Geothermal Structure in a Seismoactive Region of Central India

The geothermal structure beneath a seismoactive region of central India has been determined by using two independent geophysical parameters, i.e., Pn velocity and Curie point depth, which are temperature dependent. Pn velocity has been determined by reanalyzing deep seismic sounding (DSS) records obtained for this region. Surface heat flow has been computed using the Pn velocity data from this region and found to be 55 ± 5 mW m)2. Curie point depths have been derived from the magnetic satellite data in this region, and reveal an identical value of heat flow of around 56 ± 4 mW m)2. We estimated temperatures of 600–700 C at a Moho depth of 39 km by using surface heat flow ranging from 50 to 60 mW m)2 and a simple 1-D geothermal model. The present study suggests the presence of a brittle–ductile transition (high strength) zone ranging in depth from 20 to 35 km, where the temperatures range from 350 to 550 C. We also suggest that the nucleation of earthquakes in this region took place in a relatively high strength zone. This is supported by the fact that the focal depths of all the recent earthquakes (from 1978 to 2000 of magnitude ‡ 3.5) lie in this zone of high strength.