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., P n velocity and Curie point depth, which are temperature dependent. P n velocity has been determined by reanalyzing deep seismic sounding (DSS) records obtained for this region. Surface heat flow has been computed using the P n 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.