Seismological evidence for a decoupled lithospheric segment in south Indian shield

Abstract

Analysis of several geophysical signatures yields a new model for the south Indian continental lithosphere that shows decoupling of the upper 80km from the underlying mantle. the tomographic images map a thick high-velocity upper mantle (1-6 per cent contrast) in the depth range 80-400 km overlain by a low-velocity region with an average contrast of -3 per cent beneath the south Indian shield. Teleseismic time term analysis points the fast anisotropic axis in the NNE direction coinciding well with the major principal stress direction obtained from field observations, and modelling results from vectorial tomography technique over the entire Indian shield. the significant differences in the direction of maximum anisotropy, stress patterns and character of velocity anomalies between the upper 80km and the underlying mantle suggest the presence of a decoupled system beneath the south Indian shield.