A Study of Distortion of MT Response Functions in South India

The southern part of the Indian Peninsular shield has been broadly ,divided into various blocks and the deep crustal character of each block is believed to be distinctly different. A magnetotelluric (MT) study is proposed in this region to investigate the deep electrical structure across these blocks, Since South India is surrounded by sea, quantitative estimation of coastal effects on MT measurements made on land has been carried out by 2-D modeling for the region between 110 Nand 160 N. While a resistive (3000 Ohm.m) upper crust underlain by a lower conducting subsurface (500 Ohm.m) extending up to 80 km is assumed in the model towards landward side, a relatively conducting (500 Ohm.m) Oceanic crust has been assumed towards seaward side. The results bring out the nature of the deviations of MT response functions - apparent resistivity in E-pol, H-pol and tipper - for 1, 10, 100, 1000 sec. as observed both towards the landward side and seaward side. It is also seen that these deviations show a dis tinctly different character for the east and west coasts in that they propagate to a longer distance on the land from the east coast compared to that corresponding to the west coast.