The Ms=6.2, June 15, 1995 Aigion earthquake (Greece): Evidence for low angle normal faulting in the Corinth rift

Bernard, P; Briole, P; Meyer, B; Lyon-Caen, H; Gomez, J-M; Tiberi, C; Berge, C; Cattin, R; Hatzfeld, D; Lachet, C; Lebrun, B; Deschamps, A; Courboulex, F; Larroque, C; Rigo, A; Massonnet, D; Papadimitriou, P; Kassaras, J; Diagourtas, D; Makropoulos, K; Veis, G; Papazisi, E; Mitsakaki, C; Karakostas, V; Papadimitriou, E; Papanastassiou, D; Chouliaras, M; Stavrakakis, G

dc.contributor.author	Bernard, P	en
dc.contributor.author	Briole, P	en
dc.contributor.author	Meyer, B	en
dc.contributor.author	Lyon-Caen, H	en
dc.contributor.author	Gomez, J-M	en
dc.contributor.author	Tiberi, C	en
dc.contributor.author	Berge, C	en
dc.contributor.author	Cattin, R	en
dc.contributor.author	Hatzfeld, D	en
dc.contributor.author	Lachet, C	en
dc.contributor.author	Lebrun, B	en
dc.contributor.author	Deschamps, A	en
dc.contributor.author	Courboulex, F	en
dc.contributor.author	Larroque, C	en
dc.contributor.author	Rigo, A	en
dc.contributor.author	Massonnet, D	en
dc.contributor.author	Papadimitriou, P	en
dc.contributor.author	Kassaras, J	en
dc.contributor.author	Diagourtas, D	en
dc.contributor.author	Makropoulos, K	en
dc.contributor.author	Veis, G	en
dc.contributor.author	Papazisi, E	en
dc.contributor.author	Mitsakaki, C	en
dc.contributor.author	Karakostas, V	en
dc.contributor.author	Papadimitriou, E	en
dc.contributor.author	Papanastassiou, D	en
dc.contributor.author	Chouliaras, M	en
dc.contributor.author	Stavrakakis, G	en
dc.date.accessioned	2014-03-01T01:13:27Z
dc.date.available	2014-03-01T01:13:27Z
dc.date.issued	1997	en
dc.identifier.issn	1383-4649	en
dc.identifier.uri	https://dspace.lib.ntua.gr/xmlui/handle/123456789/12482
dc.subject	Gulf of Corinth	en
dc.subject	Normal faulting	en
dc.subject.classification	Geochemistry & Geophysics	en
dc.subject.other	GULF-OF-CORINTH	en
dc.subject.other	SEISMICITY	en
dc.subject.other	MECHANISMS	en
dc.subject.other	INVERSION	en
dc.subject.other	REACTIVATION	en
dc.subject.other	DEFORMATION	en
dc.subject.other	PROVINCE	en
dc.subject.other	SEQUENCE	en
dc.subject.other	STRAIN	en
dc.subject.other	STRESS	en
dc.title	The Ms=6.2, June 15, 1995 Aigion earthquake (Greece): Evidence for low angle normal faulting in the Corinth rift	en
heal.type	journalArticle	en
heal.identifier.primary	10.1023/A:1009795618839	en
heal.identifier.secondary	http://dx.doi.org/10.1023/A:1009795618839	en
heal.language	English	en
heal.publicationDate	1997	en
heal.abstract	We present the results of a multidisciplinary study of the M-s = 6.2, 1995, June 15, Aigion earthquake (Gulf of Corinth, Greece). In order to constrain the rupture geometry, we used all available data from seismology (local, regional and teleseismic records of the mainshock and of aftershocks), geodesy (GPS and SAR interferometry), and tectonics. Part of these data were obtained during a postseismic field study consisting of the surveying of 24 GPS points, the temporary installation of 20 digital seismometers, and a detailed field investigation for surface fault break. The Aigion fault was the only fault onland which showed detectable breaks (<4 cm). We relocated the mainshock hypocenter at 10 km in depth, 38 degrees 21.7' N, 22 degrees 12.0' E, about 15 km NNE to the damaged city of Aigion. The modeling of teleseismic P and SH waves provides a seismic moment M-o = 3.4 10(18) N.m, a well constrained focal mechanism (strike 277 degrees, dip 33 degrees, rake-77 degrees), at a centroidal depth of 7.2 km, consistent with the NEIC and the revised Harvard determinations. It thus involved almost pure normal faulting in agreement with the tectonics of the Gulf. The horizontal GPS displacements corrected for the opening of the gulf (1.5 cm/year) show a well-resolved 7 cm northward motion above the hypocenter, which eliminates the possibility of a steep, south-dipping fault plane. Fitting the S-wave polarization at SERG, 10 km from the epicenter, with a 33 degrees northward dipping plane implies a hypocentral depth greater than 10 km. The north dipping fault plane provides a poor fit to the GPS data at the southern points when a homogeneous elastic half-space is considered: the best fit geodetic model is obtained for a fault shallower by 2 km, assuming the same dip. We show with a two-dimensional model that this depth difference is probably due to the distorting effect of the shallow, low-rigidity sediments of the gulf and of its edges. The best-fit fault model, with dimensions 9 km E-W and 15 km along dip, and a 0.87 m uniform slip, fits InSAR data covering the time of the earthquake. The fault is located about 10 km east-northeast to the Aigion fault, whose surface breaks thus appears as secondary features. The rupture lasted 4 to 5 s, propagating southward and upward on a fault probably outcropping offshore, near the southern edge of the gulf. In the shallowest 4 km, the slip - if any - has not exceeded about 30 cm. This geometry implies a large directivity effect in Aigion, in agreement with the accelerogram aig which shows a short duration (2 s) and a large amplitude (0.5 g) of the direct S acceleration. This unusual low-angle normal faulting may have been favoured by a low-friction, high pore pressure fault zone, or by a rotation of the stress directions due to the possible dip towards the south of the brittle-ductile transition zone. This fault cannot be responsible for the long term topography of the rift, which is controlled by larger normal faults with larger dip angles, implying either a seldom, or a more recently started activity of such low angle faults in the central part of the rift.	en
heal.publisher	KLUWER ACADEMIC PUBL	en
heal.journalName	Journal of Seismology	en
dc.identifier.doi	10.1023/A:1009795618839	en
dc.identifier.isi	ISI:000080617100003	en
dc.identifier.volume	1	en
dc.identifier.issue	2	en
dc.identifier.spage	131	en
dc.identifier.epage	150	en