Seismic imaging of the aftershock zone of the 2001 <i>Mw</i> 7.7 Bhuj earthquake, India

Abstract

Detailed seismic tomography reveals that the 2001 Mw 7.7 Bhuj earthquake was associated with a 10–14% increase in Vp and Vs and a 10% decrease in Vp/Vs in the 10 to 35 km depth range covering a 2750 km 2 area beneath the aftershock zone. This anomaly could be attributed to the existence of a lithological heterogeneity or a pluton of mafic composition that might have intruded during the rifting in early Jurassic (∼160 Ma). The Banni basin and the Wagad uplift are found to be associated with high velocity intrusive bodies extending from 5 to 35 km depth. A few patches of low Vp and Vs and high Vp/Vs between 10 to 30 km depth have also been detected on the causative 45° south dipping north Wagad fault (NWF) for the 2001 mainshock, which may be attributed to a fluid filled fractured rock matrix.