Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts

Panel on Seismic Hazard Evaluation

Committee on Seismology

Board on Earth Sciences and Resources

Commission on Geosciences, Environment, and Resources

National Research Council

NATIONAL ACADEMY PRESS
Washington, DC 1997





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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts Panel on Seismic Hazard Evaluation Committee on Seismology Board on Earth Sciences and Resources Commission on Geosciences, Environment, and Resources National Research Council NATIONAL ACADEMY PRESS Washington, DC 1997

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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competences and with regard for appropriate balance. This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. This report was prepared with the support of the U.S. Nuclear Regulatory Commission under Award No. NRC-G-04-92-117. The opinions, findings, conclusions and recommendations expressed herein are those of the author(s) and do not necessarily reflect the views of the U.S. Nuclear Regulatory Commission. Additional copies of this report are available from: Committee on Seismology Board on Earth Sciences and Resources National Research Council 2101 Constitution Avenue, NW HA 372 Washington, DC 20418 202-334-2744 The cover photo, courtesy of Walter Hays, U.S. Geological Survey, shows damage to Nimitz Freeway resulting from the Loma Prieta earthquake of 1989. Copyright 1997 by the National Academy of Sciences. All rights reserved. Printed in the United States of America

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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts PANEL ON SEISMIC HAZARD EVALUATION CARL KISSLINGER, Chairman, University of Colorado, Boulder KEIITI AKI, University of Southern California, Los Angeles WALTER J. ARABASZ, University of Utah, Salt Lake City DENNIS K. BENSON, Appropriate Solutions, Columbus, Ohio JOHN E. EBEL, Boston College, Massachusetts THOMAS C. HANKS, U.S. Geological Survey, Menlo Park, California JAMES S. LANGER, University of California, Santa Barbara NORMAN C. RASMUSSEN, Massachusetts Institute of Technology, Cambridge LEON REITER, Nuclear Waste Technical Review Board, Arlington, Virginia DANIELE VENEZIANO, Massachusetts Institute of Technology, Cambridge National Research Council Staff WILLIAM E. BENSON, Study Director JUDITH L. ESTEP, Administrative Assistant

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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts COMMITTEE ON SEISMOLOGY THOMAS H. JORDAN, Chairman, Massachusetts Institute of Technology, Cambridge WALTER J. ARABASZ, † University of Utah, Salt Lake City F. A. DAHLEN, * Princeton University, New Jersey STEVEN M. DAY, San Diego State University, California THOMAS C. HANKS, U.S. Geological Survey, Menlo Park, California CHARLES A. LANGSTON, Pennsylvania State University, University Park THORNE LAY, University of California, Santa Cruz STEWART A. LEVIN, Mobil Exploration & Production Technical Center, Dallas, Texas STEPHEN D. MALONE, University of Washington, Seattle DONALD L. PAUL, † Chevron Petroleum Technology Company, Houston, Texas JAMES R. RICE, Harvard University, Cambridge, Massachusetts PAUL G. SOMERVILLE, Woodward-Clyde Consultants, Pasadena, California ANNE M. TREHU, Oregon State University, Corvallis JOHN E. VIDALE, University of California, Los Angeles National Research Council Staff CHARLES MEADE, Senior Program Officer WILLIAM E. BENSON, Senior Program Officer JUDITH L. ESTEP, Administrative Assistant * Term expired December 31, 1995. † Term expired December 31, 1994.

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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts BOARD ON EARTH SCIENCES AND RESOURCES J. FREEMAN GILBERT, Chairman, University of California, San Diego THURE CERLING, University of Utah, Salt Lake City MARK P. CLOOS, University of Texas at Austin JOEL DARMSTADTER, Resources for the Future, Washington, DC KENNETH I. DAUGHERTY, E-Systems, Fairfax, Virginia WILLIAM R. DICKINSON, University of Arizona, Tucson, emeritus MARCO T. EINAUDI, Stanford University, California NORMAN H. FOSTER, Independent Petroleum Geologist, Denver, Colorado CHARLES G. GROAT, University of Texas, El Paso DONALD C. HANEY, Kentucky Geological Survey, Lexington SUSAN M. KIDWELL, University of Chicago, Illinois SUSAN KIEFFER, Kieffer & Woo, Inc., Palgrave, Ontario PHILIP E. LAMOREAUX, P.E. LaMoreaux and Associates, Inc., Tuscaloosa, Alabama SUSAN M. LANDON, Thomasson Partner Associates, Denver, Colorado J. BERNARD MINSTER, Scripps Institution of Oceanography, La Jolla, California ALEXANDRA NAVROTSKY, Princeton University, New Jersey JILL D. PASTERIS, Washington University, St. Louis, Missouri EDWARD C. ROY, JR., Trinity University, San Antonio, Texas National Research Council Staff CRAIG M. SCHIFFRIES, Director THOMAS M. USSELMAN, Associate Director WILLIAM E. BENSON, Senior Program Officer ANNE M. LINN, Senior Program Officer CHARLES MEADE, Senior Program Officer LALLY A. ANDERSON, Staff Associate VERNA J. BOWEN, Administrative Assistant JENNIFER T. ESTEP, Administrative Assistant JUDITH ESTEP, Administrative Assistant

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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts COMMISSION ON GEOSCIENCES, ENVIRONMENT, AND RESOURCES GEORGE M. HORNBERGER, Chairman, University of Virginia, Charlottesville PATRICK R. ATKINS, Aluminum Company of America, Pittsburgh, Pennsylvania JAMES P. BRUCE, Canadian Climate Program Board, Ottawa, Ontario WILLIAM L. FISHER, University of Texas at Austin JERRY F. FRANKLIN, University of Washington, Seattle DEBRA S. KNOPMAN, Progressive Foundation, Washington, DC PERRY L. MCCARTY, Stanford University, California JUDITH E. MCDOWELL, Woods Hole Oceanographic Institution, Massachusetts S. GEORGE PHILANDER, Princeton University, New Jersey RAYMOND A. PRICE, Queen's University at Kingston, Ontario THOMAS C. SCHELLING, University of Maryland, College Park ELLEN K. SILBERGELD, University of Maryland Medical School, Baltimore VICTORIA J. TSCHINKEL, Landers and Parsons, Tallahassee, Florida National Research Council Staff STEPHEN RATTIEN, Executive Director STEPHEN D. PARKER, Associate Executive Director MORGAN GOPNIK, Assistant Executive Director GREGORY SYMMES, Reports Officer JAMES MALLORY, Administrative Officer SANDI FITZPATRICK, Administrative Associate MARQUITA SMITH, PC Analyst

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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is interim president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce Alberts and Dr. William A. Wulf are chairman and interim vice-chairman, respectively, of the National Research Council.

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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts Preface In the 1980s two studies produced probabilistic seismic hazard estimates for nuclear power plant sites in the central and eastern United States. The first, sponsored by the U.S. Nuclear Regulatory Commission (USNRC), was conducted by Lawrence Livermore National Laboratory. The second, sponsored by utilities in the Seismicity Owners Group, was conducted by the Electric Power Research Institute (EPRI). The studies produced similar hazard curves and generally similar estimates of relative hazard. But for several sites absolute hazard levels differed by two or more orders of magnitude. Because absolute hazard levels are important for nuclear power plant design, a new study, sponsored jointly by the USNRC, EPRI, and the U.S. Department of Energy, was undertaken by the newly formed Senior Seismic Hazard Analysis Committee (SSHAC) to determine the source of the major discrepancies in the two hazard estimates and to derive a robust probabilistic seismic hazards analysis methodology that could be used for future estimates. At the same time, the USNRC asked the National Research Council (NRC) to review the work of the SSHAC study and evaluate the proposed methodology. This review was undertaken by the Panel on Seismic Hazard Evaluation of the NRC's Committee on Seismology which followed the work of the SSHAC study and produced the present critique of the SSHAC report. Carl Kisslinger Chairman

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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts Contents     EXECUTIVE SUMMARY   1      Main Features of the SSHAC Report,   2      The SSHAC Methodology,   2      Background Workshops,   3      The Treatment of Uncertainty,   3  1   INTRODUCTION   5      What Is Seismic Hazard Analysis?,   5      Background and Context of this Report,   7      Interactions of the Panel with SSHAC,   11      Organization of the Panel's Report,   13  2   PROCESS AND DOCUMENTATION FOR A PROBABILISTIC SEISMIC HAZARD ANALYSIS   15      Level of Effort in a PSHA,   16      The Multiple Roles of Experts,   17      Technical Facilitator/Integrator,   20      The Proposed TFI Process,   21      Treatment of Expert Input,   22      Integration of Expert Opinion,   22      Weighting,   25      Dependency Among Experts,   26      Peer Review,   26      Documentation,   27  3   TREATMENT OF UNCERTAINTY   31      Is the Aleatory/Epistemic Distinction Unique and Clear?,   32      Is the Epistemic/Aleatory Separation Needed?,   34

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Review of Recommendations for Probabilistic Seismic Hazard Analysis: Guidance on Uncertainty and Use of Experts  4   SEISMIC SOURCE CHARACTERIZATION   41      Scientific Validity and Clarity of Presentation,   41      Contributions to the Development of PSHA,   44      The Outlook for Evolution of SSC,   45  5   ESTIMATION OF EARTHQUAKE-GENERATED GROUND MOTION   47      Scientific Validity and Clarity of Presentation,   47      Contributions to the Development of PSHA: Summary of the Ground Motion Workshop Results,   48      Implications for Future Ground Motion Estimation,   51  6   SUMMARY AND CONCLUSIONS   57      General Appraisal of the SSHAC Report,   57      General Shortcomings and Limitations of the SSHAC Report,   58      Some Contributions of SSHAC to Hazard Assessment,   60      The TFI Methodology,   60      Clear Definition of Experts' Distinct Roles as Proponents, Evaluators, and Integrators,   61      Results of SSHAC-Sponsored Workshops,   61     REFERENCES   63  APPENDIX A:   Acronyms   65  APPENDIX B:   Letter Report of the Panel on Seismic Hazard Evaluation, March 1995   67