Main tectonic features found in Tabgha (A) and Fuliya (B) regions (after Tibor et al.,. 2004). Bold lines mark the mapped active faults. Each survey conducted in ...
Raymond and Beverly Sackler Faculty of Exact Sciences Department of Geophysics and Planetary Sciences
Microseismic characterization of Lake Kinneret basin
Thesis submitted as partial fulfillment for the degree of Master of Science in Geophysics
B Byy
H Hiillaa N Naavvoonn
TThhiiss w woorrkk w waass ccaarrrriieedd oouutt uunnddeerr tthhee ssuuppeerrvviissiioonn ooff PPrrooffeessssoorr ZZvvii B Beenn--A Avvrraahhaam m D Drr.. H Hiilllleell W Wuusstt--bblloocchh D Drr.. R Raam mii H Hooffsstttteetttteerr
October 2011
Abstract Lake Kinneret basin (LKB) is a tectonic complex structure which is situated along a segment of the Dead Sea Transform (DST). Two fault systems which intersect under Lake Kinneret sub-bottom, basalt flows of various thicknesses and rotation of blocks north and west of the lake hampers structural interpretation of the basin. The numerous geophysical investigations which have been carried out in Lake Kinneret reveal evidence for active faulting. Seismological data as well as geological, archaeological, and historical evidence indicate that LKB is an active seismic zone crosscut by faults along which earthquakes often occur. This study aims to monitor and characterize the local seismicity which is generated by the LKB fault segments. Creating a complete seismic catalog and characterizing its weak seismicity will help assessing seismic hazards in the highly populated LKB area. A cluster of four Seismic Navigation Systems (SNS) were deployed, along the northern and north-eastern coasts of Lake Kinneret, to continually monitor the seismicity of the LKB. The SNS were deployed for a period of twelve months in Korazim, Almagor, Ma’alle-Gamla and Ramot where data were recorded in a continuous mode at sampling rate of 250 Hz. The catalog newly acquired has been completed by local earthquakes which were detected over 25 years by the Geophysical Institute of Israel (GII). The deployment of the SNS has enabled the detection of large amount of earthquakes in a short period of time and the lowering of the detection threshold of the GII catalog for local earthquakes. The results show that most of the seismic activity in the LKB is characterized by very low magnitudes. This seismic activity is concentrated mainly in the northern portion of the LKB and these events display shallow hypocentral depths. The bvalue that was calculated was rather low and might be an indication for high stress regime. Although the data is still too sparse to map the geometry of the LKB faults with accuracy, the new seismic catalog displays seismicity that can be associated to existing tectonic I
features. The Jordan fault is presently active and its southern extent probably corresponds to the eastern boundary fault of the DST within the LKB. The northern sub-basin is the most seismically active feature, possibly confirming the hypothesis of Ben-Avraham et al. (1996) that it is currently subsiding. The random distribution of events in that subbasin also supports the claim that it is highly deformed (Reznikov et al., 2004). Several earthquake clusters which were observed in the northern sub-basin seem to delimit its borders and may indicate that the LKB may function as a barrier to the movement of the DST in this section. The enhanced seismicity along the bathymetrical cliff supports the claim of Ben-Avraham et al. (1990) and Reznikov et al. (2004) that this is possibly an expression of an active fault line that may be the off-shore extension of active Tiberias fault. The Sheik Ali fault shows moderate seismicity and the absence of seismic activity south to Lake Kinneret suggests that it may be a locked segment of the DST. Nine month of continuous monitoring by four SNS has been sufficient to detect 10 times more events than the national network within the LKB. The high sampling rate records full spectrum of the event signal and thus enables the determination of the corner frequency, even for event with magnitudes as low as M L=-1.2. This new data base, supplemented by the GII local earthquake catalog, has enabled the characterization of the weak seismicity within the LKB and illuminated existing tectonic features which are presently active.
II
Many Thanks I would like to thank all those people who made this thesis possible. I owe my deepest gratitude to my supervisors:
to Zvi Ben-Avraham for the help,
attention and support, to Hillel Wust-Bloch for introducing me to the nano-seismic world and providing me with all the equipment and help necessary for this research and to Rami Hofstetter for his guidance and criticism which clarified and made this work more professional. I would also like to thank Dr. Ran Bachrach for listening, advising and teaching and to Andy Eisermann for helping with all the technical difficulties. Special thanks to the people of the Kinneret region who opened their doors for me and allowed me to dig in their private back-yards and install my equipment for more than a year: to Diego from Korazim, Orna the secretary from Almagor, Micha from Ma’alle Gamla and Yoshko from Ramot. This research would not have been possible without their hospitality. To all of my ‘Rooftop’ friends : Edan, Anastasya, Nadav, Adi, Itay, Mor, Eyal, Noam, Lilach, Ra’anan and Miki, for always being there, supporting, advising, discussing and making me laugh. And finally, I would like to thank my family for always believing in me and my beloved husband Shakked for the fun rides to Lake Kinneret, the endless help with the maintenance of the stations and for all the moral support throughout this project. Thank You!
III
Table of Contents 1
Introduction ................................................................................................................. 6 1.1
1.1.1
Tectonic settings ........................................................................................... 7
1.1.2
Geological settings ........................................................................................ 9
1.1.3
Seismicity.................................................................................................... 12
1.2
2
Research goals .................................................................................................... 17
1.2.1
Motivation for microseismic monitoring .................................................... 18
1.2.2
Objectives ................................................................................................... 18
1.2.3
Duration of data sets ................................................................................... 18
Previous investigations of the study area .................................................................. 19 2.1
Studies of the sub-bottom structure.................................................................... 19
2.1.1
Early seismic reflection and refraction investigations ................................ 19
2.1.2
Magnetic measurements.............................................................................. 20
2.1.3
Bathymetric mapping .................................................................................. 22
2.1.4
Gravity measurements ................................................................................ 24
2.1.5
Multi-channel seismic reflection survey ..................................................... 25
2.1.6
Additional geophysical studies ................................................................... 27
2.2
3
Study area ............................................................................................................. 6
Seismicity studies ............................................................................................... 28
2.2.1
Seismicity patterns ...................................................................................... 28
2.2.2
Focal plane solutions................................................................................... 30
2.2.3
Induced seismicity ...................................................................................... 31
Methods..................................................................................................................... 32 3.1
Israel Seismic Network (ISN) ............................................................................ 32
3.1.1 3.2
Data processing ........................................................................................... 32
Mini-arrays ......................................................................................................... 34
3.2.1
Data acquisition .......................................................................................... 35
3.2.2
Network coverage/detection threshold ....................................................... 37
3.2.3
Data processing ........................................................................................... 37 1
3.2.4 3.3
4
Analysis and Display.......................................................................................... 47
3.3.1
Spectrum analysis ....................................................................................... 48
3.3.2
Cross-correlation ......................................................................................... 48
3.3.3
b-value calculations .................................................................................... 48
Results ....................................................................................................................... 49 4.1
Israel Seismic Network (ISN) ............................................................................ 49
4.1.1
Spatial distribution ...................................................................................... 49
4.1.2
Zones of seismic activity ............................................................................ 49
4.1.3
Depth distribution ....................................................................................... 52
4.1.4
Magnitude distribution ................................................................................ 53
4.1.5
Temporal distribution/Seismicity rate......................................................... 54
4.1.6
Magnitude-Time frequency ........................................................................ 55
4.1.7
Event clustering in time and space.............................................................. 56
4.1.8
Corner frequency ........................................................................................ 59
4.2
Seismic Navigation System (SNS) ..................................................................... 60
4.2.1
Spatial distribution ...................................................................................... 60
4.2.2
Zones of seismic activity ............................................................................ 60
4.2.3
Depth distribution ....................................................................................... 64
4.2.4
Magnitude distribution ................................................................................ 64
4.2.5
Temporal distribution/Seismicity rate......................................................... 64
4.2.6
Magnitude-Time frequency ........................................................................ 64
4.2.7
Event clustering in time and space.............................................................. 68
4.2.8
Corner frequency ........................................................................................ 68
4.3
5
Estimation of location uncertainty .............................................................. 45
Comparing different catalogs ............................................................................. 70
4.3.1
Spatial distribution ...................................................................................... 70
4.3.2
Magnitude threshold ................................................................................... 72
4.3.3
Sampling rate .............................................................................................. 72
4.3.4
Estimation of uncertainty ............................................................................ 73
Discussion and conclusions ...................................................................................... 76 5.1
The new database (SNS catalog) ........................................................................ 76 2
5.2
Common events .................................................................................................. 76
5.3
Event magnitude ................................................................................................. 78
5.4
b-value ................................................................................................................ 78
5.5
Event clustering in space and time ..................................................................... 79
5.6
Doublets ............................................................................................................. 79
5.7
Signal spectrum .................................................................................................. 80
8.5
Patterns of seismic activity and tectonic implications ....................................... 80
5.9
Final conclusion ................................................................................................. 81
Appendix A ....................................................................................................................... 82 Stations coordinate ........................................................................................................ 82 Appendix B ....................................................................................................................... 85 Earthquake catalogs ...................................................................................................... 85 Appendix C ....................................................................................................................... 97 Corner frequencies ........................................................................................................ 97 Appendix D..................................................................................................................... 105 Earthquake clustering and doublets ............................................................................ 105
3
Table of figures Figure 1-1. Location map of the study area. ....................................................................... 7 Figure 1-2. Main tectonic features around Lake Kinneret and the adjacent areas. ............. 8 Figure 1-3a. Geological map of Lake Kinneret and the adjacent areas. ........................... 10 Figure 1-4. Velocity model of the north-eastern shores of Lake Kinneret ....................... 12 Figure 1-5. The structure of the Kinneret basin as inferred from gravity data.. ............... 14 Figure 1-6. Historical earthquakes along the DST in the past 4000 years. ....................... 15 Figure 2-1. Velocity section in Lake Kinneret.................................................................. 20 Figure 2-2. Interpretation map of Kinneret basin. ............................................................ 21 Figure 2-3. Structural map of the cover basalt in Lake Kinneret region .......................... 22 Figure 2-4. Fault map of Lake Kinneret ........................................................................... 23 Figure 2-5. Schematic map of major morphotectonic features of Lake Kinneret floor .... 24 Figure 2-6. Schematic map of the structural elements of Lake Kinneret and its vicinity..25 Figure 2-7. Major faults in Kinneret area ......................................................................... 26 Figure 2-8. Major faults in Kinneret area. ........................................................................ 27 Figure 2-9. Main tectonic features found in Tabgha and Fuliya regions ........................ 28 Figure 2-10. Reduced seismicity map of Lake Kineret region 1982-1989 ....................... 29 Figure 2-11. Fault plane solutions for 4 events in the LKB.............................................. 30 Figure 2-12. A schematic description of the suggested triggering mechanism ................ 31 Figure 3-1. Distribution of ISN stations operating from 1986 to 2010. ........................... 33 Figure 3-2. Velocity model used for locating events by jSTAR software. ........................ 34 Figure 3-3. Location map of the four SNS stations in the study area. .............................. 35 Figure 3-4. Digitizer and power-pack at Ma'alle-Gamla and Korazim ........................... 36 Figure 3-5. The alignment of the sensors in Ma'alle-Gamla mini-array. .......................... 36 Figure 3-6. Sensor buried in a sand-filled tube. ................................................................ 37 Figure 3-7. Network coverage and expected detection threshold.. ................................... 38 Figure 3-8. Screen view of Sonoview display.. ................................................................ 40 Figure 3-9. Event identification. ....................................................................................... 41 Figure 3-10a. Discrimination between explosions and earthquakes. ................................ 43 Figure 3-11. An example of graphical location. ............................................................... 45 Figure 3-12. Velocity model (Vp) used for location process in the Hypoline software. ... 47 Figure 4-1. Earthquake epicenters from the past 25 years as detected by the ISN ........... 50 Figure 4-2. Zones of seismic activity (GII catalog) and tectonic features. ....................... 51 Figure 4-3. Distribution of events in space ....................................................................... 52 Figure 4-4. Distribution of event magnitude in space....................................................... 53 Figure 4-5. Annual distribution of events that were detected in the study area. ............... 54 Figure 4-6. Monthly distribution of events that were detected in the study area over 25 years. ................................................................................................................................. 54 Figure 4-7. Magnitude-Time distribution of events detected in the study area. ............... 55 4
Figure 4-8. Magnitude-frequency relationship (b-value).................................................. 56 Figure 4-9. Clusters observed in the study area.. .............................................................. 57 Figure 4-10. Best plane fit . .............................................................................................. 57 Figure 4-11. Result of crosscorrelation between two events close in time and space ...... 58 Figure 4-12. Amplitude spectrum of displacement signal. ............................................... 59 Figure 4-13. Distribution of events epicenters as observed in nine months by SNS. ....... 61 Figure 4-14. Magnitude detection threshold. .................................................................... 62 Figure 4-15. Detection range of low magnitude events by the SNS. ................................ 62 Figure 4-16. Zones of seismic activity and tectonic features. ........................................... 63 Figure 4-17. Distribution of events in space. .................................................................... 65 Figure 4-18. Distribution of event magnitude in space..................................................... 66 Figure 4-19. Monthly distribution of events as recorded by SNS in the study area. ........ 67 Figure 4-20. Magnitude-Time distribution. ...................................................................... 67 Figure 4-21. Cumulative monthly magnitude frequency relationship (b-value). ............. 68 Figure 4-22. Result of cross-correlation between two events close in time and space ..... 69 Figure 4-23. Corner frequency as a function of magnitude. ............................................. 70 Figure 4-24. Spatial distribution of events ........................................................................ 71 Figure 4-25. Histogram of depth distribution. .................................................................. 71 Figure 4-26. Magnitude-Frequency relationship of both catalogs. ................................... 72 Figure 4-27. Spectrogram of the same earthquake ........................................................... 74 Figure 4-28. Example for different solutions for the same earthquake .................... ……75 Figure 4-29. Another example for different solutions for the same event ........................ 75 Figure 5-1. Common events as detected by SNS and ISN networks ................................ 75 Figure C-1. Mean value of frequency per magnitude ..................................................... 104
5
Chapter 1
1
Introduction
This study explores the seismicity of Lake Kinneret basin (LKB), a seismically active segment of the Dead Sea Transform (DST) based on geological, archaeological, and historical evidence (Ben-Menahem, 1991; Marco, 2008; Hamiel et al., 2009). The destructive damage that the region suffered was caused by strong earthquakes, (M≥6, Begin, 2005), rarely occurring in this area. According to Gutenberg-Richter relationship (Gutenberg and Richter, 1944), weaker earthquakes have a higher frequency of occurrence than stronger events therefore it is reasonable to expect microseismicity to be generated by fault segments that have been mapped to crosscut the LKB. Since Lake Kinneret region is an inhabited area (population of 100,000) it is important to study and map the local microseismicity, which is generated in the region. A full seismic activity catalog and its characterization are essential for seismic hazard assessment. 1.1
Study area
Lake Kinneret is a body of fresh water in the northern part of Israel which forms one of the main national water reservoirs. The lake constitutes a drainage basin to many streams from adjacent areas (Figure 1-1). The average surface area of the lake is 167 km2 and its average volume is 4*109 m3. The lake reaches a maximal length of 20 km and a maximal width of 12 km. The water level fluctuates between 209 m and 215 m below mean sea level (msl) and the maximum depth is 256 m below msl (Ben-Avraham et al., 1990). The present configuration of the lake was formed about 15,000 years ago, when Lake Lisan began its retreat (Neev, 1978). Being a major source of drinking water it has been a subject of many studies. In addition to hydrogeology, chemistry and biology studies of Lake Kinneret and the region, numerous geophysical investigations, using various methods have been carried out in the area in the past three decades (Ben-Avraham, 2004, and references therein). All investigations reveal a complex structure of Lake Kinneret sub-bottom and evidence for active faulting.
6
Figure 1-1. Location map of the study area. A) General map of the Dead Sea Transform (DST). B) DTM of Lake Kinneret and its surroundings, highlighting the morphotectonic features around the LKB (after Hall, 1993) and the converging streams. Coordinates are in Israel TM grid in meters.
1.1.1
Tectonic settings
Lake Kinneret occupies the LKB, which is located in the northern part of the southern segment of the DST (Figure 1-1). The DST is an active plate boundary, which separates the Arabian plate from the Sinai sub-plate. The fault line is more than a 1000 km long, stretching from the sea-floor spreading of the Red Sea to the zone of continental collision in the Taurus-Zagros Mountains. The motion along the DST has begun in the early Miocene with the brake up of the African-Arabian continent and was accompanied by regional volcanism and uplifting on both sides of the transform. A total of 105 km leftlateral slip is indicated by matching geometrical features across the transform and by kinematic analysis of the Arabian-African plate motion (Garfunkel, 2001). The transform movement is characterized by the development of pull-apart basins and pressure ridges 7
along the fault line. The main pull-apart basins along the southern DST (Eilat basin, Dead sea basin and Hula basin) were formed by the left-lateral motion where the fault trace bends to the left (Garfunkel, 2001). The main fault system that controls the formation of the LKB is part of the DST which trends N-S (Ben-Avraham et al., 2008). As a result of counterclockwise rotation of the Korazim block (Heimann and Ron, 1993) a secondary fault system, which trends NW-SE, crosscuts the DST under the Lake's sub-bottom and extends into the Galilee (Neev, 1978). Superposition of the displacement of the two fault systems (Figure 1-2) is the main reason for the complexity of the Kinneret basin (BenAvraham et al., 1996). Although many studies were carried out in this area, little is known of the tectonic structure of the LKB. The main question of how the eastern boundary fault of the DST is connected from the southern part of the lake to the northern part of the lake remains unanswered. Applying new data of the seismic activity might yield new information about the geometry and nature of the basin's structure.
Figure 1-2. Main tectonic features around Lake Kinneret and the adjacent areas. Faults marked in black are suspected as active and faults marked in red are active (Bartov et al., 2002; Bartov et al., 2009). Abbreviations are DST - Dead Sea Transform, AF - Almagor fault, JF - Jordan fault, SAF – Shiek-Ali Fault. The geometry of the faults under the lake is still unknown.
8
1.1.2
Geological settings
The study area includes LKB and the surrounding areas which reveal a diverse and complex geology (Figure 1-3). The northern shores of the lake are delimited by Korazim block, an elevated pressure ridge. The Korazim block is covered mostly with basalts of three separated volcanic phases (Pliocene to Pleistocene) from different sources and of Plio-Pleistocene sediments(Heimann and Ron, 1993). The sediments and the cover basalts are highly deformed by young faults (Belitzky, 1987). The rotation of the blocks along with a left-lateral slip on the Almagor fault branch of the DST is the reason for the internal deformation (Heimann and Ron, 1993). On the eastern shores, the lake is bounded by the central province of the Golan Heights, an elevated basalt plateau. Recent study of deep geological structure of the Golan Heights (Meiler, 2011) reveal a complex structure, mainly on the north eastern shores of Lake Kinneret (Figure 1-4). The subsurface structure of the Golan Heights is of a syncline, which is accommodated by Senonian–Tertiary sediments and Plio-Pleistocene basalts (Meiler, 2011). Essential differences are obvious between the geology of the eastern and the western sides of the LKB (Neev, 1978; Michelson et al., 1987). Sediments and basalts from Cretaceous to Holocene are exposed in the Eastern Galilee which delimits Lake Kinneret western shores (Neev, 1978). Eocene, Oligocene and Miocene formations are different in thickness and composition on both sides of the LKB and some formations are even missing in the Poriya Heights, when compared to stratigraphy of the southern Golan Heights (Michelson et al., 1987). Kinnarot Valley lays to the south of the Kinneret. The most direct evidence of the complex stratigraphy of the Kinneret basin is provided by Zemah1, a 4249 m deep drill-hole located in the Kinnarot valley (Marcus and Slager, 1985). The well comprises marls, clay, limestones, conglomerates, salt, basalt flows and intrusive gabbros divided into five lithological units. The geology of the basin can be inferred from the gravity data (Ben-Avraham et al., 1996). Negative gravity anomalies indicate thick sedimentary layer fill of the basin whose width and depth vary along its length axis. The gravity data indicate that the basin is divided into two sub-basins. The southern basin is the deeper sub-basin containing ca. 8 km of sediments including volcanic and intrusive evaporates. The fill under this part thins to ca. 5 km toward the Kinnarot valley in the south. The northern sub-basin is wider and shallower (Figure 1-5). 9
These investigations of the LKB show that its geology and tectonics is complex, thus making geophysical investigations very challenging.
Figure 1-3a. Geological map of Lake Kinneret and the adjacent areas. Legend is in the next page, Figure 1-3b (modified after Sneh et al., 1998).
10
Figure 1-3b. Legend of the Geological map of Lake Kinneret and the adjacent areas (modified after Sneh et al., 1998).
11
0 1
Basalt flows
2
Depth (km)
3 4 5 6 7 8 2.5
3
3.5
4 4.5 Velocity (km/sec)
5
5.5
6
Figure 1-4. Velocity model of the north-eastern shores of Lake Kinneret (modified after Meiler, 2011). The young basalt flows create an inversion of the velocity of the top layers which hampers interpretation.
1.1.3
Seismicity
Although seismicity rate along the DST is rather moderate, strong earthquakes have occurred in the region over the past 4000 years, destructing cities and causing many casualties (Ben-Menahem, 1991). Evidence for seismic activity The areas surrounding LKB suffered severe damage due to earthquakes that occurred along the DST in the past. Archeological evidence show that the A.D. 749 earthquake caused serious damage to the present Galei-Kinneret site on the western shore of the Kinneret (Marco et al., 2003) and even more destructive damage to the Susita-Hippos site on the eastern part of the Kinneret (Segal et al., 2002). A landslide which was triggered by this earthquake caused damage in Umm-El-Qanatir site, which is located 10 12
Km north-east of the Susita-Hippos site (Wechsler et al., 2009). An additional set of four earthquakes in A.D. 1202, 1546, 1759 and 1837 caused a 2.1 m horizontal offset of the Crusader Ateret Fortress north of Lake Kinneret (Marco et al., 1997; Ellenblum et al., 1998). Recent excavations of the Hellenistic compound underneath the fortress reveal that
the
total
offset
in
the
archeological
site
amounts
to
5.7
meters
(http://www.bgu.ac.il/geol/classes/iu/). Paleoseismic records in Bet-Zayda valley at the northern shores of Lake Kinneret show 2.2 m of sinistral offset attributed to the 1202 earthquake and another 0.5 m offset attributed to the 1759 earthquake (Marco et al., 2005). Another 15 m of slip was identified to have accrued over the past 5,000 years (Marco et al., 2005). Morphological expressions of earthquake related damage can be seen in the terrace view of the Golan Heights and sliding slopes. Ben-Menahem (1991) details biblical and historical evidence of earthquake related damage and lists the time and location of the events. The records show that out of 42 earthquakes with estimated magnitude of 6.7≤ML≤8.3 which originated along the DST in the past 4000 years only one originated in the study area (Figure 1-6). The earthquake originated eastward of Safed mountains (33No, 35.5Eo), in January 1837, ML=6.7, and caused the destruction of Safed and Tiberias, 3000 victims and tidal waves in Lake Kinneret (Ben-Menahem, 1991). Although past events have caused destruction in the region instrumental records since 1900 show that most of the seismic activity in the study area is of low magnitude with only 8 events between 4≤ML≤4.5.
13
Figure 1-5. The structure of the Kinneret basin as inferred from gravity data. A) Site map with the location of the three gravity profiles marked in red (modified after Ben-Avraham et al., 2008). DTM after Hall (1993). B) Three E-W gravity profiles. Dashed lines are observed gravity after corrections compared with calculated gravity (solid lines). Numbers represent the densities in kg m-3, black bold layers are basalt flows and inverted triangles mark the boundaries of the lake (Ben-Avraham et al., 1996).
14
Figure 1-6. Historical earthquakes along the DST in the past 4000 years. Red stars represent the location (Ben-Menahem, 1991) and bold numbers represent the year of the event. DTM after Hall, 1993.
Seismic parameters Previous seismicity studies have divided the southern segment of the DST into three to five segments (Shamir et al., 2001; Begin and Steinitz, 2005; Hofstetter et al., 2007). Since LKB occupies a relatively small area it is included both in the northern part of the 15
Jordan Valley segment and in the southern part of the Hula Valley segment. Therefore, in the following studies the Kinneret area will be referred to either Hula Valley or Jordan Valley. b-value The seismicity of a region is characterized by the b-value of the magnitude-frequency equation. According to the Gutenberg-Richter relationship, the frequency of earthquake occurrence is in a logarithmic relationship with the magnitude of the event given by the equation:
where N(m) is the cumulative annual number of earthquakes with magnitude greater than or equal to M, a is a constant corresponding to the Mmin for catalog completeness and b, typically close to 1, represents the seismicity of the region. The most updated calculation of b-value for the DST, with the most complete instrumental and historical data yields the value of 0.96 (Shapira, 2002, Appendix C). Investigations of smaller segments of the DST which includes LKB area resulted in the following magnitude frequency relationships: log [N(m)] =2.91-0.86M, for a 190 km segment of the DST (Ben-Menahem, 1981), log [N(m)] =3.1-0.86M, for a 430 km segment of the DST (Ben-Menahem, 1991), log [N(m)] =3.4-0.8M, for Hula Valley (Shapira and Feldman, 1987), log [N(m)] =2.36-0.85M, for northern Jordan valley (Hamiel et al., 2009). Recurrence of earthquakes The average recurrence of earthquake can be inferred from the calculation of b-value. Ben-Menahem (1981, 1991) show that the mean return period of maximum magnitude of ML=7.3 is 2,300 years for a 190 km segment of the DST and 1,500 years for a 430 km segment of the DST.
Calculation of average recurrence of earthquake magnitude
MW≥6.2 in the Jordan Valley and the Dead Sea is 400 years, and for earthquake magnitude MW≥7 is 3,000 years (Begin, 2005). The average recurrence of earthquakes in 16
Hula seismogenic zone calculated by Shapira and Hofstetter (Shapira, 2002, Appendix C) is 35 years for M≥5, 340 years for M≥6 and 4500 years for M≥7 assuming a b-value of 0.96. Slip rate and activity rate The average slip rate along the DST during the past 20 m.y. is 5.4 mm year-1 (Eyal et al., 1981). Ben-Menahem (1981) found that the seismic slip in northern Israel with rate of 1.9 mm year-1 constitutes only one third of the motion. This is in accord with 1.9 mm year-1 slip rate for the Hula seismogenic zone inferred from rate of cumulative activity based on the present seismic activity (Shapira, 2002, Appendix C). The average activity rate along the DST is 0.26 events of M≥2 per kilometer per year where in Hula Valley one gets almost half of it, with a value of 0.15 events of M≥2 per kilometer per year (Shapira, 2002, Appendix C). Overall, seismogenic zones including LKB show lower seismicity values than the whole DST or sections comprising the Dead Sea basin or Eilat basin. 1.2
Research goals
Characterization of seismicity is essential for hazard evaluation especially in a populated area along an active fault. Since the LKB generates low magnitude earthquakes, investigations require to complete the existing catalogs and to characterize the microseismic activity. Local microseismic monitoring requires the deployment of highly sensitive seismic instruments located close to the source. To lower the detection threshold and to add to the Israel Seismic Network (ISN) catalog, a cluster of four portable miniarrays was deployed temporarily within the LKB. According to Gutenberg-Richter relationship (Gutenberg and Richter, 1944) the number of earthquakes increases approximately tenfold with each drop of one unit of magnitude. The aim of deploying the mini-arrays was to lower the detection and thus obtaining a statistically meaningful data sample within much shorter monitoring period (9 months).
17
1.2.1
Motivation for microseismic monitoring
The motivation for local microseismic research lies within the fact that large data sets can be obtained in a shorter period of time. There are numerous applications of microseismic monitoring (Lee and Stewart, 1981) such as: mapping local seismicity in high resolution (Hage and Joswig, 2009b), earthquake prediction by changes of seismicity pattern (e.g., Shapira, 1990; Bouchon et al., 2011), mapping active faults for hazard assessments (e.g., Carena et al., 2002; Hage and Joswig, 2009a) and studies of induced seismicity (e.g., Simpson, 1976; Kafri and Shapira, 1990; Liu et al., 2011). Integrating microearthquake data with other geophysical information can be a powerful tool in studying the nature and state of tectonic processes (Lee and Stewart, 1981). 1.2.2
Objectives
The present investigation has three main objectives: A. Monitoring microearthquake activity of the study area and characterizing weak local seismicity. B. Evaluating the preformance of the portable mini-arrays deployed for the purpose of microseismic monitoring. C. Merging microseismicity data with ISN catalog to improve our understanding of the LKB tectonic structure. 1.2.3
Duration of data sets
Monitoring microseismic activity was achieved by deploying a cluster of four temporary mini-arrays in the study area. The data have been completed by local events detected over 25 years and included in the ISN catalog. Data processing consists of detecting, locating and characterizing seismic events. The analysis of the data is carried out by integrating two different monitoring periods: 25 years and 9 months.
18
Chapter 2 2
Previous investigations of the study area
2.1
Studies of the sub-bottom structure
In the past 30 years a number of studies using different geophysical methods were conducted in the LKB. However, several unusual features have complicated the structural interpretation (Ben-Avraham et al., 2008) : the intersection of two fault systems under the bottom of the Lake, basalt flows of various thicknesses and the rotation of Korazim block at the northern part of the lake. Consequently, different models have been proposed for the geometry of the fault segments within the LKB (e. g., Ben-Avraham et al., 1996; Hurwitz et al., 2002; Reznikov et al., 2004). 2.1.1
Early seismic reflection and refraction investigations
Seismic reflection and refraction measurements (Ben-Avraham et al., 1981) revealed a complex structure under LKB. Although the obtained seismic profiles were poor and limited both in resolution and penetration depth, indications for active faulting and subbottom structures were observed. Shallow reflection profiles indicate active faulting, concentrating along the margins. An active fault was detected in the southern margin and a zone of recent vertical movement was found in the deepest part of the lake. Folded structures were also observed along the eastern and northern margins. The refraction profiles also point out large differences in velocity structure between different parts of the LKB (Figure 2-1). Higher seismic velocities were observed in the northern section and lower seismic velocities in the southern section, which would indicate lateral anisotropies at depth. A high frequency seismic survey was conducted a few years later (BenAvraham et al., 1986) to improve the resolution of the shallow layers below Lake Kinneret. Since the previous study showed that results improve with increased frequency of the source, a shallow seismic system of 3.5 kHz was selected for the survey, as opposed to previous survey that used instruments of frequency ranges up to a few hundreds of Hz. This study resulted in no acoustic penetration over most parts of the lake. Ben-Avraham et al. (1986) explain the unexpected results with presence of high gas 19
content of the upper sedimentary layer. However, an excellent acoustic penetration was achieved over the area south of the bathymetric scarp in the southern part of the lake and at the vicinity of the hot saline submarine springs. Haddock (1999) relates this phenomenon to the existence of faults and seismic activity which release the gas bubbles from the sediments. Since there is no gas left in the sediments, acoustic penetration is not hindered.
Figure 2-1. Velocity section in Lake Kinneret (after Ben-Avraham et al., 1981). Higher velocities of the northern underlying layer indicate different composition of the layer between the northern and southern regions. Coordinates are in ICS – the old coordinate system for Israel.
2.1.2
Magnetic measurements
Magnetic data from a survey over Lake Kinnerert (Ben-Avraham et al., 1980) and magnetic measurements in the southern part of the lake (Ginzburg and Ben-Avraham, 1986) were combined to yield a magnetic anomaly map. The magnetic anomalies, which would mark the extent of volcanic bodies, follow patterns that are thought to be 20
associated with faults. The main trends stretch from north to south on both sides of the lake and are separated by a magnetically quiet zone in the center of the lake. The interpretation of the LKB structure based on the magnetic measurements is shown in Figure 2-2. Eppelbaum et al. (2004) preformed analysis of magnetic and paleomagnetic data using advanced methodology for the complicated geological environment of the LKB and the adjacent areas. Their results were integrated with seismic and tectonic data to compile a structural basalt cover map for LKB and the surroundings (Figure 2-3). Based on the integrated data, Eppelbaum et al. (2004) suggested that the eastern part of the LKB is sheared and displaced by the DST movement, the central part of the lake is a pull-apart basin and the western part is a subsided continuation of the Eastern-Galilee structure.
Figure 2-2. Interpretation map of Kinneret basin. The dotted lines show the faults as interpreted from the magnetic data (after Ginzbug and Ben-Avraham, 1986). Coordinates are in ICS – the old coordinate system for Israel.
21
Figure 2-3. Structural map of the cover basalt in Lake Kinneret region (after Eppelbaum et al., 2004). The dashed lines designate location of faults according to the integrated analysis of the magnetic data with geological and seismic data. Coordinates are in ICS – the old coordinate system for Israel.
2.1.3
Bathymetric mapping
Although high sedimentation rate of 2-7 mm year-1 (Serruya, 1973) in Lake Kinneret causes smoothening of the floor, it possible to see evidence of active faulting on the bathymetric maps (Ben-Avraham et al., 1990). Comparing the bathymetrical data with other geophysical data sets (Figure 2-4) reveals that the bathymetric features reflect deep structures (Ben-Avraham et al., 1990): a N-S trending fault located on the eastern margin is probably related to the DST; Fault segments of different trends were identified along the western coast of the lake; a N-S trending crack (along coordinate 253.5 E in ITM coordinate system) is probably the surface expression of an active fault that might be connected to Almagor fault on land; A steep bathymetric scarp at the south of the lake 22
(along coordinates 738-739 N in ITM coordinate system) is also suspected to be a surface expression of an active fault which is continuing on land towards Tiberias.
Figure 2-4. Fault map of Lake Kinneret according to detailed bathymetric, gravimetric and magnetic maps. (1) Faults on land (2) faults based on gravity data (3) faults based on magnetic data (4) faults based on bathymetric data (5) strike slip faults on land (6) hot and salty springs (after Ben-Avraham et al., 1990). Coordinates are in ICS – the old coordinate system for Israel.
Morphotectonic analysis of the bathymetric data (Belitzky and Ben-Avraham, 2004) also showed evidence of active faulting. This analysis revealed a series of morphotectonic features with different orientations (Figure 2-5). Three systems of N-S trending faults were detected along the eastern shore, at the northwestern part of the lake and at the southwestern part of the lake. A NW trending fault system was detected mostly at the western part of the lake. At the northern portion of the lake an E-W trending fault system forms the northern boundary of the basin (Belitzky and Ben-Avraham, 2004).
23
Figure 2-5. Schematic map of major morphotectonic features of the Lake Kinneret floor (after Belitzky and Ben-Avraham, 2004). Coordinates are in ICS – the old coordinate system for Israel.
2.1.4
Gravity measurements
Analysis of the gravity data together with previously obtained data (bathymetric, seismic and magnetic data) illuminates further the structure under Lake Kinneret. Ben-Avraham et al. (1996) suggest that the basin is divided into two sub-basins (Figure 2-6). A deep pull-apart basin that was formed as a result of the DST motion occupies the southern part of the lake. It is bordered by steep N-S trending faults on its eastern and western sides. The northern sub-basin, which is not symmetrical, was probably formed as a result of block rotations and by eastern Galilee branching faults. This basin is bathymetrically the deepest and probably the most actively subsiding part in the lake (Ben-Avraham et al., 1996).
24
Figure 2-6. Schematic map of the structural elements of Lake Kinneret and its vicinity. Faults are marked by heavy lines. Faults with arrows mark the interpretation of the gravity study for strikeslip faults of the DST. Dotted lines are peaks of the maximum gravity gradients. Barbed line at the north of the lake marks dipping fault under Korazim Heights (After Ben-Avraham et al., 1996). Angular arrows in the Korazim Height and the eastern Galilee mark rotations (after Heimann and Ron, 1993).
2.1.5
Multi-channel seismic reflection survey
A multi-channel seismic reflection survey was conducted in Lake Kinneret (Hurwitz et al., 2002). Interpretation of the data provides a different structural model under the lake. This study indicates that a deep pull-apart basin occupies most of the lake (Figure 2-7). The basin is bounded by N-S trending strike-slip boundary faults accommodated with marginal normal faults. Shallow pre-rift units underlie the NW part of the lake.
25
Figure 2-7. Major faults in Kinneret area as interpreted by Hurwitz et al. (2002). Abbreviations are: WMF- west marginal fault, EMF- east marginal fault, SAF- Sheik-Ali fault, AF- Almagor fault, PF- Puria fault, HF- Ha'on fault. Coordinates are in ICS – the old coordinate system for Israel.
Approximately 4 MA ago, the basin grew by northward movement of the Korazim block and the lateral slip has been transferred from the southern segment of the western boundary fault to the Galilee normal fault system. The center of the northeastern part of the lake began subsiding rapidly about 1 MA ago (Hurwitz et al., 2002). The data obtained from the study mentioned above were reprocessed and reinterpreted by Reznikov et al. (2004). The newly proposed model (Figure 2-8) shows that a deep symmetrical basin, which is bounded by eastern and western boundary faults, occupies only the southern part of the lake. This deep sub-basin is also delimited by a southern transverse fault. A zone of distortion occupies the central part of the lake and delimits a northern sub-basin from the west, where shallow pre-rift units underlies the lake floor (Reznikov et al., 2004).
26
Figure 2-8. Major faults in Kinneret area as interpreted by Reznikov et al. (2004). Abbreviations are: STF- southern transverse fault, CTZ- central transverse fault zone, JF- Jordan fault, MSF – median step fault. Polygon marks the suggested zone of intrusion. Coordinates are in ICS – the old coordinate system for Israel.
2.1.6
Additional geophysical studies
Additional geophysical studies were able to provide indications for active faulting at the basin. Heat flow measurements (Ben-Avraham et al., 1978) show high values of 75 mWm2 in Lake Kinneret. These values are distinctively higher than those on the transform flanks thus suggesting the existence of hot material below the basin and of active faulting. Electromagnetic field analysis (Goldman et al., 1996; Hurwitz et al., 1999; Goldman et al., 2004) show sharp lateral contrast in resistivity along the margins. This boundary is probably controlled by active eastern boundary faults. This contrast is also explained by fault-controlled at the northern and north-eastern part of the lake (Hurwitz et al., 1999).
27
Tibor et al. (2004) mapped active faults at the north-western margins of the Lake Kinneret using CHIRP (Figure 2-9).
Figure 2-9. Main tectonic features found in Tabgha (A) and Fuliya (B) regions (after Tibor et al., 2004). Bold lines mark the mapped active faults.
Each survey conducted in the area yielded different information about the subsurface of Lake Kinneret. Although the debate regarding these tectonic models still exists, all geophysical investigations indicate that the LKB structure is tectonically active, especially its eastern margin and the northern sub-basin. This situation guided the deployment of mini-array along the northern and northeastern shores of Lake Kinneret. 2.2
Seismicity studies
The studies described below show tectonic implications of the contemporary seismological data observed in LKB. 2.2.1
Seismicity patterns
Previous investigation of microearthquakes occurrence along the DST show tendency to cluster in space around pull-apart basins (Van Eck and Hofstetter, 1990). The microseismcity of the ISN catalog (1982-1989) in the LKB shows clustering of events in the northeastern part of the lake and along the eastern boundary fault line of the DST. There is no indication of seismic activity in the southern part of the lake. According to the study most of the events in LKB are below magnitude ML>2 where as the stronger events (ML≥2) occurs along the eastern boundary of the DST (Figure 2-10). The events in 28
the LKB appear to cluster also in time, having almost identical seismograms. Composite focal mechanism of a cluster in the Kinneret basin indicates left lateral strike-slip motion which is in agreement with the orientation of the transform (Figure 2-10). Clustering seismicity is characteristic for dilatational jogs, such as left steps on left-lateral strike-slip faults, which act as rupture arrest (Sibson, 1985). These are kinetic barriers to fault rupture which may allow delayed slip transfer. The Kinneret basin constitutes about 5 km left step on the left lateral movement of the DST (see Chapter 1). Looking at the seismicity patterns and focal plane mechanism of the LKB, Van Eck and Hofstetter (1990) suggest that the LKB, a large left step on the transform, may act as a barrier to fault rupturing.
Figure 2-10. Reduced seismicity map of Lake Kineret region 1982-1989 (modified after Van Eck and Hofstetter, 1990). Fault plane solution is of a cluster that constitutes of 5 earthquakes which occurred within less than 48 hours in an area of 1 km2. Coordinates are in ITM grid in meters.
29
2.2.2
Focal plane solutions
A set of focal mechanisms was calculated for high quality microseismic events along the DST by Hofstetter et al. (2007). The data were obtained from Israeli and Jordanian seismological networks for the period 1987 - 1996. Out of 78 events that were analyzed 4 events were located along the eastern boundary of LKB (Figure 2-11). The fault plane solutions of the events, ranging in magnitudes 1.1≤ML≤2.6, do not always agree with the orientation of the related faults. One single event of magnitude ML=2.2 shows a good fit with the strike of Sheikh-Ali fault on land. For another event of magnitude ML =2.0 there is a misfit between the determined fault plane and the fault trace it is associated to (Jordan fault). Two more events are related to the Ein-Gev fault, the southern section of the eastern boundary fault. Whereas the larger event (2.6 ML) shows a misfit between the distinguished fault plane and the related surface fault, the smaller event (1.1 ML) shows a good fit, although no fault plane was determined (Hofstetter et al., 2007). There is no systematic fit between the solutions and the faults the events are associated to.
Figure 2-11. Fault plane solutions for 4 events in the LKB (modified after Hofstetter et al., 2007) on the background of surface faults (after Bartov et al., 2002). Location of the events is marked in red circles. Arrows point to the focal mechanism of the event. Names of the related faults are in bold.
30
2.2.3
Induced seismicity
Kafri and Shapira (1990) suggested that the recorded seismic activity in the Kinneret region might be related to water level of the lake and rainfalls. To verify this hypothesis three sets of data were obtained and merged: Lake Kinneret water level (1927-1988), rainfall data from Dgania (1937-1988) and earthquakes of magnitude ML≥4 that occurred within 30 km of Lake Kinneret shores (1900-1988). The results show a correlation between the occurrences of felt earthquakes and both the beginning of the rainy season and the annual minimum water level. Kafri and Shapira (1990) gave a possible explanation for these observations as a mechanism of lubrication process. As the rainfalls start, the aquifers are recharged causing a rise in the hydrodynamic pressure. As a result, upward flows along the boundary faults of the DST, emerging as springs, are reducing the frictional strength along them (Figure 2-12). An earthquake that would have occurred later, due to the tectonic pressure, is triggered earlier by this process (Kafri and Shapira, 1990).
Figure 2-12. A schematic description of the suggested triggering mechanism as explained in the text (After Kafri and Shapira, 1990).
According to the studies mentioned above, the seismicity in the LKB is characterized by spatiotemporal clustering of low magnitude events, mainly along the eastern boundary fault of the DST and in the northern sub-basin.
31
Chapter 3 3
Methods
Data sources The seismic data for this project comes from two sources: permanent stations of the ISN and temporary mini-arrays. The ISN data are provided by the Geophysical Institute of Israel (GII) and the local microseismicity data were acquired by Seismic Navigation System (SNS) operated by Tel-Aviv University. 3.1
Israel Seismic Network (ISN)
Since 1981, the seismological division of the GII has been operating and maintaining the ISN, enabling continuous monitoring of the seismic activity in Israel (Arieh and Rotstein, 1985). Until 1994, the ISN operated SP (Short Period 0.2-12.5 Hz) seismometers but since 1996 new Broad-Band (BB) stations have been gradually added (Shapira and Avirav, 1997). The signal is digitized to sampling rates of 0.001, 0.01, 0.1, 1, 20, 40 and 50 Hz. Figure 3-1 shows the space distribution of ISN sensors, including all stations that operated since 1986 (some of which are not necessary operating today). Over the past few years, readings from Jordanian and Cyprus networks are commonly used to anchor the hypocentral location of ISN bulletin events. However, weak local events are not always detected by these far sensors and they are not included in the ISN readings for this project. The digitally recorded data are processed, analyzed and cataloged to create the ISN bulletin. The magnitude threshold of completeness for the catalog since 1986 is estimated to be M≥2 (Shapira, 2002, Appendix A). Data for this research are retrieved from the ISN bulletin for the period of 1986-2010. Locations of the ISN stations are detailed in appendix A. 3.1.1
Data processing
Events are automatically detected if the signal amplitude has reached a specific threshold level at least at three stations in a short time window of about 10 seconds. The automatically detected events are displayed, processed and analyzed using the interactive 32
program jSTAR (Polozov and Pinsky, 2007). Discrimination is performed manually by the analyst. Location is computed on the basis of P-phase and S-phase and a general velocity model for the crustal structure of Israel (Figure 3-2). Magnitude (Md) determination is based on the decay duration of the coda waves (signal duration).
Figure 3-1. Distribution of ISN stations operating from 1986 to 2010. Not all stations operated at the same time. SP stands for Short period (green triangles) and BB stands for Broad-band (red squares). MMAI is an array.
33
GII velocity model 0 Vp Vs 5
Depth (km)
10
15
20
25
30 1.5
2
2.5
3
3.5 4 4.5 Velocity (km/sec)
5
5.5
6
6.5
Figure 3-2. Velocity model used for locating events by jSTAR software.
3.2
Mini-arrays
In order to continually monitor the weak seismicity, four Seismic Navigation Systems (SNS) were deployed in the study area. Each SNS station is a sparse mini array which consists of three vertical-components (1Hz) sensors (Lennartz LE-1D) arranged in a tripartite layout around a central three-component (1Hz) sensor (Lennartz LE-3D). To maximize SNR, mini-arrays are deployed in low ambient ground noise areas, as close as possible to sources and within a media with the best possible coupling. The exact geometry of the SNS array is generally given by specific field conditions. The SNS aperture is optimized as a function of the wavelength of the signal to be detected, minimizing aliasing. With this in mind, the larger the aperture of the array, the higher the time gap of the arrival times and the better the resolution of the beam forming.
34
3.2.1
Data acquisition
The four SNS were deployed for a period of twelve months in Korazim, Almagor, Ma'alle-Gamla and Ramot (Figure 3-3). Locations were chosen on both sides of the DST, outlining a rectangle of about 8 by 13 km. Given the logistical constraints (direct access to power supply and internet, protection against animals and vandalism and accessibility for regular maintenance) the four SNS stations were installed in inhabited areas (Figure 3-4). As a result, the SNR was sometimes quite low, the sensors aperture had to be reduced to 30-70m (Figure 3-5) and the layout configuration was not optimal. In order to avoid damage from rodents while having an optimal coupling, the sensors were placed in a sand-filled tube at a depth of 50 cm (Figure 3-6). The data were recorded in continuous mode at a sampling rate of 250 Hz. The exact coordinates of the SNS and their sensors are detailed in appendix A.
Figure 3-3. Location map of the four SNS stations in the study area.
35
Figure 3-4. Digitizer and power-pack at Ma'alle-Gamla (A) and Korazim (B). Instruments were installed in populated places in order to avoid vandalism and for access to electricity, communication and regular maintenance.
Figure 3-5. The alignment of the sensors in Ma'alle-Gamla mini-array. SNC is the central 3-D sensor whereas SNE, SNN and SNW are 1-D vertical sensors.
36
Figure 3-6. Sensor buried in a sand-filled tube.
3.2.2
Network coverage/detection threshold
The closest ISN stations to the study area are GLH (14 km from the center of Lake Kinneret), MRN (25 km), KSHT (26 km), and KSDI (40 km). Unfortunately, GLH was not operating during 2010. According to Wust-Bloch and Joswig (2006), all events of magnitude ML≥0 are expected to be detected at slant distances of up to 10 km. Therefore, it was important to locate the SNS stations in such a way that maximizes the detection of low magnitude events. Figure 3-7 presents the expected detection threshold (ML=0 or more) and network coverage of the ISN and the SNS stations in the study area. 3.2.3
Data processing
Data processing consists of five main steps: data merging, event detection, event discrimination, event location and event quantification. 3.2.3.1 Data merging Since data are acquired by each SNS individually, the complete data from each SNS needed to be adjusted and merged prior to data processing. This procedure allows the determination of a single location solution for all data sets to be computed on HypoLine, the location software. 37
Figure 3-7. Network coverage and expected detection threshold. ISN stations operating in 2010 are marked in red triangle. SNS stations are marked in black triangle. Red circles are 30 km buffer from the ISN stations and mark the expected detection of events down to ML=1. Black circles are 10 km buffer from the SNS stations and mark the expected detection of events down to ML=0. Therefore, the expected detection threshold is down to ML=0 in the northern part of Lake Kinneret by the SNS. DTM after Hall (1993).
38
3.2.3.2 Event detection Event detection was carried out using the SonoView module of the SparseNet software (Joswig, 2008). This application allows displaying of the seismic data in a well arranged view to maximize the time interval of the data that can fit one screen. Data are displayed as sonograms of four stacked vertical components from each array (Figure 3-8). Sonograms are three dimensional images displaying signal energy variation as a function of time and frequency. Sonograms are obtained by sliding short FFT window of 256 samples with an overlap of 50 per cent. The result is a diagram of the Power Spectral Density in logarithmic scale which is also binned logarithmically in the frequency axis. Image of the short-time signal energy is then enhanced by equalizing to an all positive matrix which adds pre-whitening and noise muting (Joswig, 1995). Visualizing frequency distribution of signal energy as a function of time enables operator-supported detection of seismic events by pattern recognition (Joswig, 1990). This is an efficient method of identifying seismic events in low SNR conditions and discriminating them from most kinds of anthropogenic noise sources (Figure 3-9). Given the extreme broad-band of the sonogram, mono-frequencial noise sources can be filtered out easily, on single traces as well as on the four traces of the array.
39
Figure 3-8. Screen view of Sonoview display. The display shows eight intervals of three minutes with an additional one minute overlap (darkened sonograms). Each interval contains stacked sonograms of the vertical sensors of each SNS station. This visualization allows discriminations between events and non events even in a low SNR environment. A 0.6 Ml earthquake, 3.5 km from Almagor is easily detected on the middle of the fifth interval.
40
P-phase
A
S-phase
B
C
Figure 3-9. Event identification. Left side display stacked spectrogram of the vertical sensors in Ramot mini-array (Spectrograms are without pre-whitening effects, high energy is in red) and right side is the seismogram of the central sensor (images are not to scale). A) Microearthquake pattern. P-phase is visible at higher frequency than S-phase, which present higher energy. B) Teleseismic earthquake. The repeating pattern is high energy in low frequencies (f1.2 Hz) the horizontal traces (N-S and E-W) are converted to ground displacement seismogram, simulating Wood-Anderson seismograms. The maximum peak to peak amplitude it manually picked for the full waveform of the S-phase. This computation is based on extension of the standard distance correction relationship (Richter, 1958) down to 10m (Wust-Bloch, 2010).
Figure 3-11. An example of graphical location. Left side: Green Circles are ts-tp, blue hyperbolas are ∆tp and gray dashed lines are array beams from Ramot SNS. Right side: Display of highest cell count which marks the best location.
3.2.4
Estimation of location uncertainty
Errors in location cannot be quantified in a standard manner as the software displays an infinite amount of plausible solutions for source location, on the basis of independent parameters such as phase picking, model velocity, depth, etc. The total uncertainty estimation relays on a few factors: a. Picking phase onset: The main cause for errors in location results from the erroneous identification of phase onsets, which is generally caused by ambient noise and multiple arrivals of different phases to the sensor. Three-component 45
sensors are very useful for a clear identification of S onsets. The sonograms further guide phase picking and allows filtering of the data to event spectrum only. This factor, which is subjective to the decision of the analyst, is somehow attenuated by the high sampling rate which provides for better signal resolution. b. Velocity model: Since location of the event is based on velocity model, accurate information of the velocity structure is needed. The velocity model that was used as input data by HypoLine was designed on the basis of subsurface analysis for the Golan Heights by Meiler (2011) (see chapter 1.1.2). A velocity model that extends to 10 km depth was designed on the basis of observation of the southeastern part of the Golan Heights, where the lithological depth constraint is estimated to be less than 500 m. The young basalt flows outcropping towards the surface create a velocity inversion in the top two layers forcing Hypoline to compute non-unique solutions. Therefore, the two top layers were averaged into one single low-velocity new top layer. At depth below 10 km the local velocity model was completed to fit the GII model (Figure 3-12). However, this custommade velocity model does not fit the entire study area as it is composed of rather diverse geological units. In fact, it is impossible to create an adequate 1-D velocity model that would fit such a complex area where no structural continuity is observed between both sides of the DST. The use of a unique general 1-D velocity model for such a complex study area yields errors that are mostly visible in the arrival times. These errors are also observed in the GII catalog for the stations that are located west of the DST fault line. c. Slant distance: Source-to-sensor distance is also a factor that influences location accuracy. Reliable locations can be obtained within the zone included between the four SNS, even with an inaccurate velocity model, but increasing slant distant leads to increasing location errors (e.g., Van Eck and Hofstetter, 1990). For better accuracy, a three dimensional spread is necessary but not realistic for the current operation. d. Instrumental influence: The instrumental errors are negligible due to the high sampling rate and sensitivity of the system. 46
e. Calculation algorithm: Different algorithms yield different results. The RMS (Root Mean Square) that is calculated means that the solution is the most reasonable mathematically but not necessarily correct. The use of a location strategy that does not rest on the standard evaluation of residuals does not allow for the precise determination of systematic location errors for the data set acquired by the SNS. An example of how different locations can be obtained for the same event, due to the use of different parameters, is given in the next chapter. SNS velocity model 0
Depth (km)
5
10
15
20
25 2.5
3
3.5
4
4.5 5 5.5 Velocity (km/sec)
6
6.5
7
Figure 3-12. Velocity model (Vp) used for location process in the Hypoline software. The model is based on Meiler’s (2011) velocity model for the southern part of the Golan Heights. The top two layers are averaged and completed for depth more than 10 km with the GII velocity model. The Vp/Vs velocity ratio used for this model is 1.78.
3.3
Analysis and Display
Further waveform analysis of the newly acquired database and the database that was retrieved from the GII was carried out using matlab. Display on maps and spatial analysis was obtained using GIS (ESRI).
47
3.3.1
Spectrum analysis
Amplitude spectrum of the displacement signal of the GII catalog events for 2010 was displayed using jSTAR software. In order to display the amplitude spectrum of the SNS catalog events the signal was converted from velocity to displacement using integration. The conversion was carried out after filtering the signal to the range of 1 to 80 Hz which is the flat response range of the sensor. Amplitude spectrum of the central vertical sensor was plotted and the corner frequency was determined through user interface in matlab. 3.3.2
Cross-correlation
Cross-correlation was carried out for all seismograms produced by doublets, multiplets and clusters which were recorded at the same sensor. For the GII catalog the procedure was computed for 2,000 samples containing the events. The signals were first filtered by zero-phase band filter in the range of 1-7 Hz. For the SNS catalog the signals were filtered by zero-phase band filter in the range of 1-35 Hz which eliminates the influence of electrical noises and narrows the computation to signals spectrum. The procedure was performed for 4,500 samples which start from the origin time of the event. 3.3.3
b-value calculations
Calculation of b-value (Chapter 1.1.3) was performed using Maximum Likelihood Estimation using in the following formula (Bender, 1983; Shapira, 2002):
Where N is the number of earthquakes of magnitude ≥M ; Mmin is the minimal magnitude taken into consideration; Mmax is the maximal magnitude for the seismogenic zone; .
48
Chapter 4 4
Results
4.1
Israel Seismic Network (ISN)
Over 350 earthquakes ranging in magnitude 0≤Md≤3.6 were detcted in LKB area over 25 years (1986-2010) by the ISN. The events which are listed in Table B-1 (Appendix B) are limited to the area between 240≤X≤270 km and 720≤Y≤770 km in ITM grid. 4.1.1
Spatial distribution
Figure 4-1 shows the spatial distribution of the events epicenters in the LKB. The seismic activity is mainly taking place in the northwestern part of the lake. The seismic activity follows the trend of the transform fault at the northern part to the lake but as it goes into the basin it spreads to the west. The southern part of the lake is relatively quiet with an exception of activity along a diagonal trend line that crosscuts the southern part of the lake and corresponds to the bathymetrical cliff. The transform fault south to the LKB is also relatively quiet. 4.1.2
Zones of seismic activity
The study area was divided into six general tectonic provinces based on the main tectonic features (Figure 4-2). The LKB was further divided into two provinces: the northern basin (NB) and the southern basin (SB). The other provinces are in respect to the LKB: west of LKB (WLKB), east of LKB (ELKB), DST north of the LKB (NDST) and DST south of the LKB (SDST). The activity rate of seismicity was calculated and normalized per year based on the surface area of each province. The highest activity rate was observed in the NB with 6.7*10-2 events per km2. The activity in this section is mainly concentrated in the eastern part and almost no activity is observed in the vicinity of the basin faults at the northwestern part of the lake as suggested by Reznikov et al. (2004). In the southern basin (SB) the activity rate is much lower, with 1.1*10-2 events per km2. North of the LKB in the NDST zone the rate of activity is 1.6*10-2 events per km2. In this section the seismic activity is clustered strongly around the Jordan fault. In the SDST 49
zone the rate of activity is very low with 0.23*10-2 events per km2. West of the LKB, in the WLKB zone, with 0.17*10-2 events per km2, while in the ELKB zone the rate of seismic activity is twice as high with 0.35*10-2 events per km2. The seismic activity in the ELKB is mainly in the northern part of this section and in the vicinity of Sheik-Ali fault.
DST
Bathymetric cliff zone
Figure 4-1. Earthquake epicenters from the past 25 years as detected by the ISN and the closest ISN stations (black triangle) to the study area .GLH (Mevo Hamma) was not operating in 2010. DTM after Hall (1993).
50
Figure 4-2. Zones of seismic activity (GII catalog) and tectonic features. Solid black lines are potentially active faults (after Bartov et al., 2002) and active faults are marked in red (after Bartov et al., 2009). Dashed blue lines are basin faults as suggested by Reznikov et al., (2004). Colored polygons mark the area of which the rate of seismic activity was calculated for.
51
4.1.3
Depth distribution
Most of the events are located at shallow depths above 12 km (Figure 4-3). Events with deeper hypocenters tend to cluster along the transform fault while shallower events are located mainly in the northern basin.
770 765 760 755 750 745 740 735
A
B A
730 725 720 0
240
245
250
255
260
265
0
5
10
270
15 Depth (km)
20
25
30
40 35
5
30 Number of evnts
Depth (km)
10
15
20
25
C A
25 20 15
D A
10 5 0
30
0
5
10
15 Depth (km)
20
25
30
Figure 4-3. Distribution of events in space: A) map showing distribution of events by depth. Coordinates are in ITM in meters. B) Depth distribution of events parallel to the DST (N-S section). Vertical axis represents coordinates in ITM grid in kilometers. C) Depth distribution of events perpendicular to the DST (E-W section). Horizontal axis represents coordinates in ITM grid in kilometers. D) Histogram of depth distribution for the study area.
52
4.1.4
Magnitude distribution
The strongest events are located along the transform fault and the eastern margin of the LKB (Figure 4-4). The northern sub-basin generates weaker events.
3.5
770 765
3
760 2.5
755 750
2
745 1.5
740 735
A
1
B
730 0.5 725 720 0
240
245
250
255
260
265
0
5
270
10
15 20 Depth (km)
25
30
0
3.5 Figure 4-4. Distribution of event magnitude in space: A. map 3 showing distribution of events by magnitude. Coordinates are in ITM in meters. B. Magnitude 2.5 distribution of events parallel to the DST (N-S section). Vertical axis represents coordinates in ITM grid in kilometers. C. 2 Magnitude distribution of events perpendicular to the DST (E-W section). Horizontal axis 1.5 represents coordinates in ITM grid in kilometers. Color bar represents duration magnitude for 1 B and C.
5
Depth (km)
10
15
20 C
25
0.5
30
0
Figure 4-4. Distribution of event magnitude in space: A) map showing distribution of events by magnitude. Coordinates are in ITM in meters. B) Magnitude distribution of events parallel to the DST (N-S section). Vertical axis represents coordinates in ITM grid in kilometers. C) Magnitude distribution of events perpendicular to the DST (E-W section). Horizontal axis represents coordinates in ITM grid in kilometers. Color bar represents duration magnitude for B and C.
53
4.1.5
Temporal distribution/Seismicity rate
The time distribution of earthquakes does not display any specific pattern (Figure 4-5). There are years with less than 10 events and years with as many as 25 events per year. It appears that, most of the seismic activity takes place between April and July (Figure 4-6). The seismicity rate averaged over 25 years is 4.8*10-7 events per second.
Figure 4-5. Annual distribution of events that were detected in the study area.
Figure 4-6. Monthly distribution of events that were detected in the study area over 25 years.
54
4.1.6
Magnitude-Time frequency
Magnitude time frequency also shows a non-uniform temporal distribution (Figure 4-7). The b-value (Figure 4-8) was calculated using maximum likelihood estimation after neglecting 85 events whose magnitudes were not determined. The result is a b-value of 0.82 which is lower than 0.96, the value calculated for the total southern segment of the DST (see chapter 1.1.3). The magnitude completeness for this catalog is estimated to Md≥1.5, which is a lower value than Md≥2 of the total ISN catalog (Shapira, 2002, Appendix C). This is the result of better and denser spread of stations in northern Israel than in other areas. Temporal distribution 4
3.5
Magnitude(Md)
3
2.5
2
1.5
1
0.5
0
1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 2010 Year
Figure 4-7. Magnitude-Time distribution of events detected in the study area.
55
2
Cumulative annual frequency
10
1
10
b=0.82 0
10
-1
10
-2
10
0
0.5
1
1.5 2 2.5 Magnitude (Md)
3
3.5
4
Figure 4-8. Magnitude-frequency relationship (b-value).
4.1.7
Event clustering in time and space
Detailed examination of time distribution reveals groups of events which occurred very close in time. Further examination of these events reveals that they are also very close in space. These events were defined as clusters, containing 4 to 12 events which occurred within a time period of a few minutes to 23 days and located less than 2 km apart (except for one case of 2.6 km apart). The eight spatio-temporal clusters were observed in the northern sub-basin only (Figure 4-9) arranged in a narrow lineated structure, except for two clusters (1991 and April 1996) which are spread on relatively wide area. Although waveform similarity of the events in the wide-structure clusters is rather low (between 40% to 75% correlation), an attempt to fit them to a plane is shown in Figure 4-10. Nine pairs of events which are not related to any cluster occurred within a time period of less than 25 hours and located less than 1 km apart. Cross-correlating these events reveal high waveform similarity, between 60% to 87% correlation (Figure 4-11). All of these doublets occurred in the northern sub-basin. The events which are included in the clusters and the doublets are detailed in Appendix D.
56
Figure 4-9. Clusters observed in the study area. All the clusters are located in the northern subbasin. Peach polygons mark the surface area that is covered by the cluster. Notice that most of the clusters are narrow while cluster 1991 and April 1996 are wide spread. DTM after Hall (1993). Basin faults are as suggested by Reznikov et al. (2004).
N
E
E
N
Figure 4-10. Best plane fit for cluster April 1996 (right) and cluster 1991 (left). Coordinates for XY axes are in Israel TM grid in km.
57
MMA0 BHZ 11.07.2009 02:26
A
40
50
60 Time (sec)
70
80
MMA0 BHZ 11.07.2009 02:34
B
5
15
25 Time (sec)
35
45
1
C
0.8 0.6
Correlation factor
0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -2000
-1500
-1000
-500
0 Lags
500
1000
1500
2000
Figure 4-11. Result of crosscorrelation between two events close in time and space (doublet). Crosscorelation function (C) between event A and B as recorded in the MMA0 vertical sensor of Meiron array results in 87% similarity in waveform (full correlation is normalized to 1 which is 100%).
58
4.1.8
Corner frequency
Five events from 2010, which were simultaneously recorded by the ISN and the SNS, were examined for S-phase spectrum. Corner frequency could not be determined for the low magnitude events since it was not visible in the spectrum. Full spectral content of the events energy is not visible except for the 3.6 magnitude event (Figure 4-12). OFRI
6
10
A 5
10
4
Amplitude
10
3
10
2
10
1
10
0
10 -2 10
-1
10
0
10 Frequency (Hz)
1
2
10
10
OFRI
B 3
10
Amplitude
2
10
1
10
0
10
-1
10
0
10 Frequency (Hz)
1
10
Figure 4-12. Amplitude spectrum of displacement signal. A). Event of magnitude Md=3.6 as recorded in OFRI station. The corner frequency is evident at f0=6.3. B) An event, which its magnitude was not determined, as recorded in OFRI station. The corner frequency is probably too close to the nyquist frequency and therefore cannot be determined. Red curve is signal smoothing.
59
4.2
Seismic Navigation System (SNS)
A series of 121 events were detected and located between March and November 2010 in the study area, although not all 24 traces (6 per SNS) were available all the time. These events range in magnitude between -1.2≤ML≤3.9. Table B-2 (Appendix B) presents the observed events by the SNS stations of this study. 4.2.1
Spatial distribution
The located events shown in Figure 4-13 concentrate in the northern sub-basin and along the DST fault north to LKB. Although stations are located along the northern shore of the Lake Kinneret, its detection capacities extend over the whole target area (LKB). Although many weak events were located beyond the LKB, no seismic activity was observed in the southern basin or along the DST fault south to the Lake Kinneret. The magnitude detection threshold based on the SNS catalog (Figure 4-14) demonstrates that events down to ML=0 should have been detected up to 18 km from the SNS (Figure 4-15) and thus events from the southern LKB should have been detected. The calculation of distance for the magnitude detection threshold was based on ts-tp and not on the determined location. 4.2.2
Zones of seismic activity
Rate of seismic activity (Figure 4-16) was calculated for the same areas as calculated for the GII catalog (see 4.1.2) and normalized per year for comparison purpose. Results show no activity in the SDST zone, south of the LKB. The highest activity rate is observed in the NB with 91.8*10-2 events per km2. The activity in this zone is clustered in the central portion. The activity rate in the SB zone is much lower: 4.6*10-2 events per km2. In the NDST zone the rate of activity is 11.2*10-2 events per km2. In this section the seismic activity is scattered around the eastern portion close to the Jordan fault. In the WLKB and in the ELKB zones the rate of seismicity is 2*10-2 events per km2 and 4.5*10-2 events per km2 respectively. While in the WLKB the seismicity is scattered, in the ESLK it is located in the northern portion.
60
DST
Figure 4-13. Distribution of events epicenters as observed in nine months by SNS. Black triangles represent the four mini-arrays. DTM after Hall (1993).
61
4
Magnitude (ML)
3
2
1
0
-1
-2
0
5
10
15
20
25
30
35
40
Distance (km)
Figure 4-14. Magnitude detection threshold. Red curve mark the maximum distance of detecting event according to its magnitude. The distance is based on ts-tp.
Figure 4-15. Detection range of low magnitude events by the SNS. Black triangles mark the SNS stations. Blue circles are 7 km radius from each SNS station and mark the ability to detect events down to ML= -1. Green circles are 18 km radius from each SNS station and mark the ability to detect events down to ML=0. DTM after Hall (1993).
62
Figure 4-16. Zones of seismic activity and tectonic features. Solid black lines are potentially active faults and active faults are marked in red (After Bartov et al., 2002; Bartov et al., 2009). Dashed blue lines are basin faults as suggested by Reznikov et al., (2004). Colored polygons mark the area of which the rate of seismic activity was calculated for. Notice the event which is located on the Tiberias fault which is marked as active.
63
4.2.3
Depth distribution
Hypocentral depths of most events are less than 10 km (Figure 4-17). The hypocentral depths of 65 events are not constrained in a reliable manner as they are located using less than three arrays. Therefore the depth of these events was not determined except for 4 events in which additional information was used. Even though no depth is determined for these events they are still probably shallow since the slant distance of most of these events is not more than 10 km away from Almagor station (based on ts-tp). The deepest event is located along the Jordan Fault. 4.2.4
Magnitude distribution
Figure 4-18 shows that the strongest event detected was located on the DST. This event has rather high value of magnitude comparing to the averaged value of the events that were observed. The detection threshold reached the minimum value of -1.2 ML for earthquake located at about 3.5 km away from the station in Almagor. Distribution of magnitude in space does not show any correlation between depth and magnitude. 4.2.5
Temporal distribution/Seismicity rate
Monthly changes in activity are shown in Figure 4-19. The most active month is June, almost as much as March, April and November which are very active as well. There is almost no activity in July and august. In comparison to Figure 4-6 it seems that monthly changes over one year does not necessarily represent averaged monthly changes over 25 years. The seismicity rate is 5.12*10-6 events per second. 4.2.6
Magnitude-Time frequency
Magnitude-Time frequency show non uniform distribution (Figure 4-20). Calculation of b-value yields a value of b=0.58 (Figure 4-21). The magnitude completeness is estimated to reach ML≥0. The strongest event (ML=3.9) has a strong influence on the estimation of the b-value.
64
770 765 760 755 750 745 740 735 A
B
730 725 720
235 0
240
245
250
255
260
265
270
0
5
10
15
20
25
Depth (km)
Depth (km)
80 70
events Number ofof events Number
Depth (km)
5
10
15
20
C
60 50 40 30 20
D
10
25
0
0
5
10
15
20
Depth(km) (km) Depth
Figure 4-17. Distribution of events in space: A) map showing distribution of events by depth. Coordinates are in ITM in meters. B) Depth distribution of events parallel to the DST. Vertical axis represents coordinates in ITM grid in kilometers. C) Depth distribution of events perpendicular to the DST. Horizontal axis represents coordinates in ITM grid in kilometers. D) Histogram of depth distribution for the study area. Events with depth not determined were removed and are marked as zero depth in graph D.
65
25
770
3.5
765
3
760
2.5
755
2
750
1.5
745
1
740
0.5 735 A
0
B
730
-0.5 725 -1
720 235
240
245
250
255
260
265
5
270
10 15 Depth (km)
3.5
14 12
2 1.5 1
15
0.5 20
C
10 8
D
6
0
4
-0.5
2
-1
25
Number of events
Depth (km)
2.5 10
0 -2
-1
0
1 2 Magnitude (Ml)
Figure 4-18. Distribution of event magnitude in space: A) map showing distribution of events by magnitude. Coordinates are in ITM in meters. B) Magnitude distribution of events parallel to the DST. Vertical axis represents coordinates in ITM grid in kilometers. C) Magnitude distribution of events perpendicular to the DST. Horizontal axis represents coordinates are ITM grid in kilometers. Color bar represents local magnitude for B and C. D) Histogram of magnitude distribution for the study area.
66
25
16
3
5
20
3
4
25
Number of events per month
20
15
10
5
0
March
April
May
June
July August September October November Month
Figure 4-19. Monthly distribution of events as recorded by SNS in the study area.
4
3
(ML) Magnitude Magnitude(Ml)
2
1
0
-1
-2 50
100
150
200 Julian 2010 JulianDay Day
Figure 4-20. Magnitude-Time distribution.
67
250
300
350
2
frequency Cumulative monthly frequency Cumulativemonthly
10
1
10
b=0.58 0
10
-1
10
-2
10
-2
-1
0
1
2
3
4
Magnitude (Ml) Magnitude (ML)
Figure 4-21. Cumulative monthly magnitude frequency relationship (b-value).
4.2.7
Event clustering in time and space
Most of the events tend to be generated in pairs, occurring within a few minutes to a few hours apart and/or are located less than 1 km apart. Detailed examination of these events reveals that some of them are part of a cluster. Cross-correlation of these events (Figure 4-22) yields high similarity in waveform signal (58%-95%) for 8 sets of events, even in cases of very low magnitudes. Applying a lower band-pass filter (1-10Hz) improves waveform correlation results to 70%-98%. Except for one set which occurred on the transform, all doublets and the cluster occurred in the northern sub-basin. The events which are included in the cluster and the doublets are detailed in Appendix D. 4.2.8
Corner frequency
Over 270 S-phases were observed but only 244 had a reasonable spectrum with ω-3 slope. The results show decrease in the corner frequency as the event magnitude increases (Figure 4-23), although the spread of values in this graph is wide-distributed. Below ML=1 most of the events have corner frequency higher than 10 Hz, which is easily detected due to the high sampling rate. These values are higher than expected, especially for the stronger events (Table C-2, Appendix C). In previous studies of earthquakes along the DST, corner frequencies for events of Md=~3.5 tend to vary from 2 to 6 Hz and events of Md=~2.5 tend to vary from 4 to 8 Hz (Van Eck and Hofstetter, 1989; Shapira 68
and Hofstetter, 1993; Hofstetter et al., 1996; Hofstetter et al., 2008). Higher frequencies are observed in Korazim and Almagor than in Ramot and Gamla, for all events. The results are shown in Table C-1 (Appendix C). Ramot SNC-SZ 28.09.2010 22:55
A
0
2
4
6
8 10 Time (sec)
12
14
16
18
14
16
18
Ramot SNC-SZ 28.09.2010 23:07
B
0
2
4
6
8 10 Time (sec)
12
1
C Correlation factor
0.5
0
-0.5 -2000
-1500
-1000
-500
0 Lags
500
1000
1500
2000
Figure 4-22. Result of cross-correlation between two events close in time and space (doublet). Cross-correlation function (C) between event A and B as recorded in the centered vertical sensor in Ramot results in 95% similarity in waveform (full correlation is normalized to 1 which is 100%).
69
20 Gamla Ramot Korazim Almagor
18
Frequency (Hz)
16
14
12
10
8
6 -2
-1
0
1 Magnitude (Ml)
2
3
4
Figure 4-23. Corner frequency as a function of magnitude. Each color represents different SNS station as marked in the legend.
4.3
Comparing different catalogs
The data that were obtained from the GII and the SNS catalogs were compared in order to investigate the seismic behavior in two timescales with different thresholds. Below we present various aspects of this comparison. 4.3.1
Spatial distribution
Both catalogs show relatively similar spatial distribution of events. Enhanced activity concentrates in the northern sub-basin and along the DST north of Lake Kinneret (Figure 4-24). The southern part of the basin and south of the Lake is relatively quiet in both catalogs. If events with zero depth are not included, most of the epicentral depths are above 15 km (Figure 4-25). In comparison, SNS catalog presents shallower events. The reported depths from the SNS catalog are from events which were detected by 3 SNS or more. 70
Figure 4-24. Spatial distribution of events as reported by the GII catalog (left) and SNS catalog (right) on the background of suspected active faults (after Bartov et al., 2002). 30
14
A
25
B
12
Number of events
Number of events
10 20
15
8
6
10 4 5
0
2
0
5
10
15 Depth (km)
20
25
30
0 0
5
10
15
20
25
Depth (km)
Figure 4-25. Histogram of depth distribution as reported by A) GII catalog and B) SNS catalog. All events at zero depth from both catalogs were excluded. The reported depths from the SNS catalog are from events which were detected by 3 SNS or more.
71
4.3.2
Magnitude threshold
Figure 4-26 shows the cumulative magnitude frequency of both catalogs normalized to one year. The results show different behavior of the two catalogs. First, the b-value of the SNS catalog is much lower than the GII catalog b-value. Second, although the Md is not calculated exactly as ML, it appears that the SNS magnitude detection threshold is lower and the SNS system was able to detect more events. Cumulative magnitude frequency
3
10
b=0.82 b=0.58 GII-Md SNS-Ml
2
Cumulative annual frequency
10
1
10
0
10
-1
10
-2
10
-2
-1
0
1 2 Magnitude
3
4
5
Figure 4-26. Magnitude-Frequency relationship of both catalogs. The catalogs are normalized to one year.
4.3.3
Sampling rate
Full spectrum of microearthquakes can be easily observed in the SNS signal due to the high sampling rate. For events with magnitude lower than ML=2 the maximum frequency of the signal (velocity signal) could be higher than the nyquist frequency of the ISN signal (fny=20/ fny=25). Figure 4-27 illustrates the difference of the recording of microearthquaks in high sampling rate.
72
20
A Frequency (Hz)
15
10
5
0
B
10
20
30
40 Time
50
60
70
120
Frequency (Hz)
100 80 60 40 20 0
2
4
6
8
10
12
14
16
Time
Figure 4-27. The same event as recorded by A) Meiron array and B) Ramot mini-array (26.10.2010, ML=1.4). Notice that in Ramot array the spectrum exceeds 20 Hz.
4.3.4
Estimation of uncertainty
As explained in Chapter 3 (section 3.2.3), the location result is influenced by subjective parameters such as phase picking and objective parameters such as velocity model, calculation algorithm, instrument sensitivity and spread of stations relatively to the source. Two events which occurred during the period of the SNS monitoring were detected by other networks as well. The solutions given to the events are quite different from each another in hypocenter location, in depth and even in origin time. The results are shown in Figures 4-28 and 4-29. The first event (Figure 4-28) present the solutions given for the strongest event detected in the study area in 2010. The solutions are given by SNS, GII, NIC (Cyprus), CNRS (Lebanon), KAN (Turkey) and EMSC (European Mediterranean Seismological Centre). The second event (Figure 4-29) is almost 2 orders of magnitude lower and was detected by the SNS, GII and CNRS networks. CNRS uses much higher velocities and does not consider readings from Israeli stations (http://www.cnrs.edu.lb/geophysicalresearch.html). Since the event is rather far from their network and rather low in magnitude, the result is drawn northward, away from the GII and SNS solutions. 73
Therefore, evaluation of the SNS results based on other catalogs is not possible. An evaluation of the error based on quarry explosions could not have been done since the quarries in the study area are located outside the array network. The location procedure of the SNS network is based on a small number of readings so there is a great influence of the number of sensors which detected the event. If the event was detected by less than three arrays, the solution is based mainly on the radius given by the ts-tp and arrival direction based on the array structure. This could result in large errors, especially if the event was detected using only one mini-array.
Figure 4-27. Example for different solutions for the same earthquake due to the usage of different velocity models, algorithms and spread of stations relative to the source. DTM after Hall (1993). It was a felt earthquake on 20.03.2010 at 18:45 GMT. The solutions are given in the table below (notice the differences also in depth and origin time marked in red). Catalog EMSC NIC CNRS KAN GII SNS
O.T. 18:45:30.7 18:45:3 31.9 18:45:30.7 18:45:30.21 18:45:2 29.6 18:45:29.8
Latitude(N) 32.88 32.94 32.94 32.88 32.91 32.94
Longitude(E) 35.53 35.65 35.66 35.3 35.62 35.65
74
Depth(km) 12 25 4 15 13 16
Magnitude 3.6 Ml 3.5 Ml 3.6 Mc 3.6 Ml 3.6 Md 3.9 Ml
Figure 4-28. Another example for different solutions for the same event due to the use of different velocity models, different algorithms and spread of stations relative to the source. The event is a low magnitude earthquake from the 06.07.2010 at 22:12 GMT. DTM after Hall (1993).
75
Chapter 5 5
Discussion and conclusions
This research focused on the seismic activity of Lake Kinneret basin. The study was carried out in two time scales, using different detecting systems and locating algorithms. The results allow characterizing the local microseismic activity of LKB and its tectonic implications. 5.1
The new database (SNS catalog)
The four mini-arrays that were deployed along the northern and north-eastern shores of Lake Kinneret enabled the detection of large amount of earthquakes in a short period of time. The location of the mini-arrays appeared to be appropriate since most of the seismic activity occurred in the north-central part of the study area (see Figure 4-16). The detection process was preformed manually and in a different method than the detection method of the GII. Since the detection procedure is manual and does not rely on the detection of a few stations, events could be detected even by one SNS only. The use of sonograms enabled the distinction between seismic events and non-seismic events and to detect very weak events even with rather noisy background. The use of 3-D sensor in each mini-array enabled clear identification of S-phase onset resulting in more accurate picking and better discrimination between earthquakes and man-made explosion. In case of detection with only one array, the short S-P interval indicated source proximity, even if the hypocenter could not be located accurately. The high sampling rate allowed viewing full signal spectrum and clearly distinguishing the corner frequency, even for the weakest events. The newly acquired database is still not sufficient for performing robust analysis. For more accurate results and larger database, more arrays should be deployed for a longer period of time in the study area. Therefore no attempt was made to map active faults and the significance of the new catalog is mainly its detection abilities. 5.2
Common events
During the operation of the network only five common events were detected by both the SNS and the GII. Due to the use of different location algorithms, spread of the sensors 76
and velocity model, different results (epicentral locations and origin time) were obtained for the same events. The solutions of the SNS are located to the northeast (Figure 5-1), probably due to the spread of stations and the use of velocity model with slightly higher values than the GII.
Figure 5-1. Common events as detected by SNS and ISN networks. Results are presented in the table below. Event No.
SNS Z(Km)
O.T.
GII
Lon.
Lat.
ML
0
35.650
32.936
16
20100320184529
3.9
35.620
32.913
13
20100320184529
3.6
1
35.623
32.994
9
20100530114058
1.9
35.550
32.983
21
20100530114058
2
35.695
32.875
12
20100706221214
2
35.590
32.897
3
20100706221213
1.7
3
35.568
32.829
1
20100922125425
1.9
35.544
32.792
1
20100922125424
4
35.564
32.836
20101026150825
1.4
35.615
32.929
15
20101026150825
77
Lon.
Lat.
Z(Km)
O.T.
Md
5.3
Event magnitude
The seismic activity in the study area is probably characterized by small magnitudes events. Except for one event of ML=6.7 that has shaken Safed in 1837, the events in the study area in the past 100 years did not exceed ML=4.5 and most of them are below Md=2. The distribution of event magnitude shows that the eastern boundary DST fault and its continuation north on land (Jordan fault) generates the strongest events (Figure 44) whereas the northern basin generates very low magnitude events (Figure 4-18). There is no correlation between the depth and the magnitude of the events however the total range of magnitudes in this study is not more than four orders. The largest event that was detected in the study area during 2010 (ML=3.9) was not followed by any aftershocks. 5.4
b-value
The b-value of the study area that was calculated for the GII catalog is lower than the bvalue of the total transform (b=0.96) or the other basins along the transform (see chapter 1.1.3). The rather low b-value that was calculated might be a result of incomplete catalog of the study area but could also indicate different behavior of the seismicity of study area. The b-value of the SNS catalog (b=0.58) was even lower than the b-value that was calculated for the GII catalog (b=0.82). This could mean that the catalog is not complete. The incomplete catalog could a result of the fact that not all the arrays were operating all the time thus changing the borders of the study area and making it smaller. The database is rather small and consists of only 4 orders of magnitudes for the complete catalog. The strongest event is quite different from the rest of the measurements and could be an outlier. Calculating the b-value without the outlier results in a higher value but still much lower than the value of the GII catalog. This extreme low b-value could be temporal and results from changes in the stress field. Schorlemmer et al. (2005) claim that b-values are dependent on focal mechanism. Values close to b=1 are characteristic of strike-slip faults and which is in accordance with the b-value of the DST (0.96), whereas thrust faulting events have much lower values. They inferred from their study that b-value stands in an inverse relationship with differential stress (also noted by Ayele and Kulhánek, 1997) and thus it means that lower b-value results from high stress regime or might be an indicator for temporal changes in stress regime. Another explanation for low b-value is attributed 78
to locked fault segments (Amelung and Geoffrey, 1997; Wyss et al., 2004). The low bvalue of the SNS catalog could imply that the LKB is a locked segment of the DST. Since both catalogs deal with very low magnitudes, the low b-value could also be explained by different behavior of low magnitude events. It could be that the decline in frequency is because low magnitude events are not as numerous as extrapolated from the magnitudefrequency curve. 5.5
Event clustering in space and time
Although most of the events are distributed non-uniformly in the northern basin, eight clusters were identified in the GII catalog. The clusters are observed in the northern subbasin only and seem to delimit this sub-basin's borders. The enhanced activity in that area and the existing of clusters support Ben-Avraham et al. (1996) assumption that this is the most actively subsiding part of the lake. The spatial structure of the clusters is mainly long and narrow except for two wide clusters. An attempt to fit these clusters to a plane shows that the source of these events in each cluster might be from one plane (each cluster fit a different plane) which is the fault plane. Since those clusters consist of very few events, it is not certain that this is a fault plain and its parameters could not be obtained. As mentioned in chapter 2, clustering characterize basins that are formed along transform faults. The appearance of clusters in the northern sub-basin indicates that LKB may function as a barrier to the movement of the DST in this segment (Sibson, 1985; Van Eck and Hofstetter, 1990). 5.6
Doublets
The microseismic data indicate an interesting phenomenon of doublets. The occurrence of the events in both catalogs show that most of the events tend to "follow" another earthquake that occurred a few minutes to a few hours earlier. Almost half of these events have nearby epicenters and show high similarity in waveform signal, and therefore are considered as doublets. Cross-correlation of these events can be used for improving event location (re-location) and phase picking, especially when S-phase onset is not picked on the horizontal trace or when the onset is not immerged. The procedure was not preformed since the new database is not sufficient for performing robust calculations. The rest of the events which are not close in space and do not show similarity in waveform signal might 79
indicate the influence of fault balance on each other (stress shifting) especially in the northern sub-basin which is highly deformed. 5.7
Signal spectrum
The corner frequency of event increases as its magnitude decreases. The corner frequencies of the displacement signal that was observed in the SNS catalog was mainly above 10 Hz. The high sampling rate of 250 Hz of the SNS enabled recording full signal spectrum and to easily determine the corner frequency of events with magnitude as low as ML=-1.2. The relatively high values of the corner frequency might be an indication for high stress earthquakes. 5.8
Patterns of seismic activity and tectonic implications
Although different solutions, the GII catalog and the SNS catalog both indicate rather similar patterns of seismicity and illuminate tectonic features in the study area. The two main tectonic features with the most enhanced seismic activity are the northern basin of the LKB and the transform fault north of the LKB (the Jordan fault). These two features exhibit different patterns of seismic activity. The events in the vicinity of the transform are stronger, deeper and randomly scattered. On the other hand, the events in the northern basin are of very low magnitudes, occur at shallow depths and tend to cluster. These differences could indicate different seismic behavior of the basin, secondary to the transform. The activity along the Jordan fault indicates that it is presently active and the activity in the northern sub-basin supports the claim of Ben-Avraham et al. (1996) that it is presently subsiding. The geometry of the northern sub-basin faults could not be inferred from the microseismic data acquired in this study. In order to map the active faults a better spread and more sensors in the study area are needed. This way better constraints on depth and more accurate location will be achieved which are needed for high-resolution active fault mapping. In addition, more accurate 2-D velocity model should be used. Nevertheless, the non-uniform distribution of events in the northern subbasin could also be indicative for the
intense deformation that controls this part
(Reznikov et al., 2004). In the southern sub-basin almost no activity is observed except for the activity along the bathymetric cliff (along coordinates 738-739 N in ITM grid). This activity supports the claim of Ben-Avraham (1996) and Reznikov et al. (2004) that
80
this is possibly an expression of an active fault line that its extent on land is the active Tiberias fault. Reduced activity which was observed along the Sheik-Ali fault indicates that this fault is not a direct continuation of the transform. Although evidence for young faulting in the northwestern part of Lake Kinneret (see Figures 2-8 and 2-9) was indicated by previous studies (Belitzky and Ben-Avraham, 2004; Reznikov et al., 2004; Tibor et al., 2004), no seismic activity was observed in that area. This is possibly a shallow a-seismic faulting. Along the transform segments south of Lake Kinneret almost no activity was observed. The absence of seismic activity in the southern section might indicate that it may be a locked segment. 5.9
Final conclusion
A new seismic catalog was created for the LKB, adding to the existing GII catalog. The four SNS mini-arrays have managed to detect 10 times more events than the ISN and to lower the detection threshold significantly. Analysis of the GII catalog supplemented by the new SNS catalog has enabled to characterize the microseismicity of LKB. Although the tectonic structure of LKB was not resolved, the combined catalogs were able to provide new insights about the main active tectonic features of the LKB : the Jordan fault and the northern sub-basin.
81
Appendix A Stations coordinate 1. ISN coordinates The main stations that have been operated since 1986 by the GII are presented in table A-1. Abbreviations B and S under ‘Type’ stands for broad-band and shortperiod respectively.
Station Adamit Amazia Arava Ashalim Atzmon Bar Giora Mt. Berech Dead Sea Dragot Eilat Ein Gedi Haifa Heletz Hanita Harif Hemdat Hermon Hermon Horresh Jerusalem Kerren Keshet Kfar Sold Kziot Macktesh Kattan Malckishua Mt. Gilboa Mt. Meiron Manof Masada
Alias ADI AMZI ARVI ATR ATZ BGIO MBH DSI DRGI EIL ENGI HAF HLZI HNTI HRFI HMDT HRI HRMI HRSH JER KER KSHT KSDI KZIT MKT
X (m) 221570 190803 218000 165649 225510 208490 191489 237380 237267 195000 237502 202529 165600 216627 203296 249764 268771 269200 225740 218846 151552 276143 261797 142329 214430
Table A-1 Y (m) Lat. 776080 33.08 604701 31.5491 505600 30.64 542051 30.96825 747590 32.824 625560 31.722 411611 29.79253 611060 31.59 611229 31.593 398200 29.6712 597511 31.4695 742689 32.778 542000 30.965 776384 33.0827 438620 30.0364 684397 32.253 796863 33.266 796350 33.268 733650 32.698 631079 31.7724 545130 30.9952 765332 32.982 788594 33.192 535372 30.9067 539720 30.948
MMLI MGI MMR MNFI MSDA
239110 239027 237970 222716 227350
704926 705055 766130 750732 580450 82
32.4379 32.4391 32.991 32.851 31.315
Lon. 35.239 34.9123 35.187 34.6431 35.278 35.092 34.9153 35.392 35.392 34.952 35.3944 35.024 34.634 35.174 35.037 35.526 35.7338 35.75 35.28 35.1981 34.4436 35.811 35.6585 34.3978 35.151
H (km) 0.469 0.151 0 0.3498 0.515 0.76 0.842 0.01 0.012 0.2 -0.321 0.179 0.35 0.301 0.438 0.151 1.015 1.014 0.416 0.777 0.3468 0.719 0.123 0.248 0.517
Type S B S S S B S S S B S S S S B S S S S B S S B B S
35.4216 35.4117 35.417 35.2393 35.289
0.511 0.506 1.108 0.388 0.4
B S S S S
Masada Mashabei Sadde Mashabei Sadde Mei Ami Meiron Mevo Hamma Nachshon Ofer Karmit Paran Ramon Ramon Retamim Rimonim Sagi Sdom Sheizaf Shivta Saliit Yahav Yahoshafat Yatir Zofar Zur Natan
MZDA MASH
234527 179711
579776 545645
31.3096 30.996
35.3628 34.785
-0.275 0.365
S S
MSH
179710
545645
31.0012
34.7883
0.365
S
MAMI MRN GLH
213870 236986 261213
712290 768529 735539
32.505 33.0118 32.713
35.152 35.3921 35.649
0.461 0.9 0.33
S B S
NSHB OFRI KMTI PRNI RMNI RMN RTMM JVI SAGI SDOM SZAF SVTA SLTI YHV YASH YTIR ZFRI ZNT
195670 198973 173248 200303 177015 165460 169991 232184 168685 236660 157280 164060 204065 218000 188101 211009 216953 202771
638200 725278 446235 473649 500776 491580 551170 649453 457326 554100 534510 538320 683032 505600 388630 585632 497254 682891
31.833 32.6214 30.10443 30.3519 30.5964 30.511 31.051 31.938 30.2042 31.078 30.897 30.932 32.2405 30.64 29.5853 31.36255 30.554 32.239
34.947 34.9854 34.7251 35.0046 34.762 34.632 34.6863 35.339 34.6772 35.386 34.547 34.617 35.04034 35.187 34.8809 35.1157 35.1782 35.027
0 0.52 0.473 0.411 0.853 1.003 0.255 0.68 0.56 0 0.293 0.37 0.25 0 0.718 0.9021 -0.037 0.234
S S S S S S S S S S S S S S S S S S
83
2. SNS mini-arrays The locations of each sensor in the mini arrays were taken using differential GPS (Ashtech Z-XtremeTM) with RMS of -+5 mm. The location of Ma'alle-Gamla sensors were changed twice, therefore all the locations are shown in the table A-2 below.
Station Korazim Korazim Korazim Korazim Almagor Almagor Almagor Almagor Ma'alle-Gamla Ma'alle-Gamla Ma'alle-Gamla Ma'alle-Gamla Ma'alle-Gamla* Ma'alle-Gamla* Ma'alle-Gamla* Ma'alle-Gamla* Ma'alle-Gamla** Ramot Ramot Ramot Ramot
Alias SuMo45 SuMo45 SuMo45 SuMo45 SuMo46 SuMo46 SuMo46 SuMo46 SuMo42 SuMo42 SuMo42 SuMo42 SuMo42 SuMo42 SuMo42 SuMo42 SuMo42 SuMo43 SuMo43 SuMo43 SuMo43
Table A-2 Sensor Lat. SNC 32.907028 SNN 32.907116 SNE 32.906751 SNW 32.907014 SNC 32.911255 SNN 32.911439 SNE 32.911314 SNW 32.911374 SNC 32.890714 SNN 32.890901 SNE 32.890452 SNW 32.890977 SNC 32.8903059 SNN 32.8904559 SNE 32.8900392 SNW 32.8905225 SNC 32.890359 SNC 32.844467 SNN 32.844352 SNE 32.844229 SNW 32.843972
*-operating from 17.05 **-operating between 11.04 till 17.05
84
Lon. 35.551515 35.551727 35.551689 35.551082 35.602733 35.602796 35.602982 35.601776 35.687604 35.687786 35.687329 35.687436 35.6868234 35.6870234 35.6867567 35.68669 35.687456 35.668966 35.668819 35.669074 35.66888
H (m) 163 164 161 162 -15 -13 -14 -17 125 125 124 123 125 125 126 123 125 22 21 22 22
Appendix B Earthquake catalogs 1. GII catalog Table B-1 presents the observed earthquake in the study area by the GII from 1986 to 2010. O.T. stands for origin time in the format of yyyymmddHHMM. Coordinates X an Y is kilometers in Israel TM grid.
O.T.
Sec
198601280111 198606271452 198607170816 198608152207 198608200956 198609151751 198609271020 198611260147 198612202355 198702012044 198702020655 198702150551 198702191632 198703231156 198703261305 198705112247 198705312326 198706051051 198706051204 198706070133 198706090926 198706100027 198708251026 198708302031 198709262221 198710191148 198711031041 198712130655 198801120204
23.5 7.4 32.9 24.7 33.7 60 28.4 19.5 1.4 9.7 13.5 6.7 15 51.7 30.8 54.1 11 22.8 19.4 54.8 20.3 24.8 45.3 30 5.3 58.4 47.3 0.3 3.2
Table B-1 Magnitude X (Md) (km) 0 266.8 2.2 254.9 2.2 243.3 0 255.3 3.3 256 2.8 263 0 252.6 1.4 263.8 0 258.3 1.1 254.46 0 258.38 0 253.4 1 258.07 2 246.05 1.9 247.1 1.9 263.89 1.4 258.4 0 256.98 0 261.03 1.9 255.57 2.7 256.73 0 257.39 1.8 252.8 0.2 256.9 1.2 254.4 1.9 251.17 0 254.28 1.3 255.2 1.2 258.42 85
Y (km) 755.3 768.1 739.1 752.5 759.5 758.3 747.8 755.9 721.9 749.72 745.28 751.5 753.79 747.3 757.1 758.3 767.3 753.18 750.34 751.94 754.58 753.49 740.1 764.1 752.8 740.7 738.85 754 754.11
Depth (km) 4 1 17 0 5 4 8 7 20 13 11 7 15 15 2 12 7 10 2 12 11 10 10 12 13 10 2 3 12
Lat. o N 32.893 33.009 32.747 32.868 32.931 32.92 32.826 32.899 32.592 32.843 32.803 32.859 32.88 32.821 32.909 32.92 33.001 32.874 32.848 32.863 32.887 32.877 32.756 32.973 32.871 32.761 32.745 32.881 32.882
Lon. o E 35.725 35.598 35.47 35.6 35.609 35.684 35.571 35.693 35.63 35.591 35.633 35.58 35.63 35.5 35.512 35.694 35.635 35.619 35.662 35.603 35.616 35.623 35.572 35.619 35.591 35.555 35.588 35.6 35.634
198803230118 198803290906 198804101310 198805060445 198805060605 198805060645 198805072017 198805072057 198805140143 198805140147 198805190143 198805190625 198805250041 198806121516 198806290827 198806302111 198807010410 198807010425 198807021844 198807021932 198807071019 198807120009 198807211449 198807241051 198808281427 198809152356 198809191525 198810240230 198810311511 198811170402 198812042318 198812071242 198901221344 198901242037 198903102047 198903110022 198903280304 198903312145 198904070212 198904081810 198904221806 198904221806 198906041028 198906131433 198906142357
30.3 15.7 11.4 31 47.4 30.2 35.5 36.1 38.3 12.4 21.7 15.4 46.7 12.8 57 35.7 0.7 32.1 10.7 18.2 22.2 53.8 0.9 35.1 35.3 4.2 47.8 54.9 11 33.3 8.8 56.1 42.3 10.7 13.4 46.9 24.2 41 36.8 28.8 26.8 31.1 9.4 17.6 21.3
1.2 0 2 2.2 1.6 1.1 3.6 0.7 0.5 0.8 0 0 2.5 2.3 0 1.3 1.7 1.2 1.2 1.2 1.9 0.8 2 1.4 2 1.5 2 0 1.6 2 1.2 1.7 2.3 1 1.2 1.4 1.6 1.8 0 0 0 0 2.3 2.4 1.6
257.5 261.89 251.26 258.4 257.68 258.62 258.94 258.99 255 254 258 254 256.09 249.3 252.54 252.6 253.33 258 253.68 253.48 245.37 256 249.86 252 248.34 256.11 250.84 243 258 254.7 256.53 255 256.32 260.1 255.8 254.91 240.32 256.72 251.61 251.2 257.87 258.15 252.6 252.07 257.47 86
743.67 755.47 740.66 749.23 749.3 749.24 748.97 749.57 762 753 749 747 754.94 739.9 750.86 752.7 753.06 750 754.18 754.03 758.7 748 742.91 757 735.36 751.59 739.48 744 745 754.67 763.6 738.1 745.01 759.8 748.7 754.49 765.43 756.48 726.27 741.23 760.07 761.12 728 746.26 747.43
10 25 12 9 9 9 8 9 1 1 1 1 8 7 3 7 12 3 1 11 24 17 10 1 3 11 10 25 7 22 12 14 3 13 8 14 12 11 4 12 12 18 13 19 12
32.788 32.895 32.761 32.838 32.839 32.838 32.836 32.841 32.954 32.872 32.836 32.818 32.89 32.754 32.853 32.87 32.873 32.845 32.883 32.882 32.924 32.827 32.781 32.909 32.713 32.86 32.75 32.791 32.8 32.887 32.968 32.738 32.8 32.934 32.834 32.886 32.984 32.904 32.631 32.766 32.936 32.946 32.647 32.812 32.822
35.623 35.672 35.556 35.634 35.626 35.636 35.639 35.64 35.598 35.586 35.629 35.586 35.609 35.535 35.571 35.571 35.579 35.629 35.583 35.581 35.494 35.608 35.541 35.565 35.524 35.609 35.551 35.467 35.629 35.594 35.615 35.596 35.611 35.653 35.606 35.597 35.44 35.616 35.558 35.555 35.629 35.632 35.569 35.565 35.623
198906242345 198908191416 198911091008 199003111652 199004061612 199006221456 199008061045 199009241322 199011060819 199012101230 199012211524 199012270256 199012300913 199101052238 199101182235 199101201141 199101240822 199102120832 199102150738 199102240740 199104071718 199104150121 199104150503 199104160638 199104221034 199104232307 199104270713 199104291904 199105011436 199105012047 199105020614 199105021020 199105021151 199105021531 199105032207 199105090341 199105251751 199105300221 199106081935 199106101413 199107071648 199107162242 199107172324 199107212256 199107222020
24 23.3 0.7 42.8 52.5 14.8 54.9 31.2 52.5 1.6 50.4 21.5 16.9 8.3 12.9 22.9 28.7 56.9 6.7 37.1 19.7 28.3 49.8 1.3 12.8 15.1 22.3 45.6 22.4 12.1 57 51.5 44.2 25.1 19.2 44.5 3.9 34.2 33.1 25.5 55.5 39.8 9.8 55.2 38.6
0.9 2.3 1.6 1.8 1.5 1.8 2.1 2.2 2 0 1.5 1.7 2.6 0.2 0.5 0 0.5 1.4 1.7 0 1.3 2.4 1.5 1.9 0 0.5 1.3 0.7 1.2 2.2 1.4 1.5 0 2 1 0.9 1.7 1.1 0.7 0 1.3 0.8 1.2 0.7 1.7
253.45 259.2 255.6 258.67 261.8 262.9 240.52 256 258.7 241.46 252.6 257.17 254.76 241.8 258.5 252.4 258.04 243.02 256 240.44 253.8 254.7 252.9 254.1 251.9 259.1 253.4 258.8 253.4 253.2 253 254.2 253.1 254.08 253.7 255.39 256.2 258.1 263.6 240.3 251.3 255.3 254.52 259.5 264.24 87
755.36 762 754.5 740.41 748.2 756.9 767.96 767 760.3 749.29 750.9 751.88 754.11 754.1 752.1 727.2 748.38 751.32 757.1 759.79 750 750.3 747.8 749.9 737.1 762.4 750.7 759.6 750.2 748.9 748.85 748.6 749.6 749.51 748.3 747.25 758.9 759.6 763.3 748.8 729.9 752.8 752.53 760.7 750.39
3 10 1 11 0 2 7 4 13 10 23 10 15 6 18 8 19 8 1 0 0 14 0 6 7 12 0 12 0 6 0 13 0 6 6 2 16 16 12 4 0 6 8 10 17
32.894 32.954 32.886 32.759 32.829 32.908 33.007 32.999 32.938 32.839 32.853 32.862 32.882 32.882 32.864 32.64 32.831 32.857 32.909 32.934 32.845 32.848 32.826 32.844 32.729 32.957 32.852 32.932 32.847 32.835 32.835 32.833 32.842 32.841 32.83 32.821 32.926 32.932 32.965 32.834 32.664 32.871 32.868 32.942 32.849
35.581 35.643 35.604 35.636 35.67 35.683 35.442 35.609 35.638 35.451 35.571 35.621 35.595 35.455 35.635 35.567 35.63 35.468 35.608 35.441 35.584 35.594 35.574 35.587 35.562 35.642 35.58 35.639 35.58 35.578 35.575 35.588 35.576 35.587 35.583 35.601 35.611 35.631 35.691 35.438 35.555 35.601 35.592 35.647 35.697
199108152025 199108240850 199109031429 199110011253 199111180322 199111192253 199112051029 199201240319 199202172304 199204071046 199204122322 199204180325 199204271724 199205220736 199208131108 199208140109 199208212222 199209110057 199209121703 199210141849 199210202045 199210240438 199212111040 199212111041 199212231531 199301142258 199301160259 199301271641 199302210455 199302220124 199302230015 199302230515 199302230522 199303180753 199303181033 199303220315 199303232347 199304112310 199304112310 199305030600 199305212258 199305221334 199306130926 199306160715 199306270734
50.4 0.3 30.6 31.4 17.2 32.9 55.8 31.3 5.9 7.2 33.6 29.3 12.4 59.7 55.9 57.3 52.2 19.7 2 56.2 18 38.8 43.6 28.4 14.6 17 40.1 50.6 42.4 46.4 36.3 26.1 22.7 53.9 38 38 53.7 45 13.6 41.6 9.8 49.1 38.7 51.4 40.2
1.6 1.3 0 2.1 1.4 1.4 2.7 1.3 1.4 1.3 1.2 1.2 2 1.7 1.4 0.8 0 0.9 1.5 0.6 1.9 1.5 1.4 1.6 1.7 1.1 0 0.9 1.4 1.3 1.3 1.5 0 0 1.3 2 1.5 0 1.5 0.4 0 1.4 0 0 1.4
258 256.1 250.36 253.9 256.6 255.2 258.2 259.1 257.2 253.9 256 255.6 257.8 255.3 253.2 252.7 258.2 254.8 256.4 259 259.9 255.5 255.7 256.6 260.1 255.6 261.46 254.4 254.4 253 255.3 253 253.5 258.09 260 254.6 254.8 253.3 253.4 258.61 263.5 255.7 264 258.4 256.3 88
764.6 747.6 742.06 728.5 749.3 751.6 759.2 750.8 766.1 755 756.1 755.3 763.7 752 751.4 751.4 762.6 751.6 751.1 750.5 751.2 750.6 749.3 749.5 759.3 747.3 731.98 761.1 752.6 751.8 753.5 751.8 756.9 755.16 754.1 753.5 752 752.1 752.2 746.96 758.5 751.8 728 746.8 769.2
18 12 0 7 11 3 9 12 12 3 17 1 10 0 4 0 17 8 2 11 13 7 0 7 11 16 0 12 3 7 8 7 19 0 20 7 0 7 4 8 0 8 1 10 14
32.977 32.824 32.774 32.651 32.839 32.86 32.928 32.853 32.991 32.89 32.9 32.893 32.969 32.863 32.858 32.858 32.959 32.86 32.855 32.85 32.856 32.851 32.839 32.841 32.929 32.821 32.68 32.945 32.869 32.862 32.877 32.862 32.908 32.89 32.882 32.877 32.863 32.864 32.865 32.818 32.922 32.862 32.647 32.817 33.019
35.631 35.609 35.546 35.583 35.614 35.599 35.632 35.641 35.622 35.586 35.608 35.604 35.628 35.6 35.578 35.572 35.633 35.595 35.612 35.64 35.65 35.602 35.605 35.614 35.653 35.603 35.65 35.592 35.591 35.576 35.601 35.576 35.581 35.616 35.651 35.593 35.595 35.579 35.58 35.636 35.69 35.605 35.692 35.633 35.613
199306280059 199307192051 199307211322 199308012249 199310032252 199310151444 199310151919 199401261821 199402040359 199403080106 199403181355 199404221918 199404280119 199405131501 199406101913 199407021128 199407061320 199407111546 199408140534 199408171027 199408182307 199411091518 199501300856 199504140323 199505010309 199505081908 199505090240 199505132359 199505140000 199505142341 199505262039 199505270513 199505271502 199506071425 199506171032 199506291452 199508122224 199509232131 199509250054 199510161856 199511112027 199511120219 199512261754 199601012150 199603300321
32.3 57.4 13.8 25.4 13.4 54.1 2.7 44.3 43.5 13.1 54.3 3.7 23.7 37.1 9.8 50.7 46.6 48.6 29.5 14.5 10.1 32.1 4.5 57.4 0.6 20.4 23.9 37.8 16.3 2.5 55.2 50.2 12.2 28.3 42.6 33.7 40.5 57.8 22.6 34.7 53.5 56.3 13.9 57.8 27.2
0.3 1 0.6 2.6 1.8 1.5 1.4 2.2 1.3 1.6 0 1.5 0.9 1.4 0 2.9 1.4 1.4 1 1.7 0 0 2.1 0 0.9 3 1.2 0 0 1.3 1.6 0.6 0.4 1.2 1.5 1.9 2.6 1.8 1.7 0 1.6 1.7 1.4 2 1.4
254 253.8 259.7 264.5 254.3 254.2 253.9 256.9 256.7 254.9 258.3 262 254.2 255 258.1 255.2 255.4 255.1 257.1 254.31 262.1 262.2 241.1 255 252.4 252.5 259.6 258.9 251.9 253.3 254.7 253.3 252.9 264.3 262.9 263.9 258.8 251.7 255.1 251.3 258 252.9 257.6 258 256.2 89
752.1 752.2 753.7 767.1 752.1 750.1 750.1 724.4 751.9 753.5 734.1 754.4 746.2 751.1 759.9 754.2 750.3 756.1 762.8 756.85 767.3 748.7 764.7 750.9 747.8 755.7 759.2 761 761.9 755.4 753.1 753.7 753.4 758.8 754.8 754.08 742.6 762.6 755 752.6 767.1 752.8 761.5 752.2 756.9
3 1 12 0 5 6 13 13 8 3 12 6 12 5 12 1 5 10 14 3 15 15 13 21 1 2 18 17 6 9 2 3 2 1 0 5 0 6 5 20 17 5 15 16 8
32.864 32.865 32.879 33 32.864 32.846 32.846 32.614 32.863 32.877 32.702 32.885 32.811 32.855 32.935 32.883 32.848 32.9 32.961 32.907 33.001 32.834 32.978 32.853 32.826 32.897 32.928 32.945 32.953 32.894 32.873 32.879 32.876 32.925 32.889 32.882 32.779 32.959 32.89 32.869 33 32.871 32.949 32.865 32.908
35.586 35.584 35.648 35.701 35.59 35.588 35.585 35.615 35.616 35.596 35.631 35.673 35.588 35.597 35.631 35.6 35.601 35.599 35.621 35.59 35.675 35.675 35.448 35.597 35.569 35.571 35.647 35.64 35.565 35.579 35.594 35.579 35.575 35.698 35.683 35.693 35.637 35.563 35.599 35.557 35.631 35.575 35.626 35.63 35.611
199604160903 199604161240 199604162105 199604162124 199604180207 199604191750 199604201900 199604210129 199604210150 199604211730 199605161705 199606152355 199606160114 199606231731 199606241841 199606242151 199606242152 199606252119 199606260130 199607040134 199607051834 199607060923 199607151312 199608010639 199609140800 199609232304 199609272206 199610031012 199701050227 199702012329 199702082247 199702142324 199702210631 199703090215 199704021350 199704231606 199706050214 199706240656 199707071935 199712141106 199712310451 199805200528 199805290217 199806240320 199807050107
43.7 51.7 49.7 1.8 42.1 53 16.7 30.6 48.4 12.1 28 12.8 15 33.1 8.2 50.8 52.4 27.7 13.6 17 33.5 40 13 37.1 49.1 14.5 13.2 1.5 55.4 10.8 35.5 50.6 38.3 6.2 16.2 34.1 14.6 16.8 6.1 21.1 35.8 32 41.1 50.6 8.8
2.4 1.8 1.4 1.3 0 1.3 2.2 1.9 0 1.7 0.8 2 1.4 0 0 2.2 1.5 0.7 0 1.6 0 0 0.9 0 1.4 2 2.2 1.3 1.7 1 2 2.1 1.4 1.5 1.5 0 3.1 2 1.5 1.3 1.6 1.7 2.3 0.8 0
255.9 257.6 257.4 259.4 261 256 257.3 259.8 257.8 257.8 254.8 252.7 253.1 256 253.2 254.1 254.9 253.6 256.8 254.9 255.4 257.1 256.1 257.1 263.7 254 258.8 259.2 253.2 256.8 255 258.1 258.3 259.9 258 256.9 259.1 255.4 254.1 258.7 243.5 254.6 267.1 253.9 240.4 90
748.6 749 749.7 748.2 748 749.8 749.4 748 747.7 747 750.6 750.3 751.6 748.1 751 750.8 749.7 751.2 753.5 749.9 749.5 766.9 761.9 756.8 758.9 761.2 768.3 760 750 751.9 752 760.3 748.9 751.2 762.1 739.7 739 739.2 756.3 751.1 754 752.7 763.7 753.7 769.6
0 9 18 16 8 16 11 9 12 4 9 2 11 5 6 10 4 11 0 4 12 18 18 6 3 5 10 13 1 5 10 10 9 6 16 8 0 4 7 16 13 3 2 5 19
32.833 32.836 32.843 32.829 32.827 32.844 32.84 32.827 32.825 32.818 32.851 32.848 32.86 32.828 32.854 32.853 32.843 32.856 32.877 32.844 32.841 32.998 32.953 32.907 32.926 32.946 33.01 32.936 32.845 32.863 32.863 32.938 32.835 32.856 32.955 32.752 32.746 32.748 32.902 32.855 32.881 32.87 32.969 32.879 33.022
35.607 35.625 35.623 35.644 35.662 35.608 35.622 35.649 35.627 35.627 35.595 35.572 35.577 35.608 35.578 35.587 35.596 35.582 35.617 35.596 35.601 35.621 35.61 35.62 35.692 35.587 35.64 35.643 35.578 35.617 35.597 35.631 35.633 35.65 35.63 35.617 35.64 35.6 35.588 35.637 35.473 35.593 35.729 35.585 35.441
199808111705 199809140031 199811270011 199812151117 199901161806 199907291749 200006120611 200007140235 200007141811 200011011546 200011020102 200103181850 200104250137 200106060554 200107042223 200107211834 200108221122 200109120050 200109212028 200111261752 200201191205 200203010912 200203011808 200203031940 200203032145 200203131450 200203200854 200205060947 200207022001 200207032119 200207110626 200208181859 200209162335 200212230804 200301291035 200304271327 200305261726 200305281741 200305290647 200305290746 200305291003 200305310820 200306071012 200306200050 200306201651
28.2 17.1 6.5 0.5 11.1 15.8 58.7 10.9 9.3 14.2 45.5 38.4 37.9 23.5 5.5 46.6 31.1 52.7 50.3 56.8 39.7 15.9 27.3 9.2 28.2 5.1 1.4 18 58.1 40.2 13 21.8 10.1 4.7 57.3 25.1 27.7 34.7 46.3 56.6 12 15 34.5 15.8 6.1
0 0.6 2.1 3.7 1 1.8 2.4 3.3 1.7 1.5 2.2 1 3.3 1.6 2.9 1.9 1 1 0 0.9 2.9 1.3 1.7 1.7 1.3 1.6 0 2.7 1 1.1 3 1.4 0 2 0.5 1.5 1.8 0.8 2.2 1.7 1.7 1.9 1.3 1.5 1.7
246.6 245.77 250.2 258.1 245.1 258.7 253.1 256.3 258.4 267.5 263.4 256.8 258.7 259.1 258.6 254 265.4 256.8 257.8 257 257 253.9 253.7 252.5 257 253.2 256.1 256.9 259.8 256 260.2 256.9 256.9 256.7 258.8 256.7 261.5 253.5 257.8 257.2 252.1 255.2 254.8 258.3 260.8 91
755.9 755.2 745.1 742.4 733.7 748.1 752.7 756.2 760.2 758.3 756.2 763.8 736.2 760.1 751.4 753.8 757 764.6 764 734.7 757.6 750.9 751.3 750.4 753 755.7 745.8 762.1 749.2 749.8 766.9 765.1 762.7 749.9 759.5 763.1 755.6 748.4 753.9 753.6 749.1 754.1 753.1 753.4 752.6
10 0 5 2 16 15 13 4 16 10 3 14 6 15 8 4 14 18 25 18 2 2 3 0 10 14 9 10 18 19 10 15 11 18 17 12 4 4 14 5 4 3 2 11 12
32.899 32.892 32.801 32.777 32.698 32.828 32.87 32.901 32.937 32.92 32.901 32.97 32.721 32.936 32.858 32.88 32.908 32.977 32.972 32.707 32.914 32.853 32.857 32.849 32.872 32.897 32.807 32.955 32.838 32.844 32.998 32.982 32.96 32.844 32.931 32.964 32.896 32.831 32.881 32.878 32.837 32.882 32.873 32.876 32.869
35.507 35.498 35.545 35.63 35.489 35.637 35.577 35.612 35.635 35.733 35.688 35.618 35.636 35.642 35.636 35.587 35.71 35.618 35.629 35.617 35.619 35.585 35.583 35.57 35.619 35.578 35.609 35.619 35.649 35.608 35.655 35.619 35.619 35.615 35.639 35.617 35.668 35.581 35.628 35.621 35.566 35.6 35.595 35.633 35.66
200308260733 200309071613 200310280545 200312021919 200405300538 200405311725 200406150702 200407061112 200410280926 200501070414 200504172011 200507031351 200507031807 200512091439 200512091504 200608041131 200611171428 200612180858 200706151030 200706280447 200707070546 200707171057 200709151831 200710192316 200711030426 200801130832 200801190943 200802110859 200802211215 200802252153 200803240346 200803301323 200804180841 200804261510 200805021226 200805200623 200805301016 200806020058 200806060016 200806172329 200806301522 200807010103 200807020722 200808020550 200808092005
43.2 47.2 10.2 44.2 2.4 51.1 2.9 16.6 35 3.4 20.7 53.2 26.1 34.6 38.4 3.9 44.8 42 29 29.4 30.2 48.4 34.5 28.1 9.3 1 45.7 19.3 12.2 50.7 9.8 44.7 6 46.3 31.8 13.2 8.1 5.7 51.5 44.9 19.6 56.4 49.9 46.7 51
1.1 1.7 2.5 2 2.8 3.4 1.1 0 2.1 2.7 0.9 1.1 1.8 1.7 1.7 1.1 2.3 1.9 1.7 0 0.9 1.3 1.5 1 0 0 1.3 0 1.7 0.5 0 1.8 0 1.2 1.6 0 1.8 0 0 1.4 0 0 0 0 0
255.9 760.6 248.5 761.7 254.4 747.8 257.7 758.3 258.3 758.8 260.9 759.8 256.3 761.8 256.6 744.5 254.1 750.8 260.1 758 258.3 751 248.96 746.15 253.2 749.4 257.1 749 255 752.2 253.2 757.05 257.91 758.15 253.4 751.5 249.82 745.71 256 746.12 256.14 745.51 258.66 743.01 240.48 758.76 257.34 757.31 259.76 750.74 248.93 742.26 252.3 748.93 261.78 766.6 267.99 766.69 257.85 759.7 243.92 738.34 269.81 766.45 258.84 764.87 259.6 759.21 242.95 734.09 245.2 748 258.36 763.25 257.33 737.8 259.5 759 251.67 752.1 254.9 750.9 254.03 750.2 243.91 768.02 259.62 749.61 253.092 753.644 92
16 20 2 13 11 9 20 4 4 8 11 0 2 13 18 0 10 0 3 2 2 14 3 0 10 3 2 0 12 16 5 0 13 21 0 2 8 10 17 5 0 0 14 0 0
32.941 32.951 32.826 32.92 32.925 32.934 32.952 32.796 32.853 32.918 32.854 32.811 32.84 32.836 32.865 32.908 32.918 32.859 32.806 32.809 32.803 32.781 32.924 32.91 32.851 32.775 32.835 32.994 32.994 32.932 32.739 32.992 32.978 32.927 32.701 32.827 32.964 32.734 32.925 32.863 32.852 32.846 33.007 32.841 32.877
35.608 35.528 35.59 35.627 35.633 35.662 35.612 35.614 35.587 35.653 35.633 35.532 35.578 35.62 35.597 35.564 35.616 35.58 35.529 35.594 35.595 35.623 35.429 35.609 35.635 35.519 35.555 35.657 35.724 35.615 35.465 35.743 35.626 35.634 35.455 35.479 35.621 35.609 35.633 35.549 35.583 35.574 35.466 35.633 35.563
200808171247 200810031219 200811220514 200811260132 200812040026 200812040336 200901251535 200901280508 200902040116 200902040117 200902040118 200902040154 200904281425 200907081615 200907110226 200907110234 200907112010 200908082002 200909072224 200911202337 200911270003 200912220418 200912212006 201003201845 201005301140 201007062212 201007241108 201009221254 201010261508 201011132203 201012021233 201012040350
21.3 6.7 34.7 13.9 27.5 56.1 39.5 15 29.8 36.2 16.6 25.1 30.6 43.5 38.7 3.9 23.5 52.1 7.8 2.6 0.6 42.7 41.9 29.6 58.1 13.3 43 24 24.8 25.6 11.3 56.9
2.2 1.8 2.2 1.8 2.9 0 2.9 1.2 0.7 0 0.5 1.2 0 0 0 1.3 0 2.1 1.9 0 1.3 2.9 1.3 3.6 0 1.7 0 0 0 0 0 0
240.21 255.73 244.21 251.11 257.31 252.01 258.4 260 258.2 257.8 257.2 256.3 248.5 264.12 259.54 259.54 254.43 255.09 244.69 254.81 258.36 260.43 256.33 258.33 251.75 263.01 255.61 251.3 257.83 250.07 252.02 246.8
763.13 744.47 768.82 750.12 741.82 752.92 737.22 763.21 748.15 747.51 747.85 747.45 769.72 744.01 748.32 747.49 769.54 750.87 747.15 754.7 747.86 759.34 748.94 757.64 765.4 755.89 720.57 744.22 759.44 746.16 769.65 753.82
11 2 0 1 3 1 9 7 10 14 11 13 9 10 15 9 14 2 5 5 3 11 6 13 21 3 18 1 15 3 10 28
32.963 32.794 33.014 32.845 32.77 32.871 32.729 32.963 32.827 32.822 32.825 32.821 33.022 32.79 32.829 32.821 33.02 32.852 32.819 32.887 32.825 32.928 32.835 32.913 32.983 32.897 32.579 32.792 32.929 32.81 33.022 32.879
35.426 35.592 35.469 35.543 35.609 35.552 35.62 35.638 35.618 35.614 35.608 35.598 35.515 35.681 35.633 35.633 35.579 35.585 35.474 35.582 35.62 35.643 35.598 35.62 35.55 35.67 35.59 35.544 35.615 35.531 35.553 35.497
2. SNS catalog Table B-2 lists the observed earthquakes in the study area from March 2010 to November 2010. ML is the local magnitude.
Event yyyy mm 1† 2†
2010 2010
3 3
dd
HH
5 6
19 10
Table B-2 MM SS.SS 44 7
59.5080 30.5000 93
Lat. o N 32.96159 32.84465
Lon. Depth o E (km) 35.65106 15 35.70905 2
ML 0.6 0.1
3† 4† 5† 6† 7† 8† 9$† 10* 11† 12† 13† 14† 15† 16 17 18† 19 20 21 22† 23† 24† 25† 26 27† 28* 29 30† 31† 32† 33† 34† 35† 36† 37† 38† 39† 40 41 42$ 43 44† 45 46 47†
2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010
3 3 3 3 3 3 3 3 3 3 3 3 3 3 3 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 5 5 5 5 5 5 5 6 6 6 6 6
6 7 15 16 17 17 20 21 21 22 22 24 25 27 27 1 2 3 3 5 5 6 6 6 10 18 19 19 26 27 27 28 30 1 2 7 13 13 18 30 1 2 4 5 6
16 5 21 2 5 23 18 2 2 10 23 20 22 2 19 23 0 9 9 5 7 0 0 13 7 20 1 22 23 21 23 22 0 1 12 20 1 19 10 11 22 1 15 10 19
49 23 2 35 4 24 45 25 46 48 10 13 46 35 53 10 43 39 41 1 31 20 33 18 39 43 29 57 27 38 43 6 55 37 50 40 28 12 7 40 3 50 48 53 37
48.2440 56.4880 4.1840 52.0400 48.8960 30.8480 29.8360 28.2120 18.3840 16.6160 32.9920 51.0480 45.7720 4.7840 59.5560 33.6800 13.0640 7.4080 53.0800 55.1320 56.6840 46.3720 13.4880 25.1320 23.9600 9.6000 41.8480 16.2440 20.8200 21.3080 26.4520 29.8960 52.4560 24.8560 4.8840 55.7280 34.5680 21.9600 15.9520 58.7680 13.5600 49.2040 20.6320 26.7320 35.5280 94
32.83963 32.86611 32.72419 32.84868 32.88839 32.86410 32.93644 32.88027 32.92415 32.88100 32.91560 32.93929 32.83945 32.89890 32.78781 33.12626 32.93077 32.86159 32.86799 32.87750 32.88388 32.83465 32.85811 32.82877 32.89008 32.84287 32.76596 33.05055 33.02022 32.86905 32.86509 32.86307 32.86541 32.88676 32.86479 32.87446 32.86421 32.87516 33.02631 32.99353 32.84870 32.87673 32.87314 32.88983 32.93883
35.46727 35.65578 35.93121 35.61731 35.65963 35.62616 35.64989 35.59953 35.63462 35.63574 35.55404 35.61217 35.59114 35.56473 35.53722 35.59521 35.58221 35.67647 35.67888 35.60438 35.59774 35.57061 35.59663 35.57548 35.60001 35.57691 35.62923 35.59965 35.61899 35.58472 35.57855 35.63017 35.59341 35.66798 35.84121 35.62096 35.60157 35.60560 35.59632 35.62309 35.57831 35.57183 35.59006 35.66220 35.65994
13 5 6 8 1 1 16 1 0 5 5 14 2 1 2 3 5 0 0 7 10 0 3 15 9 2 4 23 1 1 2 22 9 9 5 12
1.6 1.1 1.5 0.2 0.1 -0.5 3.9 -1.2 -0.1 0.6 0.2 0.3 0.3 0.1 0.6 0.3 0.4 -0.7 -0.5 0.8 0.5 -0.1 -0.7 0 0.6 -0.4 0.5 1.1 1 0 0.6 1.2 0.6 0 2.6 -0.3 0 0.2 2 1.9 0.2 1 0.4 0.1 1.1
48 49† 50 51† 52† 53† 54† 55 56 57† 58 59 60† 61† 62† 63† 64† 65* 66* 67*$ 68* 69* 70 71 72* 73* 74* 75* 76 77 78*$ 79 80 81 82 83 84 85* 86* 87 88 89 90 91 92
2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010
6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 6 7 7 7 7 8 8 8 8 9 9 9 9 9 9 9 9 9 9 10 10 10 10 10 10 10 10 10
7 8 13 14 15 15 16 18 19 23 24 25 26 26 28 28 28 29 3 6 6 16 13 26 26 29 1 9 13 18 22 23 23 28 28 30 1 1 3 3 5 7 16 16 16
1 22 0 21 22 23 22 0 10 0 0 22 0 0 1 1 21 16 19 22 23 17 23 2 20 23 23 1 22 10 12 0 1 22 23 21 2 2 1 18 2 22 6 21 22
41 26 46 28 7 46 46 21 47 31 40 6 10 47 5 25 7 18 4 12 9 44 44 14 10 36 48 15 37 51 54 9 33 55 7 40 21 59 16 53 41 36 51 4 12
54.1200 13.0440 52.0840 49.0640 10.6960 35.6760 31.2080 54.2400 15.9320 43.3520 18.7160 24.4640 5.6480 52.1040 38.1920 49.1920 12.9560 41.4720 20.5040 14.3120 57.6520 37.3240 51.1760 59.7120 21.7360 12.5960 13.7200 52.2640 47.4080 42.9240 25.2640 31.9800 35.5200 52.2440 57.0920 8.4000 49.3960 26.7720 2.4040 17.5400 34.1600 18.0800 14.5360 44.6880 16.3880 95
32.93945 32.95837 32.87664 32.96796 32.87732 33.00936 33.03942 32.87816 33.00948 32.89407 32.82811 32.85692 32.88220 32.85527 32.84431 32.79358 32.87204 32.79073 32.82758 32.87525 32.85202 32.87836 32.82240 32.87210 32.93879 32.89032 32.83895 32.83237 32.88064 32.84814 32.82939 32.83818 32.87083 32.86501 32.86287 32.87662 32.86011 32.88157 32.89337 32.84141 32.79925 32.92885 32.85320 32.86365 32.86468
35.68685 35.60020 35.61216 35.66897 35.58748 35.63781 35.61911 35.56526 35.65233 35.57701 35.59689 35.58692 35.59829 35.58677 35.55930 35.61137 35.57975 35.56623 35.59513 35.69509 35.60711 35.59739 35.57134 35.51372 35.38314 35.54730 35.59610 35.58558 35.59451 35.60079 35.56798 35.56646 35.64177 35.60220 35.58656 35.61652 35.60700 35.58873 35.68838 35.59617 35.56010 35.70274 35.59206 35.59735 35.58904
2 3 2 1 2 0 0 2 0 2 2 2 1 13 8 12 1 1
-0.4 0.1 -0.9 1 0.4 -0.3 1.5 -0.8 1 0.1 -0.1 -0.2 -0.5 -0.4 0.2 0.2 0.4 1.3 0.2 2 0.1 -0.1 0.1 1.3 2.4 0.6 0.7 0.5 0.2 0.4 1.9 0.3 0.5 0.3 0.7 0.8 0 -0.1 0.7 0.8 1.3 0.2 0.3 0 -0.1
93 94 95 96 97$ 98 99* 100 101 102 103* 104 105 106 107* 108 109* 110* 111 112* 113 114* 115* 116 117 118 119 120* 121*
2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010 2010
10 10 10 10 10 10 10 10 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11 11
17 21 22 25 26 28 29 30 1 1 2 2 3 4 9 10 11 15 16 16 21 21 22 23 25 25 26 29 30
19 12 9 20 15 1 2 0 4 22 0 20 15 21 10 3 22 12 21 23 20 20 1 17 23 23 23 22 11
1 8 44 53 8 52 41 9 22 36 39 50 58 39 49 20 9 48 29 1 6 9 52 39 30 44 23 2 0
6.7480 16.9600 17.8400 41.9920 25.5720 38.4560 1.4760 7.5040 53.5480 32.5280 15.3960 11.7200 23.5440 16.4400 19.0320 8.9480 5.9040 45.0200 18.8840 41.5400 54.5760 12.3160 4.6760 5.2880 10.9600 35.5240 10.8640 29.6160 56.2640
32.87039 32.88032 32.84991 32.86756 32.83591 32.87328 32.88797 32.68226 32.85932 32.87531 32.84160 32.85814 32.88000 32.86780 32.87254 32.86979 32.85555 32.99035 32.87476 32.83891 32.85421 32.93173 32.89551 33.02240 32.87898 32.78665 32.93660 32.88572 32.80329
35.59085 35.59794 35.61079 35.59171 35.56367 35.59628 35.59178 35.40953 35.60200 35.51687 35.56502 35.59750 35.59701 35.59426 35.60358 35.59495 35.56299 35.63714 35.64167 35.62989 35.61210 35.59671 35.58953 35.47377 35.40467 35.44798 35.50177 35.70031 35.47292
* - Events which were located using only one mini array. † - Events which were located using 3 or 4 mini arrays. $- Common events which were detected by both the SNS and ISN. - Depth not determined.
96
2
1.5 0.8 1.1 0.1 1.4 0 -0.9 1.1 0.5 0 -0.3 0.3 0.8 0.1 1.5 0.5 0.5 0.2 0.6 0 0.6 -0.4 -0.5 1.3 1.1 1.1 0.1 0 1
Appendix C Corner frequencies The tables below present the corner frequencies which were determined on the S-phase spectrum of the SNS catalog events. F0 is the corner frequency of the displacement spectrum. ‘O.T.’ represents origin time of the events in the format of yyyymmddHHMM. Mean value and standard deviation (STD) is calculated per event (which is indicated by O.T.).The events are sorted by magnitude.
O.T. 201003210225 201006130046 201006130046 201010290241 201006180021 201006180021 201004060033 201004060033 201004060033 201004030941 201006260010 201006260010 201011220152 201004182043 201006070141 201006070141 201006260047 201006260047 201006260047 201011212009 201005072040 201005072040 201005072040 201006152346 201006152346 201006152346 201006152346 201011020039
Station Almagor Gamla Almagor Almagor Korazim Almagor Ramot Korazim Almagor Ramot Ramot Almagor Almagor Ramot Gamla Almagor Ramot Korazim Almagor Almagor Gamla Ramot Almagor Almagor Ramot Gamla Korazim Almagor
Table C-1 ML F0 -1.2 19.8 -0.9 14.4 -0.9 14.6 -0.9 17.2 -0.8 15.7 -0.8 16 -0.7 13.2 -0.7 13.3 -0.7 16 -0.5 13.1 -0.5 14.3 -0.5 15.6 -0.5 15.5 -0.4 15.5 -0.4 13 -0.4 13.4 -0.4 12.4 -0.4 13.9 -0.4 14 -0.4 15.6 -0.3 13.1 -0.3 13.4 -0.3 13.4 -0.3 13.6 -0.3 14 -0.3 14.5 -0.3 14.6 -0.3 15.8 97
Mean 19.8 14.5
STD 0 0.13
17.2 15.8
0 0.15
14.2
1.28
13.1 14.9
0 0.65
15.5 15.5 13.2
0 0 0.2
13.4
0.75
15.6 13.3
0 0.15
14.2
0.42
15.8
0
201006252206 201006252206 201006252206 201004060020 201004060020 201004060020 201006240040 201006240040 201007161744 201010010259 201010162212 201010162212 201004061318 201004061318 201004272138 201004272138 201004272138 201004272138 201005010137 201005010137 201005010137 201005010137 201005130128 201005130128 201005130128 201010010221 201010010221 201010162104 201010280152 201010280152 201011012236 201011012236 201011162301 201011292202 201003061007 201003061007 201003170504 201003170504 201003270235 201003270235 201006051053 201006051053 201006230031
Ramot Almagor Korazim Korazim Almagor Ramot Korazim Almagor Almagor Almagor Ramot Almagor Almagor Korazim Almagor Korazim Ramot Gamla Almagor Korazim Gamla Ramot Gamla Almagor Ramot Ramot Almagor Ramot Ramot Almagor Ramot Almagor Almagor Almagor Gamla Ramot Almagor Ramot Gamla Ramot Ramot Almagor Ramot
-0.2 -0.2 -0.2 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 -0.1 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1
15 15 15.4 14 15.2 16.7 15.3 15.8 14.2 15.9 14.8 16.8 13.9 14.4 11.1 11.2 11.7 11.8 13 13.1 13.4 14.5 10.7 12.3 12.4 12.1 14.3 12.5 12.2 14.6 12.5 12.6 12.5 12 8.7 10.5 11.4 11.4 9.2 14 15 15 12.4 98
15.1
0.18
15.3
1.08
15.5
0.24
14.2 15.9 15.8
0 0 0.98
14.1
0.22
11.4
0.29
13.5
0.61
11.8
0.79
13.2
1.1
12.5 13.4
0 1.2
12.5
0.08
12.5 12.0 15.2
0 0 4.71
11.4
0.01
11.6
2.44
15.0
0.01
13.1
0.57
201006230031 201006230031 201007062309 201008132344 201008132344 201010252053 201010252053 201011042139 201011042139 201011262323 201003160235 201003160235 201003160235 201005131912 201005131912 201006012203 201006012203 201006280105 201006280105 201006280105 201006280125 201006280125 201006280125 201007031904 201009132237 201009132237 201010072236 201010072236 201011151248 201003242013 201003252246 201003252246 201009230009 201009230009 201009282255 201009282255 201010160651 201010160651 201011022050 201011022050 201004020043 201004020043 201006041548
Almagor Korazim Almagor Ramot Almagor Ramot Almagor Ramot Almagor Almagor Gamla Ramot Almagor Ramot Gamla Almagor Ramot Ramot Korazim Almagor Ramot Korazim Almagor Almagor Ramot Almagor Almagor Ramot Almagor Almagor Ramot Almagor Ramot Almagor Ramot Almagor Ramot Almagor Almagor Ramot Ramot Gamla Almagor
0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.4 0.4 0.4
13.3 13.8 10.2 14.4 14.5 9 10.5 11.8 12.7 13.2 9.9 11.9 12.7 10 11 13.3 13.9 13.2 14 15.7 13.3 14.3 15.6 15.8 12.5 14 13.9 14.1 12.2 15.6 11.3 12.6 12.7 15 9 9.9 14 14.7 12.3 12.8 10.3 11.1 9.3 99
10.2 14.4
0 0.04
9.8
0.76
12.2
0.45
13.2 11.5
0 1.17
10.5
0.52
13.6
0.3
14.3
1.04
14.4
0.91
15.8 13.3
0 0.74
14.0
0.09
12.2 15.6 12.0
0 0 0.66
13.9
1.15
9.4
0.47
14.4
0.36
12.6
0.27
10.7
0.4
9.9
0.61
201006041548 201006152207 201006152207 201006152207 201006282107 201006282107 201006282107 201009181051 201009181051 201004050731 201004050731 201004050731 201004050731 201004190129 201004190129 201009090115 201009230133 201009230133 201011010422 201011010422 201011100320 201011100320 201011112209 201003051944 201003051944 201003051944 201003271953 201003271953 201004100739 201004100739 201004272343 201004272343 201004272343 201004272343 201004300055 201004300055 201004300055 201004300055 201008292336 201011162129 201011162129 201011212006 201011212006
Ramot Ramot Korazim Almagor Almagor Ramot Korazim Ramot Almagor Gamla Ramot Almagor Korazim Gamla Ramot Ramot Ramot Almagor Ramot Almagor Ramot Almagor Ramot Gamla Ramot Almagor Gamla Ramot Ramot Korazim Gamla Ramot Korazim Almagor Almagor Gamla Korazim Ramot Ramot Ramot Almagor Almagor Ramot
0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6 0.6
10.5 11 13.9 14.2 13.3 13.3 13.3 11.6 14 7.9 10.3 10.5 10.6 12.2 13 11.4 10.1 10.9 11.3 12.1 11.9 12.5 11.9 10.1 10.5 13.2 14.1 14.2 12.2 13.3 10.7 10.7 11.6 12.1 10.2 10.2 10.3 11.1 10.8 15.4 15.8 12.6 12.7 100
13.0
1.44
13.3
0.04
12.8
1.19
9.8
1.13
12.6
0.4
11.4 10.5
0 0.42
11.7
0.4
12.2
0.3
11.9 11.3
0 1.36
14.1
0.04
12.7
0.51
11.3
0.6
10.5
0.39
10.8 15.6
0 0.19
12.7
0.04
201009012348 201009282307 201009282307 201010030116 201004012310 201004012310 201004012310 201004050501 201004050501 201004050501 201004050501 201009302140 201010031853 201010031853 201010211208 201010211208 201011031558 201011031558 201004262327 201004262327 201004262327 201004262327 201006020150 201006020150 201006020150 201006142128 201006142128 201006142128 201006142128 201006191047 201006191047 201011301100 201003070523 201003070523 201004192257 201004192257 201004192257 201006061937 201006061937 201006061937 201010220944 201010220944 201010300009
Ramot Ramot Almagor Almagor Ramot Gamla Almagor Gamla Ramot Korazim Almagor Ramot Ramot Almagor Almagor Ramot Ramot Almagor Ramot Gamla Korazim Almagor Ramot Almagor Gamla Korazim Ramot Gamla Almagor Korazim Almagor Almagor Ramot Almagor Gamla Ramot Almagor Almagor Ramot Gamla Ramot Almagor Ramot
0.7 0.7 0.7 0.7 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 0.8 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1 1.1
9.4 8.4 8.9 13.8 10.1 8.4 10.4 7.2 9.5 10.1 10.2 9.5 12.2 12.3 10 10.1 11.1 11.2 9.6 9.8 10.3 11.1 10.2 10.9 11 10.6 10.7 10.7 11.1 10.3 10.3 10.5 9.8 10.9 9.1 9.7 10.2 10.3 10.5 10.6 9.3 9.7 10.1 101
9.4 8.7
0 0.24
13.8 9.6
0 0.89
9.3
1.22
9.5 12.3
0 0.04
10.1
0.03
11.1
0.07
10.2
0.56
10.7
0.34
10.8
0.2
10.3
0.03
10.5 10.3
0 0.55
9.6
0.44
10.5
0.13
9.5
0.2
10.7
0.56
201010300009 201011252330 201011252330 201011252344 201011252344 201004282206 201004282206 201004282206 201004282206 201006291618 201008260214 201008260214 201010050241 201010050241 201011231739 201011231739 201010261508 201010261508 201003152102 201003152102 201006162246 201006162246 201006162246 201006162246 201010171901 201010171901 201011091049 201003061649 201003061649 201003061649 201005301140 201005301140 201009221254 201005181007 201005181007 201007062212 201006291618 201005021250 201005021250 201005021250 201003201845 201003201845 201003201845
Almagor Almagor Ramot Ramot Almagor Ramot Korazim Gamla Almagor Almagor Ramot Almagor Almagor Ramot Ramot Almagor Ramot Almagor Ramot Almagor Ramot Gamla Almagor Korazim Ramot Almagor Almagor Gamla Ramot Almagor Gamla Ramot Ramot Gamla Ramot Almagor Ramot Gamla Ramot Almagor Gamla Ramot Almagor
1.1 1.1 1.1 1.1 1.1 1.2 1.2 1.2 1.2 1.3 1.3 1.3 1.3 1.3 1.3 1.3 1.4 1.4 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.5 1.6 1.6 1.6 1.9 1.9 1.9 2 2 2 2.4 2.6 2.6 2.6 3.9 3.9 3.9
11.2 9.4 9.5 9.4 9.5 10 10.2 10.3 11.3 10 10.9 11.7 10.7 10.9 9.6 10 8.9 11.6 10 13.8 8.3 8.8 9 10.7 8.1 8.4 9.2 7.7 9.5 10.3 7.3 8.9 8.9 7 8.5 9 8.1 9.1 9.4 9.5 6.3 7.4 7.4 102
9.5
0.09
9.5
0.06
10.5
0.49
10.0 11.3
0 0.39
10.8
0.07
9.8
0.18
10.3
1.36
10.6
2.42
9.2
0.88
8.3
0.13
9.2 9.2
0 1.09
8.1
0.8
8.9 7.8
0 0.77
9.0 8.1 9.4
0 0 0.15
7.0
0.53
The mean value of frequency and standard deviation (STD) per magnitude are listed in table C-2 and are presented in Figure C-30.
ML -1.2 -0.9 -0.8 -0.7 -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 1 1.1 1.2 1.3 1.4 1.5 1.6 1.9 2 2.4 2.6 3.9
Table C-2 Mean(f0) 19.8 15.4 15.8 14.2 14.6 14.0 14.1 15.1 15.4 12.7 12.2 13.2 12.7 12.2 11.2 12.1 10.1 10.2 10.5 9.9 10.5 10.6 10.3 9.6 9.2 8.4 8.2 8.1 9.4 7.0
STD(f0) 0.00 1.27 0.15 1.28 1.01 1.11 0.83 0.18 0.92 1.10 2.00 1.66 1.98 1.63 1.24 1.72 2.12 1.30 0.44 0.60 0.11 0.67 1.36 1.69 1.09 0.74 0.86 0.00 0.15 0.53
103
20 18
Frequency (Hz)
16 14 12 10 8
6 -2
-1
0
1 Magnitude (Ml)
2
3
4
Figure C-1. Mean value of frequency per magnitude. Black circles are the mean value and vertical lines represent the STD, according to table C-2.
104
Appendix D Earthquake clustering and doublets 1. GII catalog Details of the events which are included in the clusters are shown in Table D-1. Cluster name corresponds to the legend in Figure 4-9.
O.T. 198805060445 198805060605 198805060645 198805072017 198805072057 198805190143 198806290827 198806302111 198807010410 198807021844 198807021932 199104150121 199104150503 199104160638 199104270713 199105011436 199105012047 199105020614 199105021020 199105021151 199105021531 199105032207 199105090341 199302210455 199302230015 199302230515 199303180753 199604160903 199604161240 199604162105 199604162124
SEC 31 47.4 30.2 35.5 36.1 21.7 57 35.7 0.7 10.7 18.2 28.3 49.8 1.3 22.3 22.4 12.1 57 51.5 44.2 25.1 19.2 44.5 42.4 36.3 26.1 53.9 43.7 51.7 49.7 1.8
Table D-1 Lat. (oN) Lon. (oE) 32.838 32.839 32.838 32.836 32.841 32.836 32.853 32.87 32.873 32.883 32.882 32.848 32.826 32.844 32.852 32.847 32.835 32.835 32.833 32.842 32.841 32.83 32.821 32.869 32.877 32.862 32.89 32.833 32.836 32.843 32.829
35.634 35.626 35.636 35.639 35.64 35.629 35.571 35.571 35.579 35.583 35.581 35.594 35.574 35.587 35.58 35.58 35.578 35.575 35.588 35.576 35.587 35.583 35.601 35.591 35.601 35.576 35.616 35.607 35.625 35.623 35.644 105
Magnitude 2.2 1.6 1.1 3.6 0.7 0 0 1.3 1.7 1.2 1.2 2.4 1.5 1.9 1.3 1.2 2.2 1.4 1.5 0 2 1 0.9 1.4 1.3 1.5 0 2.4 1.8 1.4 1.3
Cluster name May 1988
July 1988
1991
1993
April 1996
199604180207 199604191750 199604201900 199604210129 199604210150 199604211730 199606152355 199606160114 199606231731 199606241841 199606242151 199606242152 199606252119 199607040134 199607051834 200305290647 200305291003 200305310820 200306071012 200306200050 200306201651 200902040116 200902040117 200902040118 200902040154
42.1 53 16.7 30.6 48.4 12.1 12.8 15 33.1 8.2 50.8 52.4 27.7 17 33.5 46.3 12 15 34.5 15.8 6.1 29.8 36.2 16.6 25.1
32.827 32.844 32.84 32.827 32.825 32.818 32.848 32.86 32.828 32.854 32.853 32.843 32.856 32.844 32.841 32.881 32.837 32.882 32.873 32.876 32.869 32.827 32.822 32.825 32.821
35.662 35.608 35.622 35.649 35.627 35.627 35.572 35.577 35.608 35.578 35.587 35.596 35.582 35.596 35.601 35.628 35.566 35.6 35.595 35.633 35.66 35.618 35.614 35.608 35.598
0 1.3 2.2 1.9 0 1.7 2 1.4 0 0 2.2 1.5 0.7 1.6 0 2.2 1.7 1.9 1.3 1.5 1.7 0.7 0 0.5 1.2
June 1996
2003
2009
Details of the events which are considered as doublets are shown in Table D-2. O.T.
sec
Lat. (oN)
198706090926 198706100027 199107162242 199107172324 199208131108 199208140109 199212111040 199212111041 199302210455 199302220124 199505270513 199505271502
20.3 24.8 39.8 9.8 55.9 57.3 43.6 28.4 42.4 46.4 50.2 12.2
32.887 32.877 32.871 32.868 32.858 32.858 32.839 32.841 32.869 32.862 32.879 32.876
Table D-2 Lon. Magnitude o ( E) 35.616 35.623 35.601 35.592 35.578 35.572 35.605 35.614 35.591 35.576 35.579 35.575 106
2.7 0 0.8 1.2 1.4 0.8 1.4 1.6 1.4 1.3 0.6 0.4
Maximum correlation factor 80% 67% 77% 64% 70% 60%
Remarks
199604160903 199604161240 200305290647 200305290746 200806301522 200807010103 200907110226 200907110234 200902040116 200902040118 200902040154
43.7 51.7 46.3 56.6 19.6 56.4 38.7 3.9 29.8 16.6 25.1
32.833 32.836 32.881 32.878 32.852 32.846 32.829 32.821 32.827 32.825 32.821
35.607 35.625 35.628 35.621 35.583 35.574 35.633 35.633 35.618 35.608 35.598
2.4 1.8 2.2 1.7 0 0 0 1.3 0.7 0.5 1.2
76% 71% 74% 87% 88%
2. SNS catalog Details of the events which are included in the cluster are shown in Table D-3. Event number 90 91 92 93 94 96 98 99 101 104 105 106 107 108
Table D-3 Lat. (oN) Lon. (oE) 32.85320 32.86365 32.86468 32.87039 32.88032 32.86756 32.87328 32.88797 32.85932 32.85814 32.88000 32.86780 32.87254 32.86979
Magnitude
35.59206 35.59735 35.58904 35.59085 35.59794 35.59171 35.59628 35.59178 35.60200 35.59750 35.59701 35.59426 35.60358 35.59495
0.3 0 -0.1 1.5 0.8 0.1 0 -0.9 0.5 0.3 0.8 0.1 1.5 0.5
107
Part of a cluster
Triplet, Part of a cluster
Details of the events which are considered as doublets are shown in Table D-4.
Event number
22 23 24 25 30 31
Lat. (oN) Lon. (oE)
32.87750 32.88388 32.83465 32.85811 33.05055
35.60438 35.59774 35.57061 35.59663 35.59965
33.02022 35.61899 44 45 59 61 81 82 93 96 98 106 107 108
32.87673 32.87314 32.85692 32.85527 32.86501 32.86287 32.87039 32.86756 32.87328 32.86780 32.87254 32.86979
Table D-4 Magnitude Julian day
35.57183 35.59006 35.58692 35.58677 35.60220 35.58656 35.59085 35.59171 35.59628 35.59426 35.60358 35.59495
0.8 0.5 -0.1 -0.7 1.1 1
95 95 96 96 109 116
1 0.4 -0.2 -0.4 0.3 0.7 1.5 0.1 0 0.1 1.5 0.5
108
153 155 176 177 271 271 290 298 301 308 313 314
Maximum Remarks correlation factor 1-35Hz 1-10Hz 80%
88%
65%
71%
84%
93%
58%
No change
66%
70%
95%
98
88%
No change
80%
86%
3.5 km apart. 4 km apart. On the transform
Multiplet, part of a cluster
References
Amelung, F. and Geoffrey, K., 1997. Earthquake scaling laws for creeping and noncreeping faults. Geophysical Research Letters, 24(5): 507-510. Arieh, E. and Rotstein, Y., 1985. A note on the seismicity of Israel (1900-1982) Bull. Seismol. Soc. Am., 75(3): 881-887. Ayele, A. and Kulhánek, O., 1997. Spatial and temporal variations of seismicity in the Horn of Africa from 1960 to 1993. Geophysical Journal International, 130(3): 805-810. Bartov, Y., Sneh, A., Fleischer, L., Arad, V. and Rosensaft, M., 2002. Map of Faults in Israel. Report GSI/29/2002, Geological Survey of Israel, Jerusalem. Bartov, Y., Sneh, A. and Rosensaft, M., 2009. Map of Active and Potetially Active Faults in Israel, An Update to GSI Report GSI/29/2002. Geological Institute of Israel, Jerusalem. Begin, Z.B., 2005. Destructive earthquakes in the Jordan Valley and the Dead Sea—their recurrence intervals and the probability of their occurrence. GSI Report GSI/12/05 (in Hebrew, English summary). The Geological Survey of Israel, Jerusalem. Begin, Z.B. and Steinitz, G., 2005. Temporal and spatial variations of microearthquake activity along the Dead Sea Fault, 1984-2004 Isr. J. Earth Sc., 54(1): 1-14. Belitzky, S., 1987. The tectonics of the Korazim Plateau. M.Sc. Thesis, Hebrew University, Jerusalem. Belitzky, S. and Ben-Avraham, Z., 2004. The morphotectonic pattern of Lake Kinneret. Isr. J. Earth Sc., 53(3): 121-130. Ben-Avraham, Z., Hanel, R. and Villinger, H., 1978. Heat flow through the Dead Sea rift. Marine Geology, 28(3-4): 253-269. Ben-Avraham, Z., Shoham, Y., Klein, E., Michelson, H. and Serruya, C., 1980. Magnetic survey of Lake Kinneret-central Jordan Valley, Israel. Marine Geophysical Research, 4(3): 257-276. Ben-Avraham, Z., Ginzburg, A. and Yuval, Z., 1981. Seismic reflection and refraction investigations of Lake Kinneret - central Jordan Valley, Israel. Tectonophysics, 80(1-4): 165-181. Ben-Avraham, Z., Shaliv, G. and Nur, A., 1986. Acoustic reflectivity and shallow sedimentary structure in the Sea of Galilee, Jordan Valley. Marine Geology, 70(34): 175-189. Ben-Avraham, Z., Amit, G., Golan, A. and Begin, Z.B., 1990. The bathymetry of Lake Kinneret and its Structural Significance. Isr. J. Earth Sc., 39(2-4): 77-83. Ben-Avraham, Z., ten Brink, U. and Reznikov, M., 1996. Gravity field over the Sea of Galilee: Evidence for composite basin along a transform fault. J. Geophys. Res., 101: 533-544. Ben-Avraham, Z., 2004. Foreword by the guest editor. Isr. J. Earth Sc., 53(3-4): i-ii. Ben-Avraham, Z., Garfunkel, Z. and Lazar, M., 2008. Geology and evolution of the Southern Dead Sea Fault with emphasis on subsurface structure. Annu. Rev. Earth Planet. Sci., 36: 357-387. 109
Ben-Menahem, A., 1981. Variation of slip and creep along the levant rift over the past 4500 years. Tectonophysics, 80(1-4): 183-197. Ben-Menahem, A., 1991. Four thousand years of seismicity along the Dead Sea Rift. J. Geophys. Res., 96(B12): 20195-20216. Bender, B., 1983. Maximum likelihood estimation of b values for magnitude grouped data. Bull. Seismol. Soc. Am., 73(3): 831-851. Bouchon, M., Karabulut, H., Aktar, M., Zalaybey, S., Schmittbuhl, J. and Bouin, M.P., 2011. Extended Nucleation of the 1999 Mw 7.6 Izmit Earthquake. Science, 331(6019): 877-880. Carena, S., Suppe, J. and Kao, H., 2002. Active detachment of Taiwan illuminated by small earthquakes and its control of first-order topography. Geology, 30(10): 935938. Ellenblum, R., Marco, S., Agnon, A., Rockwell, T. and Boas, A., 1998. Crusader castle torn apart by earthquake at dawn, 20 May 1202. Geology, 26(4): 303-306. Eppelbaum, L., Ben-Avraham, Z., Katz, Y. and Marcob, S., 2004. Sea of Galilee: Comprehensive analysis of magnetic anomalies. Isr. J. Earth Sc., 53(3): 151-171. Eyal, M., Eyal, Y., Bartov, Y. and Steinitz, G., 1981. The tectonic development of the western margin of the Gulf of Elat (Aqaba) rift. Tectonophysics, 80(1-4): 39-66. Garfunkel, Z., 2001. The nature and history of motion along the Dead Sea Transform (Rift). In: A. Horowitz (Editor), The Jordan Rift Valley, pp. 627-650. Ginzburg, A. and Ben-Avraham, Z., 1986. Structure of the sea of Galilee graben, Israel, from magnetic measurements. Tectonophysics, 126(2-4): 153-164. Goldman, M., Hurwitz, S., Gvirtzman, H. and Rotstein, Y., 1996. Application of the Marine Time Domain Electromagnetic Method in Lakes: the Sea of Galilee, Israel. Environ. Eng. Geophys., 1: 125-138. Goldman, M., Gvirtzman, H. and Hurwitz, S., 2004. Mapping saline groundwater beneath the Sea of Galilee and its vicinity using time domain electromagnetic (TDEM) geophysical technique. Isr. J. Earth Sc., 53(3): 187-197. Gutenberg, B. and Richter, C., 1944. Frequency of earthquakes in California. Bull. Seismol. Soc. Am. Haddock, E., 1999. Magnetic and seismic survey of hydrothermal saline in Lake Kinneret - A case study. M.Sc. Thesis, University of Tel-Aviv, Tel-Aviv. Hage, M. and Joswig, M., 2009a. Microseismic feasibility study: detection of small magnitude events (Ml
