HVSR-based empirical relation between predominant frequency and sediment thickness for site response assessment in and around Varanasi City, Uttar Pradesh, India
摘要
The present study evaluates sediment thickness and site-response characteristics in and around Varanasi city, Uttar Pradesh, situated within the Indo-Gangetic Plains. Ambient noise measurements from 86 locations were analysed using the horizontal-to-vertical spectral ratio (HVSR) method to derive key seismic parameters, including predominant frequency, amplification, and shear-wave velocity (Vs30). A region-specific empirical power–law relationship between predominant frequency and sediment thickness was developed and validated using quarter-wavelength estimates. Spatial maps of site-response indicators reveal pronounced lateral variations, especially along the Ganga River corridor, highlighting zones with elevated seismic amplification. The proposed empirical model provides a practical, first-order tool for estimating sediment thickness and conducting preliminary microzonation in data-sparse alluvial settings. The findings enhance our understanding of local subsurface conditions and provide valuable inputs for seismic hazard assessment and urban planning efforts in Varanasi.
Research highlightsHVSR measurements from 86 sites reveal pronounced lateral variations in site response, which are linked to alluvial stratigraphy. A region-specific empirical power–law relation between predominant frequency and sediment thickness is developed and validated. Spatial distribution map of fo, Ao, Vs30, Kg, and sediment thickness show a clear north–south gradient in subsurface conditions. Sensitivity analysis identifies Vs ≈ 700 m/s as the best match between empirical and quarter-wavelength thickness estimates. Results highlight the central–eastern floodplain as the most seismically vulnerable zone, aiding microzonation and urban planning.