Site response studies in Peshawar using the Nakamura technique of HVSR

Abstract

In this study, soil response analysis in the Peshawar district is undertaken to characterize their local effects using experimental ambient noise measurements. The Nakamura HVSR method has been used to estimate the fundamental frequency of the soils at 75 test site locations, using a 3-component tomograph. Validation of the peak frequency of amplification of soils obtained was carried out using pre-, post-, and main-event data of real earthquake records in Peshawar and at excavated test sites. It has been found that the cultivated areas exhibit a large peak of H/V amplification (4) corresponding to resonance frequencies ranging from 1.3 to 2.1 Hz in contrast to hard-rock sites with low amplification. Some hard-rock sites have a thick cover of soil and a large variation in H/V peak amplification corresponding to frequency ranges from 3.3 to 10.5 Hz. The H/V curves for most of the sites result in a single peak of large amplification and could be associated with sharp discontinuities consistent with a large velocity contrast uni-model of a single layer overlying the bedrock. The site responses of the low fundamental frequencies corresponding to large amplitude are observed to enable identifying cultivated areas that form important inputs in the seismic hazard microzonation of the Peshawar district.