Development of VS Profile Database and Proxy‐Based Models for VS30 Prediction in the Pacific Northwest Region of North America

Abstract

Models for ergodic site response are frequently conditioned on time-averaged shear-wave velocity in the upper 30 m of a site (VS30). However, in the Pacific Northwest (PNW) of North America, only 13% of the seismic recording stations contributing data to the Next Generation Attenuation-Subduction (NGA-Sub) project have measurement-based VS30 values. We present a shear-wave velocity (VS) measurement database compiled from public sources from Oregon, Washington, Alaska, and British Columbia to support the development of proxy-based methods for VS30 estimation. Using this database, we develop two proxy-based VS30 estimation procedures inspired by their successful implementation elsewhere: (1) a hybrid geology-slope approach that provides the natural log mean and standard deviation of VS30 for 18 geologic groups representative of the regional geology, including glaciation and volcanism; and (2) a geomorphic terrain-based method that provides VS30 moments for 16 global categories, 13 of which are well populated in the PNW. Of these, we recommend use of the hybrid geology-slope proxy over the terrain proxy, due to smaller dispersion of residuals and strong correlation between predictions of the two proxies. Based on these findings, we provide estimates of natural log means and standard deviations of VS30 for NGA-Sub recording stations in Ⓔ the electronic supplement to this article. In the Ⓔ electronic supplement, we also provide the estimates of basin depths (vertical depth to various VS horizons) using available 3D velocity models for the region.