Assessing site response through H/V ratio in a seismic prone area of northeast India

TL;DR

This study assesses the seismic site response in Shillong City, India, using ambient noise measurements and H/V spectral ratios, revealing local heterogeneity and resonant frequencies that correlate with geological data.

Contribution

It introduces a combined approach of ambient noise H/V ratio analysis and non-linear earthquake site response modeling in a seismically active region.

Findings

Resonant frequencies range from 3 to 8 Hz across sites.

Significant lateral heterogeneity in underlying layers.

Good correlation between H/V spectral ratios and geotechnical data.

Abstract

We endeavor to assess site response exploiting ambient noise measurements which we carried out at 70 sites in different parts of Shillong City, one of the seismically active regions. We estimate the spectral ratio from these recordings. The spectral ratios reveal the resonant frequency for Shillong City in the range of 3 to 8 Hz. Short scale spatial variation in the resonant frequencies suggests that there is prominent lateral heterogeneity in the underlying layers. Besides, a non-linear earthquake site response analysis is also attempted using available geotechnical data. A good correlation is observed between site response analysis and HVSR results constrained by wide variation of resonant frequency at short distances. The results are found to be tallying well with the geological data.