Study of Local Site Effects for Strong Motion Recording Stations of Delhi

Abstract

Effects of local site conditions on strong ground motion characteristics are a well-known phenomenon studied by many researchers. Similar studies were also carried out in past for Delhi to understand the amplification of ground motion in various locations using different methods. In this study, an attempt is made to study the amplifications in eight locations of Delhi where strong motion recording stations are located. For this study, shear wave velocity profiles were used for performing ground response analysis using equivalent linear approach. For input motion, response spectra compatible motion was used, compatible to response spectra for Rock sites as per IS 1893:2002. Transfer functions from available earthquake records and ambient vibration records were also calculated for comparison. The results obtained were presented in the form of response spectra and amplification functions for all the sites. The results suggest an amplification of the order of 2–3 with respect to actual motion at sites coming under site class D of NEHRP. No amplification was found at IMD site which suggest that it can be used as a reference site for Delhi. Other two sites with NEHRP site class C found to have amplification of the order of 1–2. Similarly, output response spectra, at surface, for all the sites except IMD and Kalkaji were found to be amplified with respect to the corresponding response spectra of IS 1893:2002.