Seismic Daylight Imaging of South Indian Lithosphere.

We present a comprehensive study of finding high-resolution lithospheric discontinuities in South India using Seismic Daylight Imaging(SDI). South India is a stable continent having Precambrian terrains such as the Mesoarchean Western Dharwar Craton (WDC), Neoarchean Eastern Dharwar Craton (EDC), and Proterozoic Southern Granulite Terrains(SGT). EDC again comprises of one the largest intracratonic basin, the Cudddapah Basin. The data used comprised teleseismic events having magnitude Ms > 5.5 and Signal to Noise Ratio(SNR) > 5. The frequency ranged from 0.1-4 Hz thereby providing vertical resolution of as high as 2 Km even for deeper seismic discontinuities. In addition to the standard P-wave autocorrelation method, we have incorporated spectral whitening to remove the bias toward lower frequency and Phase weighted stacking(PWS) to detect signals that are weak but coherent in nature. This helped immensely in getting signatures of deeper structures like Mid-Lithospheric discontinuities(MLD) and Lithosphere Asthenosphere Boundary(LAB). The Moho obtained from this study shows a thinner crust (∼35 Km) in the EDC and relatively higher (∼40-50 Km) in WDC. This was consistent with Receiver Function studies done previously. The LAB thickness obtained varied mostly around 120-170 Km. However, there were few regions with a sharp lateral variation where LAB thickness was outside the range. The Eastern coast LAB thickness was consistently thinner than the Western coast. The lateral variation of the LAB could be attributed to plume activities which might have resulted in epeirogenic upliftment and lithospheric thinning.