Site Characterization and Site Response Studies Using Shear Wave Velocity
P. Anbazhagan and T.G. Sitharam
The complete microzonation and site response studies require the characterization of subsurface materials considering local subsurface profiles of the site or region. The general site characterization comprises of the evaluation of subsurface features, material types, material properties and buried/hollow structures, by which it is determined whether the site is safe against earthquake effects. In this study, an attempt has been made to characterize the Bangalore Mahanagar Palike (BMP) area of about 220km2 using the shallow geophysical method, Multichannel Analysis of Surface wave (MASW), which identifies each type of seismic wave on a multichannel record using the refraction survey and produces shear-wave velocity (Vs) profiles. The study area of BMP has been characterized as per NEHRP (National Earthquake Hazards Reduction Program) and IBC (International Building Code) site classification using an average shear wave velocity (Vs30) of 30m, obtained from MASW. In the study area, 58 one-dimensional (1-D) MASW survey has been carried out and respective velocity profiles are obtained. The major part of the BMP area can be classified as “site class D”, and “site class C” and a smaller part in and around Lalbagh Park is classified as” site class B”. Further site response has been carried out using measured shear wave velocity and synthetic ground motion developed by Sitharam and Anbazhagan . Site response study shows that due to soil condition, large modification of wave amplitudes are observed resulting in higher peak ground acceleration when compared to rock level acceleration.