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Non-technical summary: To, Burgmann, and Pollitz (2004) studied possible triggering mechanisms of the 2001 magnitude M7.7 Bhuj earthquake in northwest India. This earthquake is one of the very few strong earthquakes in historical times to have occurred in an intra-plate region far from known major tectonic plate boundaries. In this part of India, however, there had been a previous large earthquake, the M7.7 1819 Rann of Kachchh earthquake. One of the questions To et al., (2004) attempted to answer was whether the 1819 earthquake may have influenced the later occurrence of the 2001 Bhuj earthquake through the process of stress transfer. The main contributors to stress transfer that To et al., (2004) examined was static coseismic deformation and transient postseismic relaxation of the ductile rock deep below the earthquake rupture. Their conclusion is that the combined coseismic and postseismic deformation from the magnitude 7.7 1819 earthquake added stress and encouraged subsequent failure on the 2001 Bhuj rupture fault plane. Notably, postseismic stress changes at the location of the 2001 Bhuj earthquake exceed coseismic stress changes by around a factor of 4 to 7, emphasizing the role of relaxation process at substantial distance from the causative fault. (For comparison, the Rann of Kachchh and Bhuj rupture zones are about twice as far apart as the epicentral zones of the M6.5 2003 San Simeon and M6.0 Parkfield, California earthquakes, which are predicted to have had a similar level of stress transfer between them.) The 2001 Bhuj earthquake will, in turn, lead to comparable regional stress perturbations in the Rann of Kachchh region and might result in continued enhanced earthquake activity in an extended earthquake sequence in an otherwise low strain rate, intra-plate setting.

Figure 1. The location of major faults and post-1819 earthquakes. Events of M > 5 are shown by large red star, M < 5 from USGS-NEIC catalog are shown by small red star. Dashed rectangles lines the fault geometry of the 1819, 1956, and 2001 events. The intersections of the faults with the surface are shown in thick gray lines. Yellow stars are aftershocks of the 2001 event. Click on image for the whole pdf article or on the link above.