Selection of Ground Motion Records for Two Dam Sites in Oregon

Internet-based USGS’s interactive deaggregation of probabilistic seismic hazard was used to identify principal sources of earthquake hazard at two dam sites in western Oregon. The dams are located in the western margin of the Pacific Northwest region of the United States where Cascadia Subduction Zone and shallow gridded crustal earthquakes are dominant sources of earthquake hazard. For each source, the magnitude, distance, and number of standard deviations (ε) were determined to develop target acceleration response spectra using ground motion prediction equations. The selection of ε for the gridded crustal earthquakes was different for the two sites; one site is in an area of low to medium seismicity, while the other is in a more seismically active region. Based on the number, distances, and densities of epicenters of historical earthquakes relative to each site, the first site was given an ε of 0 while the second site was given an ε of 1. Once the target response spectra were developed, the selection of ground motion records was performed using standard procedures