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:
it will increase the chances of (1) iden tifying evidence for unknown seismic sources that might extend close enough for earthquake ground mo tions generated by that source to affect the site and (2) confirming the PSHA's data base. Furthermore, be cause of the relatively aseismic nature of the CEUS, the area should be large enough to include as many historical and instrumentally recorded earthquakes for 1.165-31 1 11 'i t analysis as reasonably possible. The specified area of study is expected to be large enough to incorporate any previously identified sources that could be analogous to sources that may underlie or be relatively close to the site. In past licensing activities for sites in the CEUS, it has often been necessary, because of the absence of dat able horizons overlying bedrock, to extend investiga tions out many tens or hundreds of kilometers from the site along a structure or to an outlying analogous struc ture in order to locate overlying datable strata or uncon formities so that geochronological methods could be applied. This procedure has also been used to estimate the age of an undatable seismic source in the site vicin ity by relating its time of last activity to that of a similar, previously evaluated structure, or a known tectonic epi sode, the evidencý of which may be many tens or hundreds of miles away. In the Western United States it is often necessary to extend the investigations to great distances (up to hundreds of kilometers) to characterize a major tectonic structure, such as the San Gregorio-Hosgri Fault Zone and the Juan de Fuca Subduction Zone. On the other hand, in the Western United States it is not usually nec essary to extend the regional investigations that far in all directions. For example, for a site such as Diablo Canyon, which is near the San Gregorio-Hosgri Fault, it would not be necessary to extend the regional inves tigations farther east than the dominant San Andreas Fault, which is about 75 km (45 mi) from the site;