California Universities for Research in Earthquake Engineering Building Contractors Society of Japan UJLPE United States / Japan Loma Prieta Earthquake Project Investigations of Thirty-Three Loma Prieta Earthquake Strong Motion Recording Sites by Charles C. Thiel Jr. John F. Schneider with contributions from Susan Chang, Joseph Sun, Woodward-Clyde Consultants James Gibbs, Thomas Powers, Thomas Fumal, David Boore, William Joyner, U.S. Geological Survey Robert Steller, Robert Nigbor, Agbabian Associates Bruce B. Redpath, Redpath Geophysics Reporting information collected with the support of Building Contractors Society of Japan Electric Power Research Institute with additional support provided by U.S. Geological Survey University of California, Davis California Universities for Research in Earthquake Engineering San Francisco International Airport Authority CUREe/BCS Joint Oversight Committee: Dr. A. Endo, Kajima Corporation Dr. Y. Goto, Obayashi Corporation Dr. K. Hagio, Taisei Corporation Professor LM. Idriss, University of California, Davis Professor H.C. Shah, Stanford University Professor R. Shepherd, University of California, Irvine July 1993 © 1993 California Universities for Research in Earthquake Engineering California Universities for Research in Earthquake Engineering (CUREe) Department of Civil Engineering Stanford University Stanford, California 9305-4020 Investigations of Thirty-Three Loma Prieta Earthquake Strong Motion Recording Sites TABLE OF CONTENTS SECTIONS PAGE Preface iv 1. United States Japan Loma Prieta Earthquake Project 1 Building Contractors Society of Japan 2 California Universities for Research in Earthquake Engineering 5 Electric Power Research Institute 5 2. UJLPE Project management 6 UJLPE site investigations 7 3. The Loma Prieta earthquake 11 3.1 Overview of the Earthquake 11 3.2 Regional geological and seismological setting 13 3.3 Deep structure of the San Francisco Bay region 15 4. Strong motion observations in the Loma Prieta earthquake 22 5. Results for drilled sites 33 5.1 Sites investigated 33 5.2 Site reports 37 5.3 Electronic data base 38 6. Investigation methods 40 6.1 Geotechnical logging 40 Rock sites 40 Drilling and Sampling 40 Disposal of waste material from drilling 41 Soil sites 41 Drilling and sampling 41 Reaming and PVC casing 42 Grouting and protective covering 42 Disposal of waste material from drilling 43 6.2 Geophysical data collection for investigated sites 43 Measurement techniques and procedures 45 Suspension PS velocity logging 45 Downhole velocity surveys 49 Attenuation measurements 51 Shear-wave refraction surveys 52 7. Concluding Remarks 55 8. References 62 FIGURES 1-1 Locations of free-field strong ground motion sites. 4 3-1 Isoseismal map of the damage impacts of the Loma Prieta earthquake 12 3-2 Simplified map showing faults in the San Francisco Bay area 14 UJLPE Page i 3-3 Crustal thickness for California and adjacent regions as presented in the paper by Fuis and Mooney [1990] 17 3-4 Crustal structure in Central California along Transect C2 18 3-5 Continuation of Figure 3-4. Crustal structure in Central California along Transect C2 19 3-6 Key to symbols used in Figures 3-4 and 3-5 20 3-7 Velocity depth curves. 21 4-1 Ground stations with recorded ground motions from the Loma Prieta earthquake for which drilling has been planned or completed 27 4-2 Peak horizontal recorded accelerations for free field sites recorded during the Loma Prieta earthquake for rock, soil and soft soil sites. 28 4-3 Accelerograms for the east-west components of motions recorded at rock sites (Corralitos, Gilroy No. 1, and Santa Cruz Lick Observatory) within 20 kilometers of the source 29 4-4 Accelerograms for the east-west components of motions recorded at rock sites in San Francisco (Diamond Heights, Rincon Hill and Pacific Heights) 30 4-5 Accelerograms for the east-west components of motions recorded at soil sites in Emeryville and Oakland (Outer Wharf and 2-story building) 31 4-6 Accelerograms for the east-west components of motions recorded at the nearby Treasure Island (soil) and Yerba Buena Island (rock) sites 32 6-1 Conceptual illustration of suspension P-S logging system 47 6-2 Filtered (1000 Hz. lowpass) 78.1 foot record. 49 7-1 Composite rock shear velocity logs for suspension logged sites 56 TABLES 1-1 Strong motion sites for which site characteristics were collected during the UJLPE project 3 2-1 Original proposed listing of rock sites to be investigated 8 2-2 Original proposed rank ordering of soil sites to be drilled under UJLPE. 9 4-1 Ground stations with recorded ground motions from the Loma Prieta earthquake ordered by distant from the epicenter originally considered by JOC 23 5-1 Summary of strong motions recorded at rock sites during 1989 Loma Prieta earthquake 35 5-2 Summary of field exploration data for soil sites. 36 5-3 Summary of field exploration data recorded at soil sites during 1989 Loma Prieta earthquake 36 5-4 Strong motion sites for which site characteristics were collected during the UJLPE project 37 5-5 Single use license agreement. 39 UJLPE Page ii 6-1 Sites at which geophysics information was obtained 44 6-2 Types of geophysical data collected for investigated sites 46 7.1 Stations with recorded ground motions from the Loma Prieta earthquake with subsurface investigations 58 7.2 Summary of recorded strong motions from instrumented buildings during the Loma Prieta earthquake 58 7.3 Summary of records from other structures 61 ATTACHMENTS Tab 1 Alameda Naval Air Station Tab 2 Agnews State Hospital Tab 3 Belmont Two-story Building Tab 4 Capitola Fire Station Tab 5 Gilroy Array Number 2 Tab 6 Halls Valley Grant Park Tab 7 Hayward - CSUH Stadium Grounds Tab 8 Lawrence Livermore Site 300 Tab 9 Lexington Dam Tab 10 Martinez Veterans Administration Medical Center Tab 11 Menlo Park Veterans Administration Hospital Tab 12 Mission San Jose Fire Station Tab 13 Monterey City Hall Tab 14 Naval Station Treasure Island Tab 15 Oakland Wharf Outer Harbor Tab 16 Oakland Two-story Building Tab 17 Palo Alto Veterans Administration Hospital Tab 18 Patterson Pass Road Tab 19 Piedmont Junior High School Grounds Tab 20 Point Bonita Tab 21 Richmond City Hall Parking Lot Tab 22 SAGO South/Hollister Tab 23 San Francisco Diamond Heights Tab 24 San Francisco International Airport Tab 25 San Francisco Pacific Heights Tab 26 San Francisco Rincon Hill Tab 27 San Francisco Telegraph Hill Tab 28 San Francisco Veterans Administration Medical Center Tab 29 Santa Cruz/Lick Observatory Electronics Laboratory Tab 30 South San Francisco Sierra Point Tab 31 University of California Haviland Hall Tab 32 University of California Memorial Stadium Tab 33 Yerba Buena Island UJLPE Page iii PREFACE The advance of earthquake engineering in general, and strong motion seismology in particular, depends on data—observations and measurements of earthquake response. These data will help in formulating, calibrating and verifying existing and future analytical procedures. Over the past 60 years, and particularly in the last two decades, an unheralded group persisted in installing and maintaining strong motion instruments, just waiting for the moment when useful data would be recorded. For instruments in the San Francisco Bay area, that moment came in 1989 with the Loma Prieta earthquake of October 17. Now we have a wealth of strong motion recordings, but we do not know much about the sites where the instruments were installed and how these site conditions may have effected the recordings. In the desire for data, instruments were installed without determining the details of their supporting foundation materials. This was prudent: the number of instruments installed could thereby be substantially increased whereas site information could be collected after the earthquake. Collection of such subsurface site information was the goal of this project. The U.S. Geological Survey embarked on a program of site investigations, but was limited by budget and by the enormity of the task. The Building Contractors Society of Japan (BCS) and the Electric Power Research Institute (EPRI) recognized both the value of the strong motion data and the importance of accelerating the determination of site properties. BCS, whose members are Japanese construction firms, and EPRI, whose members are US electric power utilities, undertook at considerable expense to add important sites, a total of 33 reported here, to the catalog of those whose site characteristics have been investigated. USGS contributed expertise to these efforts. Many others also participated in this effort, including: the University of California at Davis, California Universities for Research in Earthquake Engineering (CUREe), San Francisco International Airport Authority, and Purdue University. Just as important as the commitment to the investigation work of the sponsors was their decision that the information obtained be made public for all to use. This report is the product of many individuals' and institutions' efforts. CUREe and EPRI are pleased to acknowledge the contributions of those named in the text as well as many unnamed others who recognized the value of the data and contributed unselfishly. Of the latter, those whose perseverance lead to the network of installed instruments are of particular note. The BCS/CUREe Joint Oversight Committee and the Japanese sponsors made many useful suggestions and recommendations—Drs. Endo, Goto, Hagio, Idriss, Shah and Shepherd each brought an important understanding and insight to the program that shaped its outcome. The efforts of Woodward-Clyde Consultants, Agbabian Associates and Redpath Geophysics all worked beyond their contract terms for the benefit of obtaining the information reported in this report. UJLPE Page iv CUREe gratefully acknowledges the financial support of the Building Contractors Society of Japan. On behalf of current and future research and earthquake engineering users, CUREe thanks the Building Contractors Society of Japan and the Electric Power Research Institute for having the foresight to provide the means to obtain this much needed data.