Southwestern United States Ground Motion Characterization Project Description

In response to the Nuclear Regulatory Commission's March 12, 2012 50.54(f) letter, an updated probabilistic seismic hazard analysis (PSHA) based on a Senior Seismic Hazard Analysis Committee (SSHAC) Level 3 process is required to be conducted for the western United States operating nuclear power plants. A seismic hazard analysis requires a Seismic Source Characterization (SSC) and a Ground Motion Characterization (GMC). A SSHAC Level 3 process is a formal, structured process for developing the SSC and GMC for use in the PSHA. PSHA is used as a method for accounting for uncertainty in seismic design and in calculating seismic risk.

The SSHAC process provides guidelines for how the GMC study should be conducted, including: (a) identification of significant issues and data; (b) identification and solicitation of expert opinions and alternative models; (c) evaluation of the available data, expert opinions and alternative models; (d) integration of the information into GMC models that incorporate the range of technically defensible interpretations; (e) documentation of the model development; and (f) participatory peer review of the technical results and process. As described within the SSHAC guidelines, the goal of following a SSHAC process is to provide reasonable regulatory assurance that the center, body and range (CBR) of the technically defensible interpretations (TDI) in the GMC models have been adequately captured. The Southwestern United States Ground Motion Characterization (SWUS-GMC) Project will provide a new, regional ground motion model for use in conducting probabilistic seismic hazard analyses for the southwestern nuclear facilities.

The SWUS-GM Project is sponsored by Arizona Public Service (APS), Pacific Gas and Electric Company (PG&E), and Southern California Edison (SCE).