Susan Avery, Fran Bagenal, Jack Gosling,. Jeff Hughes, Mike Kelley, Fred Rees, Pat. Reiff, and Steve Suess.-Jack Gosling, Los. Alamos National. Laboratory.
Eos, Vol. 76 No. 28, July 11, 1995 pulse was computed taking into account the electron density and energy spectrum, the concentrations of the major atmospheric con stituents and the intensities of various optical emission that occur in the upper at mosphere following this discharge. This work has been reported in a series of papers in Geophysical Research Letters. Taranenko's theoretical results provide a baseline that ex perimenters are using to interpret their data and to search for unexpected new results. Taranenko is presently a postdoctoral fel low in the Space and Atmospheric Group at Los Alamos National Laboratory, and is associ ated as well with the Department of Electrical Engineering at Stanford University as a Con sulting Assistant Professor. His present
G E O D E S Y
Editor: Duncan Agnew, University of Califor nia, San Diego, IGPP, A-025, La Jolla, CA 92093; tel. 619-534-2590
Gravity and Isostatic Anomaly Maps of Greece Produced
research interests are concentrated on the ory of the electrodynamic coupling of energy released in tropospheric lightning discharges to the mesosphere and on newly observed upward discharges that can be related to tropospheric lightning. He is studying two different mechanisms for upward electric lightning that can possibly explain high-alti tude optical flashes. One of these is based on the runaway air electron breakdown. He is doing this work in conjunction with Umran Inan, Tim Bell, Juan Rodriguez, Robert Roussel-Dupre, and Alexander Gurevich. He is also working on computer modeling of elec tron density perturbations in the ionosphere during rocket launches and computer model ing of stochastic differential equations.
3
2.67 Mg/m . W e estimate the errors of the anomalies in the continental part of Greece to be ±0.9 mGal; this is expected to be smaller over fairly flat regions. For stations whose height has been determined by level ing, the error is only ±0.3 mGal. For the marine areas, the errors are about ±5 mGal [Morelli, 1990]. At Athens University w e also compiled a data bank of the topography, covering the same area and organized in the same man ner as the gravity data bank, but with points
Nominations for the next F. L. Scarf Award are due at AGU by September 1 for the ses that contribute directly to solar-terrestrial and solar-planetary science completed during the 12 months ending June 30. Nominations can be made by any one familiar with the thesis and should be accompanied by up to three support letters from other scientists familiar with the work. A copy of the thesis should be included with the nomination package. Members of the SPA Awards Commit tee for 1994-1996 are Brian Anderson, Susan Avery, Fran Bagenal, Jack Gosling, Jeff Hughes, Mike Kelley, Fred Rees, Pat Reiff, and Steve Suess.-Jack Gosling, Los Alamos National Laboratory.
at a spacing of 2 km. On land, mean eleva tions were estimated directly from 1:50,000 topographic maps, with an estimated accu racy of ±10 m. Offshore, depths were digitized from 1:250,000 and 1:500,000 hydrographic maps and the maps of Morelli et al [1975a, b ] . All of the values were trans formed to UTM zone 34 coordinates and interpolated onto a 2-km grid to give an array of 350 by 450 points, which represent a lowpass filtered version of the topography in and around Greece.
Gravity Anomaly Map
PAGE 274 A gravity anomaly map of Greece was first compiled in the early 1970s [Makrisand Stavrou, 1984] from all available gravity data collected by different Hellenic institutions. However, to compose this map the data had to be smoothed to the point that many of the smaller-wavelength gravity anomalies were lost. New work begun in 1987 has resulted in the publication of an updated map [Lagios et al, 1994] and an isostatic anomaly map de rived from it. The gravity data cover the area between east longitudes 19° and 27° and north lati tudes 32° and 42°, organized in files of 100-km squares and grouped in 10-km squares using UTM zone 34 coordinates. Most of the data on land c o m e from the grav ity observations of Makris and Stavrou [1984] with additional data from the Institute of Ge ology and Mining Exploration, the Public Oil Corporation of Greece, and Athens Univer sity. These data were checked using techniques similar to those used in compil ing the gravity anomaly map of the United States, but the horizontal gradient was used as a check rather than the gravity difference. Marine data were digitized from the maps of Morellietal. [1975a, 1975bJ. All gravity anom aly values are referred to the IGSN-71 system, reduced with the standard Bouger density of
Fig. 1. Gravity anomaly map (in mGal). Frame is bounded by UTM Zone 34, eastings 300-1000 km, northings 4200-5100 km. Original color image appears at the back of this volume.
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Eos, Vol. 76, No. 28, July 11, 1995 Figure 2. Since the same color scale is used in both maps, it is clear that the isostatic model worked fairly well, except for the edge effects produced at the southwestern part of the re gion. The isostatic anomaly shows two main features: a dipole anomaly in the southern Aegean, and a strong negative anomaly along the western part of the mainland. W e anticipate that these maps will be useful in understanding the tectonics and geological history of this area.—E. Lagios andS. Chailas, Department of Geophysics and Geothermy, University of Athens, Panepstimioupolis, Ilissia, Athens, Greece; and R. G. Hipkin, Department of Geology and Geophys ics, University of Edinburgh, United Kingdom References
Figure 1 shows a colored version of the fi nal gravity anomaly map, which has been published in three sheets with scale 1:500,000. These are contoured at 5-mGal spacing, based on a 4-km grid of values, which is representative of the station spacing on land, although the stations at sea are spaced more widely. Figure 2 shows a map of the isostatic anomaly, produced using the
gravity and topographic data. W e first com puted the response function using a cross-spectrum method and found that an Airy compensation mechanism satisfied the resulting estimate. The part of the gravity anomaly corresponding to the isostatic re sponse function was then calculated by inverse transformation and subtracted from the Bouger anomaly to produce the map in
B O O K REVIEW Craters, Cosmos, and Chronicles: A New Theory of Earth PAGES 275, 279 Herbert R. Shaw, Stanford University Press, $79.50, xlv + 688 pp., 1994. The notion that the Earth might be influ enced significantly by external forces has always been a rather disquieting concept for geoscientists who are trained to think in terms of uniformitarianism. The mass extinc tion debates of the last 15 years and the strong disagreement among advocates of im pact and terrestrial extinction mechanisms are classic examples of this issue. A new book by Herbert R. Shaw makes the case that the evolution of the Earth and other planets has been significantly affected by extraterres trial processes throughout their histories, and these processes are part of a universal system
of coupled nonlinear oscillators. Shaw ar gues that clustered bombardment by extraterrestrial objects—along swaths that are constant over specific time periods—has been a major force for change acting in con cert with planetary geodynamic forces to shape the face of our world and the other planets in the solar system. The central thesis of Shaw's book is that uniformitarianism extends to the entire uni verse, which operates as a series of coupled nonlinear systems that influence each other over time. Shaw crosses the boundaries be tween geology, planetary science, astrophysics, and nonlinear dynamics to merge the cumulative knowledge of these di verse fields into a unified theory for how the Earth and solar system evolved. A key tenet of this theory is that the pat tern of impacts on Earth is not random as is currently accepted by most planetary scien tists. Shaw asserts that impacts display specific patterns in space and time that can
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Lagios, E., Chailas, S., Hipkin, R. G., and J. Drakopoulos, Gravity and Topographic Data Banks of Greece, University of Ath ens, Department of Geophysics and Geothermy, Publ. 4/94, 50 pp., 1994. Makris, J., and A . Stavrou, Compilation of Gravity Maps of Greece, Internal Report, Hamburg University Institute of Geophysics, 12 pp., 1984. Morelli, C. T h e regional meaning of the Bouger gravity anomalies in the Mediterra nean, J. Geodynamics, 12, 123, 1990. Morelli, C , Gantar, G., and M. Pisani, Bathymetry, gravity and magnetism in the strait of Sicily and the Ionian Sea, Boll. Geofis. Teor. Appl, 17, 39, 1975a. Morelli, C , Pisani, M., and G. Gantar, Geo physical studies in the A e g e a n Sea and in the eastern Mediterranean, Boll. Geofis. Teor. Appl, 18, 127, 1975b.
be explained in terms of a fixed Celestial Ref erence Frame (CRF) and that these impact events are a normal and important part of the evolution of our planet and the solar system. He further argues that impacts are coupled nonlinearly to plate tectonics, magmatism, geomagnetic field behavior, and biological evolution, and these endogenous processes also produce effects in the Earth system that feed back into the celestial system. Shaw also asserts that this ordering in nature is a predictable consequence of the multidimen sional and nonlinear character of natural systems, which should generate organized complexity as they evolve. Shaw argues that part of the reason w e fail to recognize the nonlinear behavior of natu ral systems is that w e tend to simplify natural behavior in linear terms, both in space and time. W e also handicap ourselves by viewing nature from a geocentric reference frame that treats extraterrestrial phenomena as ex ternal to our system, when in reality, all natural phenomena are coupled to each other in a self-referential loop of feedback processes at the extraterrestrial scale that is keyed to the CRF. Shaw argues persuasively that w e must break free of the self-imposed limitations of our traditional scientific and
Vol. 76, No. 28, July 11, 1995
Gravity Anomaly
ABOVE 270 255 - 270 2.0«>- 255 225- 2040 2Xl- 225 195 - 2Xl 180- 195 165- 180 150- 165 135 - 150 120- 135 105 - 120 90- 105 7590 6075 60 04530- 045 15- 30 015 -150 -30- -15 -45- -30 -60- -45 -75- -60 -90- -75 -105 - -90 -120 - -105 aaow -120
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