V_S30 in the NGA GMPEs: Regional differences and suggested practice

Shear-wave velocity profiles from California, Taiwan, and Japan are used to evaluate the regionalized linear V_S30 scaling in the recent NGA-West2 GMPEs. Profiles in the same V_S30 range are compared, and their differences and similarities are discussed. A simple parametric model for the median velocity profile and its standard deviation is provided for California and Japan. The model should only be used for 250 ≤ V_S30 ≤ 850m/s, representing the range of profile data availability. We make the following recommendation: for site-specific evaluations, knowledge of V_S30 alone is insufficient. A representative velocity profile should be constructed either from site-specific measurements or from measured profiles in a similar geological settings and depositional environment. The representative velocity profile should be consistent with one of the proposed profiles in terms of both its median and standard deviation, for the corresponding V_S30 model in the GMPE to be used, regardless of true geographical association.