Seismic site characterization using multichannel analysis of surface waves in the Singhbhum region of Jharkhand, India: a case study

The present study carries out subsurface exploration of Jamshedpur region using Active Multichannel Analysis of Surface Waves techniques that provide information on the different lithological characteristics. Four different sites (MASW-1 to MASW-4) were chosen in proximity to river basin to obtain a probable shear wave velocity profile. To record the raw wave field traces produced by a 10 kg sledgehammer, a linear array of 24 numbers of 4.5 Hz geophones was employed. The effects of data acquisition parameters, like sampling frequency (500 Hz, 1000 Hz, and 2000 Hz) and offset distance (1 m, 6 m, 8 m, and 20 m), were used to obtain a high-resolution dispersion image. Due to the variables selected as data acquisition parameters, the optimal set of data parameters was found, providing the best resolution of dispersion images for all the selected sites. The results indicate that the best resolution of the dispersion image was produced at an offset distance range of 6–8 m at sampling frequencies range of 500–1000 Hz at 1 m geophone spacing with five stacking, indicating a strong signal to noise ratio in a range of 80–90%. Up to a depth of ~ 3 m, stiff silty clay soil was discovered, and at depths of 30 m or more, medium- to very-dense weathered mica schist was discovered. At sites MASW-1 and MASW-3, respectively, slag fillings were found in the top layer at depths of 1.2 and 2.3 m. Greater depths of hard rock layers have also been found at site MASW-3. Locations along the river generally fall into National Earthquake Hazards Reduction Program (NEHRP) categories C or D.