HR: 0830h
AN: S51D-0080    [PDF]
TI: A New Tomographic Study of the Western Corinth Rift (Greece) Using Local Seismicity
AU: * Latorre, D
EM: latorre@geoazur.unice.fr
AF: UMR-UNSA-IRD G\'{e}osciences Azur, 250 rue Albert Einstein, Valbonne, 06560 France
AU: Virieux, J
EM: viri@geoazur.unice.fr
AF: UMR-UNSA-IRD G\'{e}osciences Azur, 250 rue Albert Einstein, Valbonne, 06560 France
AU: Monfret, T
EM: monfret@geoazur.unice.fr
AF: UMR-UNSA-IRD G\'{e}osciences Azur, 250 rue Albert Einstein, Valbonne, 06560 France
AU: Monteiller, V
EM: Vadim.Monteiller@iniv-savoie.fr
AF: Laboratoire de G\'{e}ophysique interne et Tectonophysique, Campus Scientifique B\^{a}timent Le Chablais, Le Bourget du Lac, 73376 France
AU: Vanorio, T
EM: vanorio@geoazur.unice.fr
AF: UMR-UNSA-IRD G\'{e}osciences Azur, 250 rue Albert Einstein, Valbonne, 06560 France
AU: Got, J
EM: Jean-Luc.Got@iniv-savoie.fr
AF: Laboratoire de G\'{e}ophysique interne et Tectonophysique, Campus Scientifique B\^{a}timent Le Chablais, Le Bourget du Lac, 73376 France
AU: Lyon-Caen, H
EM: lyoncaen@geologie.ens.fr
AF: Ecole normale sup\'{e}rieure, 45, rue d'Ulm, Paris, 75230 France
AB: A large dataset of more than 5,000 micro-earthquakes recorded in 1991 has been revisited in order to image the middle crust structure of the western Corinth Rift.Detailed three-dimentional P and S velocity structures and earthquake locations have been obtained by using an improved travel-time tomography method. This method is based on an iterative scheme in which, at each iteration, travel-time computation is performed using an accurate finite-difference technique and both models and location parameters are inverted simultaneously. The sensitivity of tomography results to the model parameterization and to the starting velocity model have been analyzed with different synthetic tests. Retrieved Vp and Vs models are used to deduce Vp/Vs and Vp*Vs images. The interpretation of these images allows to delineate the distribution of lithological variation, porosity and fluid saturation in the first 9 km of the crust beneath the Gulf of Corinth. Velocity images point out different features between the shallower and the deeper crust. The shallow 5 km thick structure shows WNW-ESE trending features that are related to the present-day N-S extention of the Rift. Althought extentional rate is very high in this region (about 1.5 cm/year), quite no microseismicity is observed in the first 4 km depth. On the contrary, velocity distribution changes beneath 5 km depth down to 9 km depth, where two high Vp/Vs anomalies are detected. These anomalies are located beneath the northern part of the Gulf in correspondance of a thin zone where very intense microseismicity is located. Previous magnetotelluric investigations allow us to suggest a possible correlation between this high Vp/Vs zone and a relative conductive layer identified at 9 km depth. This layer have been associated to the presence of fluid-filled cracks in the tectonometamorphic Phillite series, an inherited structure of the Hellenic mountain belt. This ductile series may constitute with the upper carbonate series of the Hellenic mountain belt a strong brittle/ductile transition.
DE: 7203 Body wave propagation
DE: 7230 Seismicity and seismotectonics
DE: 8109 Continental tectonics--extensional (0905)
DE: 8180 Tomography
SC: Seismology [S]
MN: 2003 Fall Meeting