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Seismic Hazard Analysis Application of Methodology, Results, and Sensitivity Studies XA04NO052 NUREG/CR-1582, Vol. 4 UCRL-53030, Vol. 4 INIS-XA-N--035 Seismic Hazard Analysis Application of Methodology, Results, and Sensitivity Studies D. L. Bernreuter Prepared for U.S. Nuclear Regulatory Commission Lvmwve LK"7TIM NOTICE This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, apparatus product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights. Available from GPO Sales Program Division of Technical Information and Document Control U. S. Nuclear Regulatory Commission Washington, D. C. 20555 Printed copy price: $10.00 and National Technical Information Service Springfield, Virginia 22161 NUREG/CR-1582, Vol. 4 UCRL-53030, Vol. 4 Seismic Hazard Analysis Application of Methodology, Results, and Sensitivity Studies Manuscript Completed: August 1981 Date Published: October 1981 Prepared by D. L. Bernreuter Lawrence Livermore National Laboratory 7000 East Avenue Livermore, CA 94550 Prepared for Office of Nuclear Reactor Regulation U.S. Nuclear Regulatory Commission Washington, D.C. 20555 NRC FIN No. FIN. No. A0233 ABSTRACT As part of the Site Specific Spectra Project, this report seeks to identify the sources of and minimize uncertainty in estimates of seismic hazards in the Eastern United States. Findings are being used by the Nuclear Regulatory Commission to develop a synthesis among various methods that can be used in evaluating seismic hazard at the various plants in the Eastern United States. In this volume, one of a five-volume series, we discuss the application of the probabilistic approach using expert opinion. The seismic hazard is developed at nine sites in the Central and Northeastern United States, and both individual experts' and synthesis results are obtained. We also discuss and evaluate the ground motion models used to develop the seismic hazard at the various sites, analyzing extensive sensitivity studies to determine the important parameters and the significance of uncertainty in them. Comparisons are made between probabilistic and real spectra for a number of Eastern earthquakes. The uncertainty in the real spectra is examined as a function of the key earthquake source parameters. In our opinion, the single most important conclusion of this study is that the use of expert opinion to supplement the sparse data available on Eastern United States earthquakes is a viable approach for determining estimated seismic hazard in this region of the country. CONTENTS Nomenclature . ix 1.0 introduction . I 1.1 Background . 1 2.0 Review of hazard assessment methodology used . 3 3.0 Ground motion models . 5 3.1 Background . 5 3.2 Inferring EUS ground motion . 6 3.3 Modeling uncertainty . 7 3.4 Data sets used . 8 3.4.1 Intensity attenuation data base . a 3.4.2 Strong ground motion data base . .. 9 3.5. Site correction factors . 11 3.6 Development of ground motion models . 13 3.6.1 Distance-weighted model . 13 3.6.2 Magnitude-weighted models . 16 3.6.3 Theoretical model . 18 3.7 Evaluation of ground motion models . 19 3.7.1 Scaling for magnitude . 19 3.7.2 Correction for EUS attenuation . 22 3.7.3 Correction for Bite factors . 24 4.0 Spectra based on real records . 26 4.1 Introduction . 26 4.2 Factors influencing choice of records . 26 4.3 Relation between mb and mL . 27 4.4 Adequacy of sample . 29 4.5 Records used and spectra generated . 29 4.6 Magnitude effects . 32 4.7 Distance effects . 34 4.8 Conclusions . 36 v 5.0 Discussion of results . 37 5.1 Background . 37 5.2 Summary of Appendix A . 38 5.3 Summary of Appendix . 39 5.4 Summary of Appendix C . 40 5.5 Additional sensitivity studies . 41 5.6 Discussion and conclusions . 52 References . 57 Appendix A Excerpts from the August, 1979 Draft of Seismic Analysis: Site-Specific Response Spectra Results . A-1 Appendix B Copy of May, 1980 Site-Specific Response Spectra Sensitivity Results . -1 Appendix C Copy of February, 1981 Final Repo t Seismic Hazard Analysis: Results . C-1 Appendix D Assessment of Changes in the Ossippee Attenuation Model . D-1 Appendix E Listing of Set and Set 2 . E-1 vi LIST OF TABLES 3-1. Summary of earthquakes used in the intensity data base. 9 3-2. Summary of regression analysis on site geology, using an unweighted and weighted data set. 12 3-3. Comparison of magnitude scaling in different ground motion models. 21 4-1. Values of local magnitude (M ) for L . (b)E arrived at by two different equation .. 29 4-2. Median and la peak accelerations and number of earthquakes for each set of real records . 32 5-1. No-background case for Palisades, using Experts 8 9 and 10. 43 5-2. No-background case for Big Rock Point, using Experts 8 9 and 10. 44 5-3. No-background case for Dresden, using Experts 8 9 and 10. 45 5-4. No-background case for LaCrosse, using Experts 8 9 and 10. 46 5-5. No-background case for Yankee Rowe, using Experts 8 9 and 10. 47 5-6. No-background case for Connecticut Yankee, using Experts 8 9 and 10. 48 5-7. No-background case for Millstone, using Experts 8 9 and 10. 49 5-8. No-background case for Oyster Creek, using experts 8 9 and 10. so 5-9. No-background case for Ginna, using Experts 8 9 and 10. 51 5-10. Comparison of two experts' peak ground acceleration results from Nuttli's theoretical model and synthesis. 52 Vii NOMENCLATURE Commonly used terms and abbreviations: CIT Used in referring to the data set of strong motion accelerograms and computed response spectra which the California Institute of Technology published between 1969 and 1974. CUS Central United States, roughly the area bounded in the west by the Rocky Mountains and on the east by the Appalachian Mountains, excluding both mountain systems themselves. EUS Sometimes used to denote the general geographical region east of the Rocky Mountains, and sometimes used to mean the specific region east of the Central United States (CUS). Intensity The intensity at which a specific earthquake is felt, as measured on the Modified Mercalli Scale. LLNL Lawrence Livermore National Laboratory, the overall project manager and director of this study. NRC Nuclear Regulatory Commission PGA Peak Ground Acceleration PGV Peak Ground Velocity PSA Pseudo-absolute acceleration spectrum. Also see definition of spectra below and Section of Appendix C. PSRV Pseudo Relative Velocity Spectrum. Also see definition of spectra below and Section of Appendix C. Return period Inverse of the annual risk of exceedance. SEP Systematic Evaluation Program, which includes this study. Also see Volume . Spectra used generically to refer to all the different spectra, e.g., Fourier amplitude spectra of the ground motion acceleration, the relative velocity spectra at various damping levels, etc. Also used specifically in this report: the regression analysis on spectral ordinates were at % damping for the pseudo-absolute acceleration spectra (PSA) at nine frequencies 25, 20, 12.5, 10, 5, 33, 25,1, 0.5 Hz) These were converted to PSRV by the usual relations. ix SSSP Site Specific Spectra Project TERA The corporation which served as LLNL's primary subcontractor in the development and application of the methodology presented in Volumes 2 and 3. WUS The regions in the Western United States where we have strong ground motion data recorded and analyzed. Comonly used symbols- C Coefficients of different parameters in the equations. The coefficients are determined by regression analysis. GM Ground motion parameter, used in discussing a variety oil measurements, e.g., peak acceleration (a), peak velocity M, etc. Is Local site intensity, as measured on the Modified Mercalli Scale. I0 Epicentral intensity, as measured on the Modified Mercalli Scale. M Used generically for any of the many magnitude scales but generally mb' mb (Lg), or ML. ML Local magnitude (Richter magnitude scale). mb True body wave magnitude scale, assumed to be equivalent to mb (Lg) (see Chung and Bernreuter, 1980). mb(Lg) Nuttili's magnitude scale for the Central United States. MS Surface wave magnitude Q Seismic quality factor, which is inversely proportional to the anelastic damping factor. R Distance metric, generally either the epicentral distance from a recording site to the earthquake or the closest distance between the recording site and the ruptured fault for a particular earthquake. S Site factor used in the regression analysis = for soil and = for rock sites. x 1.0 INTRODUCTION 1.1 BACKGROUND The Site Specific Spectra Project (SSSP) was conceived as a multi-method approach for determining site-specific spectra (Bernreuter, 1979a) It encompasses probabilistic approaches for predicting peak acceleration, peak velocities, and uniform hazard spectra for different return periods and also an empirical approach which includes calculation of 50th and 84th percentile spectra from ensembles of real data at different magnitudes, site conditions, and distance ranges. The probabilistic approach is basically that suggested by Cornell 1968), modified to formally incorporate 'expert" judgments. This approach is explained in detail in Volume 2. This project represented both research into the use of expert judgment in seismic hazard analysis and an effort to carry out a licensing action of the Systematic Evaluation Program (SEP). This led to conflicts between the need to obtain results that were timely for licensing requirements and the need to understand intermediate results and sensitivities before releasing the final product.
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