Earth Tremors in the Coastal Belt of Tamil Nadu and Pondicherry in September, 2001 - A Geological Analysis

The earth tremors experienced in Tamil Nadu and Pondicherry on the 26^th September 2001, is discussed on the basis of the evolution of the geological and structural setup in the coastal region, consequent on the separation of Antarctica from India in the geological past. Subsurface data obtained by drilling in the Cauvery basin bear out the definition of a number of NE-SW to NNE-SSW fault bounded ridges and depressions extending from land into the offshore area. The stupendous thickness of sediments in the structures is suggestive of the sagging of the Precambrian crystalline basement and the release of strain in the process is ostensibly manifested as earth tremors. The reported occurrence of volcanic activity off the coast and the occurrence of thermal water in deep boreholes drilled in the coastal region, both falling within the NE-SW to NNE-SSE fault system, suggest that the weak fault planes in the crust provided channel ways for the eruption of magma and dissipation of subsurface heat.