SHEAR WAVE ANISOTROPY MEASUREMENTS ABOVE SMALL EARTHQUAKES IN TRICHONIS LAKE, GREECE

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Published: Jul 27, 2016
DOI: https://doi.org/10.12681/bgsg.11830
Keywords:
shear wave splitting seismic anisotropy stress field wave propagation
V. Stavropoulou
University of Patras, Department of Geology, Seismological Laboratory
D. Giannopoulos
University of Patras, Department of Geology, Seismological Laboratory
E. Sokos
University of Patras, Department of Geology, Seismological Laboratory
K.I. Konstantinou
Department of Earth Sciences, National Central University
G.A. Tselentis
Institute of Geodynamics, National Observatory of Athens
Abstract

On April 2007, an earthquake swarm occurred in the vicinity of Trichonis Lake, western Greece. The seismic activity started on April 10th, 2007 after the occurrence of three moderate size earthquakes MW 5.0-5.2. We performed shear wave splitting measurements on seismic events recorded during the first week of the seismic activity by a portable network of 8 stations that was installed in the area by the University of Patras Seismological Laboratory. We were able to take measurements from 5 stations as the seismicity was concentrated mostly at the eastern part of the lake. Two splitting parameters were measured through the data processing, the time-delays between the fast and slow shear wave components and the polarization directions of the fast components. In general, the data analysis revealed the presence of shear wave anisotropy in the study area. The average value of normalized time-delays was calculated at 6.9 ±1.1 ms/km while the fast polarization directions had an average of 130o ±14o. The mean fast polarization directions were consistent with what is expected concerning the local stress field, as it was sub-parallel to the strike of the major faults at the eastern part of the lake and almost perpendicular to the direction of extension. Therefore, the findings can be interpreted by an anisotropic volume of stress-aligned micro-cracks within the upper crust according to the extensive dilatancy anisotropy model.

Article Details
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  • Geophysics and Seismology
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References
Bernard, P.H., Lyon-Caen, P., Briole, A., Deschamps, F., Boudin, K., Makropoulos, P.,
Papadimitriou, F., Lemeille, G., Patau, H., Billiris, D., Paradissis, K., Papazissi, H., Castarède,
O., Charade, A., Nercessian, A., Avallone, F., Pacchiani, J., Zahradnik, S. and Sacks Linde,
A., 2006. Seismicity, deformation and seismic hazard in thewestern rift of Corinth: new
insights from the Corinth Rift Laboratory (CRL), Tectonophysics, 426, 7-30.
Crampin, S. and Chastin, S., 2003. A review of shear wave splitting in the crack-critical crust,
Geophys. J. Int., 155, 221-240.
Crampin, S. and Peacock, S., 2005. A review of shear-wave splitting in the compliant crack-critical
anisotropic Earth Wave Motion, 41, 59-77.
Crampin, S., 1978. Seismic wave propagation through a cracked solid: polarization as a possible
dilatancy diagnostic, Geophys. J. R. Astron. Soc., 53, 467-496.
Crampin, S., 1993. Arguments for EDA, Can. J. Exp. Geophys., 29, 3-17.
Crampin, S., Evans, J.R. and Atkinson, B.K., 1984. Earthquake prediction: a new physical basis,
Geophys. J. R. Astron. Soc., 76, 147-156.
Crampin, S. and Gao, Y., 2006. A review of techniques for measuring shear-wave splitting above
small earthquakes, Phys. Earth. Planet. Inter., 159, 1-14.
Crampin, S., Volti, T., Chastin, S., Gudmundsson, A. and Stefánsson, R., 2002. Indication of high
pore-fluid pressures in a seismically-active fault zone, Geophys. J. Int., 151, F1-F5.
Doutsos, T., Kontopoulos, N. and Frydas, D., 1987. Neotectonic evolution of northwestern
continental Greece, Geol. Rundsch, 76, 433-450.
Doutsos, T., Piper, G., Boronkay, K. and Koukouvelas, I., 1993. Kinematics of the Central
Hellenides, Tectonics, 12, 936-953.
Evangelidis, C.P., Konstantinou, K.I., Melis, N.S., Charalambakis, M. and Stavrakakis, G.N., 2008.
Waveform relocation and focal mechanism analysis of an earthquake swarm in Trichonis
Lake, Western Greece, Bull. Seismol. Soc. Am., 98(2), 804-811.
Kassaras, I., Kapetanidis, V., Karakonstantis, A., Kaviris, G., Papadimitriou, P., Voulgaris, N.,
Makropoulos, K., Popandopoulos, G. and Moshou, A., 2014. The April-June 2007 Trichonis
Lake earthquake swarm (W. Greece): New implications toward the causative fault zone, J.
Geodyn., 73, 60-80.
Kiratzi, A., Sokos, E., Ganas, A., Tselentis, A., Benetatos, C., Roumelioti, Z., Serpetsidaki, A.,
Andriopoulos, G., Galanis, O. and Petrou, P., 2008. The April 2007 earthquake swarm near
Lake Trichonis and implications for active tectonics in western Greece, Tectonophysics, 452,
-65.
Klein, F.W., 2002. User's guide to HYPOINVERSE-2000, a FORTRAN program to solve
earthquake locations and magnitudes, U.S. Geological Open File Report 02-606, Version 1.0.
Kuo, B.Y., Chen, C.C. and Shin, T.C., 1994. Split S waveforms observed in northern Taiwan:
implications for crustal anisotropy, Geophys. Res. Lett., 21, 1491-1494.
Lee, W.H.K., Bennett, R.E. and Meagher, K.L., 1972. A method of estimating magnitude of local
earthquakes from signal duration, Open File Report, U. S. Geological Survey, 28 pp.
Lekkas, E. and Papanikolaou, D., 1997. Neotectonic Map of Greece, Aitolia-Akarnania sheet (scale
:100.000), Applied Scientific Program, University of Athens, Dept of Dynamic, Tectonic
and Applied Geology, Technical report, 148 pp.
Rigo, A., Lyon-Caen, H., Armijo, R., Deschamps, A., Hatzfeld, D., Makropoulos, K., Papadimitriou,
P. and Kassaras, I., 1996. A microseismicity study in the western part of the Gulf of Corinth
(Greece): implications for large-scale normal faulting mechanisms, Geophys. J. Int., 126,
-688.
Sokos, E., Pikoulis, V.E., Psarakis, E.Z. and Lois, A., 2010. The April 2007 swarm in Trichonis
Lake using data from a microseismic network, Proceedings of the 12th International
Congress, Bulletin of the Geological Society of Greece, Patras, May, 2010, XLIII/4, 2183-
Wessel, P. and Smith, W.H.F., 1998. New improved version of the Generic Mapping Tools Released,
EOS, Trans. Am. Geophys. Un., 79, 529.
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