Seismic anisotropy beneath the Eastern Dharwar craton

Abstract

The southeastern Indian Shield, an assemblage of several Precambrian geological terranes, carries imprints of major tectonic events, including those related to rifting contemporaneous with India-Antarctica continental separation, volcanism, and sedimentation in Gondwana. In this study, we investigate the character of seismic anisotropy underneath 14 broadband stations spanning this region, utilizing the SK(K)S and direct S waves from earthquakes deeper than 400 km. In total, 113 high-quality splitting measurements reveal that the delay times (δ t ) between the fast and slow axes of anisotropy range from 0.32 s to 1.62 s for direct S waves and from 0.31 s to 1.80 s for SK(K)S phases. The fast polarization directions at a majority of the stations are in accordance with shear at the base of the lithosphere, coinciding with the present-day motion of the Indian plate with respect to the fixed Eurasian plate as defined through the NUVEL1A plate model. The coast-parallel splitting trends in the vicinity of the Eastern Ghat mobile belt can be reconciled by invoking a combination of anisotropy frozen in the lithosphere due to continental rifting along the eastern margin of the Indian plate and active asthenospheric anisotropy.