Estimates of κ0 and Effects on Ground Motions in the San Francisco Bay Area


 Ground-motion studies are a key component of seismic hazard analyses and often rely on information of the source, path, and site. Extensive research has been done on each of these parameters; however, site-specific studies are of particular interest to seismic hazard studies, especially in the field of earthquake engineering, as near-site conditions can have a significant impact on the resulting ground motion at a site. There has been much focus on the constraint of site parameters and their application to seismic hazard studies, especially in the development of ground-motion models (GMMs). Kappa is an observational parameter describing the high-frequency attenuation of spectra, and its site contribution (κ0) has shown to be a good predictor of high-frequency ground motions; however, measurements are often limited. In this study, we develop a κ0 dataset for the San Francisco Bay area (SFBA) by estimating κ0 for 228 stations, and we produce a continuous regional map of κ0. We find κ0 to range between 0.003 and 0.072 s, with larger values concentrating on the east, north, and south sides of the bay, and lower values concentrating on the west side. We also evaluate the robustness of κ0 as a site parameter and find it to correlate with peak ground acceleration. These estimates of κ0 can add predictive power to GMMs, thus increasing the accuracy of predicted ground motion and improving the robustness of ground-motion studies in the SFBA.