Seismic Site Characterization Using Shear Wave Velocities of Gandhinagar City, Gujarat, India

Abstract

The recent devolvement in geophysical methods in particular Multi-channel Analysis of Surface Wave (MASW) technique is widely used for determining the 1D and 2D shear wave velocity of the subsurface materials. Though there are three types of MASW technique, only the data acquisition, data processing and inversion of active MASW technique are discussed in this paper. An attempt has been made to measure the shear wave velocities and hence site characterization using active MASW technique of the Gandhinagar City for engineering application. The active MASW survey consists of 24-channel Geode Seismograph with 24 geophones of 4.5Hz capacity, sledge hammer of 10kg with switch, hammer plate, and supporting software is used for the survey of Gandhinagar City. The survey points have been selected in such a way that the result represents the soil characteristics of the entire site; here the receivers are placed in linear array. Here Surfseis software is used for the data analysis. The Surfseis is designed to generate Vs of either 1D or 2D format using a simple three steps procedure: preparation of a Multichannel record, dispersion-curve analysis and inversion. The shear wave velocities (Vs) of Gandhinagar City increases with depth from 250 m/s to 450 m/s and the harmonic mean (Vs30) of Vs is in the range 250 m/s to 350 m/s up to 30 meter depth. The soil condition of Gandhinagar City is stiff soil and can not possess liquefactions.