DEPARTMENT OF THE INTERIOR DONALD PAUL HODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging-in-Publication Data Evaluating earthquake hazards in the Los Angeles region—An earth-science perspective. (U.S. Geological Survey professional paper; 1360) Bibliography: p. 471 Supt. of Docs. no.:1 19.16:1360 1. Earthquakes California-Los Angeles region. I. Ziony, Joseph. II. U.S. Geological Survey professional paper; 1360. QE535.2.U6E93 363.3'495'0979494 85-600239 1985 For sale by the Superintendent of Documents, U.S. Government Printing Office Washington, DC 20402 FOREWORD Devastating earthquakes have sporadically struck many populated centers of the United States (for example, Boston, Mass., in 1755; Charleston, S.C., in 1886; San Francisco, Calif., in 1906; Long Beach, Calif., in 1933; Tacoma and Seattle, Wash., in 1949 and 1965; Anchorage, Alaska, in 1964; and San Fer nando, Calif., in 1971). Although a damaging earthquake at a given locality in the United States is a relatively rare event, the likelihood of truly catastrophic loss of life and property is increasing as development and construction accelerate in the 39 States that lie in regions of major or moderate potential for large earthquakes. Beginning with Clarence E. Dutton's investigations of the 1886 Charleston earthquake, scientists of the U.S. Geological Survey have studied earthquakes and their effects. The great Alaska earthquake of 1964 and the 1971 San Fernando earthquake awakened officials to the threat facing many urban areas and stimulated geologists and seismologists to analyze the conditions that control the distribution of earthquake damage. The United States Congress, recognizing that the potential for large earthquakes is a national concern, enacted the Earthquake Hazards Reduction Act of 1977 (Public Law 95-124), which establishes objectives to (1) develop earthquake-resistant engineering-design methods; (2) predict earthquakes and characterize seismic hazards; (3) develop model codes for land use and construction; and (4) prepare plans for responding to major destructive earthquakes. Within these broad objectives, two major goals of the Geological Survey have been to improve methods of evaluating geologically controlled earthquake effects and to delineate earthquake hazards in major urban regions at high seismic risk. Studies for Seismic Zonation of the San Francisco Bay Region (U.S. Geological Survey Professional Paper 941-A) was a solid advance in the assessment of earthquake hazards. That report presented methods for evaluating earthquake, surface-faulting, ground-shaking, and ground-failure potential and described a multidisciplinary approach to seismic zonation. Subsequent earth-science maps and evaluations of California's San Francisco Bay region prepared by the Geological Survey were the bases for derivative maps that are now being used in engineering design, land use planning, and emergencyresponse planning to reduce future earthquake losses. Evaluating Earthquake Hazards in the Los Angeles Region-An Earth-Science Perspective, which builds on the foundations laid by the San Francisco Bay region studies, indicates how rapidly the science of earthquake hazard assessment is evolving. For example, innovative new concepts for predicting the extent and severity of strong shaking and of earthquake-triggered landsliding have resulted from research in the Los Angeles region. In presenting state-of-the-art methods, this volume describes the potential for damaging geologic and seismologic effects and demonstrates the application of evaluative techniques to selected areas of that region. We expect to publish more detailed maps of hazard potential for much of the region over the next several years. The hazard-evaluation methods described herein can also be used for evaluating and mapping earthquake hazards in other urban areas such as Salt Lake City, Utah, Seattle, Wash., and Anchorage, Alaska, all of which are vulnerable to earthquake damage. The ultimate benefits of studies such as those reported in this volume are the reduced loss of life, injury, and property damage and the continued functioning of vital services and economic activities following a potentially destructive earthquake. To achieve these benefits, scientists, engineers, and planners must cooperate in the development of useful technical products. In turn, officials in both the private sector and in the government must determine which actions acceptable to the general public can best reduce future earthquake losses. Durent. Dallas L. Peck Director, U.S. Geological Survey The earthquake threat, 1⚫ Purpose and content of this volume, 4 • Opportunities for reducing earthquake hazards, 8⚫ Users of information for reducing earth- Plate-tectonic evolution of California, 25. Present plate-tectonic setting, 25⚫ Ef- fects of continuing deformation, 27 • Pattern of active faults, 32 Pattern of dam- aging earthquakes, 32 • Pattern of modern seismicity, 33 EVALUATING EARTHQUAKE AND SURFACE-FAULTING POTENTIAL 43 Potentially active faults of the region, 43⚫ Hazards from active faults, 60 • Ex- amples of surface faulting and related effects from southern California earth- quakes, 65⚫ Predicting the future behavior of faults, 69⚫ Implications for reduc- PREDICTING EARTHQUAKE GROUND MOTION: AN INTRODUCTION 93 Developing a data base for ground-motion estimation on a regional scale, 93⚫ Predicting earthquake intensities, 94 Predicting quantitative characteristics of ground shaking. 95. Estimating ground shaking for a postulated event, 97⚫ Common means for characterizing earthquake shaking, 97 MAPPING QUATERNARY SEDIMENTARY DEPOSITS FOR AREAL VARIATIONS IN Mapping surficial geologic units, 101⚫ Surficial geologic maps, 105⚫ Description of map units, 105 • Using physical properties of surficial geologic units to estimate relative shaking response, 112⚫ Mapping shear-wave velocity groups, 114 MAPPING SHEAR-WAVE VELOCITIES OF NEAR-SURFACE GEOLOGIC MATERIALS Geologic factors affecting shear-wave velocity, 128 • Shear-wave velocity studies in the Los Angeles region, 129⚫ Shear-wave velocities in late Quaternary sedi- mentary deposits, 130 Shear-wave velocities in pre-late Quaternary bedrock materials, 135. Preparing regional maps of shear-wave velocity, 135 PREDICTING SEISMIC INTENSITIES 151 J. F. Evernden and J. M. Thomson Why ground-motion parameters saturate at high magnitude, 152⚫ Method for PREDICTIVE MAPPING OF EARTHQUAKE GROUND MOTION 203 Predictive equations, 204⚫ Using local shear-wave velocity to improve predictions PREDICTING RELATIVE GROUND RESPONSE 221 Previous studies, 221⚫ Comparative ground response in the Los Angeles region, PREDICTING EARTHQUAKE GROUND-MOTION TIME-HISTORIES 249 The earthquake rupture process, 249 How ground motions are simulated, EARTHQUAKE-TRIGGERED GROUND FAILURE EVALUATING LIQUEFACTION POTENTIAL 263 J. C. Tinsley, T. L. Youd, D. M. Perkins, and A. T. F. Chen Liquefaction and resulting ground failure, 266 Method for evaluating liquefaction potential, 287⚫ Mapping liquefaction susceptibility, 268⚫ Liquefaction susceptibility in the Los Angeles region, 276⚫ Determining liquefaction opportunity, 297⚫ Liquefaction potential maps and their limitations, 314 PREDICTING AREAL LIMITS OF EARTHQUAKE-INDUCED LANDSLIDING 317 R. C. Wilson and D. K. Keefer Landslides in historical earthquakes worldwide, 319 Examples of landslides in California earthquakes, 323⚫ Numerical models for earthquake-induced landslides, 327⚫ Severity of shaking as a function of magnitude and distance, 332⚫ Predicting the limits of landsliding from an earthquake, 335⚫ A hypothetical site evaluation, 338 EARTHQUAKE-RELATED PHENOMENA OFFSHORE IDENTIFYING POTENTIALLY ACTIVE FAULTS AND UNSTABLE SLOPES OFFSHORE 347 S. H. Clarke, Jr., H. G. Greene, and M. P. Kennedy Acquiring and interpreting marine geophysical data, 350 Potential geologic hazards in the offshore Los Angeles region, 357 EVALUATING TSUNAMI POTENTIAL 375 D. S. McCulloch Tsunami generation and propagation, 376 California tsunami history, 387⚫ Tsunami potential in coastal southern California, 392 • Tsunami hazard reduction, 402⚫ California tsunamis from 1812 to 1975, 409 APPLICATIONS PREDICTED GEOLOGIC AND SEISMOLOGIC EFFECTS OF A POSTULATED J. I. Ziony, J. F. Evernden, T. E. Fumal, E. L. Harp, S. H. Hartzell, W. B. Joyner, D. K. Keefer, Geology of the demonstration area, 415 The postulated earthquake, 417 • Surface faulting and deformation, 419⚫ Seismic intensities, 420⚫ Horizontal acceleration, velocity, and response spectral values, 423 • Time-histories of ground motion, 430⚫ Liquefaction-related ground failure, 434⚫ Landsliding, 436⚫ Other effects, 441 USING EARTH-SCIENCE INFORMATION FOR EARTHQUAKE HAZARD REDUCTION 443 W. J. Kockelman Anticipating damage to critical facilities, 443⚫ Adopting seismic safety plans, 449⚫ Retrofitting highway bridges, 454⚫ Regulating development in potential surface fault rupture areas, 457 Strengthening or removing unsafe masonry buildings, 481. Other examples, 485 REFERENCES CITED 471 PHOTOGRAPH CREDITS p.42, aerial view northwestward along the San Andreas fault near San Bernardino (D. M. Morton, USGS); p. 100, aerial view above Pomona northeastward along eastern San Gabriel Mountains and part of upper Santa Ana River basin (D. M. Morton, USGS); p. 126, determining seismic velocities of near-surface geologic materials by using a truck-mounted recording system (L. J. Hwang, USGS); p. 150, computer-generated map showing Modified Mercalli intensities for 1952 Kem County earthquake (U.S. Geological Survey Professional Paper 1223); p. 248, San Onofre Nuclear Generating Station (J. I. Ziony, USGS); p. 316, landslide triggered by 1971 San Femando earthquake on western side of Golden State Freeway (). 1. Ziony, USGS); p. 374, damage to railroad in Seward, Alaska, from tsunami waves generated by 1964 Alaska earthquake (U.S. Coast and Geodetic Survey, now the National Ocean Survey); p. 470, Olive View Hospital after 1971 San Fernando earthquake (Reuben Kachadoorian, USGS). |