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 (δt) 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.
- Received 13 January 2012.
- Revision received 13 March 2012.
- Accepted 14 March 2012.
- © 2011 Geological Society of America