Determination of Shear Wave Velocity Profile of Sedimentary Deposits in Bam City (Southeast of Iran) using Microtremor Measurements

Abstract

Site effect has been known as the major cause of large ground amplifications during several recent catastrophic earthquakes. Consequently, the evaluation of site effect is an important factor that must be considered in mitigation of earthquake hazards. Shear wave velocity is a key parameter that controls seismic response of a site. Hence its profile must be identified down to the seismic bedrock. Generally geotechnical or even geophysical methods are expensive and time consuming for this purpose. As an economical and practical substitute, microtremor measurements can be used. In order to investigate the reliability of shear wave velocity (Vs) profiling by using microtremors, a series of one-point microtremor measurements have been conducted in Bam city (southeast of Iran) which experienced the damaging earthquake of December 2003. Microtremor measurements included 49 one-point observations distributed throughout the city. Based on the H/V spectrum of microtremors, shear wave velocity profiles were determined at the measurement sites using nonlinear inverse analysis. Reliability of the method was investigated, comparing results of microtremor measurements and seismic refraction method. Ultimately, using all inverted profiles, seismic microzonation maps were developed for Bam city.