| More

ANISOTROPY STUDY OF THE FEBRUARY 4TH 2008 SWARM IN NW PELOPONNESUS (GREECE)

Views: 271 Downloads: 217
G. Kaviris, P. Papadimitriou, K. Makropoulos
G. Kaviris, P. Papadimitriou, K. Makropoulos

Abstract


The Gulf of Corinth, located in central Greece, is characterized by normal faulting and by high seismicity since the antiquity. On 4 February 2008 a seismic swarm burst in NW Peloponnesus characterized by the occurrence of two moderate-size earthquakes of moment magnitudes 4.7 and 4.5, respectively. Analysis of the data revealed the existence of shear-wave splitting. The events that were chosen for the anisotropy study fit the selection criteria, having clear and impulsive S wave arrival phases on the horizontal components. In addition, the amplitude of the S wave phase on the vertical component was smaller than on the horizontal ones. The representations that were used to determine the polarization direction of the fast split shear wave, the time delay between the two split shear waves and the polarization direction of the source were the polarigram and the hodogram. The uniform fast shear wave polarizations, irrespective of the azimuth of each event, are consistent with the general NNE-SSW direction of extension in the Gulf and, therefore, in agreement with the extensive dilatancy anisotropy (EDA) model. Finally, a decrease of the time delay values was observed after the occurrence of the first moderate earthquake, implying changes of the medium’s properties.

Keywords


Anisotropy; shear wave splitting; temporal variation; stress field; EDA model; Gulf of Corinth;

Full Text:

PDF

References


Ambraseys, N. N. and Jackson, J. A., 1990. Seismicity and associated strain in central Greece between

and 1988. Geophys. Jour. Inter., 101, 663-708.

Bernard, P. and Zollo, A., 1989. Inversion of near-source S polarization for parameters of doublecouple

point like sources. Bull. Seism. Soc. Am., 79, 1779-1809.

Booth, D. C. and Crampin, S., 1985. Shear wave polarizations on a curved wavefront at an isotropic

free surface. Geophys. J. R. Astron. Soc., 83, 31-45.

Booth, D. C., Scjleper, S., Crampin, S., Ochmann, N. and Wohlenberg, J., 1989. Shear-wave splitting

observations on Milos, Greece. Geothermics, 18, 597-610.

XLIII, No 4 – 2090

Fig. 7: Shear-wave splitting time-delays at LAKA station for the period: (A) 25 January to 2 April 2008

and (B) 3 to 6 February 2008. The arrows indicate the time of the first major event.

Bouin, M.-P., 1994. Analyse de la polarisation des ondes S en source proche: Rupture et Structure.

Phd Thesis, Universite Paris 7, Paris.

Bouin, M.P., Tellez, J. and Bernard, P., 1996. Seismic anisotropy around the Gulf of Corinth, Greece,

deduced from three-component seismograms of local earthquakes and its relationship with crustal

strain. J. Geophys. Res., 101, 5797–5811.

Coutant, O., 1996. Observation of shallow anisotropy on local earthquake records at the Garner Valley,

Southern California, downhole array. Bull. Seism. Soc. Am., 86, 477-488.

Crampin, S., 2003. The New Geophysics: shear-wave splitting provides a window into the crack-critical

rock mass. The Leading Edge, 22, 536-549.

Crampin, S. and Lovell, H. L., 1991. A decade of shear-wave splitting in the Earth’s crust: What does

it mean? What can we make of it? and What should we do next? Geophys. J. Int., 107, 387-407.

Crampin, S. and Chastin, S., 2001. Shear-wave splitting in a critical crust: II - compliant, calculable,

controllable fluid-rock interactions, in Anisotropy 2000: Fractures, converted waves, and

case studies, Proc. 9th Int. Workshop on Seismic Anisotropy, Camp Allen, 2000, eds. Ikelle, L.

T. & Gangi, T., SEG Open File Publication No. 6, 21-48.

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 Gao, Y., 2005. Comment on ‘‘Systematic analysis of shear-wave splitting in the aftershock

zone of the 1999 Chi–Chi, Taiwan, earthquake: shallow crustal anisotropy and lack of

precursory changes, by Liu, Teng, Ben-Zion, Bull. Seismol. Soc. Am., 95, 354–360.

Crampin, S. and Peacock, S., 2008. A review of the current understanding of shear-wave splitting

in the crust and common fallacies in interpretation. Wave Motion, 45, 675-722.

Crampin, S., Volti, T. and Stefansson, R., 1999. A successfully stress-forecast earthquake, Geophys.

J. Int., 138, F1–F5.

Gamar, F. and Bernard, P., 1997. Shear wave anisotropy in the Erzincan basin and its relationship

with crustal strain. J. Geophys. Res., 102, 20373-20393.

Ganas, A, Serpelloni, E., Drakatos, G., Kolligri, M., Adamis, I., Tsimi, Ch. and Batsi, E., 2009. The

Mw 6.4 SW-Achaia (western Greece) earthquake of 8 June 2008: Seismological, field, GPS observations

and stress modeling. J. Earthq. Eng., in press, 2009.

Gao, Y., Wang, P.-D., Zheng, S.-H., Wang, M., Chen, Y.-T. and Zhou, H.-L., 1998. Temporal changes

in shear-wave splitting at an isolated swarm of small earthquakes in 1992 near Dongfang, Hainan

Island, southern China. Geophys. J. Int., 135, 102–112.

Gao, Y. and Crampin, S., 2008. Shear-wave splitting and earthquake forecasting, Terra Nova, 20,

-448.

Hao, P., Gao, Y. and Crampin, S., 2008. An Expert System for measuring shear-wave splitting above

small earthquakes. Comp. Geosci., 34, 226-234.

Kaneshima, S., 1990. Origin of crustal anisotropy: Shear wave splitting studies in Japan. J. Geophys.

Res., 95, 11121-11133.

Kapetanidis, V., Agalos, A., Moshou, A., Kaviris, G., Karakonstantis, A., Papadimitriou, P. and

Makropoulos, K., 2008. Preliminary Results from the Study of a Seismic Swarm Occurred in

February 2008 in NW Peloponnesus, Greece. Book of Abstracts (Poster), 31st Gen. Ass. ESC,

p. 110, Crete, Greece.

Karnassopoulou, A., 1996. Joint investigation of source parameters and seismic anisotropy using

microearthquakes in Greece, Arkansas and Northeast Brazil. PhD thesis, University of Edinburgh.

XLIII, No 4 – 2091

Kaviris, G., Papadimitriou, P. and Makropoulos, K., 2008. An Overview of Anisotropy Studies in

Central Greece using recordings around the Gulf of Corinth (Greece) and aftershocks of the

Athens Earthquake. Short Papers, 31st ESC General Assembly, Hersonissos, Crete, Greece,

-223.

Liu, Y., Crampin, S. and Main, I., 1997. Shear-wave anisotropy: spatial and temporal variations in

time delays at Parkfield, Central California. Geophys. J. Int., 130, 771–785.

Makropoulos, K. C. and Burton, P. W., 1981. A catalogue of seismicity in Greece and adjacent areas.

Geophys. J. R. Astron. Soc., 65, 741-762.

Papadimitriou, P., Kaviris G. and Makropoulos, K., 1999. Evidence of shear-wave splitting in the

Eastern Corinthian Gulf (Greece). PEPI, 114, 3-13.

Papadimitriou, P., Kaviris G., Voulgaris, N. and Kassaras, I., 2000. Shear-wave splitting analysis

using aftershocks of the 7th September 1999 Earthquake: Preliminary Results. Ann. Geol. Pays

Hellen., 1e Serie, T. XXXVII, FASC. B, p. 89-103.


Refbacks

  • There are currently no refbacks.


Copyright (c) 2017 G. Kaviris, P. Papadimitriou, K. Makropoulos

Creative Commons License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.