Establishing Empirical Correlation between Sediment Thickness and Resonant Frequency using HVSR for the Indo-Gangetic Plain

In this study, microtremor survey was carried out at 31 locations of Indo-Gangetic Plains (IGP) using a pair of portable three-component short-period seismometers (Guralp CMG-6T-1) and Kelunji Echo Pro digital data acquisition system. The acquired raw data was processed to obtain the average H/V ratio of the ambient vibration spectrum. The frequency corresponding to the first peak of the average H/V spectrum was taken as resonant frequency of that particular site. A comparison was made between the resonant frequencies obtained from peak of the H/V spectrum with those obtained using the source–receiver function from previously published work. The results were in good agreement with each other. An empirical equation has been established for the IGP by relating resonance frequency with sediment thickness, using available data from nearby boreholes drilled up to bedrock. The empirical equation was compared with other equations available for deep soil sites, i.e. sites with soil thickness more than 750 m. Further, a combined equation was developed for the digitized data taken from previously published works of deep soil sites. Finally, it has been found that the regionspecific equation gives better estimate of sediment thickness than the other empirical equations; but in absence of such a region-specific equation, the proposed combined equation can be used for a quick preliminary assessment of sediment thickness of a deep soil region.