Determining shallow S‐Wave velocity structure and site response parameters in Gwalior basin, Central India, through microtremor measurements

Abstract The Gwalior basin in Central India is of significant geological interest due to its diverse geological formations, tectonic history and landscape features. Its location at the boundary between the stable Indian Shield and tectonically active regions to the north and east creates unique seismotectonic and stress patterns, making it different from other areas in central India. In this study, we conducted microtremor measurements at 46 uniformly distributed sites in and around the basin to evaluate the site characteristics, including shallow shear wave velocity structure (Vs). We used Tromino 3G seismometer, with a flat frequency response from 0.1 Hz to 1024 Hz, for the microtremor measurements. Most of the study area is classified as site class D, with predominant frequencies between 1.6 Hz and 2.7 Hz and peak amplitudes ranging from 3.0 to 9.0. Our results show that predominant frequencies range from 1.5 Hz to 2.7 Hz for the Quaternary formation, 2.4 Hz to 3.5 Hz for the sandstones of the Kaimur Group and 1.6 Hz to 3.6 Hz for the Gwalior Group rocks. Higher amplitude of the HVSR is observed in the northeastern and eastern parts of the basin. We also estimated a liquefaction potential index (Kg) exceeding 10 for most of the study area, indicating vulnerability under dynamic loading. The thicker alluvium deposits in the northeastern and eastern parts associated with the Swarnarekha River are confirmed by lithological data, showing lower shear wave velocities. Our results provide key parameters for understanding the seismic hazards, which can be useful for assessing seismic risks and generating a disaster risk mitigation plan for the area.