Delineation of detailed crustal seismic velocity structure and Moho depths in the Hyderabad region, eastern Dharwar craton, India

The deployment of a local digital seismic network of 10 three-component broadband seismographs in September 2020 has enabled us to report for the first time a detailed crustal velocity structure below the Hyderabad region that lies on the eastern Dharwar craton (EDC), India. This has been achieved through the differential evolution waveform inversion of radial P-receiver functions at stations from the above network. Our study reveals a 4-layered crust with a 16-km-thick high-velocity lowermost crustal layer comprising of mafic granulite, which might have been resulted from the Archean magmatism episode. The 9-km-thick upper crustal layer is modelled to be of felsic-intermediate composition with Vp of 6.27 km/s and density of 2.81 gm/cm3. The middle and upper lower crust at 9–22 km depth is inferred to be composed of basaltic composition. The modelled Moho depths vary from 35.4 to 37.6 km across the region. The average crustal thickness for the region is estimated to be (37 ± 1) km, agreeing well with the average thickness of the early and middle Archean undeformed crust in the world. Our modelling detects a NE-SW trending slight (~ 1 km) up-warping of the Moho and 16-km-thick high-velocity lower crustal mafic layer below the region occupying an area of 140 km × 130 km on the western part of the Hyderabad city where most of the earthquakes (M3.0–5.0) have occurred until today. Thus, we infer that large intraplate stresses associated with such a crustal structure in the Hyderabad region might be facilitating the crust to reach near-critical stress level; thus, small stress perturbations due to rainwater or other crustal fluid flows probably result in the observed seismicity.