Document: NRC Regulatory Guide
Document ID: cfc61809-5745-460f-8a26-13c168659924
Document Type: regulatory_guide
Title: Identification and Characterization of Seismic Sources and Determination of Safe Shutdown Earthquake Ground Motion
Source: NRC Regulatory Guide Division 1
Source URL: https://www.nrc.gov/docs/ML0037/ML003740084.pdf
Revision Date: 2023-06
Chapter: 
Section ID: RG-1.165
CFR Part: 
CFR Title: 

Content:
of the area, including the number of magnitude 5 historic earthquakes that have occurred, and thus had assumed the larger event. This analysis of the source character izations of the experts and teams resulted in the conclu sion by the analysts that a new PSHA would not be nec essary for this region because an event similar to the prehistoric earthquake had been considered in the exist ing PSHAs. A third step would be required if the site-specific geosciences investigations revealed significant new in formation that would substantially affect the estimated hazard. Modification of the seismic sources would more than likely be required if the results of the detailed local and regional site investigations indicate that a pre viously unknown seismic source is identified in the vi cinity of the site. A hypothetical example would be the recognition of geological evidence of recent activity on a fault near a nuclear power plant site in the stable conti nental region (SCR) similar to the evidence found on the Meers Fault in Oklahoma (Ref, E.2). If such a source is identified, the same approach used in the ac tive tectonic regions of the Western United States should be used to assess the largest earthquake ex pected and the rate of activity. If the resulting maximum earthquake and the rate of activity are higher than those provided by the LL.L or EPRI experts or teams regard ing seismic sources within the region in which this newly discovered tectonic source is located, it may be necessary to modify the existing interpretations by introducing the new seismic source and developing modified seismic hazard estimates for the site. The same would be true if the current ground motion mod els are a major departure from the original models. These occurrences would likely require performing a new PSHA using the updated data base, and may re quire determining the appropriate reference probability in accordance with the procedure described in Appendix B. 1.165-40 K REFERENCES E.1