Subsurface shear wave velocity characterization using P-wave seismograms in central and Eastern North America

Abstract

The time-averaged shear (S) wave velocity in the upper 30 meters of sediment (VS30) is a widely used site parameter for ground motion prediction. When unavailable from measurements, as is often the case at accelerograph stations in Central and Eastern North America (CENA), VS30 is typically estimated from proxies. We propose an alternative for CENA based on a theoretical relationship between S-wave velocity and the ratio of radial to vertical components of the compressional (P)-wave-dominated portion of the velocity time series. This method is applied to 31 CENA accelerograph sites having measured S-wave velocity profiles. Time-averaged S-wave velocities to depth z (VSZ ) from the proposed method agree well with those from measurements. We develop linear relationships between VSZ and VS30 using CENA S-wave velocity profile data. Values of VS30 established from the proposed method (including depth extrapolation) have lower dispersion relative to data (σln V =0.43) than do estimates from available CENA proxies.