Vs30 Estimate for Southwest China

Abstract

Several methods were used to estimate Vs30 from site profiles with borehole depths of about 20 m for the strong-motion stations located in Southwest China. The methods implemented include extrapolation (constant and gradient), Geomatrix Site Classification correlation with shear-wave velocity, and remote sensing (terrain and topography). The gradient extrapolation is the preferred choice of this study for sites with shear-wave velocity profile data. However, it is noted that the coefficients derived from the California data set are not applicable to sites in Southwest China. Due to the scarcity of borehole profiles data with depth of more than 30 m in Southwest China, 73 Kiknet profiles were used to generate new coefficients for gradient extrapolation. Fortunately, these coefficients provide a reasonable estimate of Vs30 for sites in Southwest China. This study showed Vs30 could be estimated by the time-average shear-wave velocity (average slowness) of only 10 meters of depth. Furthermore, a median Vs30 estimate based upon Geomatrix Classification is derived from the results of the gradient extrapolation using a regional calibration of the Geomatrix Classification with Vs30. The results of this study can be applied to assign Vs30 to the sites without borehole data in Southwest China