Estimating Soil Thickness using t he H/V Spectral Ratio Technique in CSIR-NGRI Campus, Hyderabad, India

Abstract

This article deals with a microtremor survey, which was carried out at 42 sites of CSIR-NGRI Campus (area: ~0.65 km2), Hyderabad, India using a Tromino 3G ENGY for the measurement of 20-minute interval each with the frequency of 512 Hz. The collected data were analyzed to attain a horizontal to vertical (H/V) spectral ratio of the noise spectrum with the aid of GRILLA software. The frequency corresponding to the first dominant peak of the average H/V spectrum plot was considered as the resonant frequency of that particular site. The processing included in Fourier Transformation, smoothing (~10 %) with Triangular Window, and estimating the velocity of shear wave and soil thickness based o n peaks were identified on the H/V spectral ratio from the ambient noise . The results indicate that the estimated resonance frequency varies from 52.81 to 102.81 Hz, with an average of 85.36 Hz. It is comparatively high in the elevated area, implying the thinning of shallow seismic contr ast layers. In the intermediate elevated area, this frequency decreases, and it gives the result of a t hick overlaid layer. The soil thickness estimated is an average of 0.56 m with the shear wave velocity range of 143 -190 m/s, with an average of 152 m/s. This H/V spectral ratio technique is very cost -effective for mapping the resonance frequency of any place except farmland, marshland or any place having soft soil layer.