UCLA Civil and Environmental Engineering

The time-averaged shear wave velocity in the upper 30 m of a site (V_s30) is the most common site parameter used in ground motion prediction equations for the evaluation of seismic site response. It is often the case that V_s30 is not available at sites with earthquake recordings; for example in the NGA-East site database only 45 of 1149 sites have measured values of V_s30. Accordingly, estimates of V_s30 are often made on the basis of available proxies that are widely available such as ground slope, geomorphic terrain categories, and surface geology. We compile a database of 1930 measured and inferred V_s30 values in Central and Eastern North America (CENA) to test slope and geomorphology-based proxy methods. The results indicate that these existing proxy methods are biased for sites with V_s30greater than 400 m/s. Based on a careful review of geological conditions in the CENA, we propose nineteen geologic classes based on setting (i.e., glaciated or non-glaciated), age, and depositional environmental that can form the basis for geology-based proxy estimates of V_s30 as well as for simplified stratigraphic columns.