Estimates of geothermal gradients from bottom simulating reflectors

摘要

Multi-channel seismic reflection data from two different tectonic regimes over the continental margins of India have been studied to identify the bottom simulating reflector (BSR), a prime indicator for the presence of gas hydrates in a region. Theprobable depth of occurrence of these BSRs is estimated. The estimated depths were projected on plots of hydrate stability zones calculated for different geothermal gradients. The projected depths show scatter over curves of geothermal gradients. Best-fit curves were obtained from the datasets to arrive at geothermal gradients over the two regions. The estimated geothermal gradient for Kerala-Konkan is of the order of 0.05 degree -0.055 degree C/m and for Andaman region it is in the range 0.015 degree -0.02 degree C/m. The estimated geothermal gradient over Kerala-Konkan indicates normal value, whereas for the tectonically active Andaman region, it is lower. Utilizing the published values of thermal conductivities for hydrated sediments we have determined the heat flow values. The estimated heat flow value for Kerala-Konkan region seems to be normal with hydrated sediments, whereas the value obtained for the Andaman region seems to be significantly low. Possible explanation for this anomalous behaviour has been attempted.