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

Abstract

[1] We investigate crustal properties beneath the deep crustal ($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 $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 $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.

Evaluation of crustal and upper mantle structures using receiver function analysis: ISM broadband observatory data

“…The well estimated crust-mantle boundary at a depth of 41 km is comparable with the RF results in southern peninsular India (Kumar et al 2001;Rai et al 2005). Kumar et al (2001) used 10 broadband station data of the national network for the period 1997-1999 of peninsular India including the Bokaro (BOKR) broadband station which is near to the ISM-Dhanbad (DHAN) broadband station (Fig.1).…”

Crustal density structure across the Central Indian Shear Zone from gravity data

“…According to Desai et al (2010), the underplated nature of the deep crust and the subjacent mantle rendering them transitional and the Moho is located within this transition zone. Using the receiver function measurements in the adjoining regions Rai et al (2005) presented evidences for a duplex Moho with highly mafic (V p /V s = 1.84) underplated lower crust. A high heat flow indicates that the thermal structure of the region has not yet completely stabilised despite the fact that the region experienced magmatic activity some 65 Ma ago.…”

“…It would also be ideal to carry out gravity modelling along this line while other profiles (1 and 2) on the eastern side of the region are characterised by thick Mesozoic overburden and Profile 5 on the western side is crossed by Southeast Sakoli shear. Additional constraints along the Mungwani-Rajnandgaon profile were drawn from other geophysical experiments (Mishra et al, 2000;Rai et al, 2005;Murty et al, 2008).…”

Mantle dynamics, isostasy, and the support of high terrain

“…Crustal thicknesses beneath stable cratons vary by more than 10-15 km, for instance beneath India [Gupta et al, 2003;Kiselev et al, 2008;Rai et al, 2005], Canada [e.g., Perry et al, 2002], and the Great Plains of the USA [Gilbert, 2012;Sheehan et al, 1995], as well as beneath Tibet [e.g., Tseng et al, 2009]. Again from (2), if uncompensated, such differences in crustal thickness would generate free-air and isostatic gravity anomalies approaching 200-300 mGal.…”