Lithospheric seismic structure beneath two broadband station sites of the eastern part of Chhotanagpur Plateau: New constraints from receiver functions and dispersion curves

Abstract

The Chhotanagpur Plateau in eastern India was formed due to the severe upheaval of tectonic forces deep inside the earth. The deep geological processes associated with its subsurface along with geodynamical rationales are never understood properly due to the dearth of good quality geophysical data. We use high quality teleseismic earthquakes’ waveforms (5.5 ≤ M ≤ 8.0) recorded at two seismic stations ISM and BOKR located in Dhanbad and Bokaro, respectively. These data are used to jointly model discrete but complementary datasets such as Ps and Sp receiver functions and Rayleigh wave group velocity dispersion curves via Very Fast Simulated Annealing (VFSA). A two-step optimization procedure is carried out to find the best fitting models and associated uncertainties in terms of Posterior Probability Density (PPD) functions. Our results reveal that on an average the eastern part of Chhotanagpur plateau which is mostly composed of Granite Gneiss Complex with high heat flow is characterized by the thick crust. For ISM station up to ∼150 km depth, Vp and Vs vary between 6.1 km/s–8.4 km/s and 3.3 km/s–4.8 km/s, respectively. We observe that Vp and Vs ranges between ∼6.2 km/s to ∼8.3 km/s and ∼3.2 km/s to ∼4.6 km/s, respectively, for seismic station BOKR. We find that the crustal thickness beneath seismic stations ISM and BOKR is ∼43 and ∼44 km, respectively. The higher values of Poisson’s ratio (>0.25) for station ISM and BOKR are 0.30 and 0.29, respectively which may indicate the presence of partial melt present in the lower crust.