Seismic Site Characterization of Delhi region using Microtremor Studies

Abstract

The microtremor method has proved to be the most inexpensive and convenient technique to estimate fundamental frequencies of soft deposits. The microtremor measurements at 144 sites were performed in Delhi region using MR2002 CE equipment exactly at the same locations where the seismic refraction and MASW tests were carried out to find the site response. One-hour data is recorded at each test location and analysis was done for getting the average H/V resonance spectra. Based on the analysis, a classification is proposed with four categories (T1, T2, T3 and T4) based on the shape of the H/V spectra, predominant frequency and soil characteristics. Since the detailed (bore hole data) soil profile at all these locations is available, the resonance frequency is compared with sedimentary thickness. It is observed that the resonance frequency is high at ridge areas and very low in places with high sedimentary thickness close to Yamuna river. That is, the peak of the response spectra is shifted to lower frequency values with increasing sedimentary thickness. That means the resonance frequency depends inversely on the soil thickness.