Seismic evidence for significant crustal thickening beneath Jabalpur earthquake, 21 May 1997, source region in Narmada-Son lineament, central India

摘要

We investigate crustal properties beneath the deep crustal ( similar to 35 km) Jabalpur earthquake of 21 May 1997, Narmada-Son Lineament (NSL), central India, in search of a possible cause of stress accumulation in the region. Teleseismic receiver functions computed at nine digital seismographs along a 250 km long profile suggests Moho downwarp to similar to 52 km across the width of the lineament, in contrast with an average 40 km depth elsewhere. In addition, the crust beneath the NSL has higher V-p/V-s of 1.84 compared to similar to 1.73 in the surrounding, suggestive of a high-density mafic mass at depth that compensates the crustal root, also supported by small topographic variation ( 200 m) across the lineament. Presence of such an anomalous mass in the deep crust may lead to gravitationally induced stresses in the lower crust that contribute to the failure of rock along the pre-existing Narmada-Son fault leading to the earthquake in deep crust.