence for the thrusting evolution of the Sultandağı as postulated earlier. Introduction The city of Afyon lies at the apex of the Isparta Angle and is located on the transition of West Anatolia Extensional Province and Central Anatolia Ova Province that are the two of the major neotectonic provinces of Turkey (Bozkurt, 2001). This region is under the influence of extensional tectonic regime characterized as graben-horst structures bounded by normal faults. The main fault system in this area is called Sultandağı Fault (Sengor et al., 1985, Saroglu et al., 1987) which is about 65 km long with a generel strike of about N65oE. The Sultandağı fault had been silent until October 1, 1995 earthquake with a magnitude of ML= 5.9. This shocking earthquake was followed by two more devastating earthquakes on Februrary 3, 2002 with magnitudes of Mw=6.5 and Mw=5.8. These last earthquakes caused damage and moderate human casulties. Because of lack of seismicity, complex tectonic regime around the city of Afyon has not been extensively studied. There are conflicting and limited suggestions in early studies that explain the features and mechanism of Sultandağı Fault. Among these early studies, Boray et al. (1985) indicates that this fault played an important role in the formation of Isparta Triangle and activated as a dextral strike-slip fault during neotectonic era. Şaroglu et al. (1987) reports that this dextral strike-slip fault continued its activity as a high angle thrust fault with strike slip component. Barka et al. (1995) describes Sultandağı Fault with a thrust mechanism that is developed under the influence of Isparta Angle that exhibits a compressional regime in the Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 323


neotectonic era. Kocyigit (2002) reports that the Sultandağı fault is a normal fault causing the formation of Eber and Aksehir lakes, and discusses that terraces, hanging valleys, and alluvion fans, as inclined to the fault may be the field evidence demonstrating that the Sultandagi fault is still active. These early studies are limited and the information they provide appear to be somewhat speculative. Although the previous studies identified the fault system and described the morphological features, insufficient evidence for the seismotectonic regime of the region may only be clarified through a representative velocity structure. Obtaining a detailed P-wave velocity structure is important not only for clarifying the tectonic ambiguity but also for the future seismic risk analysis and risk mitigaiton studies. In this study, we utilize local earthquake tomography using the aftershocks of February 3, 2002 earthquake, and present a detailed 3-D P-wave velocity structure of the Sultandagi region. The tomographic inversion was carried out using the program SIMUL2000 (Thurber 1983, 1993; Ebehart-Phillips 1986) that uses damped least square technique and utilizes approximate ray tracer with pseudo bending (Um and Thurber, 1987). We used VELEST as described by Kissling et al. (1994) and Kissling (1988) for the estimation of the minimum 1-D velocity model as required for obtaining high quality aftershock parameters, and generating the 3-D initial velocities. This study is the first comprehensive work in providing the geophysical evidence for the Sultandağı fault system. Local earthquake data for 3D inversion The local earthquake data used in this study are the aftershocks of two main earthquakes occured on February 3, 2002. A seismic network containing 28 Reftek-125 recorders with 4.5 Hz vertical component seismometers were installed around the Sultandağı fault soon after these earthquakes. Station coordinates were determined by the GPS measurements while their elevations were directly interpolated from 1/25 000 scaled topographic maps with an accuracy of ±80 m. The network continously recorded for a duration of 60 days at a sampling rate of 100 sps. The intense sesimicity during the observation period allowed us to record a data set of 1069 good quality local events with 19571 P-phase arrival times. Preperation of the 3-D inversion requires a careful selection of the events. We assumed an event to be good quality if recorded by at least 10 stations with an azimuthal gap (GAP)0.5 was assumed to be well resolved for this study.

Figure 1 Horizantal grid design and the ray coverage for the 3-D inversion. Open circles are selected aftershocks, dark triangles are the seismic stations, and the crosses are the nodes used in the tomographic inversion.

Figure 2 Comparison of the north-south velocity cross sections obtained from 10x10 km (a) and 5x5 km (b) grid-node spacing.

Figure 2 compares the sections obtained from 5x5 km and 10x10 km grid spacing, respectively. These sections may provide evidence about the root of the Sultandağı extending to a depth of 10 km. Although speculative because of the poor resolution, the 6 km/s contour beneath the mountain as shown in the Figure 2b, appears to be higher than the encompassing units, and a low velocity zone seems to be dipping beneath the mountain. However this dipping Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 325


low velocity zone is clearly visible in Figure 2(b), and appears to be unique. This dipping velocity feature seems to coincide with Saroglu et al.’s hypothesis (1984)’s that this fault activated as a thrust at the begining of the neotectonic era. Since our model and array barely cover the mountain, it may be difficult to elaborate more on thrusting. Conclusions This study is the first comprehensive work on Sultandağı fault system. Based on the interpretation of the tomographic images, we characterize three tectonic features; a low velocity zone dipping beneath the Sultandağı may be the geophysical evidence of the thrusting evolution; 2) a transition zone as identified with high velocity rising toward the surface between the linear trend at the east and the earthquake nest at west appears to exist; 3) the seismogenic zone has a thickness of 9 km. Moreover, the depth of the basement of the Aksehir Basin within the Sultandağı fault zone is only a few kilometers as identified with a low velocity horizon in the NW-SE direction. Acknowledgments Serdar Özalaybey from Earth and Marine Sciences Research Institute of Marmara Research Center of Tubitak helped us at every stage while completing this project. Fuat Şaroğlu helped us understand the geological evolution of the region. Bülent Kaypak shared his experiences about the use of SIMUL2000 and Generic Mapping Tool (GMT). We acknowledge Scientist Cultivation Group (BAYG) of Tubitak for providing the primary author with scholarship. References Barka, A., Reilinger, R., Şaroğlu, F. & Şengör, AMC., 1995, The Isparta Angle: Its importance in the Neotectonics of the Eastern Mediterranean Region. IESCA Proceedings, 1, 3-18. Boray, A., Şaroğlu, F., Emre, Ö., 1985, Isparta Büklümü’nün kuzey kesiminde doğu-batı daralma için bazı veriler., Jeoloji Mühendisliği Bülteni, 23,9-20. Bozkurt, E., 2001, Neotectonics of Turkey-a synthesis, Geodinamica Acta, 14, 3-30. Ebehart-Philips, D., 1986, Three-dimensional velocity structure in northern California Coast Ranges for inversion of local earthquakes arrival times, Bull. Seimol. Soc. Am., 76, 10251052. Kissling, E., 1988, Geotomography with Local Earthquake Data., Rev. Geophys., 26, 659-698. Kissling, E., Ellsworth, W.L., Ebehart-Phillips, D., Kradolfer, U., 1994, Initial reference models in local earthquake tomography, J. Geophys. Res., 99, 19635-19646. Koçyiğit, A., 2002, Nature of Neotectonic Regime within the Isparta Angle: origin of Eğirdir Lake, Aktif Tektonik Araştırma Grubu Altıncı Toplantısı, bildiri özleri, MTA, Ankara. Şaroğlu, F., Emre, Ö., Boray, A., 1987, Türkiye’nin diri fayları ve depremsellikleri. MTA Rapor No. 8174, pp. 3945. Şaroğlu, F., Emre, Ö., Kuşçu, İ., 1992, Türkiye aktif fay haritası. MTA, Ankara. Şengör, A.M.C., Görür, N., Şaroğlu, F., 1985, Strike-slip faulting and related basin formation in zones of tectonic escape: Turkey as a case study, in strike-slip faulting and basin formation, Spec. Publ. Soc. Econ. Paleontol. Mineral., 37, pp. 227-264, Eds. Biddle K. T., & Christie-Blick, N. Thurber, C.H., 1983, Earthquake locations and three-dimensional crustal structure in Coyota Lake area, central California., J. Geophys. Res., 88, 8226-8236. Thurber, C.H., 1993, Local Earthquake Tomography: velocities and Vp/Vs theory in seismic tomography: Theory and Practice, pp.563-583, Eds. Iyer H.M. & Hirahara K., Chapman & Hall, London. Um, J., Thurber, C., 1987, A fast algorithm for two point ray tracing., Bull. Seismol. Soc. Am., 77, 792-986.


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STOCHASTIC MODELLING OF THE RELAXATION PROCESS AFTER THE M=9.0, SUMATRA EARTHQUAKE OF DECEMBER 26, 2004; PRELIMINARY ANALYSIS Dragomir Gospodinov1, Vassilis Karakostas2, Ritsa Papadimitriou2 1 Geophysical Institute of the Bulgarian Academy of Sciences, 4000 Povdiv, Bulgaria 2 Geophysics Department, University of Thessaloniki, GR54124 Thessaloniki, Greece

Introduction One of the strongest earthquakes after 1900 with magnitude M=9.0 took place on December 26 in Sumatra, Indonesia, causing a tsunami wave and more than 150,000 casualties. The shock triggered numerous aftershocks some of them being very strong and causing secondary aftershock activity. At a first glance the temporal characteristics of the aftershock process seem quite different from the MOF model and this is why we decided to perform a more detailed preliminary analysis of the relaxation process in time on the available aftershock data. There have been many approaches to model the gradual decay of triggered aftershocks after a strong earthquake sequence. The most widely used model is the so called Omori Law (Omori, 1894), which later was transformed to the modified Omori formula (MOF). It assumes that all events in an aftershock sequence are triggered by the stress field change after the main shock. For more complex situations as is the case of twin main shocks both followed by aftershocks or existence of secondary aftershocks after the strongest aftershocks, Ogata (1988) introduced the idea of self-similarity into the MOF by assuming that aftershocks can be induced by preceding aftershocks and thus led to the proposal of the epidemic-type aftershock sequence (ETAS) model. This model and the MOF provide two competing alternatives to model the temporal distribution of aftershocks; the main shock triggers all aftershocks against the possibility that each aftershock can trigger subsequent events. Considering the Bath’s law in seismology (Bath, 1965), we thought that it could be appropriate to apply the RETAS model (Gospodinov & Rotondi, 2004), a variant of the restricted trigger model, in which only earthquakes with magnitude bigger or equal to some threshold can be ‘parents’. A goal of this paper is to verify versions of the RETAS model (including the MOF and the ETAS model) for the analysis of the aftershock sequence after the M=9.0 earthquake that took place on December 26 in Sumatra, Indonesia. RETAS model conditional intensity For the ETAS model the conditional intensity function contains the times and magnitudes of all events which have occurred before time t :

λ (t | H t ) = µ + ∑ t i 7.0 occurred along the NAFZ (Toksöz et al, 1979; Barka, 92; 96; 2002). The 17 August 1999 earthquake (M=7.4) was the last one of this series. Nearly three months after the 17 August Izmit earthquake, the 12 November 1999 Duzce earthquake (M=7.1) occurred on the western part of the NAFZ and several researches are interested in this region (Toksöz et al., 1999, Barka, 1999). The aim of this study is to obtain further insights about spatial variation of stress regime along a large transform fault using the Gephart inversion method and to analyse the temporal variation of the stress regime prior to the 1999 Izmit earthquake. Method To calculate the stress tensor from the focal solutions we used the method developed by Gephart and Forsyth (1984), Gephart (1990). Data used in the inversion is the orientation of Pand T-axes of 230 fault plane solutions. Basic presumptions of this method are (a) deviatoric stress is temporally and spatially uniform over the region under study (b) earthquakes are shear dislocations episodes on pre-existing faults (c) the displacement along faults does not influence the stress regime (d) slip occurs in the direction of the resolved shear stress on the fault plane. The method yields a stress tensor represented by the three principal stress components, namely, maximum compression (σ1), intermediate compression (σ2), minimum compression (σ3) and the stress magnitude ratio defined as R= (σ2-σ1)/(σ3-σ1). The value of R is an indicator of the dominant stress regime acting in the region under investigation: R=0 when σ1=σ2 (biaxial deviatoric compression or state of confined extension), R=1 when σ2=σ3 (uniaxial deviatoric compression or state of confined compression) and R=0.5 when σ1=σ2=σ3 (uniform triaxial compression) (Christova and Tsapanos 2000). The combination of these four parameters (σ1,σ2,σ3 and R) is called a stress model and the model that most closely matches the whole observed data set is called the best-fitting stress model. The best-fitting model is searched for in a grid over the four model parameters, systematically adjusting one at a time through a wide range of possibilities (Gephart, 1990). The measure of misfit is given by the smallest rotation about an axis of any orientation that brings one of the nodal planes and its slip direction into an orientation consistent with the stress model (Slancova et al 2000). Thus, for each stress model, the misfits between the orientation of the observed data and prediction are estimated and summed. The minimum misfit is the one that yields the smallest sum of misfits and is selected as the regional stress tensor for the region. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

394


Discussion and Conclusion The P-and T- axes obtained from the focal mechanisms of 230 events 1.3 ≤ MW ≤ 7.4 occurred in the region between the westernmost NAFZ and the easternmost NAT during 19432003 are used to estimate the stress tensor acting in the region. Data are collected from several articles and the Harvard CMT catalogue. The misfit errrors, F, between the observed and predicted P- and T- axes found at all the subregions in the range from 4o to 8o suggesting the existence of a homogeneous stress field. R values are in the range of 0.3 to 0.6 suggesting a stress regime from pure strike-slip to transtension. Summary of the results of inversion for the subregions studied is given in the Table 1. Region Duzce Akyazi Izmit Cinarcik Middle Marmara Saros Eastern KAT Middle KAT Western KAT

N

σ1

σ2

σ3

R

F

23 11 39 60 19 24 7 15 32

(112/21) (143/38) (139/27) (131/10) (128/34) (112/23) (125/76) (125/76) (270/10)

(350/54) (315/52) (99/56) (253/71) (85/48) (358/45) (115/14) (96/12) (156/67)

(56/28) (50/4) (51/19) (38/17) (68/22) (51/36) (65/3) (188/7) (4/21)

0.3 0.6 0.6 0.6 0.5 0.4 0.6 0.6 0.4

4.6 5.4 7.9 8.3 5.9 5.9 4.9 5.1 3.2

Table 1 N is the number of focal solutions used for inversion, F is misfit and R= (σ2-σ1)/(σ3-σ1).

The stress axes directions (σ1 (grey) and σ3 (white)) obtained from the stress tensor analysis for all the subregions are given in the Figure 2. As seen in the Figure 2, while the maximum principal stress axis σ1 is rotated from NW-SE in Duzce to E-W in Evia Basin the minimum principal stress axis σ3 is changed from NE-SW to N-S, smoothly. The NAFZ changes direction from E-W to WSW to the west of 27.5o obtained from GPS studies (Pinar et al., 2003). The roles of the NAFZ and the continuation into the Aegean known as the NAT for westward moving Anatolian Block are clearly seen from the principal stress axis directions. These results are in very good agreement with the GPS velocity vector directions (McClusky et al, 2000).

Figure 2 The stress axes directions [σ1 (grey) and σ3 (white)] obtained from the stress tensor analysis for all the subregions.

In addition, the focal mechanism solutions taken from Evans et al. (1985) occurred around the Gulf of Izmit in 1980 show strike-slip mechanisms with normal components. The focal mechanism solutions obtained from Ergin et al. (1997) occurred in the same region in 1996 three Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 395


years prior to the 17 August 1999 Izmit earthquake have larger normal faulting components than the events occurred in 1980. Also, the stress tensor inversion results we obtained using the events taken from Ergin et al. (1997) occurred in 1996 yield a heterogeneous stress field. This heterogeneity might be a harbinger of the large earthquake occurred in the region. References Barka, A. A., 1999, The 17 August, 1999, Izmit earthquake: Science, v. 285, p. 1858–1859. Barka A.A., 1992. The North Anatolian fault zone. Ann.Tectonicae, 6, 164-195. Barka, A.A., 1996, Slip distribution along the North Anatolian Fault associated with the large earthquakes of the period 1939 to 1967, Bull. Seism. Soc. Am., 86 (5), 1238-1254. Christova C., Tsapanos, T., 2000, Depth distribution of stresses in the Hokkaido Wadati-Benioff zone as deduced by inversion of earthquake focal mechanisms, J. Geodynamics, 30, 557573. Ergin, M., Aktar, M., Bicmen, F., Yoruk, A., Yalcın, N., Kuleli, S., 1997, Izmit Körfezi mikrodeprem calısması, ATAG, Birinci Toplantısı, ITU, İstanbul. Evans, R., Asudeh, I., Crampin, S., Ucer, S.B., 1985, Tectonics of the Marmara Sea region of Turkey: new evidence from micro-earthquake fault plane solutions, Geophys. J. R. astr. Soc., 83, 47-60. Gephart, J.W., Forsyth, W.D., 1984, An Impromovent Method for Determining the Regional Stress Tensor Using Earthquake Focal Mecanism Data: Applications to the San Fernando Earthquake Sequence, J. Geophys. Res., 69, 9305-9320. Gephart, J.W., 1990, FMSI: a Fortran Program for inverting Fault/Slickenside and Eartquake Focal Mechanism Data to Obtain the Regional Stress Tensor, Comput. Geosci., 16,953989. Kiratzi, A.A., 2002, Stress tensor inversions along the westernmost North Anatolian Fault Zone and its continuation into the North Aegean Sea, Geophysical Journal International, 151, 360–376. McClusky, S., Balassanian, S. Barka, A., Demir, C., Ergintav, S., Georgiev, I., Gurkan, O., Hamburger, M., Hurst, K., Kahle, H., Kastens, K. Kekelidze, G., King, R., Kotzev, V., Lenk, O., Mahmoud, S., Mishin, A., Nadariya, M., Ouzounis, A., Paradissis, D., Peter, Y., Prilepin, M., Reilinger, R., Sanli, I., Seeger, H., Tealeb, A., Toksoz, M.N., Veis G., 2000. Global Positioning System constraints on plate kinematics and dynamics in the eastern Mediterranean and Caucasus. Journal of Geophysical Research B: Solid Earth, Vol. 105, Issue 3, 5695-5719. McKenzie, D.P., 1970, The Plate Tectonics of the Mediterranean Region, Nature, 226, 239-241. McKenzie, D.P., 1972, Active Plate tectonics of the Mediterranean Region, Geophys. J.R. Astr. Soc., 30 (2), 109-185. Papadimitriou, E.E. and Sykes, L.R., 2001, Evolution of the stress field in the North Aegean Sea (Greece), Geophys. J. Int., 146, 747-759. Papazachos, C.B., Kiratzi, A.A., 1996, A detailed study of the active crustal deformation in the Agean and surrounding area, Tectonophysics, 253, 129-153. Pınar, A., Y. Honkura, K. Kuge, 2003, Moment tensor inversion of recent small to moderate sized earthquakes: Implication for seismic hazard and active tectonics beneath the Sea of Marmara, Geophys. J. Int., Vol. 153, 133-145. Slancova A., Spicak A., Hanus, V., Vanek, J., 2000, Delimitation of domains with uniform stress in the subducted Nazca plate. Tectonophysics, 319, 339-364. Şengör, A.M.C., Yılmaz, Y., 1981, Tethyan Evolution of Turkey: a Plate Tectonic Approach, Tectonophysics, 75, 181-241. Toksöz, M.N., Shakal, A.F., Michael, A.J., 1979. Space-time migration of earthquakes along the North Anatolian Fault zone and seismic gaps, Pageoph, 117, 1258-1270. Toksoz, M. N., R.E. Reilinger, C.G. Doll, A.A. Barka, N. Yalcin (1999). "Izmit (Turkey) earthquake of 17 August 1999: First Report." Seism. Res. Lett., 70(6), 669-679. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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POTASSIUM MAGNETICS TECHNOLOGY FOR EARTHQUAKE RESEARCH Ivan Hrvoic GEM Systems Inc., Canada

Magnetic search for Earthquake precursors goes back more than 25 years, and it’s been disappointing and frustrating most of the time. Crucial parameters of magnetics search require instruments with: (a) (b) (c)

High sensitivity Good long-term stability Possibility of suppression or elimination of the influences of non-earthquake origins i.e. environmental variations of all sorts (including diurnal variations, ionspheric variations etc.), and anthropogenic variations.

The last requirement proved itself as a most formidable one considering very local character of earthquake based magnetic anomalies further obstructed by even a slight conductivity of the crust above hypocenter, due to skin effect problems. Obviously, all measurements must be differential. Early attempts were based on “long base” differential measurements, reference magnetometer being far away from “active” magnetometers. Long-term stability of the order of magnitude nT was a result and a precious few positive results were achieved, often in the atmosphere of not the highest confidence in magnetometers when potential malfunctions could be interpreted as the precursors. Relatively recent use of inexpensive search (induction) coils produced some positive results due to favourable magnetic sensor – earthquake hypocenter geometry a vicinity of the instrument to the hypocenter. We have used some of the positive results (especially Loma Prieta precursor to 1989 San Francisco Earthquake) to estimate a value of dipolar magnetic moment generated by the earthquake. We were, to some extent speculatively, determined an order of magnitude of magnetic moments expected to be generated by earthquakes of various intensities. The results are not very encouraging but they to a great extent explain a lack of good results over all those years of serious efforts to obtain magnetic precursors. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 397


Our findings indicate (see a table 1 of magnetic moments related to earthquake magnitude and their fields at given distances) that we can only hope to detect strong earthquakes, starting with magnitude of 5 or more, and even this in very small area around the epicenter, subject to the depth of hypocenter. Short base or real gradient measurement is a relatively new idea based on greater emphases of gradients on nearer sources of magnetic field i.e. better elimination of relatively farther sources of magnetic interferences. Generally, gradients of magnetic dipoles fall off faster than the total field i.e. smaller gradients at the distance in question will require increased sensitivity of the magnetometer. Potassium Supergradiometer is an instrument that provides an extreme sensitivity (at least shortterm). Let’s see its basics. All alkali group and Helium 4 optically pumped magnetometers use valence electrons for generation of Electron Spin Resonance signals with frequency proportional to the applied magnetic field. Due to the influences of the particular nucleus, ESR shows a spectrum of lines, each line shifted in magnetic field according to a specific orientation of the nucleus. Influences of Caesium and Rubidium nuclei are relatively weak and the spectrum of ESR lines is not spread. For Caesium the whole spectrum lies within 20 nT. Rubidium and Caesium optically pumped magnetometers can only operate with the whole ESR spectrum lumped together. A problem is this lump’s changes shape as the angle between sensor axis and magnetic field direction changes, and the acquired readings follow the lump’s peak. This “heading error” is originally so large for Caesium (up to 20 nT) that the researchers had to resort to a “split beam” technique that allows improved symmetry of the spectrum lump: Now the heading error is within nT or a fraction of nT depending on how well the two halves of the beam are aligned. It is still considerable. In the process the sensitivity of the instrument plummeted about one order of magnitude. Potassium nucleus exhibits relatively strong influence on ESR spectrum and the spectral lines are well separated and spread. Operation using a single narrow line is possible and it can be realized by locking an auxiliary voltage controlled oscillator (VCO) to the spectral line instead of letting the system oscillate. As a result the sensitivity is preserved and we have very high absolute accuracy and a minimal “heading error” in tens of pT range. Sensitivity of potassium magnetometers depends principally on sensor size and with the largest sensors (15cm dia cells) we achieved some 0.05 pT rms for 1 reading per second. This sensitivity is sufficient for a short base gradiometer use in earthquake research. Integration in time is also possible (earthquakes are typically slow processes) further improving the sensitivities. With some 100m spacing at 1 reading per second we can break 1fT/m gradient and with integration perhaps 0.1 or 0.01 fT/m could be achieved.


398


We have presently two Supergradiometers installed – one in Southern Israel some 20km North of Eilat and the other in Oaxaca Province of Mexico. Israel installation has provided some 3 years of data while Mexican installation is just about starting. Other installations in India are now contemplated.

Earthquake Magnitude

Estimated Magnetic Moment Am2

8

3.6 x 1013

7

1.1 x 1012

6

5

4

3.6 x 1010

1.1 x 109

7

Magnetic Fields & Gradients Distance from Hypocenter 50km

100km

200km

400km

28.8 nT

3.6 nT

0.45 nT

56 pT

Field

1.728 pT/m

108 fT/m

6.75 fT/m

0.042 fT/m

Gradient

0.91 nT

0.114 nT

14.22 pT

1.77 pT

Field

54.6 fT/m

3.4 fT/m

0.21 fT/m

0.013 fT/m

Gradient

28.8 pT

3.6 pT

0.45 pT

56 fT

Field

]

1.73 fT/m

0.108 fT/m

0.91 pT

0.114 pT

0.0546 fT/m

6.75 aT/m

0.042 aT/m

Gradient

14.22 fT

1.77 fT

Field

3.4 aT/m

0.21 aT/m

0.013 aT/m

Gradient

28.8 fT

3.6 fT

0.45 fT

56 aT

Field

1.73 aT/m

0.108 aT/m

0.007 aT/m

3.6 x 10

Table 1

Figure 1 GSMP-20S3 SuperGradiometer


Gradient


Figure 2 Location of Earthquake Studies in Progress in Dead Sea Rift area, Israel.

Fiure 3 SuperGradiometer installed near Eilat, Israel within the framework of a joint Canada-Israel research project. Sensors and mounting platforms are shown.


400


O19 - 04

PREDICTABILITY AND UNPREDICTABILITY OF LARGE EARTHQUAKES AND THE PREDICTION OF VRANCEA EARTHQUAKES George Purcaru Institute of Meteorology and Geophysics, Frankfurt, Germany

George Purcaru , Dr. Phil., Seismology, University of Oulu, Finland , graduated from the University of Bucharest, Faculty of Mathematics-Physics. He also finished one‘s studies at (evening) Bucharest University in Philosophy. He worked in seismology at the Astronomical Obsevatory of Bucharest, Center of Geophysics of Academy of Sceince of Romania and Institute of Geology and Geophysis. From 1974 he continued the activity at NORSAR Institute of the Royal Council of Science and Technology, Oslo. In 1976 moved to the Institute of Meteorology and Geophysics, J. W. Goethe University in Frankfurt am Main, concentrating on basic research in seismology, and teaching in earthquake prediction. George Purcaru is interested in principal in: the physical foundation of earthquke occurrence, stochastic models of earthquakes, deterministic and probabilistic forecasting, artificial intelligence, energetic balance and advanced quantification of earthquakes at different scales, earthquake precursos for probabilistic methods of prediction, and plate tectonics. George Purcaru is life member of American Geophisical Union and Seismological Society of America, Asian Seismological Socity, European Advisors Committee of Earthquake Prediction of the Council of Europe decided by Council of Ministers of EU, expert/advisor of NATO research programs. He is responsible of Working Group – Metods and Algorithms of Prediction in the European Seismological Commission.

The problem of predictability - a fundamental problem of any kind of science - of the large, or disastrous, earthquakes is presently a major challenge of earthquake seismology. In spite of the significant progress made in the last 30yrs, since the physical foundation of scientific prediction (Fedotov, 1965) almost all shallow large, or significant, interplate earthquakes remained unpredicted. Only a very few were successfully predicted, regarding the location and size, and the time scale (short- to long-term). The long-term predictions are the most frequent. I summarize different views and our present level of understanding the physics of earthquakes with emphasis on unpredictability and predictability. Finally, I consider my prediction model of large M>6.7- 6.8 earthquakes in the Vrancea region, both prediction-success and predictionfailure (surprise). I found that at the root of unpredictability the basic difficulties are: (1) the complexity of earthquake occurrences in space-time and size in very different tectonic settings, (2) insufficient understanding of the earthquake physics, based on theoretical approaches and simulations that be tested against complete and precise observational data, (3) actual seismological observation data for both large scale (e.g. rupture zone, seismic moment, average stress drop, etc), and smaller Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 401


scale (eg. asperity, barrier) they are still not conclusive for explaining seismicity structures (patterns) to be uniquely relevant to predictions, (4) strongly heterogeneous distribution of the slip, and stress with its perturbations and localized concentrations which lead to unexpected nucleation of an earthquake, (5) inversion models of the rupture are still not unique to be useful for interpreting the observations to have predictive power. (6) unexpected change of regular repeating of a large earthquake at the same rupture zone, leading to intermittence, (7) impossibility to know directly the (absolute) stress level, useful in relation to the failure threshold and criticality, and (8) absence of specific prediction laws for particular seismic zones. These provide physical-observational components of prediction failures and false alarms in both deterministic and probabilistic approaches. Some significant examples are considered. In the Vrancea region the large intermediate depth earthquakes (H = 60-180 km) are intraplate, inslab earthquakes.Table 1 shows the largest events since 1940. The location of the 1940 earthquake is improved using more data. The estimated moment magnitude Mw is 7.5-7.7, based on Purcaru (1974, 1979). M = MGR is the Gutenberg-Richter magnitude. The 1st line gives the nucleation time and the second is CMT, HRV. DATE O. T. Lat. Lon h, km MGR Mw 10 11 1940 01:34:08.5 45.77°N 26.60°E 122.2 7.4 7.6 (7.5-7.7) 04 03 1977 19:21:55.6 45.78 19:22:10.8 45.23

26.70 26.17

88.6 83.6

7.2

7.45

30 08 1986 21:28:37.1 45 52 21:28:51.0 45.76

26.27 26.53

135.8 132.7

7.0

7.2

30 05 1990 10:40:07.7 45.85 10:40:12.7 45.85

26.64 26.66

89.9 74.3

6.8

6.9

Table 1

First, Purcaru (1974) found, from a detailed analysis of large historical earthquakes (11001973) and the estimated magnitudes (Purcaru, 1979), a prediction specific law by introducing the concepts of ‘quasicycle’ and ‘supercycle’ for the forecast of large (M > about 6.75) and largest M > about 7.25) earthquakes in Vrancea. Second, the constructed quantitative model revealed three ‘time-magnitude bands’ in a century, as periods of time containing almost all large and largest earthquakes. The time-bands of highest activity of large and largest events were found to be during the years 0 - 10 (period P1), 30 – 40 (period P2) and 70-90 (period P3) of each century. The reapeat quasicycles are about: 96 yrs in the period P1, 100 yrs in P2 and 104 yrs in P3. The supercycles have a duration of about 300 yrs.The average errors were also estimated, and the model is for long-term prediction. Due to the error-interval a prediction of a future event is possible only within the given interval, and therefore no precise year of the next large earthquake in Vrancea can now be made, and reliably justified. The model predict the next large event in 2000-2010. The model predicted successfully the1977 earthquake in the period P3, but the 1986 and 1990 events were unpredictable. Our prediction law is phenomenological, and in view of (1) – (8), and following Purcaru (2002) we suggested a complex physical model: (a) the 1940 event seems multiple complex, it may have ruptured (down-dip) entirely the slab along strike (NESW). The 1977 event was similar, and with a rupture area S = 70-(20-25) km² and source process 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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duration = 20 sec, (b) In contrast, it ruptured the upper part of the slab, and also down-dip (Figure 2, the red arrow). (b) the rupture zones of 1940 and 1977 are distinct, not-overlapping, (c) if at the asperity spatial sub-scale the ruptures are heterogeneous (at least in 1977) in terms of asperity area and asperity stress drop then it is the variability of the failure, critical stress thresholds that control the repeat of these large earthquakes, (d) the largest high strength zones (asperities) would be the major component of the size of the earthquake, together with the rupture area, (e) if also the thresholds are, in phase, close to failure they are basically governing the repeat time; higher are the thresholds, longer is the repeat time, (f) the 1986 and 1990 events are, however, simple earthquakes, where the first ruptured up-dip (Figure 2, green arrow), The different directions (down-/up-dip) are much important in seismic hazard when they correspond to different depth intervals. For proving if this is a characteristic of Vrancea earthquakes more cases are required.

Figure 1



Figure 2

References Fedotov, S. A., 1965, Regularities of the distribution of strong earthquakes in Kamchtka, the Kurile Island and northeastern Japan. Tudy Inst. Fiz. Zemly AN SSSR, 36, p. 66-93, (in Russian). Purcaru, G., 1974, Quasi- and supercyclicity of earthquakes and time-magnitude gaps in earthquake prediction. Semiannual Techn. Rept. NORSAR, Scientific. Report No. 673/74, 1 Jan.-30 Jun., p. 53-55. Purcaru, G., 1979, The Vrancea, Romania, earthquake of March 4, 1977–A quite successful prediction. Phys. Earth Planetary Interiors, 18, p. 274-287. Purcaru, G., 2002, The physical foundation of seismic cycles of large Romanian, and on the next large earthquake in Vrancea. EOS, Trans. Amer. Geophys. Union, v. 83, no.19, p. 974.


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EXPLORATION CASE HISTORIES& RISK MANAGEMENT

O20 - 01

THE PRE-SALT PROSPECTIVITY OF THE CENTRAL TRANSYLVANIAN BASIN - A KEY TO THE LAST UN-DRILLED PLAY IN ROMANIA ? R. Grunwald, U. Schulz Winterhall AG, Germany

Summary New exploration efforts have been undertaken by the consortium Wintershall and Romgaz in the Southern Transylvanian Basin, Block Transylvania Sud since 2001. As a result of an integrated approach a new play has been identified in the Pre-Salt besides of firming up a number of Post-Salt Leads. In addition to conventional 2D seismic focusing on the Post-Salt succession, one seismic line has been recorded as a converted shear-wave test line, using new digital multi component geophones of Vectorseis type. This line was connecting the Pre-Salt well Brateiu-2 drilled down-dip of the presented Pre-Salt Lead. Good AVO class II/III indications in the Eocene erosive remnant, sub-cropping the Tortonian Salt and the presence of a DHI on PP-data, absent on the PS-data could be an indication on the presence of moveable Hydrocarbons. Revision of thermal maturity modelling, integration of all available well bore data and structural re-interpretation of producing fields as well as geochemical analyses provide a conclusive picture of a new Petroleum Play in the Pre-Salt. Introduction The joint exploration venture of Wintershall and Romgaz was conducted in the southern part of the Transylvanian basin, block Transylvania Sud. The 2D survey shot in this block covered an area of about 800 km² south of the river Tirnava Mare between the cities of Medias and Sighisoara. The block extends in the W-E direction from 24°23‘ to 25°02‘ and in the N-S direction from 45°58‘ to 46°16’, respectively. Geomorphology, characterized by steep slopes and incised river valleys with elevations ranging from 300 m to 700 and heavy vegetation, complicate seismic acquisition. The primary exploration target, the Neogene sands, occur in a depth between 500 to 3000 m as stacked reservoir seal pairs.



The scope of the present work was to examine the hydrocarbon potential of the Pre-Salt horizons, e.g. the clastic layers of Eocene age, sub-cropping the Tortonian Salt as erosional remnants across the Tirnave Graben, at a depth of 3500 m to 4500 m Geologic Setting The Transylvanian basin is an intra-m ontane basin surrounded by the Apuseni Mountains in the West and the Carpathian mountains in the North, East and South. It is a rift basin controlled by a deep (half-) Graben feature where it reaches a maximum depth of 7-8 km in the central-southern part, the so-called Tirnave Depression. The sedimentary sequence can be stratigraphically split into two units: the Pre-Salt (mainly Triassic to Cretaceous marls and limestones), and the Post-Salt (Badenian to Pliocene marls, shales and sandstones). The salt is acting as a detachment unit for the younger Tertiary layers during the final Early Miocene compressional events. In the centre of the basin, the Tirnave Depression is located, a North-South trending half Graben. The western rim of this deep sediment filled through is characterized by extensional movements, whereas the eastern rim of this depression is more influenced by compressional tectonics. Both rims of this Graben are formed by basement highs, most likely of Triassic age, uplifted from around 8 km depth to about 3 km. Within the Tirnave Graben, at the border between Block Tr.-Sud and Tr.-Centru, a Pre-Salt lead is located. This lead is defined as a potential gas bearing Eocene sandstone lying directly under and pinching out against the Badenian Salt. This pinch-out situation defines a possible stratigraphic trap (Figure 1).

Figure 1


406


The presence of a Pre-Salt source rock and its maturity has been discussed and postulated in various exploration attempts in the northern part of the Transylvanian Basin, which is different to the setting in the southern part of the Basin (Oligocene bituminous shale absent). A few PreSalt wells have been drilled in an unfavorable position with respect to Pre-Salt on the Graben shoulders of the basin. The presence of thermogenic gas is proven and documented in the Transylvanian Basin. The most likely age of the indicated source is Albian and consists of deep marine shales, (Harms & Brady, 1993). The evaluation of thermal modelling studies with the nearby wells in the Transylvanian depression show, that the peak oil generation and the gas window is reached at depths between 4600 and 5500 meters respectively. Seismic and Well Database In 2001, the Romanian contractor Prospectiuni has acquired 640 km of 2D seismic data in the survey area. The line spacing was 2 km along strike of the Graben and 4- 5 km along dip. The main focus of this survey has been the Post-Salt section. Dynamite was used as the seismic source; both shot and geophone groups were spaced at 25 m distance with a split spread configuration: Therefore, the maximum offsets range from -3750 m to +3750 m, thus allowing for sufficient offset (AVO) coverage also for the deep target. Due to the rough terrain (part of the area not accessible by vehicles), two SP patterns have been used in the survey: a) Single deep holes (12 m) drilled by trucks and b) pattern shots (3x3 m) drilled by portable hand drills. The single holes were charged with 1 kg of dynamite and the patterns by 0.5 kg per hole. In May 2002, one seismic line has been recorded as a converted shear-wave test line using new digital multi component geophones of Vectorseis type. This line was connecting a Pre-Salt well drilled 4 km WNW down-dip of the envisaged Pre-Salt lead. In 2004, 35 km of conventional infill seismic had been acquired, reducing the line spacing across the prospect to 1-2 km. Seismic Amplitude Analysis and Geologic Fingerprints Due to the lack of acoustic logs for the Pre-Salt section, AVO analysis was restricted to reconnaissance AVO attributes derived after relative true amplitude (RTA) processing, like: a) Intercept*Gradient product (I*G), a good AVO class II/III indicator, responding to porosities down to 15% (as calibrated in the productive Post-Salt section); b) λρ−µρ attribute (Figure 2). These Lame’ parameters have been estimated in reconnaissance mode from integration of P- and S-wave reflectivities obtained via weighted stacking (Smith & Gidlow, 1987). In the up-dip, pinch-out position of the deltaic Eocene fan complex, a distinct and consistent AVO anomaly appears, indicating a possible change from water to gas/light oil. This AVO anomaly can be picked on a few 2D seismic lines over a substantial area. The second part of seismic amplitude analysis employed the signal comparison of compressional (PP) and converted (PS) wave data obtained from the multi-component 2D line. In the Post-Salt section (proven to be gas-bearing), the analysis revealed the fact that the ‘bright Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 407


spot’ zone corresponding to high-porosity gas-bearing sandstones on PP-data was absent on the PS seismic, thus confirming the nature of the Post-Salt bright spot as a true DHI. In the Pre-Salt, the strong amplitudes within the fan complex on PP-data are absent on the PS-data as well. Multi-component data analysis leads to increased confidence of a valid Pre-Salt DHI (Figure3).

Figure 2

Down-dip of the fan complex towards NW, the Eocene conglomeratic sandstone has been penetrated by well Brateiu-2 with a thickness of 80 m. The sandstone was water bearing and flowed with a maximum rate of about 1800 bbl of water /day. 15 km to the NW of our Pre-Salt prospect, well Deleni 6042 penetrated the Tortonian Salt at the rim of the Tirnave Graben, and drilled into Jurassic dolomites, where light oil shows have been seen on fractures (pers. comm., Pal Kosa - Well Site Geologist). The depth of the encountered hydrocarbons corresponds to a position below the base of the fan complex, thus giving the possibility of vertical HC migration into the Pre-Salt reservoir. Further evidence is given by the physically produced amounts of 48° API condensate in a nearby Post-Salt gas field above a faulted salt window, south of the Pre-Salt prospect. Due to the very low temperature gradient in the Post-Salt, and the relatively shallow average depth of the Post-Salt strata (< 2500 m), condensate could not have been generated in the Post-Salt, but must have been migrated into the Post-Salt reservoirs from a mature Pre-Salt source rock. This source rock, most likely of Albian age, has generated gas and light oil. Conclusions AVO and multi component seismic amplitude analysis integrated with geologic observations and re-evaluation of old well data has helped to identify a new exploration lead in the Pre-Salt section of the Transylvanian basin. This lead is represented by an Eocene fan 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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complex pinching out against the Badenian Salt. To our understanding, this exploration play is restricted to the Tirnave Graben located between blocks Tr. Sud and Tr. Centru, where the lower Tertiary section is present, the suspected Albian source rock is existent and buried deep enough to generate proven thermal gas or light oil. Evidence for light oil generation is given by condensate production in a Post-Salt gas field superimposed on a faulted salt window. Faults and the absence of the Badenian Salt form the escape route for hydrocarbons generated in the Cretaceous source rocks.

Figure 3



O20 - 02

RESERVOIR OPTIMIZATION OF THE SOUTHERN LICENSE AREA OF PRIOBSKOYE FIELD, WESTERN SIBERIA, RUSSIA Tatyana Kruchkova1, Vadim Savostikov1, Nik Kalita2, Hector Ruiz2, Edgar Carvajal2 1 Sibneft, Moscow, Russia 2 Schlumberger, Moscow, Russia

This paper demonstrates the usefulness of integrated geophysical, geological, and engineering models in improving oil recovery. Priobskoye field, discovered in 1982, ranks among giant fields in terms of geological and recoverable oil reserves. The field is located in Western Siberia and consists of a northern and southern license areas (figure 1). This paper addresses development of the Southern License Area (SLA), which contains 40 percent of total field reserves. Given the complex geological structure of the Neocomian shelf-slope deposits, poor flow properties, and insufficient exploration and seismic maturity, development of the field was delayed ten years after its discovery.

Priobskoye Field

Southern License Area

Figure 1 Location of Priobskoye Field, Western Siberia.

Before development could commence, several far-reaching questions needed to be answered: • Will the development of the SLA be economic? • How are geological reserves distributed and where are prospects located? • What is the value of geological modeling and reservoir simulation? • Should the well pattern be regular? Is there any preferred flow direction? • What, if any, is the best way to stimulate wells? 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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In 2000, the first production wells in a pilot area were located on the basis of a geological model generated from sparse 2D-seismic and exploration-well data. Results were disappointing, with only 7 wells out of 13 drilled being successful. The operator, Sibneft, reached a painful decision to suspend production drilling and to acquire a costly 900 sq km 3D seismic survey to generate an improved geological model. The contractor, GeoSies, delivered the first results of 3D seismic interpretation in 2002. The new 3D seismic data allowed identification of three major productive reservoirs in the Neocomian deposits (AS10.1, AS10.2 and AS11.2) , paleo- and seismo-stratigraphic analysis, accurate horizontal and vertical delineation of sand packages, and prediction of nonreservoir areas. Neocomian strata formed by gradual lateral, east-to-west, filling by clastic sediment of a relatively deep marine basin, resulting in the clinofrom nature in the AS10.1, AS10.2 and AS11.2 reservoirs. The paleogeographic setting includes coastal, shelf , shelf slope, and deepwater marine deposition systems. The offshore area consists of an aggradation/erosion terrace that dips slightly toward the basin center. Shales covered the surface of the terrace during a short transgression. During the subsequent regression sands were deposited on the terrace and into offshore areas toward the basin center. Some sediment was deposited toward the slope foot, thus forming lenticular clinoform sandstone/siltstone packages. The rate of deposition exceeded the rate of basin subsidence. This was one of the main conditions that controlled formation of sandstone/siltstone deposits at the shelf-slope areas and deep-water marine sediments. Alternation of sand and shale layers, visible in cross-sections, reflects sea-level fluctuation. Also, deepwater currents contributed to the distribution of sediment along the foot of the shelf slope. Deltas were significant sources of sediment for deposition of shelf-slope and deep-water marine sand packages. Bar and channel sands can be identified on log curves. Bars occupy paleoshelf zones between delta-front distributary channels, whereas shelf-slope and deep-water sand packages are located basinward from the distributary channels.

Figure 2 Slice of pseudo-sonic cube for the AC10.2 reservoir showing paleo-relief. Brown areas are highporosity reservoirs (continuous sandstone areas), whereas green and white areas are nonreservoir. Note the feeder channels from the shelf to the deep-water area.



Within this complex geologic setting, the interpretation of 3D seismic data focused on the prediction of sand bodies with viable pay thickness. Major sedimentary cycles were correlated using a seismic amplitude cube. Further, paleo-relief at the base of each cycle was reconstructed for each reservoir (figure 2). Facies distributions were determined for the shelf, slope and deepwater reservoirs. A generic transform for each facies was used to convert the seismic amplitude cube into a pseudo-sonic cube. Because only five sonic logs were acquired from wells in the seismic survey area, neutron logs, which were acquired for all wells from the surface to total depth, were converted into pseudo-sonic log curves. From this, the entire seismic dataset, classified in terms of facies, was converted into a pseudo-sonic cube. The deepest productive reservoir, AS11.2, has the largest reserves. The reservoir consists mainly of shelf-slope and deep-water sandstones. A system of feeders for supply of sediment to deep-water fans is clearly visible in the data.. The AS10.2 reservoir (figure 2) consists of a large fan that formed at the toe of the paleo-slope, in deep water. Sand body geometries and feed channels are clearly visible in the pseudo-sonic cube. The shallowest reservoir interval, AS10.1, was deposited mainly in shelf environments. Wells drilled in these thick, highly permeable sandstones have high production rates and stable behavior. In the field, sandstone and siltstone reservoirs typically are 20 to 30 m thick. Shelf, slope, and deep-water marine bodies in the AS11.2 interval superimpose on one another, suggesting they are part of a single depositional cycle. Shelf slope and deep-water sandstones of the AS10.2 and AS10.1 reservoirs fill the paleo-depressions along the edges of the preceding depositional cycle fans. Thus, the AS10.1, AS10.2 and AS11.2 sand bodies overlap only in the central part of the Southern License Area. If only the AS11.2 is productive in the eastern part and only the AS10.1 is productive in the south, the risk of drilling dry holes increases. The acoustic impedance cube was converted into a porosity cube using petrophysical relationships. This cube was used to predict both pay thickness and reservoir permeability for geological modeling. Core, well test, and log data were used to derive reservoir permeability. Individual petrophysical relationships between sandstone porosity and permeability were derived for shelf, shelf-slope, and deep-water facies in each reservoir. Significantly, productive Neocomian reservoirs consist of isolated, slightly permeable sandstone and siltstone lenses, which are enclosed in shale. Sandstones are never underlain by free mobile water. That is, no aquifer is present, which necessitates an effective pressure maintenance system, in this case waterflooding. Oil is produced in three areas: southern, central and northern. The southern area, where only AS10.1 sands are productive, was developed first. The seismically defined geological model allowed identification of the most productive reservoirs and avoid drilling dry holes. Reservoir simulation models were run for various well patterns. Simulation showed that optimal patterns were a modified line drive waterflooding for the shelf area of the reservoir and peripheral waterflooding for the shelf-edge area, with a producer-to-injector ratio of 2:1. Initial plans were to develop the central area using a seven-spot pattern, oriented 315º. All three reservoirs, which are productive in this area, were to be fractured and were to be produced commingled. However, the AS10.1 sands were deposited in a high-energy shelf setting and, consequently, have good reservoir properties. In contrast, the AS10.2 and AS11.2 reservoirs were deposited at significant distance from the shoreline and have low permeability. Log and Modular Dynamic Tester (MDT) data indicate that highly permeable AS10.1 sand is depleted at the highest rate and that this interval will absorb most of injected water (80%). The contrast in properties of the three reservoir intervals forced commingled injection into all the three reservoirs to be abandoned. Alternatively, a split injection system was devised, with the AS10.1 interval being injected separately from the other two intervals. The selection and orientation of the well pattern has been critical to successful development of the central area. Given that the optimal half length of hydraulically induced fractures has been designed for each well, and ranges from 60 to 150m, whereas the ideal well spacing is 500m, it is imperative to orient the well pattern correctly to avoid premature water 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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breakthrough. An initially inaccurate evaluation of the principal stress direction resulted in very rapid watering-out of three wells in the central area, where alternating producers and injectors were aligned with the actual fracture direction. The injection lines were rapidly reoriented parallel to the water breakthrough. The choice of injection-line orientation subsequently was supported by a Formation Micro Imaging (FMI) log (figure 3) which provides the maximum horizontal stress direction, borehole breakouts and direction of induced fractures

Figure 3 Maximum stress orientation 170±10°, determined from FMI logs (rose diagram), corresponds to maximum injection orientation (blue arrow).

This integrated approach to reservoir development and application of advanced technology for 3D seismic interpretation allowed precise prediction of pay zones in the Priobskoye field, while avoiding drilling dry holes. Hydraulic fracturing brought about high commercial oil production rates. Advanced technologies such as formation imaging, reservoir simulation, use of modular dynamic tester, and production logging provided better insight into the reservoir structure.



O20 - 03

AFRICAN PLATFORM - ALBANIA THRUST BELT RELATIONSHIP AND HYDROCARBON PROSPECTS TRENDS Engjell Prenjasi1, Stavri Dhima2, Shaqir Nazaj1, Frederik Qyrana3 1 Polytechnic University of Tirana, Albania 2 Ministry of Industry and Energy, Tirana, Albania 3 National Scientific Hydrocarbon Center, Fier, Albania

Recent exploratory works have added and improved information on tectonic setting and oil-gas-bearing perspective of onshore and offshore areas of the Western Albania. So, it’s possible to make out the following main tectonic units and oil-gas prospects trends: 1. African platform with its parts, pre-Apulia zone, as well as Paxos (Greece) or Sazani (Albania) ones. This unit enters partially into Albania offshore and onshore, as a big monocline composed of the Cretaceous to the Oligocene carbonates that dip northeastwards under Albania Thrust Belt; 2. Albania Thrust Belt: It represents a tectonic assemblage composed of several tectonic zones that lie southeast-northwestwards in direct northern continuation of the Hellenic Napes. The Thrust Belt consists of four rocky formations as follow: a. The Carbonate formation ranges from the Upper Triassic to Eocene age. They often are interrupted by the evaporate rocks of the lower part of the Upper Triassic, which have emerged from their normal position owing to a common effect of tectonic forces and diapirism; b. The Flysch formation of the Oligocene that often increases considerably its thickness, due to a triple effect of lithological changes, tectonic folding and clay diapirism. (Prenjasi, 1991, 1997); c. The Flyschoid formation of the Upper Oligocene - Lower Miocene, which consists chiefly of thick bedded sandstone intercalations, puddings, silts and clays; d. The pre-molasses formation of the Burdigalian - Tortonian included, that consists chiefly of massive marls and marl clays with intercalation of lithothamnium limestone. The three first formations set up the Lower Tectonic Stage of the Albania Thrust Belt. While the pre-molasses deposits of the Burdigalian - Tortonian set up the Middle Tectonic Stage. (Plaku et al., 1962; Dalipi et al., 1987). 3. Circum-Adriatic Fore-deep: It is filled up with molasses deposits of the Serravallian-Messinian and late molasses of the Pliocene that set up the Upper Tectonic Stage, which lies unconformable on both units; the African Platform and 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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Albania Thrust Belt. Nevertheless, the Neogene’s structures of the Circum-Adriatic basin more or less must have inherited the form of the anticline structures of the Lower Tectonic Stage. Sometimes the unconformity between the tectonic stages becomes gradually invisible. (Bakiaet al., 1987). Thrusting of the Albania thrust belt, like the Western Hellenic Napes (Jacobshagen et al., 1987) onto the African platform and molasses cover have created some serious difficulties in respect of obtaining seismic information on the structural and tectonic features along the thrust front area and eastwards platform dip (Figure 1). Therefore, for the time being, it is very difficult to connect and interpret the rare fragmental seismic horizons under the thrust plane. The thrust contact is obvious at the outcrop area of the African platform and Albania thrust belt, at Llogara Pass, in southwestern Albania. Farther south and northward the trace of the thrust is completely masked under molasses deposits of the Circum-Adriatic Fore-deep. Nevertheless, locally it's possible to depict reliably the spatial position of the frontal thrust plane dip. Geo-seismic data, as well as drilled wells ones suggest that the lonian and Kruja (Gavrovo) zones represent the western part of the Albania Thrust Belt, which consists of several anticline lines separated by the relevant syncline ones. All structural lines lie southeast-northwestwards up to their progressive interruption against the thrust front plane. The three above mentioned bulky tectonic units of the Western Albania have significant interest for oil exploration as follow: The first trend of the spatial location of the hydrocarbon prospects belongs to the anticline lines of the Thrust Belt. Each anticline line consists of several eroded anticlines and anticline structures overlain by flysch. The latter, often are masked by transgressive molasses deposits or by eroded and thrusted structures (Prenjasi, 1991). Existence of steep flanks and closures in most of the anticline carbonate structures overlain by folded flysch, often have created big problems for seismic survey. The same acquisition method applied in the Sazani zone has turned out no effective in the Thrust Belt territory. Therefore, it has not been possible to record the top Eocene level of the carbonate structures overlain by flysch in the thrust belt part of Albania’s Southern Offshore. Nevertheless, depiction of the geological setting and carbonate oil prospects of this offshore part (Western and Eastern Sasaj. After Prenjasi E. et al 1994) could be possible owing to complex interpretation of several detailed geological data observed along the coastline area, as well as some relatively poor data of few onshore seismic lines. On the other hand, discovering and prognosticating of the oil-gas bearing sandstone beds in molasses deposits of Miocene and Pliocene age are based on offshore and onshore seismic survey data. However, in cases of sandstone target, during oil and gas exploration is very necessary to investigate on the sandstone lithological changes, as well as on the existence of the longitudinal closure of the Sasaj bay. Another obstacle in respect of obtaining seismic information is the existence of many local thrusts, often of considerable horizontal amplitude, within the Thrust Belt, and especially along its thrust front. In these occurrences, the top Eocene limestone boundary is not recorded as usually in a form of a two or a three-phase horizon associated with transparent facies above and under the horizon. Nevertheless, substantial acquisition improvements are achieved due to fold increase up to 48%, charge whole depth of 30m, charge size of 5-7 kg and the short trace interval of 25m instead of 50m. Additionally, it is required further integration of all exploratory geoseismic methods through Iterative Modeling Approach. Also, possible direct contacts between the limestone of the African platform and the limestone of the Albania thrust belt along the thrust plane in depth might have brought about the depleting of the former traps. Presumably, aggressive movement of the underground waters has caused a potential impact, shifting or destroying the oil accumulations within this tectonic setting framework. So, are the examples of obtaining of almost the same very low salinity water from Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 415


two wells (Vlora-5,6), which have penetrated into the Eocene limestone of the Vlora prospect, respectively at about 4500 and 4800m (Figure 1). The depth of the oil prospects of the Thrust Belt ranges from 100 m to below 6500 m. The second trend of the spatial spread of the hydrocarbon prospects in the Western Albania belongs to the Sazani zone.

C

N1b1b

B A

N 1 1a

Figure 1 Cross geo-seismic profile III-III: Direct contact between carbonates of the Albania thrust belt (OTC) and the pre-Apulia Foreland (FTC) may be the reason of the presence of fresh waters in a considerable deep prospect (Vlora) in Albania thrust belt. BPT- base of Pliocene transgression, BMTbase of Messinian transgression, OTC - orogeny top carbonates, OTHF - Thrust belt front, FTC - preApulia platform top, eroded carbonates, Mz - Pg2 - Carbonate sequence of Mesozoic-Eocene in thrust belt, Mz-Pg33 Carbonate of Mesozoic-Oligocene in platform

There are several carbonate structures and erosion mounts overlain by unconformable premolasses or molasses deposits of the Neogene’s series of Burdigalian to the Pliocene age included. Surely, this type of prospects is threatened by possible direct communication between the eroded limestone and the sandstone beds above as it resulted in one dry well drilled on a spectacular erosion carbonate mount, in Adriatic offshore. Thirdly there are some oil and gas prospects located within the circum-Adriatic Fore-deep. The seismic surveys carried out in this unit have resulted in solving some seismic stratigraphy and structural problems, as well as partial solution of the chronological order of the tectonic faults. Also, there are applied seismic procedures of sequence analyze for making out deposition sequences on the bases of reflection terminations. While the lithological changes within a seismic sequence are interpreted through the facies analyses, considering both the apparent forms of the reflections and their characteristics. Considering carefully all the above mentioned geological and seismic achievements, times after time are discovered several gas fields in the sandstone beds of the molasses and late molasses of the anticline structures of the Upper Tectonic Stage. On the contrary, some nonaccurate depictions of the distribution of sandstone beds, tectonic features and the abnormal pressures phenomena within the Circum-Adriatic basin have brought about some dry wildcats and developed wells. Conclusions Faced problems and negative recent exploration results do not imply poor hydrocarbon perspective in Albania. On the contrary, many oil and gas opportunities exist, but they need more accurate acquisition, processing, reprocessing and interpretation of the all complex methods data. Above all, it is necessary to realize an exact depiction of spatial position for all structural 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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elements of each hydrocarbon prospect. So, accurate detailed revision of surface geological mapping is among the first musts in order to detect, and interpret reliably the presence of possible difficulties as steep flanks and closers, evaporate and clay diapirism, thrust of eroded structures, transgressive covers, etc. Tackling these problems rightly needs carrying out some methodical seismic lines and latter on shooting additional lines strictly oriented according to geological duties. Also, applying programs of direct exploration for hydrocarbons, that might be realized through the Strat Works and the other programs of Landmark Company will bring about better results. References Bakia, H., Thomai, L., 1976, Geological setting and oil-gas bearing perspective of the ''Cakrani'' region. Bakia, H., Yzeiri, D., Dalipi, H., Dhimulla, I., 1987, Geological setting and oil gas-bearing perspective of the Kruja, Ionian, Sazani zones and circum-Adriatic Depression . Jacobshagen, V., Durr, S.E., Kockel, F., Koop, O.K., Kovolozyk. G., 1987, Structures and geodynamic evolution of the ''Aegean'' region. Plaku, K., Hoxha, Sh., 1962, Geological setting and oil-gas bearing perspective of the ''GorishtCakran-Ballsh'' region. Prenjasi, E., 1991, Doctor Thesis: “Tectonic setting and present spatial position of the carbonate structures overlain by flysch in the Ionian zone” Prenjasi, E., Jano, K., 1994, "Geologic-geophysical synthesis of the Block-5 of Albania Offshore”. Prenjasi, E., 1997, Geological setting and oil-gas bearing perspective of the ''Perati'' region.



O20 - 04

THE ROLE OF GEOPHYSICS IN THE MINISTRY OF ENVIRONMENT AND WATER MANAGEMENT’S NEW STRATEGY ON THE PROTECTION OF THE SOIL AND OF THE SUBSOIL Sulfina Barbu, Nicolae Heredea Ministry of Environment and Water Management, Bucharest, Romania

Provisions of the Government Programme 2005-2008 In accordance with the Government Programme 2005-2008 the Ministry of Environment and Water Management has developed a new organizatory structure within witch the specific environmental problems for soil and subsoil as well as the problems of unregenerative resources will be dealt with in an unitary framework at the level of a new general specialized department. The organizatory structure and the attributions of the new general department The name of this new structure is: “General Department for the Conservation of Nature, Biodiversity, Biosecurity, Soil and Subsoil”. We emphasize the large significance we attribute to the concept of “conservation of nature” that also refers to non-living nature, to mineral nature, to earth as a solid and cosmic body. At the moment the general department has a number of 16 attributions, tasks or directions of activity. Among these two are specific to the problems of geologic environment: • It coordinates the activity of implementation of the environmental politics regarding sustainable management of natural unregenerative resources, the ensuring of the quality and of the protection of soil and subsoil, the supervision of environmental radioactivity and radioprotection, in conformity with the European and international demands and standards for the ensuring of sustainable development: • It elaborates projects of official normative documents, methodological norms and instructions of appliance for ensuring sustainable management of natural unregenerative resources and for investigating the quality of soil, subsoil and of environmental radioactivity or decides on the projects of official normative documents elaborated by other ministries for these fields. Other 10 attributions are in common for both the field of biodiversity and biosecurity and geologic environment. Expressed in a synthetic form they refer to: applicability of strategies and programmes; implementation of politics; elaboration of strategies; management of protected areas; legislative proposals; participation in authorization activities; information dissemination; monitoring similar activities; references to EU demands; cooperation with different structures. Only 4 from the attributions of the general department are specific to the field of biodiversity and biosecurity. The structure and the attributions of the new division “ The Office for the Protection of the Soil and of the Subsoil” Now this office has the following staff structure: a) Office head – superiour counselor; b) superiour counselor; 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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c) principal counselors; d) debutants. Hiring conditions ask for college graduates in the field of geologic sciences and soil sciences. The attributions of the office at the beginning of its activity are the following: • It coordinates the organization of activities of monitoring the soil and the subsoil and of the environmental radioactivity and of the quality of the natural unregenerative resources; • It develops and promotes economic instruments of environment for the applicability of the principles of sustainable development at the consumption of unregenerative natural resources; • It promotes bringing about a national network of control and monitoring of the quality of the geologic environment; • It coordinates the activity of the laboratories for environmental radioactivity and geologic analyses; • It participates in the coordination of the activities of the development and of the management of geologic protected areas; • It coordinates and promotes the bringing about of some reference instruments for the condition of the environment, as are the national geochemist maps, geologic maps, maps of natural and antropic maps, maps of natural hazard, hydro-geological maps, geophysical maps etc. • It elaborates and promotes projects of official normative documents, methodological norms and instructions of applicability in the field of the investigation and the evaluation of pollution in soil and subsoil, of ecological cleaning and recovery of the contaminated geologic areas and of the areas radioactively contaminated; • It participates in the secretariats of risk on natural phenomena and disasters and on the control of environmental accidents; • It promotes technical and economical instruments for the evaluation of damages caused by the pollution of the soil and subsoil for cleaning, decontamination and ecological recovery. The role of geophysics in the new directions of activity regarding the geologic environment The role that we want to attribute to geophysics in the field of environment sciences and that we have considered in the structure and the activities of the Minister of Environment and Water Management and that we will prepare for the subordinate structures and in coordination with the regional and local activities, do not differ from the position and role that geophysics has within the earth sciences. We underline the necessities of using geophysics in the field of environmental protection as: • An instrument of drawing tomographies of the subsoil, 2D or 3D; • An instrument of investigating the quality and the condition of geological environment; • An instrument of investigation and knowledge of pollution phenomena in the geologic environment; • An instrument of knowledge of the dynamics of the physico-chemistry phenomena to depth areas where human activities take place; • An instrument of knowledge of the earth structure, of the phenomena that occur/ may occur, with an impact on development/ human communities and on the equilibrium/ stability of the environment; • An instrument of achieving quantified quantitative or semi-quantitative regarding the investigated geological environment; • An instrument of monitoring “in situ” and/or “on line” Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 419


In a methodological package that we are taking into consideration and which includes the minimal demands for the investigation of the quality of the geological environment (soil and subsoil), the geophysical investigation is situated on the first place together with the geochemical investigation and geological observations of surface destined to be achieved in the first stage of investigation. After that, other categories of depth geological or laboratory works depending on the objectives and on the necessities follow. We also mention our necessity to use geophysics, through all the organizatory structures that promote and practice it: higher specialized education, university research, traditional geophysical research, geophysical services offered by public or private companies, or in other important directions: • As an instrument of economical efficiency of the costs of environmental investigations in soil and subsoil by obtaining a good proportion price/knowledge/quality especially taking into consideration the fact that the financial potential in the field of environment is significantly lower than for example that from the field of prospection, exploration or exploitation of natural resources; • As the main source of promotion on the Romanian environmental market of new methodologies, techniques and equipments of research of the geologic environment; • As a source of specialists who will migrate towards the field of environmental protection to find jobs in the structures of the Ministry of Environment and Water Management, in structures of local and central administration, in the specialized divisions of the companies that offer environmental services. Invitation to collaborate This material is not actually a classic scientific project. It is probably a project of environmental politics focused on the protection of the geologic environment and on the use of geophysics in this direction. Nevertheless, for the Romanian geophysical community, and also for the Balkan, European and International ones, we consider that it is important to know the official directions of development for the activities of the Ministry of Environment and Water Management for the environmental factor “earth= soil+subsoil=geological environment”, as well as our intentions to use geophysics in the field of environmental protection. In accordance with the existing strategy and programmes we appreciate that in approximately one year, the market of geophysical works for environmental protection will significantly develop. This is why we invite all the Romanian geophysical groups to get ready for the competition. We would be very happy to receive your assistance, -experience, technical-scientific knowledge, human potential-, in our effort to prepare very well the future geophysical activities in the field of environmental protection. The Romanian market will open completely after accession in the EU, including the market for specialized works in the environmental field. We also invite our colleagues from abroad to participate in environmental works on the Romanian market. Ministry of Environment is open to any contacts, consultations and collaborations from abroad. In the same time we address this invitation to collaborate to the whole Romanian geological community.


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O20 - 05

THE LEGAL FRAMEWORK THAT CONTROLS THE EXPLORATION ACTIVITIES IN ROMANIA. RESULTS OF THE OPERATING PETROLEUM AGREEMENTS AND NEW OPPORTUNITIES M. German1, N. Pandele2, P. Cristian2, P. Aurel3 1 NAMR, Bucharest, Romania 2 Petrom, Ploiesti, Romania 3 Romgaz, Medias, Romania

National Agency For Mineral Resources Main competencies: • concession, according to the law, through petroleum agreements, of the exploration and exploitation rights for petroleum blocks located onshore and offshore; • granting the national transportation system and the public property of petroleum operations in the oil terminals; • issuing specific technical instructions and regulations, which represent the secondary legislation applied to the petroleum sector; • establishing the reference oil and gas prices for royalty calculation; • monitoring on-going petroleum agreements, permits and notifications, including the payment to the state budget of the petroleum royalty; • establishing taxes and tariffs applied to the petroleum operations, including the petroleum transportation through the national pipeline system; • administration of the national petroleum fund of resources and reserves; • establish and administrate the national data base; • ensuring for the oil and gas deposits rational exploitation, in accordance to adequate technologies and equipments, for each type of petroleum operation; • certification of competency of the natural and legal persons involved in petroleum operations and monitoring their activity. Petroleum Legislation • • • • •

1924 – The first Mining Law, which included provisions regarding the concession of petroleum exploration and production activities; 1937 – A new Mining law, improved due to the important increase of petroleum activities recorded in 30’s; 1942 - First Petroleum law - in the condition of the World War II, was very strict and protectionist; 1995 – Petroleum Law No. 134; 2004 – Petroleum Law No. 238. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 421


Main Results obtained under the Provisions of the Petroleum Law No. 134/1995 1996-2004 • • • • •

established new relationship between the state as owner of the mineral resources and the state companies; the administration documents, subsequently changed to concession agreements, allow both concession transfer, and association between Romanian and foreign companies; the National Agency for Mineral Resources was set up, in 1993; open exploration areas were offered in 6 licensing rounds. As a result, NAMR concluded exploration agreements for 24 blocks with international oil companies or consortiums; 70% of the prospective area is already under exploration, development and production agreements.

Petroleum Law No. 238/2004 -Improvements Provided by the new law •

• • • •

The current law defined 40 terms and expressions, allowing a better understanding of the legal provisions, in comparison with only 14 terms explained in the replaced law. Among the new definition we mention: operator, underground storage, transit, national petroleum transportation system and provision for abandonment. The data and confidentiality regime is more clearly stipulated in the new law and details are provided by Methodological Norms. The right of use and access to the land, necessary to conduct the petroleum operations includes new methods – sale and purchase, land exchange, lease, concession, or association between the land owner and the title holder. The new law allows the private property of the new pipelines, which are not part of the national petroleum transportation system, making possible new investments. The transit pipelines will be built based on inter-governmental agreements, approved by special laws and their legal status will be stipulated by those laws. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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• • • • •

• • • • •

The rules applicable to the national transportation system ensuring the transportation and transit of petroleum are in accordance with EU regulations. The term of the concession agreement is now up to 45 years, comparing with 30 years provided by the replaced law. The administration right was removed, equal treatment is granted for Romanian and foreign companies, either state owned or private property. The public offering rounds for the concession blocks could be organized whenever is requested, not only on a yearly basis, as stipulated in the replaced law. In this way, the petroleum agreements will be finalized a few months earlier than before. The public offering will follow a bidding procedure, transparent and non-discriminatory, established by Norms, on the international practice basis of the petroleum sector. Under the provisions of the new law the Concession Law No. 219/1998 is not applied anymore. The direct result will be the decreasing up to 6 month of the term to establish a winner and to conclude a concession agreement. The stability of the agreement is granted by the provision stipulating that the petroleum agreements remain valid for their entire length, except the case of adopting a new legal provision more favorable to the title holder. The preemption right of the Romanian State to purchase the oil and gas produced under petroleum agreements was removed. The title holder has the obligation to record in the accounting books and the right to deduct annually a provision for abandonment and environment restoration. The title holder has the right to conduct underground storage operation, in their depleted fields, based on NAMR approval. The other rights of the title holder stipulated by the Law 134/1995, including assignment, association, unitization, arbitration, both Romanian and international court were maintained.

Methodological Norms ¾ ¾ ¾ ¾ ¾ ¾ ¾

access to the data and information; rules applicable to petroleum concessions; bidding procedures including provisions concerning the schedule of the bidding rounds, available data, content of the bids, bidding opening, the evaluation criteria and formal objections; classification of petroleum resources and reserves; the content of the petroleum book; title holder obligation regarding petroleum operations; granting procedure.

Technical Instructions new provisions for establishing and administration the Petroleum Book; improvement of the NAMR control of the drilling, rehabilitation, exploitation and abandonment operations; rules for the compensation of the damages produced by petroleum operations to the legal and private persons; new provisions concerning geological and technical reports, requested by NAMR; the establishment of the reference prices for oil and gas, used for the royalty payment calculation. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 423


New romanian legislation • • • • • • •

is in accordance to the Communitaire Aquis; increases the transparency and equity of the biding rounds organization; regulates new aspects, as underground storage and transit; simplifies the petroleum royalty calculation and payment to the state budget; makes possible the private property on pipelines, including transit pipeline; all protectionist provisions against foreign or private investors were removed; all provisions encouraging the bureaucracy were changed.


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O20 - 06

RISK MANAGEMENT FOR COMPETITIVE E&P

P. Neculae, G. Duta, D. Caminschi, A. Sauciuc, M. Zamfirescu, D. Popescu, A. Dragomir, C. Popa Petrom, Ploiesti, Romania

Risk Management is a mature discipline with its own processes, tools and techniques, and with consensus about its main concepts and practices. Nevertheless, projects still fail to meet their objectives and businesses are deprived of the benefits, despite the theory that risk management should contribute success. Why is risk management failing to live up to its potential? The focus is almost entirely tactical, and does not consider strategic sources of risk which might affect either the project or the wider business. Risk management commonly restricts its scope to dealing only with uncertainties that have a potentially adverse effect, in other words threats. This ignores upside risk, or opportunity, which can be viewed as risk with positive impact. The current tendency of risk management to deal only with tactical threats in the project arena reduces the ability to tackle the strategy/tactics gap, since the risk process only considers one side of the equation. The failure on the risk management side can be overcome by widening the scope of risk management to encompass both strategic risks and upside opportunities, creating an integrated approach. To bridge the gaps between strategic vision and tactical project delivery, two modifications are required to the scope of the typical risk process:

include strategic elements include opportunities

The primary requirement for implementing strategic risk management is to identify those strategic objectives which might be affected by uncertainty. In the same way that the typical tactical threat-based risk process can be extended to deal with strategic risks by focusing on strategic objectives, the process ca be modified to address opportunities, including upside risk. Benefits of an Integrated Approach:

Bridging the strategy/tactics gap to ensure that project delivery is tied to organizational needs and vision. Identifying risks at the strategic level which could have a significant effect on the organization, and enabling these to be managed proactively. Providing useful information to decision-makers when the environment is uncertain, to support the best possible decisions at all levels. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 425


The organization of the Integrated Risk Management system in Petrom (Enterprise Wide Risk Management) is tailored to Petrom’s organizational structure: risk reporting covers the four business segments (E&P, Refining, Marketing and Finance) as well as the Corporate Functions. Risk Management Stages:

Risk Identification Risk Evaluation Risk Control Risk Reporting

The aim is to obtain a comprehensive overview of all major risks and areas of risk, particularly those that could endanger the continued existence of the business. For the purposes of analysis, the risks are classified into categories, which serve to group risks of similar types and help of recognition of the enterprise-wide impacts of different risks. Risks in technological environment

Market price risks

Risks in political environment

HR related risks

Risks in legal environment

Security risks

Risks in economic environment

Environmental risks

Market risks (sales)

IT risks

Market risks (supply)

Reputation risks

Project risks / acquisition

Organizational risks

Business process risks

Hazard risks

Risks relating to assets and facilities

Compliance risks

Risks related to quality and service

Innovation risks

Investment and major acquisition risks

Safety and health risks

Financial risks Categories of risk identified within OMV Group

The paper presents a series of risk management examples in Petrom E&P activities, ranging from exploration to production and completion: ► ► ► ► ►

3D Seismic Survey for Reducing Risk and Improving Economics Risk Management in Log Data Acquisition/Interpretation Probabilistic Reserves Evaluation on Sopot Structure Using Risk Assessment to Design Drilling Fluids - Well OB1 BRAGAREASA Risk Management in Production, Frac-Pack Technology Description

3D Seismic Survey for Reducing Risk and Improving Economics The key to success is the ability to map potential reservoir units and plays, understand and predict lithology, generate prospects with associated reserves and risk in a very short time and then communicate the results of the evaluation to technical and business people who will make the financial decisions. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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Braided channel identifiable only by 3D

Figure 1 The geometry of this channel is not distinct from the conventional 2D interpretation

Risk Management in Log Data Acquisition/Interpretation The risks emerge from different directions: Drilling (fluid types, ROP, formation damage etc.) / Tool related (types, inherent limitations, applicability) / Processing derived / Interpretation (types, software) / Expertise level Log data acquisition & interpretation in Romania are also subjected to extra risks derived from particular situations. Possibly Gas by RST

1/200 scale After perforations: 2031 - 2028 >> Gas 59000 m3/day

Figure 2 Contesti RST study for hydrocarbon identification

Risk Management in Production: Frac-Pack Technology Case Study – 30 bis Balteni Frac-pack job Well 30 bis Balteni Production Forecast

High 16 Water Li q ui d ra te , n

Frac-

14

80 70

liquid rate net rate water cut

12

60 50

10

40

8

watercut( )

6 4

30 20

Water limit

10

2 0

- Date of finishing drilling - Perforating date 29.07.1998 Formation Meotian IV (unconsolidated sands) Job purpose: IP increase and reduce fines migration phenomenon Job data 14.09.2004

9 111 123 45 678 911 112 34 567 891 11 123 456 789 11 112 345 67 891 111 234 5 200

200

200

200

0

200

year/mont

Well 30 bis Balteni Real Production History Frac-

24 High

22 Water

Li q ui d ra te ; n

20

70

liquid rate net rate water cut

18 16 14

60 50

Unexpected watercut increase

40

12 10

30

8 6

20

4

Water limit

10

2 0

Calculated fracture geometry

80

91 11123 45678 91111 2345 67891 11123 45678 9111 12345 67891 11123 45 200

200

200

200

0

200

year/mont



Conclusions: ► Everyday E&P specialists operate with RISK ► Working in teams improves the risk management RESULTS ► PETROM has started to INTEGRATE risk management in it’s business processes ► RISK MANAGEMENT leads to E&P SUCCESS References Brown, A.R., 2004, Interpretation of Three-Dimensional Seismic Data. Negut, A., 1985, Carotajul geofizic. Schuyler, J., 2004, Decision Analysis Collection. Jain, K.C., 1982, Concepts and Techniques in Oil and Gas Exploration. Imai, M., 1995, Gemba Kaizen. Yilmaz, O., 2001, Seismic Data Analysis: Processing, Inversion and Interpretation of Seismic Data. Rose, P.R., 2001, Risk Analysis and Management of Petroleum Exploration Venture. Neculae, P., Caminschi, D., Baleanu, I., 1995, Risk Analysis for Romanian Offshore Black Sea. Negoita, V.G., 1975, Interpretation of the Well Logs acquired by the DRR Method.


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P1 - 01

SEISMIC REGISTRATION OF THE PLIO - QUATERNARY DEPOSITS Spiro Bonjako1, Ilia Fili2, Marjeta Bonjako3, Luan Hasanaj1 1 National Scientific Hydrocarbon Centre, Fier, Albania 2 Polytechnic University, Tirana, Albania 3 Technological University “I. Qemali”, Vlora, Albania

Summary During the seismic survey, a qualitative change is observed when sections are placed near eaich other even when the field parameters are the same. The surface influence is a known phenomenon. In this article is shown something about the seismic phenomenon related to the near surface changes in the Plio-Quaternary deposits in the Frakulla anticline. Near surface Lithostratigraphy In this article we are dealing with the profiles which are located on “Frakulla” anticline, where Pliocene (N2) deposits outcrop. According to the geological map, the central part and the western flank are covered by Quaternary deposits. The profile 1/1 from the picket 200 to the west and the profile 2/1 from the station 150 to the west, pass over the Quaternary deposits, which are composed of two lithological units: the field space which begins from the picket 150 of both profiles to the west is composed of suargila and weathering zone of the low velocity, or the soil with the thickness 2 – 5 meter. The higer area, which lies from the picket 150 to the station 200 of the profile 1/1 is composed of non cemented gravels and conglomerates. Its thickness is 5 – 15 m. They are good infiltration deposits, without the presence of the water bearing layer. This is because of water flowing in great quantities westward. The Pliocene deposits of “Helmësi” suit, 1 (N2 ), are composed from clays and lens or thin Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 433


and fine intercalation sandstones. These deposits are plastic and running under of water effect. These deposits take part only in one part of profile 2/1. The deposits of “Rrogozhina” suite, (N22), are presented in the lower part (N22a) from medium to microgravelitic sandstones. Sometimes they are cemented and sometimes not. On outcrop they are in contact with atmospheric waters. In periclines and the flanks they form a good water bearing basin. The upper part of N22b is made of sandy-conglomeratic layers which are slightly cemented. Their thickness is 1-2 to 7-10 meters. The parameters of seismic registration During the seismic registration in profile 1/0, we can’t notice a clear view of the geologic structure in depth. For this, later on are made registrations and attempts to improve the parameters, because the near surface deposits were not appropriate to transmit the seismic wave which are originated from the shots into the wells. Profile 1/1 and 2/1 are registered with the same parameters. The comparison between the two the parameters of registration is as follows: Energy source Chard size Source depth Number holes Geophones location Pattern of geophones Geophone type Distance of group Station interval Field spread

Profile 1/0 dynamite 6 x 1.5 kg. 12 meter 6 36 linear SM4 10Hz 84 meter 50 meter 1-48 x 52-

Profile 1/1, 2/1, ect. dynamite 1.5 kg. 20 meter 1 18 linear SM 4 10 Hz 40 meter 30 meter 1-150 x 151-300

24

75

99 Coverage

Profile 1/0

Profile 1/1


434


Parametric changes were made taking in consideration earlier wave view in this surface conditions. It was predicted that the reduction of the interval between the stations, the increase of multiple and the shot in the depths of more than 12 meters and drilling through much more consolidated layers, although the number of the wells, would have good results in the improvement of the quality of seismic registration. The decrease of the grouping base has been done to avoid as much as possible the interferences among the channels and other possible influences considering that the relief from the station 150 in the East of the profile 1/1 and 2/1 were in the form of a hill with distinctive quota changes. The profile 1/1 is almost at the same position as the profile 1/0, with the only change that station of 1/0 profile were two fold. So, making it possible to do a comparison under the some conditions. Conclusions There are evidence improvements of the profile 1/1 compared to the profile 1/0. This has been achieved as a result of the change of parameters in the field registration. We can easily notice the two flanks of anticline structures in the deposits of Pliocene as well as those of the Messinian. There can also be clearly seen some faults, which are connected not only by the data taken from drilling of the wells, but also by the surface features of the area. The study of the area has continued in the profiles 2/1, 3/1 etc. These profiles pass over the deposits that are different from the profile 1/1. The shots in the profile 1/0 ( between the station 300-400 ) have been carried out in the sandstone and conglomerate beds that have not been cemented. There are also not water bearing layers of the Quaternary. This has led to a considerable absorption of the elastic wave of the shot. In the more western direction of the station 300 there are improved conditions because of the existence of the water bearing layers since there are lowering quotes from the east to the west side.



Pliocene formations in the more eastern part of the station 400 are not favourable because they have a bed cementing, that’s why there can often been found poor and dry clay layers.

The parameter changes in the profile 1/1, the increase of multiple and the shot in the lowermost level where the cementing of the layers of Quaternary period or those of Pliocene in the more eastern direction have improved the quality of seismic registration. In fact, the seismic registration near the north side seems to be of a better quality than of the profile 1/1. This is as a result of the influence caused by changes of deposits in the profile 1/1 during the Quaternary. They are hilly area in the station 150-200, while in the north they are in the valley and have a lot of water bearing layers. Also the lithological changes of the Pliocene deposits toward the north have influenced to this improvement. The further processing of these methods will play an important role. By means of sequential comparisons as well as increase of the number of analysis of the seismic signal properties we have made it possible to improve even the profile 1/1 in despite of the unfavourable condition near the surface.


436


P1 - 02

ALGORITHMS FOR NUMERICAL EVALUATION OF SPECTRA IN MICROSEISMIC Virgil Bardan, Dorel Zugravescu, Laurentiu Asimopolos ”Sabba S. Stefanescu” Institute of Geodynamics of Romanian Academy, Bucharest, Romania

Summary Usually, microseismic survey includes the direct interpretation of Fourier spectra, the calculation and study of spectral relations between reference and studied site or the determination of spectra relations between horizontal and vertical spatial components. For this reason the evaluation of spectral amplitudes is a very important operation in processing of microseismic signal. Microseismic signal is a random process with certain properties. These properties are described by concepts as particular realization, statistical and temporal average values, power and amplitude spectral densities, average power. The amplitude spectral density of a random microseismic signal contains information about peculiarities in structure and mechanical parameters of the subsurface. It is presented an algorithm for the evaluation of amplitude spectral density of a random microseismic signal which is observed in a point at the Earth’s surface. This evaluation implies the stacking of power spectral densities corresponding to a number of particular realizations. The optimum number of stacking is obtained when the average power becomes stable. A particular realization has to be observed for a very long period. For this reason it is presented another algorithm for the numerical evaluation of the spectrum for a particular realization represented by a very large number of samples, but which uses an FFT subroutine with a far smaller length. Introduction Microseisms are Earth’s surface weak background oscillations. Microseismic signals can be used successfully for getting information about peculiarities in structure and mechanical parameters of subsurface zones because they are always present at any point on the Earth surface and measurements themselves both in methodical and expense aspect are much easier, as a rule, compared to other seismic methods. For this reason many geophysicists developed the methods utilizing microseisms as a sounding signal. More or less established terminology was fixed in this area. The distribution between long-period (T >1 s) and short-period (T < 1 s) corresponds to the traditional distinction between “microseisms” with natural origin and “microtremors” with artificial origin. Microseisms are widely used for site response effect studies. It is recognized as an important factor to be considered in seismic microzonation. Microseisms appear as a result of atmospheric perturbation transmission for the waters of oceans and propagate over continental surface as Love and Rayleigh types waves. A high efficiency of their propagation is explained by their surface nature. The higher frequency microtremors are mainly generated due human activity and weather instabilities. Gorbatikov et al (2004-I and II) presented a number experimental results to demonstrate the application of developing method of microseismic sounding for a number of geological objects typical in oil and gas industry and other geological structures. The distribution of microseism amplitudes was measured for different frequencies in the range from hundredth parts of Hz to several Hz at polygons on the surface above the investigated objects. Each case revealed that objects with higher seismic velocities appeared on the surface as zones of shadow with depressed values of amplitudes, whereas structures with lower seismic velocities appeared as areas with increased amplitudes. Therefore, this method of microseismic sounding implies Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 437


calculation and study of spectral relations between reference and studied site. Other microseismic methods include the direct interpretation of Fourier spectra or the determination of spectra relations between horizontal and vertical spatial components. For this reason, in this paper we present algorithms for numerical evaluation of spectra in microseismic survey. Algorithms for numerical evaluation of spectra Because of the microseismic signals which can be recorded in a point from the Earth’s surface are considered a random signal we mention some concepts from the random signal theory (see, for example, Spataru, 1966). A random signal, respectively a stochastic process, is represented by a function of two real parameters ξ(k,t)= ξ(k)(t), where k takes the values in a space of samples and t takes the values on the time axis. For t=t1 we obtain ξ(k)(t1) which is a random variable defined on the space of k numbers. By ξ(t) we denote the space of functions ξ(k)(t), where k can take all values on the real axis. The deterministic signal ξ(k)(t) is “a particular realization” or “a representation” of the stochastic process ξ(t) (another notation for ξ(k,t)). From statistical average values of the random signal ξ(t) we mention the following: average value

ξ( t 1 ); quadratic average value ξ 2 ( t 1 ); dispersion σ 2 ( t 1 ); and autocorrelation function B ξξ ( t 1 , t 2 ) = ξ( t 1 )ξ( t 2 ). From the temporal average values of the stochastic process ξ(t), which are defined for a particular realization ξ(k)(t), we mention the following: temporal average value ξ ( k ) ( t ) which represents the continuous component of the deterministic signal; temporal 1 T / 2 (k ) quadratic average value [ξ ( k ) ( t )]2 = lim ∫ [ξ ( t )]2 dt which represents the average power T →∞ T − T / 2

of the deterministic signal; and temporal autocorrelation function R (ξξk ) (τ) = ξ ( k ) ( t )ξ ( k ) ( t + τ) . A

stochastic process ξ(t) is stationary in large sense if the temporal average values ξ( t 1 ), ξ 2 ( t 1 ) and σ 2 ( t 1 ) don’t depend of t1. A stationary stochastic process ξ(t) is ergodic if the statistical average values are equal to temporary average values. Analyzing microseismic data and taking in consideration the way of their generation and behavior, it can conclude that the microseismic signals recorded in a point on the Earth’s surface are described as an ergodic stochastic process ξ(t). In addition, if microseisms are Love and Reyleigh waves then ξ( t 1 ) = ξ ( k ) ( t ) =0, ∀t 1 , ∀k ∈ R (because these waves can be approximated by sinusoidal signals). This equation implies ξ 2 ( t 1 ) = σ 2 ( t 1 ) = [ξ ( k ) ( t )]2 , ∀t 1 , ∀k ∈ R . A particular realization ξ(k)(t) of the stochastic process ξ(t) isn't a signal of finite energy, therefore it has not spectrum. For this reason we consider the truncated particular realization ξ (Tk ) ( t ) = ξ(k)(t) for t ≤ T / 2 and equal to zero for t > T / 2. Parceval theorem for the deterministic signal ξ (Tk ) ( t ) can be written: 2

PT( k )

(k ) 1 T / 2 (k ) 1 ∞ (k ) 1 ∞ X T (ω) 2 2 = ∫ [ξ ( t )] dt = ∫ [ξ T ( t )] dt = dω, T −T / 2 T −∞ 2π ∫−∞ T

(1)

2

where PT( k ) , X (Tk ) (ω) / T and X (Tk ) (ω) / T approximate the average power P ( k ) , the power spectral density X ( k ) (ω) stochastic

process 2

2

and, respectively, the amplitude spectral density X ( k ) (ω) of the

ξ(t)

if

T

is

very

2

large.

That

lim X (Tk ) (ω) / T = X ( k ) (ω) and lim X (Tk ) (ω) / T = X ( k ) (ω) . Certainly,

T →∞

T →∞

lim PT( k ) = P ( k ) ,

is,

T →∞

in


438

the

above


definitions, in stead of the interval {-T/2, T/2] we can consider the interval [0, T] because ξ(t) is a stationary stochastic process. Using a microseismic data set, which was recorded in a point at the Earth’s surface with sampling interval ∆t=1/70≈0.014 s, we try to illustrate the way of realizing the numerical evaluation of the amplitude spectral density for the corresponding random process denoted by ξ(t). In Figure 1 we present five particular realizations ξ (Tk ) ( t ) recorded on the intervals [0,T], where T takes following values: 127∆t =1.81 s; 511∆t =7.3 s; 1023∆t =14.61 s; 2047∆t =29.24 s; and 4095∆t=58.5 s. In Figure 2 is presented the amplitude spectral density X (Tk ) (ω) / T of the particular realization in Figure 1e, which is recorded on the interval [0, T] with T=58.55 s and represented by N=4096 samples. The Nyquist frequency is 35 Hz and ∆f=70/4096=0.017 Hz. Using formula X (Tk ) (ω)

2

1 (2) dω π ∫2 πf1 T we can evaluate the average power corresponding to observational period T. The frequencies f1 and f2 define the bandregion of the process. In our example we can take f1=0.1 Hz and f2=1 Hz because we suppose that the microseisms are Reyleigh waves. Enlarging T we try to obtain a stable value for the average power PT( k ) , what means also a stable spectral density. In Figure 3 it PT( k ) =

2 πf 2

is presented the amplitude spectral density X (Tk' ) (ω) / T' of a particular realization recorded on the interval [0, T’], where T’=44T=2576.2 s. In spite of this large T’ we could not obtain a stable spectral density. On the other hand we obtained a stable value for the average power of the process and a stable amplitude spectral density X (ΣkT) (ω) / T stacking the power spectral densities corresponding to the 44 particular realizations which were recorded on intervals of duration T (see Figure 4). Numerical evaluation of a spectral density for a particular realization is done by using a FFT (fast Fourier transform) subroutine, whose maximum length in common programming languages is 4096 or 9192. In microseismic survey one encounters particular realizations with a very large length. For example, in Figure 3 is presented the amplitude spectral density of a microseismic signal reprezented by 44*4096 samples. For this reason we describe an efficient algorithm for the spectral evaluation of a signal represented by M=KN samples using a FFT subroutine with the length of N=2p, where the factor K doesn’t have to be a power of 2 (see Sorensen and Burrus, 1993). Conclusions In this paper we have presented two algorithms: the first for the evaluation and stabilization of amplitude spectral density of a random microseismic signal which is observed in a point at the Earth’s surface; the second for the numerical evaluation of the spectrum for a particular realization represented by a very large number of samples, but which uses an FFT subroutine with a far smaller length. References Gorbatikov, A.V., Kalinina, A.V., Sidorov, V.A., Postnov, A.V., Odinstov, A.L., 2004-I, Microseismic sounding in the oil & Gas complex objects control problems: Expanded Abstracts of 66th EAGE Conference – Paris, P221. Gorbatikov, A.V., Kalinina, A.V., Volkov, V.A., Arnoso, J., Vieira, R., Velez, E., 2004-II, Results of analysis the data of microseismic survey at Lanzarote Island, Canary, Spain: Pure and Applied Geophysics, 161, 15611578. Sorensen, S., Burrus, B. V., 1993, Efficient computation of the DFT with only a subset of input or output points: IEEE Trans. Acoustic, Speech and Signal Processing, SP-41, 1184-1200. Spataru, A., 1965, Teoria Transmisiunii Informatiei: Editura Tehnica, Bucuresti.



Figure 1 Particular realizations

ξ T( k ) ( t ) recorded with

∆t=1/70≈0.014 s on the intervals [0,T], where T takes following values: 127∆t =1.81 s (a); 511∆t =7.3 s (b); 1023∆t =14.61 s (c); 2047∆t =29.24 s (d); and 4095∆t= 058.5 s (e).

Figure 2

(k )

Amplitude spectral density X T (ω) / T of

a particular realization recorded on the interval [0, T], where T=58.55 s. The Nyquist frequency is 35 Hz. The spectral density is represented for five frequency scales corresponding to the following bands: 0-2.18 Hz (a); 0-4.37 Hz (b); 0-8.75 Hz (c); 0-17.5 Hz (d); and 0-35 Hz (e).

(k )

Figure 3 Amplitude spectral density X T ' (ω) / T ' of a particular realization recorded on the interval [0, T’], where T’=44T=2576.2 s. The Nyquist frequency is 35 Hz. The spectral density is represented for five frequency scales corresponding to the following bands: 0-2.18 Hz (a); 0-4.37 Hz (b); 0-8.75 Hz (c); 0-17.5 Hz (d); and 0-35 Hz (e).

Figure

X (ΣkT) (ω)

4

Amplitude

spectral

density

/ T obtained from the stack of 44 power

spectral densities corresponding to 44 particular realizations which were recorded on intervals of duration T. The Nyquist frequency is 35 Hz. The spectral density is represented for five frequency scales corresponding to the following bands: 0-2.18 Hz (a); 0-4.37 Hz (b); 0-8.75 Hz (c); 0-17.5 Hz (d); and 0-35 Hz (e).


440


P1 - 03

POSSIBILITIES OF APPLICATION COMPARATIVE ANALYSIS OF SEISMIC MIGRATION IN 2D SEISMIC DATA REPROCESSING Slobodan Ž. Stanić1, 2 , Ratko Ružić1 , Ljiljana Zorić1 , Zorica Vitas- Djokić2 1 NIS-Naftagas, Geophysical Institute, Beograd, Serbia and Montenegro 2 University of Beograd, Faculty of Mining and Geology, Beograd, Serbia and Montenegro

Summary Among seismic methods used for hydrocarbon exploration, special role belongs to seismic reflection method and vertical seismic profiling. Adequate application of these methods makes possible analysis of even extremely geologically complicated space. Seismic reflection method means very complex technological procedure, which includes all available scientific and technical skills in domain of geology, geophysics and other scientific and technical disciplines. One of the unique approaches within processing and interpretation of seismic reflection exploration is comparative analysis of seismic migration before and after stacking. Application of comparative analysis can be successfully applied within VSP, 2D, 3D and 4D seismic exploration. The most confident data are obtained from high-quality seismic data, however, its application is useful also in 2D seismic data processing, which are, according to the nowadays experience, not enough confident. However, if analyzed through comparative analysis, they are reliable base for geological interpretation. Introduction Within seismic reflection method of exploration, some procedures of data processing can be solved in various ways. Different approach, way and technique, significantly improves the procedure, offering possibility of wider analysis of the problem. Large amount of useful information offers comparative analysis within solving one procedure of data processing. Studied problem in general is not solved by application of only one method. That is why it is necessary to solve it in various ways, by available programme solutions. Application of modern computers within seismic offers a series of possibilities for practical application of seismic migration at non-stacked and stacked seismic data in time and depth domain within 2D, 3D and 4D seismic exploration. By comparation and analysis of results of applied migration before and after stacking within various programme solutions, makes possible better analysis of the study area. As application of seismic data processing before stacking at the start of the data processing, rough reconstruction of the study area is possible, that is – great number of information necessary for correct choice of parameters for the further stages of processing is available. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 441


By application of the both methods of seismic migration for the same data and their comparation analysis, better processing is possible, but also preliminary interpretation at the already migrated data, which presents intro to more detailed study of the studied seismogeological problem. Application of comparative analysis of seismic migration within seismic data reprocessing Significance of application of seismic migration comparative analysis is noticeable at examples of 2D seismic exploration, performed at the study area characterized by complex geological structure. Very often, it is not possible to clearly define positions of the first seismic wave arrivals in 2D seismic data, and to position them precisely, even after application of one or the other method of seismic migration. In that case, application of seismic migration comparative analysis is a useful solution.

Figure 1 Non-migrated seismic section (a) and corresponding migrated seismic section obtained by application of seismic data comparative analysis (b). Data are related to the area of Pannonian basin (Documentation of NIS-Naftagas).

On the basis of application of seismic migration comparative analysis in data of 2D seismic reflection exploration at the area of the Pannonian basin, Figure 1 is obtained. It can be concluded that this procedure is very reliable way of solving migration problem even in cases with bad signal-noise ratio and when coverage is 10-20 traces/CDP position. With this example of land exploration (Figure 1), it is concluded that it is correct way of solving migration problem in land seismics. Application of comparative analysis means type of detailed and special processing of seismic data, which was of limited application in the past. Nowadays, such limitations are reduced to minimum, enabling application even the most complex cost-efficient software packages. The treated example was followed by additional analysis of migration velocities and comparative analysis of seismic migration before and after stacking.


442


Such way of application of comparative analysis makes possible successful use of the data obtained by previous 2D seismic investigations, as well as rational performing of 3D and 4D seismic exploration in the regions where it is necessary. Note that the suggested method is, first of all, tool for 3D and 4D seismic exploration, but also way of improving quality of 2D seismic data (particularly in cases referring to intervals of space and time sampling, and bed signal/noise ratio). The example treated in this paper is just of that type (sampling interval 4 ms, receiver interval 80 m), when, beside very rough recording parameters, after comparative analysis application, reliable image of the study area was obtained. Conclusions Comparative analysis can be treated as one of universal approaches, enabling to get reliable data on the basis of several methods of one processing procedure. However, it can also be treated as new way in solving problems of seismic migration, offering basis to combined application of seismic migration with other processing procedures, which understands correction of parameters of some processing procedures, first of all – migration, DMO, velocity analysis, NMO and deconvolution. In that way, preconditions for solving problems of reconstruction of the study area, which are not solved by only one method (or such solution would be incompletely). That was very useful within 2D seismic data reprocessing during seventies and eighties, making important source of information for further 3D and 4D exploration. Suggested way of solving problems of reconstruction of the recorded half-space and determining migration velocities, presented through comparative analysis of seismic migration does not offer final solution for all cases, but is one of the most reliable ways within seismic data processing and interpretation, enabling obtaining real seismic data even in the cases when 2D seismic data are of bad quality. Such results present safe foundation for the further 3D and 4D exploration for the same study area, although they are enough for solving appropriate seismogeological problem. References Focus 4.0 applications, CogniSeis Bringing a World of information into Focus, Houston, USA. Martinović, S., Stanić, S., Stefanović, D., 1996, Requirements of oil industry for modern geophysical technologies. Proceedings of Modern trends of development in geophysics, Beograd. Stanić, S., 1996, Possibilities of application comparative analysis of seismic migration before and after stacking, Proceedings of Modern trends of development in geophysics, Beograd.



P1 - 04

WAVELET DECOMPOSITION AS A TOOL FOR SEISMIC RANDOM NOISE REMOVAL Hosein Hashemi, Navid Amini Institute of Geophysics of Tehran University, Tehran, Iran

Summary Random noise attenuation always is a sensitive step in seismic data processing. In this paper, it is found that wavelet decomposition is a good approach for removing seismic random noise. Method of threshold analysis on basis of wavelet decomposition for finding better correlation coefficient which results in better S/N ratio, moreover the algorithm is so fast and easy to run. Introduction Seismic random noise attenuation is one of the great challenges for geophysicists in recent decade. Abma (1994) used prediction filtering techniques for random noise removal. The method has its own disadvantages and produces flaws in presence of high amplitude noise. Using adaptive procedures for synthetic aperture radar (SAR) images and seismic datasets were presented by Ristau and Moon (2001). They performed a comparison between some adaptive filters for these data. Mismatch between statistical noise model and noise of the data set partially invalidate the use of adaptive filters. Some new methods in inversion were presented by Abma (2001).However this method has good advantages for high-amplitude noise, but they deal with the general non -uniqueness answer for inversion. The de-noising methods based on wavelet decomposition appear mainly initiated by Donoho and Johnstone in the USA, and Kerkyacharian and Picard in France. They considered that this topic is one of the most significant applications of wavelets. In this paper, the method of threshold analysis on basis of wavelet decomposition presents for synthetic seismogram and the result shows high correlation between de-noised and noise free records. Basics of the method Wavelet analysis is capable of revealing aspects of data that other signal analysis techniques fail. Furthermore, because it affords a different view of data than those presented by traditional techniques, wavelet analysis can often compress or de-noise a signal without appreciable degradation. De-noising and compression are interesting applications of wavelet packet analysis. The wavelet packet de-noising or compression procedure involves three steps: 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

444


1. Decomposition For a given wavelet, compute the wavelet packet decomposition of signal x at level N. 2. Thresholding of wavelet packet coefficients For each packet (except for the approximation), select a threshold and apply thresholding to coefficients. Threshold analysis will be done by trial and error so as to optimize the results to acheive the best S/N ratio. 3. Reconstruction Compute wavelet packet reconstruction based on the original approximation coefficients at level N and the modified coefficients. Synthetic data The model consists of four horizontal reflectors. Their thicknesses are 100, 600 and 2400 meters and velocities are 750, 1600, 4000 and 5200 m/s, respectively. Forward synthetic algorithm follows general seismic hyperbola formula. Two shot records was generated by the PerLab software , Figure 1 shows the noise free shot record and Figure 2 shows the same section plus random noise.

Figure 1 Noise free shot-record

Threshold analysis starts scanning the range of 0 – 80. For each value of threshold the above 3 steps followed and cross correlation of de-noised and free of noise shot records is computed. Figure 3 obviously shows the maximum value of correlation coefficient occurred in 26. Applying this value to noisy shot record, results best de-noised data. Figure 4, shows the denoised shot record for threshold value 26. Comparing of figures 2 and 4, exactly shows the success of the method in random noise attenuation. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 445


Figure 2 Noisy shot record.

Figure 3 Threshold analysis and finding maximum correlation coefficient.


446


Figure 4 Shot record after de-noising.

Conclusions Applying different threshold values in wavelet decomposition function jointly with crosscorrelation of de-noised and noise free section result in fast and optimized response for random noise removal. First impression to this method open new horizons for having better quality shot records for seismic data processing and finally better images of sub-surface. Frequency contents of the signals must be considered, because the algorithm fairly smoothen the high frequencies. Acknowledgements The authors must appreciate the Persia Geo-Processing company for offering this chance to use their signal processing laboratory and software. And special thanks to Institute of Geophysics, University of Tehran for providing documentation and useful debates. References: Abma, R., Clarebout, J., 1994, Signal and noise separation applications, SEP-82,213-234. Abma, R., 1994, Spurious event generation with f-x and t-x prediction, SEP-82, 235-244. Abma, R., 2001, Enhanced random noise removal by inversion ,SEP-84, 1-344. Donoho, D.L., 1995, De-Noising by soft-thresholding, IEEE Trans. on Inf. Theory, vol. 41, 3, 613–627. Donoho, D.L., Johnstone, I.M., Kerkyacharian, G., Picard, D., 1996), Density estimation by wavelet thesholding, Annals of Stat., 24, 508–539. Ristau J.P., Moon, W.M., 2001, Adaptive filtering of random noise in 2-D geophysical data, Geophysics, 66, 342-349.


ENGINEERING, ENVIRONMENTAL & ARCHAEO-GEOPHYSICS

P2 - 01

THE WATER-SATURATED ROCK SEARCHING AND MAPPING BY GEOELECTRIC METHODS

S.P. Levashov1 , N.A. Yakymchuk2 , I.N. Korchagin3 , Yu.M. Pyschaniy2 , Yu.N. Yakymchuk2 1 Institute of Applied Problems of Ecology, Geophysics and Geochemistry, Kiev, Ukraine 2 Management and Marketing Center of Institute of Geological Science, Kiev, Ukraine 3 Institute of Geophysics of Ukraine National Academy of Science, Kiev, Ukraine

Summary The results of using the geoelectric methods for the searching and contouring of the zones with increased water containing rocks are given. The received data show that the geoelectric methods allow to map water-containing areas and to define theirs bedding depths. Introduction The original express-technology of geoelectric investigation (the compact measuring equipment, methods of the undertaking the field measurements, algorithm and software for registrations, processing and interpretation of the geoelectric observations data) allows effectively to solve the broad circle ecological, engineering-geological, hydro-geological and geological-geophysical problems [1-2]. In particular, technology was used for mapping zones of the oil contamination, for localizations of area with the raised moistening of soil, for studying the landslide processes and collapse [1-8], for finding and localizations man-caused drain from reservoir and underground water communication, etc. The technology was also used when undertaking the investigations for the water-bearing layers searching on Turkey and Ukraine territory. Express-technology components and equipments. The technology is based on the study of the geoelectric medium parameter in pulsed unsteady electromagnetic fields, as well as the quasi-stationary electrical Earth field and its spectral characteristics over the investigated objects. It combines the method of formation of short-impulse electromagnetic field (FSPEF), flux-meter survey and vertical electric-resonance sounding (VERS). 1. The FSPEF method is based on studying of the process of the short-impulse electromagnetic field formation in small-sized dipole ferrite antennas. The application in this modification of the method of short but high-power electric pulses gives us an opportunity to refuse the use of long lines and to reduce the energy consumption. Moreover, small-sized dipole ferrite antennas and power supply let us reduce the observation period in the observation point, consequently, to raise the productivity and efficiency of the developed modification in comparison with the traditional ones. 2. The flux-meter survey is carried out to measure the vertical component intensity of the Earth electrical field over the investigated objects. This information gives us an opportunity to get the thickness evaluation of the “anomaly polarized layers” in the anomalies zones. 3. Vertical electric-resonance sounding is based on the research of the processes of natural medium polarization and spectral characteristics of natural electric field over the investigated object. As far as the horizontally stratified cross-sections are concerned, this technology gives a possibility to efficiently divide the cross-section on separate stratigraphic subsections in the sounding site and to determine its depth with high accuracy. Sounding effectiveness rises considerably if in the regions in view there are documented parametric boreholes which give the possibility to “standardize” sounding diagram – to link separate meaning intervals with the corresponding stratigraphic layers. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

448


The geoelectric investigations results. At July 2002 geophysical investigations for searching and mapping zones win increased water containing rocks were conducted in the outskirts of the city Mush (Turkey) The area of geoelectric survey in the Mush region constitutes 12 km sq. There were made observations by FSPEF method in 3127 measurements station in the car and foot manner within this area. The VERS in the modification of determination the total thickness of the water containing collectors were fulfilled in 250 stations. The VERS in the modification for the vertical cross-section constructing were carried out in 20 stations. E, V/m-1 1850

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Figure 1 The map of underground water reservoir locations on the south of city Mush. 1- ERS points; 2 – waypoints of measurements by FSPEEF method; 3 – VERS profiles; 4 underground water reservoir locations; 5 – roads.

Figure 2 Z1 point.

Limestone

The VERS results in the

The maps of zones with increased water containing rocks are construct in southern part of the city Mush region as a result of geoelectric investigations (Figure 1). The VERS diagrams in sounding points (Figure 2) and the vertical geological-geoelectric cross-sections are created through mapped zones with the water containing collector separation (Figure 3). The following data are installed in the complex geophysical investigation results: 1. The dislocated thick masses of schist rock serves as the main collectors in the region. The average thickness of these rocks in the areas constitutes 250-300 m. The schist lies on the monolithic thick mass of limestone. The collector areas are located in the tectonic fracture zones, having in most cases the linear stretching 2. The most intensive zone is located along right influx of the Mush River in the southern part of investigation region (Figure 1). The selected zone contains several horizons of water containing collectors with 40-60 m thickness. 3. In zone of vertical cross-sections along the lines 1-1a and 2-2a (Figure 3) the main water horizons inhere below erosion cut of the Mush River. The springs eat at the expense of surface water horizon in this part of areas, average depth of which consists 5-10 m. The total thickness of collector horizons for this zone exceeds 100 m. 4. The most intensive zone of watered rocks is located along the line of cross-section 3-3a (Figure 3). The total thickness of water horizons exceeds 200 m for some areas. The upper water horizon lies on 30-50 m depths. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 449

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Figure 3 The geological-geoelectrical cross-sections along the profiles 1-1a, 2-2a, 3-3a. 1 – limestone; 2 – slate; 3 – quaternary breeds; 4 – underground water collectors.

Figure 4 The map of geoelectric anomaly on the survey data by method of the formation short pulsed electromagnetic field within the POS "Kamenogorka" region. 1 - scale of FSPEF anomaly intensities (zones of raised watering are shown by the blue colors tones); 2 - tectonic fracture zones; 3 - points of the FSPEF method survey; 4 - points of the sounding by VERS method.

Figure 5 The map of water-bearing layer V3 thickness, built on the VERS data (APL of "waterbearing layer" type"). 1 - scale of the layer thickness with low resistance in meters; 2 - VERS points, offered for boring; 3 - points of the VERS sounding; 4- tectonic fracture zones.


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a) b) Figure 6 The VERS results in region of the bored borehole (a) and in point B2, recommended for boring (b).

Figure 7 The map of water-bearing layer V2 thickness, built on the VERS data (APL of "water-bearing layer" type"). 1 - scale of the layer thickness with low resistance in meters; 2 - VERS points, offered for boring; 3 - points of the VERS sounding; 4- tectonic fracture zones. Figure 8 Correlation cross-section on VERS data along profile 5-5а within the POS "Kamenogorka" territory. 1 points of the VERS sounding; the anomalous polarized layers of the type of: 2 - loam; 3 – clayey sediment with the sandstone and chalk layers; 4 - a sandstones with the clay layers; 5 granite; 6 – clayey sediment; 7 - waterbearing layer; 8 - gruss.

Geoelectric investigations by FSPEF and VERS methods were conducted on the pumping-over station (POS) "Kamenogorka" territory for the water-bearing layer findings and mapping, as well as for determinations of the optimum places of the water-supply borehole location. Earlier, the borehole of 120 m depth was bored on POS territory. Borehole has opened the crystalline basement rocks, however productive water-bearing layer was absent. The geoelectric anomalies were revealed by FSPEF method in south part of POS "Kamenogorka" territory, which can be conditioned by water-bearing layers presence in crosssection (Figure 4). The anomalies are extended along two directions and sooner whole are connected with the fracture zone in the basement rocks. The “weakened” zones, which appeared as a result of tectonic fracture of the rocks, are the track of underground water migration. The ravine was formed in southwest direction along the line of chosen tectonic fracture outside the POS territory. The detailed investigations for water-bearing layers searching were conducted in south part of POS territory and for its limit, from southwest side. Vertical sounding was executed in process of the studies along five profiles. Three intervals of anomalous polarized layer (APL) of the "waterJournal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 451


bearing layer" type V1, V2, VЗ are chosen in sedimentary cover of cross-section 120-130 m depths interval. 1. The water-bearing layer V1 is chosen in interval of the depths 10.5-11.5 m. The layer thickness is 1-2 m. It is present practically on the whole POS territory. The fine-grained sand, which is revealed in the 10.2-11 m depths interval when boring the borehole, is water-bearing collector of the layer. 2. The water-bearing layer V2 is extended along the tectonic fracture lines (Figure 7). The layer thickness increases in southwest direction aside the ravine. The depth of layer bedding constitute 2530 m. The layers VI and V2 unite in region of the ravine. In north easterly part of area the waterbearing layer practically disappears. This is indicative that layer V2 increases, in the main, by surface waters. The weakened zones by tectonic fracture with layer of sand and loam serves as water-bearing collector, sooner whole. 3. The layer VЗ is chosen in the tectonic fracture region in the 115-125 m depths interval (Figure 5). The width of the zone reaches 80 m. The maximum thickness of the water-bearing zones gravitates to central part of tectonic fracture zones and forms 8-10 m. The roughly granular sand and weakened zones of the sandstone are collector of the water-bearing layer. The layer V3 can be used for water supply of POS "Kamenogorka". The sounding points B2-B5 were recommended for undertaking the boring for water. The columns of the geological construction of the sedimentary cover rocks are formed in these points on the sounding data. We shall indicate also that electricresonance sounding was organized also in region of the bored borehole on water (Figure 6a). We can see from the figure follows that water-bearing layers of significant thickness are absent here. In the 105-117 m depths interval, which is recommended for water scoop, water-bearing layer was not revealed also. The borehole in point B2 (Figure 6b) has opened second water-bearing layer at the depth 30 m. Information about third water-bearing layer is absent while. Correlation cross-sections of the sedimentary cover construction along five profiles are built also on the VERS data. The structure of the geological cross-section along profile 5-5а is brought on Figure 8. Conclusions The zones of the water-bearing collector spreading and zones of underground water flow migration are revealed and outlined as a result of undertaking geoelectric investigation. The efficient values of the water-bearing layers vertical thickness are determined on the geoelectric survey data. The received results have demonstrated in practice the possibility of the express-technologies of geoelectric investigations using for searching and contouring the water-bearing layer in surface and determination of their bedding depth in cross-section. The investigations of such nature are executed rather operative and quickly with this technologies using. The measurement data processing and interpretation in field condition allows directly on place of the undertaking the measurements to indicate the borehole locations. References Bokovoy, V.P., Levashov, S.P., Yakymchuk, M.A., Korchagin, I.N., Yakymchuk, Ju.M., 2003, Mudslide area and moistening zones mapping with geophysical methods on the slope of the Dniper river in Kyiv: Extended abstracts book. Volume 2. 65nd EAGE Conference and Technical Exhibition. Stavanger, Norway, 2 – 5 June 2003. Poster presentations. Absr. P208, 4 pages. Levashov, S.P., Yakymchuk, M.A., Korchagin, I.N., Pyschaniy, Ju.M., Yakymchuk, Ju.M., 2003, Electric-resonance sounding method and its application for the ecological, geologicalgeophysical and engineering-geological investigations. 66nd EAGE Conference and Technical Exhibition. Paris, France, 7 – 10 June 2003. CD-ROM Abstracts volume.


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P2 - 02

USE OF GEOELECTRIC METHODS FOR THE GEOLOGICALENGINEERING CONDITIONS ESTIMATION WITHIN THE BRIDGE CONSTRUCTION SITES S.P. Levashov1 , N.A. Yakymchuk2 , I.N. Korchagin3 , E.P. Ivanchenko4, N.G. Dravert2 1 Institute of Applied Problems of Ecology, Geophysics and Geochemistry, Kiev, Ukraine 2 Management and Marketing Center of Institute of Geological Science, Kiev, Ukraine 3 Institute of Geophysics of Ukraine National Academy of Science, Kiev, Ukraine 4 Institute of Engineering Prospecting and Research “Energoproekt”, Kiev, Ukraine

Summary Geoelectric methods may be used for obtaining a proximate estimation of geological engineering conditions in the bridge construction sites at the initial stage of works. The methods can help in determining the depth of occurrence of the crystalline basement, thickness of loose sediments, as well as in mapping the zone of tectonic deformations and breaking. Introduction. The geophysical investigations (on the surface and in the Dnieper and Stary Dnieper Rivers area) and drilling works for making the project of construction of the motor highway over the Dnieper River in the city of Zaporozhie was performed with the aim of: a) lithological dismembering of thickness of sedimentary soils, distinguishing the clayey and sandy varieties in the thickness; b) determination of the occurrence depth of the roof of crystalline rocks and distinguishing the fissured zones in it and the supposed zones of tectonic deformations, zone of breaking; determination, if possible, of the thickness of granite crust of weathering; e) determination of the occurrence depth of crystalline rocks in the Dnieper and Stary Dnieper water area (within the band, 100 m wide, with the center on the bridge axis) and distinguishing the fissure zones and tectonic zones in crystalline rocks. Geophysical investigations The complex of works included: a) the surface geophysical investigations (the area investigations – geoelectric and seismic-acoustic methods; profile investigations – seismic and electric survey); b) investigations in the river water area (seismic-acoustic method); c) geophysical investigations in the holes (radioisotope logging and seismic sonic tests of the interhole space). Geoelectric and seismic-acoustic investigations were carried out at the initial stage of the works with the aim of obtaining the proximate estimation of geological engineering conditions of the construction sites. Investigations were carried out by the methods of formation of the short-pulse field (FSPEF), vertical electric-resonance sounding (VERS) and seismicacoustic sounding [1, 2]. The results mainly obtained by these methods are presented below. Geoelectric works by the FSPEF method were carried out in separate profiles with the step of 2 m. Linear geoelectric anomalies of the type of the “zone of tectonic deformations” were distinguished. In accordance with the anomalous field of FSPEF the linear zones of possible deformations of the basement rocks were mapped. The VERS sounding was carried out within the construction sites of the bridge supports. The VERS points were distributed on the outline of the sites and in their centers. Vertical crosssections along the diagonals of rectangular areas were made by VERS results. Seismic-acoustic sounding with the step of 1 m and seismic-acoustic cross-sections were made along the diagonal profiles for separate sites. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 453

ENGINEERING, ENVIRONMENTAL & ARCHAEO-GEOPHYSICS p1

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Figure 6. A map of the roof of the crystalline basement (the right bank, the Stary Dnieper region). 1 – zone of tectonic deformations.

Figure 7 A map of loose sediments in the site N 8. 1 – zones of deformations; 2 – the line of profile 1-1 a.


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Results of geophysical works The maps of the roof contours of the crystalline basement (Figure 6) and thickness of loose sediments (Figure 7) were compiled as a result of the works on each site. The cross-sections of the roof of crystalline basement were drawn (Figure 3-5). Linear deformations of the upper part of the crystalline basement were distinguished and traced. Site N 1 – the left Dnieper River bank A downdip block of the basement, which is rather connected with the zone of breaking of sublatitudinal strike, was revealed on the map of contours of the crystalline basement roof in the western part of the site adjacent to the Dnieper water area. Several submeridional smallamplitude tectonic deformations cutting the sections of the highway construction have been found. Thickness of loose sediments in the region of the downdip block is 15-18 m, in the western part it reaches 26-30 m. The VERS profile 3-3 a, 1000 m long, is made from the northwest to the south-east; it runs in the region of the hole N 181, drilled in the center of the downdip block. The central part of the profile passes through the quarry worked out during the construction of the old bridge. The VERS profile 2-2a, is made from the river bank along the highway axis in the north-east direction (Figure 3). Site N 2 – The Khortytsya Island, the right bank of the Dnieper Several zones of tectonic deformations, which extend from south-west to north-east have been distinguished within the site. A vertical section along the profile 2-2a (Figure 4) has been made along the road axis. Site N 3 – The Khortytsya Island, the left bank of the Stary Dnieper The lifted block of the basement bounded by tectonic deformations in its western and eastern sides has been distinguished in the central part of the site. Thickness of loose sediments increases in the western and eastern sides of the lifted block. Site N 4 – the right bank of the Stary Dnieper River A system of small blocks bounded by small-amplitude tectonicdeformations (Figure 6) has been distinguished within the sites; a vertical cross-section has been made along the road. Site N 5 – a sand quarry, the right bank of the Stary Dnieper River The investigation results are presented by three maps and three cross-sections. The occurrence depths of the crystalline basement in the northern and southern parts of the site are in the range of 23-27 m. The down dip block with the depth of 35-36 m has been found in the central part. Thickness of the crust of weathering reaches 3 m in the down dip block. The down dip block is traced by tectonic deformations in its margins. Site N 6 – a viaduct across the motor road and railway in the region of Sovetsky prospect The maps of thickness of loose sediments and a roof of the high density rocks, as well as the cross-sections along two axes of the motor road. Site N 7 – a viaduct across the Metallurgov St., is located along the Tyulenin Street The maps of thickness of loose sediments and the basement roof have been compiled. The block of the basement is lifted in the southern part of the site. The depth to the basement in the central part of the site increases from 21 m to 37 m. A cross-section has been plotted along Tyulenin Street (Figure 5).


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Site N 8 – a viaduct under Lenin Street Thickness of the sedimentary rock mass in the site is from 33 m in the north-western part to 39 m in the center of the site where inconsiderable zone of breaking the basement rocks has been distinguished (Figure 8). Site N 9 – the left bank, the overpass across the Aluminievaya Street A number of tectonic deformations have been distinguished within the site. The deformation is traced along the road in the eastern part of the site. Here, the basement rocks are most dislocated and the crust of weathering is rather thick. The zone of deformations in the eastern part reaches 58 m. Site N 10 – the left bank, an overpass across the approach lines Thickness of loose sediments in the site decreases eastwards. A Bridge Across the Yuzhny Bug River Geophysical works in the region of construction of the motor-road bridge across the Yuzhny Bug River in the district of Porik settlement were carried out in January 2004. The investigation task was to determine thickness of the sedimentary rock mass (depth to the roof of crystalline basement), to find out availability of tectonic deformations in the region of construction of the bridge, to make geological-geophysical cross-sections along the road. The investigations were carried out on the left and the right banks of the river, as well as along the existing timber bridge across the river. The survey holes were bored simultaneously with geophysical works. Results of geophysical works Data of geophysical surveys performed permitted to compile; a) a map of the sedimentary rock mass (loose sediments) thickness on the 1: 000 scale (Figure 8); b) a map of thickness of the weakened zone in the mass of granite rocks on the 1:1000 scale (Figure 9); c) a cross-section of the upper part of loose sediments in the region of the Yuzhny Bug River water area on the 1-200 scale (Figure 11); d) a cross-section along the motor road across the Yuzhny Bug on the 1:500 scale (Figure 10). No linear tectonic deformations were found within the ridge construction area by the data of the area surveys by FSPSF. The zones of the rocks crushing and high moistening of the sedimentary cover were not revealed from results of the seismic-acoustic sounding on the left and right banks. The echo ranging of the river bottom with the step of 2 m was performed in the river water area along the timber bridge. The river depth and bottom configuration were determined. Maximum depth of the river at its right bank H =2.2 m (Figure 11). The depths of occurrence of the crystalline basement were established and a map of the sedimentary cover thickness was compiled proceeding from the data of vertical electric resonance sounding. The basement roof is submerged from the north-east to the south-west. Crystalline rocks outcrop on the left bank, northwards of the bridge. In the south-western part of the site the occurrence depth of the basement roof is 10 m. A little uplift of the basement which continues in southern direction was found out in the water area region. A bed of low-density rocks was found on the right bank of the river in the basement rocks (Figure 10); it can be connected with granite-gneissic interlayer in the granite massif. The average thickness of the bed is 2 m, depth of occurrence of the upper margin in the bridge region is 7-8 m, in the north-western part of the site – 15-16 m. Conclusions The proximate estimate of geological engineering conditions of the bridge construction sites at the initial stage of works may be fulfilled by means of geoelectric methods of formation Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 457


of the short-pulse field and vertical electric resonance sounding. These methods can help to determine the occurrence depth of the crystalline basement, thickness of loose sediments, as well as to map the zones the occurrence depth of the crystalline basement, thickness of loose sediments, as well as to map the zones of tectonic deformations and crushing. Geophysical methods were used to examine the sites of construction of the bridge supports on the right and left bank of the Dnieper and Stary Dnieper Rivers. The depths to the roof of crystalline rocks, thickness of weathered granite layer and sedimentary rocks were determined within the limits of each site. References Bokovoy, V.P., Levashov, S.P., Yakymchuk, M.A. Korchagin, I.N., Yakymchuk, Ju.M., 2003, Mudslide area and moistening zones mapping with geophysical methods on the slope of the Dniper river in Kyiv: Extended abstracts book. Volume 2. 65nd EAGE Conference and Technical Exhibition. Stavanger, Norway, 2 – 5 June 2002. Poster presentations. Absr. P208, 4 pages. Levashov, S.P., Yakymchuk, M.A., Korchagin, I.N., Pyschaniy, Ju.M., Yakymchuk, Ju.M., 2003, Electric-resonance sounding method and its application for the ecological, geological-geophysical and engineering-geological investigations: 66nd EAGE Conference and Technical Exhibition. Paris, France, 7 – 10 June 2003. CD-ROM Abstracts volume.


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P2 - 03

USING GEOPHYSICAL METHODS TO IDENTIFY ALTERATION ZONES IN AN ABANDONED MINING SITE L. Carvalho1, E. Ramalho1, S. Barbosa2 1 Instituto Nacional De Engenharia, Tecnologia E Inovacao, Portugal 2 EXMIN, Portugal

Summary The ability of Geophysical methods in identifying either faults or conductive zones was used to understand two geological and hydrogeological critical zones near the Prado Velho abandoned uranium mine site, Portugal. Considering that this old open pit is one of the chosen sites to be used in the near future as a “Waste Containment Deposit”, a collecting site of mining wastes from other adjacent mines, detailed information about the development in depth of the geological features was needed. Therefore, the joint use of electromagnetic, electrical and both refraction and reflection seismics, has allowed establishing 2-D synthetic models showing alteration zones and faults location in depth, that control groundwater circulation. Mining waste deposition in the open pit may cause environmental problems that can, therefore, be predicted and prevented. Introduction Among the 61 old uranium abandoned mines, Prado Velho stands as one of the three mining areas selected for the construction of a “Waste Containment Deposit”, according to “The Waste Management Criteria and Strategy” developed by EXMIN (2002-2003). A “Waste Containment Deposit” is defined has a collecting site of mining waste from other adjacent mines. The Prado Velho site has an available volume of approximately 210.000 m3 and has a centralized geographic location, very favorable for this purpose. Since 2004, different types of site characterization studies are being conducted by EXMIN, aiming at establishing the geoenvironmental feasibility for such a containment proposal. To a successful achievement of these purposes, the best understanding of groundwater drainage potential through the identified fractured systems is needed. Therefore, a geophysical survey involving several methods in the geological and hydrogeological critical areas was conducted with the aim of characterizing the open pit limits, especially in depth and under the water level, and confirming existing faults and fractures that may increase the risk of interactions between the waste deposit and the ground environment. Geological framework The Prado Velho open pit is an old uranium mining site, located in the Central Region of Portugal (figure 1), which was exploited from 1977 to 1982. Its exploitation was initially conducted as an underground mine that, for technical and economical reasons, was progressively Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 459


developed into an open pit. The regional lithology is a two-mica porphyritic coarse-to-mediumgrained granite (figure 1), where transmissivity is usually extended along short distances, through more permeable fractures. One of the objectives of these site investigations is to get a better understanding of the local and natural drainage conditions and to predict the potential of future water interaction from the “Containment Deposit” and contaminants spreading (radionuclides and metallic elements) in fractured aquifer systems. Geophysical surveys – data acquisition, processing and interpretation Two lines were chosen to conduct electromagnetics EM34, electrical, seismic reflection and refraction surveys. These lines were located NW and SE of the old mine open pit, accordingly to the direction of the main geological features identified (figure 1). For both lines, data processing was similar and had the objective of drawing two schematic models highlighting main alteration and fracturing zones. From these results a well supported decision regarding future use of the old open pit in mining waste storage could be taken. Electromagnetics Geonics EM34-3 was conducted every 10 meter in both lines (figure 1), using 10m, 20m and 40m length cables. Data processing used software developed by Santos Figure 1 – Geological map of the old Prado Velho Mine, with location (2004), using a smooth of geophysical surveys with different methods. inversion algorithm to constrain each conductivity block to be dependent of its neighbours, so that an approach of the 2-D electrical conductivity distribution could be visualized. It has allowed profile modeling into three different resistivity layers. Several vertical electrical soundings (VES) in both lines were also conducted (figure 1), so that results could be integrated. Seismic refraction data was acquired along almost full length of the lines, in order to provide information about the alteration degree from the velocity models. A layout of 24, 50 Hz vertical geophones with a 2 m spacing was employed. Several spreads were therefore used for each line. End-off shots were fired with 1 m and 20 m (when possible) offsets to the nearest receiver. To constrain the uppermost layers, shots were fired inside the receiver spread every 10 m. Reflection data was also acquired in confirmed or probable fault zones. A shot spacing of 2 m was therefore used in these areas, with a source to nearest receiver offset of 1 m. In both methods data was acquired using an accelerated weight-drop seismic source (Gisco AWD-550T) and a 24 bit digital data acquisition system (Seistronix RAS-24). A 0.5 ms sampling rate with a total recording length of 500 ms were used. Refraction interpretation of the data was performed using commercial software based on the delay-times method and ray-tracing (Haeni et al., 1987). The delay-times method is used to obtain a first 2.5D velocity model which is refined with a three step iterative process of observed and calculated arrival time residuals minimization. Velocities are determined by a weighted (by receiver number) average of a simple linear regression of the time-distance curves and the generalised reciprocal method (Palmer, 1980) were reciprocal times are available. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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Reflection data was processed with the Seismic Processing Software-SPWTM using a standard flow: trace editing, gains, frequency filtering, first arrival mute, desconvolution, frequency filtering and amplitude equalization, velocity analysis, NMO correction and stack, automatic residual statics (surface consistent), DMO integral correction (Ylmaz, 2001), FK migration with stretch (Stolt, 1978) and post-stack filtering. Depth conversion of the profiles was performed using stacking velocities. Alteration zones were related with faults, dykes or the water table and conceptual models for both profiles were created based on data from the several geophysical surveys. A common location is provided in each profile and relates to figure 1. NW Line Each result obtained for this line shows high heterogeneity, resulting from the geological complexity of the area (figure 2). SSE part of the profile appears to have lower shallow alteration, with resistivity values between points 1 and 5/6 that generally correspond to altered granite. P-wave velocities are higher than in the NNW part of the profile supporting this conclusion. In point 7, there is a fracture that can go deeper, as seen in figure 2. In depth, results seem to indicate the existence of a fractured zone with a complex geometry; near point 10, several fractures almost reaching surface are seen, causing discontinuities in the resistivity values and in the refractors depth, down to about 40m depth. The most important feature in this profile is from point 17 towards NNW, altered and fractured, maybe filled with the mapped basic rock dykes. This is inferred from the low resistivity values and low P-wave velocities. This zone, located in the northern prolonging of the N40-45ºW direction fault system mapped inside the open pit, has characteristics that correspond to higher altered deeper zones.

Figure 2 NW Line. a) Resistivity section of the inverse EM34 model. b) Seismic refraction interpretation. Average velocities of P-waves for each spread. c) Reflection profile: depth conversion from stacking velocities (base). Red dashed lines correspond to probable faults. Blue correspond to observed and interpreted dykes.

SE Line In this line (figure 3), granite alteration is lower and laterally more uniform in the near surface (about 20 m) compared to the NW line. The zone with lowest resistivities, above 12m depth is related with water table location, dividing saturated from unsaturated zones. This homogeneity is broken by the existence of deep faults, from the fault system with N40-45ºW, crossing longitudinally the open pit (points 2, 4-5) and, probably, the fault system with N5055ºW, near point 10, showing a shallow fault that doesn’t seem to reach ground surface. Between points 3 and 9, the resistivity section shows an altered granite zone at about 50m depth, which according to the interpretation of the seismic reflection profile may be the result of deeper fractures, not reaching the ground surface. Resistivity decrease in points 11 and 12 at about 50m depth may also correspond to a deeper fault. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 461


Figure 3 SE Line. a) Resistivity section of the inverse EM34 model. b) Seismic refraction interpretation. Average velocities of P-waves for each spread. c) Reflection profile: depth conversion from stacking velocities (base). Red dashed lines correspond to probable faults.

Conclusions Joint interpretation of all used geophysical methods confirms mapped faults and detected previously unknown faults. It also allowed assessing their local importance regarding groundwater circulation. SE line shows less alteration than the NW line. Figure 4 a) and b) shows synthetic conceptual models corresponding to this interpretation of all used geophysical methods to a depth of about 60m in the NW and SE profiles. These models are a compromise among every method used, since they reflect different material properties. In both profiles, porosity was estimated considering only average resistivity values to each material, using Archie’s Law with parameters defined by Shon (1996).

(a)

(b)

Figure 4 Synthetic conceptual models for NW (a) and SE (b) profiles, after a joint interpretation for all shallow geophysical data. Dashed black lines: possible faults, not clearly inferred in every geophysical method. Numbers in the model correspond to physical properties of Table 1. Solid black lines: interpreted faults in each geophysical methods. Deeper faults correspond to seismic reflection interpretation in figures 2c and 3c. Material 1 2 3

Characteristics

Resistivity (Ω.m)

Highly altered/ fractured granites Altered granites Low altered/fractured to unaltered/unfractured granites

Vp (m/s)

< 100

1.92

100-600 > 600

1100-3500 >3500

0.62-1.92 10 Hz) or low period and also blasting duration under one second. But if there is repeated blasts having a high acceleration as well as high explosive amount, then there will be observable cracks in the plaster and damages in the surrounding structures. Introduction In recent years, one of the most important problems which different sectors such as quarries, building, mining, and pipeline encounter is shakings that occur as a result of blasts. The usage of ground acceleration measurements has increasingly been a great importance in the investigation of environmental problems which is caused by shakings from the blasts. These analyses can currently be made with the evaluations of acceleration records of the shakings in the time and frequency domains. In this way, dynamic information has been provided in the evaluation of environmental effects of shakings, forecasting and preventing of the problems. Shaking of the buildings in the disquiet level by reason of blasts has introduced the importance of the frequency in the blasts. In experimental studies, it is well known that buildings have a frequency level between 5 and 20 Hz, namely small (Siskind et al., 1980). Shakings between these frequency intervals can cause the resonance in the surrounding structures. In general sensitivity, walls have the frequency lag between 15 and 20 Hz while columns and joists of the buildings (skeleton of the building) have a frequency between 5 and 10 Hz and this sensitivity show the importance of frequency in the blasts (Dowding, 1992). If the oscillation period of the building is accordance with the oscillation of the earth, structure takes the maximum damage during the shaking. So, the most critical situation in the blasts is that premonitory wave frequency is equal to or slightly larger than the self-structure frequency. As the consequence of the investigations, in some cases even no damage is happened, feelings and anxieties, people experiences the serious shaking in these cases, completely grow out of the low 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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frequency characteristics (Bilgin et al., 1999), because low frequency waves are easily felt by people. Because the frequencies especially under 10 Hz constitute the great displacements and unit deformation with high-level in the ground, the damage probability also increases (Siskind et al., 1980). Analyses The selected two quarries for the investigation and the coordinates of eight measurement stations are shown in Figure 1. Dynamite was used as explosive for blasts. In accordance with the aim of study, location of the structures existing in the surrounding of the two quarries and distance of the structures from the quarries are firstly determined. Considering the positions of structure in the vicinity, necessary acceleration records are recorded as three components. By analyzing the maximum acceleration values, frequency contents, and amplitudes of records which is obtained with accelometer, it is investigated whether there are great differences among the records depending on the explosive material quantity, point of blast, and distance of measurement location. Geologic formation of the area of two quarries is mainly composed of the andesitic-basaltic lava pyroclastic with gray color and basaltic lavas (in Figure 2). Three components of acceleration records of 24 are received in 8 measurement stations but 13 of these are examined. Information of these 13 records consist of the acceleration components (north-south, horizontal, N-S, and east-west, vertical, E-W), maximum acceleration values, and distance between blasting point and measurement station. All these details are given in Table 1. Telekom

4537600

St 5 193 m

175 m

4537500

Elf

4537450

Latitude (m)

St 2

Polygon

4537550

Quarry Area-2 151 m House St 4

St3 4537400

P.s 2 St 1

4537350

527 m 258 m

4537300

222 m Quarry Area-1

St 8

4537250

St 7

4537150 569300

569400

125 m

Villas

Village

4537200

88 m St 6

569500

569600

Longitude (m)

569700

569800

569900

Figure 1 The locations of blasting and position of the measurement station according to each other.

In this study, spectral analysis of acceleration records of shakings caused by blasts which is made in two different quarries in Trabzon are performed and examined the effects of the shakings to surrounding structures (e. g., private and public domain, personal homes). Also, frequency spectrum of acceleration records from blasts is calculated and the maximum acceleration versus dominant frequency and the maximum amplitude distributions are evaluated. Conclusions are commented in the damage effects. The frequency-dependent behaviors of each component of acceleration records were calculated by using Fourier transformation method. The calculated amplitude spectra were separately evaluated by means of frequency-amplitude relations. The dominant frequencies or Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 469


periods were optimally determined from amplitude spectra for each record. For dominant frequency value, it was taken frequency value that presents maximum amplitude value on spectrum. To reduce ambient noises on these records and make them interpretable clearly, Butterworth filter was applied with suitable cut-off frequency and filter degree. For display purposes, amplitude spectra were normalized according to maximum amplitude value involved.

Figure 2 The geological map of the area for quarries.

No Date

1 2 3 4 10 11 12 13 19 20 21 22 24

18.06.2004 18.06.2004 21.06.2004 21.06.2004 24.06.2004 24.06.2004 25.06.2004 25.06.2004 28.06.2004 28.06.2004 01.07.2004 05.07.2004 08.07.2004

Max. Accel. (g) 0.01671 0.0112 -0.00834 0.00763 -0.00293 -0.00523 0.0349 0.0325 0.0229 0.00089 0.9449 0.02653 0.18165

Dominant (Hz) N-S E-W 37 42 34 42 33 34 32 35 18 16 13 14 37 38 33 43 18 18 27 28 32 32 41 41

Freq. Distance (m) Vert. 35 258 29 258 26 193 34 193 17 527 17 527 38 151 37 151 42 175 175 24 88 32 222 24 125

Station Blasting Position Position Sta.1 Sta.1 Sta.2 Sta.2 Sta.3 Sta.3 Sta.4 Sta.4 Sta.5 Sta.5 Sta.6 Sta.7 Sta.8

Area-1 Area-1 Area-2 Area-2 Area-1 Area-1 Area-2 Area-2 Area-2 Area-2 Area-1 Area-2 Area-1

Table 1 The results of acceleration records analyzed. The maximum acceleration values in this table present the maximum acceleration of three components records.

An example acceleration record obtained from a blasting in area-2, at July 1,2005 is shown in Figure 3 (number 21 in table 1). The sampling time is 0.01 second and Nyquist frequency is 50 Hz. The maximum horizontal acceleration, which is commonly used in engineering studies to measure amplitude of displacement, was observed as 0.45090g (441 gal) on N-S component of this record shown in Figure 3a. The maximum acceleration values were observed as 0.3697g (362 gal) on E-W components and as 0.9449g (926 gal) on vertical component. Note that the maximum acceleration value on Vertical component is quietly high. The calculated amplitude spectra for each component are shown in Figure 3b. For Butterworth filters used in study, cut-off frequency was used as 2.5 Hz and degree of filter was 3. Furthermore, spectrum was smoothed by moving average with 51 points. Dominant frequency values were determined as 27 Hz (0.037 s) on N-S and E-W components and as 24 Hz (0.042 s) on vertical component from results spectra. Although high horizontal acceleration value is observed on N-S component, dominant frequency value is outside of natural frequency of structures. In establishing studies of damage, it is known that many factors are important and 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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evaluated many informed together. However, it is emphasized that frequency-amplitude relations of acceleration records are very important to explain amount of damages in surrounding structures than maximum horizontal acceleration. Results After the some blasts which caused the high horizontal acceleration values, that any important large damage (such as falling down, sliding, collapse, tilting) did not occur in surrounding structures is based on that records mostly have low amplitudes at low frequencies and high amplitudes at high frequencies (or low periods) and also blasting duration under one second. But, repetition of these applications frequently and usage of abundant explosive material will cause the serious damage such as cracks in the vicinity of the blasting fields and toiling of the buildings. For this reason, if the frequency-amplitude relations of acceleration records are previously considered, it can be prevented damage effects caused by vibrations, which will be occurred in the opening of the quarries.

(a)

(b)

Figure 3 a) Three components acceleration record on date of July 1, 2005 (number 21 in Table 1), b) Amplitude spectra of these components in (a). Some information is givens on figure.

References Siskind, D. E, Stagg, M. S., Knopp, J. W., Dowding, C. H., 1980, Structure Response and Damage Produced by Ground Vibration from Surface Mine Blasting, USBM, RI 8507. Dowding, C. H., 1992, Monitoring and Control of Blast Effects, SME Mining Engineering Handbook. Bilgin, H. A., Esen, S., Kılıç, M., 1999, Effects on Building of Earth Vibrations based on Blast and Importance of Amplifying Factors (in Turkish), 16th Mining Congress, p.25-32, June 1999, Ankara, Turkey. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 471


P2 - 06

GEOPHYSICAL METHODS FOR THE STUDY OF THE INTERACTION BETWEEN THE RETAININE WALL AND THE UNSTABLE GROUND V. Ciszkowski, L. Bogateanu, G. Popescu, G. Ticu, M. Ciuperceanu Railway Study and Design Institute, Bucharest Romania

Along Simeria – Petrosani railway line between km 60+597 and 60+950, on the left side (track II), there is a retaining wall with cast-in-place concrete foundation and prefab elements for the rest of the height. Following the landslides over the wall crown into the track formation level, draining works were carried out for the slope behind the retaining wall in 1998. On March 28th 2005, it was found out that the prefab elements of the retaining wall are displaced towards the railway line and the cast-in-place concrete elevation is damaged between km 60+740 and km 60+760. As a result of the rains in April 2005, the walls deformations have increased, culminating in the prefab elements falling over track II and closing the railway traffic along this railway track.

To design the consolidation works, a geo-physical study is required to establish the flowing directions of the waters to the slope on the left side of the railway line as well as to estimate the earth masses involved in the landslides. To clarify the problems raised by the designer, geo-physical investigations have been carried out by electrometric methods, using the vertical electric sounding procedure (V.E.S.) and by seismic methods, using the refraction elastic longitudinal waves recording procedure. The electric resistivity values as well as the values of the traveling speed values of the longitudinal elastic waves are determined in this lithologic area by the presence of the 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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underground water, by the interaction between the unstable ground and the retaining wall and by the wet landslide phenomenon over the time. The soils carried away in the recent sliding process are mainly composed of clayey sandy silt of very reduced consistency at the upper side caused by the infiltration water. The old and consolidated adobe deposit is made out of clayey silts, sandy silts, silty clay, sandy clay, silty sands and even clean sands (as lens-form elements). The base rock is represented by a flooded sandstone. GEOELECTRIC MAP at 2.5 m depth 60

4

Depth (m)

50 40

3

30 20 10

2

0

sev1

sev20

sev11

sev2

sev19

sev12

sev3

sev18

sev13

sev4

sev17

sev14

sev5

sev16

60 4'

sev15

50 sev21

sev6

sev7

sev22

sev8

sev23

sev9

sev24

sev25

40 3'

20 2'

60+680 60+700 60+720 60+740 60+760 60+780 60+800 60+820 60+840 60+860 60+880 60+900

10 0

Crown edge

Kilometer

Movement direction of the earth masses during the recent landslides

Directions of underground water infiltration Direction of the potential tension generated by the interaction between the unstable ground and the retaining wall

30

2

2'

Geophysical profiles

GEOELECTRIC MAP at 5 m. depth 60 4

Depth (m)

50 40

3

30

sev20

sev11

sev19

sev12

sev18

sev13

sev17

sev14

sev16

sev15

60 4'

50 sev21

sev22

sev23

sev24

40 3'

20 10 2 0

30 20

sev1

sev2

sev3

sev4

sev5

sev6

sev7

sev8

sev9

sev25

2'

60+680 60+700 60+720 60+740 60+760 60+780 60+800 60+820 60+840 60+860 60+880 60+900

Kilometer

10 0

Crown edge

The geo-electric sections analysis and the analysis of the geo-electric maps at 2.5 m. and 5m depth from the ground level provides the following information: • The earth involved in the recent landslide is flooded, which produces deep minimum electrometric values; at the upper part, there are maximum electrometric values caused by the macro-fissures in the landslide material. • Displacement of the unstable ground from the lateral sides, converging to the area affected by the recent landslide (km 60+740/760). • In the investigated area between km 60+740/770 and km 60+850/870, the underground waters flow downstream. • Due to the interaction between the unstable ground and the retaining wall, the landslide material is subject to compression, causing an increase of the electric resistivity. • In the area affected by the recent landslide, due to the compression loosening phenomenon, the electric resistivity is lower. • The maximum electrometric value between Km 60+770 and Km 60+820 indicates a compression of the landslide area at present, which brings about a future landslide risk. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 473


Depth (m)

THE GEOELECTRICAL SECTION 3 - 3' 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13

60+700

60+720

60+740

60+760

60+780

60+800

60+820

60+840

60+860

60+880

60+900

Kilometer

The underground water adobe flow is highlighted by electrometric minimum and by picks of the electrometric minimum oriented towards the surface. On the railway left side slope, in the natural ground there is an infiltration water circulation at km 60+720/740, km 60+760/780 and km 60+860/880.

Depth (m)

THE GEOELECTRICAL SECTION 2 - 2' 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 -11 -12 -13

60+680

60+700

60+720

60+740

60+760

60+780

60+800

60+820

60+840

60+860

60+880

60+900

Kilometer

The geo-electric sections show the presence of the gradient of electric resistivity decrease in depth determined by the clayey nature of the sedimentary material, as well as the water presence in the base rock. The extension of the electrometric anomalies is pointed out as well.

Clay rock resulted from an old landslide Base rock

Depth (m)

Sedimentary material involved in the recent landslide

3 - 3' SEISMIC SECTION from geotechnical point of view s31

0 -4 -8 -12

380

Depth (m)

s21

s22

60+660

s23

2200

2700 60+680

o.s.1

60+700

s34 400

1400

60+720

60+740

s24

s25

340

1400

o.s.1

3000

3000

2200

Kilometer SEISMIC section 2-2' from geotechnical point of view

1200

900

s33

340

1000

60+700

0 -4 -8 -12 -16 -20

s32

60+760

s26

s27

320

320

s28 280 o.s.1 1000

2800

2200

60+720

60+740

60+760

Kilometer


474

o.s.2

3200 60+780

60+800


From geo-technical point of view, the seismic sections 2-2’ (7 m. upstream from the crown edge) and 3-3’ (28 m. upstream from the crown edge) indicate the following: • For the unstable sedimentary material, the values of the propagation speeds for the elastic longitudinal waves range between 280 m/s and 400 m/s. • For the flooded stable base rock, the values of the propagation speeds for the elastic longitudinal waves range between 2200 m/s and 3200 m/s. • Between the unstable sedimentary material and the base rock, there is old consolidated sedimentary material that was involved in the landslide in the past and now the values of the propagation speeds for the elastic longitudinal waves range between 900 m/s and 1400 m/s. • The seismic horizon O.S.1, which corresponds to the recent landslide plane, indicates that the landslide phenomenon has a medium depth (maximum 9.5 m); horizontally, it has more than 150 m length on the slope upstream the railway line.

Depth (m)

On the slope placed on the left side of Simeria – Petrosani railway line between Km 60+740 / Km 60+820, due to the excess of humidity on the slope and the large extent of unstable ground, a pressure was created upon the retaining wall that crushed at Km 60+740/760; the risk of propagating the ground instability between km 60+760/820 is still high. 1-1' SEISMIC SECTION from geotechnical point of view

s11 s12 900 -2 2200 -6 60+700 60+720

s13

s14

s15

s16

s17

s18 2500

60+740

60+760

60+780

o.s.2

60+800

Kilometer

The seismic section 1-1’ resulted from the measurements between the two railway lines show that the railway infrastructure is stable even if the bearing layer represented by an old consolidated sedimentary material suffered sliding processes in the past, but it was not any more involved in the recent sliding process. The bearing layer consists in clayey sandy silts with very semi-hard consistency. Lab analysis carried out on soil samples confirmed the following data obtained by geophysical investigations: The sliding plans have been pointed out based on the drill shearing noticed in the cores and based on the slickenside areas also noticed in the cores. The results of the lab tests on the geo-technical drill samples carried out in the sliding face show the presence of the cemented clayey sand, of the very hard clayey silt, very hard sandy clay and very hard clay. After two weeks from the geo-physical measurements carrying out, another retaining wall section has crashed at km 60+770, confirming the compression of the sliding face pointed out by the electrometric measurements. The information obtained from the geo-physical investigations was confirmed by the geotechnical study and indicates the necessity to extend the consolidation works for the retaining wall, including sector km 60+720/820 as well.



P2 - 07

GEORADAR METHOD TO MONITOR RAILWAY INFRASTRUCTURE V. Ciszkowski1, P Curcaneanu1, E. Oltean2, L. Bogateanu1, G. Ticu1, M. Ciuperceanu1 1 Railway Study and Design Institute, Bucharest, Romania 2 Design Institute for Road, Water, and Air Transport, Bucharest, Romania

Following the heavy rains in August 2004 in Constanta area, the railway line ConstantaMangalia was unstable. This instability brought about the breaking of track 2 before crossing the Danube-Black Sea Lock (km 232+950 – km 233+100).

After this event to find out the causes of the railway line instability we decide to investigate the railway infrastructure using geophysical methods. Mainly, the geo-physical measurements have been carried out using the radio wave recording method (geo-radar). The geo-radar recordings on the ground have been carried out using multi-antenna RIS2K/MK geo-radar, to localize the railway survey layers, using three 400 Mhz main antennae 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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situated at the sleepers end and railway axis, as well as two emergency/auxiliary antennae, one of 200 Mhz and the other one of 600 Mhz. The antenna has mono-static layout, the transmitter (TX) and the receiver (RX) allow getting information from the whole studied area up to 3.00 m depth. For the signal sizing, during the purchasing stage, they used the set of options of the program offered by the manufacturing company. First of all the results of the geo-radar measurements that had been carried out in the area the year before were analyzed (April 16, 2003). Based on the geo-radar measurements Map isobaths (bathimetric contour) containing the isobaths at the base of the ballast. Line I Line II

MAP WITH ISOBATHS (3D) at the ballast base following the information of the georadar measurements carried out on April 16. 2003

Studying the isobaths map, we can note that even in 2003 there appeared some ballast pockets mainly centered between the two railway tracks. The widest ballast pocket was situated near the area that was affected by the falling down of the railway infrastructure in August 2004. To study the infrastructure condition after the deterioration of the railway line, geophysical investigations have been performed using the geo-radar method. In order to obtain railway infrastructure data using other geo-physical methods, micro-seismic and electrometric procedures have been used. For the micro-seismic measurements, a device has been used having equidistance between geophones of 20 cm and the electrometric measurements have been carried out using a Schlumberger gradient device. The geo-technical investigations consisted in performing excavations and geo-technical drillings.Based on the information resulted from geophysical measurements, from the excavations and from the geo-technical drillings carried out on October 2004, the Map (3D) has been updated with the isobaths at the ballast base, showing the railway infrastructure state after its deterioration. Updating the Map with isobaths at the ballast base makes evident the changes that have appeared in time at this stratigraphical limit.



Line I Line II

MAP WITH ISOBATHS (3D) at the ballast base following the information of the geophysical measurements, excavations and geotechnical drilling carried out in October 2004

The unconsolidated rocks (crushed stone and ballast) are characterized by a travel speed of the elastic wave from 170 m/s to 285 m/s, and their electric resistivity has values between 50 ohm m. and 7000-ohm m. The clayey compacted filling of the fill has the elastic wave travel speed between 360 m/s and 460 m/s, and their electric resistivity is between 15-ohm m. and 70 ohm m. The large range of variation on horizontal and vertical axis of the electric resistivity values of the fill material caused a large variation of the electromagnetic waves traveling speed (radio). In order to establish the proper average traveling speed of the electromagnetic waves in the railway fill, besides the comparing of the traveling speed of the electromagnetic waves resulted from the dielectric constant of the railway fill material, the sizing procedure of the radar measurements have been also used, comparing with the depth resulted from the classical geotechnical methods (open wells). The analysis of the results obtained by the railway infrastructure investigation using the three geo-physical methods (electrometric, seismic and geo-radar) points out the geo-radar method superiority as regards accuracy and the rapidity of this investigation method. Although, as it is shown in the filtered radargram in the area where the ballast pockets are generated, reflections occurred determined by the crushed stone/ballast mixtures and for the right identification of the reflection corresponding with the ballast base, it is imposed to compare the radar-gram with the data obtained from the geo-technical or seismic investigations.


478


The calibration of the radar measurements imposed an average value for the travel speed of the radio waves of 90 mm/ns.

0,00

0,50

depth (m)

1,00

ballast base

1,50

2,00

2,50

232+500

232+550

232+600

232+650

232+700

232+750

232+800

232+850

232+900

232+950

kilometer

THE FILTERED RADARGRAM

The stratigraphic limit at the ballast base has been changed a lot in time: horizontal and vertical extensions of the old ballast pockets. From the above-mentioned ballast pockets the widest is the one located near the area affected by the falling down of the railway infrastructure in August 2004, between Km 232+820 and Km 232+950. Following the heavy rains in August 2004, the water in these ballast pockets could not be discharged, this being the main reason causing the instability of the railway infrastructure. The periodical monitoring of the raiway infrastructure using the georadar methods makes possible to avoid, in future, this kind of unfortunate events caused by instability phenomena.



P2 - 08

IMPLEMENTATION OF GEOPHYSICS IN CONTAMINANT HYDROGEOLOGY Snezana Komatina-Petrovic Geophysical Institute, NIS, Naftages, Beograd, Serbia And Montenegro

Summary For the purpose of the study of the pollutant migration, in other words – of the spatial distribution of indicators within a front, numerous hydrogeological and hydrogeochemical methods have been developed. However, it is noticeable that possibilities of geophysical methods have not been completely exploited so far. Precise measurements of various physical parameters and fields of variables, can certainly contribute to solution of the following problems: estimation of depth and lithological content of the layer covering the aquifer under consideration, determination of an appropriate autopurification role in the aquifer vulnerability to pollution, estimation of permeability, degree of anisotropy, hydrodinamic features and, in greater or less extent, prediction of the contaminant migration within the aquifer. In the paper, degree of applicability of geophysical methods in detecting and monitoring groundwater contamination under typical hydrogeological conditions is discussed. Introduction In evaluation of aquifer vulnerability to pollution, geophysical methods are used in three basic domains: 1. Analysis of aquifer geometry – whenever determining aquifer boundaries is possible, geophysical methods are applied. In some cases, it is possible to define only top layer/aquifer or aquifer/bottom layer interface, but, for hydrogeologists, such information is also useful (Komatina M., 1984/1990). 2. Defining aquifer contamination by mineral or organic deposits influencing change of water resistivity. Such deposits originated artificially (discharge into rivers or just to the aquifer system) or naturally (salt water penetration in the coastal zone). 3. Determining filtration characteristics of the top layer and hydrodynamic parameters of the aquifer (Komatina-Petrovic S., 2004). It is possible to make correlation between physical parameters obtained by geophysical methods and hydrodynamic properties of the aquifer, or to correlate parameters of the top layer obtained by geophysical methods and grain-size analyses. As results of geophysical data processing, the following parameters of geological formations are obtained: density (gravity method), rate of elastic waves propagation (seismic reflection and refraction methods), magnetic susceptibility (magnetics), resistivity (electric and 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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electromagnetic methods), radiation (radiometry) and temperature (measuring temperature gradients, infrared method). For hydrogeological exploration, so-called “indirect” methods are used, that is methods directing to convenient conditions for aquifer presence. Choice of the method (or several methods) depends on electric characteristics of the investigated area and lithology of defined geological formations (Komatina-Petrovic S., 2005). Problems of groundwater contamination and monitoring solved by geophysical methods 1. Determining aquifer geometry and analysis of the top layer. The most often used geophysical methods for solving this task are electrics and seismics. Hydrogeological exploration in Quaternary deposits and shallow horizons of Neogene sediments refers to determining horizons presented by high-resistivity water-bearing gravel-sand material (Komatina M., 2004). As the bottom layer of the deposited material is made of lowresistive impermeable clay-marl sediments, electric soundings is useful in distinguishing the deposits. Soundings is also applied for determining thickness of impermeable hanging-wall, not only in the case of alluvial aquifer, but also of the first Neogene waterbearing horizon. Seismic methods are implemented in all stages of hydrogeological exploration. Velocity of seismic waves propagation depends on rock density and presence of water and clay. Seismic refraction method is applied for determining lithologic structure of rocks and zones with similar corresponding characteristics. Very often, it is performed simultaneously with electrics – while seismics solves the aquifer geometry, electrics serves for analysis of lithological changes within. The most realistic cross-section of geological formations containing groundwater is certainly that, obtained by well-logging – interpretation of the results makes precise identification of water-bearing and impermeable layers possible, as well as water characteristics along the whole profile of the borehole. Applying one or several methods, it is easy to define boundaries of the layers, porosity, places of water recharge, direction and velocity of groundwater flow, rocks and water temperature, water mineralization, etc. For analysis of the top layer into certain lithologic formations in the cross-section, results of electric survey are widely used (soundings, soundings – IP, mapping). If necessary, seismic survey is also performed. The survey is based on significant differences in velocities of seismic waves propagation through the typical formations. 2. Distinguishing groundwater level. For free-surface aquifers, piezometric surface is within formation containing groundwater, and it could be registered by electric soundings or refraction seismics. In the curve of electric soundings, it is necessary to define thickness of dry (high-resistive) sands and water-bearing (resistive) sands, and on the basis of the relation, depth of groundwater presence is obtained. Application of seismic refraction method is also possible, since noticeable contrasts exist in velocities of longitudinal waves propagation for unsaturated and completely saturated medium. For the area where GWL is present, characteristic velocity of longitudinal waves propagation varies in the following range: 1450-2700 m/s. 3. Determining groundwater chemical content. Changes in percentage content of dissolved salts in the aquifer system influence the resistivity values of the terrain. Aquifer – to – water resistivity ratio is described by formation factor F. Total porosity of the aquifer depends on: quantity of dissolved salt, salt origin and temperature. So, in exploration of water chemical content, important role belongs to electric methods (Komatina-Petrovic S., 1994). 4. Clay content in sediments. As in the former case, for determining this factor, electric methods only are applied. Drop of electric resistivity directs to clay presence within the aquifer or to increase of salt content within. For example, in the case of transformation of Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 481


fine sands into clayish sandstone, and then into sandy clays, resistivity is a function of clay permeability. 5. Analysis of filtration characteristics. Changes of the total aquifer porosity affect electric resistivity of the aquifer. Following increase of cementation factor, the changes increase. So, for weathered formations (for example, sand or gravel), change of porosity has less effects onto resistivity values than in the case of consolidated formation. Determining total porosity of the aquifer containing clay component is pretty uncertain, in comparison to non-clayish. However, on the basis of anisotropy analysis, it is possible to define porosity distribution. In defining porosity of non-clayish weathered layers, seismic refraction method is also used. For determining filtration velocity in lowpermeable rocks, thermometry surveys are performed, and for the top-layer zoning, correlation of geophysical data with values of filtration coefficients (obtained by grainsize investigations) is very useful. 6. Determining transfer velocity of wet front and contaminant. To determine filtration velocity through low-permeable rocks of the top layer, thermometry is carried out. As a very important and useful supplementary tool for monitoring migration of the wet front, in other words – of the contaminant through aeration zone, well logging is applied, enabling: distinguishing permeability of investigated complex in depth; control determining of filtration velocity in points of observation boreholes and continuous monitoring of the plume. One of the actual tasks of geophysics is more precise evaluation of applicability of some methods and their development in improving precision of measurements important for analysis of hydrogeological characteristics. Of course, development of numerical modeling methods and software tools for more precise graphical and mathematical data processing is included (Komatina-Petrovic S., 2005a). Conclusion Soil and groundwater are under significant effects of numerous pollutants from the surface (related to agriculture, oil industry, industrial, mining and municipal waste water, etc.), as well as local accidental contamination effects. That is why a special attention is directed to research of process of the contamination migration, not only through the covering (protecting) layer, but also its dispersion into the groundwater. Today, there is a considerable body of literature on the problem, and the knowledge on causes, conditions, scale and consequences of groundwater contamination has been significantly improved. Analysis of characteristics of the contaminant source and its transport is, in great extent, related to typical aquifers, because they are characterized by numerous specific features. Solving the problem of detecting and monitoring the soil and groundwater contamination, as one of actual tasks, is also possible on the basis of sophisticated geophysical methods, developed during the last two decades. That is reason why importance and advantages of developing such methodological approach to the actual problem of groundwater contamination, for which solving is carried out voluminous hydrogeological exploration and significant financial resources spent, should be outlined. In this paper, on the basis of the world literature, as well as experience of the author, degree of applicability of geophysical methods in detecting and monitoring groundwater contamination under typical hydrogeological conditions is discussed.Besides, one of the main goals is to make a relevant base for planning preventive and protective measures of some groundwater sources. Geophysicists have not paid special attention to the cited problems, or not 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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in the extent enabling closer link between geophysical field measurements and defining contaminant migration within aquifers. Important contribution of geophysics is expected, first of all, in quantification of the whole series of geological – hydrogeological and other parameters (terms), as: thickness of lithological layers, grain-size content, representative hydrogeological parameters of the top layer and the aquifer, chemical content of groundwater, velocity and duration of wet front through the covering layer and contaminant dispersion, groundwater level, etc. Of course, in their parameter analysis and synthesis, too. References Komatina, M., 1984/1990, Hydrogeological exploration, Vol. I – IV. Geozavod, Beograd (in Serbian). Komatina, M., 2004, Medical Geology. Effects of geological environments on human health. Elsevier, Amsterdam, 435 p. Komatina-Petrovic, S., 1994, Geophysical methods application in groundwater natural protection against pollution. Environmental Geology; Vol.2; Springer International; pp.53-60. Komatina-Petrovic, S., 2005a, Detecting groundwater pollution and monitoring by geophysical methods. Foundation Andrejevic, Beograd, 150 p (in Serbian). Komatina-Petrovic, S., 2005, Environmental Geophysics. Geophysics and environmental protection. DIT NIS-Naftagas, Novi Sad, 350 p (in Serbian).



P2 - 09

SEISMIC ACOUSTIC RESEARCH ON IDENTIFICATION OF ARCHEOLOGICAL SITES IN SUBMERSIBLE ZONES Anghel Sorin, Ion Gabriel National Institute for Marime Geology and Geoeoecology – GeoEcoMar, Bucharest, Romania

Summary In Romania, geophysical methods are normally used to estimate the distribution of cultural relics, before digging. Objects of archeological interest are usually located within a few meters of the surface. The used equipment belongs to the seismic –acoustic reflexion systems category and it is usually used to detailed investigation of the submersible sediment structure. A great contrast of acoustic impedance and therefore a correct identification of reflecting are also when in the sediment mass there are some bodies with acoustic impedance very different from that of the sediments, like archeological buildings. Introduction Ones of the oldest fortress - type settlements are Greek colonies in Dobrogea, really considered the most ancient cities in Romania (e.g. Argamum,Histria, Tomis and so on). In the last flourished period of the Roman Dobrogea, between 4th – 7th centuries a. D., the fortifications along the Danube were strengthened, and other fortress were inside built (e.g. Ulmetum, Argamum, Petra). The last fortress is considered the first antique settlement in our country, as it was mentioned by an antic literary source (Barnea 1976).

Figure 1 The global plane of Agamum archeological site

Seismic–acoustic research was made with specific equipment (“X-Star Full Spectrum Subbottom Profiler”) which works with frequency modulation in the range of 2-16 Hz. The vertical resolution of this system is better than 1 decimeter. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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The research has been performed in turbo mode with 12 emission of signal/sec. In order to solve the archeological research objectives (identification of some possible 1 meter width walls). Data have been recorded on thermic paper as depth sections on which the GPS format position information have been noted. The location of works has been noted. The location of works has been performed with a Global Positioning System, Sercel type – NR. 109 GPS. Principle of method The used equipment belongs to the seismic –acoustic reflexion systems category and it is usually used to detailed investigation of the submersible sediment structure. In a vehicle, pulled by the boat with the collecting data system, there is the seismic source. This produces the mechanical acoustics waives which excite the medium. Besides the source, there are the receptions elements (hydrophones group) which catch the compression waive reflected by the interfaces from the analyzed medium, interfaces which separate domains with deferent acoustics impedances. The cached signal is counted and processed in order to be graphically represented as seismic acoustics sections of reflexion, sections that fallow the structure of the acoustics impedance contrasts of the analyzed medium. The method is based on reflexion capacity of the separation interfaces between different granulometer types which form marine, fluvial and other type sediment mass. The physical parameters which condition the identification of interfaces in the seismic acoustic sections of reflexion are the contrast of physical properties. This means the speed of the mechanical waives used to excite the sediments, as well as the density of the mass crossed by the mechanical waives produced by the seismic acoustics source. A great contrast of acoustic impedance and therefore a correct identification of reflecting are also when in the sediment mass there are some bodies with acoustic impedance very different from that of the sediments, like archeological buildings. In the archeological submersible the vertical resolution (1/4 of average length wave of the seismic – acoustic used source) of the used equipment is enough sufficiently (that is a minimal high of 10cm of a submersible wall).

Figure 2 The plane of seismic acoustic profiles and the interpretative elements

Methodology Approximate length of the defense wall along with the promontory cliff Dolosman is about 315 m (Figure 1). Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 485


Seismic acoustic works have been projected in order to perform profiles parallel with the coastline in the Argamum fortress zone, at an equidistance less then 10 m, being possible interception of some possible antic buildings inside of the Razelm Lake (Figure 2). The configuration of the promontory cliff Dolosman indicates past and present erosion of this. In the Figure 3 is a reconstruction of this unchanged configuration.

Figure 3 The graphic reconstruction paleo-cliff Dolosman

Figure .4

A first element isolated on seismic acoustic sections is presented in the Figures 4 and . This elements could represent a part of some antique building which resisted erossion.


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Figure 5

Conclusions The interpretative elements identificated on seismic acoustic registered sections can represent parts of small dimensions of some antique buildings which resisted to erosion action, but which don’t evidently group themselves in the coherent elements to suggest the presence some antique complexes. The seismic acoustic works were prospected to make in the form of some almost parallel profiles with coastline in the zone of Argamum fortress, at distance smaller than 10m, in order to find possible antique submersible buildings in the Razelm Lake. References: Bleahu, M., 1962, Observation sur l’evolution de la zone d’Istria au cours des trois dernièrs millénaires. Rev. Géol. Géogr., VI, 2, 333-343. Chepalyga, A.L., 1985, Inland Sea Basins. In: Late Quaternary environments of the Soviet Union. A. A. Velichko. Minneapolis, Univ. Minnesota Press, 229-247. Fedorov, P. V., 1971, Postglacial transgression of the Black Sea. Internat. Geol. Rev., 14 (2), 160-164. Panin, N., 1974, Evoluţia Deltei Dunării în timpul Holocenului, Inst. Geol., Stud. Tehn. Econom., Seria H, Geol. Cuaternar., 5, 107-121, Bucureşti. Panin, N., Panin, Ş., Herz, N., Noakes, J.E., 1983, Radiocarbon dating of Danube Delta deposits, Quaternary Research, 19, 249-255, Washington. Panin, N., 1983, Black Sea coast line changes in the last 10,000 years. A new attempt at identifying the Danube mouths as described by the ancients. Dacia, N.S., XXVII, 1-2, 175184, Bucarest. Panin, N., 1989, Danube Delta genesis, evolution and sedimentology. Rev. Roum. Géol. Géophys., Géographie, 33, 25-36, Bucureşti. Panin, N., 1996, Danube Delta genesis, evolution and sedimentology. Geo-Eco-Marina, 1, 11-34, Bucharest-Constantza. Serebryanny, L.R., 1982, Postglacial Black-Sea coast fluctuations and their comparison with the glacial history of the Caucasian high mountains region. In: P.A. Kaplin et al. (eds.) Sea and Oceanic Level Fluctuations for 15000 Years (in Russian). Nauka, Moscow, 161-167, Moskva. Sorokine, I., 1982, The Black Sea. Ed. Nauka Acad. Sc. U.S.S.R.: 216 p., Moskva. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 487

REGIONAL GEOPHYSICS & GEOTECTONICS

P3 - 01

STRATIGRAPHIC INTERPRETATION OF DEPOSITIONAL SEQUENCES AT THE AEGEAN SEA EXIT OF CANAKKALE STRAIT Bedri Alpar Istanbul University, Institute of Marine Sciences and Management, Istanbul, Turkey

Summary The Aegean exit of the Canakkale Strait controlled the water exchange between the Aegean and Marmara seas during the past glacial/interglacial stages. High resolution seismic reflection data indicated numerous continuous and well-bounded seismic reflections developed on the Miocene basement during upper Pliocene and Holocene times. The Plio-Quaternary sediments are composed of mostly continental clastics. Sediment deposition was controlled mainly by fluvial discharges (mainly Karamenderes River), by sea-level oscillations which determined the proximity of basins to river mouths, and by oceanographic conditions. Three distinct depositional areas as thick as 130 m were defined. Introduction Northeastern Aegean Sea and the Canakkale (Dardanelles) Strait have been on a sea corridor between the Mediterranean and the Black Sea (a part of the Neogene Paratethys) since Middle-late Miocene. Major geodynamic processes which controlled the structural evolution of the region in Middle Miocene to Quaternary times mainly resulted from the westward migration of the North Anatolian Fault in the Late Miocene–Early Pliocene and the formation of the North Aegean Trough. The latter is a deep (1200-600 m) elongated depression extending from the Sporades basin to the Saros Gulf and bounds the study area to the north. Its southern slopes are delineated by steep fault scarps, which represent the sharp contact with the shallow continental platform of the study area. The Aegean and Marmara seas were joined during the interglacial stages and separated again during the glacial stages. The region was developed on a Miocene basement during upper Pliocene and Holocene times under the control of global sea level changes and regional uplift, as evidenced by the Quaternary marine terraces of 4-5, 12-15, 30-35 and 115 m along the strait. Sediment deposition was controlled mainly by fluvial discharge, by sea-level oscillations which determined the proximity of basins to river mouths, and by oceanographic conditions. The most important fluvial input is from the Karamenderes River which drains the metamorphic mountainous area of the Biga Peninsula. The valley bottom of the Karamenderes River today is characterized by a buried meander river. The purpose of this work is to investigate the upper Pliocene–Holocene sedimentary sequences and structure of the Aegean exit of the Canakkale Strait. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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REGIONAL GEOPHYSICS & GEOTECTONICS Material and Method A total of 260 km high resolution seismic reflection lines (1.25 kJ sparker) have been shot and bottom samples have been recovered (Figure 1). The system gave a penetration of up to 150 m in the sediments of the region which express a variety of textures at surface. Particle grain size analysis of bottom samples was performed using wet sieving. The stratigraphic framework was reconstructed using a sequence stratigraphic approach. Sedimentary units permitted the interpretation of the environmental setting from the seismic data. Seismic units represent groups of seismic reflections whose parameters (configuration, amplitude, continuity, and frequency) differ from those of adjacent groups (Mitchum et al., 1977). Results and Discussion The sea floor, sedimentary layers and basement give rather continuous and high amplitude reflections on the seismic sections (Figure 1). Sediment samples indicated that gravel and shelly sands were dominant close to coastal lines and sand was dominant between Gokceada and Gelibolu Peninsula. These coarser-grained sediments may correspond to the relict deposits which are formed under shallower water-higher energy conditions in the latest Pleistocene-Early Holocene. Grain size is reduced and the silt and clay ratio is increased while the water depth is increasing. Shelly mud is dominant between the islands and two mud and muddy sand facieses are distributed between the Bozcaada Island and the Biga Peninsula.

Figure 1 Sparker seismic profiles and interpretation showing seismic units mentioned in text.

The sea floor morphology is mainly controlled by the undulation of base rocks. The highest bathymetric slopes bound the Gelibolu Peninsula and the northern shores of the Gokceada Island. Bathymetry shows a meandering channel that is bounded by 70 m isobath and trending NE-SW (Figure 2a). Folded base rocks form a sill at the strait’s exit and 60-65 m below msl. It has a concave shape in planar view between the Tavsan islands and SE Gokceada (Figure 2b). Because it is shallower than the fossil shores in the Aegean Sea (115 m below msl; van Andel and Lianos, 1984) it played an important role in the paleo-oceanographic conditions of the Sea of Marmara during the late Quaternary times. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 489

REGIONAL GEOPHYSICS & GEOTECTONICS Seismic Units Throughout the study area the acoustic basement is made up of folded layers of Miocene times. The basement and overlying Plio-Quaternary sediments were represented by continuous and well-bounded seismic reflections. The deepest high-amplitude reflections represent the acoustic basement. This reflector can be interpreted as the Pliocene erosion surface (Cagatay et al., 1998; Yaltirak et al., 1998). The highest depth to the basement from present sea level is somewhere between Gokceada and Bozcaada. The Pliocene erosion surface was partially controlled by almost vertical faults. The folding of sedimentary layers which are contiguous or close to the basement bounded by these faults may indicate that these faults are strike-slip and possibly developed along some previous normal faults in their routes. This development coincides with that of the Anafartalar thrust fault on the Gelibolu Peninsula (Upper Pliocene – Lower Pleistocene) when the eroded material due to uplift of Gelibolu Peninsula was transported to the Marmara and Aegean Seas (Yaltirak et al, 2000).

Figure 2 (a) Bathymetry. (b) Distribution of seismic unit 2 and the sill between them. Main fold and faults on land are from Cagatay et. al, 1998 and Yaltirak et al, 2000.

Three depositional areas which are composed of mostly continental clastics are distinctive on records. The first one is towards deeper shelf areas between Gokceada and Bozcaada with a thickness of at least 130 m (Figure 2b), especially. The second depositional area with a maximum thickness of 85 m is placed between the Aydincik and Mehmetcik Points (Figure 2b). Third depositional area is offshore Yenikoy. These depositional areas are believed to be made up of the sediments transported by the Karamenderes River. They should have been deposited during the postglacial times towards northeast into the North Aegean Trough and westward into the Aegean between the islands. Four seismic units were recognized (units 1, 2, 3 and 4, from younger to older) above the Pliocene erosion surface. Using seismic characteristics together with stratigraphic relationships among various units and the physical continuity with rocks outcropping along the coast, we attempted to correlate each seismic unit to a geologic one. Unit 1: The topmost is a rather thin (0-10 ms) post-transgression unit (Holocene) which covers all sedimentary units and occasionally the basement. An exception is around fixes 113115 of line 08, south of Gokceada where a thick (20 ms) sand bar was discovered below shelly surficial material. Unit 2: Holocene blanket is underlain by a deltaic unit with a maximum thickness of 40 ms. It has sigmoidal and oblique clinoforms toward deep basins (e.g. fixes 25-23 of line 01 and 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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REGIONAL GEOPHYSICS & GEOTECTONICS 178-176 of line 12). They show toplap and onlap configurations. The foreset–topset transition of this unit at the shelf break suggests that the sea level was lowered between 95-120 m. This unit should have been deposited during the latest glacial stage and the following early phase of deglaciation (25-13 ka BP). Similar progradational deltaic sequences occur along the coasts of western Anatolia where they are found below the present day deltas at 100-110 m water depths. Their upper parts are dated by the 14C method to be 14-10 Ka BP (Aksu et al., 1987). Unit 3 (upper Pleistocene): Deltaic clastics are underlain by a seismic sequence distinguished by parallel and sub-parallel reflections and coastal onlaps. This unit overlies the Miocene basement rocks (around fixes 123-127 of line 08 and 178-176 of line 12) and also another sequence (fixes 12-4 of line 01 and 189-183 of line 12) under it, and its thickness changes between 0 and 40 ms. According to its seismic character and configuration, this unit should have been deposited when the sea level was high. This unit can be correlated with the Marmara formation (upper Pleistocene) described by Sakinc and Yaltirak (1997) along the southern coasts of Thrace. Unit 4 (Akchagylian): This bottommost sedimentary unit lies on the Miocene basement discordantly (e.g. fixes 12-3 of line 01 and 189-183 of line 12) and correlated with the Conkbayiri and Ozbek formations (middle Pliocene-lower Pleistocene) on land. Similar to those observed on land, this unit was eroded away to a great extend and overlaid by Unit 3 discordantly. Conclusion The base rock (Miocene) is made up of folded layers throughout the study area. The erosion surface (Pliocene) developed on this basement during middle Miocene times was partially controlled by strike-slip faults. In early Pliocene important transgressions occurred. At the end of Pliocene, sea-level rose more and connected with the Marmara Basin. In the region, sea-level decreased during the glacial stages while the Mediterranean conditions prevailed during the interglacial stages. Sea-level rose last time in Holocene and connected with the Marmara Basin. The thick deposits of unit 2 in depositional areas are the products of the sediments transported into the deep troughs in the Aegean Sea by the paleo-Karamenderes river mainly during the postglacial times. In addition to its control on the water exchange between two marine realms, the 60-65 m sill at the strait’s Aegean exit should have been played an important role in the direction of sediment transportation. References Aksu A.E., Piper D.J.W., Konuk T. (1987). Late Quaternary tectonic and sedimentation history of outer Izmir and Candarli Bays, western Turkey. Marine Geology, 76, 89-104. Mitchum, R.M., Vail, P.R., Sangree, J.B. (1977). Seismic stratigraphy and global changes of sea level, part 6: stratigraphic interpretation of seismic reflection patterns in depositional sequences. In: Payton, C.E. (ed) Seismic Stratigraphy-Applications to Hydrocarbon Exploration. AAPG Mem, 26, 117–133. Sakinc, M., Yaltirak, C. (1997). Guney Trakya sahillerinin denizel Pleistosen cokelleri ve paleocografyasi. MTA Dergisi, 119, 43-62. van Andel, T.H., Lianus, N. (1984). High-resolution seismic reflection profiles for reconstruction of the postglacial transgressive shorelines: An example from Greece. Quaternary Res., 22, 31-45. Cagatay, N., Gorur, N., Alpar, B., Saatcilar, R., Akkok, R., Sakinc, M., Yuce, H., Yaltirak, C., Kuscu,İ. (1998).Geological evolution of the Gulf of Saros, NE Aegean Sea, Geo-Mar Let, 17,1-9. Yaltirak, C. Alpar, B., Yuce, H. (1998). Tectonic elements controlling the evolution of the Gulf of Saros (Northeastern Aegean Sea), Tectonophysics, 300, 227-248. Yaltirak, C. Alpar, B., Sakinc, M., Yuce, H. (2000). Origin of the Strait of Canakkale (Dardanelles): regional tectonics and the Mediterranean–Marmara incursion, Mar. Geol. 164, 139-156. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 491


P3 - 02

UPPER CRUSTAL STRUCTURE OF THE VRANCEA ZONE AND FOCSANI BASIN FROM SEISMIC VELOCITY MODELLING AND POTENTIAL FIELD DATA Andrei Bocin1, Randell Stephenson2, Ari Tryggvason3, Ionelia Panea1,Victor Mocanu1, Franz Hauser4, Liviu Matenco1,2 1 Faculty of Geology and Geophysics, University of Bucharest, Bucharest, Romania 2 Faculty of Life and Earth Sciences, Vrije Universiteit, Amsterdam, Netherlands 3 Department of Earth Sciences, Uppsala University, Uppsala, Sweden 4 Geophysical Institute, University of Karlsruhe, Germany

The Vrancea Zone displays intense and persistent seismic activity comprising crustal and intermediate depth earthquakes, with magnitudes up to 7.5, accompanied by rapid neotectonic uplift that has been geodynamically linked with rapid subsidence in the adjacent Focsani Basin (Matenco and Bertotti, 2000) and in 2001 a 140-km long deep seismic profile (DACIA-PLAN) was acquired across this part of the southeastern Carpathian arc (Figure 1). Initial interpretations of DACIA-PLAN seismic data collected in 2001 indicate that high velocity rocks (basement?) are at a shallower depth than predicted by geologically constructed cross-sections in the Vrancea Zone and that the Carpathian external nappe pile is underlain by a thick, previously unknown (rift?) sedimentary basin that appears to localize the crustal depth seismicity. The new results need to be tested and placed in the context of the geology and evolution of the Carpathian arc as a whole, that formed between the European, Apulian, and related microplates during Triassic to Early Cretaceous extension and Late Cretaceous to Miocene contractional events (e.g., Burchfiel, 1976; Sandulescu, 1988; Csontos, 1995 (and references therein)., 1988; Visarion et al., 1988).

Figure 1 Tectonic setting of the DACIA-PLAN seismic profile (black line labeled DP) in southeastern Europe, crossing the seismically active Vrancea Zone of the southeastern Carpathian Orogen and its foreland basin, the Focsani Basin. Also shown are the locations of recently acquired seismic refraction/wide-angle reflection profiles VRANCEA-1999 and VRANCEA-2001

The DACIA-PLAN deep reflection seismic data were modelled using FAST (First Arrival Seismic Tomography; Zelt and Barton, 1998) and Pstomo_eq (Tryggvason et al, 2002) firstarrival tomography programs. A high resolution 2.5D velocity model of the upper crust along the seismic profile was determined and the results show that the data fairly accurately resolve the transition from sediment to crystalline basement beneath the Focsani Basin, where industry seismic data are available for correlation, at depths up to about 10 km. However, in the area where little to no subsurface information was previously available, in the Focsani-Vrancea 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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REGIONAL GEOPHYSICS & GEOTECTONICS transition zone, complex structural geometries were revealed implying significant involvement of basement rocks in thrust units and/or significant post-thrusting uplift of the basement horizon. The implications of this are of significance to understanding the kinematics of shortening in the Carpathian external thrust belt in general and, hence, for the geodynamic and ongoing landscape evolution of the Vrancea-Focsani area. The tomographic velocity models need to be refined using (forward and inverse) ray-tracing techniques and can also be tested and further evaluated by integration with models of detailed potential field data. Existing potential field data have insufficient resolution for these purposes. Therefore, part of the complex study is a campaign in 2005 to collect high resolution potential field data (gravimetric and magnetic data) on the DACIA-PLAN profile in order to obtain a more detailed, integrated geological-geophysical model of upper crustal structure in the Vrancea-Focsani area. The new (potential field) data set will of high quality and will be unique for the Romanian Carpathians.

Figure 2 (a) The initial model adopted for tomographic inversion based on first-arrival phase velocities; (b) the starting model for the final tomographic inversion step, derived after both forward modelling and tomographic inversions, needed in order to derive the ray paths close to what were determined to be their final locations; (c) the final P-wave velocity model, shown only for the region which is affected by the seismic rays during the final inversion step; (d) recorded travel times for a subset of data that were used in the forward modeling compared to computed travel times for the same shots for the final P-wave velocity model; (e) the cell hit-rate for the final model after tomographic inversion of all the 46000 travel times; and (f) the final mean data residual distributed on all receivers along the profile.


REGIONAL GEOPHYSICS & GEOTECTONICS DACIA-PLAN seismic data and method of analysis DACIA-PLAN seismic profile is about 140 km long and has a NW-SE orientation, crossing the seismically-active Vrancea Zone of the southeastern Carpathians orogenic belt and the foreland Focsani Basin. The primary goal of DACIA-PLAN was the acquisition of a multifold deep seismic reflection image using stand-alone seismic recorders. The DACIA-PLAN seismic data were recorded using approximately 640 autonomous onecomponent digital seismographs (“Texans”). These were set out at (nominally) 100 m intervals on three successive deployments using 334 recorders on Deployment 1 and the full contingent of recorders on Deployments 2 and 3 (637 and 632), recording 29, 47, and 55 explosive shots respectively. As such the respective lengths of deployments 1-3 were 22.1, 55.8, and 55.9 km, which included some overlap of recordings between deployments 1 and 2 and 2 and 3. Nominal shot spacing was 1 km but varied according to the availability of appropriate drilling and shooting circumstances. In total, 127 successfully detonated shots were recorded on 67951 seismic traces. A minimum phase bandpass filter (4-16 Hz) and AGC were applied to all shot gathers. Of the 67951 traces recorded, 46235 were considered robust enough to be used in the inversion. PStomo_eq is a travel time tomography algorithm (Tryggvason et al, 2002) which handles both controlled (known time and location) and earthquakes sources. The inversion is performed with the conjugate gradient solver LSQR (Paige and Saunders, 1982). The drawback in this approach is that no secondary phases, such as reflections, can be used in the modelling. The strengths are that a first arrival is always found and that the finite difference time and ray tracing computations are very fast and stable. Ray tracing (Zelt, C. A. and R. M. Ellis, 1988) is a program to trace rays in 2-D media for rapid forward modelling and inversion of refraction and reflection travel times. The velocity model is composed of a sequence of layers separated by boundaries consisting of linked linear segments of arbitrary dip. Layer boundaries must cross the model from left to right. Layer thicknesses may be reduced to zero to model pinchouts or isolated bodies.

Figure 3 The main features of the final velocity model (Fig. 5c) – thickest dashed line corresponding to the ~4.5-5.5 km/s velocity transition (~base of sedimentary succession along the profile), thinnest dashed line to the ~4.5-5.0 km/s velocity transition near the south-eastern end of the profile, and the intermediate thickness dashed line to the ~2.5-3.0 km/s velocity transition (~base of Quaternary) – superimposed on a geological cross-section modified from Cloetingh et al. (2004; cf. Matenco and Bertotti, 2000, cf. Tarapoanca et al., 2003).

Potential field data For the purpose of obtaining higher resolution of the upper crustal structure, a campaign to collect potential field data (gravimetric and magnetic data) will be acquired in 2005 on the same profile as DACIA-PLAN lies. Gravimetric field station spacing is 250 m (a GPS survey, which will take place in the same time frame with the potential field campaign, will provide the coordinates with high accuracy) while magnetic station are due to be set every 125 meter. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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Figure 4 The existing gravimetric and magnetic data (academic data) compared with seismic tomographic model

Results Velocity structure in the resulting 2.5D tomographic model (Figure 2) and 2D ray tracing model (there were ray traced all phases – reflected, refracted and difracted waves) is imaged to a depth of about 5 km within the western part of the DACIA-PLAN profile, where it crosses the external thin-skinned thrust belt of the East Carpathians (Vrancea Zone), and up to about 10 km further to the east, beneath the thick Tertiary Focsani Basin. Depth to basement, as well as lateral structural heterogeneity at the basement level, beneath the Focsani Basin resolved by the tomographic model is highly co relatable with structure in this area based on the interpretation of numerous industry seismic reflection lines. Accordingly, the tomographic velocity structure implied for the foreland basin-thrust belt transition zone and the external thrust belt itself, where independent seismic constraints on geological architecture at depth are essentially lacking, are considered to be fairly robust. The results in this area strongly imply that pre-Tertiary basement in the Vrancea Zone is shallower (100 km. Preliminary results indicate a subhorizontal lower crustal and upper mantle fabric underlying the entire basin. Single-fold shot gathers throughout the 240-km profile consistently display subhorizontal to gently east dipping reflectors at intervals from 6-25 sec TWTT. Stacked data also show strong reflectivity of the crust observed on the shots and suggests subhorizontal reflective packages can be traced for tens of kilometers. Evidence for crustal-scale dipping discontinuities is notably absent. These results appear to preclude the presence of former subduction zones within the region imaged by the DRACULA I profile. The eastern end of the profile lies adjacent to the Vrancea Seismic Zone, displaying volumetrically concentrated intermediate-depth seismicity. With a seismic transect through Transylvania we are equipped to investigate the geometry of the crust in this region and evaluation it’s relation to the Vrancea Seismic Zone. Interpretation of the subhorizontal fabric within the mantle lithosphere awaits further analysis. Introduction The DRACULA I profile (Figure 1) one of three deep seismic reflection profiles collected as part of Project DRACULA (Deep Reflection Acquisition Constraining Unusual Lithosphereic Activity), imaged the highly reflective crust of the Eastern Carpathian hinterland during the summer of 2004. Chosen for its proximity to the Vrancea Seismic Zone (VSZ), the DRACULA I reflection seismic profile extends NW from the VSZ across the Persani Mountains into the Transylvanian Basin. Using 20 kg explosive sources at nominally 1 km intervals we recorded 640 channels per shot in a roll along spread. Data were recorded to 60 sec, achieving a total of profile length of 240 km of deep data. The motivation for collecting this line is explore the relationship of the VSZ, if any to, the crustal structure of the Transylvanian Basin. While current seismic and fault activity in the Eastern Carpathian hinterland is relatively subdued compared to the active deformation processes taking place in the foreland, we postulate that processes occurring now in the VSZ began within the Transylvanian crust. Quaternary basin formation and geologically young volcanism observed in the hinterland lends further credence to the necessity of closer examination of the Carpathian hinterland if present foreland activity is to be understood in context with the system as a whole. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 497


Figure 1 Geotectonic map of Romania showing CDP locations of DRACULA I through the hinterland of the Eastern Carpathians and proximity in relation to the Vrancea Seismic Zone.

Numerous models have been set forth to explain seismicity associated with the VSZ. This paper presents three models: Oceanic subduction and slab retreat, subduction in place, and continental lithosphereic delamination Figure 2 A), B) and C) respectivly. A) The ‘Oceanic slab break-off and retreat’ (Linzer 1996) model suggests that subducted oceanic slab broke away from the plate and drifted laterally west under the Carpathians to its present location under the VSZ. Implications for this model necessitate the existence of a subduction fabric in the crust, and the presence of suture zone west of the Carpathians. B) The ‘Subduction in place’ model (Wortel and Spakman, 2000; Gvirtzman, 2002) provides for remnant subduction as the means of creating the VSZ, but fails to offer explanation for Neogene volcanism 150 km to the west. C) Lastly, the ‘Continental lithosphereic delamination’ (Knapp et al. in press) model uses the delamination definition Bird (1977) presented, where thick, dense, gravitationally unstable continental crust detaches from the overlying crust before descent into the mantle. This model suggests there should be evidence of crustal faults that offset the Moho caused by the descending mechanically coupled material.

Figure 2 Three models developed to explain the existence of the Vrancea Seismic Zone. The extent of DRACULA I is defined by the blue box and shows the potential of being well suited to image the geometry of the Transylvanian crust allowing assessment of competing hypotheses for the observed Vrancea seismicity. A) The ‘Oceanic slab break-off and retreat’model, B) the ‘Subduction in place’ model, and C) the ‘Continental lithosphereic delamination’ (Knapp et al. in press).


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Figure 3 Shot gather of FFID 56 displayed to 30 sec (left). This shot, like many DRACULA I shots, show the features seen in the expanded views: 3.1) a clear sediment-basement contact reflector, 3.2) continuous lower crustal reflectivity around 6.0-12.0s TWTT, and 3.3) and unexpected mantle reflectors here seen at around 15.020.0 sec, but also occurring on other shots as deep as 30.0s TWTT. Data shown here has had an AGC (1000) and Bandpass (8-12.5-40-45) filter applied.

Methodology The DRACULA I profile was designed to provide a lithosphere-scale image of the Transylvanian basin adjacent to the VSZ, and thereby provide critical data to evaluate competing hypotheses for origin of intermediate-depth seismicity. Seismic processing has produced preliminary results to date, but the potential of the data has not yet been achieved. Due to cultural complications during source deployment we were unable to maintain the nominal 1 km shot spacing we desired. Though this will not compromise the data quality, it has slowed the pace of processing because each shot geometry is different for its associated receiver spread. Periodically, during processing an error is discovered and operations are halted until the geometry is fixed. As errors are discovered and corrected during processing we will gain more confidence in the observations made from the data. Results Single-fold shot gathers repeatedly image (1) a strong reflector (basement cover contact?) at ~1.6-2.0 s TWTT (~3-5 km) within the Transylvanian basin (Figure 3.1), (2) strong subhorizontal reflections beneath the Persani Mountains that may represent either structural elements or igneous intrusive features (3) subhorizontal to gently E-dipping reflections beneath the Eastern Carpathians at 6.0-8.0 s TWTT that may be the downdip continuation of regional Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 499

REGIONAL GEOPHYSICS & GEOTECTONICS detachment faults of the Carpathian nappes (Figure 3.2), and (4) strong sub-horizontal and laterally continuous reflectivity, beginning at 6-10 s TWTT (15-25 km) and continuing downward in some cases to as much as 30 s (greater than 100 km), clearly within the upper mantle (Figure 3.3). A preliminary stack shows: (1) the geometry of the basement contact thinning as it approaches the Persani Mountains, (2) continuity of reflectors as seen shot gathers at TWTT of 6.0-8.0s, and 10.0-15.0s. Some of these reflective layers are identifiable for ~60 km. Conclusions An interpretation for the strongly layered upper mantle and the absence of a clear break in reflectivity across the Moho is still premature, but it would appear that geologic processes in the Transylvanian mantle have imparted reflection fabrics similar to those seen in the lower crust on many deep reflection profiles. Of particular significance is the pervasively subhorizontal geometry of reflective layering throughout the Transylvanian crust and upper mantle. This observation alone appears to preclude the presence of a former subduction zone anywhere within the 240-km transect of the profile. These observations would appear to argue against a subduction origin for intermediate depth seismicity in the Vrancea Zone. References Bird, P., 1978, Initiation of intracontinental subduction in the Himalaya, Journal of Geophysical Research, A, Space Physics, 38 (B10): 4975-4987. Gvirtzman, Z., 2002, Partial detachment of a lithospheric root under the southeast Carpathians: Toward a better definition of the detachment concept, Geology, 30, 51-54. Knapp, H.J., Knapp, C.C., Raileanu, V., Matenco, L., Mocanu, V., Dinu, C., in press, Crustal constraints on the Origin of Mantle Seismicity in the Vrancea Zone, Romania: The Case for Active Continental Delamination, Tectonophysics Special Issue on “CarpathianPannonian System”. Linzer, H-G., 1996, Kinematics of retreating subduction along the Carpathian arc, Romania, Geology, 24: 167-170. Wortel, M. J. R., Spakman, W., 2000, Subduction and slab detachment in the MediterraneanCarpathian region, Science, 290 (5498), 1910-1917.


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GEODINAMIC EVOLUTION OF THE EASTERN CARPATHIANS - BLACK SEA REGION Ion Morosanu Prospectiuni S.A., Bucharest, Romania

The analysis of the seismic and well data on the Carpathians-Black Sea area illustrates that its contemporary structure resulted from large-scale extensional-inversional processes. In the East-Southeast of Europe, before the Middle Jurassic, were two platforms: an old one-East European Platform and a younger one, represented by West European Platform, Panonian-Transylvanian Block and Moesian Platform. Between these two platforms has existed a suture zone. It is represented by the Green Schists trend. Initially, on the western and southern margins of the East European Platform a regional detachement surface was formed. On this surface, a huge extensional blocks moved westward and southward. So, a large extensional-depressional area was born. The western branch of this area represents the trough of the Eastern Carpathians that has been formed by the collapse and slide of the Green Schists westward (Figure 1). The southern branch is more complicate. The regional detachement surface is placed inside of the Eastern European Platform at its southern margin. On this surface, a huge extensional block moved southward opening behind of it, a large West-East depressional area (Bîrlad-Krîlov-Karkinit depression). These two (the high block and depressional area) are well-know as a Scythian Platform. After my opinion these two zones represent parts of the East European Platform and must be named different. So, the depressional area was named Bîrlad-Krîlov-Karkinit depression (in fact a huge trough with riftogene character) and the uplifted and slide block- the Scythian Block (Moroşanu,2002) (Figure 2). The Scythian Block includes some highs, swells or steps (last two names are especially from the russian terminology) namely: Chilia-Snakes’ Island high, Marginal step, Kalamit swell, lower Crimea- Azov-Reazan high. The opening is progressive southward and a new large depressional area, between Green Schists Block and the Scythian Block, with riftogene characteres also, appears. It is composed by North Dobrogea-Histria depression, Crimea-Caucaz trough and East-Black Sea Basin (s.l.). The last two depressions are separated by the Shatsky ridge (Figure 2). It is possible that this ridge to have the same nature with Scythian Block. In Central Dobrogea and Black Sea Basin the green schists constitutes a crest, so called Green Schists-Midia Crest (Moroşanu, 2002), which are continuated to south-east with Andrusov-Arhangelski ridge. These ridge can be constituted by green schists, too. Northward and southward this high crest is limited by the normal listric faults (in Romanian area, they are known as the Peceneaga-Camena and Capidava-Ovidiu faults). Southward of this ridge there is Moesian Platform which has been affected by the extensional movements too, and a new riftogene depressional area was formed in Lower Cretaceous. This depression is currently called the West-Black Sea Basin. This depression is limited westward by the north-south Midia-Tiulenovo block and southward, by a crest, currently represented only by Akçakoca high (Figure 2). Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 501

REGIONAL GEOPHYSICS & GEOTECTONICS In conclusion, the Carpathian trough-North Dobrogea-Histria Depression-East Black Sea Basin can be considerate a long depressional area with riftogene character, formed between two platforms: East European Platform and West-Southwestern European Platform.It has been progressive open by the extensional movements, started in Upper Jurassic till Albian inclusive in Black Sea Basin, Upper Cretaceous in Continental Dobrogea, Sarmatian at the west of Danube and Eocene, in the Eastern Carpathians. Also, in Upper Jurassic-Lower Cretaceous other two depressional areas were opened. These two are situated on the East European Platform (Bîrlad-Krîilov-Karkinit depression) and on the Moesian Platform (West Black Sea Basin). The inversional movements carried out differences between Black Sea and Eastern Carpathians areas, especially in the duration and intensity of its. While in the Black Sea area the extensional features are not destroied by the inversional movements being visible like a simple reverse faults on the northern margin of the Histria Depression, in the Eastern Carpathians area these are destroied, and are visble only the overthrust nappes, as result of the inversional movements. The Black Sea Basin can be considered as a typical, but complex, rift basin. His margins display the evidence of an extensional tectonic. Here the syn-rift Upper Jurassic-Albian formations were deposited. Later, the post-rift Upper Cretaceous-Eocene formations filled the troughs. The end of this period is marked by an important erosional surface. In Oligocene time an important subsidence accompanied by a major inversional period begun.In this period Crimea Block begun an anti-clockwise rotational mouvement and, on this way, the megadepressional area has been devided: Histria Basin and Eastern Black Sea Basin (s.s.). Also, the Karkinit Depression, from north, was enlarged taking a triangle form. Due to the same rotational movement an important faulting event appear: the Nistru Fault which affects the Scythian Block and Andrusov-Arhangelsky Ridge and in the same time the Crimea mountains chain were born with east-weat direction (Figure 2). Other main events of this inversional period, in the Black Sea area are: the rise of the Crimea-Caucaz belt, together with fore- and back- depressions, the important inversions from Histria Depression (Moroşanu,1996) and North-Dobrogea, the overthrust of BalkanidesPontides and the lower intencity inversions from the Moesian Platform and Scythian Block (Moroşanu,2001, Popovici,1989). This compresional period ended in the Upper Oligocene for the West and North Black Sea regions, but it continued in the East-Black Sea regions in Mio-Pliocene to Quaternary. In the Eastern Carpathians region, it is presumed that the post-extensional period covers the Oligocene time, the inversional movements beginning immediately from Lower Burdigalian. The intencity of the inversional movements is more than in Black Sea basin. As a result, the Eastern Carpathian Nappes were born. During of Lower Sarmatian these movements have been stoped. It is possible that the return of the inversional movements to be present in the Pliocene-Quaternary period, especially in the Carpathian Bend area. In the Black Sea, the rotation of the Crimea Block continued until the Neogene (Okay et al., 1994) and it is possible, the opening of the Braşov-Ciuc depressional area, situated behind of Carpathian Bend area and filled with Pliocene-Quaternary formations, represents a result of it. So, this depression was born by movement of the blocks from north-eastern compartiment of Intra-moesian fault to south-east, towards appel zone created by rotation of the Crimea block. This appeal zone is sustained by numerous listric faults with slide blocks towards south-east, visible in Cobalcescu area, from Black Sea. These faults affect the Cretaceous to Quaternary formations ( Moroşanu, 2002). In conclusion, the Eastern Carpathians Trough, North Dobrogea, Histria Depression and East Black Sea Basin have been formed like a megadepression between East European Platform and Moesian Platform-Transylvanian Block, while the Bîrlad-Karkinit Depression and West Black Sea Basin, like depressions as a result of the East European and Moesian Platforms partial destruction. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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REGIONAL GEOPHYSICS & GEOTECTONICS References Moroşanu,I., 1996, Tectonic setting of the Romanian Offshore at the Pre-Albian Level, in G.Wessely and W.Leibl, ed.,Oil and Gas in Alpidic Thrusbelts and Basins of Central and Eastern Europe, EAEG Special Publication, 5, p. 315-323. Moroşanu,I., 2001, Geological Framework of the Romanian Black Sea Shelf and the Position, Conturing and Evolution of the Histria Depression,in Proceedings of the 2nd International Symposium on the Petroleum Geology and Hydrocarbon Potential of the Black Sea Area,1996,Sile-Istanbul, Special Publication,4,p.105-148. Moroşanu,I., 2002, Post Jurassic Tectonic History and Geodinamics of the Blac Sea Region,in Special Publication of the EAGE 64th Conference & Exhibition-Florence, Italy. Okay,A.I., Celal Şengör,A,M., Naci Görür, 1994, Kinematic History of the Opening of the Black Sea and its Effect on the Surrounding Regions, Geology,v.22,p.267-270. Popovici, S.V., 1989, Structural Peculiarities of the Mezo-Cainozoic Formations on the Northwestern Shelf of the Black Sea. Geotectonika, 6, p. 81-89

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P3 - 05

SYNOPTIC AERO MAGNETIC AND GRAVITY MAPS IMPLEMENTATION OF THE OAS – GUTAI – TIBLES MOUNTAINS (ROMANIA)

Viorel Cristian Sprinceana, Adrian Popescu, Cristina Petrescu, Steluţa Prisecaru, Mihai Nedelcu, Vlad Zorilescu, Mircea Albaiu Prospectiuni S.A., Bucharest, Romania

The geological research developed on Oas - Gutai - Tibles Mountains area have conducted to a significant volume of geological, geochemical and geophysical data, mainly through prospecting works done by the specialists of "Prospectiuni" S.A. Bucharest and S.C. "IPEG Maramures" S.A. Consequently, became as a stringent requirement drawing up a synthesis of the geological, geochemical and geophysical data, and to be the basis of the consequent projects regarding the areas with gold and/or polymetallic minerals. Thereby, in 1996 The National Agency for Mineral Resources approved the geological project regarding geological, geochemical and geophysical data synthesis on Oas – Gutai – Tibles Mountain area, performed by S.C. "IPEG Maramures" S.A. and S.C. "Prospectiuni" S.A. The main goal of this project was to draw up the synthetic geological, geochemical and geophysical maps, at 1:25,000 scales for the entire area of the Oas Gutai – Tibles Mountains. The data basis set up for each of the performed gravity and aeromagnetic prospecting is the exclusive desert of Prospectiuni’ synthesis and the processing data crews for minerals. The target of this study is to introduce the aeromagnetic and gravity synoptically image for the entire area and to outline some tectonic and structural regional elements, inferred as result of various analytical processing of the rough data. In Oas - Gutai – Tibles Mountain area, during 1950 - 1970 was done gravity prospecting with detail network. Subsequent, during 1970 - 1996 period, the gravity research was reperformed with an increased detail network, within the areas with possible economic interest for mining activity. Using these data basis, the authors of this paper set up a single data basis, containing Bouguer gravity anomaly recordings (343,076 values), computed for 2.40g/ccm density. This single data basis allowed Bouguer anomaly map drawing up for the entire area (figure 1). In 1969, a team led by Tr. Cristescu, performed, within the Neogene’s volcanic zone from Baia Mare area, a ∆T aeromagnetic measurement with detailed network. The measurements were done from helicopter, on panels, with lines spread at 200 m. Within each panel, the measurements were performed at variable altitudes, depending on relief elevation, thus the helicopter to fly at 200-300 m altitude above the topographic surface. Consequent to specific measuring and processing, the rough values of the total component intensity of the magnetic field, for each observation point, were converted in relative values. In order to obtain an image of the anomalous components of the magnetic field, the rough data were amended with the normal field correction, on the base of the well-known formula (in which the normal field is considered to be expressed analytical by a Taylor series, until the second order terms inclusively, of a function that defines the dependence of a geomagnetic element of λ longitude and φ latitude where is determined). It was used the computing formula for 1980.5 epoch. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 505


Figure 1 Bouguer gravity anomaly map of the Oas – Gutai – Tibles Mountains - H=0 m, d=2.40 g/ccm (grid size: 2000 x 2000 m)

Figure 2 – Detailed aeromagnetic map of the Oas – Gutai – Tibles Mountains (grid size: 2500x2500 m)


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REGIONAL GEOPHYSICS & GEOTECTONICS From the computed values was subtracted the quantity of +350 nT, the difference between the Sibiu reference value (used in the calculation formula) and Baia Mare, so all the ∆Ta values practically represent the variation of the anomalous component of the geomagnetic field vs. this point. The detailed aeromagnetic map drew up in this manner is presented in figure 2.

Figure 3 Horizontal gravity gradient map of the Oas – Gutai – Tibles Mountains (shaded relief map illuminated from the north, gradient method: central difference, shading method: lambertian reflection)

Figure 4 Horizontal aeromagnetic gradient map of the Oas – Gutai – Tibles Mountains (shaded relief map illuminated from the north, gradient method: central difference, shading method: lambertian reflection)


REGIONAL GEOPHYSICS & GEOTECTONICS Consequently, ordet to outline some regional structural and tectonic elements, were achieved miscellaneous analytical processing, as follows: total horizontal gravity gradient map (figure 3), the averaged gravity map with the sides of 4000 and 6000m (figure 5), the residual gravity anomaly maps accordingly to both averaging sides (figure 6), the map of the total horizontal aeromagnetic gradient (figure 4). Unlike the images from the surface geological mapping, that often include subjective interpretations, those resulted from geophysical methodology always represent absolute information, meaning quantitative values of some well determinate physical values. Depend on us, geophysicists, that these data interpretation to be more exactly. The various analytical processing methodologies of the rough data (e.g. maps of the total horizontal gradient) are able, in case are distinguished significant contrasts of the physical properties, to facilitate the geological interpretation of the geophysical data. This paper desire to be one interactively, thus any initiated person - geologist or geophysicist, to reveal itself some structural – tectonic elements with regional feature (direction of the regional faults - Dragos Voda, Bogdan Voda, location of some volcanic or sub-volcanic complex bodies - Tibles, Mogosa, Zdarcea, Ignis, Rotunda, Socea etc., east-western tectonic partition at crystalline basement – horsts: Negresti Oas, Seini-Ulmoasa-Chiuzbaia and grabens south Gherta Mica-Lechinta, Racsa-Blidari), without subjective interferation in their interpretation. It is easy to appreciate the fact that some structural - tectonic undetermined aspects are eliminated using in tandem the both methodologies of geophysical prospecting.

Figure 5 The averaged gravity map – side 6000 m of the Oas – Gutai – Tibles Mountains

Figure 6 The residual gravity map of the Oas – Gutai – Tibles Mountains


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P3 - 06

TECTONIC CONTROLS ON THE COAL FORMATION IN THE PTOLEMAIDA BASIN (NORTH OF GREECE) Daniela Mitru1, Constantin Pene2 1 T.E.I.-Kozani, Kozani, Greece 2 Bucharest University, Faculty of Geology and Geophysics, Bucharest, Romania

Summary The Neoalpine strike-slip movements created at the beginning of the Lower Miocene a large tectonic graben where the coal-bearing Florina-Ptolemaida-Kozani basins were developed. The Neogene deposits consist of two formations with an interlayered sequence of lignite that is separated in two distinctive series. The measurements of the fault elements in outcrops and the processing and the interpretation of these data shows that in the study area there are a main fault system with NW-SE and NE-SW directions. The former of these are considered as the marginal faults, which formed the original tectonic graben, the latter ones caused the traverse, to the general graben trend, fragmentation and formed subgrabens and small horsts, which give the actually shape of the Ptolemais Basin. These changes create the suitable conditions of marsh environment, clime and water depth for the aquatic flora growing-up, that later will supply the organic material for the lignite generation. General stratigraphic and structural settings The margin and basement of the basin consists of the crystalline schist of the Pelagonic zone and of the superimposed Mesozoic cover. This zone consists of crystalline basement with granite intrusions, Permian - Lower Triassic (clastic deposits with intercalations of volcanic rocks, weakly metamorphosed), Middle Triassic - Jurassic - Lower Cretaceous (carbonate deposits, weakly metamorphosed), then ophiolites on the basin margins. The Upper Cretaceous consists of conglomerates, limestones and flysch deposits. These deposits are covered by the Neogene formations that are represented by two formations with an interlayered coal-bearing sequence. The Lower Neogene Formation (Upper Miocene-Lower Pliocene) is predominantly calcareous, in alternation with clays and sands and the Upper Neogene Formation (Upper Pliocene) consist of clays and marls with sand intercalations. Finally they are covered by the Quaternary formations (Figure 1). The Neogene deposits from these basins is different both the type of sedimentation and of composition of sediments as well as by variation of type of lignite, which they content. After Koukouzas and Kotis (1993) the sediments of Neogene are separated in two distinctive series: (1) the Lower Neogene series (Upper Miocene – Lower Pliocene), which contains lignite xylitic of "Komnina type" and (2) the Upper Neogene series (Pliocene), which contains lignite of "Ptolemais type". The lignite of "Ptolemais type" appears in form of thin beds, sometimes laminated and more rarely compact with conspicuous horizontal fissility. In their natural state, appear a dark grey to greyish black colour, is soft and weather readily in the air. The number and the thickness of beds are variable from zone to zone till their total disappearing (Figure 2). The lignite beds pass laterally through intermediate lignite marls and Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 509

REGIONAL GEOPHYSICS & GEOTECTONICS clay at beds with clays and marls. The maximum thickness of the lignite layers is of 2-4 m. The basin is a large tectonic graben with a main fault system of NW-SE and NE-SW directions that born at the beginning of Neogene (Anastopoulos and Koukouzas, 1972, Anastopoulos and Broussoullis, 1973). The purpose of this paper is to investigate the main tectonic settings that create the conditions for the deposition of the organic material and its conservation and transformation in coals.

Figure 1 Tectonic map of the Ptolemaist Basin with the main lines of fractures (modified and completed after Koukouzas and Kotis, 1993).


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REGIONAL GEOPHYSICS & GEOTECTONICS Methods and results The research was performed during two stages. In the first stage during field trips have been effected in every outcrop more than 100 measurements of the fault elements. The geological observations especially on the coal layers completed the field researches. The processing and the interpretation of the geological data were done in the second stage. Their results have been represented on the rose diagrams that have been superimposed on the geological map of the studied area (Figure 1). The interpretation of the results shows that the synorogenic movements of the Neoalpine folding created at the end of the Tertiary period a large tectonic graben. The prevailing faults of the area have NW - SE and NE - SW directions. The former of these are considered as the marginal faults, which formed the original tectonic graben, the latter ones caused the traverse, to the general graben trend, fragmentation and formed subgrabens and small horsts, which give today's picture of Ptolemaida basin. From south to north there are the grabens: Kozani - Servia, Sarigiol, Ptolemaida, the lake Petron - Limnihoriou and Florina. These grabens are separated by the horsts: Kila – Galani - Proskinatariou, Sf. Hristoforou - Komanou, Klid - Xino Nero - Aetos.

Figure 2 The eastern part of the lignite Mavropighi quarry.

The faults with direction NW - SE formed due to extensional forces, which activated on NE - SW direction in Upper Miocene - Pliocene. The faults with NE-SW direction formed because of extensional forces on NW - SE direction, which activated in the Lower Pleistocene. Younger faults than the previous with directions N-S and E-W to ENE-WNW are also observed in basin and at its margin as well. From those above it is observed that the action field of extensional forces presents from Miocene superior to Pleistocene inferior, a rotation on NE-SW to NW-SE direction. All these faults are normal faults with the greatest jump of faults until 60 meters, without to be constant on the whole long of fault. The changes of jump are explicated by continue activity of faults, due to plasticity of sediments and of compressions and curvatures suffered by these when they are changing the place. The faults NW-SE are developed vertically until some meters over to geological roof of lignite, those on E-W direction until in the floor of Quaternary sediments yellow sandy, and those NE-SW until the floor of Quaternary sediments of red colour or a little above of them. Due Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 511

REGIONAL GEOPHYSICS & GEOTECTONICS to the tectonic movements the lignite beds as well as the sediments above and below them show a slight folding and in places, have a slight dip (3o - 5o) to the SW, while they are almost horizontal in the greatest part of their extent. The observed erosion of the Neogene and Quaternary sediments is also a result of these movements. Rupture tectonic conditions prevail in the marginal rocks with the faults of the mentioned directions. The Triassic - Jurassic rocks are traversed by faults of NNE-SSW strike and WNW dip, and the Upper Cretaceous rocks by faults of NW-SE strike and NE dip. The result from a geometrical point of view is that the Upper Pliocene sediments follow the morphology of the metamorphic basement, forming a megaflexure with axis striking NE-SW and presenting large radius of curvature. This macrostructure is also accompanied by the significant presence of reverse faults. These appear before and after a big normal fault. The reverse faults are of the second order and originate in forces of compression, which acted in different zones. Conclusions The study of the lithostratigraphic and structural information shows that the coal formation is the result of the changing of the geological conditions. The interpretation of the geological data shows that the synorogenic movements of the Neoalpine folding created at the end of the Tertiary period a large tectonic graben. Here during Neogene period took place a special process of sedimentation. The observations and measurements in the outcrops show that in the time of deposition of the lower sequence, the subsidence rate was greater than the sedimentary rate that maintained the high level of water and deposition of the fine mineral material too. In the final part of sedimentation of the lower sequence change the relation between subsidence rate, water level and sedimentary rate, that is the first two diminished and the last increased. The result was the basin filling with fine sediments and changing of deep lake in a marsh. These changes create the suitable conditions of environment, clime and water depth for the aquatic flora growing-up, that later will supply the organic material for the lignite generation. The purpose of this paper is to investigate the main tectonic settings that create the conditions for the deposition of the organic material and its conservation and transformation in coals. References Anastopoulos I., Koukouzas C., 1972, Economic geology of the Southern part of Ptolemais lignite basin (Macedonia - Greece). Geol. Geoph. Res. I.G.S.R.X. XVI, nr.1 Athens, 188p. (in Greek, with English summary). Anastopoulos I., Broussoullis I., 1973, The Kozani - Servia lignite basin. Min. Dep. Res.nr.1,I.G.M.E.,Athens, 77 p. (in Greek). Koukouzas C., Kotis, Th., 1993, Lignite deposits in the Florina and Ptolemais Basin(MacedoniaGreece). A geological field trip guide book. 45th Annual Meeting(ICCP). Techn. Univ. Min. Res. of Crete, 25p.


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STUDY OF SALT MOVEMENT MECHANISMS IN THE TRANSYLVANIAN BASIN Constantin Pene, Octavian Coltoi Bucharest University, Faculty of Geology and Geophysics, Bucharest, Romania

Summary The Badenian salt in the Transylvanian Basin has an almost continuously development. Just in the eastern part of the basin there are some small zones where the salt is absent. The top of the salt layer is highly undulating, while the base is nearly horizontal. The manifestation of the salt movement has been different in the Transylvanian Basin. In the central part there are salt pillows, salt layers and piercement of salt. In this zone the salt is not outcropping and its flow produced only the doming of the overlying deposits. In the eastern and western parts of the basin the Badenian salt flow determined an intensively deformation of the overlying rocks and the formation of the salt diapirs and salt wall growth. In these areas the salt even outcrops within a few sectors. The aim of this paper is to investigate the causes that created zones with different intensity of the diapirism. The authors used the simplest mathematical model of an elastic plate overlying a viscous fluid. Introduction The Transylvanian Basin, together with the other neighboring depressions (Pannonian, Bârgau, Maramureş depressions), is considered a Carpathian central depression (Ciupagea et al., 1970). In the Romanian tectonic map Dumitrescu et al. (1962) have represented Transylvanian Basin as an intermountain depression. In fact, these different opinions show the same structural model. The Transylvanian Basin is the deepest and the most extended depression of this kind in Romania, but it is not very large basin on a worldwide scale. It is of elliptical form elongated on N-S direction, the length is of ca. 300 km and its width is of ca. 200 km. The geological setting of the Transylvanian Basin is determined by the surrounding system of the Carpathian orogene. The Eastern Carpathians, Southern Carpathians and Apuseni Mountains surround it (Figure 1). The study of the geological and geophysical data show that the sedimentary cover of the Transylvanian Basin is formed during at least six sedimentary cycles: (1) Permian – Triassic, (2) Jurassic – Lower Cretaceous, (3) Upper Cretaceous, (4) Paleogene, (5) Lower Miocene and (6) Upper Miocene – Pliocene. This paper is focussed on the researches of the last two sedimentary cycles (Lower Miocene and Upper Miocene – Pliocene). Generally they consist of Badenian, Sarmatian and Pliocene deposits. The Badenian is composed of marls with Globigerina, Dej tuff and salt formation overlain by horizon with Radiolarians and marls with Spirialis. The Sarmatian and Pliocene formations consist of marls and claystones with intercalations of sands and sandstones. The study of the evolution of Badenian salt is the main purpose of this paper. The gravimetric, magnetometric and some seismic information show that the Transylvanian Basin is limited by very deep faults that are considered to be crustal fractures (Figure1). Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 513


Methods and Results The Badenian salt covers almost overall the Transylvanian Basin. Just in the eastern part in some small areas it is absent. The manifestation of the salt movement has been unequal and different in the Transylvanian Basin. The structure of Badenian salt is different from a zone to another one. These zones are divided as following: (1) the external zone of the crustal fractures that surround the basin (Figure1). In this zone the tabular structure is the main form of salt and the salt layers dip with 10-50 centerward of the basin. In some areas of this zone on the seismic profiles have been identified small salt pillows that produced a gentle deforming of the overburden. In the western, northern and southern parts of the basin this tabular structure is large (more than of 30 km) while in the eastern part it is narrow (less than 5 km). The salt thickness is of 30-40 m. (2) the internal zone where, due to the salt diapirism the structures are intenssively folded. The salt diapirs develop in the eastern and western parts of the basin and the main elongation of the diapirs is in the NNW-SSE direction. In this zone the salt flow reached the last stage of salt diapir and salt wall growth because of the buoyancy. The salt outcrops in some areas and here it is exploited. The thickness of salt wall is more than 2000 m. (3) the central zone of the basin where the top of the salt layer is highly undulating, while the base is nearly horizontal. The salt is not outcropping here and its flow produced an intense doming of the overlying deposits. This zone can be separated in two main areas located south and north of Mureş River. The southern zone is the deepest part of the Transylvanian Basin with the Badenian salt at depths that exceed 4500 m. The salt pillows and the piercement of the salt are the main salt structures. The salt thickness in the axis of piercement does not exceed 500 m and the thickness of 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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REGIONAL GEOPHYSICS & GEOTECTONICS overlying deposits is more than 4000 m. In the northern part the depth of Badenian salt is less than 3000 m. The salt structure is represented by salt pillow, salt piercing and salt diapir, but the salt is not outcropping (Figures 2 and 3). In the axis of the diapirs the salt thickness is more than 1900 m, and the overburden thickness is very variable (at least of 1000 m). The salt flow determined the folding of the overlying rocks and the formation of large domes in the Upper Miocene and Pliocene deposits.

This different distribution of the salt structures in the Transylvanian Basin suggests that the salt movement has been initiated and driven by at least four mechanisms. The following mechanisms could be implied in the salt flow: (1) salt buoyancy, (2) differential sediment loading, (3) flexural buckling of the overburden and (4) drag by overburden. To evaluate which mechanism dominates in the salt flow in the Transylvanian Basin a simple model has been used considering an elastic plate overlying a viscous fluid. In this model the viscous fluid is the layer of Badenian salt and the elastic plate is represented by the overburden composed of Upper Miocene and Pliocene deposits. The simplest mathematical model uses some equations after Turcotte and Schubert (1982), Cohen and Hardy (1996) and Waltham (1996) for the calculation of the pressure gradient in the vertical and horizontal direction, the horizontal velocities of the salt and overburden, the total flux of salt in horizontal direction, the shear stress applied to the base of the plate. The vertical pressure gradient was calculated considering a constant density of overburden (2500 kg/m3) in correlation with the different sedimentary rate of the Upper Badenian (450 m/Ma), Sarmatian (150 m/Ma) and Pliocene (80 m/Ma). The initial salt thickness was variable less than 300 m south of Mureş River and more than 500 m in the other zones of the basin. The amplitude and the wavelength of folding as well as the others parameters (the thickness of the overburden and of the salt in the apex of the structures as well as in the adjacent synclines) were measured on the seismic profiles in the correlation with the well logs (Figs. 2 and 3). The amplitude of folding in the central zone, north of Mureş River, is more than 1000 m and south of this river is less than 300 m. The wavelength of folding in central zone is less than 9 km. In the eastern and western parts of the basin with an intense diapirism the amplitude exceeds 1500 m and the wavelength of folding is more than 15 km. These values were used to calculate the flexural rigidity of overburden. The different values of wavelength and flexural rigidity suggests that in the eastern and western part of the basin acted both compressive buckling and salt buoyancy. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 515


In the north of the basin the compressive forces have a small value and in south they did not act and the salt kept its tabular form. Conclusions The results of this study suggest that in the Transylvanian Basin acted all four mechanisms of salt flow. The initiation of salt movement is not only the result of buoyancy. It was initiated by drag of the overburden in the eastern and western part of the basin where the sedimentary environment of the Sarmatian deposits is of deltaic type. These deposits slipped centerward of the basin and dragged the Badenian salt. In east and west a strong horizontal compressive stress dominantly on the E-W direction acted at least in the main tectonic phases during Upper Sarmatian, Pliocene and Pleistocene and produced an intense flexural buckling of the overburden. It determined the intense salt diapirism in the eastern part and western part of the basin. The calculation of the vertical pressure gradients in correlation with sedimentary rates suggests that the differential sediment loading initiates the salt movement when the thickness of overburden is higher than 1000 m. The greatest thickness of the overburden in the central zone, south of the Mureş r. (more than 4500 m) and the initial salt thickness less than 300 m suppressed the diapirism of the salt. The salt flow northward Mureş r. determined diapirism and piercing because the salt thickness is more than 500 m, its overburden thickness is less than 3000 m and wavelength of the folding is less than 9000 m. References Ciupagea, D., Paucă, M., Ichim, Tr., 1970, Geology of Transylvanian Depression (in Romanian), Editura Academiei RSR, Bucureşti, 256 pp. Dumitrescu, I., Săndulescu, M., Lăzărescu, V., Mirăuţă, O., Pauliuc, S., Georgescu, C., 1962, Mémoire à la carte tectonique de la Roumanie. Ann. Inst. Geol. Géoph., XXXII, Bucharest, pp. 5-97. Turcotte, D.I., Schubert, G., 1982, Geodinamics – Application of Continuum Physics to Geological Problems. Willey, New York. Waltham, D., 1997, Why does salt start to move? Tectonophysics, 282, pp.117-128.


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P3 - 08

THE MICROFABRIC OF THE CRYSTALLINE ROCKS FROM BADEANCA VALLEY, LEAOTA MTS, ROMANIA Ema Bobocioiu Caracas, Denisa Jianu, Gheorghe C. Popescu Bucharest University, Faculty of Geology and Geophysics, Bucharest, Romania

The studied area lies in the south of Leaota Mts., in the Curvature of the Eastern Carpathians, at the limit with the Southern Carpathians. The Ialomita and Dambovita valleys delimit it. This area is mainly characterized by the presence of gneiss with plagioclase, gneiss with albite and garnets, amphibolites. Some minor occurrences of micaschists, quartzites and eclogites have also been reported, The presence of Co-Ni-Bi assemblages, Fe sulphides, hematite, Cu-bearing pyrite ores, etc in small occurrences or disseminated in base rocks attracted some interest from economic geologists. In this paper we report a structural and geologic study of this region which constitutes the basis for an integrated genetic model of the ore deposits. We base our analysis on the study of foliation and lineation of the metamorphic rocks. The foliation is defined as the layering of rocks and it occurs when a strong compressive force is applied from one direction to a recrystallizing rock. This causes the platy or elongated crystals to grow with their long axes perpendicular to the direction of the force. The mineral lineation is given by the quasi-one-dimensional preferred orientation of crystals on the foliation planes. Using these data we separate two deforamtional regimes: plastic and brittle. The plastic deformation is associated with a solid-state sin-cinematic crystallization with a large number of tectonic bodies (=lithons) whose fabric lies within two extremes: planar (for the tabular and sub-tabular lithons) and linear (for the monoaxial lithons). The macro-, mezzo- and microscopic analysis of the foliation (Figure 1) showed that: • The foliation determines the shape of the lithons, which can be tabular, concentric cylindrical or concentric ellipsoidal; the shape of the lithons varies greatly (planar, undulated, crossing planar); • The foliation is marked by phyllosilicates; • The dip of the foliation varies largely and can be grouped in several main ranges; • The abundant hydrated minerals (micas and chlorites) on the sliding surfaces show that the solid-state sin-cinematic crystallization took place in the presence of fluids; • The kinematic indicators suggest that the foliation acted as non-affine sliding surfaces; • The sliding was penetrative, the whole mass of rocks has been deformed due to shear. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 517


Figure 1 Foliation planes on Badeanca V., Leaota Mts., Carpathians, Romania

The field observations together with microscopic analysis of the oriented thin sections showed several groups of lineation (mineral, aggregate, lithonic, etc). The lineation has been generated during a penetrative sliding. Its direction is parallel to the rock movement. Figure 2 shows the several domains of mineral lineation separated by the field observations. The main features are: • The mineral lineation from the monoaxial lithons is parallel to their elongation axis • The mineral lineation from the tabular lithons may coincide with the mineral lineation of the monoaxial lithons • A main domain with WNW-ESE lineation is separated (Figure 1). Within this domain several sub-domains are observed: NNW-SSE (mainly on the left versant of Badeanca V.), NNE-SSW (Brusture and Danis valleys – right affluents of Badeanca V. – and on Mihai and Purcareata valleys – left affluents of Badeanca V.), ENE-WSW (mainly on the right versants of Brusture and Danis valleys). 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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Figure 2 Lineation direction on Badeanca V., Leaota Mts., Carpathians, Romania

This large number of lineation domains is due to a single homogeneous domain, broken in a later stage. The different lithons have been translated and rotated, resulting in the scattering of the mineral lineation and the appearance of different sub-domains. The brittle deformation generated a large number of fissures and cracks. Almost all the lithons have been affected by a brittle deformation perpendicular to the lineation. This deformation determined the appearance of several tectonic blocks in the Leaota Mts. Four fracture systems are separated in the south of Badeanca Valley: N-S, E-W, NW-SE and NE-SW (Figure 3). The existence of many friction planes with mirror polish and the sliding striations show that the fracture surfaces functioned as active sliding surfaces. The large dip of the fracture planes and the low inclination of the sliding striations (around 20 degrees) suggest that these planes functioned as strike-slip faults. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 519


Figure 3

Fracture planes on Badeanca V., Leaota Mts., Carpathians, Romania


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P3 - 09

ALMAS-STANIJA: EPITHERMAL MINERALIZATIONS INTERRELATED WITH AN UNDERLYING PORPYRY COPPER SYSTEM (SOUTHERN APUSENI MOUNTAINS, ROMANIA Tiberius Popa, Silvia Popa Prospectiuni S.A, Bucharest, Romania

Summary The Almas-Stanija (A-S) ore field from“Golden Quadrilateral” is located in the Southern Apuseni Mountains of western Romania, in the Zlatna-Stanija neogne volcanic structure. A-S structure comprises two interconnected magmatic-hydrothermal systems: the low sulphidation type of polymetalic gold + silver veins like a transitional epithermal system, which underlying a porphyry system situated in the depth of the geological structure. The studies show the evolution of an early magmatic pattern of alterations (propylitic and potassic-biotitic alteration) to a composite pattern alteration (adularia, intermediate argillic, sericitic and silica alteration), resulting by interaction with ground water. In A-S area, the vein systems near surface are contained within a large alteration envelope that includes the adjacent Almas-Neagra, Muncaceasca East, Muncaceasca West and PopaStanija deposits.The host rocks have undergone propylitic- potassic –intermediar argillitic sericitic -silicification alteration, increasing in intensity to mineralise veins. Mineralization is hosted in veins, fracture zones, stockworks and breccias, predominantly within igneous rocks, sometimes within the Cretaceous sediments and rarely in ophiolites. The veins have strike lengths of around 3-500 metres, and have been traced for approximately 500 metres down dip. Mineralization shows typical zonation patterns, from gold and silver-rich near surface, to more base metal-rich, then copper-rich ores with depth. The porphyry copper-gold system is situated approximately 400 meters below the present surface in Muncaceasca West area. The porphyry mineralization is hosted in the microdiorite intrusion that contains sulphides (pyrrhotite + chalcopyrite + pyrite + molybdenite + magnetite) stockworking. Introduction The Almas-Stanija ore field from“Golden Quadrilateral” is located in the Southern Apuseni Mountains of western Romania, in the Zlatna-Stanija neogne volcanic structure, exposed as a linear shape with 30 x4 km dimensions, adjacent to the Zlatna-Stanija sedimentary basin. Here there are the precious metal (Au, Ag), base metal (Pb, Zn) and porphyry copper mineralization, appearing in steeply quartz-carbonate veins, large metasomatic pyrite lenses, hydrothermal breccias and stockworks, which are hosted by Miocene andesitic stocks and lava flows, ophiolitic basement and Cretaceous sedimentary rocks. The mineralization consist predominantly of sulfides (pyrite, chalcopyrite, sphalerite, and galena), sulfosalts of As, Sb, and Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 521

REGIONAL GEOPHYSICS & GEOTECTONICS gold. The A-S ore field comprises the following ore deposits: Almas, Muncacesca Est, Muncacesca West, Stanija, which were explored and have been mined to some degree over a long period of time. Geological Setting The South Apuseni Mountains district represents an internal part of the Carpatho-Pannonian Cenozoic calc-alkaline belt. The district covers an area of about 900 km2 and includes numerous porphyry-types (Bostinescu, 1984). Mineralization is associated with calc-alkaline Neogene igneous rocks that were intruded through pre-Mesosoic low- grade metamorphics, Mesozoic rocks (Ianovici, et al., 1976). The Neogene magmatic activity and related hydrothermal mineralization are controlled by strikeslip fault system forming pull-apart basins (Drew & Berger 2001). The geology of the A-S ore field consists of a middle Jurassic ophiolites basement and a variety of overlying Cretaceous sediments, including flysch Figure 1 Almas-Stanija geological deposits conglomerates, sandstones, carbonaceous Map with relationship between shales, siltstones and calcareous sediments. The alteration and ore bodies systems sediments were deposited in marine and non-marine environments; some of them have been juxtaposed by intense structural activity, including thrusting, during the Cretaceous. Neogene andesitic sequences have resulted belong the calc-alkali volcanism during the middle to late Miocene. The Neogene andesitic intrusions (stocks) are located in Fericeaua Hill, Neagra Hill, Ungurului Hill, Magura Hill and are associated by lava flows in Negrii Hill and Ludului Hill and by associated breccia bodies (Bradisor, Villanela, Magura, Fericeaua). Volcanic centres were aligned along the series of northwest and west-northwest trending fault zones and constituted the point of convergence of subsequent hydrothermal activity and associated mineralization. The volcanic centers trending are: Neagra Hill-Ungurului Hill; Fericeaua-Acra Hill. In the depth, Fericeaua Hill developed a potassic altered microdiorite stock and associated with a porphyry system, which will evolve. At the shallow levels on an extended zone there are present hydrothermal systems, as a result of the cooling intrusions and active groundwater convection cells.

Figure 2- 3D view of underground level of and DDH301 showing the epithermal systems and porphyry copper system in Almas-Stanija ore field

Alteration and Mineralization Geological field data joining with drill data and mining data reveal the A-S structure comprises two interconnected magmatichydrothermal systems: the low sulphidation type of polymetalic gold + silver veins like a transitional epithermal system, which underlying a porphyry system situated in the depth of the geological structure. Drilling and underground data point out that epithermal mineralization, as veins, mineralised-breccia bodies cross-cut the upper part of porphyry system. The circulation of the reduced near neutral fluids generates the potassic alteration. At the shallow the mineralization style is gold


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REGIONAL GEOPHYSICS & GEOTECTONICS and silver rich ores, more silver and base metal rich mineralization styles. In depth typical porphyry copper systems with associated potassic and phyllic alteration styles are developed. Mineralization is hosted in veins, fracture zones, stockworks and breccias, predominantly within igneous rocks, sometimes within the Cretaceous sediments and rarely in ophiolites. In A-S area, the vein systems near surface are contained within a large alteration envelope that includes the adjacent Almas-Neagra, Muncaceasca East, Muncaceasca West and PopaStanija deposits. The field mapping and microscopic analysis, it was identified a zoning of alteration selvages.The host rocks have undergone propylitic- potassic –intermediar argillitic sericitic -silicification alteration, increasing in intensity to mineralise veins. The Muncaceasca West deposit is located in the west-central part of the area. The Muncaceasca West deposit consists of a series of steeply dipping, northwest trending veins that occur above a porphyry copper-gold system approximately 400 metres below the present surface. The deeper porphyry system exhibits classic alteration types normally associated with this style of mineralisation, including: • potassic zone of porphyry copper system has the assemblages: biotite ± K-feldspar+ +quartz ± rutile ± pennine + sulphides (pyrrhotite+chalcopyrite+pyrite+molybdenite+ magnetite); • potassic zone is surrounded by phyllic zone, characterised by the assemblages: sericite +carbonate ± chlorite ± biotite ± quartz ± rutile+sulphides± magnetite; • a distal propylitic assemblage (chlorite + pyrite + epidote + carbonate) is a diffuse and widespread fringe around the margins of the deposits. The porphyry mineralization is hosted in the microdiorite intrusion that contains sulphide stockworking. The typical porphyry assemblages were establishing: 1. for the interval m 400-700: [quartz + biotite + alkali feldspar + tourmaline+ (hematite?) + pyrite + pyrrothine + chalcopyrite +Au, Ag + sphalerite + molibdenite + galena + tetrahedrite]; 2. for the interval m700-1300: [quartz + alkali felspar + biotite/chlorite + tourmaline + rutile + anatase +magnetite + pyrrothite + pyrite+chalcopyrite + (native Au) + molibdenite + marmatitic sphalerite + galena + galeno-bismuthine(?)]. Quartz-calcite-sulphides veins cross the porphyry system. The veins, breccias and stockwork zones (25-Corabia Vein with the branches: Haber, Scarii, Spoiala and Robotin; hydrometasomatic pyrite lenses, stockworks, the Rosia group with the veins: 18, 19, Vâna Mare, Fântâna, Tulnic, Iolanda) are hosted in an andesite sub-volcanic intrusion and in the surrounding Cretaceous sediments and volcaniclastics. The quartz-calcite veins can be traced for over 500 meters along strike and up to 500 meters down dip. The Muncaceasca East deposit is situated immediately east of Muncaceasca West. The vein group (1 vein, 2 vein, 3 vein, 4 vein and B vein) consists of a number of quartzcarbonate-sulphide veins, with associated stockwork and breccia zones, hosted in an andesitic sub-volcanic intrusion and associated extrusive rocks. The Popa-Stanija area is located, immediately north of Muncaceasca East and Muncaceasca West. It consists of a number of epithermal quartz-carbonate vein and stockwork systems that are hosted in a porphyritic andesitic sub-volcanic intrusion (Ungurului Hill) and associated extrusive rocks, and to a lesser degree, in Cretaceous sediments. The area consists of a number of related vein and stockwork systems, known from west to east as Malita-Colt group, Stanija group (with the veins: Vilanela, Ana, Ludovica, Lazar, Villanela, Teluros, Fortuna, Aurel, Gratiela Emanuel, Butac, Sfânta Treime, Iulius, Wolhirth, Sever, Viorel, Elvira, Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 523

REGIONAL GEOPHYSICS & GEOTECTONICS Ieronim, Andronic), Piua, Bradisor stockworck, Barburisca stockwork and Magura (breccia-vein Magura, 17 vein, 650 vein, 500 vein, Sorina vein). Veins and fractures contain abundant sulphides, including pyrite, marcasite, galena, sphalerite and chalcopyrite. Mineralization shows typical zonation patterns, from gold and silver-rich near surface, to more base metal-rich, then copper-rich ores with depth. The vein systems generally have overall thicknesses of between 20 and 40 metres. Individual veins are steeply dipping, and have a northwest strike direction. Strike lengths in the order of 500 metres are reported. The Almas-Neagra vein system is located immediately east of Muncaceasca East. It consists of two groups of mineralised vein systems, known as the southern vein group, and the central vein group. The southern vein group (2- Concordia vein) is hosted in a quartz andesite sub-volcanic intrusion (Neagra stock).The central group (Dascaleasca, Gheorghe, Ovidiu, Alexandru, Horatiu, Tulia, Elena and also her ramifications) is hosted in the contact zone between the andesitic intrusion and Law Cretaceous sediments. The veins attain thicknesses of up to 4 meters, and have been traced along strike for up to 600 meters. They are sometimes associated with large zones of mineralized breccias. Characteristic for these veins was association gold–galena. Conclusions In A-S structure, a vertical and lateral zonation of mineralization is present varying with depth and distance from up flow zones. The geological data reveal a horizontal and vertical alteration zoning which surrounding the vein systems, increasing in intensity to mineralize veins. Mineralization consists of epithermal gold- base metal mineralization and porphyry copper mineralization, associated with intense hydrothermal activity. A model of polyphasal overprinting events is more suitable for this case (Cioflica &Lupulescu, 1998), similarly as the conceptual model elaborated by Corbett&Leach (1996). The convective circulation of the hydrothermal solutions expanded a halo of overlay potassic-intermediate argillisation–sericitic alterations around the veins The epithermal mineralization is hosted in veins, fracture zones, stockworks and breccias, predominantly within volcanic rocks, sometimes within the Cretaceous sediments and rarely in ophiolitic rocks. Precious metal mineralization occurs in veins and stockwork systems near surface. The porphyry mineralization is hosted in a porphyritic andesitic intrusion (microdiorite stock) that contains abundant quartz veinlets and sulphide stockworking. Pyrrhotite, chalcopyrite, pyrite, magnetite, molibdenite assemblage is the dominant in porphyry copper system. References Bostinescu, S., 1984, Porphyry –Copper systems in the South Apuseni Mountains- Romania, p161-174, An. Inst. Geol. Geo.f, vol.LXIV Cioflica, G., Lupulescu, M., 1998, Epithermal gold deposits and their relationship to underlying porphyry copper deposits, Rom. J. of Min. Deposits, vol 78, suppl.1,pp. 12-16 Corbett, G.J., Leach, T.M., 1998, Southwest Pacific rim gold-copper systems: Structure, alteration and mineralization. Economic Geology, Special Publication 6, 238 p., Society of Economic Geologists. Drew, L.J., Berger, B. R., 2001, Model of the porphyry copper/polimetallic vein kin-deposit: Application in the Metaliferi Mountains, Romania. In Piestrynski, A. et. al. (eds) Mineral deposits at the beginning of the 21st century-Proceedings of the joint 6th biennal SGA-SEG meeting, Krakow, Poland, 26-29 August, 519-522. Ghitulescu, T.P., Socolescu, M., 1941, Etude géologique et minière des Monts Métallifères (Quadrilatère aurifère et régions environnantes). Annuaire de L’Institute Géologique de Roumanie, XXI, 181-464 Ianovici, V., et al., 1976, Geologia Muntilor Apuseni, Ed. Academiei, Bucuresti. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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THE RESPONSE OF THE INTRAPLATE MESOZOIC BASINS AT THE SOUTHERN MARGIN OF THE EUROPEAN PLATE TO THE COMPRESSIONAL EVENT IN THE NORTHERN TETHYS AT THE TRIASSIC – JURASSIC TRANSITION

J.Świdrowska1, M.Hakenberg1, A Seghedi2, B. Poluchtovich3, I. Vishniakov3 1 Institute of Geological Sciences, Polish Academy of Sciences, Warszawa, Poland 2 Geological Institute of Romania, Bucharest, Romania 3 Ukrainian State Geological Research Institute, Ukrainian Comitee on Geology and Utilization of Mineral Resources, Lviv, Ukraine

Basins discussed developed in the southern margin of European plate and are presently involved in the SE part of the Mid-Polish Swell (Poland), Stryj Depression (Ukraine), Moldavian Platform (Romania) and pre-Dobrogea Depression (Ukraine). Main part of them developed along the Trans-European Suture Zone. Southern boundary of sediment recognition is limited by depth sinking beneath the Miocene Carpathian Foredeep together with the stack of Outer Carpathian flysch nappes and thrust sheets. In the case of pre-Dobrogea Depression Mesozoic platform deposits are in tectonic contact (along the Sf. Gheorghe Fault) with the Cimmerian orogen of North Dobrogea (Seghedi, 2001). On palaeogeographic maps, this segment of the European plate margin contacts the Eastand West-Mediterranean Tethys realms. Their evolution differs significantly and various solutions of palaeogeographic patterns are proposed (e.g. Dercourt et al., 2000; Stampfli et al., 2001; Golonka, 2000, 2004). Assuming that horizontal compressional stresses related to collisional plate coupling can be transmitted over great distances and create tectonic conditions for intraplate basins development (Zoback, 1992; van Wees & Stephenson, 1995; Ziegler et al., 1998), we searched an answer for the questions: 1) Does the evolution of basins accommodation space, which occurred within the European plate margin, reflect rather West- or East-Mediterranean tectonic events in Northern Tethys? 2) What kind of pattern of microplates, subduction zones and spreading axes of Northern Tethys seems to be most probable, taking into account the compressional events on the European plate margin? The analysis is based on the relationships between facies and thickness patterns. Rapid isopachs course changes, zones of great thickness gradients and facies alternations made possible the identification of synsedimentary faults activity determining basin geometry and tectonic conditions of its origin. We focused our interests on one of the episodes of plate reorganization at the Triassic – Jurassic transition. The episode of great regional break in the sediment record comes into evidence on the Upper Triassic map of this area. Two unconformities: base-Norian and base-Rhaetian were identified in the SE segment of the Mid-Polish Trough (Samsonowicz, 1929; Ziegler, 1990). The Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 525

REGIONAL GEOPHYSICS & GEOTECTONICS second one is responsible for an angular unconformity between Upper Triassic and Lower Jurassic sediments and, first of all, for the broad latitudinal uplift of the southern European margin (Cloetingh, 1986; Ziegler, 1990). The Mid-Polish Trough was closed from the South at the transition from the Triassic to the Jurasic; further to the East, in Stryj Depression and on Moldavian Platform, there are no Triassic sediments. The basin of pre-Dobrogea Depression represents the southern slope of the European edge. Buckling of southern European plate margin was the result of great compressional stresses originated during the closure of Palaeotethys Ocean, docking of the Cimmerian microplates and graduate closure of the Küre-Crimea basin (Ustaömer &Robertson, 1997; Nikishin et al., 2001) (the Black Sea back-arc basin of Cloetingh, 1986 and Ziegler, 1990). These tectonic events are noted in palaeogeographical reconstructions (Dercourt et al., 2000; Stampfli, et al, 2001; Nikishin et al., 1998, 2001; Golonka, 2004). The broad area where denudation prevailed persisted also during the Early Jurassic, including also the pre-Dobrogea Depression. The position of North Dobrogea before/during this collision was interpreted in different ways (see Seghedi, 2001). The shallow shelf depositional environments of the Upper Triassic deposits in pre-Dobrogea Depression, contrasting with the basinal Tethyan facies in the North Dobrogea just south from Sf. Gheorghe Fault (SGF), as well as the lack of Lower Jurassic deposits to the North of this fault and turbidite sedimentation in Tulcea Zone suggest that these two areas, coupled along SGF, originally were distant one from another. We suppose that the North Dobrogea Variscan Massive was initially located much more to the West (like the Moesian Plate on the reconstructions of Stampfli et al., 2001; Banks & Robinson, 1997), in the easternmost fragment of Meliata Ocean (Golonka et al., 2000; Golonka, 2004). The eastward shallowing of Middle and Late Triassic facies in the North Dobrogea (Seghedi, 2001, Figure 5) rather eliminates the correlations with the Küre-Crimea basin back-arc basin. The large transform fault dividing the Mediterranean realm into western (Meliata Ocean) and eastern (Vardar Ocean) parts is observed on some of Tethys maps (Stampfli et al., 2001; Golonka, 2004). Assuming, that North Dobrogea remained on the eastern side of this transform fault, it would be easier to explain there the orogenic deformations of the Cimmerian collision in this area. Three observations and/or assumptions laid in the basis of proposal of ND history (Figure 1) during Late Triassic plate reorientation: 1) oblique direction of Paleotethys subduction against Eurasian margin (Stampfli et al., 2001; Golonka, 2004); 2) Halstatt-Meliata Ocean and Crimea-Küre Basins belonged to genetically same belt of back-arc basins of the Paleotethys Ocean and 3) reverse polarity of subduction zones along Eurasian margin: Paleotethys northwarth – marginal basins southwards (Plasienka et al., 1997; Ustaömer & Robertson 1997; Nikishin et al., 2001). Sinistral movement along the thinned Eurasian rim and the northern Paleotethys margin ought to be simple consequences of these ascertainments (Fig.1A). The sigmoidal shape of tectonic units observed in North Dobrogea bounded by two faults, SGF and Peceneaga-Camena Fault (PCF) (Seghedi, 2001, Fig. 4), could be treated as structural evidence of left-lateral component during Late Triassic compression in this area. It was coupled with southward consumption of ND basin and resulted in NE vergence of the tectonic units (Figure 1B). 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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On the other hand, there is no tectonic connection between the southern part of Mid-Polish Trough to the West and the western Tethys domain. At the Triassic – Jurassic transition, the Tethyan units – the Pieniny Klippen Belt and the Tatra Mts. – persisted as part of European plate margin. Profiles of the Tatra autochtonous cover reveal the same “Eo-Cimmerian” gap and unconformity (Lefeld, 1973) as observed in the Polish segment of European plate. Aknowledgment This work has been supported by the grant from the Polish Committee for Scientific Research (KBN grant no. 3 PO4D 068 22). References Banks Ch.J., Robinson A.G., 1997, AAPG Memoir, 68, 53-62. Cloetingh S., 1986, Geol. Mijnbouw. 65, 103-117. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 527

REGIONAL GEOPHYSICS & GEOTECTONICS Dercourt J., Gaetani M., Vrielynck B., Barrier E., Biju-Duval B., Brunet M.F., Cadet J.P., 2000, Crasquin S., Sandulescu M. (eds), Atlas Peri-Tethys Palaeogegraphical Maps. Golonka, J., Oszczypko, N., Ślączka, A., 2001, Ann. Soc. Geol. Pol., 70, 107-136. Golonka, J., 2004, Tectonophysics, 381, 235-273. Lefeld, J., Budowa Geologiczna Polski, 1, part 2, (470-471) Nikishin, A., Cloetingh, S., Brunet, M-F., Stephenson, R.A., Bolotov, S.N., Ershov, V., 1998, Peri-Tethys Memoir 3, Mem. Mus. Nat. D`Hist. Nat., 177, 163-176. Nikishin, A.M., Ziegler, P.A.., Panov, D.I., Nazarevich, B.P., Brunet, M-F., Stephenson, R.A., Bolotov, S.N., Korotaev, M.V., Tikhomirov, P.L., 2001, Peri-Tethys Memoir 6, Mem. Mus. Nat. D`Hist. Nat., 186, 295-346. Plasienka, D., 1997, in: Geological evolution of the Western Carpathians, 1-24. Samsonowicz, J., 1929, Spraw. PIG, 1/2, 1-249. Seghedi A., 2000, Peri-Tethys Memoir 6, Mem. Mus. Nat. D`Hist. Nat., 186, 237-257. Stampfli, G.M., Mosar, J., Favre, P., Pillevuit, A., Vannay J-C., 2001, Peri-Tethys Memoir 6, Mem. Mus. Nat. D`Hist. Nat., 186, 51-108. Ustaömer, T., Robertson, A., 1997, AAPG Memoir, 68, 255-290. Van Wees, J.-D., Stephenson, R.A., 1995, Tectonophysics, 252, 163-178. Zoback, M.L., 1992, J. Geophys. Res. 97, (11703-11728). Ziegler, P.A. (ed), 1990, Geological Atlas of Western and Central Europe. Ziegler, P.A, 1998, Tectonophysics , 300, 103-129.


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AN ANALYSIS OF THE GEOMAGNETIC STORM IN LOCAL COORDINATES AND TIME B. Srebrov, I. Cholakov Geophysical Institute, Bulgarian Academy, Sofia, Bulgaria

Introduction The geomagnetic storm is caused, as is known, by the interaction between an interplanetary disturbed structure, formed in interplanetary space, and the magnetosphere. This structure is formed by solar events, such as Coronal Mass Ejections ( CMEs). On the ground the variations of the geomagnetic field during the storm dependent on the Earth surface coordinates and the local time. The local variations of the geomagnetic field, during the geomagnetic storm are considered, by the Fourier analysis, which is effective for the investigation of an impulse phenomena as the geomagnetic storms. Already Chapman [1] has analyzed a great number of geomagnetic storms with the same intensity and starting time. In his work the components of the Dst variation are functions of the magnetic latitude up to 900 . It is larger at low latitudes. The D component of Dst is much smaller than H. Thus the field vector of Dst is practically parallel to the earth surface excepting the polar regions, where the vertical component Z has bigger positive changes. Description of the geomagnetic storm The geomagnetic field variation during a geomagnetic storm have distribution on the Earth surface and is a function of time t. This distribution for points with dipole spherical coordinates θ (the geomagnetic latitude up to 900) and ϕ (the geomagnetic longitude) is:

B(θ , ϕ , t ) = M (θ , ϕ ) + D(θ , ϕ , t ) ,

(1)

if the quiet-day variation RS is eliminated. In this equation M (θ , ϕ ) is the main magnetic field and D(θ , ϕ , t ) is the disturbed part of the geomagnetic field. The main part of the geomagnetic field, as is known, consists of a longterm secular variation which is eliminated too. The following Fourier-series expansion is about the disturbed geomagnetic field part: D(θ , ϕ , t ) = C0 (θ , t ) + ∑ Cn (θ , t ) sin[ nϕ + α n (θ , t ) ] n

where, a n (θ , t ) is the phase angle. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 529

(2)


The Chapman analysis of the geomagnetic storm clearly reveals that the first and second terms in this equation are the axial symmetric and asymmetric parts of the disturbed geomagnetic field, from this follows:

D(θ , ϕ , t ) = Dst (θ , t ) + DS (θ , ϕ , t ) .

(3)

Here, the function Dst (θ , t ) is the universal time (UT) part of disturbance in the stormtime. The field of Dst mainly determined by inside sources but as the Earth is not a good electric conductor the changes of the external magnetic field induce earth currents.The latter are on the Earth’s surface and they contribute much to the variations of the geomagnetic field on the Earth surface. These currents screen the deeper earth layers by the external variations. In equation 3 DS (θ , ϕ , t ) is the variation dependent on local time, which is caused by the asymmetric part of the magnetospheric ring current. The ionospheric current systems also influence this part of the disturbed field. In this case the variation are named disturbed diurnal variation and is marked with by SD. The induced earth currents are mentioned above, contribute to these local changes and are different on the various parts of the earth surface. After substitution of expression (3) in equation (1) for the distribution of the geomagnetic field during the geomagnetic storm we have: B(θ , ϕ , t ) = M (θ , ϕ ) + Dst (θ , t ) + DS (θ , ϕ , t )

(4)

This equation describes the geomagnetic storm as a function of the coordinates and the time and can be used to obtain the geomagnetic field in each point from the Earth surface during the storm. The definition (4) of B(θ , ϕ , t ) is equaley applicable to all three magnetic elements but the magnetic field, due to the symmetric zonal current system in the equatorial plane is paralel to the dipole axis and is seen mainly in the H component (for small Dst ( Z ) and Dst ( Y ) values derived from averages of several magnetic storms, see (Sugiura and Chapman, 1960)). An analysis of a concrete geomagnetic storm The method described in the second part of this paper is applied for investigation of the geomagnetic field variation during a concrete geomagnetic storm, recorded in Geomagnetic Observatory (GMO) Panagjuriste ( PAG), in the interval 21-22 02. 1994 which started with SSC. Registrations in the GMO PAG The disturbed H (to be more precise (H-Base value)) magnetic field component, registered in GMO PAG is shown in figure 1. As from the magnetogram seen the variation of the H component, in this case, has an amplitude of 160 nT. The mean decreasing of this magnetic element is approximate by 120 nT. This is one typical variation for SSC geomagnetic storm in the GMO PAG with a middle amplitude. An analysis of the geomagnetic storm of 21-22 04 1994 The global Dst variation for the discussed geomagnetic storm is shown in figure 2. As can be seen from the picture the amplitude and decreasing for this geomagnetic index are approximately in a similar range as in GMO PAG. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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On figure 3 the calculated local DS variation, during the same storm, for the point with the dipole coordinates of the GMO PAG is shown. As it is clear from the picture this variation has small amplitude and decreasing. It is clearly visible that in this case there are oscillations with duration approximately few hours and one day. A commentary about the nature of these oscillations is mentioned above, in section 2. The similar analysis of the many cases of storms in the concrete observatory can be used for the investigation of the relationships between the global indexes and the local DS variation. The comparision of the results from an investigation of the DS variation for the observatories at a short distance can show some typical local manifestations of the geomagnetic storm, which is important for the geomagnetic storm prognosis. Conclusions In this paper the Fourier-series analysis is used for an investigation of the local flow of the geomagnetic storm. The developed method is equally applicable for all observatories with low and middle latitude but is not applicable for the north observatories because the magnetic storm in these regions have different manifestations. This is so because, as it known, at high latitudespolar regions the auroral current system has a too great impact. That is why in the method described in the present work terms, which describe the influence of the auroral current system, are not included.The derivation of the DS variation and the parts this variation by using of the Fourier analysis is important for undestanding the local parameters of geomagnetic field changes during the geomagnetic storm. The common investigation of the local flow of the geomagnetic storm for a concrete observatory must include many cases of storms during different solar cycles with a various solar activity.

700

675

(H-Base), nT

650

625 600

575 550

525 500

00.21.02.94

00.22.02.94

00.23.02.94 time

Figure 1



50.00

Dst, nT

0.00

-50.00

-100.00

-150.00

00.21.02

00.22.02

00.23.02

time

Figure 2

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DS, nT

700

650

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00.21.02.94

00.22.02.94

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Figure 3 References Akasofu S., Chapman S., 1972, Solar-Terrestrial Physics, Oxford at the Clarendon Press.


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MAGNETIC PROPERTIES OF THE TYPICAL UKRAINE SOILS. RESULTS OF THE INVESTIGATIONS Anatoliy Sukhorada, Aleksandr Menshov Taras Shevchenko Kyiv National University, Ukraine

Summary The basic problems of the investigations of the magnetic properties of the typical Ukraine soils, main tasks are considered. The results of researches of vertical and lateral (spatial) distributions of magnetic properties of the typical Ukraine soils. Introduction Magnetometry has been an instrument for solution of many applied tasks for a long time. For the first time a magnetic method found the application at the prospecting of the strongly magnetic ores in Sweden, and it was used in Russia at the end of XIX century. Then magnetometry became an effective method for solution such classic geophysical tasks as exploration of minerals, magnetic mapping and others. All the territory of Ukraine was covered with magnetic chart in this way. Today's realities of the state of problem of magnetometry in Ukraine compel us to search new directions of applications of magnetometry, which are on the border of a few different sciences. And magnetometry of soils is one of them. Before, soils were accepted only as layer-hindrance at geophysical investigations. But it is not right. The most magnetic types of soils (such as chernozems, grey forest soils, chestnut soils) can be the main source of the anomalous magnetic field of the investigated area, if soils superpose low-magneticn rocks. It is common situation in Ukraine, especially in perspective oil and gas provinces. Thus, information about magnetic properties of soils is very important working out such tasks as detailed mapping, interpretation of the low amplitude magnetic anomalies [1]. Also, environmental magnetism is intensively developing in the world [2,3]. And this new direction of magnetometry is developing in Ukraine too [4,5]. Such investigations are used by us on the most technogenic polluted territories of the large megapolyses. Among them there are Krivyi Rig, Mariupol, Dnepropetrovsk and etc. The results of these investigations show frequent growth of the magnetic susceptibility (MS) in the overhead part of soil cover on the most polluted areas in comparison unpolluted standard areas. Now we pay a great attention to researches of these unpolluted areas which are located practically in all agroclimatic territories of Ukraine. During the last years new scientific direction of geophysics of pedosphereagrogeophysics is intensively developing in Ukraine. It is the use of the magnetic methods in the Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 533


agriculture. The first results show close dependence of soil-humus and magnetic properties of the soils. And it is the basis of creation of the geophysics of the double-duty. It puts us the necessity of creation of magnetic models of the soil cover. For these tasks we use different parameters of magnetic researches and the main are as following: magnetic susceptibility (or induced magnetization Ji), natural remanent magnetization (Jn (NRM)), summary magnetization (JΣ) (vectorial sum natural remanent magnetization and induced magnetization). Original investigations of the summary magnetization are very important [6]. It is basic factor of creation of the magnetic anomaly which is generated with a soil cover. And only with the summary magnetization we can estimate the contribution of the soil cover to forming of the anomalous magnetic field. It is necersary to have the exact information about the local anomalous magnetic field and its vertical gradient to work out this problem. And it is important to create the technology of measuring this field in moving, for example during the agricultural works. We will consider this questions on the examples of the most typical situations for Ukraine. Results We investigate magnetic properties of the typical Ukraine soils in a few directions. They are: 1. Distribution of magnetic properties of soils on vertical line (along the soil profiles). 2. Distribution of magnetic properties of soils on lateral( spatial distribution). It is rather wide complex of tasks. Among them there are: magnetic properties of soils from different agroclimatic Ukraine zones, changes of magnetic properties at crossing of different forms of landscapes, etc. For studying distribution of summary magnetization on vertical line we organized special soil-geophysical profiles. Their depth is about 1-2 meters (along full humus horizons). The orientated samples were taken from all principal soil horizons with traditional paleo- and pedomagnetic technology for their next laboratory studying. Samples had to represent natural structure of the soil section. Studying of the distribution of summary magnetization on lateral was carried out on the territories, which have the most typical soil cover and landscapes for Ukraine. The magnetic parameters were measured in laboratory conditions with the astatic magnetometer LAM-24, rock-generator JR-4, kappabridge KLY-2 and dual frequency magnetometer MS-2. We investigated magnetic parameters for such agroclimatic Ukraine zones: Woodlands, Forest-steppe, Steppe and Dry Steppe. The main investigated types of soils are: swamp soils, meadow soil, soddy-podzolic soils, grey forest soils, chernozems and chestnut soils. Consider the distribution of the magnetic parameters on vertical line for different soil types and on depending of agroclimatic zones of Ukraine. The first example is distribution of the summary magnetization for chernozems of Forest-steppe (Poltava region, area Konony, figura1). The special soil cut is characterized with podzolized chernozem. The curve has two maximums on the depth 10 and 25 sm (JΣ=36*10-3 and 27*10-3 A/m accordingly). It is humus and humuselluvial horizons. Parent rock is presented by two types, so there are two horizons (depth ≈ 60-70 and depth ≈ 70-90 sm). The values of the summary magnetization fall in the parent rock horizons (J establishing new basic gravity network, > leveling of high precision, > regional gravity survey, > vertical deflection by astrogeodetic measuring, > creating of digital terrain model. History Gravity Network of First Order During 1952/53 on territory of former Yugoslavia, it was established a Gravity Network of First Order on 15 stations, by using of Worden gravity meter. In the next table, there are presented some of relevant data related to Gravity Network of First Order. Table 1 Number of stations Number of triangles max number of measuring of the same line min number of measuring of the same line max positive error max negative error mean error

15 14 7 4 +0.14 mGal - 0.10 mGal 0.056 mGal

Gravity Network of Second Order Gravity Network of Second Order is developed within the stations of first order at mean distance of about 10 km and error estimation that is not great of 0.05 n , where n is number of stations in polygon. The analyses show that these measuring were made with high quality, but they were not performed continuously and without planning for whole territory of Serbia. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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GIS, DATABASES & DIGITAL MAPPING

Basic Gravity Network The field works on Basic Gravity Network were finished in period of 1964-1967. In the next table are presented some relevant data on Fundamental Gravity Network of Yugoslavia. number of polygons mean extent of polygons min number of lines in polygon total number of stations in network mean distance between stations in network total length of network estimation of standard deviation

Table 2 55 370 km 5 1500 10 km 12000 km 0.026 mGal

Connecting to IGSN 71 Four stations from Gravity Network of First Order (three in Belgrade and one in Zagreb) are included into network IGSN 71 in 1951, by J.Martin (according to Bilibajkic, P. at all., 1979). After analysis of the results, it was concluded that our network is about 15 mGal higher than IGSN 71. New Fundamental Gravity Network The main reason for establishing of New Basic Gravity Network is adequate maintenance of network and monitoring by government institutions, that was no practiced with previous works. The work on the Network will be performed by measuring of gravity differences by SCINTREX CG-5 Gravity Meter on 55 polygons in 126 directions and 89 duplicate measurements. Forming of the New Fundamental Gravity Network may be presented into few acitivities: (1) Performing of disposition of measuring stations; (2) Methods of measuring and realisation of field works and (3) Processing the data. The starting idea was that the Fundamental Gravity Network should be performed on stabilised stations. For this purpose, measurements will be done on fundamental geodetic points, that are 37 such stations in Serbia (without Kosovo). Considering the great distances between fundamental geodetic points, it was neccessary to include some stations of Referent Geodetic Network of Serbia to assign of mean distance between stations up to 30 km. The number of these stations for Fundamental Geodetic Network is 38. On the basis of all relevant data given in the paper, the Network is formed and it is shown on Figure 1. The total number of poligons is 55, and total number of stations of gravity Network is 75. The measuring in the field will be performed by SCINTREX CG-5 Gravity meter. Test measuring in the field is done at several Fundamental geodetis stations. An example of these measurements is shown on Figure 2. References Bilibajkic, P. at all., 1979: Explanation for the Gravity Map of Yugoslavia - Bouguer Anomalies - 1:500000, Prepared by: Enterprise for Applied Geophysics "Geofizika" Zagreb and Institute for Geological and Geophysical Research Belgrade, Belgrade, pages 67. Starcevic, M., at all., 2004: Project: The New Basic Gravity Network of Serbia, Republic Geodetic Authority, Belgrade.



1 2 4

5

3

9

8

7

6

12 10

11 13

16 15

14

21

17

18

22

20

27

19

30

26 23

28

25

24

29 31

36 32

37

34

33

38

42

35

39

41 49

40 48 45

43

47

46

51 50

44

52 53

54

55

Figure 1 Disposition of the stations of New Fundamental Gravity Network of Serbia

Figure 2 SCINTREX CG-5 Gravity meter at the Fundamental geodetic station


678


P10 - 02

GEOINFORMATIZATION OF GEOPHYSICAL DATA FOR MANAGEMENT OF NATURAL RESOURCES IN REGION OF TIRANA-DURRES-KABAJE, ALBANIA 1

Fatbardha Vincani1 , Piro Leka2 AGS, Department of Geoinformation, Tirana, Albania 2 AGS, Geophysical Center, Tirana, Albania

Introduction During a period of about 20 years in the lowland of Adriatic Sea, region of Tirana – Durres – Kavaje (TDK) many geophysical researches were carried out with electrometric, magnetometric and radiometric methods and many data sets on the surface as well as in the depth have been accumulated Diversified themes and the tasks that were resolved concerned Geomorphology, Geology, Agrogeology, Hydrogeology, Engineering Geology, Geophysics and Environment studies. To become more useful this research information for the civil society it is realized the geoinformation of the geological-geophysical database for management of natural resources and ground in lowland Adriatic Sea of TDK region (figure 1). 4700000

B.CURRI KO PLIK

KRUMA

SHKO DER

KUKES

PUKE

4650000

PESHKOPI

LAÇ

BURREL

KRUJE TIRANE

DURRES

A D R I A T IC

KAVAJE 4550000

BULQIZE

LIBRAZHD ELBASAN

ONIA M A C ED

4600000

SEA

RRESHENI LEZHA

PEQIN LUSHNJE GRAMSH KUÇOVE FIER

POGRADEC

BERAT KORCE DEVOLL

BALLSH

4500000

ÇOROVODE

VLORE

ERSEKE

TEPELENE PERMET 4450000

GJ IRO KASTER DELVINE SARANDE

4400000

4 3500 00

Fig. 1

4 4000 00

4 4500 00

4 5000 00

Site of planchettes in Tirana- Durres-Kavaje region

Studied planchettes during 2001 year Studied planchettes during 2003 year

Studied planchettes during 2002 year



This study is realized with the aim to standardize the information system process, mapping, qualification, coordination etc. and its experiences will help in other regions of Albania. Methods The realization of the tasks and the objectives of geoinformatization geophysical data at TDK region is related with the GIS application program, according to the creation concept of data base with contemporary level of geological service, in totally. Processing has passed some phases like : data preparation, information etc., which are summarized as follow: 1. The collection and filtration of obtained geophysical data according to digitalized planchettes; 2. The realization of digital process for GIS according to corresponding planchettes of studied region; 3. Processing for GIS (Clean-Up, topology, data base table and link process); 4. Application of appropriate softwares for the resolve of tasks about research thematics; 5. Entry of their computing model; 6. The collection, standardization of informatic products in computer DBASE at the complete state and available to print. Realization of GIS Based on the existing technology (hard-software) GIS at TDK region is realized for 20 planchettes, at 1:25000 scales, for the following components of Environmental Geological Maps series: Topography, Geomorphology, Geology, Agrogeology, Hydrogeology, Engineering Geology, Geophysics and Environment. After digitalis and processing of planchettes separately, their joint is also accomplished to be presented in an unique one. 19° 30' 41° 20'

B

75

44

07

43

76

77

78

79

80

stalla

10 Rrashbulli

45

82

83

43

10

B

Gjepalaj (Terezie)

L

10

19°37'30'' 41° 20'

84

B

10

Likeshi

32.0

54.0

10

78

128.0

satalla

10

sera

k. Gjatë

144.0

stalla

10

Rrethi

Arapaj (Domeve)

Çatos

Thickness (m)

Symbol

I A N

73

s ne Po ku

va e Çeta faqja

10

Shkallnueri

15

4

107.0 Rromanati (Bletaj)

Çizmeli

Manskuria (Çaush)

10

m.Olezes

3

L

k. Dargjata

Rromanati

10

73

5

fusha e Bozaxhise

4

k. Thanes Manskuria (Tush)

Manskuria (Gjuzet)

Rromanati (Shabie)

10

141.0

113.0 127.0

L

Bozanxhia (Gjymsej)

72 71.0

1-2-3

Qp3

12

B. The sediments of basement of Quaternary Deposits. B

L

5

Tilaj (Tropollinjte)

10 311.0

5

br

Seferaj (Ajazet)

pishë kasolle

kasolle 256.7

7

L Kryemedheji Tilaj (Gezdar)

0

10

Bozanxhia (Troblini)

310.0

Kryemedheji (Gjazet)

76

i egu

Ly

t pshi

12

317.0

m. Zhuritit

L

Zhurja

B

299.0

stalla

10 77

g-s

Qh2 Alluvial sediments, gravel, sand.

a s

Qh 2 Marine sediments, sand. m Swampy sediments, ooze and sand o-s with organic matter. s Qh 2 Lagoonal-swampy sediments, sand and ooze with organic matter Alluvial sediments, clay and silt aQh 1 (first terrace). Qp -h The sediment of piedmont slope, sand, ps 3 silt, clay with rock peaces. Qp3 The alluvial sediments of second terrace. s-o

Qh

l

c-si

Tilaj Xherolijt)

101.0

118.0

3 75

Romanati (Romalli)

71.0

45

43

9

271.0

Kryemedheji (Dervish)

70

41° 15'

L

t

71

Bozaxhia

hi

12. The alluvial sediments of second terrace.

12

stalla

Manskuria (Veze)

k.Ullinjt e Ramit

7

ps

10. The sediment of piedmont slope, sand, silt, clay with rock peaces.

elektrop.

sh . Ly

9. Alluvial sediments, clay and silt (first terrace).

5

4 4

10

10

1

10

4 156.0

Shkallnueri (Vargje)

126.0 Shkallnueri )Dedaj)

128.0

74

L

Maskuria

105.4

10 L

10

148.0

m.Shkembi Kavajes

Lithological, genetic and ages classification (formational)

Rromanati (Stretaj)

I

Shkallnueri (Xhalaj)

D U R R E S

3 - 5 - 10 deri 20

Qh1

O

R E

Z

T

HOLLOCENIK I HERSHEM

A

O

4

142.0

k. Zhurit

baraka

U K

N E

k. Planës

Element of inclination 75

10

72 9

K

PLEISTOCENIK I SIPERM

B

135.0

112.0

3

5. Swampy sediments, ooze and sand with organic matter.

Contours of alluvial gravel and sand thickness

15

plep

4

5

122.0

L

3. Marine sediments, sand. 4. Alluvial sediments, gravel, sand. ooze

Geological cross section I - I

I

76 92.0

Hardhishta (Kokomani)

15

Rromanati (Memaj) k. Dumetit

83.0

74

7. Lagoonal-swampy sediments, sand and ooze with organic matter

10

10 k. Ramës 143.8

GULF

1

1-3-5

4 7

1

L 47.0

1. Alluvial sediments, gravel, sand.

3

5 Qh2

System

Eratemi

Agrogeological Layer

stalla

10

10

10

5

E

HOLLOCENIK I VONSHEM

0.1-1.5

10

128.0

plep

10Shkallnueri Formational and Lithological Description

R

K

Lithological Column

tes

Section

I

10

stalla

56.0

75

Lithostratigraphic scheme

elektrop.

9

Hardhishta

9

84.0

k.Hakles

20

4

No normal geological boundary

Likeshi (Koklevora)

ish

Arapaj

76.0

Arapaj

76.0

L

Pjezga

10

L

dh

4

10

45

Har

56.0

77

B

rr

fush

10

10

10 85.0

aç Sh

112.0

ae

91.0 k.Dokeve

rr.

ës

k. Çallikut

fush

7

ku

L

I

121.3

stalla

76

baraka

Likeshi (Çalliku)

Xhafzotaj (Pjeshkeza)

ae

54.0

50

10

Normal geological boundary

baraka

k.Kecave

L

Arapaj

Geological boundary and structural element

motop

B

108.0

stalla

77

Legend

Këneta

35

30

10

78

81

sera

Rrethi (Legasen)

radiostac. Xhafzotaj

Tilaj L

78

Zhurja (Qaf-Shkalla)

Seferaj

79

80

81

82

83

43

84

kasolle

Q

Para

The sediments of basement of Quaternary Deposits.

41° 15' 19° 37' 30''

1 km

Geological cross section I - I NE

SW 20 100 80 60 40

42 10

57 1

25

1

10

20 100

Fig. 2

9 B

80 60 40

In Figure 2 one of the surface geological map with thickness contours of Quaternary deposits is presented for K-34-100-A-a (Rrethi) planchette, at 1:25000 scale, where other elements like the site of planchette, lithostratigraphic scheme, geological cross-section and legend are shown too. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

680


For geophysical data geoinformatization in this planchette (Figure 3) the results of Electrometric methods carried out for water studies, the rock-salt researches, microzone Durres region and mining geological works are mainly utilized. 41

11

12 13

29

36/1 35

4578000

186

40

14 19 18

166 30 168 15 6 11

188 56 187

17 163

34

162 4576000

49

42/1

33 32

56/1

Hardhishte

60

Pr 24 36

57 152 1157 56 25 155

47 4574000

Romanat Er

ze

n

R

iv

Du rre

4572000

er

s Gu lf

4570000

108

4375000

4377000

4379000 0

500

4381000 1000

4383000

m

Electrometric surveys for water studies Electromtric surveys for rock-salt researches Electrometric surveys for microzone Durres region

11 40

Dug well Boreholes Applied EVS

Fig. 3 The map of observation sites, K-34-100-A-a (Rrethi)

In applied electrometric surveys for the water studies have separated ones for the site of areas or sectors more important for aquifers at “Romanat“ region, at 1:25000 scale. Based on the obtained data processing are created the resistivity, the thickness of gravel layer, “ρ x h” production for gravel quality maps as well as topographic ones. Boreholes in areas, where have more high values of “ρ x h” production have intersected gravel layer with good water permeability (Figure 4). The mapping process has served as geologo-hydrological-geophysical model for aquifers gravel layer at Durres-Shijak landlow. At pseudo-2D section 24 of Romanat region the presence of two gravel layers with different thickness and resistivity is observed. The first layer, near the surface with values of electrical resistivity 30-100 ohmm, of thickness 20-100 m is located at (102-108) pk., while the second layer with values of electric resistivity 102-131 ohmm and of thickness 70–120 m is located at (92-102) pk. 29 and 31 boreholes have intersected the gravel layer with good water permeability at 20 m quota, with 100 m and 90 m respectively thickness at argil sediment (Figure 5).



No gravel layer Under 100 ohmm 100 - 200 ohmm Upper 200 ohmm Applied EVS Positive well Negative well

0- 5m 5 - 10 m 10 - 15 m 15 - 20 m

2

under 500 ohmm 2

500 - 1000 ohmm 2

1000 - 2000 ohmm 2 Up to 2000 ohmm

Figure 4 Resistivity, thickness, σ x h production of gravel layer, Romanat Hardhisht region NE SW

Depth (m)

Erzen F.

30 ES 92

ES 108 ES 96 W 29 SE 94 68

20

W 31

ES 100

ES 102 25 100

ES 104 24 58

ES 106 15 30

37

29

25

20

30

102

131

10 9 24

0

200

400

600

21

4

15

0

80

1000

1200

1400

1600

1800

2000

2200

Distance (m)

Fig. 5

Resistivity pseudo - 2D section 24, Hardhishte region Legend 0 - 30 ohmm - argil 60-130 ohmm - gravel

SE 96

W 31

Aplied EVS Well

Conclusions Geoinformatization of obtained data from the electrometric, magnetometric and radiometric surveys at Landlow Adriatic Sea, Tirana – Durres – Kavaja region during the period of about 20 years, is tested along some phases, related to the data processing and scientific information standardization. It is realized GIS application system in this region, in compilation of 20 maps (planchettes), at 1:25000 scales, with total necessary components of Environmental Geological Maps series: Topography, Geomorphology, Geology, Agrogeology, Hydrogeology, Engineering Geology, Geophysics and Environment. References Cara F., Vinçani F., Leka P., Hyseni R., 2003 - Complex economical valuation of Quaternary deposition according to the environmental geological map series. Albanian Workshop 18 December 2003, Tirana, Albania. Hoxha J., Vinçani F., Leka P., Dhimitri A., 2003 – The maps of Quaternary Depositions such as the part of the Geological-Environmental Maps series for the evaluation of ground and resources, Tirana- Durres- Kavaje region. Albanian Workshop 29-31 March 2004, Tirana, Albania. Leka P., Vinçani F., 2003 – Administration of territory and natural resources: Geology- Territory-Environment of Tirana – Durres – Kavaje during 2001-2003 years (Geophysics). Center of Geophysics, Tirana, Albania. Tehessalov L.E., 2003 - Integrated information system for solution of nature use problems, Geoinformatica N. 2, April- January 2003, Moscow, Russia.


682


P10 - 03

DIGITAL PETROLEUM DATABANK AS A POWERFUL TOOL FOR FUTURE NEED'S PREDICTION OF OIL COMPANIES (EXPERIENCES AND SOLUTIONS) Navid Amini, Hosein Hahsemi Institute of Geophsyics, University of Tehran, Iran

Introduction In these days, benefits of having a database and a data management system are so essential for many oil companies, especially whom are active in exploration & upstream sector. Most of the companies prefer to establish a database for managing immense volume of data that have been recorded since early years of exploration up to now. In these data banks, the data consists of geophysical, surveying, drilling, reservoir engineering, petrophysical and geological data. These data are in variety of formats, hard copy and digital that should be converted to standard formats for archiving. In this paper we are going to say some of our experiences that we obtained during recent projects. Upstream Geographical Information Systems of an international oil company approximately has more than 1000 data layers with various scales and special assortments including descriptive information derived from operations and more than 20 applications have been implemented in it, for data entry and retrieval. These applications have more than hundreds different data entry forms. Why a data base? As the global need to energy resources increases the need for finding new reservoirs increases too. On the other hand in order to decrease the risk of dry wells, companies prefer to do more studies in oil filed before drilling. So the volume of data has become very large, and storing this volume of data is a problem. Seismic data are a good case that are recorded on tapes and tapes need to a climate controlled environment, these tapes occupy a large amount of space and danger always threaten them, also quality decreases after few years and they should be duplicated to new tapes to prevent probable damage to the archive. This jobs are very time and money consuming but unavoidable, because the operation cannot be repeated. Another problem is data retrieval. The data that is archived should be retrievable as soon as possible. One of most important draw backs of traditional archiving systems is hard procedure of data retrieval, though more than 70% of geophysicists are not satisfied with the mechanism (Chidwick, 1996); this bad performance limits companies to use their old experiences, such as experiences from former operations in an area or extracting new information by reprocessing old data with modern tools. And most important, searching through these archives is very hard and we’d better to say they are not retrievable. These reasons justify establishing a data base. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 683


How a data base? The data base that you are going to design should have some specifications that facilitate data archiving and data retrieval. The most important part of a data base is the structure of its algorithm (software). It wouldn’t be an exaggeration to say that the number of geophysicist members of a data base designing team should be more than programmers, because the geophysicists are end users of this system, and it should satisfy them at first step. The great remedy is to either design or buy an existing database package. Any way, the data base should be flexible and can adapt it self to ongoing changes. In the last step a GIS based GUI can join to data base in order to facilitate data retrieval. For example in one of our projects a Customized version of DISCover is implemented, which contains different modules such as: DISCover , Map Browser, DISCover , Map Server, DISCover , Map Linker, Security Core to control access levels, DAS (Digital Archive System) and much more. An object oriented structure is strongly recommended; because data retrieval becomes faster also in business relations between companies the discrete objects are more applicable and useful (Chidwick, 1996); like a special seismic line and so on. The data base should have ability of archiving variety of standard formats of data, it’s very ideal if it can reformat data to other formats in order to compress or view data, for example SEGY to ASCII and vice versa. They were some characteristics of a good data base, but it is empty yet and we should fill it. Data gathering & feeding When a data base is established at the beginning, we encounter a huge volume of data that should be archived. In other word, the new projects that are in operation can be archived gradually as the work progresses, but in old projects we have a cumulated large amount of data that archiving them is a serious problem. One of good solutions for this problem is establishing a data gathering & feeding group. This group works temporally and tries to compensate years which the company hadn’t any data base. The feeding group has several categories: Subsurface & Surface geology, Tectonics, Geophysics, Geochemistry, Paleontology, surveying, reservoir, well test, petrophysics and Drilling group. Each category consists of some semi-skilled people that have educations related to their work and some operators. These semi-skilled people extract information from reports and maps and organize them and operators enter that information to data base. Each of these categories has some supervisors from client that supervise and control the quality of their works and help them in organizing data. Feeding the data base needs a close cooperation between company’s experts, supervisors and feeders. In fact this cooperation cannot be formed easily, because the data owner and data base maker ideas are different, or maybe the importance of a data base is not understood by the oil company. Conclusions Establishing a data base is unavoidable in most of oil companies, because they can use their valuable experiences easily and rescue expensive data from degradation. Designing a data base is a vital step that needs prediction of future’s needs. Also data base feeding, needs to a group that can compensate years which it hadn’t any data base. This data base will help companies for making better decisions about their future programs and decrease the risks.


684


Digital Documents GIS Layers

DISCover™ System Management Facilities

DISCover™ Core System

Layer Data Set

Descriptive Data Set

Relative Descriptive Data

Digital Documents Data Set

DISCover™ Map Internet

Browser

DISCover™ Map

DISCover™ Application(S)

Server Network Area DISCover™ Map Linker

DISCover™ Security Core

- DISCover™ GIS solution infrastructure -



References Bartz, W. E., 1994, Data management: Present state and future trends, 64th Ann. Internat. Mtg: Soc. of Expl. Geophys., 1619. Chidwick, J. M., 1996, Seismic data management systems: Issues and advantages, 66th Ann. Internat. Mtg: Soc. of Expl. Geophys., 993-996. Chang, H. H., Barron, C. F., Hussein, H. S. and Barnes, B. S., 1991, Data management in 3-D marine seismic processing, 61st Ann. Internat. Mtg: Soc. of Expl. Geophys., 1381-1382. Staerkebye, J., Knudsen, K. R., Tonstad, K., Bomstad, K. and Torbjornsen, S., 1994, A joint Norwegian data management project for E & P data: A new challenge for the oil industry, 64th Ann. Internat. Mtg: Soc. of Expl. Geophys., 850-852.


686


P11 - 01

STATISTICAL ANALYSIS OF THE AFTERSHOCK SEQUENCES THAT OCCURRED IN TURKEY DURING 1995-2004 Serkan Öztürk, Yusuf Bayrak Karadeniz Technical University, Department of Geophysics, Trabzon, Turkey

Summary A statistical analysis on eight aftershock sequences distributed on the different regions of Turkey is examined in this study. A complete and homogenous catalog of aftershock sequences is provided for the main earthquakes with MD≥5.2, which occurred in Turkey the last nine years. The data used are taken from KOERI. The positive relations between the numbers of aftershocks, maximum magnitude of aftershocks, aftershock area versus the magnitude of the main shock, b-value and minimum magnitude of aftershocks, and p-value and c-value are calculated, whereas a negative relation between b-value and maximum magnitude of aftershocks is observed. However, no correlation is found between b-value, p-value, c-value versus the magnitude of the main shock, p-value versus the maximum and minimum magnitude of aftershocks, and b and p-value. Regarding the faulting types, it is not observed a relation between the seismicity parameters and faulting types. On the other hand, physical properties of the seismicity parameters of aftershock sequences may be controlled by the rupture mechanism of the main shock and geological structure of an aftershock region. Introduction The statistical properties of the occurrence of aftershocks have long been one of the main objects of seismological studies in connection with the processes of earthquake generation and may be a factor to be considered in a general study of earthquake occurrence. The main properties of aftershock sequences have been described by many seismologists (e.g., Utsu, 1961; Ranalli, 1969; Guo and Ogata, 1997; Drakatos and Latoussakis, 2001). The tectonic setting and the mode of faulting are factors other than the fault surface properties that might control the behavior of the sequences (Kisslinger and Jones, 1991). Characteristics of sequences that may provide useful information are the spatial distribution, the total number of aftershocks, and the rate with which the sequence days with time. In this study, a statistical analysis of the spatial and temporal characteristics of the aftershock sequences, which recently occurred in Turkey, of Dinar earthquake of 1 October 1995, İzmit earthquake of 17 August 1999, Düzce earthquake of 12 November 1999, Afyon earthquake of 3 February 2002, Tunceli earthquake of 27 January 2003, Bingöl earthquake of 1 May 2003, Denizli earthquake of 26 July 2003, and Erzurum earthquake of 28 March 2004 is made. The aim of this investigation is to determine reliable relations between the parameters such as the magnitude of the main shock, the number of the aftershocks, aftershock area, the magnitude of the maximum and minimum aftershocks, b-value of frequency-magnitude distribution, p-value describing the decay rate of aftershock activity, and c-value that depends on the rate of activity in the earliest part of the sequences. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 687


Data and Result of Statistical Analysis The data used in this study are taken from the website of the Bogazici University, Kandilli Observatory and Earthquake Research Institute (KOERI). The catalogs are homogenous for duration magnitude, MD, and contains about one month’s time period from the main shock. A list of 8 aftershock sequences, which includes the maximum (Mamax) and minimum (Mamin) magnitudes of aftershocks as well as the general information of the earthquake occurrence, is given in Table 1. Also, the magnitude of the main shocks (MD), the number of aftershocks (N), completeness magnitude (Mc), aftershock area, and b, p, and c-values for each aftershock sequence are given in Table 2. The estimate of Mc is based on the assumption of G-R’s powerlaw distribution against magnitude and is used in the calculation of b-values, while M≥Mc is selected for the calculation of p-values. Year

Month

Day

Date

Latitude

Longitude

1995 1999 1999 2002 2003 2003 2003 2004

10 08 11 02 01 05 07 03

1 17 12 03 27 01 26 28

15:57:12.6 00:01:39.1 16:57:19.5 09:11:28.0 07:26:22.0 03:27:04.0 11:36:49.0 06:51:09.0

38.06 40.75 40.76 38.58 39.46 39.01 38.11 39.88

30.15 29.86 31.16 31.25 39.77 40.47 28.89 40.87

Depth (km) 5.0 17.0 10.0 5.0 5.0 5.0 4.3 5.0

Magnitude (MD) 6.0 6.7 6.5 6.0 6.2 6.4 5.2 5.3

Mamax

Mamin

4.9 5.5 5.4 5.3 4.2 4.6 4.7 4.0

2.9 2.3 2.3 2.5 3.0 2.7 2.2 2.7

Faulting Type NF SSF SSF NF SSF SSF NF SSF

NF: Normal Faulting, SSF: Strike Slip Faulting Table 1. Catalog of the aftershock sequences in Turkey (1995-2004)

A complete and homogenous catalog of aftershock sequences is provided for the main earthquakes with MD≥5.2, which occurred in Turkey the last nine years. Figure 1 shows the result of analysis. Several relations are investigated for the whole data set. Following formulas are developed between the N and MD, Mamax and MD, aftershock area (A, in km2) and MD, bvalue versus Mamax and Mamin, and p-value and c-value using the least squares method:

LogN = 0.59M D − 1.08 Ma max = 0.59M D + 1.24 LogA = 0.44M D + 15.83 b = 3.86 − 0.53Ma max b = 1.20Mamin − 1.79 p = 1.21c + 0.71

(1) (2) (3) (4) (5) (6)

Earthquake

Log N

MD

Log A (km2)

Mc

M≥Mc

c-value

b-value

p-value

1 October 1995 Dinar Earthquake 17 August 1999 İzmit Earthquake 12 November 1999 Düzce Earthquake 3 February 2002 Afyon Earthqauke 27 January 2003 Tunceli Earthquake 1 May 2003 Bingöl Earthquake 26 July 2003 Denizli Earthquake 28 March 2004 Erzurum Earthquake

311

6.0

18.8664

3.0

3.3

0.362

b=1.52±0.04

p=1.06±0.17

1082

6.7

18.7907

2.8

3.1

0.158

b=1.04±0.03

p=0.84±0.07

961

6.5

18.5503

2.8

3.2

0.344

b=0.96±0.05

p=1.36±0.12

124

6.0

18.5467

3.1

3.1

0.130

b=0.77±0.10

p=0.92±0.13

171

6.2

18.5986

3.0

3.1

0.050

b=2.21±0.04

p=1.04±0.09

459

6.4

18.5110

3.2

3.3

0.303

b=1.51±0.04

p=0.77±0.10

116

5.2

17.9008

3.0

3.0

0.427

b=1.15±0.06

p=1.28±0.23

150

5.3

18.2636

3.0

3.0

0.000

b=1.23±0.08

p=0.51±0.07

Table 2 Characteristic parameters and statistics of the aftershock sequences


688


Figure 1 Relationships between the seismicity parameters of the aftershock sequences

The variability of seismicity parameters for aftershock sequences may be related to the tectonic condition of the region such as material properties, slip, stress, and velocity, and rupture mechanics during the main shock (Bayrak and Öztürk, 2004). For the aftershock sequences, it can be drawn some figures and from these figures it can be taken several statistics on the occurrence of aftershocks. Utsu (1961; 1969) is made a statistical study of aftershocks from 1926 through 1959 and stated a relation between aftershock area, maximum magnitude of aftershocks versus the magnitude of the main shock, and b and p-values, however, not a relation p-value and the magnitude of the main shock. Also, Drakatos and Latoussakis (2001) analyzed a catalog of aftershock sequences in Greece and suggested a linear relation between the numbers of aftershocks, maximum magnitude of aftershocks versus the magnitude of the main shock. As Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 689


shown in Figure 1, there are positive correlations between the numbers of aftershocks, maximum magnitude of aftershocks, aftershock area versus the magnitude of the main shock, b-value and minimum magnitude of aftershocks, and p-value and c-value. On the contrary, there is a negative relation between b-value and maximum magnitude of aftershocks. However, no correlation is found between b, p, and c-values versus the magnitude of the main shock, p-value versus the maximum and minimum magnitude of aftershocks, and b and p-value. Also, regarding the faulting types, we could not observe a linear relation between these aftershock parameters and faulting types. Thus, the rupture mechanism of the main shock and geological structure of an aftershock region may control the statistical variations of the seismicity parameters of aftershock sequences. Conclusions A statistical analysis of the spatial and temporal characteristics of eight aftershock sequences, which recently occurred in Turkey, is made in this study. For this purpose, a complete and homogenous catalog of aftershock sequences is provided for the main earthquakes with MD≥5.2, which occurred in Turkey the last nine years. The catalogs prepared for this study are taken from KOERI and contain the aftershock sequences of Dinar earthquake of 1 October 1995, İzmit earthquake of 17 August 1999, Düzce earthquake of 12 November 1999, Afyon earthquake of 3 February 2002, Tunceli earthquake of 27 January 2003, Bingöl earthquake of 1 May 2003, Denizli earthquake of 26 July 2003, and Erzurum earthquake of 28 March 2004. The relation between the parameters of the aftershock sequences, N-MD, Mamax-MD, A-MD, b-Mamax, b-Mamin, b-MD, p-MD, p-Mamax, p-Mamin, c-MD, p-b, and p-c, have been investigated using the data of eight aftershock sequences with the least squares method. It is observed positive relations between the N and MD, Mamax and MD, A and MD, b and Mamin, and p and cvalues. On the contrary, a negative relation is found between b and Mamax. However, there is no relation between b and MD, p and MD, p and Mamax, p and Mamin, c and MD, p and b-values, and faulting types and these aftershock parameters. Thus, it can be said that the spatial and temporal properties of aftershock sequences are strongly related rupture mechanics during the main shock and local material properties with in the crust. References Bayrak, Y., Öztürk, S., 2004, Spatial and temporal variations of the aftershock sequences of the 1999 İzmit and Düzce earthquakes, Earth Planets Space, 56, 933-944. Drakatos, G., Latoussakis, J., 2001, A catalog of aftershock sequences in Greece (1971-1997): Their spatial and temporal characteristics, Journal of Seismology, 5, 137-145. Guo, Z., Ogata Y., 1997, Statistical relation between the parameters of aftershocks in time, space, and magnitude, J. Geophys. Res., 102(B2), 2857-2873. Kisslinger, C., Jones L. M., 1991, Properties of aftershock sequences in Southern California, J. Geophys. Res., 96(B7), 11,947-11,958. Ranalli, G., 1969, A statistical study of aftershock sequences, Ann. Geofisica, 22, 359-398. Utsu, T., 1961, A statistical study on the occurrence of aftershocks, Geoph. Mag., Tokyo, 30, 521-603. Utsu, T., 1969, Aftershocks and earthquake statistics (I): Some parameters which characterize an aftershock sequence and their interrelations, J. Faculty Sci., Hokkaido University, Ser. VII (Geophys.), 3, 129-195.


690


P11 - 02

MECHANICAL COUPLING OF MANTLE SEISMICITY AND CRUSTAL-SCALE FAULTS IN THE SE CARPATHIAN FORELAND Dana M. Mucuta, Camelia C. Knapp University of South Carolina, Columbia, USA

Summary An inexpensive and uniquely suited method involving the integration of active and passive-source seismic data is employed in order to study the nature of the relationships between crustal seismicity and geologic structures in the southeastern Carpathian foreland of Romania, and the possible connection with the Vrancea Seismogenic Zone (VSZ), one of the most active seismic areas in Europe. This study makes use of two reprocessed 20 seconds two-way travel time (TWTT) seismic reflection profiles (Ramnicu Sarat and Braila) from the Focsani Basin and crustal seismicity (down to 50 km) data available from the Romanian Earthquake Catalog. The goal of this study is to establish whether there is a mechanical coupling between the Southeastern Carpathian foreland deformation and Vrancea mantle seismicity in order to discriminate between competing hypotheses explaining the spatial and temporal setting of VSZ. Introduction The Carpathians are considered to have formed during two main orogenic phases, the first in the Late Cretaceous, coinciding with the closure of the Tethys Ocean, leading to the amassing of the inner crystalline thrust sheets and a later phase in the Early to Middle Miocene that formed the exterior nappes (Sandulescu, 1984). Presently the Carpathian nappes sit on the EastEuropean Platform to the east, the Moesian Platform to the south and the Dacia-Tisza Plate to the west, enveloping the Transylvanian Basin in the middle and surrounded by foreland basins both east and south. Located at the bend area between the Southern and Eastern Carpathians, the Vrancea Seismogenic Zone exhibits a peculiar type of mantle seismicity not readily explained by classical subduction. Though subject of many studies, the geodynamic setting of the Vrancea area is still subject of debate and conclusive constraints need to be found in order to explain its confined spatial extent with earthquakes occurring regularly (~ 25 years), in a 30 by 70 km2 area and to depths of up to 220 km, essentially in a vertical cylinder atypical of a Wadati-Benioff plane. Historically, mantle earthquakes are understood and explained by subduction of brittle, dense oceanic lithosphere underneath oceanic or continental lithosphere (Isacks et al., 1968), with earthquake hypocenters aligning along Wadati-Benioff planes marking the subducting slab. Therefore it is not surprising that subduction is the most favored hypothesis to explain mantle earthquakes in the Vrancea Area. Bird (1979) proposed delamination as a model for continental lithosphere with large and gravitationally unstable orogenic roots and Seber et al., (1996) Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 691


proposed delamination as an alternative for intermediate-depth earthquakes in the Alboran Sea. Delamination is thought to be caused by gravitational instability of over-thickened lithosphere that detaches along a horizontal interface in the lithosphere and sinks into the mantle (Figure 1c) and is currently considered as an alternative hypothesis for explaining Vrancea mantle earthquakes. The Focsani Basin, located in the SE Carpathian foreland, in front of the Vrancea area is only a small part of the foreland basin formed during and after the Alpine continental collision and it drew a lot of attention due to its (1) vicinity to the VSZ, (2) sedimentary thickness (~18 km of Miocene to Quaternary sediments), (3) ongoing subsidence (rates of 2mm/year), (4) localized and unusually low topography, (5) crustal scale faults oriented NNW-SSE, (6) documented normal faults concentric about the Vrancea area and (7) wide spread crustal seismicity in what seems to be a compressional regime (Cornea et al. 1981, Radulescu, 1988, 1996, Matenco, 2000). It also has economic significance due to its oil fields thus numerous seismic lines, both shallow (5 s) and deep (16-20 s), were acquired in the basin, providing data for the oil industry as well as for scientific research. Crustal seismicity of magnitudes less than 6 is recorded in the foreland and is spatially offset (~50-100 km eastward) from mantle seismicity in the Vrancea area but there are good reasons to believe that the two seismogenic areas are connected and are, in fact, governed by the same geologic process. Based on recent results from reprocessed deep seismic lines in the Focsani Basin (Mucuta et al., submitted) along with crustal seismicity data, spatially integrated in a GIS format we attempt to resolve the nature of this relationship and at the same time bring a better understanding of the processes driving it. Hypotheses and current results The debate on the nature of the processes controlling the unusual intermediate depth seismicity, volcanism and surface deformation in the Vrancea area currently involves three main models (Figure 1 a, b, c): a) The ‘subduction in place’ hypothesis (Wortel and Spakman, 2000; Gvirtzman, 2002) assumes subduction of oceanic lithosphere at the location of the present day VSZ thus accounting for the seismicity but fails to explain the presence of the Neogene age volcanic chain ~150 km towards the west. It does offer a valid explanation for the ongoing subsidence in the Focsani Basin possibly triggered by the pull of the inferred subducting slab supposedly still attached to the upper mantle. b) The ‘oceanic slab break-off and retreat’ hypothesis (e.g. Linzer, 1996) presumes that a remnant of the Tethys oceanic lithosphere subduction detached from where the youngest volcanic mountains (Persani) are and migrated laterally to its actual position under the VSZ thus accounting for the location of the calc-alkaline volcanic occurrences and the present-day occurrences of mantle earthquakes in VSZ. However, the decoupling between the crust and the mantle fails to explain (1) the subsidence of the foreland in front of VSZ, and (2) how stress is transmitted through the asthenospheric gap between the inferred detached slab and the crust, to account for the intermediate-depth seismicity. c) The ‘continental delamination’ hypothesis assumes that a mass of continental lithosphere (Knapp et al., in press) is delaminating along a horizontal mid-lithospheric interface and sinking into the mantle thus accounting for the present-day seismicity which does not align along a dipping Wadati-Benioff plane but clusters in such a narrow volume. The active subsidence of the Focsani Basin would indicate that, in this case, the delaminating body is still attached to the crust underneath the basin. Two deep (20 s TWTT) seismic reflection profiles, recorded in the SE Carpathian foreland, ~70 km eastward of VSZ, were reprocessed, targeting the lower crust structures. A detailed description of the processing techniques used and images of seismic sections were provided in (Mucuta et al., submitted). The interpreted (~70 km long, 60 km deep) combined cross-section (Figure 1d) reveals (1) a thick sedimentary cover increasing in thickness towards VSZ, (2) thinning of the crystalline crust towards VSZ inconsistent with westward subduction, 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

692


substantiated by (3) an east dipping Moho, (4) strong fracturing of the basement by seemingly normal faults, and (5) evidence for the crustal scale fault Peceneaga-Camena with offsets both in the sedimentary section and at the Moho level. The east dipping Moho and the thinning of the crust towards VSZ challenge the subduction in place hypothesis that would require a Moho dipping towards the seismically active Vrancea area as well as crustal thickening towards VSZ.

Figure 1 Hypotheses tested: a) Subduction in place; b) Slab break-off; c) Continental delamination. Color coding: continental crust (orange), oceanic crust (purple), mantle lithosphere (red), sedimentary cover (gray), asthenosphere (white). Blue dots represent earthquake hypocenters. Black box represents location of interpreted section on right (d); d) Interpretation of reprocessed deep seismic lines integrated in a transect traversing the VSZ.

Methodology Based on these results we now address spatial and temporal relationships between the seismogenic foreland crustal structures, especially related to neo-tectonic deformation, with the seismogenic mantle body, thus attempting to provide an important constraint on the geodynamic evolution of the VSZ. We attempt at this time to verify the validity of the slab break-off hypothesis by testing the alternative mechanical coupling hypothesis and for this we make use of seismological data from the Romanian Earthquake Catalog, specifically crustal seismicity occurring in the foreland. In order to obtain the most reliable spatial analysis, crustal events with M>2.5 will be relocated using velocity functions derived from velocity analysis of reprocessed seismic sections. This will not only give accurate locations but it will also determine the depth range and type of focal mechanisms responsible for the crustal seismicity. Relocated events are to be projected onto the seismic sections in order to tie faults and hypocenters and establish their spatial relationships and in doing so identify the distribution, type and geometry of active crustal faults and their possible continuation in the upper mantle. Surface geology, topography, seismic sections and relocated events will be integrated in a GIS database enabling geo-referencing, accurate positioning and analysis of spatial relationships between crustal and upper-mantle structures and seismicity. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 693


Conclusions Relocation of crustal seismicity and projection of hypocenters onto available seismic sections from the SE Carpathian foreland is seen as a conclusive means of addressing the mechanical coupling hypothesis between the foreland crustal structures and Vrancea mantle seismicity. If the ‘mechanical coupling’ hypothesis proves to be valid, the implication is that the Vrancea seismogenic body is most likely undetached from the overlying crust thus the current model for the geodynamic evolution of the VSZ that involves subduction ~150 km toward the NW and slab break-off would have to be seriously revised. Previous results, attained by reprocessing of the two deep seismic lines, already question the validity of the subduction in place hypothesis therefore one hypothesis that deserves due consideration and thorough analysis is the continental delamination hypothesis making the VSZ an uniquely suited place to study such a geologic process. References Cornea, I., Radulescu, F., Pompilian A., Sova, A., 1981, Deep seismic sounding in Romania, Pure Appl. Geophys., 119, 1144-1156. Gvirtzman, Z., 2002, Partial detachment of a lithospheric root under the southeast Carpathians: Toward a better definition of the detachment concept, Geology, 30, 51-54. Isacks, B., Oliver, J., and Skyes, L. R., 1968, Seismology and the new global tectonics, Journal of Geophysical Research, 73: 5855-5899. Knapp, H., J., Knapp, C., C., Raileanu, V., Matenco, L., Mocanu, V., Dinu, C., 2005, Crustal constraints on the Origin of Mantle Seismicity in the Vrancea Zone, Romania: The Case for Active Continental Delamination, Tectonophysics Special Issue on “CarpathianPannonian System”. Linzer, H-G., 1996, Kinematics of retreating subduction along the Carpathian arc, Romania, Geology, 24: 167-170. Matenco, L., Bertotti, G., 2000, Tertiary tectonic evolution of the external East Carpathians (Romania), Tectonophysics, 316 (3-4): 255-286. Mucuta, D., Knapp, C., Knapp, J., Constraints from Moho Geometry and Crustal Thickness on the Geodynamic Origin of the Vrancea Seismogenic Zone (Romania), submitted to the SEISMIX 2004 Tectonophyics Special Volume. Radulescu, F., 1988, Seismic models of the crustal structure of Romania, Rev. Rom. de Geol., Geophys. et Geographie, Volume 32. Radulescu, F., Mocanu, V., Nacu, V., Diaconescu, C., 1996, Study of recent crustal movements in Romania: a review, J. Geodynamics, Vol. 22, no. ½, pp. 33-50. Sandulescu, M., 1984, Geotectonica Romaniei (Geotectonics of Romania), Ed. Tehnica, Bucharest, 450 pp (in Romanian). Seber, D., Barazangi, M., Ibenbrahim, A., Demnati, A., 1996, Geophysical evidence for lithospheric delamination beneath the Alboran Sea and Rif-Betic mountains, Nature, 379: 785-790. Wortel, M.J.R., Spakman, W., 2000, Subduction and slab detachment in the MediterraneanCarpathian region, Science, 290 (5498), 1910-1917.


694


P11 - 03

IRAN EARTHQUAKES AND THE CRUSTAL STRUCTURE INFERRED FROM RAYLEIGH WAVES OBSERVED IN TURKEY Timur Tezel1, Murat Erduran1, Özcan Çakir1, Ömer Alptekin2 1 Karadeniz Technical University, Trabzon, Turkey 2 Istanbul University, Istanbul, Turkey

Summary The shear wave velocity structure of region between central Turkey and Iran is determined using single-station measurements of Rayleigh wave group velocities in the 8-50 second period ranges. Group velocity dispersion data of fundamental mode Rayleigh waves for 5 wave paths that are constituted from 4 earthquakes which are recorded at MALT (Malatya) and ISP (Isparta) stations. Dispersion curves are measured by applying the multiple filter technique to properly rotated three component digital seismograms. A differential inversion technique is applied to these group velocity dispersion data to determine the S-wave velocity structures of the crust and upper mantle. The results demonstrate that the area has a crustal thickness varying between 4050 km and uppermost mantle S-wave velocities between 4.1-4.3 km/s. Introduction The purpose of this study is to determine the S-wave velocity structure of the crust and upper mantle region between central Turkey and Iran by surface wave dispersion analysis and to expound the related tectonic significance. Extracting the fundamental mode of surface waves and determining their dispersion it is possible to estimate the average structure of the earth along the path that waves have travelled. Turkey is one of the most seismically active regions in the world. It is located within the “Mediterranean Earthquake Belt”, whose complex deformation results from the continental collision between the African and Eurasian plates. This activity is the result of interactions between northward moving African and Arabian plates and the relatively stable Eurasian plate (Bozkurt, 2001). The interaction of the Arabian plate with the Eurasian plate has played a major role in building the young mountain belts along the Zagros-Bitlis continentcontinent collision zone. Arabia’s northward motion is considered to be the primary driving force behind the present-day westerly escape of the Anatolian plate along the North and East Anatolian fault zones as well as the formation of the Turkish and Iranian plateaus. Chen and Molnar (1980), concluded that uppermost mantle compressional wave velocities over a broad region in Turkey are 7.73 km/s and lie beneath a crust of uniform but poorly determined thickness, moreover, the crustal thickness for Iran varies between 34-49 km from north to the south. Hearn and Ni (1994) showed that low Pn velocities (5.0) and adequate epicenteral distance for surface wave study. Rayleigh and Love wave components are obtained by rotating Z, EW and NS components into the vertical, radial and transverse components. Unfortunately, due to complication of the radiation patterns and propagation effects, sometimes the qualities of one or two components may not be so good. Poor data from such cases were not used for this study.

Figure 1 Used epicenters and stations. Triangles and stars are indicating stations and earthquake epicenters, respectively.


696


Method The Rayleigh wave data is taken from the vertical component. During computation of observed group velocities, firstly the records are corrected for instrumental response and than a %10-cosine time window with maximum 5 km/s, and minimum 2 km/s group velocity limits are applied. To see the signal to noise improvement at lower periods, seismograms are band-pass filtered at 8-80 sec cut off periods with a two sided, two poled Butterworth filter. A multiple filtering analysis (Dziewonski and Hales, 1972; Herrmann, 1973) was applied to each surface wave train to obtain the fundamental mode group velocity curve. Surface waves are effected from the phase uncertainties at the source. Therefore, the inversion results of surface waves show some scattering and may differ for each earthquake (Erduran, et.al.,2001). Thus, in using the single station technique to determine the crust and upper mantle structure from surface waves, it is convenient to have a statistical average by using the data from more than one earthquake. Three component seismogram of May, 28,2004 quake recorded at MALT station and typical contoured plots of relative amplitude of wave energy arrivals at MALT station showed in figure 2 for the vertical component of Rayleigh wave. We also used a phase-matched filter (Herrin and Goforth, 1977; Goforth and Herrin, 1979) to identify and remove multipathing arrivals to improve the quality of the determined dispersion curves. To obtain models for region, we used inversion theory, as first proposed by Backus and Gilbert (1970). In the present study we used an interactive program developed by Russell et al. (1984). That program inverts observed group velocities for plane-layered shear velocity structure and uses singular value decomposition (Lawson and Hanson 1974) in stochastic or differential form (Russell 1987). Our inversion starts with an initial model, which is constituted, based on half-space earth model and it has 5 km/s velocity for all layers and uses a non-linear iterative procedure to arrive at a model that satisfies the data. We used a differential inversion method. The differential inversion process minimizes both the magnitude of the error vector between observed and computed velocities and differences between adjacent layers, thereby minimizing large velocity changes between adjacent layers. And in this study we assumed to Poisson’s ratio is 0.25 for all layers. After inversion as mentioned above, if successful convergence has been achieved between observed and computed dispersion curves, theoretical group velocities should agree with observed values within the data uncertainties. We also constituted resolving kernels with the same program packet and resolving kernels refer to sensitivity to shear velocities given reference depths. Our observed and average group velocity curves, estimated shear-wave velocity model and resolving kernels are showed in figures 3 (a), (b) and (c) respectively. 1.00E+5

Z 0.00E+0

-1.00E+5 2.00E+5

NS 0.00E+0

-2.00E+5 1.00E+5

EW 0.00E+0

-1.00E+5 0

200

400

600 SECOND

800

1000

1200

Figure 2 Three component seismogram of May, 28,2004 recorded at MALT station (on the left side) and typical contoured plots of relative amplitude of wave energy for the vertical component of Rayleigh wave (on the right side).


SEISMOLOGY & EARTHQUAKES 4.0

(b)

3.5

DEPTH (KM)

GROUP VELOCITY (KM/S)

(a)

2.0

3.0

2.5

Observed Rayleigh waves Average

2.0 10

100

PERIOD (S)

DEPTH (KM)

(c)

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

RESOLVING KERNELS 2.0

S-WAVE VELOCITY (KM/S) 2.5

3.0

3.5

4.0

4.5

5.0

4.5

5.0

Moho d=45 km Vs=4.15 km/s Average velocity model

2.5

3.0

3.0 7.0 14.5 23.5

35.0

47.5

67.5

3.5 0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

4.0

Figure 3 (a) Observed and average group velocity curves, (b) The estimated shear-wave velocity model (horizontal bars indicate the model uncertainties), (c) Resolving kernels

Results and Conclusions In this study our inversion results indicate that the moho depth in other words crustal thickness is varying between 40–50 km and shear-wave velocity is between 4.1-4.3 km/s at uppermost mantle. Resolving kernels are indicating that our inversion results reliable to 67.5 km depth. Moreover, estimated velocity model showed that there are high velocity values (i.e. ~2.75 km/s) at shallow depths. As mentioned above the Pn velocities lower than normal values for crustal areas beneath Iran-Turkish Plateau because of the active tectonic and volcanism. So, this low velocity values relate to the deformation result of the continental collision processes. References Bozkurt, E., 2001, Neotectonics of Turkey – a synthesis, Geodinamica Acta 14, 3-30. Chen, C. Y., Molnar, P., 1980, The Uppermost Mantle P Wave Velocities Beneath Turkey and Iran, Geophys. Res. Lett., 7, 77-80. Dziewonski, A., Hales, A. L., 1972, Numerical Analysis of Dispersed Seismic Waves, In: Methods in Computational Physics, Vol. 11, Bruce A. Bolt (Editor), 39-85, Ac. Press. Erduran, M., Çakır, Ö., Çınar, H., 2001, Anadolu kabuk yapısının bölgesel Rayleigh ve Love yüzey dalgaları ile yorumu, Jeofizik, 15, 51-62, (In Turkish). Goforth, T., Herrin, E., 1979, Phase-Matched Filters: Application to the Study of Love Waves, Bull. Seism. Soc. Am., 69, 27-44. Herrmann, R.B., 1973, Some Aspects of Band-Pass Filtering of Surface Waves, Bull. Seism. Soc. Am., 63, 663-671. Lazki, A., Sandvol, E., Seber, D., Barazangi, M., Türkelli, N., Mohamed, R., 2004, Pn Tomographic imaging of mantle lid velocity and anisotropy at the junction of the Arabian, Eurasian and African plates. Geophys. J. Int., 158, 1024-1040. Necioğlu, A., 1999, Determination of crustal and upper mantle structure between Iran and Turkey from the dispersion of Rayleigh waves, Journal of the Balkan Geophysical Society, Vol.2, No 4, p.139-150. Russell, D. R., Herrmann, R. B., Hwang, H. J., 1984, SURF; An Interactive Set of Surface Wave Dispersion Programs for Analyzing Crustal Structure, Earthquake Notes, 55, p. 13.


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P11 - 04

CHARACTERISTICS OF THE FOCAL MECHANISM OF THE EARTHQUAKES IN ROMANIA Andrei Bala1, Mircea Radulian1, Emilia Popescu1 Cristoforos Benetatos2 1 National Institute for Earth Physics, Bucharest, Romania 2 Aristotle University of Thessaloniki, Geophysics Department, Thessaloniki, Greece

Introduction The Carpathian Orogen is of Alpine age, composed of many Mesozoic and Cenozoic terranes. Back-arc volcanism, and back-arc extension in the Pannonian area, accompanied the Neogene subduction. A bent paleosubduction zone was recognized in the Eastern Carpathians, along which the original oceanic basement of flysch and the Subcarpathians nappes were consumed. The tectonic plate evolution of the whole Carpathian Arc and Pannonian back-arc Basin indicates that at least three tectonic units have been in contact the East European Plate, the Moesian plate and the Intra-Alpine plate. Some new studies proposed an unstable triple junction model in the area in the Vrancea area (Besutiu, 2001). Only aA small portion of this zone is still seismically active, in the Vrancea area, in the crust and in the intermediate depth domains as well, where the prominent beand toward West of the SE Carpathian Arc lies above a nest of strong recent earthquakes (1940, Mw = 7.7; 1977, Mw = 7.5; 1986, Mw = 7.2; 1990, Mw = 6.9 ) situated between 60 and 200 km depth. This is the only place in the entire Carpathians where folding and thrusting occurred during Pleistocene in the outermost zones between two deep faults in the Moesian Platform. Recent moderate crustal seismic activity (between 10 - 50 km depth and Mmax = 5.5), which together with intermediate depth seismicity, produce high seismic risk in a densely populated area. Catalogue of focal mechanisms for Romanian earthquakes The purpose of this paper is to represent graphically and to interpret the results of the most comprehensive catalogue of Romanian earthquakes for which fault plane solutions are available at the present. We started from a catalogue comprisinge526 seismic events covering the time interval 1929-1997. The catalogue summarizes all theiinformation providedgby different authors (see (Radulian et al., 2002). A number of 68 earthquakes with computed focal mechanism were recently added to the original catalogue, resulting in an up-to-date 594 events database for the period 1929 – 2004. The parameters of the fault plane solutions for the earthquakes occurred after 1994 were computed. The magnitude is given either in MS scale or in ML scale, as it was in the original sources. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 699


In order to have an unique magnitude measure for all earthquakes of the catalogue we used an empirical relation determined using 36 events for converting the local magnitude ( ML- based on duration measurement ) to surface-wave magnitude (MS): MS =1.3156 * ML – 1.92131

(1)

First we analyzed the subset of 68 most recent events. Only 17 events are in the depth range 0 – 80 km, most of them in the Vrancea region, with only 3 having the epicentres along the Intramoesian Fault. In the range of 80 – 100 km depth no focal mechanism of an earthquake was obtained (see Figure 1). The rest of 51 events were generated in the depth range of 100 – 175 km, most of them having an reverse faulting. The last earthquake in the catalogue is a moderate Vrancea earthquake of Mw = 6.0 occurred at h = 112 km depth. This is the best ever recorded earthquake in Romania.. Several representations were carried outon the subset data from Figure 1: 1. Computing the slip vectors of the nodal plane A and represent them on a map and on several depth sections; 2. Computing the stress orientation due to the focal mechanism of the earthquakes and plot them (see Figure 2); 3. Represent the fault plane solutions and the fault length.

Figure 1. Vertical cross section representing the focal mechanism of the earthquakes occurred between from the period 1998 and 2004 (67 events); the position of the cross section on the map of Romania is given in the right corner.

Graphical representation using the focal mechanisms of the Romanian earthquake catalogue 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

700


The focal mechanisms are graphically represented with the computer program RAKE. This program was developed in the Aristotle University of Thessaloniki by Eleni Louvari..The following steps are followed: 1. Convert the catalogue from EXCEL format to the format accepted by the program RAKE; 2. Plot the focal mechanisms on maps and in different depth sections; 3. Plot the seismicity: time variation of seismic activity in terms of depth and magnitude; 4. Compute the stress orientation as resulted fromearthquake focal mechanism and plot them; 5. Represent the fault plane solutions and the fault length. 6. All these parameters are equally important in the determination of the actual tectonic stress in an area where some 3 – 4 destructive earthquakes appear per century. Representing the whole data set (1929 – 2004) The epicentres of the crustal earthquakes (0 – 40 km)are scattered overthe Romanian territory with noteworthy increase of density in the known seismic areas. Asexpected, they cover almost the whole range of nodal plane orientations, as the crustal faults on which they develop have almost all the orientations and slip directions. The intermediate depth earthquakes are confined to a narrow region NE-SW oriented, roughly like the seize of a rectangle of 80 x 30 km2. For better representing them graphically, the catalogue was subdivided in several depth zones, eachof 40 km in depth. 1. The first two zones (40 – 80 km depth and 81 – 100 km depth) are combined in a single onefor the depth interval 40 – 100 km. The same corners were chosen for all sections at 460 / 260 N and 450 / 280 N on a NW – SE direction. Maximum magnitude of the earthquakes in this depth range is 7.2. N P Axis T Axis

W

E

S

Figure 2 Diagram representing the directions of P and T axes of the earthquakes from Fig.1. The diagram is an equal area projection of the lower hemisphere of the focal sphere.

2. The second zone: 101 – 140 km depth interval. Earthquakes of magnitude 7.0 and 6.0 were recorded in this depth range. 3. The third zone: 141 – 180 km depth interval. A great earthquake of magnitude 7.4 was recorded inthis depth range. Conclusions Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 701


The subset of the focal mechanism catalogue of Romanian earthquakes of 1998-2004, represented in Figure 1, is a valuable addition to the original published catalogue (for the earthquakes occurred until 1997) It is proved to be also a good subset sample, with the same characteristics of the whole catalogue: 1. For the crust, the only clustering which is visible is for the dip angle with two pronounced maxima around 500 and 900. The lack of near horizontal fault planes (δ < 300 ) is an indicator of a strike-slip component predominance; 2. In the first domain of intermediate depth earthquakes (40 – 100 km), enhancements of the strike angle distribution are outlined for two conjugate azimuths (around 300 and 3000, respectively), in agreement with the geometry of the Vrancea seismogenic zone, with the seismicity mainly oriented on a NE – SW distribution. The slip is strongly clustered around 900 direction, indicating a clear reverse faulting mechanism on steeply dipping faults (Bala et al., 2003); 3. For the second domain of intermediate depth earthquakes (101 – 140 km depth), it seems that the nodal planes are slightly rotated towards a predominant N – S direction. It is interesting to note that this change is also emphasized by tomography studies, which show a rotation of the lower part of the high-velocity body beneath the Carpathians Arc Bend from a NE – SW direction to a N – S direction (Martin et al., 2004); 4. In the deepest part (h > 140 km) of the subcrustal body the strike angles are more randomly distributed, with some enhancements around 600, 1600 and 3000. Again the slip angle indicates the pronounced dip-slip faulting, but with an increase of a secondary strike-slip component. For the entire subcrustal domain, a clear tendency for the P axis to become horizontal and for the T axis to become vertical is outlined. This tendency is stronger as depth is greater. It reflects a predominant compressive stress regime in the Vrancea intermediate depth range (40 – 180 km ). Acknowledgements This work have been done in the framework of the COST 625 Action: “3-D Monitoring of Active Tectonic Structures” which made possible aShort Time Scientific Mission (STSM) for one of the authors (A. Bala). This author wishes to thank Dr. Luigi Piccardi, president of the Management Committee of the COST 625 Action, for his help. Special acknowledgements are for Prof. Anastasia Kiratzi from the Aristotle University of Thessaloniki, Geophysical Department for hosting the author in the frame of Short Time Scientific Mission, for guiding his scientific work and for the computer program RAKE. The results will be used in CERES contract no. 3-1/5.11.2003. References Bala, A., Diaconescu, M., Biter, M., 2001. Spatial distribution of the earthquakes in the Vrancea zone and tectonic correlations, Romanian Journal of Physics, 46, no. 7-8. 459 – 474. Bala, A., Radulian, M., Popescu, E., 2003. Earthquake distribution and their focal mechanism in correlation with the active tectonic zones of Romania, Journal of Geodynamics, 36, 129 – 145. Besutiu, L., 2001. Vrancea active seismic area: a continental unstable triple junction?, Rev. Roum. GEOPHYSIQUE, 45, 59 – 72. Martin, M., Wenzel, F. and the CALIXTO working group, 2004. High-resolution Teleseismic Body Wave Tomography Beneath SE-Romania (II): Imaging of a Slab Detachment Scenario, submitted to Geophys. J. Int. Radulian, M., Mandrescu, M.N., Panza, G.F., Popescu, E., Utale, A., 2000. Characterization of Seismogenic zones of Romania, Pure Appl. Geophys., 157, 57 – 77. Radulian, M., Popescu, E., Bala, A., Utale, A., 2002. Catalog of fault plane solutions for the earthquakes occurred on the Romanian territory, Romanian Journal of Physics, 47, no. 5–6, 663 – 685.


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P11 - 05

LOCAL SEISMIC EFFECTS AS RESULTED FROM A SEISMIC EXPERIMENT IN ROMANIA Victor Raileanu, Andrei Bala, Bogdan Grecu National Institute for Earth Physics, Bucharest, Romania

Introduction Observational and experimental data proved that the local geology strongly influence the size and distribution of earthquake damages. Anywhere one or more instrumental recordings of the seismic events are available a spectral analysis can identify the frequencies where the soil amplification occurred. For a more complete analysis – densely distributed seismic instruments over the studied region are required. An empirical alternative solution to the instrumental data for estimation of the local effects of earthquakes could be the analysis of microtremors or waves generated by explosions. A reason supporting this alternative is that the microtremors and aftershock studies are based on the same methods to seek for the spectral peaks which are considered to stand for the resonant frequencies of the site. The microtremors method was and still is applied in different countries such as Japan, Mexic, USA and others. A combination of microtremors and earthquake data has been used in Romania to evaluate the site response in Bucharest, followed by a study of site response due to some large Vrancea earthquakes. The Nakamura’s or microtremors method uses a single three component station analysis of microtremors and compares the spectral amplitudes of the horizontal and vertical records. It was applied in different seismic areas and showed some agreement with other results obtained using the spectral analyses of aftershocks or S- and coda waves of the main earthquakes. Nakamura's single station method provides closer results to earthquake data than the soil/rock station pair microtremors method. Spectral peaks are occurring at the same fundamental periods, while the amplitudes of this peaks might be different from one method to the other. Data processing and results Observational data proved that the amplification of microtremors and coda amplitudes in a site is the result of the trapped seismic energy in sedimentary layers. Nakamura showed that the effects of the Rayleigh waves are removed by using the ratio of the horizontal/vertical spectrum components for a seismic station. The peak of the fundamental period is produced by the vertical component of the Rayleigh wave going towards zero. The practical method to evaluate the frequencies where peak amplifications are occurring is to compute the spectral ratios of spectra of the horizontal component (H)/vertical component (V). This study uses 3 components records of the signals generated by explosions along the VRANCEA2001 seismic refraction line running on an alignment WNW-ESE of ~450 km long, from east of the Tulcea town in the Dobrogea, through Vrancea region, to Aiud town in Transylvania, Figure 1, 10 big shots (300-1500 kg charge) have generated the seismic energy for deep crustal investigations. From easternmost end of the line to Aiud town about 150 digital portable instruments with three component receivers (Mark Products, L-4-3D, 1Hz resonant frequency) were deployed. The final seismic records consist of useful seismic signal in the first tens of seconds and of ambient noise in the rest. Such a seismic record represents a complex signal emerged from the deep crustal levels and modulated by the shallow local geology. Influence of the local geology is extracted by using the Nakamura's method. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 703


In the followings we analyze seismic records in 20 sites from the eastern end of line near the Black Sea to the western end near Apuseni Mountaines collected from four shots groupped around each site: Dunavatul de Jos, Cataloi, Macin, Braila, Maxineni, Gulianca, Mihalceni, Bogza, Bordesti, Dumitresti, Vintileasca, Papauti, Moacsa, Valea Crisului, Aita Mare, Hoghiz, Rupea, Bradeni, Medias and Sancrai-Aiud, Fig.1. Geologically speaking all sites are placed on the Quaternary, Neogene or older sedimentary cover of the North Dobrogea Orogen, Moesian Platform/ Focsani Depression, the Eastern Carpathians Nappes and the Transylvanian Depression. A spectral analysis of the first 40 s of each component of is done using a Fast Fourier Transform procedure. The output signal of the spectral analyses is computed within the range 0.1-20 Hz having 200 samples. Then a spectral ratio of Horizontal/Vertical components is computed. The analyzed seismic signal comprises influence from seismic sources, propagation paths and local geology of site. Comparing different spectral ratio curves for the same site but for different shots, they show both common and particular features. The latter are very probably related to the seismic sources and propagation paths, while the common features are caused mainly by local geology. If several spectral ratio curves for the same site but for different shot points are added then the common features will be enhanced and the others will be diminished. The last procedure points out the spectral peculiarities of the site geology and it was applied for our studied sites. Finally more curves of the spectral ratios are derived from seismic records collected from four shots for each site out of the twenty sites. The results for eight sites (Sancrai-Aiud, Rupea, Paputi, Vintileasca, Mihalceni, Braila, Macin, Dunavatul de Jos) are displayed as averaged curves of spectral ratios and plus/minus one standard deviation curve for each site (Figure 2). Conclusions The results point out that amplitude and frequency of the spectral ratios are a function not only of epicentral distance from source to site and energy released by seismic source, but also of the local geological. It is noticed that for the same site and different sources, the frequency windows with high spectral ratios are about the same, regardless of the position and magnitude of the source, which suggest a strong influence of the local conditions upon the spectral content of the signal. Analyses of the spectral ratios show two major distinct cases: • a major peak with high amplitudes (1.7-2.5 units) within the range of frequencies from 1- 5 Hz (0.2-1 s period) for the Dunavatul de Jos, Macin, Rupea and partly for Papauti and Sancrai-Aiud sites; here one or a few shallow thin layers (tens of meters thickness) comprising soft rocks overlie a very thick layer with hard rocks; a secondary peak suggests a thinner layer belonging to the shallow geology; beyond 5 Hz (0.2 s) amplitudes oscillate around one unit; • a peak area within the 0.1-2.5 Hz (0.4-10 s) window with amplitudes of 1.2-1.4 units followed by some insignificant peaks with amplitudes ≤ 1; this is the case for: Braila, Mihalceni, and Vintileasca sites where a thick pile of sediments (hundreds of meters thick) comprising soft and hard rocks generates those low resonance frequencies. Spectral ratio analysis applied on seismic records from explosions proved that the local geology plays a major role in determining of the resonance frequency and amplification in a particular site. In some sites where a shallow, thin and soft sedimentary layer overlies a thicker and hard layer then a high and distinct peak of spectral ratio occur for frequencies > 1 Hz. If a thick mixture of soft and hard sediment pile dominates the sedimentary upper section of a site then we can expect some low resonance frequencies < 2-3 Hz.


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Sancrai-Aiud

Spectral ratio (H/V)

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0 5 10 15 20 5 10 15 20 Fig.2. Spectral amplif ications (thick line) in eight sites, see Fig.1. Plus/minus one standard deviation is drawn with dashed line. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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P11 - 06

GPS AND DEMETER/ICE SPACE OBSERVATIONS: CASE STUDY OF ADRIATIC SEISMIC EVENTS E. Cristea1, M.Y. Boudjada1, K. Schwingenschuh1, J.J. Berthelier2, M. Vellante3, P. Nenovski4, M. Parrot5, P. Pesec1, H.O Rucker1,6, M. Stachel1, W. Voller1, W. Magnes1 1 Space Research Institute, Austrian Academy of Sciences, Graz, Austria 2 Centre d'Etude des Environnements Terrestre et Planétaires Observatoire de Saint-Maur, France 3 Department of Physics, University of l'Aquila, l’Aquila, Italy 4 Geophysical Institute, Sofia, Bulgaria 5 Laboratoire de Physique et Chimie de l'Environnement, Orleans, France 6 Institute of Physics, Karl-Franzens University, Graz, Austria

Summary We report on the analysis of two seismic events which occurred on 24th and 25th Nov., 2004, in the Adriatic region, at the geographic coordinates of (45.66° N; 10.64° E) and (43.24° N; 15.58° E), respectively. Both events had a magnitude bigger than 5 and were separated by a distance of about 594 km. These earthquake events are combined to VLF space observations and ground measurements performed by the DEMETER/ICE experiment and GPS permanent stations, respectively. A method is applied and used to find an eventual correlation between these seismic events and the space observations. This method is principally based on a statistical approach which lead to: (a) study the VLF and the GPS temporal variations four weeks before and after the earthquakes, (b) classify the observed features, and (c) estimate the measurement accuracy and the corresponding source of errors. The main outputs are discussed and combined to previous studies. Introduction Two earthquakes with magnitudes of 5.30 and 5.20 occurred on the 24th and respectively 25th of November 2004 in the Adriatic region (see the map). The daily solutions of several GPS stations operating in the area (see Figure 1) were analyzed in a trial to find a correlation between the earthquakes and the GPS time series of coordinates as well as with the data provided by the Demeter satellite. Use of GPS permanent stations in geodynamics Tectonic plates present relative movements of a few cm per year, and their boundaries are recognized as an earthquake environment. Among different techniques monitoring these zones, GPS delivers position accuracies down to the sub-cm level. The tendency towards near real time and high-resolution data acquisition is an important step in eventual hazard mitigation. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 707


If appropriately situated, GPS permanent stations can monitor earthquakes. An earthquake usually lasts several seconds and it may be observed in the GPS data depending on its magnitude and on the distance of the GPS station from the epicenter. Statistical study of GPS observations For a better image of the phenomena, there have been considered nine weeks of daily solutions, with the two earthquakes occurring in the fifth week. Figure 2 shows the time series of the daily solutions of North, East and Up for one of the closest stations (ASIA), with days 32 and 33 are the days when the earthquakes occurred.

Figure 1 GPS Permanent stations used in the analysis

Figure 2

Time series of coordinates (N, E, U)


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Based on these time series, Figure 3 shows the corresponding histograms:

Figure 3 Histograms of the N, E, U of the four stations

The histograms in figure 4 show a normal distribution of the time series of coordinates. Therefore a Gauss curve was fit to the data, in order to estimate the dispersion (i.e. σ around the average noise level.

Figure 4 ASIA Gauss fit; noise_N=4.95e-005; noise_E=-2.95e-005; noise_U=4.3e-005

DEMETER / ICE experiment The data provided by the DEMETER satellite has been studied above the required location within the same period of time.

Four VLF components are principally observed during two study periods. They correspond to 95% of the total recorded emissions. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 709


Combining the two periods, we have found that: • • •

Orbital features (LT, Latitude, Longitude) show similar variations with a particular decrease of the VLF emissions at longitude of about 220°. Frequency (fmin and fmax) occurrences are identical. The four VLF components: a) Continuum: maximum frequency shifts from 2 kHz to 4 kHz b) Drifting emissions: Two frequency maxima: 12 kHz and 18 kHz c) Bursty radiations: 80% were observed during the upward half orbit

For a better correlation between the GPS and DEMETER data, a higher resolution of GPS data is necessary. This will lead to study the total electron content (TEC) provided by the GPS signal over the seismic regions. In our paper we will detail the applied method for both types of observations, i.e DEMETER / ICE and GPS.


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P11 - 07

EMPIRICAL EVALUATION OF SITE EFFECTS IN ROMANIA BY MEANS OF H/V SPECTRAL RATIOS Bogdan Grecu1 , M. Radulian1, M. Popa1, K.-P. Bonjer2, Andrei Bala1, Victor Raileanu1 1 National Institute for Earth Physics, Bucharest, Romania 2 University of Karlsruhe, Germany

The strong earthquakes from the last two decades (the 1985 Guerrero Michoacan earhquake, Mexico, the 1994 Loma Prieta earthquake, California, the 1995 Kobe earthquake, Japan) have outlined the influence of the local geological conditions on the ground motions during the earthquakes. In Romania, the studies of the August 30, 1986 (Mw = 7.2) and May 30, 1990 (Mw = 6.9) earthquakes have also shown the important role played by the local and regional conditions in the distribution of the effects of the Vrancea intermediate earthquake (Mandrescu, 1995). The local response is a fundamental component in seismic hazard assessment and may be evaluated by different empirical methods based on seismic records. These methods can be separated in two main categories: methods used to calculate the site response with respect to a reference site (e.g. located on a hard rock) and methods which don’t need a reference site, the so called non-reference techniques. For the first ones, if two sites have similar source and path effects, and if the reference site has a negligible site response, then by dividing the spectrum of the measured earthquake motion at a site by that of the reference site one can estimate the site response (Borcherdt, 1970). These approaches identify the fundamental resonant frequency and are considered to be the most reliable (Borcherdt and Glassmoyer, 1992; Beresnev et al., 1998; Hartzell, 1998). Not always a reference site is easy to find and thus other methods had to be developed. In 1989 Nakamura assumed that the site response could be estimated from the horizontal-to-vertical ratio of microtremors, using a single recording station. Although the results of this technique are controversial regarding the amplification level, it was largely used at many sites all over the world by different authors (Lermo and Chavez-Garcia, 1993, 1994; Field and Jacob, 1995; Theodulidis et al., 1996; Konno and Ohamachi, 1998; Mucciarelli, 1998). Lermo and Chávez-García (1993) applied Nakamura’s technique to seismic recordings of earthquakes (S-waves parts) and concluded that this approach (the receiver function technique, Langston, 1979) is able to estimate reliably the frequency of the fundamental resonant mode and correctly predicts the amplification level. In the present paper we concentrate on evaluating site effects at more then 50 seismic stations by applying the last two approaches (Nakamura’s method and the receiver function technique) to noise and to earthquake data recorded during the CALIXTO experiment. The local soil conditions at the considered sites vary from metamorphic rock to thick and water-saturated sedimentary formation. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 711


The CALIXTO 99 (Carpathian Arc Lithospheric X-Tomography) tomographic experiment (Martin et al., 2001) was performed in Romania in 1999 in the framework of the Collaborative Research Center 461 programme (Wenzel, 1997). The general purpose of the experiment was the 3-D image determination of the geodynamic evolution of the Carpathian Arc, and in particular, the evolution of the lithospheric slab in the upper mantle. The CALIXTO network (Figure 1) consisted Figure 1 Distribution of CALIXTO stations. Station E03 is in 120 stations with velocity sensors (30 marked with black circle broadband and 90 short-period). At each CALIXTO station, ground motion was recorded continuously over a 6 month time interval, between May and November 1999. Based on international experiences, the used noise data consisted of several selected segments of 30 seconds. This time window is proven to be sufficiently long to provide stable results. The selected time windows were Fourier transformed using cosine tapering before transformation. After data smoothing, the resultant horizontal spectrum of the EW and NS channels was calculated, and in order to obtain the spectral ratio, the resultant horizontal spectrum was divided by the spectra of the vertical channel (Nakamura’s estimate). Finally, the spectral ratio at a site was calculated as the average of each individual ratio from the same site. The seismic noise field is controlled by several parameters including source characteristics, propagation effects and site conditions. Common microtremor sources include, but are not limited to, cultural activity, wind, weather fronts and sea waves. Variations between microtremors spectra for different components, used to obtain the average spectra, are shown in Figure 2 as examples.

Figure 2 Fourier spectra of microtremors measured at station E03 (see Figure 1) for Z, NS and EW components. The thick orange line represents the average of the spectra.

While the shape of the spectra is very similar for the three components, the H/V ratio obtained at station E03 (Figure 3) has a well pronounced peak at the frequency of 3 Hz. The amplitude of this peak is a factor of 3. A second peak, smaller in amplitude than the first one, can be seen 8 Hz. A number of 56 earthquakes with magnitude between 3.0 and 4.2 were recorded by the CALIXTO stations during May-November 1999. The earthquake data used in this study consisted of 10 seconds of the S-wave parts of the seismograms. The S-wave window contains the strongest part of the seismic recording. In order to select the useable S-windows, we calculated the Fourier amplitude spectrum for both S-window and pre-event seismic noise. We selected only those recordings for which the signal-to-noise ratio is sufficiently high. After 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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selecting the S-wave data, we calculated the spectral ratio for each window by dividing the resultant horizontal spectrum by the vertical one. Finally, the spectral ratio at a site was calculated as the average of each individual ratio from the same site. An example of an H/V ratio obtained from earthquake data is presented in Figure 4a. 7

H/V SPECTRAL RATIO

6 5 4 3 2 1 0 0.1

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Figure 3 The average H/V ratio obtained from noise data (27 noise windows) for station E03. The dashed lines represent the plus/minus standard deviations. 7

H/V SPECTRAL RATIO

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Figure 4a. The average H/V ratio obtained from earthquake data (20 earthquakes) for station E03. The dashed lines represent the plus/minus standard deviations.

The shape of the spectral ratio obtained from earthquake data shows similarities to the one obtained from noise recordings, but with some noticeable differences: the peak at 3 Hz is still present, but with higher amplitudes; a peak around 2.3 Hz appears in case of the spectral ratio obtained from earthquake data and the peak around 1 Hz, due to a pronounced trough in the vertical spectrum (see figure 4b), becomes well developed. Another peak with smaller amplitude can be seen around 0.4 Hz, while the peak at 8 Hz observed for spectral ratio obtained from noise data is shifted to 7 Hz. The clear peak at 3 Hz observable in both ratios, obtained from noise and earthquake data respectively, is related to a surface layer which overlies a structure with higher impedance. In such cases, which we consider as “ideal cases”, the Nakamura approach identifies well the frequency of the fundamental mode of the studied site, while the prediction of the amplification level has still some question marks. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 713


Figure 4b. Fourier spectra of S-wave windows used for obtaining the H/V ratio in figure 4a. The thick orange line represents the average of the spectra.

Our study shows also differences in the spectral ratios estimated from noise data and those determined from earthquake data for stations for which the structure beneath is very complex. In such situations the interpretation of the H/V ratios is difficult to make. An image of the subsurface structure by other methods is mandatory. References Beresnev, I. A., Field, E. H., Van Den Abeele, K., and Johnson, P. A., 1998, Magnitude of nonlinear sediment response in Los Angeles basin during the 1994 Northridge, California, Earthquake, Bull. Seism. Soc. Am. 88, 1079-1084. R. D. Borcherdt, 1970, Effects of local geology on ground motion near San Francisco Bay, Bull. Seism. Soc. Am. 60, p. 29-61. Borcherdt, R., Glassmoyer, G., 1992, On the characteristics of local geology and their influence on the ground motions generated by the Loma Prieta earthquake in the San Francisco bay region, California, Bull. Seism. Soc. Am. 82, 603-641. Field, E. H., Jacob, K. H., 1995, A comparison and test of various site-response estimation techniques, including three that are not reference-site dependent, Bull. Seism. Soc. Am. 85, 1127-1143. Hartzell, S., 1998, Variability in nonlinear sediments response during the 1994 Northridge, California, earthquake, Bull, Seism. Soc. Am. 88, 1426-1437. Konno, K., Ohmachi, T., 1998, Ground-motion characteristics estimated from spectral ratio between horizontal and vertical components of microtremors, Bull. Seism. Soc. Am. 88, 228-241. Langston, C., 1979, Structure under Mount Rainier, Washington, inferred from teleseismic body waves, J. Geophys. Res., 84:4749-4762. Lermo, J., Chavez-Garcia, F. J., 1993, Site effect evaluation using spectral ratios with only one station, Bull. Seism. Soc. Am. 83, 1574-1594. Lermo, J. Chavez-Garcia, F. J., 1994, Are microtremors useful in site response evaluation?, Bull. Seism. Soc. Am. 84, 1350-1364. Mandrescu N., 1995, The 1986 (30 August) and 1990 (30 and 31 May) subcrustal earthquakes: geological and seismological semnifications, St. Cerc. Geofizica, tom 33, p. 31-49. Martin, M., Achauer, U., Kissling, E., Mocanu, V., Musacchio, G., Radulian, M., Wenzel, F. and CALIXTO Working Group, 2001, First results from tomographic experiment CALIXTO’99 in Romania, Gephys. Res. Abst., 3: SE1.02. Mucciarelli M., 1998, Reliability and applicability of Nakamura’s technique using microtremors: an experimental approach, Journal of Earthquake Engineering, 4, 625-638. Nakamura, Y., 1989, A method for dynamic characteristics estimation of subsurface using microtremor on the ground surface. QR of RTRI, Vol. 30, No.1, 25-33. Theodulidis, N., Bard, P.Y., Archuleta, R. and Bouchon, M., 1996, Horizontal-to-vertical spectral ratio and geological conditions: the case of Garner valley downhole in Southern California, Bull. Seism. Sos. Am. 68, 767-779. Wenzel, F., 1997, Strong earthquakes: a challenge for Geosciences and Civil Engineering – a new collaborative research center in Germany, Seism. Research Letters, 68, 438-443. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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GEOLOGICAL INFLUENCE OF THE 1940 AND THE 1977 VRANCEA EARTHQUAKES IN NORTHERN BULGARIA Margarita Matova Geological Institute, Bulgarian Academy of Sciences, Sofia, Bulgaria

Summary The strong intermediate 1940 and 1977 Vrancea earthquakes cause numerous seismic effects in the countries of the Eastern and the Central Europe. Very often the earthquake effects are of significance for the next development of the damaged territories and the society. One of the damaged countries is Bulgaria. The 1977 earthquake provokes important human and material losses. Introduction The data for the influence of the 1940 Vrancea earthquake in the country are relatively limited. The seismic event occurred during the period of the Second World War. The information for the seismic effects related to the 1977 Vrancea earthquake was received as a result of large participation of different state and regional institutions. The earthquake was happened in the peacetime and after the successful finalization of the UNESCO Balkan seismic project. The final results of the study take place in a monograph “Vrancea earthquake in 1977. After-effects in the People’s Republic of Bulgaria” (1983). Applied methods The applied methods include mainly the accumulation and analysis of the seismological information, the field studies of the geological and the seismotectonic situation, also the laboratory investigations of collected rock samples. The seismological information is received partially from the written correspondence with numerous settlements, partially from the seismological interpretation of the recorded seismic movements. The geological and the seismotectonic field observations in the first days after the main shock are of great significance for the analysis of the deformation. The laboratory study permits to obtain knowledge for the main rock characteristics.



Information for the main seismic effects The data for the seismic influence from the Vrancea region are based on earthquake’s catalogues, publications and field investigations. The strongest intermediate-depth Vrancea earthquakes attract the attention. The strongest ones are the 1940 (Mw=7.7) and the 1977 (Mw=7.5) Vrancea earthquakes (Radulian et al., 2002, Bonjer et al., 2002). The information for the 1940 Vrancea earthquake is taken from catalogue (Kirof, 1941). The data for the 1977 Vrancea earthquake are based on publications and field investigations. The field research is accomplished from several collectives of numerous experts-geologists, seismologists and seismic engineers. A lot of Institutes and Laboratories of the Bulgarian Academy of Sciences, from the Sofia University “Kliment Ohridski” participated in the field works. The chief-coordinator of the geologists from the Geological Institute and the Sofia University was Acad. Prof. Ek. Bonchev. The main results of the field, laboratory and theoretical investigations are included in special monograph. Its title is “Vrancea Earthquake in 1977. Its after-effects in the People’s Republic of Bulgaria”. The Editor-in-Chief of the monograph is Acad. G. Brankov (1983). The accent of the recent investigation will be on the seismo-geological and hydroseismological effects. The data for the 1940 Vrancea earthquake are very limited in the literature, but the sames for the 1977 Vrancea one are various and very important. Very short geological notes regarding the investigated territory The Northern Bulgaria represents the southern part of the Moesian Platform. The basement of the platform includes generally metamorphic rocks. These rocks are very dense. Their elasticity and strength are significant. The sediment rocks are very well represented in the platform cover. The density of the different sediments are variable, but their values are lower than the values of the rocks in the basement. The sediments have differences in the mechanic, physic-chemical features, thickness and fracturing. They have specific porosity and water lading. Respectively the distribution of the seismic waves in the platform is influenced from a number of rock characteristics of the regions and the localities. Seismo-geological manifestations It is possible to suppose the appearance of local seismo-geological deformations along the Danube River coast during the 1940 Vrancea earthquake. These seismo-geological manifestations could take place between the towns of Lom and Silistra or along about 75% of the Bulgarian coast of Danube River and the adjacent territories. It is an area where the seismic intensity is of VII degrees MSK. The lithological and the relief conditions permit the development of various seismogeological phenomena. In the regions of the towns of Nikopol and Svishtov, also in the same of the towns of Oryahovo and Rousse, the situation is the most favorable for the manifestations of fractures, landslides, rockfalls and land subsidence. In the cited territories the activation or the new formation of local and sometimes of regional landslides, rockfalls and land subsidence could not be excluded during the 1940 Vrancea earthquake. The fractures could be well represented as well. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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The fractures, the landslides and the rockfalls are widely distributed also as a result of the 1977 Vrancea earthquake. The VII degree’s seismic influence is more limited in the space during 1977 than the same related to the 1940 Vrancea earthquake. During the 1977 Vrancea earthquake the damaged area was about 50% of the Bulgarian coast of the Danube River and the adjacent territories. The considerable fracturing of the coast caused important difficulties in the activities of the Danube ports. The fractures were the most numerous in the towns of Svishtov, Rousse and Nikopol. Their distribution was significant also in the towns of Oryahovo, Tutrakan and Silistra. The landslides and the rockfalls deformed a lot of sectors in the abrupt Danube coast. They destroyed numerous man-made constructions related to the economic life of the country. They provoked difficulties in the transport relations. The land subsidence had relatively limited manifestation. The subsidence took place in faulted territories of the Danube ports. They were well expressed in the towns of Svishtov and Rousse. The geomorphologic and the geological conditions in the regions of the towns of Nikopol, Svishtov and Rouse contributed the development of two kinds of processes. They were related to the appearance or to the additional activation of landslides, rockfalls and land subsidence. The landslides, the rockfalls and the land subsidence were of regional or of local significance. In a lot of cases they were of local importance. Hydro-seismogeological effects I could not find data for this kind of effects related to the 1940 Vrancea earthquake. The cause could be the wartime and the absence of special interest for these effects. There are information and investigations for the hydro-seismogeological effects as a result of the 1977 Vrancea earthquake. The geological, the geomorphologic and the hydrogeological situation contribute the development of considerable number of landslide, land subsidence and liquefaction manifestations. The hydrogeologically induced manifestations of landslides, land subsidence, the liquefaction and the changes in the water characteristics were observed generally in the territory along the Danube River coast and its tributaries. They took place in settlements, in sectors of the transport net and in agricultural territories. They provoked significant damages for the population of the Northern Bulgaria. Conclusions Strong, numerous and periodically manifested intermediate-depth Vrancea earthquakes provoked significant seismo-geological (fractures, landslides, rockfalls and land subsidence) and hydro-seismogeological effects (liquefaction, landslides, land subsidence and changes in the water characteristics) in the territory of the Northern Bulgaria. The effects are dangerous for the population and the geological environment. The investigated effects are related to significant damages of the society, because they cause human losses and destruction of the created by the society constructions. They are risky for numerous monuments from the national and the world cultural heritage as well. The seismo-geological and hydro-seismogeological effects need special studies for the accumulation of additional knowledge for their distribution and development. The information Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 717


for the hydro-seismogeological effects will be applied in the UNESCO-BAS Project “SeismoHydrogeological Vulerability of the Environment and Society in the Balkan Region”(20042006). The good-made studies could be applied for the activities related to the reduction of the manifestations of the seismic effects in the future. Acknowledgement Numerous colleagues of the Geological Institute had made intensive field studies of the 1977 Vrancea earthquake’s effects. Acad. Prof. Ek. Bonchev, Prof. Dr. P. Gočev, Prof. Dr. V. Kostadinov, who are not alive now, participated in the field investigations. The results of their works related to the 1977 Vrancea earthquake are of great importance for the seismic investigations in Bulgaria. References Bonjer, K.-P., Rizescu, M., Grecu, B., Sokolov, V., Radulian, M., Dinu, C., 2002, Ground motion pattern of large and moderate intermediate depth Vrancea earthquakes: first steps towards the generation regional shakemaps in Romania, - Book of Abstracts for the International Conference “Earthquake Loss Estimation and Risk Reduction”, October 2426, 2002, Bucharest, Romania, p. 54. Brankov, G. (ed.), 1983, Vrancea Earthquake in 1977. Its after-effects in the People’s Republic of Bulgaria. Publishing House of Bulgarian Academy of Sciences, Sofia, Bulgaria, 428 p. Kirof, K., 1941, Tremblements de terre en Bulgarie. Liste des tremblements de terre recentis pendant les années 1931-1940. Publishing House of Ya. Bozhinov, Sofia, Bulgarie, 112 p. Matova, M., 2000, Certain effects of seismic liquefaction in Bulgaria. – Proceedings of the Third Japan-Turkey Workshop on Earthquake Engineering, Istanbul, Turkey, p. 21-28. Radulian, M., Bala, A., Popescu, E., 2002, Fault plane solutions as indicators of specific stress field characteristics in Vrancea and the adjacent seismogenic zones. - Book of Abstracts for the International Conference “Earthquake Loss Estimation and Risk Reduction”, October 24-26, 2002, Bucharest, Romania, p.52.


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3D VELOCITY STRUCTURE OF THE 2003 BAM EARTHQUAKE AREA (SE IRAN): EXISTENCE OF A SHALLOW BRITTLE LAYER AND ITS RELATION TO THE HEAVY DAMAGES Hossein Sadeghi1, S. M. Fatemi Aghda2 , Sadaomi Suzuki3, Takeshi Nakamura4 1 Ferdowsi University of Mashhad, Iran 2 Tarbiat Moallem University, Iran 3 Tono Research Institute of Earthquake Science, Japan 4 Kyushu University, Japan

Summary In order to understand the generation mechanism of the Bam earthquake (Mw 6.6), we defined high resolution three-dimensional P- and S-wave velocity and Poisson’s ratio structures of the fault zone. 19,490 P- and 19015 S-wave high quality arrival times from 2396 aftershocks recorded by a temporal high sensitivity seismic network installed in the epicentral region have been inverted. Obtained aftershock distribution clearly delineates the fault plane about 4.5 km west of the known Bam fault. The fault plane steeply dips westward and strikes nearly northsouth. Significant velocity variations of up to 5% are revealed in the aftershock area. Velocity models of seismogenic region are fairly well resolved to a depth of 14 km. At about 2-5 km depth, low velocity anomalies for P-wave are seen in the area, while for S-wave high velocity anomalies are prominent. This shows low Poisson’s ratio anomalies in the shallow part of the fault which correspond to the large slip zone. The low-Poisson's ratio can be explained as brittle rocks and suggested the existence of a shallow asperity. A zone of low Vs and high Poisson’s ratio is clearly imaged in the depth range from 5 km at about (29.11N, 58.35E) and to 10 km toward the south at about (29.02N, 58.35E). This zone suggests the existence of ductile rheologies at seismogenic depths. A small region of high Vp surrounded by low Vp anomalies is imaged at 6km depth beneath the Bam city. This image and the evidences of a growing anticline for the prominent escarpment of the Bam fault may delineate an increased pressure zone by uplifting of the ductile materials. Therefore we suggest the presence of ductile rocks and a strong and brittle shallow asperity of overlying rocks. Uplifting of the ductile rocks causes an active compression to grow the flexure scarp of the Bam fault. Rupturing of the shallow strong and brittle rocks probably made a fresh strike-slip fault that is responsible for the very strong ground motions and intense damage in the Bam Earthquake. Introduction On Friday December 26, 2003, a powerful earthquake in southeastern Iran caused catastrophic damage to the ancient city of Bam, and neighboring villages. In terms of loss in life and casualties, this earthquake was the worst in the year 2003. Near 19% of the population were killed and tens of thousands of people were injured. More than 85% of buildings were destroyed in the Bam area as estimated by the Iranian local government. The main reason for such massive damage may be the poorly constructed houses of unreinforced mud bricks. However, the damage Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 719


was disproportionately and unexpectedly large in comparison with the magnitude of the earthquake. The Bam fault which has long been recognized for its distinctive fluxture scarp, extends along the west side of Baravat village about 5 km southeast of the Bam city. Just after the earthquake it was assumed that the mainshock had occurred in the geological Bam fault. However nobody could find any clear evidence of dislocation on this Quaternary fault. The Bam mainshock was followed by a series of aftershock events. Nakamura et al. (2005) recorded several thousand aftershocks during the period from February 6, 2003 to March 7, 2003. The spatial distribution of aftershock hypocenters is closely linked to the geometry of the fault zone that ruptured the mainshock. They located accurate hypocenters of 2789 aftershocks. The aftershock location does not correspond to the geological Bam fault. The epicenter distribution is linearly over a 20 km in parallel with a line about 3.5 km west of the Bam fault, and the hypocenter distribution shows a nearly vertical trend or a slight tendency to lie farther west with increasing depth from 0 km to 16 km. They proposed the “Arg-e-Bam fault” as the source fault to distinguish it from the Bam fault. In the present study, we have applied seismic tomography to arrival time data generated by the Bam earthquake aftershocks recorded by the temporal high sensitive seismic network (Nakamura et al., 2005; Suzuki et al., 2005). In addition to high quality P-wave first arrival times, high quality S-wave arrival times were also collected since all the stations used are threecomponent seismograph. These data allowed us to determine detailed three-dimensional (3-D) Pand S-wave velocity and Poission’s ratio image in the source area of the Bam earthquake. Data and method The aftershock activity of the 2003 Bam earthquake has been monitored by a seismic network consisting of 9 temporal stations. Each station was equipped with a highly sensitivity, three-component velocity type seismometer with a natural frequency of 1Hz, and GPS timing system (Suzuki et al., 2005). The waveform data were continuously recorded at a sampling rate of 100Hz by a 16-bit-data-logger. We selected useful data set of 2396 aftershocks among 2789 aftershocks which Nakamura et al. (2005) accurately located by the double difference method (Waldhauser and Ellsworth, 2000) using a one dimensional (1-D) local velocity model. All the 2396 events were recorded at least by 7 stations and hypocentral locations are estimated accurately to 0.07, 0.05, and 0.16 km for the N-S, E-W, and depth respectively. The magnitudes of aftershocks are from M 0.1 to 3.1. We use the tomographic method developed by Zhao et al. (1992) to determine the 3-D velocity structures of P and S–waves in the source area of the Bam earthquake. A 3-D grid net is set up in the study area of 58.25E – 58.50E and 28.9N-29.2N with a grid spacing of 0.05 degree in the horizontal direction. Five layers of grid nodes are set up at 0, 3, 6, 9, and 14 km depth. A total of 38505 phases data consisting of 19490 P and 19015 S wave arrival times are used. The unknown parameters are hypocenter locations and velocities at the grid nodes, which are determined in an iterative inversion process. The velocity at any point in the model is calculated by linearly interpolating the velocities at the eight grid nodes surrounding that point. After the Vp and Vs images are determined, we determine Poisson’s ratio distribution. Results and discussion We solve 2369 4 hypocenters parameters and 120 Vp and Vs parameters at grid nodes where more than 100 rays passed. The root-mean-square (rms) of arrival time residuals was reduced by 17% and 12% for the P-wave and S-wave, respectively. The final rms is 0.042 sec for P-wave and 0.065 sec for S-wave data, indicating the high quality of the arrival time data. Precise aftershock distribution shifts Nakamura et al. (2005) proposed source fault about 1 km to the west, and suggest that the earthquake ruptured a fault which is located about 4.5 km west of the known Bam fault. Epicentral and hypocentral distribution of the aftershocks are shown in Fig. 1. The figure shows the images in the vertical cross sections of Vp, Vs and 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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Poisson’s ratio along and perpendicular to the Bam aftershock alignment. The north-south cross section along profile AB images the earthquake fault plane. The east-west cross sections CD and EF are perpendicular to the fault plane at 29.10N, through the Bam city, and at 29.05N, south off the city, respectively. We can see high Poisson’s ratio in the surface material down to about 1 km. This may indicate a thick layer of unconsolidated or poorly consolidated sediments. As seen in cross-sections AB and EF (Fig. 1-e) there is no such high Poisson’s ratio for the surface layers in the area south of the city of Bam. Fielding et al. (2005) described that only the area south of Bam has clear expressions of surface rupture. This mechanical behavior and its Poisson’s ratio may indicate that the near-surface material contains a much thinner layer of soft sediments.

Figure 1 (a) Epicentral distribution of the 2396 relocated aftershocks in this study. (b)Rupture propagation derived from teleseismic data (Yamanaka, 2003). (c-e) Vertical cross-sections of P-wave and S-wave velocity perturbations and Poisson’s ratio. Small black crosses denote the aftershocks within a 2 km width along the profile.



Figure 1-b shows the slip distributions on the fault plane during the Bam earthquake mainshock, inferred from teleseismic body waves (Yamanaka, 2003). Areas with large slips exist in the shallow part of the fault. Using radar data, Wang et al. (2004) determined that the maximum slip occurred at a depth of about 3 km and Fialko et al. (2005) indicated that most of the seismic moment release at a depth of 4–5 km. These depths correspond to the low Poisson’s ratio area which is detected at the depth range of about 2-5 km in Fig.1-e, suggesting a shallow rupture of the strong and brittle rocks probably made a fresh fault that may be responsible for the very strong motions and intense damage in the Bam Earthquake. Generally, it is expected that such asperities locate in areas with fewer aftershocks. Although a lesser density of the aftershocks distribution can be found in the location circled on Fig 1-b (red circle), the overall distribution is relatively uniform on the fault plane. The low Vs and high Poisson’s ratio are clearly imaged at about 5 km depth beneath the Bam city (29.11N, 58.35E) and extends to about 10 km depth toward south (29.02N, 58.35E) as shown in the profile AB of Fig. 1-d and 1-e. As evidenced by the Ts-Tp of about 1 second measured on the Bam strong motion accelerograph station, the focus of the Bam earthquake may be located in this south-dipping, NS elongated zone of low Vs and high Poisson’s ratio. The low Vs and high Poisson’s ratio may point to the existence of ductile rheologies. The evidences of a growing anticline for the prominent escarpment of the Bam fault (e.g., Okumura et al., 2005) lead us to discuss that the small region of high Vp beneath the Bam city which surrounded by low Vp anomalies at 6km depth (profile CD of Fig. 1-c), may result by an uplift of the ductile rocks. Uplifting of the ductile rocks forms an increased pressure zone with high Vp and causes an active compression to grow the flexure scarp of the Bam fault. Acknowledgments We thank Dr. T. Matsushima, Dr. T., Ito, Dr. S.K. Hosseini, A. J. Gandomi, and M. Maleki for help with fieldwork, data analysis and their constructive discussions. References Berberian, M., 1976, Contribution to the seismotectonics of Iran (Part II). Documented earthquake faults in Iran. Geological Survey of Iran Report, 39, 517p. Fialko, Y, Sndwell, D, Simons, M, Rosen, P., 2005, Three-dimensional deformation caused by the Bam, Iran, earthquake and the origin of shallow slip deficit .Nature 435, 295-299. Fielding, E., Talebian, M., Rosen, P., Nazari, H., Jackson, J., Ghorashi, M., Walker, R., 2005, Surface ruptures and building damage of the 2003 Bam, Iran, earthquake mapped by satellite synthetic aperture radar interferometric correlation. J. Geophys. Res. 110, B03302, doi:10.1029/2004JB003299 Nakamura, T., Suzuki, S., Sadeghi, H., Fatemi Aghda, S. M.,Matsushima, T., Ito, Y., Hosseini, S. K., Gandomi, A. J., Maleki, M., 2005, Source fault structure of the 2003 Bam earthquake, southeastern Iran, inferred from the aftershock distribution and its relation to the heavily damaged area: Existence of the Arg-e-Bam fault proposed. Geophys. Res. Lett. 32, L09308, doi:10.1029/2005GL022631, 2005 Okumura, K., Kondo, H., Azuma, T., Echigo, T., Hessami, k., 2005, Surface effects of the December 26th, 2003 Bam earthquake along the Bam fault in southeastern Iran. Bull. Earthq. Res. Inst., Univ. Tokyo, (in press). Suzuki, S., Fatemi Aghda, S.M., Nakamura, T., Matsushima, T., Ito, Y., Sadeghi , H., Maleki, M., Gandomi, A.J., Hosseini, S.K., 2005, Temporal seismic observation and preliminary hypocenter determination of aftershocks of the 2003 Bam earthquake, southeastern Iran, Bull. Earthq. Res. Inst., Univ. Tokyo, 79, 37-45. Waldhauser, F., Ellsworth, W. L., 2000, A double-difference earthquake location algorithm: Method and application to the northern Hayward fault. Bull. Seismol. Soc. Am., 90, 1353-1368. Zhao, D., Hasegawa, A., Horiuchi, S., 1992, Tomographic imaging of P and S wave velocity structure beneath northeastern Japan. J. Geophys. Res. 97, 19909-19928. Yamanaka, Y., 2003, Seismological Note: No.145, Earthquake Information Center, Earthquake Research Institute, University of Tokyo. (Available at http://www.eri.u-tokyo.ac.jp/sanchu/Seismo_Note/EIC_News/ 031226f.html) Wang, R., Xia, Y., Grosser, H., Wetzel, H.U., Zschau, J., Kaufmann, H., 2004, The 2003 Bam (SE Iran) earthquake: precise source parameters from satellite radar Interferometry. Geophysical Journal International, 159, 3, 917922.


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CONTRIBUTION TO THE ESTIMATION OF SEISMIC HAZARD IN BANAT REGION (ROMANIA) Traian Moldoveanu Institute of Geotechnical and Geophysical Studies - GEOTEC, Bucharest, Romania

Summary Located in the southwestern of Romania, the Banat region is characterised by a relevant seismic activity. So, in this century, 28 earthquakes with M≥4.1 (I0≥VI) were identified; the strongest (M=5.7, 5.6, 5.6) occurred in the second part of 1991, the year of the highest observed seismicity. The events have a shallow depth. The correlation of the earthquake foci with local tectonics is remarkable. To estimate the seismic hazard in the Banat region were used the theory of the largest values (GI and GIII distribution) and Cornell's method. The characteristic parameters of Gumbel's distribution for two time intervals (1901-1993; 1871-1993; M≥4.1/I0≥VI), are computed. The values obtained (in terms of M and I0; time interval of sampling-10 years) are very close. One notice the values obtained for GI: b=0.95, u=4.6, T(6.0)=210years; Mmax(P=1%)=5.7; Mmax(P=0.5%)=6.0. The last value is very close to Mmax=6.3, obtained by the application of GIII distribution. The difference δM=Mmax-Mobs=0.6 is acceptable. The seismic hazard is expressed by the exceedance of the probability of some parameters (M, I0, a) in a certain period. The use of Cornell's method allow to draw up the isoacceleration contours for diferent periods. The quantitative study of the Banat region seismicity confirms its high seismic potential and the necessity to adopt real measures for the antiseismic protection in this area. Introduction The Banat region located in the southwestern part of Romania , Figure 1, is characterized by a relevant, seismic activity. During the 1794-1993 period, 43 earthquakes with M≥4.1 (I0≥VI) were identified, but the strongest events (Ms=5.7, 5.6, 5.6) occurred during the last years. The second part of 1991 was the period of the highest observed seismicity in the Banat region. The events have a shallow focus (maximum 25 km, minimum 4 km) and are associated with aftershocks and/or foreshocks. The correlation of the earthquake focus with the local tectonics is remarkable. Seismotectonic conditions Carried out for the Banat seismic area, the seismotectonic studies pointed out the neotectonic activity implications of the area on the regional and total seismicity, the relation between the tectonic structure and the history of the tectonic movements which finalized the Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 723


present ensembles, geotectonics and the distribution of the recorded local earthquake epicenter. From the Banat area the seismotectonic analysis map, Figure 2, pointed out a remarkable earthquake focus correlation with tectonics, the submit faults respectively. Before 1990, the Banat area was located according to the Romanian standard of seismic zonation (STAS 11100/193), most of it on the 6 degree macrozone of seismic intensity and a little part on 7 degree macrozone. As a result of the strong earthquakes produced in the Banat zone, nearby Banloc (12.07.1991; Ms=5.7; I0=VIII MSK), Herculane (19.07.1991; Ms=5.6; I0=VIII MSK) and Voiteg (02.12.1991; Ms5.6; I0=VIII MSK), Figure 1, the STAS 11100/1-93 standard was replaced by a new SR 11100/1-93 seismic zonation standard, Figure 3. Seismic hazard estimation for the Banat area For the seismic hazard estimation of the Banat area there were used the following statistical-probability proceedings and methods: frequency-magnitude relation; the extreme value method (Gumbel I and III distributions); the Cornell-Vanmarcke. For the frequency-magnitude relation determination there were used these expressions: a. Gutenberg-Richter relation (1956): b. log n(≥ M ) = a − bM (1) Using the data from Table 1, the following relation was obtained:

log( N c / year) = 2.21 − 0.68M

(2)

The graphic representation is shown in Figure 4. c. The Hwang and Huo(1984) modification of the Gutenberg-Richter relationship is:

n(≥ M ) = e 5.093−1.571M (1 − e −1.571( M

max

−M )

) /(1 − e −1.571( M

max

− 4.1)

)

(3)

when the threshold magnitude is selected M0=4.1, α=2.2118ln10=5.093 and β=0.682ln10= 1.571. The graphic representation of Hwang and Huo relation is presented in Figure 4. The maximum credible magnitudes estimated for the Banat seismogenic region is Mmax= 6.0 - 6.3 (Moldoveanu,Tr., 1996). For Mmax = 6.3, the magnitude of the Banat earthquakes with 50, 100 and 475 year mean return period are: M = 5.5, M = 5.8 and M = 6.1-6.2. To estimate the seismic hazard in the Banat region the theory of the largest value Gumbel's distribution was used:

G I (m) = exp{− exp[ −α (m − u )]}

(4)

G III (m) = exp{−[(ω − m) /(ω − u )]k }

(5)

The characteristic parameters of Gumbel's distribution for two time intervals (1901-1993; 1871-1993; M≥4.1/I0≥VI), are computed. The values obtained (in terms of M and I0; time interval of sampling-10 years) are very close. One notices the values obtained for GI distribution: b=0.95, u=4.6, T(6.0 =210years, Mmax(P=1%)=5.7; Mmax=6.3, obtained by applying the GIII distribution. The difference δM=Mmax-Mobs=0.6 is acceptable. The graphic representation obtained through the application of Gumbel I and III distribution for magnitude (Ms) and the epicenter intensity (I0) are presented in Figure 5 and Figure 6. For the application of the Cornell - Vanmarcke method the following data and hypotheses were considered: model: source - line (fault); existence of eight source - line (faults), Figure 3; 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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the attenuation relation of acceleration: horizontal (aH), established by Macropoulos and Barton (1985, Eq. 6) and Stamatovska and Petrovski (1991, Eq. 7) respectively:

a H = 2164e 0.7 M ( Rh + 20) −1.8 [cm / s 2 ]

(6)

aH = 534.355e0.4608M ( Rh + 25) −1.14459 [cm / s 2 ]

(7)

S

S

The use of Cornell's method allows to draw up the iso-acceleration contours for the return periods of 50, 100, 200 and 475 years. In Figures 7 and 8 there are presented the iso-acceleration contour maps for the return periods of 100 and 475 years. In Figures 9 and 10 there are presented the iso-intensity contour maps for the return periods of 50 and 100 years. Conclusions The Banat area, located in the south-west of Romania, is characterised by an important seismic activity pointed out by the activity in the last ten years (for example 1991).The estimation synthesis of the seismic hazard for this area is distinguished by the maps with isoaccelerations, Figure 7 and 8, and iso-intensities, Figure 9 and Figure 10. The iso-intensitiy maps presented in Figures 9 and 10 represent a proposal for the Banat area seismic zonation. The quantitative study of the seismicity of the Banat region confirms its high seismic potential and the necessity to adopt real measures for the antiseismic protection in the area.

BANAT REGION

Figure 1 Epicenters of earthquakes(M≥5;1901-1991).

Figure 2 Seismotectonic map.

Figure 4 Magnitude recurence relation for the Banat seismic region Figure 3 Seismic zonation (SR 11100/1-1993).



Figure 5 Banat seismic region.

Figure 6 Banat seismic region.

Figure 8

Figure 7

Figure 9

Figure 10


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SEISMOTECTONICS OF THE FORELAND OF THE ROMANIAN CARPATHIANS CHARACTERIZATION OF SEISMIC SOURCES AND INSIGHTS ON SEISMIC HAZARD ANALYSIS Coneliu Dinu1, Traian Moldoveanu2 , Vlad Diaconescu1, Liviu Matenco3,1 1 Faculty of Geology and Geophysics, University of Bucharest, Romania 2 GEOTEC S.A., Bucharest, Romania 3 Netherlands Research School for Integrated Solid Earth Science, The Netherlands

Summary This study aims to define and characterise the main crustal seismic source regions for the Romanian Carpathian Foreland by means of corelation of recent and active tectonics with crustal earthquakes distribution. Based on extensive depth and surface data on active tectonics, several regions of active crustal deformation with specific geometry and kinematics were determined. Crustal earthquakes were grouped in seismic sources in respect to the previously established tectonic background, each source comprising genetically linked earthquakes randomly distributed along active or potentialy active faults within the same fault system from a specific region. Each source was characterised in terms of geometry, magnitude distribution, maximum possible magnitude, seismic activity, frequency and frequency/magnitude distribution, as basic parameters for crustal seismic hazard asassement. Tectonic background The foreland of the Romanian Carpathians consits of several continental blocks (figure 1) with different thermo-mechanical age reflected in significant variations of the flexural behavior in front of the advancing orogenic system up to Late Miocene collision and also on bulk strain partitioning among these blocks and localization of post -collisional Pliocene-Quaternary deformation mostly in the vicinity of the block contacts and inside the western Moesian domain, Figure 1 General map of Romania; major faults and tectonic units the “weakest” part of the within the Carpathian foreland are represented foredeep system. The geometry of the foredeep basins and the structural pattern of the Pliocene-Quaternary deformations have been analyzed (Matenco et al, 2004) based on remote sensing and geomorphological interpretation and on combined surface (faults expression, geometry and kinematics at outcrop scale) and depth (seismic interpretation) structural analysis. The main active fault systems that may induce crustal seismicity within the Carpathian foreland have been evidenced and analyzed in terms of genetic relationship, geometry and kinematics. Seismic expression of the main active fasult syustems is presented in figure 2. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 727


Some of the structures reflect reactivation of older Platform blocks contacts (Trotus Fault, Pecenega-Camena Fault, Sf. Gheorghe Fault, Intramoesian Fault) whereas others are related with mostly extensional deformation within the foredeep basins superposed on the younger Moesian crust (Focsani Basin-Vrancea crustal area and western Moesian Platform).

Figure 2 – Interpreted seismic lines across the main tectonic contacts within the foreland showing quaternary reactivation mostly in the proximity of the orogen – insets with profiles loclization; A) Trotus Fault; B) Pecenega-Camena (left) and Sf. Gheorghe (right) fault systems; C) Intramoesian Fault

Crustal seismicity The distribution of crustal eartquakes (figure 3) was obtain compiling all published catalogues. Crustal earthquakes data were integrated in a GIS database and analyzed in connection to active tectonic features and major crustal faults. Data on crustal and lithosphere thickness and rheology, variation of geophysical characteristics, distribution of horizontal and vertical movements were incorporated in the data base to constrain the seismotectonic model. The seismic sources were defined according to active tectonics model, each source comprising genetically linked fault systems with random distribution of earthquakes foci among faults belonging to the same source (figure 4). All subcrustal intermediate depth earthquakes that occur in the Vrancea area, related to downgoing of a sub-vertical slab in the bend zone of the East Carpathians were grouped in “Vrancea intermediate source” the only one extensively 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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studied up to now. Four crustal sources have been defined for romanian foreland: Vrancea crustal source, comprising earthquakes mostly related to extentional structures on the western falnk of the Focsani Basin, Pecenga-Camena Fault Source, Sf. Gheorghe Fault Source and Intramoesian Fault Source, comprising earthqukes related to each major fault system local reactivation in specific kinematic context. In addition to the crustal sources within the Romanian foreland, another crustal seismic source from NE Bulgaria (Sabla area) was defined and characterized due to high seismic hazard induced for the hole area by its high magnitude earthquakes.

Figure 3 Distribution of crustal earthquakes

Figure 4 Seismic sources



As an example, figure 5 presents the characterization of the Pecenega-Camena Fault Source. Pecenega-Camena Fault is a major crustal fault that makes the boundary between the North Dobrogea Orogen and the Moesian Platform. It acted as a sinistral strike-slip boundary, with many associated faults and related structures up to the Middle Cretaceous time, when the two continental blocks where welded together. This fault was at least locally reactivated in younger tectonic episodes, including recent to nowadays activity. West of the Danube, on NW direction, where the sedimentary cover of the fordeep thickens progressively towards the East Carpathian Orogen, the Pecenga-Camena Fault diverge in a anatomizing fault system, tens of kilometers width, dominated by normal faults. This system was formed successively during Sarmatian, Pontian, Dacian, Romanian and Quaternary time, in a transtensive regime characterize by NE-SW extension.

Figure 5

Conclusions Even not as significant as Vrancea inermediate depth seismicity, crustal seismicity within the Carpathians foreland has an important contribution to the seismic hazard. By an inegrated neotectonic – seismological aproach we defined several siesmic source regions, each source comprising genetically linked structures from a specific area, with equal probabillity of earthquake occurence along any structure within the source. Each source was characterised in terms of geometry, magnitude distribution, maximum possible magnitude, seismic activity, frequency and frequency/magnitude distribution, as basic parameters for crustal seismic hazard asassement. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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BOREHOLE GEOPHYSICS & RESERVOIR INVESTIGATIONS

P12 - 01

STRESS FIELD ORIENTATION IN THE TRANSYLVANIAN BASIN INFERRED FROM BOREHOLE MEASUREMENTS Dorel Zugravescu, Gabriela Polonic, Victor Negoita Institute of Geodynamics “Sabba Stefanescu” of the Romanian Academy, Bucharest, Romania

Introduction The Transylvanian Basin is located in the Eastern part of the Alps-Carpathian-Pannonian system on the Romanian territory. It has a roughly circular shape and a Cretaceous to Miocene 8 km thickness sedimentary fill. The basin margins are represented by the East Carpathian Mountains, the South Carpathian Mountains and the Apuseni Mountains. As a result of its tectonic evolution, the Transylvanian Basin is characterized by the following peculiar features: normal thickness lithosphere (100 km), low heat flow (30 – 60 mWm-2) and a crustal thickness of 33 – 36 km, increasing from the central area to the basin borders. Nevertheless, the geodynamic information related to the present day-stresses acting within the terrestrial upper crust of the Transylvanian Basin is very scarce and the few data coming from previous published papers (Negut et al., 1994; Zugravescu et al., 1999) have not been included in the World Stress Map (Fucks et al., 1999). That is why in the last five years the research programs of the Geodynamic Institute of the Romanian Academy were directed on topics concerning a better understanding of various geodynamic processes taking place in this areal. Among other things it represents an intensively explored region for hydrocarbon resources, in which during the last 60 years a lot of gas deposits have been discovered. More than 2000 boreholes drilled in this region investigated the entire Pliocene and Miocene sedimentary fill from the ground surface to 5 km deep. For this reason the stress study of the Geodynamic Institute was entirely based on borehole geophysical measurements existing in the archives of oil and gas companies, and consequently without any extra-cost. Methodology used for borehole data processing With this end in view, the available well log suites coming from 53 exploration boreholes whose bottom holes-depth were less than 4 km have been selected, collected and finally processed. All these boreholes have been geophysically investigated in open hole conditions with Schlumberger and Wester Atlas equipments including always the Stratigraphic High-Resolution Dipmeter Tool (SHDT) or the Dipmeter. The field data processing was performed according to the Schlumberger instructions, the interpretation methods devised in our institute were based on the "breakout technique" both of them being finally coupled in a such way to comply with the requests of the World Stress Map. In this context we want to mention that special rules were assessed in order to ascertain the causes of breakouts (initiation and enlargements) on the basis of well wall stability and the pressure differential between the drilling mud and the fluid filling the rock pore space. In our breakout inferred stress study of the Transylvanian Basin upper crust we consent with the linear, isotropic poroelastic stress-strain theory assuming the strain plane orthogonal to the borehole axis. On these terms the ellipsoid of stresses was defined by giving the directions of its three axes and the corresponding stress magnitudes S1, S2, S3, known as principal stresses. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 731


Roughly speaking within depositional basin, whether tectonically inactive or undergoing extension, the maximum stress (S1) is represented by the geostatic load/overburden, both intermediate stress (S¬2) and least stress (S3) being located in the horizontal plane. The combination of extensional and strike slip regimes existing in the Transylvanian Basin supported our assumption to consider that the principal stress is oriented vertically (S1 = Sv), the greater horizontal stress as being (S2 = SH) and finally, the least horizontal stress to be (S3 = Sh). The last horizontal stress was expressed as a fraction of the geostatic load (S1) using a variable coefficient whose value was calculated on the basis of Poisson's Ratio. Both, rock elastic parameters Poisson's Ratio and Young's modulus have been derived in our study from wave velocities and bulk volume densities recorded by well logging measurements. The final results of our determinations related to stress horizontal components-orientations have been presented in two different variants: 1. A graphical one, in which all maximum stress component-azimuths were plotted on a regional map as arrows, indicating at the base of arrow the geographical co-ordinates / borehole site locality. 2. A second one, displaying the so called "stress file" prepared and stored in the Stress Data Bank of the Geodynamic Institute. This stress file includes a lot of informations concerning: well geographical co-ordinates, borehole intervals with continuous SHDT/Dipmeter measurements, the type of other recorded well logging measurements, lithology of geological formations passed through, boundaries between them on the basis of geological age, physical and chemical characteristics of drilling mud, borehole deviation, pressure and bottom hole maximum temperature, etc. On the basis of different physical measurements acquired during the well logging operations (Gamma Ray Radioactivity, Spectral Log, Neutron and Density Log, Sonic Log, Electric resistivity / conductivity and Dipmeter) the following types of information were also established and reported to in the "stress data file": •the azimuth of maximum horizontal principal stress; •the azimuth of least horizontal principal stress; •the magnitude of the above mentioned stresses for some "in house studies". Because the basical data of our study have been provided by the open hole-geophysical measurements performed during the drilling period of gas producing-wells, we have been constrained to present the distribution of stress orientation within the Transylvanian Basin in a closed relation to the framework of gas-geological activity. Presentation of the results The main characteristics of stress orientation in the five groups of gas producinggeological structures are presented below: Northern Group: The areal of this group (Fig. 1) is situated on the northern part of the Mures river, being enclosed in the polygon formed by the following localities: Cluj – Dej – Bistrita – Grebenis – Ludus – Turda. Among the most representative gas producing-geological structures we mention: Sarmasel, Buza, Strugureni, Delureni, Grebenia, Zau de Campie. The extreme values of maximum stress orientation are: 80° - 130°. The average value of all stress orientations is 104°. Western group: The areal of this group (Fig. 1) is situated between Mures and Tarnava Mare rivers, being enclosed in the polygon formed by the following localities: Turda – Ludus – Iernut – Tarnaveni – Deleni – Blaj. Among the most representative gas producing-geological structures we recall: Bogata, Iernut, Deleni, Tauni, Cetatea de Balta, Ludus. The extreme values of maximum stress orientation are: 72° - 112°. The average value of all stress orientations is 92°. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

732


Figure 1 The directions of maximum horizontal stresses in the Transylvanian Basin.

Southern group: The areal of this group (Figure 1) is situated between Tarnava Mare and Olt rivers, being enclosed in the polygon formed by the following localities: Ludus – Sibiu – Ucea – Agnita – Sighisoara – Copsa Mica. Among the most representative gas producing-geological structures we mention: Alamor, Rusi, Ilimbav, Sasaus, Copsa Mica, Noul Sasesc. The extreme values of maximum stress orientation are: 10° - 45°. The average value of all stress orientations is 25°. Eastern group: The areal of this group (Figure 1) is situated near the Eastern Carpathians border, being enclosed in the polygon formed by the following localities: Agnita – Rupea – Odorhei – Sovata – Ghindari – Sighisoara. Carrying on, some of the most representative gas producing-geological structures are listed: Daia-Telina, Bunesti, Cristur, Lupeni, Porumbeni, Soimus, Eliseni. The extreme values of maximum stress orientation are: 60° - 135°.The average value of all stress orientations is 104°. Central group: This group (Figure 1) is located exactly in the center of the Transylvanian Basin possessing common borders with all the four gas producing-geological structure groups reported to formerly. The approximate areal is situated in the polygon formed by the following localities: Sighisoara – Magherani – Reghin – Craiesti – Band – Medias – Dumbraveni. From the most representative gas producing-geological structures may be mentioned: Corunca, Tg. Mures, Eremieni, Bazna, Dumbravioara, Petrilaca, Filitelnic, Nades. The extreme values of maximum stress orientation are 110° - 175°. The average value of all stress orientations is 150°. As a general observation, in the Transylvanian Basin most of the variations related to stress orientation within the depth interval "ground surface – Saliferous Upper Miocene" follow a normal (perpendicular) direction against the Carpathian mountainous chain. The stress orientation found on some geological structures (Sarmasel 118°, Bogata 112°, Altana 20°, Nocrich 8°, Sasaus 38°, Bunesti 86°, Feliceni 132°) are relevant in this respect. Yet, some characteristic behaviours of stress orientations on the Transylvanian Basin zone need to be Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 733


remarked and discussed. The first one is represented by the "Central group" where the average stress orientation of 150° is equivalent to the general stress orientation trend existing in the Central and Western Europe (the so called Midplate stress domain) with average stress orientation of 145°. The second one, is represented by the most south-western zone of the Transylvanian Basin where an obvious N-S direction of stress orientation was pointed-out, more or less equivalent to the stress orientation noticed in the south of Poland as well as in the most eastern part of Slovakian territory (Fuchs et al., 1999). In addition, for this south-western part of the basin we suppose the existence of some deep local fault processes generating stress field perturbations. The quality data resulted from our 53 stress orientation-determinations assigned according to the "World Stress Map ranking quality scheme" may be placed between A and C rank orders. It is opportune to recall that WSM quality scheme starts with the best A ranking quality and ends to E ranking quality. Our 53 selected stress orientation-determinations may be integrated in the ranking scheme as follows: (A = 7, B = 22 and C = 24 determinations) and therefore, the specific percentages related to the data quality are (A = 13.2%, B = 41.5%, C = 45.3%). Stress magnitudes have also been calculated for some special works, on the basis of well logging data and pressure measurements recorded during the drilling period of the boreholes. Generally, in the Transylvanian basin the vertical stress increases with depth taking for the vertical stress gradient values between 22 MPa/km and 24 MPa/km. Formation fluid pressure gradients in the Pliocene-Post Salifeorus Upper Miocene depth interval seldom exceed 13 MPa/km, few occurrences of 15-16 MPa/km in the Filitelnic – Corunca gas fields being recorded. In such circumstances the least horizontal stress gradients calculated on the basis of Poinson's ratio and vertical stress gradient indicated values of 13-15 MPa/km, confirming several leak-off tests carried out during the drilling period of boreholes. Finally, the analysis of stress magnitudes stated that maximum principal stress is vertical, while the minimum horizontal stress is roughly 62% of the vertical stress magnitude; the average values of these two stress-gradients are respectively 23 MPa/km and 14.2 MPa/km. Conclusions The present stress study, undertaken by the Institute of Geodynamics of the Romanian Academy, used the available well log suites collected from 53 boreholes and finally processed. The field data processing was performed according to Schlumberger instructions, the interpretation method devised in our institute was based on the "breakout technique", both of them being finally coupled in such a way to comply with the requests of the World Stress Map quality conditions. The Transylvanian Basin areal was divided into five distinct zones on which the stress orientation-determinations have been carried out, the final scheduled results being presented in a graphical form (Fig. 1). References Fuchs, K., Müller, B., Sperner, B., Reinecker, J., 1999, World Stress Map of the Central and Eastern Europe, WSM Project-Document, Rel, 1999, Heidelberg Acad. of Sci. and Human., Karlsruhe Univ. Geophys. Institute. Negut, A. et al., 1994, Stress orientation determination in Romania by borehole break-outs. Geodynamic significance. Rev. Roum. Géol. Géophys. Géogr., Géophysique, 38, 45-46. Zugravescu, D., Polonic, G., Negoita, V., 1999, A preliminary report on the break-out inferred stresses in the Transylvanian Basin. Romanian Journal of Tectonics and Regional Geology. Vol. 77, Supplement no.1, 43-44.


734


P12 - 02

THE CONTRIBUTON OF GEOPHYSICAL METHODS TO FORMATION EVALUATION OF FRAKULLA GAS FIELD Aleksander Gjika1 , Xhemil Buzi2, Jovan Sota1 , Ilir Varfi2, Drita Buzi2 1 National Scientific Hydrocarbon Centre, Fier, Albania 2 Albpetrol Sh.A, Patos , Albania

Summary In this article is treated in a concise manner the contribution of geophysical methods (seismic & well logging) in evaluation of structural model and of the perspective areas for new gas pool discoveries. Interpretation and confrontation of the data taken by well drillings, seismic profiles and well loggings have better clarified the tectonics, the spread of sandstone bodies, pool types and the proper relations for formation evaluation of Frakulla gas field. Introduction Frakulla gas field is located on the western part of Albania. The exploration works have been initiated on 1960. The first drillings are realised in conformity with two cross and longitudinal sections. The discovery of industrial gas flow is verified during testing of Fr- 4 well. It is restudied and evaluated in 1971 and Fr- 10, 11, 17, 19 wells were projected and drilled. The exploitation of these wells reflected industrial gas flow and proved the discovery of new pools on the North side of the gas field. The discovery of the new pools on the East and West is realised in Fr- 43 and 44 wells. In this oil field 86 wells are drilled and only in 32 of them is taken gas flow. Gas reserves are about 400 x106 m3. Geological Setting Frakulla structure is the part of the Neogene anticlinal Vlore-Panaja-Trevllazer range and lie down on the south part of Adriatic basin. It is stratigraphically represented by deposits of Neogene age (Serravalian stage to Pliocene included) which are placed with stratigraphic and angular unconformity on the lateral parts of the basin. The structure is formed as a result of mud diapir growth (figure 1) and is surrounded with many gas sandstone layers in all directions (figure 2). Frakulla gas field is presented as a complicated tectonic structure with faults on both its flanks and seems as a horst (figures 1, 3). To identify tectonic of the studied region a considerable seismic profiles (fig. 3, lit.1) were processed and interpreted that were corrected with well log data run in drilled wells. At the surface it is presented as an anticlinal structure with North-South extension and 1.5 x 3 km dimensions. The formation of Frakulla gas field is composed of sandstone layers of sand-clay facies from its base up to Gips level. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 735


Fig.3 Migrated seismic section

The most of gas bearing layers are encountered between 200 m and 1700 m depth (figure 2) and are of lithologo-structural and tectonic types. The better potential pool is encountered in the Fr- 19 and Fr- 30 wells and is composed of 5 layers with 5-10 m thickness each. Gas reserve of this pool is about 100 x 106 m3.

Formation evaluation by well loggings. The information taken by well logs, carried ed out in the drilled wells of this gas field, is versatile. To evaluate lithology, petrophysical parameters and gas saturation of sandstone layers full suit logs in all drilled wells were run. We have identified the spread of sandstone through log correlations and have determined 4 base horizons which have been named G, R, R1 and Y (figure 4). This interpretation has helped petroleum engineers to determine with precission tectonic setting, the spread laws of sandstone bodies and time after time to project new exploration wells. R – Y thickness, as it is seen in figure 4, has a visible change from a section to many sandstones at Fr-74 to a section almost clayey at Fr- 40 well. Based on detailed correlation we draw a map with the spread of every sandstone layer and their lithological closing boundaries (figure 5). According to this map we observe that the area on the South of Fr-110 well has interest for exploration of gas pools. In this area is projected a new well, Fr- 47 ( figure 5) in which is anticipated to discover new gas layers on the interval from G to Y horizon with expected reserves about 6x 106 m3 gas (figure 4). Another perspective area for the discovery of the new gas pools is that on the South-West part of the Fr- 27 well where is projected Fr-47 well (figures 1, 5).


736


We have determined the porosity of the sandstone layers by using acoustic and density logs. The porosity from acoustic log is evaluated by confrontation of Dt versus porosity determined at the laboratory. For Frakulla gas field, with a possible error of ± 5 %, the following equation is used: Φ=

where:

∆t − 170 600

%

(1)

Φ - porosity about acoustic log Dt – transit time reading on the sonic log in front of studied layer in µ sec/ft or µ sec/m.

The porosity by density log is evaluated using the known equation: Φ= where:

ρ ma − ρ h ρ ma − ρ f

%

(2)

Φ - porosity about density log ρ ma – matrix density of the rock ρ h - formation bulk density ( log value)

ρ f - density of the fluid saturating the rock immediately surrounding the borehole – usually mud filtrate = 1 g/cc. The matrix density of the Frakulla sandstone layers is 2.65 g/cc, so the porosity by density log is evaluated by the following equation: Φ=

2.65 − ρ h 2.65 − 1.0

%

(3)

To calculate the water saturation (Sw) of the invaded zone in a formation next to borehole we have used the famous equation of the Archie as following: Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 737


(S w ) n =

where:

a * Rw Φ m * Rt

%

(4)

Sw – water saturation of the uninvaded zone n - saturation exponent, which varies from 1.8-4.0 but normally is 2.0. Rw – formation water resistivity at formation temperature Φ - porosity m – cementation exponent Rt – true resistivity of the formation.

Comparing this equation with laboratory determination of Sw, we draw the conclusion that the best equation is it that proposed by Humble: (0.62 * Rw )1 / 2 Sw = (Φ 2.15 * Rt )1 / 2

(5)

We have taken good results in evaluation of Sw for clean sandstone layers with the thickness greater than 1.5 m. During exploitation of 86 layers, 82 of them have reflected industrial gas flow. It is taken no good results in calculation of Sw for sandstone layers with high clay content and thickness smaller than 1,5 m. This needs for an attention to improve the 5 equation making correction for thin bed and clay content. The evaluation of Sw for this kind of layers is generally done in a qualitative manner. Conclusions • • • •

Frakulla structure is formed as a result of mud diapir growth accompanied by high tectonic on both flanks. In Frakulla formation 4 correlation horizons are distinguished that have helped to determine with precision the tectonic setting and the spread of sandstone bodies. The best areas for discovering new gas layers are those on the South of Fr- 110 well and on the South-West of the Fr-27 well. The 1, 2, 5 equations give satisfactory results in calculation of porosity and water saturation for clean sandstone layer with thickness greater than 1.5 m. We recommend to apply these equations in other oilfields with the same characteristics.

References Fili, I. et al., 2002, Geologo-Geophysical study of Frakulla structure to determine the perspective areas for the discovery of new pools, Fier 2002. National Scientific Hydrocarbon Center Library. Buzi, XH. et al., 2000, The formation evaluation of sandstone and carbonate reservoirs by well loggings. Fier, National Scientific Hydrocarbon Center Library.


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P12 - 03

A MULTI-AZIMUTH VSP EXPERIMENT FOR FRACTURE ORIENTATION DETECTION IN HMD FIELD ALGERIA Chegrouche Farid, Babaia Foudil ENAGEO, Algeria

Summary Natural micro-fractures are very important in the control of production in the hydrocarbon reservoirs. The presence of the vertical fractures in the rock mass causes the split of the incident shear wave into two approximately orthogonal components with different velocities. Splitting shear wave analysis permits the estimation of fracture orientation. In the offset VSP experiment, converted SV waves are generated with varying strengths at particularly all depths. Consequently, the converted Sv waveforms partially overlap with direct P waveforms makes the separate event analysis difficult and inaccurate. In this paper, an automatic picking technique was used to accurately compute travel time of P and Sv down-wave. The polarization angles are determined from particles motion analysis. The interval velocities Vp and Vs were than computed using the travel time inversion technique. In this study, an attempt was made to determine the orientation of natural fractures using splitting shear wave technique and P wave velocity anisotropy from four offset VSP data acquired with different azimuths in the same well. Introduction The characterization of the fractured reservoirs in HMD field is a challenging task because of the complexity of the fracture geometry. While the fractures are the single most important future controlling fluid flow in the reservoirs with poor porosity, good knowledge about fractures strike may significantly increase oil recovery. Various methods exist that help determining the fractures orientation (anisotropy) such as VSP. The resolution of the subsurface anisotropy using multi-components VSP experiment depends critically on the geometric distribution of raypaths sampled. Raypaths at inappropriate azimuths and incidence angles may not contain enough information about the anisotropy. In this paper, we have used two approaches to investigate the fractures orientation which are the splitting shear wave and P wave velocity variation with incidence angles. Stratigraphy The reservoir under investigation is sandstone (about 90m) in which the upper part is saturated by oil with a poor porosity. The prevailing stress field at reservoir’s depth cause microfractures associated with faulting. To investigate this fault, four fixed offset VSP were acquired. Acquisition and data processing The 3C geophone was used to record the complete seismic wavefield propagating from different offsets and azimuths using a P-wave vibrator as energy source. Conventional processes were applied to construct the subsurface image, and special processes which maintain the amplitude variations in order to determine the rock properties. The data were horizontally oriented to the direction of maximum direct P-wave arrival energy (figure 1). Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 739

REC_DEPTH

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1082 1242 1402 1562 1722 1882 2042 2202 2362 2522 2682 2842 3002 3162 3312 3457


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The particle motion analysis was performed to determine the P and SV waves polarization information, used later to maximize the P and SV down waves energy in the vertical plan. Splitting shear wave identification The VSP have the advantage of recording the full seismic waveform propaga-ting in the subsurface at a short interval witch makes them ideal tools for detecting the anisotropic zone. The observed SV waves were generated Azimuth A Azimuth B by mode conversion of incidence P wave on subsurface interface of high impedance contrast. It is well known that shear-wave splitting from PS converted waves contains information on subsurface fractures and azimuthally anisotropy. The fracture orientation is determined from the particle motion’s direction of fast shear wave (S1). HT

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The analysis method involves: Selecting a shear-wave event. Rotating the horizontal seismograms into radial and transverse components. Maximizing the P and SV wave in the vertical plan. Picking the shear-wave’s arrival times. Computing the polarization’s direction using the particle motion diagram in the horizontal plan (Hs, Ht). If a second split shear wave is identified, the time delay is measured.

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In this case, we have used the downgoing Sv events generated by two strong conversion interfaces (Aptien and Lias S1). Figure 2 shows the polarization diagram for Sv wave generated by Lias S1 interface for selected depths above, within and below the reservoir. After analyzing the particle motion of the two selected events for different azimuths we observed that the SV wave has kept the usual direction of propagation (source –receivers) and that its second component didn’t appear. Even though the geological information confirms the presence of the vertical natural micro fractures, the splitting shear wave couldn’t be identified. The result above leads us to investigate the anisotropy through the P wave velocity variation with offset. P wave velocity anisotropy Since we couldn’t identify the splitting shear wave over all azimuths, we tried to determine the fracture’s orientation using the P wave velocity anisotropy. To investigate this later, we have studied the P wave velocity variation with azimuths using the anisotropic ratio (Kabaili and Schmitt 1996): (Vmax −Vmin ) / Vmax ; Where Vmax is the maximum velocity assuming equal to oblique velocity derived from offset VSP using the incidence angles of direct arrivals and Vmin is the vertical velocity calculated from zero offset VSP. Velocity [m/sec] 3000

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The incidence’s angles estimated from hodogram vary with depth because of changing geometric relationship between the source and receivers and of refraction of the downgoing P wave as it passes through media with different velocities. We have compared the theoretical incidence’s angles computed from a synthetic model using the velocity derived from zero offset VSP and the hodogram angle of incidence estimated from experiment offset VSPs. In the reservoir zone, we have found that the theoretical incidence’s angles are more vertical than the observed angles. The difference between the theoretical and the observed angles depends on the azimuth. This anomaly can be attributing to the azimuthally anisotropy. To confirm this assumption we must compare the vertical and oblique P wave velocities. The vertical component of velocity at the receiver array for a given source position was calculated directly from the arrival times of the zero offset VSP. Meaningful interval velocities from offset VSP can only be computed if we have a good idea of the incidence’s angles. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 741


Supposing that there are no severe lateral variations, the oblique component of velocity was computed using the travel time inversion technique, where the incidence’s angles were automatically estimated. Figure 3 illustrates that the oblique and vertical velocities converge in most investigated depths except in the reservoir zone. The results are summarized in Table 1. We denote that the incidence’s angles increase with the offset, consequently, we can attribute the anisotropy ratio’s variation to the azimuthally anisotropy. The rose-plot (figure 4) help us to determine the preferred fracture direction witch correspond to the most important anisotropy ratio. In our case, the preferred direction of wave’s propagation on the rose plot is about 168°. VSP

Azimuth

Offset

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A B C D

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1300 2500 2200 2300

29° 45° 43° 38°

Anisotropy ratio 05.75 14.03 07.80 27.05

Table 1 P wave velocity anisotropy ratio and incidence’s angles vs. azimuth.

Offset B=2500m θ = 45° 5.75 %

14.03 %

Pu

7.8 %

Offset C=2300m θ = 43°

Offset A=1300m θ = 29°

27.05 % Offset D=2200m θ = 38°

Figure 4 Rose-plot representing the anisotropy ratio distribution vs. azimuth.

CONCLUSION Even though the geological information confirms the presence of the vertical natural micro fractures, the splitting shear wave couldn’t be identified. This is probably due the geometry witch is inadequate for this problem (very large offsets). Although the B, C and D offsets are practically equal (similar angles of incidence), the ratio corresponding are different. Consequently, the velocity variations are rather related to the azimuth. As a conclusion, the reservoir is an azimuthally anisotropic model and the direction of fracturing plane is perpendicular to the direction of maximum anisotropy ratio (azimuth=165º).


742


P12 - 04

THE POSSIBILITIES OF CLAY MINERALS NATURE IDENTIFICATION BY GEOPHYSICAL LOGS Mihaela - Liana Negut1, Aurelian Negut2 1 Petrom - OMV Group, Bucharest, Romania 2 University of Bucharest, Faculty of Geology and Geophysics, Bucharest, Romania

Summary The identification of clay mineral type using Spectral Natural Gamma Ray Log and Absorption Photoelectric Index (Pe) Log are analyzed in the paper. On some selected examples, the methodology of processing, representation and interpretation are illustrated. The informative potential and limitations which appear in the practical application of these procedures are also underlined. Applications and implications of mineralogical nature of clays knowledge in geological formations crossed by hydrocarbon exploration wells are mentioned in the paper. Introduction The identification of clay minerals type - main constituents of sedimentary rocks - became possible by application in the geophysical investigation programs of hydrocarbon exploration wells of Spectral Natural Gamma Ray Log, recording three distinct contributions of main radioelements U, Th and K to natural radioactivity and of Spectral Gamma-Gamma Log, which records simultaneously the density (δ) and absorption photoelectric index (Pe) of formations. These two types of geophysical logs represent the primary observation data used for nature identification of clay minerals type. Three types of frequency crossplots are used: Th vs. K, Pe vs. K and Pe vs. Th / K. Depending of chemical and mineralogical composition of clays, on these crossplots some distinct theoretical sectors (zones) are delineated for every clay mineral. The frequency crossplots obtained for real observation data show a points distribution which, depending of coverage on the theoretical domain, offer a suitable and quick means for qualitative identification of clay mineral type throughout analyzed depth interval. Case studies Using Spectral Natural Gamma Ray and Absorption Photoelectric Index logs data, the dual frequency crossplots mentioned above were built for distinct geological formations from 36 wells located in different hydrocarbons geological units in Romania (Figure 1) (Neguţ, 2003). The frequency of observation points on a distinct domain (sector) allows the clay minerals identification. For majority of analyzed wells and formations, main interpretation was done using the Th vs. K crossplot. Principally, the Pe vs. K and Pe vs. Th / K confirm the interpretation obtained from Th vs. K crossplots. An important limitation in Pe vs. K and Pe vs. Th / K use appear for heavy drilling fluids, weightened with barite. The barite has a very high absorption photoelectric index (Pe ≈ 27 b/e). Its accumulation in a mud cake, especially for thick mud cakes, throw off the Pe curve from typical theoretical limits of sedimentary formations; it becomes useless both in the analyses for clay minerals identification and, generally, for the complex formation evaluation using geophysical logs. It is well-known that Pe parameter, in favorable conditions, may be used for lithology identification of formations crossed by boreholes. Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 743


In some wells, glauconite has been identified, especially on the spectral crossplots Th vs. K. Its presence indicate a slowly sedimentation in a marine environment. For example, in the SSirna well, the glauconite was met in all analyzed formations: Sarmatian, Badenian, Senonian, Turonian, Albian, Barremian and Valanginian. It is possible that glauconite, clearly indicated on the Th vs. K crossplot, is not observed in the Pe vs. Th / K and Pe vs. K crossplots (when recorded Pe values equal 1.8 - 5.1 b/e), due to its small content in the formation to significant modification of Pe. A set of frequency crossplots (Fig. 2 - a, b, c), as an example, are presented for Dacian formation of P-Monteoru well (1030 - 2033 m). For a high number of observation points, the Th vs. K crossplot (Fig. 2a) allows identification of the following minerals: illite (low content), mixed clay minerals (prevalent) and montmorillonite. K = 1.5 - 2.5 %, Th = 10 - 12.5 ppm. The Pe vs. Th / K (Fig. 2b) and Pe vs. K (Fig. 2c) crossplots confirm the interpretation of the Th vs. K crossplot; Pe = 2 - 3 b/e. It is possible that illite and mixed clay minerals to derive by transformation of initial formation montmorillonite. The implications of mineralogical clay nature knowledge of formations crossed by boreholes The mineralogical clay identification of the formations in the hydrocarbon exploration wells has multiple implications, namely: 1. In the formation evaluation process using geophysical logs, at least as four main aspects: • The best selection for analyzed area of geological model and, consequently, correct selection of needed processing parameters; • The selection of the best indicator for clay content evaluation of formations. The quantitative evaluation, with single clay content indicator, on the whole stratigraphic interval crossed by borehole, may be erroneous; the best indicator may be chosen according with type of present clay minerals identified by spectral frequency plot Th vs. K. For the majority of analyzed cases, recommended clay content indicators are: Th spectral component and combined spectral component (Th + K). • Correct qualitative interpretation of geophysical logs, particularly of nuclear logs, with possible explanations for the anomalous zones. For example, in the presence of illite, as prevalent clay mineral, significant influences may appear on thermal neutron logs responses (standard neutron-neutron log, compensated neutron porosity log or sigma log) due to the Boron content (σ capt. = 750 barns) of illite. • The presence of montmorillonite as prevalent clay mineral may be correlated with undercompacted shales, in the special studies for identification and evaluation of overpressured zones in the hydrocarbon exploration. 2. The optimum selection of drilling regime or production tests of wells, mainly by special drilling fluids or completion fluids (at perforation), when crossing formations with montmorillonite, to prevent well-known technical complications or decreasing of reservoir rock productivity. 3. The definition of depositional environments. Potassium, Thorium and Uranium, as elements quantitatively defined by natural gamma spectral logs, have certain characteristic occurrences, transport relationships and chemical properties which provide some elements concerning the depositional environment definition (Western Atlas International, 1992). References Negut, M.L., 2003, Contributions to geophysical logs applications for solving some particular geological problems in hydrocarbon exploration, Ph.D. Thesis, University of Bucharest. Western Atlas International, Inc., 1992, Introduction to Wireline Log Analysis. Schlumberger, 1990, Clay, Silt, Sand, Shales. A Guide for Well-Log Interpretation of Siliciclastic Deposits. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

744


Figure 1 The map of wells location used for clay minerals type identification using geophysical logs.

Fig 2a - Frequency crossplot, P - Monteoru well - Dacian (1030-2033 m), Th vs. K.



Figure 2b

Figure 2c

Frequency crossplot, P - Monteoru well - Dacian (1030-2033 m), Pe vs. Th / K.

Frequency crossplot, P - Monteoru well - Dacian (1030-2033 m), Pe vs. K.


746

PHYSICAL PROPERTIES OF ROCKS

P13 - 01

ELECTRICAL CHARACTERISTICS OF GNEISSES FROM GOLD-PRODUCTIVE AND NON PRODUCTIVE STRATA Sergiy Shepel Institute of Geophysics of National Academy of Sciences of Ukraine, Kiev, Ukraine

Summary This article presents the results of experimantal studies of electrical characteristics of sets of different gneisses from the central part of the Ukrainian Precambrian Shield (Ukraine) in different condition of moisture and under high temperature. It is shown that mean values of electrical conductivity decreases from the dry to the water-saturated state. That transition is especially significant in high-resistivity rocks.Certain differences of electrical parameters of dry, air-dried and water-saturated rocks of the potentially gold-productive and non-productive gneissic series at the different temperature (T) and pressure (P) conditions are established. They are clearly differentiated by the degree of electrical polarizability, relative dielectric permeability (ε) and electrical resistance (ρ). Introduction It is know that the Earth’s crust of ancient shields consists of the upper, granite or granitegneiss, and lower, basalt, layers. Gneisses of different origin and composition in the upper layer often have different texture/structure characteristics. They belong to the most widely spread metamorphic rocks there. For this reason comprehensive studies of their physical properties, including properties at high PT-conditions, are very important. Without sufficient petrophysical data many general as well as particular geological/geophysical problems are hard to solve. The biotite gneisses (40 samples) were taken from the cores of shallow exploration boreholes (up to 500 m deep) of the Ingul-Ingulets region (the central part of the Ukrainian Precambrian Shield), in the area of potentially gold-productive layers of biotite gneisses.They consists of plagioclase (14-43 %), quartz (7-53%), biotite (18-36 %) and accessory minerals (15%). Sometimes microcline (1-15%), garnet and cordierit are also encountered. The gneisses are characterised by a lepidogranoblastic structure, while their texture is usually schistose due to the parallel oriented biotite flakes. Technic of researches At the present article in laboratory conditions the specific electrical resistance on a direct current (ρ=), alternating current of 1 kHz (ρ∼) and relative dielectric permeability on frequencies 1 (ε1) and 700 kHz (ε7) dry, air-dry, water-saturated samples of rocks were investigated at normal conditions and at high temperatures up to 900oC. Relative dielectric permebility is the ratio of dielectric permeability of the medium to that of a vacuum. Rock samples of 20 mm diameter and 5 mm thickness were used in determination of electrical resistance and capacitance. The test results were then re-calculated into into the spesific electrical resistance and relative dielectric permeability. To expel moisture, the samples were kept in an oven at 105oC for 5-6 hours. Then the samples were put into a dessicator where they were cooled down to room temperature while remaining in a completely dry state. The air-dry samples contained moisture Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 747


absorbed from the air. It should be noted here that the amount of water in the samples can vary substantially depending on the humidity of the atmosphere. The installation, created by us, for reseaches of temperature dependences of electrical properties of mineral substance allows to carry out experiences in an interval up to 1200oC. It consists of blocks of high temperature and measuring. First includes the furnace, thermocouple with millivoltmeter, ampermeter and transformer. Second consists of the control panel, of ohmmeter, of measuring instrument of capacities and bridge of an alternating current. The temperature experiences were carried out in environment of air on dry samples. Results It was established that the polarisation capacity coefficient η of the great majority of biotite gneisses is below 2 %, which is typical for rocks that are not prone to polarisation. However, the types of rocks studied are clearly differentiated even within this narrow range of η. Coefficient η increases considerably when the potentially gold-productive strata are approached. In the latter case, the gneisses characterised by lower ρ and higher relative dielectric permeability. Under natural conditions, gneisses wich have formed in the upper layers of the Earth’s crust are water-saturated. At least to a depth of several dozen kilometes, they are virtually fully saturated with fluids of different mineralisation level. This is the reason why studies of physical properties of rocks at different contents of fluids and different concentrations of solts in solution is important. Electrical resistivity (direct current) of biotite gneisses completely saturated with distilled water is reduced by ≈ 3 orders of magnitude from 1,3*109 to 1,0*106 Ωm. The following relationship is clearly manifested: the higher the electrical resistivity of samples in a dry state the more intensive is its drop due to saturation with fluids. For this reason, the difference between some paricular samples in their electrical resistivity decreases significantly. Electrical properties of biotite gneisses from the potenthially gold-bearing and the barren strata were also measured at temperatures up to 900oC. The results of these experiments are shown in Fig and Table. The table, in addition to electrical resistivity logarithm at 200oC and 900oC (log ρ200 and log ρ900) presents activation energies of current carriers (E0), the logarithm of the pre-exponential coefficient (lg ρ0) of gneisses in different temperature ranges as well as dielectric permeability at 200oC and 900oC (ε200 and ε900) measured for 700 kHz. The previously established difference in electrical resistivity of such gneisses is retained at high temperature. The gneisses from the potentially gold-bearing strata are characterised by lower electrical resistivity in the entire temperature range.Thus the electrical resistivity logarithm of the potentially gold-bearing strata varies within the 7,11—7,68 range, and the average value is 7,46. The gneisses from the non-productive strata have higher log ρ (7,76—8,31), the average being 7,96. Thus, the difference amounts to 0,5 order of magnitude. The potentially gold-bearing gneis strata are charaterised by higher dielectric permeability under normal PT conditions. This can be clearly discerned for air-dried and water-saturated rocks. The difference between ε of potentially-productive and non-productive strata is more obvious in water-saturated rocks and at lower frequencies. Similar differentation of dielectric permeability is also manifested in the 100—900oC temperature field. As the temperature increases, the difference in ε between two types of gneisses becomes considerably greater. Thus, the data on variation of electrical resistivity and dielectric permeability with temperature are indicative of significant differences in their characters for gneisses from the potentially gold-productive and non-productive strata. Conclusion Thus, the data on variation of ρ and ε in normal conditions and with temperature are indicative of significant differences in their characters for gneisses from the potentially goldproductive and non-productive strata. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

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Sample lg ρ 200 No. 1

7,68

2

7,62

3

7,46

4

7,11

5

7,92

6

8,09

7

7,76

8

8,31

9

7,76

E 00 lg ρ 00 0,40 ( 100 0,44 ( 100 0,52 ( 100 0,46 ( 100 0,46 ( 100 0,39 ( 100 0,47 ( 100 0,15 ( 100 0,41 ( 100

lg ρ01

E 02 lgρ 02

lgρ900

Direct current 3,8 0,83 0,7 - 275 ) ( 275 - 580 ) 3,3 0,86 -1,2 - 275 ) ( 275 - 580 ) 1,6 0,77 -0,9 - 250 ) ( 250 - 550 ) 2,7 0,75 -1,1 - 200 ) ( 200 - 650 ) 2,9 0,83 -0,6 - 300 ) ( 300 - 600 ) 3,9 0,79 0,1 - 300 ) ( 300 - 600 ) 2,9 0,79 -0,5 - 250 ) ( 250 - 650 ) 5,2 0,92 -1,7 - 200 ) ( 250 - 500 ) 3,2 0,77 -0,1 - 250 ) ( 250 - 550 )

1,08 -1,8 ( 580 - 780 ) 1,20 -2,6 ( 580 - 730 ) 1,64 -1,5 ( 650 - 750 ) 1,1 -2,2 ( 700 - 800 ) 1,21 -2,2 ( 650 - 750) 1,46 -0,9 ( 650 - 850 ) 1,03 -1,7 ( 650 - 750 ) Anomaly at Т > 500 °С 0,88 -0,6 ( 650 - 850 )

2,80

f = 700 кГц 12,0 95,2

2,52

12,4

96,4

3,17

15,9

74,3

2,32

14,1

80,2

3,06

14,0

83,2

3,46

-

-

3,22

-

-

3,47

-

-

3,41

-

-

E 01

ε200

ε 900

Temperature ranges (oC) are shown in brackets, activation energy is measured in eV, and electrica l Resistivity in Ωm. The first four specimens represent the potentially gold-productive strata, while the rest of them represent the non productive strata.

Table Electrical properties of gneisses at high temperatures 2 4 6 8 10

a 0.8

2 4 6 8 10

1.2

1.6

2

2.4

2.8

227

144

Т, С

2.4

2.8

b 977 0.8

560

352

1.2

1.6

2

0

1000 / Т , К

-1

Figure Log ρ of gneisses from the potentially gold-bearing strata (a) and the barren strata (b) as a function of temperature. The measurements were carried out for direct current (solid lines) and alternating current (dashed lines) of 1kHz.



P13 - 02

THERMOBARIC VARIATIONS OF THE MAGNETIC CHARACTERISTICS OF SOME MINERAL FORMATIONS Boris Ya. Savenko, Valeri A. Korchin, Aleksander S. Nekh Institute of Geophysics National Academy of Sciences, Kiev, Ukraine

Introduction Modern thermobaric studies in the field of experimental petrophysics make it possible to obtain quite diverse information on the origin and variation pattern of magnetic properties, composition and the state of a mineral substance under the conditions of great depth. Besides, they can be widely used in development of deep petrophysical models of the geological medium, interpretation of the geophysical medium and interpretation of the geophysical observation results (1-3 etc.). As a rule, in calculations on magnetic models of the Earth's crust, the inductive component is regarded as having the major role. However there is a whole series of rocks whose remanent magnetization is much larger than the inductive one. The deep rocks with prevalent remanent magnetization, constantly affected by the earth's magnetic and thermal fields, are the real sources of regional magnetic anomalies mider the coudifious of litostatic pressure. The magnetic state of rocks, due to the resultant effect of the inductive Ii, and residual magnetization In, depends on the content and the kind of the ferromagnetic. It also depends on the effect of the temperature T and the pressure P, which increase with depth, oxidationreduction potential of the mineral medium and some other factors. The ferromagnetic minerals defining magnetism of crustal materials and the observed anomalous magnetic field are mainly magnetite, titanomagnetite and pyrrhotine. Studies of magnetic properties of rocks as a function of deep PT-conditions is of utmost importance for petromagnetic modeling. For this reason, the experiments are set up in the laboratory, designed to reproduce the conditions similar to those at the depths in the crust where ferromagnetic components of the mineral material are located. This paper presents an analysis and summation of results of experimental investigations of thermobaric variations and the possible distribution of remanent saturation magnetization Irs and magnetic susceptibility æ with depth for most typical igneous rocks with ferromagnetic components, collected in different areas of Ukraine, and similar associations and ores from some geological provinces other countries. The laboratory experiments have been made on more than 280 samples by methods worked out by the authors and on respective equipments and instruments including those made by regional PT-programs (2,3 etc.). Experimental results and discussion The magnetite-bearing rocks of this set of samples included those most common in the crust's mineral formations, where magnetite is an accessory mineral, syngenetic with the rock's formation time, and also as a product of its geological history. Figures I-I carries information on thermobaric demagnetization of remanent saturation magnetization of rocks of different origin and basicity, and consequently different distribution in the crust down to 20 km. Analysing the experimental data, the Irs/Irso, parameter was used, corresponding to a certain depth calculated with the PT-program for temperature and pressure variation in deep layers of particular geological regions. 4th Congress of the Balkan Geophysical Society, 9-12 October 2005, Bucharest, Romania

750


Figure 1 Ranges of relative changes of mean values of remanent saturation magnetization Irs of some igneous rocks and ores by experimental PT-data. 1 magnetitebearing rocks (a - ultrabasic, b - basic, c – acid); 2 titaniummagnetite-bearing rocks (volcanites and basalts): a- T c ≈ 200-300 ○ C, b- T c ≈ 300-400 o C, c - Tc ≈ 400500oC; 3 - pyrrhotine-bearing (a - ores, b – rocks).

Figure 2 Mean values of relative changes of magnetic susceptibility æ of igneous rocks of the Ukrainian Precambrian Shield under P and T effect with depth. 1- f(P), 2- f(T), 3f(PT).

Residual saturation magnetization of the mineral formations studied varies over a wide range of values. First of all, it depends on the type of rock and under what conditions it formed. The origin of magnetite, its structure and the presence of various impurities and inclusions define the behavior of Irs in PT-experiments and its distribution in deep layers of the earth's crust. The maximum decrease of Irs (for all the samples studied) was typical of the early stage of application of high P and T. Pressure played a greater role in thermobaric demagnetization here. Titanomagnetite-bearing rocks included samples of basaltoids of different composition and genesis from several geological region of Ukraine and some other areas. Magnetic properties of these formations are characterised by remanent magnetization playing a prevailing role. Its contribution into total magnetization is much higher than that of induction magnetization. Figures 1-2 illustrates results of PT-experiments and the distribution of remanent saturation magnetization with depth for volcanic rocks of different petrographic compositions. The scatter of Irs of the liparite-basalt series volcanic rocks can be explained by titanomagnetite composition, different Tc values (200-500°C) and different extent of low- and high-temperature oxidation. Most samples with Tc>200°C and below 400°C lose their remanent magnetization at Journal of the Balkan Geophysical Society, Vol. 8, 2005, Suppl. 1 751


approximately 10-12 km. It can be expected than, in volcanic rocks with 400