Shear wave anisotropy of the Godavari rift in the south Indian shield: Rift signature or APM related strain?

Shear wave splitting analysis using SKS, SKKS and S waveforms recorded at eight broadband seismic stations within and in the vicinity of the Proterozoic Godavari rift system in the south Indian shield yielded 104 new measurements of azimuthal anisotropy. Our results reveal that the delay times lie between 0.70 and 1.20 s, similar to the previous measurements from the Indian shield. The orientations of fast polarization directions at most of the stations within and beyond the rift are generally aligned orthogonal to the rift axis, consistent with asthenospheric flow in the extension direction. Absence of clear evidences for a preferentially thinner lithosphere beneath the Godavari rift or anomalously high heat flow values coupled with the fact that the NE oriented fast polarization directions are also close to the APM direction of the Indian plate, result in an ambiguity in interpreting the results as being due to strain related to plate motion or signatures of rifting. A thin lithosphere beneath the rift suggests that the source of anisotropy is likely to be in the asthenosphere. In such a scenario, either the mechanism of (1) active rifting where the asthenospheric flow drives the rifting or (2) passive rifting where mantle flow responds to lithospheric thinning caused by far field stresses or (3) present day APM related strain appear to be the plausible mechanisms for forging the observed anisotropy.