Crustal and lithospheric thinning beneath the seismogenic Kachchh rift zone, Gujarat (India): Its implications toward the generation of the 2001 Bhuj earthquake sequence

► Estimated the variation in Moho thickness (34-43 km) and lithospheric thickness (62-92 km) in Kachchh suggesting a crustal as well as asthenospheric thinning beneath the Kachchh rift basin, relative to the surrounding un-rifted zones. ► The marked velocity decrease associated with the lithosphere-asthenoshere boundary (LAB), observed over an area of 120 km × 80 km, and the isotropic study of xenoliths from Kachchh provides evidence for local asthenospheric updoming with pockets of partial melts of CO2 rich lherzolite beneath the Kachchh seismic zone that might have caused by rifting episode (at 88 Ma) and the associated Deccan thermal-plume interaction (at 65 Ma) episodes. ► The coincidence of area of crustal (3-7 km) as well as asthenospheric (6-14 km) thinning and confined aftershock activity beneath the central Kachchh rift zone proposes a possible key role played by volatiles containing CO2 emanating from the upper mantle in generating lower crustal aftershock activity in the region for last nine years. ► It is also inferred that large stresses in the denser and stronger lower crust (at 14-34 km depths) induced by ongoing Banni upliftment, crustal intrusive, marked lateral variation in crustal thickness and related sub-crustal thermal anomaly play a key role in nucleating the lower crustal earthquakes beneath the Kachchh seismic zone.