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The Loma Prieta (Santa Cruz Mountains), California, Earthquake of 17 October 1989

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The Loma Prieta (Santa Cruz Mountains), California, Earthquake of 17 October 1989 SPECIAL PUBLICATION 104 PHYSICAL SCIENCES | LIBRARY UC DA I CALIFORNIA DEPARTMENT OF CONSERVATION D Division of Mines and Geology ( THE RESOURCES AGENCY STATE OF CALIFORNIA DEPARTMENT OF CONSERVATION GORDON K. VAN VLECK GEORGE DEUKMEJIAN RANDALL M.WARD SECRETARY FOR RESOURCES GOVERNOR DIRECTOR DIVISION OF MINES AND GEOLOGY JAMES F. DAVIS STATE GEOLOGIST Cover Photo: View to the south of Hazel Dell Road, located in the Santa Cruz Mountains about 8.5 kilometers north of Watsonville. The large fissures in the road were caused by lateral spreading due to lique- faction of saturated sediments in Simas Lake and intense shaking associated with the fVL 7.1 Loma Prieta earthquake (note leaning telephone pole). Simas Lake, located just west of Hazel Dell Road, is a closed depression formed by recurring surface fault rupture along the San Andreas fault. Photo by W. A. Bryant, 10/18/89. irf . y//V THE LOMA PRIETA (SANTA CRUZ MOUNTAINS), CALIFORNIA, EARTHQUAKE OF 17 OCTOBER 1989 Edited by Stephen R. McNutt and Robert H. Sydnor Special Publication 104 1990 Department of Conservation Division of Mines and Geology 1416 Ninth Street, Room 1341 Sacramento, CA 95814 3 .- v«^ 1 '" ''* * * .' C3Mte* it Si J r- f %lti' i--' /J '-%J. #• 1 CONTENTS INTRODUCTION v Stephen R. McNult and Robert H. Sydnor SECTION I. The Earthquake \ Geologic and Tectonic Setting of the Epicentral Area of the Loma Prieta Earthquake, Santa Cruz Mountains, Central California 1 David L. Wagner Seismological Aspects of the 17 October 1989 Earthquake 1 Stephen R. McNutt and Tousson R. Toppozada SECTION II. Earthquake Effects Strong Ground Shaking from the Loma Prieta Earthquake of 17 October 1989 and Its Relation to Near Surface Geology in the Oakland Area 29 Anthony F. Shakal, Mark J. DeLisle, Michael S. Reichle, and Robert B. Darragh Preliminary Analysis of Processed Strong Motion Data from the Loma Prieta Earthquake 47 Michael S. Reichle, Robert B. Darragh, Moh-Jiann Huang, Tianqing Cao, Ute R. Vetter, and Anthony F. Shakal Landslide Features and Other Coseismic Fissures Triggered by the Loma Prieta Earthquake, Central Santa Cruz Mountains, California 59 Thomas E. Spittler, Edwin L. Harp, David K. Keefer, Raymond C. Wilson, and Robert H. Sydnor Coastal Bluff Landslides in Santa Cruz County Resulting from the Loma Prieta Earthquake of 17 October 1989 67 Robert H. Sydnor, Gary B. Griggs, Gerald E. Weber, Richard J. McCarthy, and Nathaniel Plant The Search for Fault Rupture and Significance of Ridgetop Fissures, Santa Cruz Mountains, California 83 Earl W. Hart, William A. Bryant, Christopher J. Wills, and Jerome A. Treiman Coseismic Bedding Plane Faults and Ground Fissures Associated with the Loma Prieta Earthquake of 17 October 1989 95 William R. Cotton, William L. Fowler, and Joan E. Van Velsor Earthquake Damage in Soquel Demonstration State Forest, Santa Cruz County 105 Trinda L. Bedrossian and Julie A. Sowma Representative Damage Photographs from the Loma Prieta Earthquake 1 13 David R. Montgomery SECTION III. Earthquake Response High-Altitude U-2 Photography for Post-Earthquake Disaster Assessment 121 Charles R. Real, Robert E. Yoha, and Fumio Kaneko Loma Prieta Earthquake Response Activitiesv; of the Division of Mines and Geology 127 Robert Streitz, Robert H. Sydnor, Allan G. Barrows, and Thomas E. Spittler Summary of Damage and Losses Caused by the Loma Prieta Earthquake ...... 131 Stephen R. McNutt Lomai Prieta and EarthquakeEartl Preparedness ..o. 139 Richard A. Andrews in Digitized by the Internet Archive in 2012 with funding from University of California, Davis Libraries http://archive.org/details/lomaprietasantac104cali INTRODUCTION by Stephen R. McNutt and Robert H. Sydnor The Loma Prieta earthquake of 17 October 1989 did more to make people in California aware of earthquake hazards than any other single event of the last 18 years. The event killed 63 people, injured 3,757, left over 12,000 homeless, and caused over $5.9 billion in damage (California Office of Emergency Services, written communication, April 12, 1990). Damage occurred over a wide area (Figure 1) and included effects of strong shaking and various forms of ground failure including liquefaction. The earthquake has provided a wealth of new data, has prompted new legislation, and has refocused discussions on numerous topics related to hazards mitigation. A significant earthquake always provides an opportunity to learn, to respond, and to refocus hazard mitigation efforts. This Special Publication primarily documents actions of the California Department of Conservation's Division of Mines and Geology (DMG) to respond to and study the earthquake. The report contains a variety of information on seismological and geological features of the event. The intended readers are primarily other researchers and government agencies, but much of the information provided will also be useful to the media and the public. DMG ROLE AND ORGANIZATION DMG is the State geological survey, with a staff of 144 people and an annual budget of ap- - proximately $ 1 2 million. It has three primary functions: ( 1 ) Geologic Hazards Reduction to prevent loss of life and property from geologic phenomena including earthquakes, fault move- ments, volcanic eruptions, landslides, and erosion; (2) Mineral Resources Conservation - to promote the development, use and reclamation of land and mineral resources consistent with sound conservation practices; and (3) Basic Investigations - to establish and maintain a baseline of geological, geophysical, and seismological information. The organization consists of five main programs, four of which responded to the 17 October 1989 earthquake. The five are: (1) Environmental Protection; (2) Geologic Hazards Assessment; (3) Earthquake Engineering; (4) Geologic Information and Support; and (5) Mineral Resource Development (no response). Response consisted of collecting, compiling, analyzing, and interpret- ing a wide variety of data and communicating results to many levels of users. DMG has produced Special Publications and other books on significant earthquakes since the Kern County earthquake of 1952 (Oakeshott, 1955). The most recent such efforts were Special Publication 66 on the 1983 Coalinga earthquake (Bennett and Sherburne, 1983) and Special Publication 68 on the 1984 Morgan Hill earthquake (Bennett and Sherburne, 1984). DMG produces such reports when specific circumstances warrant the effort. CONTENTS OF THIS REPORT This report is a collection of 14 papers representing the efforts of 35 authors. Most of the papers are by DMG staff members and thus provide a record of DMG actions. The editorial phi- losophy was to allow each paper to stand alone and to include the appropriate and necessary papers so that the pertinent information was contained in one volume. The time frame of the publication (about 4 to 6 months after the earthquake) permitted the information contained to be more complete than initial reports that were prepared about one month after the event. Many results, however, cannot yet be regarded as definitive. 122° 30 122° 00' 121°30' Figure 1 . Mainshock epicenter of Loma Prieta earthquake and inferred fault rupture relative to areas of larger after- shocks, abundant ground cracks, and landslides and to limits of structural damage. Also shown are locations of major damaged structures and principal areas of ground cracks and liquefaction (source: Plafker and Galloway, 1989). VI This Special Publication is divided into EXPLANATION three sections. The first focuses on the earth- quake itself and its geologic seismologic D and Fault rupture of Loma Prieta earth- setting. The second section focuses on selected u 1 — quake-Arrows show relative horizon- 70 effects of the earthquake and study by several tal movement; small arrow and numeral show direction and amount DMG programs. Key contributions are those on of dip; U, upthrown side; strong ground motion, landslides, and fault D, downthrown side evaluation. The third section focuses on Fault -Dashed where approximately response and evaluation. located Special effort has gone into providing * Main shock epicenter many high quality figures and complete tables the publication. Area of aftershocks and abundant land- throughout This was done to mm slides make the volume useful as a reference work on the Loma Prieta earthquake and on related /////// Area of ground cracks possibly related to faulting geologic phenomena. For example, much of the information contained in the volume will be Approximate limit of major structural damage useful as background information when the next M> 7 earthquake strikes California. Approximate limit of landslides © Prominent area of liquefaction The choice of topics was made to highlight DMG activities and to provide balance. How- ® Damaged bridge ever, it was not possible to cover every aspect Damaged dam ® of the earthquake. For example, liquefaction Damaged two-story viaduct ® and several engineering aspects of the event have received only limited attention here. These Figure 1. Continued have received adequate attention elsewhere (e.g., Plafker and Galloway, 1989). GENERAL INFORMATION The Loma Prieta earthquake epicenter is located in the Laurel quadrangle, U.S. Geological Survey 7.5-Minute Series (Topographic), and immediately adjacent to the Loma Prieta quadrangle of the same series. The epicenter was located in the Forest of Nisene Marks State Park. The event occurred in the southern Santa Cruz Mountains, a physiographic feature which appears in most world atlases; Loma Prieta is the highest peak in these mountains and is located just a few kilometers from the epicenter. Under contract from the California Coastal Commission, the Division of Mines and Geology and the U. S. Geological Survey have cooperatively prepared a comprehensive set of seven regional geologic maps which cover the entire California continental margin at a scale of 1 :250,000. Map area 5, covering the Santa Cruz and Monterey Bay area, is scheduled to be published in mid- 1990; see Cockerham and others (1990) and McCulloch and Greene (1990). The new 1 :750,000-scale State Fault Activity Map (Jennings, 1991, in preparation) will delineate active faults in California using a five color classification scheme for recency of faulting.
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