Elastic thickness and isostatic coherence anisotrophy in the South Indian Peninsular shield and its implications

Abstract

We present measurements of the mechanical strength of the lithosphere of the South Indian Peninsular Shield (SIPS). Values of Effective Elastic Thickness (Te) were obtained from azimuthally averaged coherence measurements γ 2 (\k\) between Bouguer gravity and topography using a multitaper method (MTM) and a mirrored periodogram method (MPM). Values of Te from MTM (11-16 km) are consistently lower than those from MPM (20-31 km) and are contained within the seismogenic thickness (Ts), substantiating earlier measurements in shield regions that have been tectonically inactive for a long time. The 2D coherence function γ 2 (k) calculated with the MTM reveals little mechanical anisotropy in the SIPS. We conduct analyses of different provinces within the SIPS and show how the results correlate with maximum horizontal stress orientations (σ Hmax) and heat flow measurements. Local processes appear to influence the strength of the SIPS lithosphere more profoundly than processes occurring at the plate boundary.