Evaluation of seismic site effects for bangkok deep basin

In this study, seismic site effects of Bangkok focusing on deep basin structures are investigated. In the first part, shear wave velocity profiles from surface to bedrock of 16 sites were explored by microtremor array measurement with Spatial Autocorrelation method. The shear wave velocity of sedimentary layers exhibits low value as the average from the surface to 30-m depth is less than 180 m/s and the inferred depth of bedrock varies from 550 to 800 m. In the second part, equivalent linear analysis of the studied sites were conducted in order to examine the ground response and to propose seismic zonation accordingly. The input ground motions were selected and scaled to have response spectra matched with the conditional mean spectrum at several periods. The results of spectral accelerations (Sa) from deep basin models were discussed with the former models having shallow structures. Deep basin effects on long period Sa were indicated. Finally, seismic zonation was proposed based on the design Sa. The distinction between the zones is mainly from the long period effects at 2 second.