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:
lower hazard estimate with an exceptionally strong technical basis. However, it is expected that large uncertainties in estimating seismic hazard in the CEUS will continue to exist in the future, and substantial delays in the licensing process will re sult from trying to justify a lower value with respect to a specific site. In general, major recomputations of the LLNL and EPRI data base are planned periodically (approximate ly every ten years), or when there is an important new finding or occurrence. The overall revision of the data base will also require a reexamination of the reference probability discussed in Appendix B. E.2 POSSIBLE SOURCES OF NEW INFORMATION THAT COULD AFFECT THE SSE Types of new data that could affect the PSHA re sults can be put in three general categories: seismic sources, earthquake recurrence models or rates of de formation, and ground motion models. E.2.1 Seismic Sources There are several possible sources of new informa tion from the site-specific investigations that could af fect the seismic hazard. Continued recording of small earthquakes, including microearthquakes, may indi cate the presence of a localized seismic source. Paleo seismic evidence, such as paleoliquefaction features or displaced Quaternary strata, may indicate the presence of a previously unknown tectonic structure or a larger amount of activity on a known structure than was pre viously considered. Geophysical studies (aeromagnet ic, gravity, and seismic reflection/refraction) may iden tify ckustal structures that suggest the presence of previously unknown seismic sources. In situ stress measurements and the mapping of tectonic structures in the future may indicate potential seismic sources. Detailed local site investigations often reveal faults or other tectonic structures that were unknown, or re veal additional characteristics of known tectonic struc tures. Generally, based on past licensing experience in the CEUS, the discovery of such features will not re quire a