High precision earthquake locations in Koyna-Warna seismic zone reveal depth variation in brittle-ductile transition zone

Abstract

The Koyna-Warna region located in the southwestern part of Deccan Volcanic Province is known for sustained seismicity during the last four decades. Catalog P and S phase data of local earthquakes recorded by the Koyna-Warna digital network were used to relocate 609 earthquakes using double difference algorithm. The relocated seismicity patterns delineate the presence of three fault segments and variation in the brittle-ductile transition depths amongst the individual faults as the earthquake foci in the north are limited up to 11 km depth whilst in the south they are confined up to 6-8 km. The focal mechanism solutions also indicate distinct styles of faulting amongst the three inferred fault segments. The variation in brittle-ductile transition zone is probably controlled due to the geometry of the fault system and the effective stress. Copyright 2005 by the American Geophysical Union.