VS30 – A site-characterization parameter for use in building Codes, simplified earthquake resistant design, GMPEs, and ShakeMaps

VS30, defined as the average seismic shear-wave velocity from the surface to a depth of 30 meters, has found wide-spread use as a parameter to characterize site response for simplified earthquake resistant design as implemented in building codes worldwide. VS30 , as initially introduced by the author for the US 1994 NEHRP Building Code, provides unambiguous definitions of site classes and site coefficients for site-dependent response spectra based on correlations derived from extensive borehole logging and comparative ground-motion measurement programs in California. Subsequent use of VS30 for development of strong ground motion prediction equations (GMPEs) and measurement of extensive sets of VS borehole data have confirmed the previous empirical correlations and established correlations of SVS30 with VSZ at other depths. These correlations provide closed form expressions to predict S30 V at a large number of additional sites and further justify S30 V as a parameter to characterize site response for simplified building codes, GMPEs, ShakeMap, and seismic hazard mapping.