New Design Spectral Acceleration of Soft and Deep Deposits in Bangkok

In this paper, seismic site effects considering deep deposits were investigated in order to propose new design spectral acceleration (Sa) for Bangkok. Site characteristics such as predominant periods and shear wave velocity profiles from surface to basement were surveyed using microtremor observation techniques; the H/V spectral ratio and the Centerless Circular Array method (CCA). The results of shear wave velocity were used to construct soil models for site response analysis using the input motions selected and scaled to match the uniform hazard spectra with the Conditional Mean Spectrum (CMS) concept. The results of Sa were considered for their similarity of shape and the vicinity, then the area is sub-divided into three zones. The proposed Sa curves are considerably distinct from the Sa in the present design standard which was derived based on limited information of site characteristics. The new Sa exhibit long period amplifications resulting from effects of deep deposits.