Effect of Sudden Shear Wave Velocity Contrast at Shallow Layer Interfaces on the Seismic Site Response for Charleston, SC

摘要

In practice, seismic site response analysis is often conducted with the entire soil profile being divided into a number of sub soil layers and site-specific parameters, such as shear wave velocity (V_s), damping and modulus reduction, are assumed to be constant within the extent of each layer. In this study, the effect of large contrast in V_s at shallow layer interfaces on the computed surface response is investigated considering the geologic and seismic settings for the Charleston, SC area. The Vs profiles with sudden contrast at shallow depth were smoothened systematically using various hypothetical gradients to obtain derived Vs profiles. The computed responses from the original and the derived profiles were then compared. The hypothetical profiles produced lesser shear strains and greater surface accelerations as compared to the corresponding original profiles with significant V_s contrast. Therefore, such simplification of V_s profiles should be avoided in site response analysis, unless they represent actual geologic conditions.