Postseismic deformation and stress changes following the 1819 Rann of Kachchh, India earthquake: Was the 2001 Bhuj earthquake a triggered event?

Abstract

The 2001 Mw 7.6 Bhuj earthquake occurred in an intraplate region with rather unusual active seismicity, including an earlier major earthquake, the 1819 Rann of Kachchh earthquake (M7.7). We examine if static coseismic and transient postseismic deformation following the 1819 earthquake contributed to the enhanced seismicity in the region and the occurrence of the 2001 Bhuj earthquake, ∼100 km away and almost two centuries later. Based on the Indian shield setting, great rupture depth of the 2001 event and lack of significant early postseismic deformation measured following the 2001 event, we infer that little viscous relaxation occurs in the lower crust and choose an upper mantle effective viscosity of 1019 Pas. The predicted Coulomb failure stress (DCFS) on the rupture plane of the 2001 event increased by more than 0.1 bar at 20 km depth, which is a small but possibly significant amount. Stress change from the 1819 event may have also affected the occurrence of other historic earthquakes in this region. We also evaluate the postseismic deformation and ΔCFS in this region due to the 2001 event. Positive ΔCFS from the 2001 event occur to the NW and SE of the Bhuj earthquake rupture. Copyright 2004 by the American Geophysical Union.