Evidence for reactivation of new faults and seismicity migration away from the causative fault of the 2001 MW 7.7 Bhuj earthquake, western India

The Kachchh Rift Basin of western India that hosted the devastating 2001 MW 7.7 Bhuj earthquake has been witnessing minor to moderate seismicity since then. In this study, we relocated all the earthquakes recorded between 2006 and 2018 and utilized a set of 4285 best located earthquakes to investigate orientation and depth distribution of the currently active faults. It is revealed that the present seismic activity is primarily aligned along two planes—one steeply dipping (∼60◦) to the northeast with a NW–SE strike and the other gently (∼34◦) dipping to the SSW, striking WNW–ESE. The traces of these fault surfaces coincide with the Kachchh Mainland fault (KMF) and the North Wagad Fault (NWF) when extrapolated to the surface, respectively. Activity along the NWF has been shown in earlier studies, however, clear evidence of activity along the steep north-dipping KMF is presented for the very first time. Thrust earthquakes dominate the NWF while strike-slip earthquakes are seen across the KMF. Our results show that the two fault surfaces converge between 70.30◦E and 70.43◦E longitudes in the depth range 22–32 km, this convergence zone hosted the largest earthquakes (ML 4.7–5.1) between 2006 and 2018 and the hypocentre of 2001 main shock also coincide with it. The earthquakes occurring in the interfault region show major strike-slip motion and are probably influenced by the relative motion between the NWF and KMF and activity along the South Wagad Fault, which hosted the 2001 earthquake is meagre during 2006–2018.

A schematic showing the orientation and depth distribution of the surfaces which are seismically active within the Kachchh region.

Citation: Himangshu Paul , M. Ravi Kumar and Santosh Kumar, 2021. Geophys. J. Int. 226, 1800–1813 https://doi.org/10.1093/gji/ggab188 external link