SEISMIC TOMOGRAPHY OF THE SOUTH INDIAN SHIELD

The South Indian shield, evolved through the accretion of several geologic units, provides a unique natural laboratory to explore and test the geodynamic hypotheses submitted to explain the origin and evolution of continents, nature of dissimilarity between continent and ocean, mountain building processes, intra-continental disruptions etc. Aiming at unfolding the mysteries of this vibrant geodynamic setup with an efficient geophysical explorer, a teleseismic depth sounding research program has been initiated at the NGRI that includes 3-D velocity tomography, imaging of lithospheric scatterers, shear wave splitting (anisotropy) and shear wave crustal modeling. Major results from this research initiative include: ■ Presence of a thick upper mantle high velocity in large segment of the south Indian shield. ■ Evidence for anomalous crustal thickening and low velocity in the uppermost upper mantle ( till atleast 200 km) beneath the high grade terrain. ■ Anomalous upper mantle low velocity signatures form the north west part of Deccan trap, Godavari rift and Kaladgi–Bhima Precambrian basins. ■ Image of crustal topography in south India. ■ Presence of dominant scatterers in lower crust/upper mantle beneath the Closepet granite. ■ Near similar upper mantle anisotropy beneath Hyderabad and Poona seismological stations.