Should average shear-wave velocity in the top 30 m of soil be used to describe seismic amplification?

Abstract The average velocity of shear waves in the top 30 m of soil, ν L , has become the parameter used by many engineering design codes and most recently by published empirical-scaling equations to estimate the amplitudes of strong ground motion. Yet there are few studies to determine whether this is a meaningful parameter to use—and whether estimates that do use it are reliable. In 1995, the authors studied this problem and concluded that ν L should not be used. We reported then that an older site characterization in terms of the soil site parameter proposed by Seed et al. [1] , s L , worked better because it included a measure of the thickness of the soil layers to considerably greater depths. Our report, however, made no difference; numerous papers continued to be published based only on scaling in terms of ν L , and worse, they also ignored the geological site conditions. The purpose of this paper is to emphasize that the average shear-wave velocity in the top 30 m of soil should not be the only site parameter used to scale strong-motion amplitudes. While the search continues for the more meaningful site parameters to use in empirical scaling of strong earthquake ground motion, it is better to use s L to describe the amplification of seismic waves by soil deposits near the surface.