Passive-Source Seismic Imaging of the Crust and Upper Mantle beneath the 2001 Mw 7.7 Bhuj Earthquake Region, Gujarat, India

Abstract

Abstract Variations in crustal and lithospheric thicknesses below the Kachchh rift (KR) zone have been investigated employing the joint inversion of P receiver functions (RF) and Rayleigh‐wave and Love‐wave group velocity dispersion (5–70 s) on the broadband waveforms of teleseismic events. Estimated crustal and lithospheric thicknesses at 15 broadband sites led to the delineation of an updoming of 4–7 km in the Moho and 6–12 km in the asthenosphere beneath the central KR relative to the surrounding unrifted regions. The Moho depths vary from 35 to 42 km and lithospheric thicknesses range from 62 to 78 km. The observed marked shear velocity reduction (2%–6%) at the lithosphere–asthenosphere boundary (LAB) over an area of 120 km×80 km suggests the presence of patches of partial melt in the asthenosphere below the KR, evidencing the possible presence of imprints of the Deccan–Reunion mantle plume. The coincidence of the area of updoming of the Moho and asthenosphere, and the confined aftershock activity below the central KR implies that these patches could provide a high input of volatile CO 2 into the lower crust, which might play a key role in generating the continued aftershock activity in the region since the occurrence of the 2001 M w 7.7 Bhuj mainshock.