ML003739321

Draft Regulatory Guide DG-1032 (Previously Issued as Draft DG-1015), Identification and Characterization of Seismic Sources and Determination of Safe Shutdown Earthquake Ground Motion

ML003739321
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Issue date:	02/28/1995
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U.S. NUCLEAR REGULATORY COMMISSION February 1995 OFFICE OF NUCLEAR REGULATORY RESEARCH Division I Task DG-1032 0o DRAFT REGULATORY GUIDE __Contact:

A.J. Murphy (301)415-6010 1 DRAFT REGULATORY GUIDE DG-1032 2 (Previously issued as Draft DG-1015) 3 IDENTIFICATION AND CHARACTERIZATION OF SEISMIC SOURCES AND DETERMINATION OF 4 SAFE SHUTDOWN EARTHQUAKE GROUND MOTION 5 A. INTRODUCTION 6 The NRC has recently proposed amendments to 10 CFR Part 1 eactor Site 7 Criteria," in the Federal Register on October 17, 1994 (59 FR 55). In the proposed 8 Section 100.23, "Geologic and Seismic Siting Factors," pyr), "Geological, 9 Seismological, and Engineering Characteristics," woulree i that the geological, 10 seismological, and engineering characteristics of, 1 it its environs be l~ ~ $ p a d q u a t v l a i n o h 11 investigated in sufficient scope and detail to adeate evaluation of the 12 proposed site, to provide sufficient inform~ti'

/ ort evaluations performed to 13 arrive at estimates of the Safe Shutdown E uia Ground Motion (SSE), and to permit I adequate engineering solutions to actu*P,"I,<'

4, tnal geologic and seismic effects at --5 the proposed site. Data on the v b1iarb)4ro9u'und motion, tectonic surface deformation, 16 nontectonic deformation, earthqu 'Ie r rence rates, fault geometry and slip rates, 17 site foundation material, and"'sei s y induced floods, water waves, and other siting 18 factors would be obtained by',revi" ing pertinent literature and carrying out field 19 investigations.

20 In the props,,,d,, Section 100.23, paragraph (d), "Geologic and Seismic Siting 21 Factors," would I d r 1 ,,hat the geologic and seismic siting factors considered for 22 design , etrmination of the SSE for the site, the potential for surface 23 tectonic and 1 noni ctonic deformations, the design bases for seismically induced floods 24 and wa,,r ,wa',a,' 'and other design conditions.

This regulatory guide is being issued in draft form to involve the public in the early stages of the development of a regulatory position in this area. It has not received complete staff review and does not represent an official NRC staff position.

Public comments are being solicited on the draft guide (including any implementation schedule) and its associated regulatory analysis or value/impact statement.

Comments should be accompanied by appropriate supporting data. Written comments may be submitted to the Rules Review and Directives Branch, DFIPS, Office of Administration, U.S. Nuclear Regulatory Commission, Washington, DC 20555. Copies of comments received may be examined at the NRC Public Document Room, 2120 L Street NW., Washington, DC. Comments will be most helpful if received by May 12, 1995. Requests for single copies of draft guides (which may be reproduced) or for placement on an automatic distribution list for single copies of future guides in specific divisions should be made in writing to the U.S. Nuclear Regulatory Commission, Washington, DC 20555, Attention:

Office of Administration, Distribution and Mail Services Section.

1 In the proposed Section 100.23, paragraph (d)(1), "Determination of the 2 Safe Shutdown Earthquake Ground Motion," would require that uncertainty 3 inherent in estimates of the SSE be addressed through an appropriate analysis, 4 such as a probabilistic seismic hazard analysis or suitable sensitivity 5 analysis.

6 This guide is being developed to provide general guidance on procedures 7 acceptable to the NRC staff to (1) conduct geological, geophysical, 8 seismological, and geotechnical investigations, (2) identify and characterize 9 seismic sources, (3) conduct probabilistic seismic hazard analyses, and (4) 10 determine the SSE for satisfying the requirements of the proposed Section 11 100.23. 12 This guide contains several appendices that address the objectives 13 stated above. Appendix A contains a list of definitions of pertinent terms. 14 Appendix B describes the procedure used to determine the reference probability 15 for the SSE exceedance level. Appendix C discusses the development of a 16 seismic hazard information base and the determination of the probabilistic 17 ground motion level and controlling earthquakes.

Appendix D discusses site 18 specific geological, seismological, and geophysical investigations.

Appendix 19 E describes a method to confirm the adequacy of existing seismic sources and 20 source parameters as the basis for determining the SSE for a site. Appendix F 21 describes procedures to determine the SSE. 22 Regulatory guides are issued to describe and make available to the 23 public such information as methods acceptable to the NRC staff for 24 implementing specific parts of the Commission's regulations, techniques used 25 by the staff in evaluating specific problems or postulated accidents, and 26 guidance to applicants.

Regulatory guides are not substitutes for 27 regulations, and compliance with regulatory guides is not required.

28 Regulatory guides are issued in draft form for public comment to involve the 29 public in the early stages of developing the regulatory positions.

Draft 30 regulatory guides have not received complete staff review and do not represent 31 official NRC staff positions.

32 Any information collection activities mentioned in this regulatory guide 33 are contained as requirements in the proposed amendments to 10 CFR Part 100 34 that would provide the regulatory basis for this guide. The proposed amend 35 ments have been submitted to the Office of Management and Budget for clearance 36 that may be appropriate under the Paperwork Reduction Act. Such clearance, if 2 I obtained, would also apply to any information collection activities mentioned

' 2 in this guide. 3 B. DISCUSSION 4 BACKGROUND 5 A probabilistic seismic hazard analysis (PSHA) has been identified in 6 the proposed Section 100.23 as one of the means to address uncertainties in 7 estimates of the SSE. The proposed rule further recognizes that the nature of 8 uncertainty and the appropriate approach to account for it depend on the 9 tectonic regime and parameters such as the knowledge of seismic sources, the 10 existence of historical and recorded data, and the understanding of tectonics.

11 Therefore, methods other than probabilistic methods such as sensitivity 12 analyses may be adequate for some sites to account for uncertainties.

13 Appendix A, "Seismic and Geologic Siting Criteria for Nuclear Power 14 Plants," to 10 CFR Part 100 is primarily based on a deterministic methodology.

15 Past licensing experience in applying Appendix A has demonstrated the need to __ 16 formulate procedures that quantitatively incorporate uncertainty in the 17 evaluation of seismic hazards. A deterministic representation of seismic 18 sources and ground motions at a site does not explicitly provide a 19 quantitative representation of the uncertainties in scientific interpretations 20 of geological, seismological, and geophysical data. 21 Probabilistic procedures were developed during the past 10-15 years 22 specifically for nuclear power plant seismic hazard assessments in the Central 23 and Eastern United States (CEUS) (the area east of the Rocky Mountains), also 24 referred to as the Stable Continent Region (SCR). These procedures provide a 25 structured approach for decisionmaking with respect to the SSE when performed 26 together with site-specific investigations.

A PSHA provides a framework to 27 address the uncertainties associated with the identification and 28 characterization of seismic sources by incorporating multiple interpretations 29 of seismological parameters.

Within the framework of a probabilistic 30 analysis, uncertainties in the characterization of seismic sources and ground 31 motions are identified and incorporated in the procedure at each step of the 32 process for estimating the SSE. The role of site-specific regional and site 33 geological, seismological, and geophysical investigations is to develop 34 geosciences information about the site for use in the detailed design of the 3 1 facility, as well as to ensure that the seismic hazard analysis is based on 2 up-to-date information.

3 Experience in performing seismic hazard evaluations in active plate 4 margin regions in the Western United States (for example, the San Gregorio 5 Hosgri fault zone and the Cascadia Subduction Zone) has also identified 6 uncertainties associated with the characterization of seismic sources (Refs. 7 1, 2, and 3). Sources of uncertainty include fault geometry, rupture 8 segmentation, rupture extent, seismic-activity rate, and earthquake occurrence 9 modeling.

As is the case for sites in the CEUS, alternative hypotheses and 10 parameters must be considered to account for these uncertainties.

11 Uncertainties associated with the identification and characterization of 12 seismic sources in tectonic environments in both the CEUS and the Western 13 United States should be evaluated.

Therefore, the same basic approach can be 14 applied to determine the SSE. 15 APPROACH 16 The process to determine the SSE at a site should include: 17 18 1. Site- and region-specific geological, seismological, geophysical 19 and geotechnical investigations, and 20 2. A probabilistic seismic hazard assessment.

21 CENTRAL AND EASTERN UNITED STATES 22 The CEUS is considered to be that part of the United States east of the 23 Rocky Mountain front, or east of Longitude 1050 West (Refs. 4 and 5). To 24 determine the SSE in the CEUS, an accepted PSHA methodology with a range of 25 credible alternative input interpretations should be used. For sites in the 26 CEUS, the seismic hazard methods, the data developed, and seismic sources 27 identified by Lawrence Livermore National Laboratory (LLNL) (Refs. 4, 5, and 28 6) and the Electric Power Research Institute (EPRI) (Ref. 7) have been 29 reviewed and accepted by the staff. The LLNL and EPRI studies developed data 30 bases and scientific interpretations of available information and determined 31 seismic sources and source characterizations for the CEUS (e.g., earthquake 32 occurrence rates, estimates of maximum magnitude).

4 1 In the CEUS, characterization of seismic sources is more problematic S2 than in the active plate-margin region because there is generally no clear 3 association between seismicity and known tectonic structures or near-surface 4 geology. In general, the observed geologic structures were generated in 5 response to tectonic forces that no longer exist and bear little or no 6 correlation with current tectonic forces. Thus, there is greater uncertainty 7 in making judgments about the CEUS than there is for active plate margin 8 regions, and it is important to account for this uncertainty by the use of 9 multiple alternative models. 10 The identification of seismic sources and reasonable alternatives in the 11 CEUS considers hypotheses presently advocated for the occurrence of 12 earthquakes in the CEUS (for example, the reactivation of favorably oriented 13 zones of weakness or the local amplification and release of stresses 14 concentrated around a geologic structure).

In tectonically active areas of 15 the CEUS, such as the New Madrid Seismic Zone, where geological, 16 seismological, and geophysical evidence suggest the nature of the sources that 17 generate the earthquakes in that region, it may be more appropriate to 18 evaluate those seismic sources by using procedures similar to those normally 19 applicable in the Western United States. 20 WESTERN UNITED STATES 21 The Western United States is considered to be that part of the United 22 States that lies west of the Rocky Mountain front, or west of approximately 23 1050 West Longitude.

For the Western United States, an information base of 24 earth science data and scientific interpretations of seismic sources and 25 source characterizations (e.g., geometry, seismicity parameters) comparable to 26 the CEUS as documented in the LLNL and EPRI studies does not exist. For this 27 region, specific interpretations on a site-by-site basis should be applied 28 (Ref. 1). 29 The active plate margin region includes coastal California, Oregon, and 30 Washington.

For the active plate margin region, where earthquakes can often 31 be correlated with known tectonic structures, those structures should be 32 assessed for their earthquake and surface deformation potential.

In this 33 region, at least three types of sources exist: (1) faults that are known to be 34 at or near the surface, (2) buried (blind) sources that may often be 35 manifested as folds at the earth's surface, and (3) subduction zone sources, 5 I such as those in the Pacific Northwest.

The nature of surface faults can be 2 evaluated by conventional surface and near-surface investigation techniques to 3 assess strike, geometry, sense of displacements, length of rupture, Quaternary 4 history, etc. 5 Buried (blind) faults are often accompanied by coseismic surficial 6 deformation such as folding, uplift, or subsidence.

The surface expression of 7 blind faulting can be detected by mapping the uplifted or down-dropped 8 geomorphological features or stratigraphy, survey leveling, and geodetic 9 methods. The nature of the structure at depth can often be evaluated by core 10 borings and geophysical techniques.

11 United States subduction zones are located in the Pacific Northwest and 12 Alaska. Seismic sources associated with subduction zones are sources within 13 the overriding plate, the interface between the subducting and overriding 14 lithospheric plates, and intraslab sources in the interior of the downgoing 15 oceanic slab. The characterization of subduction zone seismic sources 16 includes consideration of the following:

three-dimensional geometry of the 17 subducting plate, rupture segmentation of subduction zones, geometry of 18 historical ruptures, constraints on the up-dip and down-dip extent of rupture, 19 and comparisons with other subduction zones worldwide.

20 The Basin and Range region of the Western United States, and to a lesser 21 extent the Pacific Northwest and the Central United States, include temporal 22 clustering of earthquakes.

Temporal clustering is best exemplified by the 23 rupture histories within the Wasatch fault zone in Utah and the Meers fault in 24 central Oklahoma, where several large late Holocene coseismic faulting events 25 occurred at relatively close intervals (hundreds to thousands of years) that 26 were preceded by long periods of quiescence that lasted thousands to tens of 27 thousand years. Temporal clustering should be considered in these regions or 28 wherever paleoseismic evidence indicates that it has occurred.

29 C. REGULATORY POSITION 30 1. GEOLOGICAL, GEOPHYSICAL, SEISMOLOGICAL, AND GEOTECHNICAL INVESTIGATIONS 31 1.1 Comprehensive geological, seismological, geophysical, and 32 geotechnical investigations of the site and regions around the site should be 33 performed.

These investigations are performed primarily to gather information 34 needed to confirm the suitability of the site and to gather data pertinent to 6 1 the safe design and construction of the nuclear power plant. Appropriate 2 geological, seismological, and geophysical investigations are described in 3 Appendix D to this draft guide. Geotechnical investigations are described in 4 Regulatory Guide 1.132, "Site Investigations for Foundations of Nuclear Power 5 Plants" (Ref. 8). Another important purpose for the site-specific 6 investigations is to determine whether there are new data or interpretations 7 that are not adequately incorporated in the existing PSHA databases.

Appendix 8 E describes a method to evaluate new information derived from the site 9 specific investigations in the context of the PSHA. 10 These investigations should be performed at four levels, with the degree 11 of their detail based on distance from the site, the nature of the Quaternary 12 tectonic regime, the geological complexity of the site and region, the 13 existence of potential seismic sources, the potential for surface 14 deformations, etc. The levels of investigation are: 15 1. Regional geological and seismological investigations such as 16 geological reconnaissances and literature reviews should be 17 conducted within a radius of 320 km (200 miles) of the site 18 to identify seismic sources (seismogenic and capable 19 tectonic sources).

20 2. Geological, seismological, and geophysical investigations 21 should be carried out within a radius of 40 km (25 miles) in 22 greater detail than the regional investigations to identify 23 and characterize the seismic and surface deformation 24 potential of any capable tectonic sources and the seismic 25 potential of seismogenic sources, or to demonstrate that 26 such structures are not present. Sites with capable 27 tectonic or seismogenic sources within a radius of 40 km (25 28 miles) may require more extensive geological and 29 seismological investigations and analyses (similar in detail 30 to investigations and analysis usually preferred within an 31 8-km (5-mile) radius).

32 3. Detailed geological, seismological, geophysical, and 33 geotechnical investigations should be conducted within a 34 radius of 8 km (5 miles) of the site, as appropriate, to 7 I evaluate the potential for tectonic deformation at or near 2 the ground surface and to assess the ground motion 3 transmission characteristics of soils and rocks in the site 4 vicinity.

Investigations should include monitoring by a 5 network of seismic stations.

6 4. Very detailed geological, geophysical, and geotechnical 7 engineering investigations should be conducted within the 8 site (radius of approximately 1 km) to assess specific soil 9 and rock characteristics as described in Regulatory Guide 10 1.132 (Ref. 8). 11 1.2 The areas of investigations may be expanded beyond those specified 12 above in regions that include capable tectonic sources, relatively high 13 seismicity, or complex geology.

14 1.3 It should be demonstrated that deformation features discovered 15 during construction, particularly faults, do not have the potential to 16 compromise the safety of the plant. The two-step licensing practice of 17 requiring applicants to acquire a Construction Permit (CP), and then during 18 construction apply for an Operating License (OL), has been expanded to allow 19 for an alternative procedure.

The requirements and procedures applicable to 20 NRC's issuance of combined licenses for nuclear power facilities are in 21 10 CFR 52.71. Applying the combined licensing procedure to a site could 22 result in the award of a license prior to construction.

During the 23 construction of nuclear power plants licensed in the past two decades, 24 previously unknown faults were often discovered in site excavations.

Before 25 an OL would be issued, it was necessary to demonstrate that the faults in the 26 excavation posed no hazard to the facility.

Under the combined license 27 procedure, these kinds of features should be mapped and assessed as to their 28 rupture and ground motion generating potential while the excavations' walls 29 and bases are exposed. Therefore, a commitment should be made, in documents 30 (Safety Analysis Reports) supporting the license application, to notify the 31 NRC staff when excavations are open for inspection and to geologically map all 32 excavations.

8 1 1.4 Sufficient data to clearly justify all conclusions should be 2 presented.

Because engineering solutions cannot always be demonstrated for 3 the effects of permanent ground displacement, it is prudent to avoid a site 4 that has a potential for surface or near-surface deformation.

Such sites 5 normally will require extensive additional investigations.

6 1.5 For the site and the area surrounding the site, the lithologic, 7 stratigraphic, hydrologic, and structural geologic conditions should be 8 characterized.

The investigations should include the measurement of the 9 static and dynamic engineering properties of the materials underlying the site 10 and an evaluation of physical evidence concerning the behavior during prior 11 earthquakes of the surficial materials and the substrata underlying the site. 12 The properties needed to assess the behavior of the underlying material during 13 earthquakes, including the potential for liquefaction, and the characteristics 14 of the underlying material in transmitting earthquake ground motions to the 15 foundations of the plant (such as seismic wave velocities, density, water 16 content, porosity, elastic moduli, and strength) should be measured.

17 2. SEISMIC SOURCES SIGNIFICANT TO THE SITE SEISMIC HAZARD 18 2.1 A seismic source is a general term referring to both seismogenic 19 sources and capable tectonic sources. The main distinction between these two 20 types of seismic sources is that a seismogenic source would not cause surface 21 displacement, but a capable tectonic source causes surface or near-surface 22 displacement.

23 Identification and characterization of seismic sources should be based 24 on regional and site geological and geophysical data, historical and 25 instrumental seismicity data, the regional stress field, and geological 26 evidence of prehistoric earthquakes.

Investigations to identify seismic 27 sources are described in Appendix D. The bases for the identification of 28 seismic sources should be documented.

A general list of characteristics to be 29 evaluated for a seismic source is presented in Appendix D. 30 2.2 As part of the seismic source characterization, the seismic 31 potential (magnitude and recurrence rate) for each source should be 32 determined.

9 1 2.2.1 For sites located in the CEUS, the seismic sources and 2 data that have been accepted by the NRC staff in past licensing decisions may 3 be used to estimate seismic potential.

It is necessary to use a variety of 4 approaches to estimate the maximum magnitude for a seismic source in the CEUS 5 because there is uncertainty about the underlying causes of earthquakes 6 because of lack of active surface faulting.

Also, there is a short historical 7 record and low seismicity rate. The determination of the maximum magnitude 8 for each identified seismic source is based on the maximum historical 9 earthquake, the pattern and rate of seismic activity, the Quaternary (2 10 million years and younger) characteristics of the source, the current stress 11 regime (and how it aligns with the known tectonic structures in the source), 12 and paleoseismic data. These seismic sources and their parameters should be 13 used to judge the adequacy of seismic sources and parameters used in the LLNL 14 or EPRI PSHA. 15 2.2.2 For sites located within the Western United States, 16 earthquakes can often be associated with known tectonic structures.

For 17 faults, the maximum magnitude earthquake is related to the characteristics of 18 the estimated rupture, such as the length or the amount of fault displacement.

19 The following empirical relations can be used to estimate the maximum 20 magnitude from fault behavioral data and also to estimate the amount of 21 displacement that might be expected for a given magnitude.

It is prudent to 22 use several of these different relations to obtain an estimate of the 23 earthquake magnitude.

24 1. Surface rupture length versus magnitude (Refs. 9-12). 25 2. Subsurface rupture length versus magnitude (Ref. 13). 26 3. Rupture area versus magnitude (Ref. 14). 27 4. Maximum and average displacement versus magnitude (Ref. 13). 28 5. Slip rate versus magnitude (Ref. 15). 29 Fault hazard analyses in the Western United States using these and other 30 methods should consider the frequency of occurrence and calculated slip rates 31 on faults based on the geochronology of strata and crosscutting relationships.

10 1 Additionally, the phenomenon of temporal clustering should be considered when -2 there is geological evidence of its past occurrence.

3 2.2.3 For sites in the Pacific Northwest and Alaska, the maximum 4 magnitude must be assessed for subduction zone seismic sources. Worldwide 5 observations indicate that the largest known earthquakes are associated with 6 the plate interface, although intraslab earthquakes also have large 7 magnitudes.

The assessment of plate interface earthquakes can be based on 8 estimates of the expected dimensions of rupture or analogies to other 9 subduction zones worldwide.

10 3. PROBABILISTIC SEISMIC HAZARD ANALYSIS (PSHA) PROCEDURES 11 A PSHA should be performed for the site as it allows the use of multiple 12 models to estimate the likelihood of earthquake ground motions occurring at a 13 site, and a PSHA systematically takes into account uncertainties that exist in 14 various parameters (such as seismic sources, maximum earthquakes, and ground 15 motion attenuation).

Alternative hypotheses are considered in a quantitative 16 fashion in a PSHA. The PSHA can be used to evaluate the sensitivity to the 17 varying significant parameters and to identify the relative contribution of 18 each seismic source to the hazard. 19 The following steps describe a PSHA procedure that is acceptable to the 20 NRC staff. The details of the calculational aspects of the PSHA are included 21 in Appendix C. 22 1. Perform regional and site geological, seismological, and 23 geophysical investigations in accordance with Regulatory 24 Position 1 and Appendix D. 25 2. For CEUS sites, perform an evaluation of LLNL or EPRI 26 seismic sources in accordance with Appendix E to determine 27 whether they are consistent with the site-specific data 28 gathered in Step 1 or require updating.

The PSHA should 29 only be updated if it will lead to higher hazard estimates.

30 3. Perform the LLNL or EPRI probabilistic seismic hazard 31 analysis (for CEUS sites only) using original or updated 11 I sources as determined in Step 2 or a site-specific PSHA for 2 sites in other parts of the country. The ground motion 3 estimates should be made for rock conditions in the free 4 field or by assuming hypothetical rock conditions for a 5 nonrock site to develop the seismic hazard information base 6 discussed in Appendix C. 7 4. Using the reference probability (IE-5 per yr) described in 8 Appendix B, which is applicable to all sites, determine 5% 9 of critically damped median spectral ground motion levels 10 for the average of 5 and 10 Hz, Sa_1 0 , and for the average 11 of 1 and 2.5 Hz, Sa.25. Appendix B discusses situations in 12 which an alternative reference probability may be more 13 appropriate.

The alternative reference probability is 14 reviewed and accepted on a case-by-case basis. Appendix B 15 also describes a procedure that should be used when a 16 general revision to the reference probability is needed. 17 5. Deaggregate the hazard in accordance with Appendix C to 18 determine the controlling earthquakes (i.e., magnitudes and 19 distances).

Document the hazard information base as 20 discussed in Appendix C. 21 4. PROCEDURES FOR DETERMINING THE SSE 22 After completing the PSHA (See Regulatory Position 3) and determining 23 controlling earthquakes, the following procedure should be used to determine 24 the SSE. Appendix F contains an additional discussion of some of the 25 characteristics of the SSE. 26 1. With the controlling earthquakes determined as described in 27 Regulatory Position 3 and by using the procedures in Draft 28 Standard Review Plan (SRP) Section 2.5.2 (which may include 29 the use of ground motion models not included in the 30 probabilistic seismic hazard analysis but that are more 31 appropriate for the source, region, and site under 32 consideration or that represent the latest scientific 12 1 development), develop 5% of critical damping response 2 spectral shapes for the actual or assumed rock conditions.

3 2. Use S,.-1o to scale the response spectrum shape corresponding 4 to the controlling earthquake.

If, as described in Appendix 5 C, there is a controlling earthquake for S.,,..,5 determine 6 that the S,.5_Io scaled response spectrum also envelopes the 7 ground motion spectrum for the controlling earthquake for 8 S°.,_2. 5 Otherwise, modify the shape to envelope the low 9 frequency spectrum or use two spectra in the following 10 steps. See additional discussion in Appendix F. For the 11 rock site go to Step 4. 12 3. For the nonrock sites, perform a site-specific soil 13 amplification analysis considering uncertainties in site 14 specific geotechnical properties and parameters to determine 15 response spectra at the free ground surface in the free 16 field for the actual site conditions.

17 4. Compare the smooth SSE spectrum or spectra used in design 18 (e.g., 0.3g, broad-band spectra used in Advanced Light Water 19 Reactor designs) with the spectrum or spectra determined in 20 Step 2 for rock sites or determined in Step 3 for the 21 nonrock sites to assess the adequacy of the SSE spectrum or 22 spectra.

23 To obtain an adequate design SSE based on the site 24 specific response spectrum or spectra, develop a smooth 25 spectrum or spectra or use a standard broad band shape that 26 envelopes the spectra of Step 2 or Step 3. 27 Additional discussion of this step is provided in 28 Appendix F. 29 D. IMPLEMENTATION 30 The purpose of this section is to provide guidance to applicants and 31 licensees regarding the NRC staff's plans for using this regulatory guide.13 1 This proposed revision has been released to encourage public 2 participation in its development.

Except in those cases in which the 3 applicant proposes an acceptable alternative method for complying with the 4 specified portions of the Commission's regulations, the method to be described 5 in the active guide reflecting public comments will be used in the evaluation 6 of applications for construction permits, operating licenses, early site 7 permits, or combined licenses submitted after the implementation date to be 8 specified in the active guide. This guide would not be used in the evaluation 9 of an application for an operating license submitted after the implementation 10 date to be specified in the active guide if the construction permit was issued 11 prior to that date.14 REFERENCES 2 1. Pacific Gas and Electric Company, "Final Report of the Diablo Canyon 3 Long Term Seismic Program; Diablo Canyon Power Plant," Docket Nos. 50 4 275 and 50-323, 1988.1 5 2. H. Rood et al., "Safety Evaluation Report Related to the Operation of 6 Diablo Canyon Nuclear Power Plant, Units I and 2," NUREG-0675, 7 Supplement No. 34, USNRC, June 1991.2 8 3. Letter from G. Sorensen, Washington Public Power Supply System, to 9 Document Control Branch, USNRC.

Subject:

Nuclear Project No. 3, 10 Resolution of Key Licensing Issues, Response; February 29, 1988.' 11 4. D.L. Bernreuter et al., "Seismic Hazard Characterization of 69 Nuclear 12 Plant Sites East of the Rocky Mountains," NUREG/CR-5250, Volumes 1-8, 13 January 1989.2 14 5. P. Sobel, "Revised Livermore Seismic Hazard Estimates for Sixty-Nine 15 Nuclear Power Plant Sites East of the Rocky Mountains," NUREG-1488, 16 USNRC, April 1994.2 17 6. J.B. Savy et al., "Eastern Seismic Hazard Characterization Update," 18 UCRL-ID-115111, Lawrence Livermore National Laboratory, June 1993.' 19 (Accession number 9310190318 in NRC's Public Document Room) 20 'Copies are available for inspection or copying for a fee from the NRC 21 Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing 22 address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax 23 (202)634-3343.

24 2Copies are available for inspection or copying for a fee from the NRC 25 Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing 26 address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax 27 (202)634-3343.

Copies may be purchased at current rates from the U.S. 28 Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 29 (telephone (202)512-2249);

or from the National Technical Information Service 30 by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161.15 1 1 7. Electric Power Research Institute, "Probabilistic Seismic Hazard 2 Evaluations at Nuclear Power Plant Sites in the Central and Eastern 3 United States," NP-4726, All Volumes, 1989-1991.

4 8. USNRC, "Site Investigations for Foundations of Nuclear Power Plants," 5 Regulatory Guide 1.132.2 6 9. D.B. Slemmons, "Faults and Earthquake Magnitude," U.S. Army Corps of 7 Engineers, Waterways Experiment Station, Misc. Papers S-73-1, Report 6, 8 1977. 9 10. D.B. Slemmons, "Determination of Design Earthquake Magnitudes for 10 Microzonation," Proceedings of the Third International Microzonation 11 Conference, University of Washington, Seattle, Volume 1, pp. 119-130, 12 1982.' 13 11. M.G. Bonilla, H.A. Villabobos, and R.E. Wallace, "Exploratory Trench 14 Across the Pleasant Valley Fault, Nevada," Professional Paper 1274-B, 15 U.S. Geological Survey, pp. Bl-B14, 1984. 16 12. S.G. Wesnousky, "Relationship Between Total Affect, Degree of Fault 17 Trace Complexity, and Earthquake Size on Major Strike-Slip Faults in 18 California" (Abs), Seismological Research Letters, Volume 59, No. 1, 19 p. 3, 1988. 20 13. D.L. Wells, and K.J. Coppersmith, "New Empirical Relationships Among 21 Magnitude, Rupture Length, Rupture Width, Rupture Area, and Surface 22 Displacement," Bulletin of the Seismological Society of America, Volume 23 84, August 1994. 24 14. M. Wyss, "Estimating Maximum Expectable Magnitude of Earthquakes from 25 Fault Dimensions," Geology, Volume 7 (7), pp. 336-340, 1979. 26 15. D.P. Schwartz and K.J. Coppersmith, "Seismic Hazards: New Trends in 27 Analysis Using Geologic Data," Active Tectonics, National Academy Press, 28 Washington DC, pp. 215-230, 1986.16 1 APPENDIX A S2 DEFINITIONS 3 Controlling Earthauakes

-- In the probabilistic seismic hazard analysis 4 (PSHA), the controlling earthquakes are characterized as mean magnitudes and 5 distances derived from a deaggregation analysis of the PSHA. The controlling 6 earthquakes are the earthquakes used to estimate ground motions at the site. 7 There may be several controlling earthquakes for a site. 8 Intensity

-- The intensity of an earthquake is a measure of vibratory ground 9 motion effects on humans, human-built structures, and on the earth's surface 10 at a particular location.

Intensity is described by a numerical value on the 11 Modified Mercalli scale. 12 Magnitude

-- An earthquake's magnitude is a measure of the strength of the 13 earthquake as determined from seismographic observations.

14 Nontectonic Deformation

-- Nontectonic deformation is distortion of surface or 15 near-surface soils or rocks that is not directly attributable to tectonic 16 activity.

Such deformation includes features associated with subsidence, 17 karst terrane, glaciation or deglaciation, and growth faulting.

18 Safe Shutdown Earthquake Ground Motion (SSE) -- The Safe Shutdown Earthquake 19 Ground Motion is the vibratory ground motion for which certain structures, 20 systems, and components would be designed, pursuant to the proposed Appendix S 21 to 10 CFR Part 50, to remain functional.

22 Seismic Source -- A "seismic source" is a general term referring to both 23 seismogenic sources and capable tectonic sources.

24 Capable Tectonic Source -- A "capable tectonic source" is a tectonic 25 structure that can generate both vibratory ground motion and tectonic 26 surface deformation such as faulting or folding at or near the earth's 27 surface in the present seismotectonic regime. It is described by at 28 least one of the following characteristics:

A-I 1 a. Presence of surface or near-surface deformation of landforms or 2 geologic deposits of a recurring nature within the last 3 approximately 500,000 years or at least once in the last 4 approximately 50,000 years. 5 b. A reasonable association with one or more large earthquakes or 6 sustained earthquake activity that are usually accompanied by 7 significant surface deformation.

8 c. A structural association with a capable tectonic source having 9 characteristics of section a in this paragraph such that movement 10 on one could be reasonably expected to be accompanied by movement 11 on the other. 12 In some 'cases, the geological evidence of past activity at or near 13 the ground surface along a particular capable tectonic source may be 14 obscured at a particular site. This might occur, for example, at a site 15 having a deep overburden.

For these cases, evidence may exist elsewhere 16 along the structure from which an evaluation of its characteristics in 17 the vicinity of the site can be reasonably based. Such evidence is to 18 be used in determining whether the structure is a capable tectonic 19 source within this definition.

20 Notwithstanding the foregoing paragraphs, structural association 21 of a structure with geological structural features that are geologically 22 old (at least pre-Quaternary), such as many of those found in the 23 Central and Eastern region of the United States will, in the absence of 24 conflicting evidence, demonstrate that the structure is not a capable 25 tectonic source within this definition.

26 Seismogenic Source -- A "seismogenic source" is a portion of the earth 27 that has uniform earthquake potential (same expected maximum earthquake 28 and frequency of recurrence) distinct from other regions. A seismogenic 29 source will generate vibratory ground motion but is assumed not to cause 30 surface displacement.

Seismogenic sources cover a wide range of 31 possibilities from a well-defined tectonic structure to simply a large 32 region of diffuse seismicity (seismotectonic province) thought to be 33 characterized by the same earthquake recurrence model. A seismogenic A-2 I source is also characterized by its involvement in the current tectonic 2 regime (the Quaternary, or approximately the last 2 million years). 3 Stable Continental Region -- A "stable continental region" (SCR) is composed 4 of continental crust, including continental shelves, slopes, and attenuated 5 continental crust, and excludes active plate boundaries and zones of currently 6 active tectonics directly influenced by plate margin processes.

It exhibits 7 no significant deformation associated with the major Mesozoic-to-Cenozoic 8 (last 240 million years) orogenic belts. It excludes major zones of Neogene 9 (last 25 million years) rifting, volcanism, or suturing.

10 Tectonic Structure

-- A tectonic structure is a large-scale dislocation or 11 distortion, usually within the earth's crust. Its extent may be on the order 12 of tens of meters (yards) to kilometers (miles).A-3 1 APPENDIX B 2 REFERENCE PROBABILITY FOR THE EXCEEDANCE LEVEL 3 OF THE SAFE SHUTDOWN EARTHQUAKE GROUND MOTION 4 B.1 INTRODUCTION 5 This appendix describes the procedure used by the NRC staff to determine 6 the reference probability, an annual probability of exceeding the Safe 7 Shutdown Earthquake Ground Motion (SSE) at future nuclear power plant sites, 8 that is acceptable to the NRC staff. The reference probability is used in 9 Appendix C in conjunction with the probabilistic seismic hazard analysis 10 (PSHA). 11 B.2 REFERENCE PROBABILITY FOR THE SSE 12 The reference probability is the annual probability level such that 50% 13 of a set of currently operating plants (selected by the NRC, see Table B.1) 14 has an annual median probability of exceeding the SSE below this level. The 15 reference probability is determined for the annual probability of exceeding 16 the average of the 5 and 10 Hz SSE response spectrum ordinates.

17 B.3 PROCEDURE TO DETERMINE THE REFERENCE PROBABILITY 18 The following procedure was used to determine the reference probability 19 and should be used in the future if general revisions to PSHA methods or data 20 bases result in significant changes in hazard predictions for the selected 21 plant sites in Table B.1. 22 The reference probability is calculated using the Lawrence Livermore 23 National Laboratory (LLNL) methodology and results (Refs. B.1 and B.2) but is 24 also considered applicable for the Electric Power Research Institute (EPRI) 25 study (Refs. B.3 and B.4). This reference probability is also to be used in 26 conjunction with sites not in the Central and Eastern United States (CEUS) and 27 for sites for which LLNL and EPRI methods and data have not been used or are 28 not available.

B-I I The final SSE ground motion at a higher reference probability may be 2 more appropriate and acceptable' considering the slope characteristics of the 3 site hazard, the overall uncertainty in calculations (i.e., differences 4 between mean and median hazard estimates), and the knowledge of the seismic 5 sources that contribute to the hazard. Reference B.4 includes a procedure to 6 determine an alternative reference probability on the risk-based 7 considerations; its application will also be reviewed on a case-by-case basis. 8 B.3.1 Selection of Current Plants for Reference Probability Calculations 9 Table B.1 identifies plants, along with their site characteristics, used 10 in calculating the reference probability.

These plants represent relatively 11 recent designs that used Regulatory Guide 1.60, "Design Response Spectra for 12 Seismic Design of Nuclear Power Plants" (Ref. B.5), or similar spectra as 13 their design bases. The use of these plants should ensure an adequate level 14 of conservatism in determining an SSE consistent with recent licensing 15 decisions.

16 B.3.2 Procedure To Establish Reference Probability 17 Step 1 18 Using an accepted methodology, calculate the seismic hazard results for 19 the site for spectral responses at 5 and 10 Hz (as stated earlier, the staff 20 used the LLNL methodology and associated results as documented in Refs. B.1 21 and B.2). 22 23 Step 2 24 Calculate the median composite annual probability of exceeding the SSE 25 for spectral responses at 5 and 10 Hz using median hazard estimates.

The 26 composite annual probability is determined as: 27 Composite probability

= 1/2(al) + 1/2(a2) 28 ' The use of a higher reference probability will be reviewed and accepted on 29 a case-by-case basis.B-2 I where al and a2 represent median annual probabilities of exceeding SSE 2 spectral ordinates at 5 and 10 Hz, respectively.

The procedure is illustrated 3 in Figure B-i. 4 Step 3 5 Figure B-2 illustrates the distribution of median probabilities of 6 exceeding the SSEs for the plants in Table B.1 based on the LLNL methodology 7 (Refs. B.1 and B.2). The reference probability is simply the median 8 probability of this distribution.

9 For the LLNL methodology, this reference probability is IE-5/yr and, as 10 stated earlier, is also to be used in conjunction with the current EPRI 11 methodology (Ref. B.3) or for sites not in the CEUS.B-3 I B-4 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 Table B.1 Plants/Sites Used in Determining Reference Probability Plant/Site Name f Soil Condition Primary/Secondary*

Limerick Rock Shearon Harris Sand -S1 Braidwood Rock River Bend Deep Soil Wolf Creek Rock Watts Bar Rock Voqtle Deep Soil Seabrook Rock Three Mile Is. Rock/Sand

-S1 Catawba Rock/Sand

-S1 Hope Creek Deep Soil McGuire Rock North Anna Rock/Sand

-S1 Summer Rock/Sand

-S1 Beaver Valley Sand -S1 Byron Rock Clinton Till -T3 Davis Besse Rock LaSalle Till -T2 Perry Rock Bellefonte Rock Callaway Rock/Sand

-S1 Commanche Peak Rock Grand Gulf Deep Soil South Texas Deep Soil Waterford Deep Soil Millstone 3 Rock Nine Mile Point Rock/Sand

-S1 Brunswick Sand -S1

• If two soil conditions are listed, the first is the primary and the second is the secondary soil condition.

See Ref. B.1 for a discussion of soil conditions.

W x L) 0 Q) L) '4 0 o4-) 0 S.-onse e Spectral Response Figure B.1 Procedure to Compute Probability of Exceeding Design Basis Comp. Prob. = 1/2(al) + 1/2(a2) B-5 5 Hz Spectral Resp SI Median Hazard Curv C1) N = 10 Hz Spectral Response " Median Hazard Curve CV).al a2 L.q L0) QA '-.1 2 3 II I LLNL Median Hazard Values For the SSE Average of 5 and 10 Hz 1.0 i i JIT I ' 1, 0.9 0 0 0.8 0 0 a 0 c 0 0.7 a 0 S~0-4-j -0 0 O0 -0 0 O > 0.5------------

4©- 0 -0 0 e 0.3 0 . ar ED 0 aD 0 (9 0 0.2 a 0 0 0 0.1 a 0 0 al I1I I IIi I I i 0. 0~ 10 10 -7 10 -6 10 -5 10 Composite Probability 2 Probability of Exceeding SSE 3 Figure B.2 Probability of Exceeding SSE using Median 4 LLNL Hazard Estimates B-6 1 REFERENCES 2 B.1 D.L. Bernreuter et al., "Seismic Hazard Characterization of 69 Nuclear 3 Plant Sites East of the Rocky Mountains," NUREG/CR-5250, January 1989.2 4 B.2 P. Sobel, "Revised Livermore Seismic Hazard Estimates for Sixty-Nine 5 Nuclear Power Plant Sites East of the Rocky Mountains," NUREG-1488, 6 USNRC, April 1994.2 7 B.3 Electric Power Research Institute, "Probabilistic Seismic Hazard 8 Evaluations at Nuclear Power Plant Sites in the Central and Eastern 9 United States: Resolution of the Charleston Earthquake Issue," Report 10 NP-6395-D, April 1989. 11 B.4 Attachment to Letter from D. J. Modeen, Nuclear Energy Institute, to 12 A.J. Murphy, USNRC,

Subject:

Seismic Siting Decision Process, 13 May 25, 1994.3 14 B.5 USNRC, "Design Response Spectra for Seismic Design of Nuclear Power 15 Plants," Regulatory Guide 1.60.2 16 2 Copies are available for inspection or copying for a fee from the NRC 17 Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing 18 address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax 19 (202)634-3343.

Copies may be purchased at current rates from the U.S. Government 20 Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone (202)512 21 2249); or from the National Technical Information Service by writing NTIS at 5285 22 Port Royal Road, Springfield, VA 22161. 23 3 Copies are available for inspection or copying for a fee from the NRC 24 Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing 25 address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax 26 (202)634-3343.

B-7 APPENDIX C 2 DETERMINATION OF CONTROLLING EARTHQUAKES AND DEVELOPMENT 3 OF SEISMIC HAZARD INFORMATION BASE 4 C.1 INTRODUCTION 5 This appendix elaborates on the steps described in Regulatory Position 3 6 of Draft Regulatory Guide DG-1032 to determine the controlling earthquakes 7 used to define the Safe Shutdown Earthquake Ground Motion (SSE) at the site 8 and to develop a seismic hazard information base. The information base 9 summarizes the contribution of individual magnitude and distance ranges to the 10 seismic hazard and the magnitude and distance values of the controlling 11 earthquakes at the average of 1 and 2.5 Hz and the average of and 5 and 10 Hz. 12 They are developed for the ground motion level corresponding to the reference 13 probability as defined in Appendix B to this regulatory guide. 14 The spectral ground motion levels, as determined from a probabilistic 15 seismic hazard analysis (PSHA), are used to scale a response spectrum shape. 16 A site-specific response spectrum shape is determined for the controlling 17 earthquakes and local site conditions.

Regulatory Position 4 and Appendix F 18 to this regulatory guide describe a procedure to determine the SSE using the 19 controlling earthquakes.

20 C.2 PROCEDURE TO DETERMINE CONTROLLING EARTHQUAKES 21 The following is an approach acceptable to the NRC staff for determining 22 the controlling earthquakes and developing a seismic hazard information base. 23 This procedure is based on a de-aggregation of the probabilistic seismic 24 hazard in terms of earthquake magnitudes and distances.

Once the controlling 25 earthquakes have been obtained, the SSE response spectrum can be determined 26 according to the procedure described in Appendix F to this regulatory guide. 27 Steg 1 28 (a) Perform a site-specific PSHA using the Lawrence Livermore National 29 Laboratory (LLNL) or Electric Power Research Institute (EPRI) methodologies 30 for Central and Eastern United States (CEUS) sites or perform a site-specific C-I 1 1 PSHA for sites not in the CEUS or for sites for which LLNL or EPRI methods and 2 data are not available, for actual or assumed rock conditions.

The hazard 3 assessment should be performed for spectral accelerations at 1, 2.5, 5, 10, 4 and 25 Hz, and the peak ground acceleration.

A lower-bound magnitude of 5.0 5 is recommended.

The PSHA should include an uncertainty assessment.

6 (b) Determine the following parameters as part of the assessment for 7 each ground motion measure: 8 Total hazard in terms of the median (50th percentile), mean, 85th, 9 and 15th percentile hazard curves. 10 De-aggregated median hazard results for a matrix of magnitude 11 distance pairs discussed in Step 3. As a part of the information 12 base, de-aggregated results for mean hazard results may also be 13 useful. 14 These results obtained from the de-aggregation of the median hazard are used 15 to determine the SSE and to develop the seismic hazard information base. 16 Step 2 17 (a) Using the reference probability as defined in Appendix B to this 18 regulatory guide, determine the ground motion levels for the spectral 19 accelerations at 1, 2.5, 5, and 10 Hz from the total median hazard obtained in 20 Step 1. 21 (b) Calculate the average ground motion level for the 1 and 2.5 Hz and 22 the 5 and 10 Hz spectral acceleration pairs. 23 Steps 3 to 5 describe the procedure to develop the seismic hazard 24 information base for each ground motion level determined in Step 2. This 25 information base will consist of: 26 Fractional contribution of each magnitude-distance pair to the 27 total median seismic hazard. 28 Magnitudes and distances of the controlling earthquakes.

C-2 1 The ground motion levels for the spectral accelerations at 1, 2.5, 2 5, and 10 Hz defined in Step 2. 3 The average of the ground motion levels listed above at the 1 and 4 2.5 Hz, Si.2 5 , and 5 and 10 Hz, Ss.5o, spectral accelerations 5 corresponding to the reference probability.

6 Step 3 7 Using the de-aggregated median hazard results from Step 1, at the ground 8 motion levels obtained from Step 2 calculate the fractional contribution to 9 the total median hazard of earthquakes in a selected set of magnitude and 10 distance bins (Section C.3 provides magnitude and distance bins to be used in 11 conjunction with the LLNL and EPRI methods) for the average of I and 2.5 Hz 12 and 5 and 10 Hz. The median annual probability of exceeding the ground motion 13 levels calculated in Step 1 for each magnitude and distance bin and ground 14 motion measure is denoted by Hmd,. 15 The fractional contribution of each magnitude and distance bin to the 16 total hazard for the average of 1 and 2.5 Hz, P(m,d)1 , is computed according 17 to: ( Hd,) p(m,d)1 = 2 (P Hdf) (Equation

1) f -1,2 m d 2 18 where f = 1 and f = 2 represent the ground motion measure at 1 and 2.5 Hz, 19 respectively.

20 The fractional contribution of each magnitude and distance bin to the 21 total hazard for the average of 5 and 10 Hz, P(m,d)2 , is computed according 22 to: C-3 E~ H~d,) f-1,2 P(m,d)2 2 (Equation

2) m d 2 1 where f = 1 and f = 2 represent the ground motion measure at 5 and 10 Hz, 2 respectively.

3 Step 4 4 Review the magnitude-distance distribution for the average of 1 and 2.5 5 Hz to determine whether the contribution to the hazard for distances of 100 km 6 or greater is substantial (on the order of 5% or greater).

7 If the contribution to the hazard for distances of 100 km or greater 8 exceeds 5%, additional calculations are needed to determine the controlling 9 earthquakes using the magnitude-distance distribution for distances greater 10 than 100 km (63 mi). This distribution, P>1 0 o(m,d)1 , is defined by: P>i00 (md)j P(m, d) 1 (Equation

3) Pd P(m, d)1 m d>100 11 The purpose of this calculation is to identify a distant, larger event 12 that may control low-frequency content of a response spectrum.

13 The distance of 100 km is chosen for CEUS sites. However, for CEUS 14 sites and sites not in the CEUS the results of full magnitude-distance 15 distribution should be carefully examined to ensure that proper controlling 16 earthquakes are clearly identified.

17 Step 5 18 Calculate the mean magnitude and distance of the controlling earthquake 19 associated with the ground motions determined in Step 2 for the average of 5 20 and 10 Hz. The following relation is used to calculate the mean magnitude C-4 1 using results of the entire magnitude-distance bins matrix: M (5-10 Hz) = E m F P(m,d)2 m d (Equation 4)where m is the central magnitude value for each magnitude bin. The mean distance of the controlling earthquake is determined using results of the entire magnitude-distance bins matrix: Ln {DL (5-10 Hz)} = E Ln(d) E P(m,d)2 d m (Equation 5)5 where d is the centroid distance value for each distance bin. 6 Step 6 7 If the contribution to the hazard calculated in Step 4 for distances of 8 100 km or greater exceeds 5% for the average of 1 and 2.5 Hz, calculate the 9 mean magnitude and distance of the controlling earthquakes associated with the 10 ground motions determined in Step 2 for the average of 1 and 2.5 Hz. The 11 following relation is used to calculate the mean magnitude using calculations 12 based on magnitude-distance bins greater than distances of 100 km as discussed 13 in Step 4: M (1-2.5 Hz) =E m E P>100(m,d) 1 m d >100 (Equation 6)where m is the central magnitude value for each magnitude bin. The mean distance of the controlling earthquake is based on magnitude distance bins greater than distances of 100 km as discussed in Step 4 and determined according to: C-5 2 3 4 14 15 16 17 Ln {D (1-2.5 Hz)} = E Ln(d) E P>100(m,d) 2 (Equation

7) d >100 m 1 where d is the centroid distance value for each distance bin. 2 Step_7 3 Determine the SSE response spectrum using the procedure described in 4 Appendix F of this regulatory guide. 5 C.3 EXAMPLE FOR A CEUS SITE 6 To illustrate the procedure in Section C.2, calculations are shown here 7 for a CEUS site using the 1993 LLNL hazard results (Refs. C.1 and C.2). It 8 must be emphasized that the recommended magnitude and distance bins and 9 procedure used to establish controlling earthquakes were developed for 10 application in the CEUS where the nearby earthquakes generally control the 11 response in the 5 to 10 Hz frequency range and larger but distant events can 12 control the lower frequency range. For other situations, alternative binning 13 schemes as well as a study of contributions from various bins will be 14 necessary to identify controlling earthquakes consistent with the distribution 15 of the seismicity.

16 Step 1 17 The 1993 LLNL seismic hazard methodology (Ref. C.I and C.2) was used to 18 determine the hazard at the site. A lower bound magnitude of 5.0 was used in 19 this analysis.

The analysis was performed for spectral acceleration at 1, 20 2.5, 5, and 10 Hz. 21 Step 2 22 The hazard curves at 1, 2.5, 5, and 10 Hz obtained in Step 1 are 23 assessed at the reference probability value of 1E-5/yr, as defined in 24 Appendix B to this regulatory guide. The corresponding ground motion level 25 values are given in Table C.I.C-6 Table C. 1 Ground Motion Levels 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 C-7 Frequency (Hz) 1 2.5 7 5 10 Spectral Acc. (cm/s/s) 139 373 396 374 The average of the ground motion levels at the 1 and 2.5 Hz, Sa.12.2, and 5 and 10 Hz, S.,-,,, are given in Table C.2. Table C.2 Average Ground Motion Values S.,_25 (cm/s/s) 256 S.5_10 (cm/s/s) 385 Step 3 The seismic hazard is de-aggregated for the matrix of magnitude and distance bins as given in Table C.3. Table C.3 Recommended Magnitude and Distance Bins Distance Magnitude Range of Bin Range of Bin (km) 5 -5.5 5.5 -6 6 -6.5 6.5 -7 >7 0-15 15-25 25-50 50-100 100-200 200-300 > 300 A complete probabilistic hazard analysis was performed for each bin to determine the contribution to the hazard from all earthquakes within the bin, 26 27 1 1 2 3 4 5 6 7 8 C-8 e.g., all earthquakes with magnitudes 6 to 6.5 and distance 25 to 50 km from the site. Using de-aggregated median hazard results, the fractional contribu tion of each magnitude-distance pair to the total hazard is determined.

Tables C.4 and C.5 show P(m,d)1 and P(m,d)2 for the average of 1 and 2.5 Hz and 5 and 10 Hz, respectively.

Table C.4 P(m,d)1 for Average Spectral Accelerations 1 and 2.5 Hz Corresponding to the Reference Probability Distance Magnitude Range of Bin Range of Bin (ki) 5 -5.5 5.5 -6 6 -6.5 6.5 -7 >7 0-15 0.139 0.043 0.000 0.000 0.000 15-25 0.052 0.032 0.000 0.000 0.000 25-50 0.018 0.016 0.000 0.000 0.000 50-100 0.005 0.021 0.002 0.000 0.000 100-200 0.002 0.031 0.114 0.000 0.000 200-300 0.000 0.012 0.036 0.000 0.000 > 300 0.000 0.000 0.005 0.066 0.406 Table C.5 P(m,d)2 for Average Spectral Accelerations 5 and 10 Hz Corresponding to the Reference Probability Distance Magnitude Range of Bin Range of Bin (km) 5 -5.5 5.5 -6 6 -6.5 6.5 -7 >7 0-15 0.417 0.097 0.000 0.000 0.000 15-25 0.220 0.079 0.000 0.000 0.000 25-50 0.080 0.042 0.000 0.000 0.000 50-100 0.004 0.014 0.001 0.000 0.000 100-200 0.000 0.008 0.031 0.000 0.000 200-300 0.000 0.001 0.004 0.000 0.000 > 300 0.000 0.000 0.000 0.000 0.002 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 1 Step 4 2 Because the contribution of the distance bins greater than 100 km in 3 Table C.4 does account for more than 5% of the total hazard for the average of 4 1 and 2.5 Hz, the controlling earthquake for the spectral average of I and 5 2.5 Hz will be calculated using magnitude-distance bins for distance greater 6 than 100 km. Table C.6 shows P,>oo (m,d)1 for the average of 1-2.5 Hz. 7 Table C.6 8 P, 1 0 , (m,d), for Average Spectral Accelerations I and 2.5 Hz 9 Corresponding to the Reference Probability 10 11 12 13 14 15 16 Figures C.1 to C.3 show the above information in terms of the relative 17 percentage contribution.

18 Steps 5 and 6 19 To compute the controlling magnitudes and distances at 1-2.5 Hz and 5-10 20 Hz for the example site, the values of P>1 0 0 (m,d)1 and P(m,d)2 are used with m 21 and d values corresponding to the mid-point of the magnitude of the bin (5.25, 22 5.75, 6.25, 6.75, 7.3) and centroid of the ring area (10, 20.4, 38.9, 77.8, 23 155.6, 253.3, and somewhat arbitrarily 350 km). Note that the mid-point of 24 the last magnitude bin may change because this value is dependent on the 25 maximum magnitudes used in the hazard analysis.

For this example site, the 26 controlling earthquake characteristics (magnitudes and distances) are given in 27 Table C.7.C-9 Distance Magnitude Range of Bin Range of Bin (km) 5 -5.5 5.5 -6 6 -6.5 6.5 -7 >7 100-200 0.003 0.046 0.170 0.000 0.000 200-300 0.000 0.018 0.054 0.000 0.000 > 300 0.000 0.000 0.007 0.098 0.604 2 Magnitudes and Distances of Controlling Earthquakes from the 3 LLNL Probabilistic Analysis 4 5 6 7 8 Step 7 1-2.5 Hz 5 -10 Hz M .and D . > 100 km MC and D, 6.9 and 286 km 5.4 and 18 km 9 The SSE response spectrum is determined by the procedures described in 10 Appendix F. 11 C.4 SITES NOT IN THE CEUS 12 The determination of the controlling earthquakes and the seismic hazard 13 information base for sites not in the CEUS is also carried out using the 14 procedure described in Section C.2 of this appendix.

However, because of 15 differences in seismicity rates and ground motion attenuation at these sites, 16 alternative magnitude-distance bins may have to be used. In addition, as 17 discussed in Appendix B, an alternative reference probability may also have to 18 be developed, particularly for sites in the active plate margin region and for 19 sites at which a known tectonic structure dominates the hazard.C-10 Tabl e C. 7 1 median Figure C.1 Full Distribution for Average of 5 and 10Hz C-1l 50 40 30 20 0-15 10>7 mag-bins dist-bins Figure C.2 Full Distribution for Average of I and 2.5Hz C-12 median c 0 c 0 0 1 Figure C.3 Renormalized Hazard Distribution for Distances

> 100km for average of 1 and 2.5Hz C-13 1 REFERENCES 2 C.1 P. Sobel, "Revised Livermore Seismic Hazard Estimates for Sixty-Nine 3 Nuclear Power Plant Sites East of the Rocky Mountains," NUREG-1488, 4 USNRC, April 1994.' 5 C.2 J.B. Savy et al., "Eastern Seismic Hazard Characterization Update," 6 UCRL-ID-115111, Lawrence Livermore National Laboratory, June 1993 7 (Accession number 9310190318 in NRC's Public Document Room). 8 'Copies are available for inspection or copying for a fee from the NRC 9 Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing 10 address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax 11 (202)634-3343.

Copies may be purchased at current rates from the U.S. 12 Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 13 (telephone (202)512-2249);

or from the National Technical Information Service 14 by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161. C-14 APPENDIX D 2 GEOLOGICAL, SEISMOLOGICAL, AND GEOPHYSICAL INVESTIGATIONS 3 TO CHARACTERIZE SEISMIC SOURCES 4 D.1 INTRODUCTION 5 Seismic sources are areas within which future earthquakes are likely to 6 occur at similar recurrence rates. Geological, seismological, and 7 geophysical investigations provide the information needed to identify and 8 characterize source parameters, such as size and geometry, and to estimate 9 earthquake recurrence rates and maximum magnitudes.

The amount of data 10 available about earthquakes and their causative sources varies substantially 11 between the Western United States (west of the Rocky Mountain front) and the 12 Central and Eastern United States (CEUS), or stable continental region (SCR) 13 (east of the Rocky Mountain front). Furthermore, there are variations in the 14 amount and quality of data within these regions. In active tectonic regions 15 the focus will be on the identification of both capable tectonic sources and 16 seismogenic sources. In the CEUS, identifying seismic sources is less certain 17 because of the difficulty in correlating earthquake activity with known 18 tectonic structures and the lack of adequate knowledge about earthquake 19 causes. 20 In the CEUS, several significant tectonic structures exist and some of 21 these have been interpreted as potential seismogenic sources (e.g., New Madrid 22 fault zone, Nemaha Ridge, and Meers fault). There is no single recommended 23 procedure to follow to characterize maximum magnitude associated with such 24 candidate seismogenic sources; therefore, it is most likely that the 25 determination of the properties of the seismic source will be inferred rather 26 than demonstrated by strong correlations with seismicity or geologic data. 27 Moreover, it is not generally known what relationships exist between observed 28 tectonic structures in a seismic source within the CEUS and the current 29 earthquake activity that may be associated with that source. Generally, the 30 observed tectonic structure resulted from ancient tectonic forces that are no 31 longer present, thus a structure's extent may not be a very meaningful 32 indicator of the size of future earthquakes associated with the source. The 33 historical seismicity record, the results of regional and site studies, and D-1 I 1 judgment play key roles. If, on the other hand, strong correlations and data 2 exist suggesting a relationship between seismicity and seismic sources, 3 approaches used for more active tectonic regions can be applied.

4 The primary objective of geological, seismological, and geophysical 5 investigations is to develop an up-to-date, site-specific earth science data 6 base that supplements existing information (Ref. D.1). In the CEUS the 7 results of these investigations will also be used to assess whether new data 8 and their interpretation are consistent with the information used as the basis 9 for accepted probabilistic seismic hazard studies. If the new data are 10 consistent with the existing earth science data base, development of new 11 seismic sources is not required.

For sites in the CEUS where there is 12 significant new information (see Appendix E) provided by the site 13 investigation, and for sites in the Western United States, site-specific 14 seismic sources are determined.

It is anticipated that for most sites in the 15 CEUS, new information will have been adequately bounded by existing seismic 16 source interpretations.

17 The following is a general list of characteristics to be determined for 18 a seismic source for site-specific source interpretations:

19

• Source zone geometry (location and extent, both surface and subsurface).

20 Description of Quaternary (last 2 million years) displacements (sense of 21 slip on the fault, fault length and width, area of the fault plane, age 22 of displacements, estimated displacement per event, estimated magnitude 23 per offset, and displacement history or uplift rates of seismogenic 24 folds). 25

• Historical and instrumental seismicity associated with each source. 26 Paleoseismicity.

27 Relationship of the potential seismic source to other potential seismic 28 sources in the region. 29 Maximum magnitude earthquake that can be generated by the seismic 30 source, based on the source's known characteristics, including 31 seismicity.

D-2 0 Recurrence model (Frequency of earthquake occurrence versus magnitude).

2 Other factors that will be evaluated, depending on the geologic setting 3 of a site, such as: 4 Effects of human activities such as withdrawal of fluid from or 5 addition of fluid to the subsurface, extraction of minerals, or 6 the construction of dams and reservoirs.

7 Volcanism.

Volcanic hazard is not addressed in this regulatory 8 guide. It will be considered on a case-by-case basis in regions 9 where this hazard exists. 10 Other factors that can contribute to characterization of seismic 11 sources such as strike and dip of tectonic structures, 12 orientations of regional and tectonic stresses, fault segmentation 13 (along both strike and downdip), etc. 14 D.2. INVESTIGATIONS TO EVALUATE SEISMIC SOURCES 15 D.2.1 General 16 Investigations of the site and region around the site are necessary to 17 identify both seismogenic sources and capable tectonic sources and to 18 determine their potential for generating earthquakes and causing surface 19 deformation.

If it is determined that surface deformation need not be taken 20 into account at the site, sufficient data to clearly justify the determination 21 should be presented in the application for early site review, construction 22 permit, operating license, or combined license. Generally, any tectonic 23 deformation at the earth's surface within 40 km (25 miles) of the site will 24 require adequate examination to determine its significance.

Potentially 25 active tectonic deformation within the seismogenic zone beneath a site will 26 have to be assessed using geophysical and seismological methods to determine 27 its significance.

28 Engineering solutions are generally available to mitigate the potential 29 vibratory effects of earthquakes through design. However, adequate 30 engineering solutions cannot always be demonstrated for mitigation of the D-3 1 1 effects of permanent ground displacement phenomena such as surface faulting or 2 folding, subsidence, or ground collapse.

For this reason, it is prudent to 3 select an alternative site when the potential for permanent ground 4 displacement exists at the proposed site (Ref. D.2). 5 In most of the CEUS, as determined from instrumentally determined 6 earthquake hypocenters, tectonic structures at seismogenic depths often bear 7 no relationship to geologic structures exposed at the ground surface.

8 Possible geologically young fault displacements either do not extend to the 9 ground surface or there is insufficient geologic material of the appropriate 10 age available to date the faults. Capable tectonic sources are not always 11 exposed at ground surface in the Western United States as demonstrated by the 12 buried (blind) reverse causative faults of the 1983 Coalinga, 1988 Whittier 13 Narrows, 1989 Loma Prieta, and 1994 Northridge earthquakes.

These factors 14 emphasize the need to not only conduct thorough investigations at the ground 15 surface but also in the subsurface to identify structures at seismogenic 16 depths. 17 The level of detail for investigations should be governed by knowledge 18 of the current and late Quaternary tectonic regime and the geological 19 complexity of the site and region. The investigations should be based on 20 increasing the amount of detailed information as they proceed from the 21 regional level down to the site area (e.g., 320 km to 8 km distance from the 22 site). Whenever faults or other structures are encountered at a site 23 (including sites in the CEUS) either in outcrop or excavations, it is 24 necessary to perform many of the investigations described below to determine 25 whether or not they are capable tectonic sources.

26 The investigations for determining seismic sources should be divided 27 into three levels, Regional, Site Vicinity, and Site Area. Regional 28 investigations should extend to a distance of 320 km (200 mi) from the site, 29 and data should be presented at a scale of 1:500,000 or smaller. The regional 30 investigations should be planned to identify seismic sources and describe the 31 Quaternary tectonic regime. The investigations should include a comprehensive 32 literature review supplemented by focused geological reconnaissances based on 33 the results of the literature study (including topographic, geologic, 34 aeromagnetic, and gravity maps, and airphotos).

Detailed investigations at 35 specific locations within the region may be necessary if potential capable 36 tectonic sources, or seismogenic sources that may be significant for 37 H~termining the SSE, are identified.

D-4 I Reconnaissance level investigations, which may need to be supplemented 2 at specific locations by more detailed explorations such as geologic mapping, 3 geophysical surveying, borings, and trenching, should be conducted in the site 4 vicinity to a distance of 40 km (25 mi) from the site; the data should be 5 presented at a scale of 1:50,000 or smaller.

6 Detailed investigations should be carried out in the site area within a 7 radius of 8 km (5 mi) from the site, and the resulting data should be 8 presented at a scale of 1:5000 or smaller. The level of investigations in the 9 site vicinity should delineate the geologic regime and the potential for 10 tectonic deformation at or near the ground surface. The investigations should 11 use the methods described in subsections D.2.2 and D.2.3 that are appropriate 12 for the tectonic regime to characterize seismic sources.

13 The site vicinity and site area investigations may be asymmetrical and 14 may cover a larger area than those described above in regions of late 15 Quaternary activity, regions with high rates of historical seismic activity 16 (felt or instrumentally recorded data), or sites that are located near a 17 capable tectonic source such as a fault zone. 18 Data from investigations at the site (approximately 1 square kilometer) 19 should be presented at a scale of 1:500 or smaller. Important aspects of the 20 site investigations are the excavation and logging of exploratory trenches and 21 the mapping of the excavations for the plant structures, particularly those 22 that are characterized as Seismic Category I. In addition to geological, 23 geophysical, and seismological investigations, considerable geotechnical 24 engineering investigations as described in Regulatory Guide 1.132 (Ref. D.3) 25 should be conducted at the site. 26 The investigations needed to assess the integrity of the site with 27 respect to effects of potential ground motions and surface deformation should 28 include determination of (1) the lithologic, stratigraphic, geomorphic, 29 hydrologic, geotechnical, and structural geologic characteristics of the site 30 and the area surrounding the site, including its seismicity and geological 31 history, (2) geological evidence of fault offset or other distortion such as 32 folding at or near ground surface within the site area (8 km radius), and (3) 33 whether or not any faults or other tectonic structures, any part of which are 34 within a radius of 8 km (5 mi) from the site, are capable tectonic sources.

35 This information will be used to evaluate tectonic structures underlying the S36 site area, whether buried or expressed at the surface, with regard to their 37 potential for generating earthquakes and for causing surface deformation at or D-5 1 near the site. The evaluation should consider the possible effects caused by 2 human activities such as withdrawal of fluid from or addition of fluid to the 3 subsurface, extraction of minerals, or the loading effects of dams and 4 reservoirs.

5 D.2.2 Reconnaissance Investigations, Literature Review, and Other Sources of 6 Preliminary Information 7 Regional literature and reconnaissance-level investigations can be 8 planned based on reviews of available documents and the results of previous 9 investigations.

Possible sources of information may include universities, 10 consulting firms, and government agencies.

A detailed list of possible 11 sources of information is given in Regulatory Guide 1.132 (Ref. D.3). 12 D.2.3 Detailed Site Vicinity and Site Area Investigations 13 The following methods are suggested but they are not all-inclusive and 14 investigations should not be limited to them. Some procedures will not be 15 applicable to every site, and situations will occur that require 16 investigations that are not included in the following discussion.

It is 17 anticipated that new technologies will be available in the future that will be 18 applicable to these investigations.

19 D.2.3.1 Surface Investigations 20 Surface exploration needed to assess the neotectonic regime and the 21 geology of the area around the site is dependent on the site location and may 22 be carried out with the use of any appropriate combination of the following 23 geological, geophysical, seismological, and geotechnical engineering 24 techniques, but not all will be carried out at a given site. 25 D.2.3.1.1.

Geological interpretations of aerial photographs and other 26 remote-sensing imagery, as appropriate for the particular site conditions, to 27 assist in identifying rock outcrops, faults and other tectonic features, 28 fracture traces, geologic contacts, lineaments, soil conditions, and evidence 29 of landslides or soil liquefaction.

D-6 1 D.2.3.1.2.

Mapping of topographic, geologic, geomorphic, and hydrologic 2 features at scales and contour intervals suitable for analysis, stratigraphy 3 (particularly Quaternary), surface tectonic structures such as fault zones, 4 and Quaternary geomorphic features.

For offshore sites, coastal sites, or 5 sites located near lakes or rivers, this includes topography, geomorphology 6 (particularly mapping marine and fluvial terraces), bathymetry, geophysics 7 (such as seismic reflection), and hydrographic surveys to the extent needed 8 for evaluation.

9 D.2.3.1.3.

Identification and evaluation of vertical crustal movements 10 by (1) geodetic land surveying to identify and measure short-term crustal 11 movements (Refs. D.4 and D.5) and (2) geological analyses such as analysis of 12 regional dissection and degradation patterns, marine and lacustrine terraces 13 and shorelines, fluvial adjustments such as changes in stream longitudinal 14 profiles or terraces, and other long-term changes such as elevation changes 15 across lava flows (Ref. D.6). 16 D.2.3.1.4.

Analysis of offset, displaced, or anomalous landforms such 17 as displaced stream channels or changes in stream profiles or the upstream 18 migration of nickpoints (Refs. D.7 -D.12); abrupt changes in fluvial deposits 19 or terraces; changes in paleochannels across a fault (Refs. D.11 and D.12); or 20 uplifted, downdropped, or laterally displaced marine terraces (Ref. D.12). 21 D.2.3.1.5.

Analysis of Quaternary sedimentary deposits within or near 22 tectonic zones, such as fault zones, including (1) fault-related or fault 23 controlled deposits including sag ponds, graben fill deposits, and colluvial 24 wedges formed by the erosion of a fault paleoscarp and (2) non-fault-related, 25 but offset, deposits including alluvial fans, debris cones, fluvial terrace, 26 and lake shoreline deposits.

27 D.2.3.1.6.

Identification and analysis of deformation features caused 28 by vibratory ground motions, including seismically induced liquefaction 29 features (sand boils, explosion craters, lateral spreads, settlement, soil 30 flows), mud volcanoes, landslides, rockfalls, deformed lake deposits or soil 31 horizons, shear zones, cracks or fissures (Refs. D.13 and D.14).D-7 I D.2.3.1.7.

Estimation of the ages of fault displacements by analysis of 2 the morphology of topographic fault scarps associated with or produced by 3 surface rupture. Fault scarp morphology is useful in estimating age of last 4 displacement, approximate size of the earthquake, recurrence intervals, slip 5 rate, and the nature of the causative fault at depth (Refs. D.15 -D.18). 6 D.2.3.2 Seismological Investiqations 7 D.2.3.2.1.

Listing of all historically reported earthquakes having 8 Modified Mercalli Intensity (MMI) greater than or equal to IV or magnitude 9 greater than or equal to 3.0 that can reasonably be associated with seismic 10 sources, any part of which is within a radius of 320 km (200 miles) of the 11 site (the site region). The earthquake descriptions should include the date 12 of occurrence and measured or estimated data on the highest intensity, 13 magnitude, epicenter, depth, focal mechanism, and stress drop. Historical 14 seismicity includes both historically reported and instrumentally recorded 15 data. For pre-instrumentally recorded data, intensity should be converted to 16 magnitude, the procedure used to convert it to magnitude should be clearly 17 documented, and epicenters should be determined based on intensity 18 distributions.

Methods to convert intensity values to magnitudes in the CEUS 19 are described in References D.1, D.19, D.20, and D.21. 20 D.2.3.2.2.

Seismic monitoring in the site area should be established as 21 soon as possible after site selection.

For sites in the CEUS, a single large 22 dynamic range, broad-band seismograph may be adequate.

For sites in the 23 Western United States, a network of at least five such seismographs would be 24 deployed within 25 km (15 mi) surrounding the site. 25 The primary purposes of seismic monitoring are to obtain data from 26 distant earthquakes, to determine site response, and provide assurance that 27 there are no significant sources of earthquakes within the site vicinity.

For 28 sites in the Western United States seismic monitoring could help locate any 29 ongoing seismicity that may indicate capable faulting within the site 30 vicinity.

31 Monitoring should be initiated up to five years prior to construction of 32 a nuclear unit at a site and should continue for at least five years following 33 initiation of plant operation.

D-8 D.2.3.3 Subsurface Investioations 2 Subsurface investigations in the site area and within the site vicinity 3 to identify and define seismogenic sources and capable tectonic sources may 4 include the following investigations.

5 D.2.3.3.1.

Geophysical investigations such as air or ground magnetic 6 and gravity surveys, seismic reflection and seismic refraction surveys, 7 borehole geophysics, and ground-penetrating radar. 8 D.2.3.3.2.

Core borings to map subsurface geology and obtain samples 9 for testing such as examining the properties of the subsurface soils and rocks 10 and geochronological analysis.

11 D.2.3.3.3.

Excavating and logging of trenches across geological 12 features as part of the neotectonic investigation and to obtain samples for 13 the geochronological analysis of those features.

14 At some sites, deep soil, bodies of water, or other material may obscure 15 geologic evidence of past activity along a tectonic structure.

In such cases, 16 the analysis of evidence elsewhere along the structure can be used to evaluate 17 its characteristics in the vicinity of the site (Refs. D.12 and D.22). 18 D.2.4 Geochronoloqy 19 An important part of the geologic investigations to identify and define 20 potential seismic sources is the geochronology of geologic materials.

The NRC 21 is currently supporting a research project to develop a data base on which to 22 base a future regulatory guide on geochronological methods. This guide will 23 contain an up-to-date bibliography of state-of-the-art documents on 24 geochronology.

The availability of this guide will be published in the 25 Federal Reqister.

26 An acceptable classification of dating methods is based on the rationale 27 described in Reference D.23. The following techniques, which are presented 28 according to that classification, are useful in dating Quaternary deposits.D-9 1 D.2.4.1 Sidereal Dating Methods 2 Dendrochronology

-tree-ring analysis -age range is from modern 3 times to several thousand years (Refs. D.24 and D.25). 4 Varve chronology

-0 to 10,000 years (Ref. D.26). 5 6 D.2.4.2 Isotopic Datinq Methods 7 9 Radiocarbon for dating organic materials

-100 to 40,000 (up to 8 100,000 years using AMS) (Refs. D.27 and D.28). 9 0 Potassium argon for dating volcanic rocks ranging in age from 10 about 100,000 to 10 million years (Refs. D.27 and D.29). 11 9 Argon 39 -Argon 40, for dating relatively unweathered igneous and 12 metamorphic rocks -100,000 to unlimited upper limit (Ref. D.30) 13 0 Uranium series uses the relative properties of various decay 14 products of .3 8 U or 2 3 5 U. Ages range from 10,000 to 350,000 years 15 (Ref. D.27). 2 3 5 U/2 3 8 U can yield between 40,000 and 1,000,000 years 16 (Ref. D.31). 17 Uranium Trend -for relatively undisturbed soils ranging in age 18 from 100,000 to 900,000 years (Ref. D.32). 19 D.2.4.3 Cosmogenic Isotopes -for dating surficial rocks and soils. 20 Nuclides 3 6 C1, "°Be, 2 1 Pb, and 2 6 Al -age range varies within the 21 Quaternary according to isotope tested (Refs. D.33 and D.34). 22 D.2.4.4 Radiopenic Dating Methods 23 Thermoluminescence (TL) -for dating fine-grained eolian and 24 lacustrine, and possibly alluvium and colluvium as well -age 25 range is from 1,000 to 1,000,000 years (Refs. D.27 and D.35). 26 Electron spin resonance (ESR) is used for sediments, shells, 27 carbonates, bones, and possibly to date quartz that formed in 28 fault gouge during the fault event -age range is from 50,000 to 29 500,000 years (Ref. D.36). 30 Fission Track -for dating minerals such as zircon and apatite, 31 with fissionable uranium in volcanic rocks -100 to several 32 million years (Refs. D.27 and D.37). D-10 1 D.2.4.5 Chemical and Biological Dating Methods 2 Obsidian and Tephra Hydration

-age range is from 200 to several 3 million years (Ref. D.38). 4 Amino Acid Racemization

-for fossils, shells, and bones -age 5 range is from 100 to 1,000,000 years (Refs. D.39 and D.40). 6 Rock varnish chemistry

-cation ratio of manganese, iron, and clay 7 coatings on desert stones -age range is 1,000 to 40,000 years 8 (Ref. D.41). The results of this method are controversial and its 9 use is not recommended pending further validation.

10 D.2.4.6 Geomorphic Datinq Methods 11 Soil profile development

-for analysis of the upper few meters of 12 stable soils -age range is from 1,000 to 1,000,000 years (Refs. 13 D.27, D.42 through D.47). 14 Rock and mineral weathering

-for measuring the progression of 15 weathering, such as thicknesses of weathering rind development on 16 the margins of clasts, hornblende etching, limestone solutioning, 17 etc. -age range, depending on material -10 to 1,000,000 (Ref. 18 D.27). 19 Geomorphic position -fluvial and marine terraces, and glacial 20 moraines -1,000 to 1,000,000 years (Ref. D.48). 21 Rate of deposition

-lacustrine, playa, and sometimes alluvial 22 deposits -tens to millions of years (Ref. D.26) 23 Scarp degradation

-works best in coarse unconsolidated alluvium 24 age range is from 2,000 to 20,000 years (Refs. D.15 and D.49). 25 D.2.4.7 Correlation Dating Methods 26 0 Lithostratigraphy

-correlation of distinctive geologic units 27 between sites -age range is from 0 to 4.5 billion years (Ref. 28 D.50) 29 Tephrochronology

-volcanic ash layers interbedded with 30 sedimentary deposits -age range is from zero to several million 31 years (Refs. D.51 and D.38).D-11 I 1 0 Paleomagnetism

-most igneous and sedimentary rocks containing 2 hematite and magnetite

-age range is from 0 to 5,000,000 years 3 (Ref. D.27). 4 0 Archeology

-deposits associated with archeological materials 5 (Ref. D.52). 6 0 Paleontology (marine and terrestial)

-fossil-bearing rocks or 7 soils -age range is from 0 to 1 billion years (Ref. D.53). 8 0 Lichenometry

-used to estimate ages from sizes of lichens 9 growing on gravel or boulders (such as glacial deposits) (Ref. 10 D.54). 11 In the CEUS, it may not be possible to reasonably demonstrate the age of 12 last activity of a tectonic structure.

In such cases the NRC staff will 13 accept association of such structures with geologic structural features or 14 tectonic processes that are geologically old (at least pre-Quaternary) as an 15 age indicator in the absence of conflicting evidence.

16 These investigative procedures should also be applied, where possible, 17 to characterize offshore structures (faults or fault zones, and folds, uplift, 18 or subsidence related to faulting at depth) for coastal sites or those sites 19 located adjacent to landlocked bodies of water. Investigations of offshore 20 structures will rely heavily on seismicity, geophysics, and bathymetry rather 21 than conventional geologic mapping methods that can normally be used 22 effectively onshore. However, it is often useful to investigate similar 23 features onshore to learn more about the significant offshore features.

24 D.2.5 Distinction Between Tectonic and Nontectonic Deformation 25 Nontectonic deformation, like tectonic deformation, at a site can pose a 26 substantial hazard to nuclear power plants, but there are likely to be 27 differences in the approaches used to resolve the issues raised by the two 28 types of phenomena.

Therefore, nontectonic deformation should be 29 distinguished from tectonic deformation at a site. In past nuclear power 30 plant licensing activities, surface displacements caused by phenomena other 31 than tectonic phenomena have been confused with tectonically induced faulting.

32 Such features include faults on which the last displacement was induced by 33 glaciation or deglaciation; collapse structures, such as found in karst D-12 I terrain; and growth faulting, such as occurs in the Gulf Coastal Plain or in 2 other deep soil regions subject to extensive subsurface fluid withdrawal.

3 Glacially induced faults generally do not represent a deep-seated 4 seismic or fault displacement hazard because the conditions that created them 5 are no longer present. However, residual stresses from Pleistocene glaciation 6 may still be present in glaciated regions, although they are of less concern 7 than active tectonically induced stresses.

These features should be 8 investigated with respect to their relationship to current in situ stresses.

9 The nature of faults related to collapse features can usually be defined 10 through geotechnical investigations and can either be avoided or, if feasible, 11 adequate engineering fixes can be provided.

12 Large, naturally occurring growth faults as found in the coastal plain 13 of Texas and Louisiana can pose a surface displacement hazard, even though 14 offset most likely occurs at a much less rapid rate than that of tectonic 15 faults. They are not regarded as having the capacity to generate damaging 16 earthquakes, can often be identified and avoided in siting, and their 17 displacements can be monitored.

Some growth faults and antithetic faults 18 related to growth faults are not easily identified; therefore, investigations S g19 described above with respect to capable faults and fault zones should be 20 applied in regions where growth faults are known to be present. Local 21 human-induced growth faulting can be monitored and controlled or avoided.

22 If questionable features cannot be demonstrated to be of non-tectonic 23 origin they should be treated as tectonic deformation.

D-13 1 REFERENCES 2 D.1 Electric Power Research Institute, "Seismic Hazard Methodology for the 3 Central and Eastern United States," EPRI NP-4726, All Volumes, 1988 4 through 1991. 5 D.2 International Atomic Energy Agency, "Earthquakes and Associated Topics 6 in Relation to Nuclear Power Plant Siting," Safety Series No. 50-SG-S1, 7 Revision 1, 1991. 8 D.3 USNRC, "Site Investigations for Foundations of Nuclear Power Plants," 9 Regulatory Guide 1.132.' 10 D.4 R. Reilinger, M. Bevis, and G. Jurkowski, "Tilt from Releveling:

An 11 Overview of the U.S. Data Base," Tectonophysics, Volume 107, pp. 315 12 330, 1984. 13 D.5 R.K. Mark et al., "An Assessment of the Accuracy of the Geodetic 14 Measurements that Led to the Recognition of the Southern California 15 Uplift," Journal of Geophysical Research, Volume 86, pp. 2783-2808, 16 1981. 17 D.6 T.K. Rockwell et al., "Chronology and Rates of Faulting of Ventura River 18 Terraces, California," Geological Society of America Bulletin, Volume 19 95, pp. 1466-1474, 1984. 20 D.7 K.E. Sieh, "Lateral Offsets and Revised Dates of Prehistoric Earthquakes 21 at Pallett Creet, Southern California," Journal of Geophysical Research, 22 Volume 89, No. 89, pp. 7641-7670, 1984. 23 'Copies are available for inspection or copying for a fee from the NRC 24 Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing 25 address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax 26 (202)634-3343.

Copies may be purchased at current rates from the U.S. 27 Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 28 (telephone (202)512-2249);

or from the National Technical Information Service 29 by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161. D-14 I D.8 K.E. Sieh and R.H Jahns, "Holocene Activity of the San Andreas Fault at 2 Wallace Creek, California," Geological Society of America Bulletin, 3 Volume 95, pp. 883-896, 1984. 4 D.9 K.E. Sieh, M. Stuiver, and D. Brillinger, "A More Precise Chronology of 5 Earthquakes Produced by the San Andreas Fault in Southern California," 6 Journal of Geophysical Research, Volume 94, pp. 603-623, 1989. 7 D.10 R.J. Weldon, III, and K. E. Sieh, "Holocene Rate of Slip and Tentative 8 Recurrence Interval for Large Earthquakes on the San Andreas Fault, 9 Cajon Pass, Southern California," Geological Society of America 10 Bulletin, Volume 96, pp. 793-812, 1985. 11 D.11 F.H. Swan, III, D. P. Schwartz, and L. S. Cluff, "Recurrence of Moderate 12 to Large Magnitude Earthquakes Produced by Surface Faulting on the 13 Wasatch Fault Zone," Bulletin of the Seismological Society of America, 14 Volume 70, pp. 1431-1462, 1980. 15 D.12 Pacific Gas and Electric Company, "Final Report of the Diablo Canyon 16 Long Term Seismic Program; Diablo Canyon Power Plant," Docket Nos. 50 17 275 and 50-323, 1988.2 18 D.13 S.F. Obermeier et al., "Geologic Evidence for Recurrent Moderate to 19 Large Earthquakes Near Charleston, South Carolina," Science, Volume 227, 20 pp. 408-411, 1985. 21 D.14 D. Amick et al., "Paleoliquefaction Features Along the Atlantic 22 Seaboard," U.S. Nuclear Regulatory Commission, NUREG/CR-5613, October 23 1990.1 24 D.15 R.E. Wallace, "Profiles and Ages of Young Fault Scarps, North-Central 25 Nevada," Geological Society of America Bulletin, Volume 88, pp. 1267 26 1281, 1977. 27 2 Copies are available for inspection or copying for a fee from the NRC 28 Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing 29 address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax 30 (202)634-3343.

D-15 1 D.16 R.E. Wallace, "Discussion--Nomographs for Estimating Components of Fault 2 Displacement from Measured Height of Fault Scarp," Bulletin of the 3 Association of Enqineerinq Geologists, Volume 17, pp. 39-45, 1980. 4 D.17 R.E. Wallace, "Active Faults, Paleoseismology, and Earthquake Hazards: 5 Earthquake Prediction--An International Review," Maurice Ewing Series 4, 6 American Geophysical Union, pp. 209-216, 1981. 7 D.18 A.J. Crone and S. T. Harding, "Relationship of Late Quaternary Fault 8 Scarps to Subjacent Faults, Eastern Great Basin, Utah," Geology, Volume 9 12, pp. 292-295, 1984. 10 D.19 O.W. Nuttli, "The Relation of Sustained Maximum Ground Acceleration and 11 Velocity to Earthquake Intensity and Magnitude, State-of-the-Art for 12 Assessing Earthquake Hazards in the Eastern United States," U.S. Army 13 Corps of Engineers Misc. Paper 5-73-1, Report 16, 1979. 14 D.20 R.L. Street and F.T. Turcotte, "A Study of Northeastern North America 15 Spectral Moments, Magnitudes and Intensities," Bulletin of the Seismo 16 logical Society of America, Volume 67, pp. 599-614, 1977. 17 D.21 R.L. Street and A. Lacroix, "An Empirical Study of New England Seis 18 micity," Bulletin of the Seismological Society of America, Volume 69, 19 pp. 159-176, 1979. 20 D.22 H. Rood et al., "Safety Evaluation Report Related to the Operation of 21 Diablo Canyon Nuclear Power Plant, Units I and 2," USNRC, NUREG-0675, 22 Supplement No. 34, June 1991.' 23 D.23 S.M. Colman, K.L. Pierce, and P.W. Birkeland, "Suggested Terminology for 24 Quaternary Dating Methods," Quaternary Research, Volume 288, pp. 314 25 319, 1987. 26 D.24 R. Page, "Dating Episodes of Faulting From Tree Rings: Effects of the 27 1958 Rupture of the Fairweather Fault on the Tree Growth," Geological 28 Society of America Bulletin, Volume 81, pp. 3085-3094, 1970.D-16 1 D.25 B.F. Atwater and D.K. Yamaguchi, "Sudden, Probably Coseismic 2 Submergences of Holocene Trees and Grass in Coastal Washington State," 3 Geolociv, Volume 19, pp. 706-709, 1991. 4 D.26 J.P. Bradbury, W.E. Dean, and R.Y. Anderson, "Holocene Climatic and 5 Limnologic History of the North-Central United States as Recorded in the 6 Varved Sediments of Elk Lake, Minnesota:

A Synthesis," in J.P. Bradbury 7 and W.E. Dean, editors, Elk Lake. Minnesota:

Evidence for Rapid Climate 8 Chanqe in the North-Central United States: Boulder Colorado, Geological 9 Society of America Special Paper 276, 1993. 10 D.27 J.F. Callender, "Tectonics and Seismicity," Chapter 4 in "Techniques for 11 Determining Probabilities of Events and Processes Affecting the Perfor 12 mance of Geologic Repositories," NUREG/CR-3964 (SAND 86-0196), Volume 1, 13 Edited by R. L. Hunter and C. J. Mann, pp.89-125, June 1989.1 14 D.28 D.J. Donahue, T.W. Linick, and A.J.T. Jull, "Isotope-ratio and 15 Background Corrections for Accelerator Mass Spectrometry Radiocarbon 16 Measurements," Radiocarbon, Volume 32, pp. 135-142, 1990. 17 D.29 G.B. Dalrymple and M.A. Lamphere, "Potassiurm-Arqon Dating," San 18 Francisco, W.H. Freeman and Co., 1969. 19 D.30 I. McDougall and T.M. Harrison, "Geochronology by the 4 0 Ar/'9 Ar Method," 20 New York, Oxford University Press, 1988. 21 D.31 D.R. Muhs and B. J. Szabo, "Uranium-Series Age of the Eel Point Terrace, 22 San Clemente Island, California," GeoloUy, Volume 10, pp. 23-26, 1982. 23 D.32 M. Ivanovich, A.G. Latham, and T.L. Ku, "Uranium-Series Disequilibrium 24 Applications in Geochronology," in M. Ivanovich and R.S. Harmon, 25 Editors, Uranium-Series Disequilibrium.

Applications to Earth, Marine 26 and Environmental Sciences, 2nd Edition, Oxford University Press, 27 pp. 63-94, 1992.D-17 1 D.33 M.G. Zreda et al., "Cosmogenic 3 6 C1 Production Rates in Terrestrial 2 Rocks," Earth and Planetary Science Letters, Volume 105, pp. 4-109, 3 1991. 4 D.34 K. Nishizumi et al., "Production of " 0 Be and 2 6 Al by Cosmic Rays in 5 Terrestial Quartz in situ and Implications for Erosion Rates," Nature, 6 Volume 319, pp. 134-136, 1986. 7 D.35 S.L. Forman, "Applications and Limitations of Thermoluminescence To Date 8 Quaternary Sediments," Quaternary International, Volume 1, pp. 47-59, 9 1989. 10 D.36 M. Ikeya, T. Miki, and K. Tanaka, "Dating of a Fault by Electron Spin 11 Resonance on Intrafault Materials," Science, Volume 215, pp. 1392-1393, 12 1982. 13 D.37 N.D. Naeser and C.W. Naeser, "Fission-Trace Dating," in W.C. Mahney, 14 editor, Quaternary Dating Methods, New York, Elsevier, pp.87-100, 1984. 15 D.38 S. Self and R.J.S. Sparks, editors, "Tephra Studies," Proceedings of the 16 NATO Advanced Studies Institute, Tephra Studies as a Tool in Quaternary 17 Research, D. Reidel Publishing Co., Dordrecht, Holland, 1981. 18 D.39 J.L. Bada and P. M. Helfman, "Amino Acid Racemization Dating of Fossil 19 Bones," World Archeoloql, 1975. 20 D.40 J.L. Bada and R. Protsch, "Racemization Reaction of Aspartic Acid and it 21 Use in Dating Fossil Bones," Proceedings of the National Academy of 22 Science, Volume 70, pp. 1331-1334, 1973. 23 D.41 R.I. Dorn and D.H. Krinsley, "Cation-Leaching Sites in Rock Varnish," 24 Geolociv, Volume 19, pp. 1077-1080, November 1991. 25 D.42 M.N. Machette, "Dating Quaternary Faults in the Southwestern United 26 States by Using Buried Calcic Paleosols," U.S. Geological Survey Journal 27 of Research, Volume 6, pp. 369-381, 1978. D-18 I D.43 M.N. Machette, "Soil Dating Techniques, Western Region (United States)," 2 Open-file Report OFR-82-840, U.S. Geological Survey, pp. 137-140, 1982. 3 D.44 L.D. McFadden and J. C. Tinsley, "Soil Profile Development in Xeric 4 Climates:

A Summary," in J. C. Tinsley, J. C. Matti, and L. D. 5 McFadden, eds., Guidebook, Field Trip No. 12, Geological Society of 6 America, Cordillera Section, pp. 15-19, 1982. 7 D.45 J.W. Hardin, "A Quantitative Index of Soil Development from Field 8 Descriptions:

Examples from a Chronosequence in Central California," 9 Geoderma, Volume 28, pp. 2-18, 1982. 10 D.46 J.C. Matti et al., "Holocene Faulting History as Recorded by Alluvial 11 Stratigraphy Within the Cucamonga Fault Zone; A Preliminary View," 12 in J. C. Tinsley, J. C. Matti, and L. D. McFadden, eds., Guidebook, 13 Field Trip No. 12, Geological Society of America, Cordillera Section, 14 pp. 29-44, 1982. 15 D.47 O.A. Chadwick, S. Hecker, and J. Fonseca, "A Soils Chronosequence at 16 Terrace Creek: Studies of Late Quaternary Tectonism in Dixie Valley, 17 Nevada," Open-file Report 84-0090, U.S. Geological Survey, 1984. 18 D.48 E.A. Keller and T.K. Rockwell, "Tectonic Geomorphology, Quaternary 19 Chronology and Paleoseismicity," in J.E. Costa, editor, Developments and 20 Applications of Geomorphology, Springer-Verlag, New York, pp. 203-239, 21 1984. 22 D.49 R.C. Bucknam and R.E. Anderson, "Estimation of Fault-Scarp Ages from a 23 Scarp-Height-Slope-Angle Relationship," Geology, Volume 7, pp. 11-14, 24 1979. 25 D.50 K.L. Pierce, "Dating Methods," Active Tectonics, National Academy of 26 Sciences, Washington, DC, pp. 195-214, 1986. 27 D.51 P.D. Sheets and D.K. Grayson, editors, Volcanic Activity and Human 28 EcoloQy, Academic Press, New York, 1979.D- 19 1 D.52 R.T. Saucier, "Geoarchaeological Evidence of Strong Prehistoric 2 Earthquakes in the New Madrid (Missouri)

Seismic Zone," Geology, Volume 3 19, No. 4. pp. 296-289, 1991. 4 D.53 P.C. Valentine, "Zoogeography of Holocene Ostracoda off Western North 5 America and Paleoclimatic Implications," U.S. Geological Survey 6 Professional Paper 916, 1976. 7 D.54 W.W. Locke, J.T. Andrews, and P.J. Webber, "A Manual for Lichenometry," 8 Technical Bulletin 26, British Geomorphological Research Group, Norwich, 9 University of East Anglia, 1979.D-20 I APPENDIX E 2 PROCEDURE FOR THE EVALUATION OF NEW GEOSCIENCES INFORMATION OBTAINED FROM THE 3 SITE-SPECIFIC INVESTIGATIONS 4 5 E.1 INTRODUCTION 6 This appendix provides methods acceptable to the NRC staff for assessing 7 the impact of new information obtained during site-specific investigations on 8 the probabilistic seismic hazard analysis (PSHA). 9 Regulatory Position 4 in this guide describes acceptable PSHA analyses 10 that were developed by Lawrence Livermore National Laboratories (LLNL) and the 11 Electric Power Research Institute (EPRI) to estimate the controlling 12 earthquakes and to develop the Safe Shutdown Earthquake ground motion (SSE). 13 The procedure to determine the SSE outlined in this Draft Regulatory Guide 14 DG-1032 relies primarily on either the LLNL or EPRI PSHA results for the 15 Central and Eastern United States (CEUS). It is necessary to evaluate the 16 geological, seismological, and geophysical data obtained from the site 17 specific investigations to demonstrate that these data are consistent with the 18 PSHA data bases of these two methodologies.

If significant differences 19 between the investigation results and the PSHA data base are identified and 20 these differences would result in a significant increase in the hazard 21 estimate for a site, the PSHA may have to be modified to incorporate the new 22 information.

23 E.2 POSSIBLE SOURCES OF NEW INFORMATION THAT COULD AFFECT THE SSE 24 Types of new data that could affect the PSHA results can be put in three 25 general categories:

seismic sources, earthquake recurrence models or rates of 26 deformation, and ground motion models. 27 E.2.1 Seismic Sources 28 There are several possible sources of new information from the site 29 specific investigations that could effect the seismic hazard. Continued 30 recording of small earthquakes, including microearthquakes, may indicate the E-I 1 presence of a localized seismic source. Paleoseismic evidence, such as 2 paleoliquefaction features or displaced Quaternary strata, may indicate the 3 presence of a previously unknown tectonic structure or a larger amount of 4 activity on a known structure than was previously considered.

Future 5 geophysical studies (aeromagnetic, gravity, and seismic reflection/refraction) 6 will probably identify crustal structures that suggest the presence of 7 previously unknown seismic sources. In situ stress measurements and the 8 mapping of tectonic structures in the future may indicate potential seismic 9 sources.

10 Detailed local site investigations often reveal faults or other tectonic 11 structures that were unknown, or reveal additional characteristics of known 12 tectonic structures.

Generally, based on past licensing experience in the 13 CEUS, the discovery of such features will not require a modification of the 14 seismic sources provided in the LLNL and EPRI studies. However, initial 15 evidence regarding a newly discovered tectonic structure in the CEUS is often 16 equivocal with respect to activity, and additional detailed investigations are 17 required.

By means of these detailed investigations, and based on past 18 licensing activities, previously unidentified tectonic structures can usually 19 be shown to be inactive or otherwise insignificant to the seismic design basis 20 of the facility, and a modification of the seismic sources provided by the 21 LLNL and EPRI studies will not be required.

On the other hand, if the newly 22 discovered features are relatively young, possibly associated with historical 23 earthquakes that were large and close to the proposed facility, a modification 24 may be required.

25 Of particular concern is the possible existence of previously unknown, 26 potentially active tectonic structures that could localize moderate-sized, but 27 potentially damaging, near-field earthquakes or could cause surface 28 displacement.

Also of concern is the presence of structures that could 29 generate larger earthquakes within the region. 30 Tnve+tigations to determine whether there is a possibility for permanent 31 ground displacement are especially important in view of the provision to allow 32 for a combined licensing procedure under 10 CFR Part 52 as an alternative to 33 the two-step procedure of the past (Construction Permit and Operating 34 License).

In the past at numerous nuclear power plant sites, potentially 35 significant faults were identified when excavations were made during the 36 construction phase prior to the issuance of an operating license, and E-2 I extensive additional investigations of those faults had to be carried out to 2 properly characterize them. 3 E.2.2 Earthquake Recurrence Models 4 There are three elements of the source zone's recurrence models that 5 could be affected by new site-specific data: (1) the rate of occurrence of 6 earthquakes, (2) their maximum magnitude, and (3) the form of the recurrence 7 model, for example, a change from truncated exponential to a characteristic 8 earthquake model. Among the new site-specific information that is most likely 9 to have a significant impact on the hazard is the discovery of paleoseismic 10 evidence such as extensive soil liquefaction features, which would indicate 11 with reasonable confidence that much larger estimates of the maximum 12 earthquake would ensue than those predicted by the previous studies. The 13 paleoseismic data could also be significant even if the maximum magnitudes of 14 the previous studies are consistent with the paleoseismic earthquakes if there 15 are sufficient data to develop return period estimates significantly shorter 16 than those previously used in the probabilistic analysis.

The paleoseismic 17 data could also indicate that a characteristic earthquake model would be more 18 applicable than a truncated exponential model. 19 In the future, expanded earthquake catalogs will become available that 20 will differ from the catalogs used by the previous studies. Generally, these 21 new catalogues have been shown to have only minor impacts on estimates of the 22 parameters of the recurrence models. Cases that might be significant include 23 the discovery of records that place earthquakes in a region that had no 24 seismic activity in the previous catalogs, the occurrence of an earthquake 25 larger than the largest historic earthquakes, re-evaluating the largest 26 historic earthquake to a significantly larger magnitude, or the occurrence of 27 one or more moderate to large earthquakes (magnitude 5.0 or greater) in the 28 CEUS. 29 Geodetic measurements, particularly satellite-based networks, may 30 provide data and interpretations of rates and styles of deformation in the 31 CEUS that can have implications for earthquake recurrence.

New hypotheses 32 regarding present-day tectonics based on new data or reinterpretation of old 33 data may be developed that were not considered in the EPRI or LLNL PSHA. Any 34 of these cases could have an impact on the estimated maximum earthquake if the 35 result is larger than the values provided by LLNL and EPRI.E-3 1 E.2.3 Ground Motion Attenuation Models 2 Alternative ground motion models may be used to determine the site 3 specific spectral shape as discussed in Regulatory Position 4 and Appendix F. 4 If the ground motion models used are a major departure from the original 5 models used in the hazard analysis and are likely to have impacts on the 6 hazard results of many sites, a reevaluation of the reference probability may 7 be needed using the procedure discussed in Appendix B. Otherwise, a periodic 8 (e.g., every ten years) reexamination of PSHA and the associated data base is 9 considered appropriate to incorporate new understanding regarding ground 10 motion models. 11 E.3 PROCEDURE AND EVALUATION 12 The EPRI and LLNL studies provided a wide range of interpretations of 13 the possible seismic sources for most regions of the CEUS, as well as a wide 14 range of interpretations for all the key parameters of the seismic hazard 15 model. The first step in comparing the new information with those 16 interpretations is determining whether the new information is consistent with 17 the following LLNL and EPRI parameters:

(1) the range of seismogenic sources 18 as interpreted by the seismicity experts or teams involved in the study, (2) 19 the range of seismicity rates for the region around the site as interpreted by 20 the seismicity experts or teams involved in the studies, and (3) the range of 21 maximum magnitudes determined by the seismicity experts or teams. The new 22 information is considered not significant and no further evaluation is needed 23 if it is consistent with the assumptions used in the PSHA, no additional 24 alternative seismic sources or seismic parameters are needed, or it supports 25 maintaining or decreasing the site median seismic hazard. 26 An example is an additional nuclear unit sited near an existing nuclear 27 power plant site that was recently investigated by state-of-the-art 28 geosciences techniques and evaluated by current hazard methodologies.

29 Detailed geological, seismological, and geophysical site-specific 30 investigations would be required to update existing information regarding the 31 new site, but it is very unlikely that significant new information would be 32 found that would invalidate the previous PSHA. 33 On the other hand, after evaluating the results of the site-specific 34 investigations if there is still uncertainty about whether the new information E-4 1 will affect the estimated hazard, it will be necessary to evaluate the s- 2 potential impact of the new data and interpretations on the median of the 3 range of the input parameters.

Such new information may indicate the addition 4 of a new seismic source, a change in the rate of activity, a change in the 5 spatial patterns of seismicity, an increase in the rate of deformation, or the 6 observation of a relationship between tectonic structures and current 7 seismicity.

The new findings should be assessed by comparing them with the 8 specific input of each expert or team that participated in the PSHA. 9 Regarding a new source, for example, the specific seismic source 10 characterizations for each expert or team (such as tectonic feature being 11 modeled, source geometry, probability of being active, maximum earthquake 12 magnitude, or occurrence rates) should be assessed in the context of the 13 significant new data and interpretations.

14 Usually the new information will be within the range of interpretations 15 in the existing data base, and the data will not result in an increase in 16 overall seismicity rate or increase in the range of maximum earthquakes to be 17 used in the probabilistic analysis.

It can then be concluded that the current 18 LLNL or EPRI results apply. It is possible that the new data may necessitate 19 a change in some parameter.

In this case, appropriate sensitivity analyses 20 should be performed to determine whether the new site-specific data could 21 affect the ground motion estimates at the reference probability level. 22 An example is a consideration of the seismic hazard near the Wabash 23 River Valley (Ref. E.1). Geological evidence found recently within the Wabash 24 River Valley and several of its tributaries indicated that an earthquake much 25 larger than any historic event had occurred several thousand years ago in the 26 vicinity of Vincennes, Indiana. A review of the inputs by the experts and 27 teams involved in the LLNL and EPRI PSHA's revealed that many of them had made 28 allowance for this possibility in their tectonic models by assuming the 29 extension of the New Madrid Seismic Zone northward into the Wabash Valley. 30 Several experts had given strong weight to the relatively high seismicity of 31 the area, including the number of magnitude 5 historic earthquakes that have 32 occurred, and thus had assumed the larger event. This analysis of the source 33 characterizations of the experts and teams resulted in the conclusion by the 34 analysts that a new PSHA would not be necessary for this region because an 35 event similar to the prehistoric earthquake had been considered in the 36 existing PSHAs.E-5 I A third step would be required if the site-specific geosciences 2 investigations revealed significant new information that would substantially 3 affect the estimated hazard. Modification of the seismic sources would more 4 than likely be required if the results of the detailed local and regional site 5 investigations indicate that a previously unknown seismic source is identified 6 in the vicinity of the site. A hypothetical example would be the recognition 7 of geological evidence of recent activity on a fault near a nuclear power 8 plant site in the stable continental region (SCR) similar to the evidence 9 found on the Meers Fault in Oklahoma (Ref. E.2). If such a source is 10 identified, the same approach used in the active tectonic regions of the 11 Western United States should be used to assess the largest earthquake expected 12 and the rate of activity.

If the resulting maximum earthquake and the rate of 13 activity are higher than those provided by the LLNL or EPRI experts or teams 14 regarding seismic sources within the region in which this newly discovered 15 tectonic source is located, it may be necessary to modify the existing 16 interpretations by introducing the new seismic source and developing modified 17 seismic hazard estimates for the site. The same would be true if the current 18 ground motion models are a major departure from the original models. These 19 occurrences would likely require performing a new PSHA using the updated data 20 base, and may require determining the appropriate reference probability in 21 accordance with the procedure described in Appendix B.E-6 I REFERENCES 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 E-7 E.1 Memorandum from A. Murphy, NRC, to L. Shao, NRC,

Subject:

Summary of a Public Meeting on the Revision of Appendix A, "Seismic and Geologic Siting Criteria for Nuclear Power Plants," to 10 CFR Part 100; Enclosure (Viewgraphs):

NUMARC, "Development and Demonstration of Industry's Integrated Seismic Siting Decision Process," February 23, 1993.1 E.2 A.R. Ramelli, D.B. Slemmons, and S.J. Brocoum, "The Meers Fault: Tectonic Activity in Southwestern Oklahoma," NUREG/CR-4852, US NRC, March 1987.2 'Copies are available for inspection or copying for a fee from the NRC Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax (202)634-3343.

2 Copies are available for inspection or copying for a fee from the NRC Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax (202)634-3343.

Copies may be purchased at current rates from the U.S. Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 (telephone (202)512-2249);

or from the National Technical Information Service by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161.

1 APPENDIX F 2 PROCEDURE TO DETERMINE THE SAFE SHUTDOWN EARTHQUAKE GROUND MOTION 3 F.1 INTRODUCTION 4 This appendix elaborates on Step 4 of Regulatory Position 4 of Draft 5 Regulatory Guide DG-1032, which describes an acceptable procedure to determine 6 the Safe Shutdown Earthquake Ground Motion (SSE). The SSE is defined in terms 7 of the horizontal and vertical free-field ground motion response spectra at 8 the free ground surface. It is developed with consideration of local site 9 effects and site seismic wave transmission effects. The SSE response spectrum 10 is determined by scaling a spectral shape determined for the controlling 11 earthquakes to the average ground motion levels for 5 and 10 Hz (So..,o), and 1 12 and 2.5 Hz (S,._2.,)

determined in Step C.2 of Appendix C to this guide. 13 It is anticipated that a regulatory guide will be developed that 14 provides guidance on assessing site-specific effects and determining smooth 15 design response spectra, taking into account recent developments in ground 16 motion modeling and site amplification studies (e.g., Ref. F.1). 17 F.2 DISCUSSION 18 For engineering purposes, it is essential that the design ground motion 19 response spectrum be a broad-band smooth response spectrum with adequate 20 energy in the frequencies of interest.

In the past, it was general practice 21 to select a standard broad-band spectrum, such as the spectrum in Regulatory 22 Guide 1.60 (Ref. F.2), and anchor it to a peak ground motion parameter 23 (usually peak ground acceleration), which is derived based on the size of the 24 controlling earthquake.

During the licensing review this spectrum was checked 25 against site-specific spectral estimates derived using Standard Review Plan 26 2.5.2 procedures to be sure that the SSE design spectrum adequately enveloped 27 the site-specific spectrum.

These past practices to define the SSE are still 28 valid and, based on this consideration, the following three possible 29 situations are depicted in Figures F.1 to F.3. 30 Figure F.1 depicts a situation in which a site is to be used for a 31 certified design with an established SSE (for instance, an Advanced Light 32 Water Reactor with 0.3g PGA SSE). In this example, the certified design SSE 33 spectrum compares favorably with the site-specific response spectra determined F-I 1 in Step 2 or 3 of Regulatory Position 4. 2 Figure F.2 depicts a situation in which a standard broad-band shape is 3 selected and its amplitude is scaled so that the design SSE envelopes the 4 site-specific spectra.

5 Figure F.3 depicts a situation in which a specific smooth shape for the 6 design SSE spectrum is developed to envelope the site-specific spectra. In 7 this case, it is particularly important to be sure that the SSE contains 8 adequate energy in the frequency range of engineering interest and is 9 sufficiently broad-band.

F-2 U 4-) U a, CL V.)1.75 7.5 Frequency, Hz Figure F.1 Use of SSE Spectrum of a Certified Design 1.75 7.5 Frequency, Hz Figure F.2 Use of a Standard Shape for SSE Sa,5-10 Smooth Broad-Band Spect rum 1.75 7.5 3 Frequency, Hz Figure F.3 Development of a Site-Specific SSE Spectrum above figures illustrate situations for a rock site, for conditions the SSE spectra are compared at free-field after site amplification studies as discussed in Step 4 of Position 4)F-3 0.3g S.a, S.C-)2 4-, o.-a, a, C C-, Cu C-)4 5 6 7 (Note: The other site performing Regulatory 1.5 .I t II 1 REFERENCES 2 F.1 Electric Power Research Institute, "Guidelines for Determining Design 3 Basis Ground Motions," EPRI Report TR-102293, Volumes 1-4, May 1993. 4 F.2 USNRC, "Design Response Spectra for Seismic Design of Nuclear Power 5 Plants," Regulatory Guide 1.60.' L 6 'Copies are available for inspection or copying for a fee from the NRC 7 Public Document Room at 2120 L Street NW., Washington, DC; the PDR's mailing 8 address is Mail Stop LL-6, Washington, DC 20555; telephone (202)634-3273; fax 9 (202)634-3343.

Copies may be purchased at current rates from the U.S. 10 Government Printing Office, P.O. Box 37082, Washington, DC 20402-9328 11 (telephone (202)512-2249);

or from the National Technical Information Service 12 by writing NTIS at 5285 Port Royal Road, Springfield, VA 22161. F-4 I REGULATORY ANALYSIS 2 A separate regulatory analysis was not prepared for this regulatory 3 guide. The draft regulatory analysis, "Proposed Revision of 10 CFR Part 100 4 and 10 CFR Part 50," was prepared for the proposed amendments, and it provides 5 the regulatory basis for this guide and examines the costs and benefits of the 6 rule as implemented by the guide. A copy of the draft regulatory analysis is 7 available for inspection and copying for a fee at the NRC Public Document 8 Room, 2120 L Street NW. (Lower Level), Washington, DC, as Enclosure 2 to 9 Secy 94-194.RA-I UNITED STATES NUCLEAR REGULATORY COMMISSION WASHINGTON, D.C. 20555-0001 FIRST CLASS MAIL POSTAGE AND FEES PAID USNRC PERMIT NO. G-67 OFFICIAL BUSINESS PENALTY FOR PRIVATE USE, $300