Mantle deformation beneath the southern part of Western Ghats

Abstract:

Upper mantle anisotropy provides significant insights to the mantle deformation of a region. In the present study, we utilized the core refracted shear phases (SKS) to decipher the upper mantle anisotropy beneath the southern part of Western Ghats using two methods viz., (i) Rotation Correlation (RC) and (ii) Minimum Energy (SC) with the help of SplitLab software. For this analysis, we considered 375 SKS waveform recorded at 7 broadband seismological stations. Results reveal a significant variation in the fast polarization direction i.e., from N6° to N173° with varying delay times (δt) from 0.3 s to 2.1 s. Majority of the results indicate two major fast polarization directions i.e., NNW-SSE and NE-SW with variable delay times. The NE-SW direction is parallel to the Apparent Plate Motion (APM) of the Indian sub-continent estimated from the NUVEL1A model, suggesting that shear at the base of the lithosphere is one of the dominant mechanisms for anisotropy in the study region. Moreover, the observed coast parallel fast axis polarization direction i.e., NNW-SSE with strong delay time could be due to the edge flow associated with the transition from a thicker to thinner lithosphere resulted from the rifting processes. In contrast to these results, we observed multiple fast polarization directions at PCH station close to the coast, varying from N19.3° to N163.8° with delay times ranging from 1.1 s to 1.3 s. These multiple fast axis polarization directions close to the west coast in the study region suggests complex anisotropy.