On the mechanism and source parameters of the deep crustal Jabalpur earthquake, India, of 1997 May 21: constraints from aftershocks and changes in static stress

The 1997 May 21 Jabalpur earthquake (m(b) = 6.0) occurred in the lower crust of the ENE- WSWtrending Narmada-Son palaeorift zone in central India known as the Narmada-Son lineament (NSL). We correlate the aftershock distribution of this earthquake with the computed changes in static stress caused by slip on the earthquake rupture in order to constrain some of the source parameters of the main event. We estimate that the downdip edge of the earthquake rupture extended up to a depth of about 38 km and that the majority of the aftershocks occurred due to unclamping in the hangingwall near the downdip edge of the rupture. Considering the intermediate to moderately high heat flow in the region, we suggest that (1) high pore pressure in the lower crust, which developed due to the dehydration of the serpentinite body during previous episodes of thermo-tectonic processes, (2) a lower frictional coefficient possibly arising due to fractured rocks at depth, (3) a higher strain rate, and (4) the favourable influence of N-S compression due to the motion of the Indian plate are responsible for the infrequent earthquakes in the lower crust of the NSL zone.