In January 2012, the Central and Eastern United States Seismic Source Characterization for Nuclear Facilities report was jointly published by the Nuclear Regulatory Commission (NRC), Department of Energy (DOE), and the Electric Power Research Institute (EPRI) as NRC NUREG-2115, DOE/NE-0140, and EPRI 1021097. The report provided a new seismic source characterization (SSC) model for the central and eastern United States (CEUS).
The CEUS SSC model was developed using an updated earthquake catalog, a full assessment and incorporation of uncertainties, and a range of diverse technical interpretations from the larger technical community. It was prepared using a Senior Seismic Hazard Analysis Committee (SSHAC) Level 3 assessment process in accordance with guidance in NUREG/CR-6372, “Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts.”
In mid-2014, an error was identified in the published maximum magnitude (Mmax) distributions for a number of the CEUS SSC seismotectonic model zones. The error was promptly communicated to utility seismic hazard representatives, NRC and DOE representatives, and key technical experts involved in the development of the CEUS SSC model.
The objective of this report is to document reviews performed to determine the extent of condition of the Mmax error and the potential impacts of the error on seismic hazard calculations. This report documents the originally published and corrected Mmax values and the results of evaluations performed to assess impacts on the recurrence parameters, seismic hazards, and ground motion response spectra (GMRS) estimates at two sites within or near the affected seismotectonic zones.
The evaluations were performed in close consultation with the three CEUS SSC sponsors (NRC, DOE, and EPRI) and represent consensus conclusions.
A review was performed for all of the seismotectonic zone Mmax distributions using the methodologies described in Section 5.2 of the CEUS SSC report. The calculations were repeated, and a corrected set of Mmax distributions was developed. The corrected Mmax distributions were then used to reevaluate the recurrence parameters following the methods described in Section 5.3 of the CEUS SSC report.
A sensitivity study was performed to determine the impacts of the corrected Mmax distributions. Two sites were selected in or near the zones with the greatest Mmax changes. Updated seismic hazards and GMRS estimates were computed for those sites using the corrected Mmax distributions and updated recurrence parameters. Comparisons were made for each site using uniform hazard response spectra (UHRS) at 10-4 and 10-5 mean annual frequencies of exceedance as well as the GMRS.
Minor Mmax distribution corrections were identified for the PEZ-N, PEZ-W, IBEB, SLR, and MidC A through D seismotectonic zones.
Sensitivity studies at two sites showed that there are negligible impacts on the recurrence parameter results as well as calculated seismic hazard and GMRS results. These impacts are within the level of precision associated with the standard reporting of GMRS, which leads to the conclusion that it is not necessary to incorporate the corrected Mmax values into the CEUS model or the published CEUS SSC report.
Applications, Value, and Use
The evaluations in this report show that the identified Mmax errors in the CEUS SSC report produce negligible impacts on seismic hazard and GMRS calculations. Therefore, seismic hazard and GMRS calculations performed using the published Mmax distributions in the CEUS SSC report are not degraded by the Mmax changes, and the corrected Mmax values do not have to be incorporated into the CEUS model or the published CEUS SSC report.