Seismic Evidence of Thickened Crust Beneath Eastern Part of Chhotanagpur Plateau, India

Date: 4/25/2019

Time: 11:00 AM

Room: Pike

The Chhotanagpur Plateau is mostly composed of old cratonic rocks of Proterozoic age where seismological studies have rarely been accomplished to decipher the underlying seismic velocity structure of lithosphere. To solve the mystery associated with deep geological and tectonic features of this part of Indian shield, we use teleseismic earthquake data (5.5≤M≤8.0) from years 2007 to 2017 recorded at two broadband seismic stations located in Indian cities of Dhanbad and Bokaro, respectively. The complementary constraints imposed by disparate datasets such as Ps and Sp receiver functions and Rayleigh wave group velocity dispersion curves are utilized to jointly model the P-and S-wave velocity profiles. The optimization of the cost function is performed via Very Fast Simulated Annealing (VFSA). This joint inversion technique conducts its multiple searches in predefined model space to find various acceptable velocity profiles to quantify the uncertainties associated with the best fitting model.

Our results suggest that the eastern part of Chhotanagpur plateau which is mostly composed of Granite Gneiss Complex has thickened crust as compared to the central and western part of Indian Shield. From the surface to the depth of ~150 km, the Vp and Vs range between 6.1-8.4 km/s and 3.2-4.8 km/s, respectively. We estimate the Moho at ~43 km and ~44 km for seismic stations located in Dhanbad and Bokaro, respectively. The large values of Poisson’s ratios (~0.29) in the crust of eastern part of Chhotanagpur Plateau indicate that the partial mafic material may be present in the lower crust.

Presenting Author: Mukesh K. Das

Authors