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:
ified when excavations were made during the construction phase prior to the is suance of an operating license, and extensive additional investigations of those faults had to be carried out to properly characterize them. E.2.2 Earthquake Recurrence Models There are three elements of the source zone's recur rence models that could be affected by new site-specific data: (1) the rate of occurrence of earthquakes, (2) their maximum magnitude, and (3) the form of the recur rence model, for example, a change from truncated ex ponential to a characteristic earthquake model. Among the new site-specific information that is most likely to have a significant impact on the hazard is the discovery of paleoseismic evidence such as extensive soil lique faction features, which would indicate with reasonable confidence that much larger estimates of the maximum earthquake than those predicted by the previous studies would ensue. The paleoseismic data could also be sig nificant even if the maximum magnitudes of the pre vious studies are consistent with the paleo-earthquakes if there are sufficient data to develop return period esti mates significantly shorter than those previously used in the probabilistic analysis. The paleoseismic data could also indicate that a characteristic earthquake model would be more applicable than a truncated expo nential model. In the future, expanded earthquake catalogs will become available that will differ from the catalogs used by the previous studies. Generally, these new cata logues have been shown to have only minor impacts on estimates of the parameters of the recurrence models. Cases that might be significant include the discovery of records that indicate earthquakes in a region that had no seismic activity in the previous catalogs, the occur rence of an earthquake larger than the largest historic earthquakes, re-evaluating the largest historic earth quake to a significantly larger magnitude, or the occur rence of one or more moderate to large