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Strong Ground Motion The Lorna Prieta, California, Earthquake of October 17, 1989-Strong Ground Motion ROGER D. BORCHERDT, Editor STRONG GROUND MOTION AND GROUND FAILURE Thomas L. Holzer, Coordinator U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1551-A UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1994 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Manuscript approved for publication, October 6, 1993 Text and illustrations edited by George A. Havach Library of Congress catalog-card No. 92-32287 For sale by U.S. Geological Survey, Map Distribution Box 25286, MS 306, Federal Center Denver, CO 80225 CONTENTS Page A1 Strong-motion recordings ---................................. 9 By A. Gerald Brady and Anthony F. Shakal Effect of known three-dimensional crustal structure on the strong ground motion and estimated slip history of the earthquake ................................ 39 By Vernon F. Cormier and Wei-Jou Su Simulation of strong ground motion ....................... 53 By Jeffry L. Stevens and Steven M. Day Influence of near-surface geology on the direction of ground motion above a frequency of 1 Hz----------- 61 By John E. Vidale and Ornella Bonamassa Effect of critical reflections from the Moho on the attenuation of strong ground motion ------------------ 67 By Paul G. Somerville, Nancy F. Smith, and Robert W. Graves Influences of local geology on strong and weak ground motions recorded in the San Francisco Bay region and their implications for site-specific provisions ----------------- --------------- 77 By Roger D. Borcherdt and Gary Glassmoyer Ground response on Treasure Island ....................... 109 By Kyle M. Rollins, Michael D. Mchood, Roman D. Hryciw, Matthew Homolka, and Scott E. Shewbridge 123 Behavior of young bay mud from the Marina District of San Francisco under static and cyclic simple shear ............................................ ------------- 145 By Nicholas Sitar and Rodrigo Salgado 111 Deep instrumentation array at the Treasure Island Naval Air Station ----------------------------------------- 155 By Pedro de Alba, Jean Benoit, Daniel G. Pass, John J. Carter, T. Leslie Youd, and Anthony F. Shakal Site response in Oakland, California, near the failed section of the Nimitz Freeway ......................... 169 By E.H. Field, Susan E. Hough, Klaus H. Jacob, and Paul A. Friberg Aftershock observations from a dense array in Sunnyvale, California .................................... 181 By Arthur Frankel, Susan E. Hough, Paul A. Friberg, and Robert Busby A three-dimensional simulation of seismic waves in the Santa Clara Valley, California, from an aftershock ...................... --------- - ------- -------- --- 197 By Arthur Frankel and John E. Vidale Site-response models from high-resolution seismic reflection and refraction data recorded in Santa cmz, California ................................. - --------- 217 By Robert A. Williams, Edward Cranswick, and Kenneth W. King Variation of seismic site effects in the Santa Cruz Mountains, California -- ------ -- -------- - ------ ------- ---- 243 By Grant T. Lindley and Ralph J. Archuleta A postearthquake reevaluation of seismic hazard in the San Francisco Bay region -------- -------- ---------- 255 By Janice M. Murphy and Steven G. Wesnousky THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: STRONG GROUND MOTION AND GROUND FAILURE STRONG GROUND MOTION SYNOPSIS By Roger D. Borcherdt, U.S. Geological Survey CONTENTS mitigation measures for larger earthquakes likely to oc- cur much closer to densely urbanized areas in the San Francisco Bay region (Housner and Penzien, 1990). Page The earthquake generated an especially important data Introduction ............................................................... A1 Earthquake rupture and crustal-propagation effects -------------- 1 set for understanding variations in the severity of strong Effects of local geologic deposits ------------------------------------ 2 ground motion. Instrumental strong-motion recordings Implications of strong-motion recordings .................... 2 were obtained at 131 sites located from about 6 to 175 Implications of aftershock recordings ......................... 4 km from the rupture zone. This set of recordings, the Implications for seismic hazard in the San Francisco Bay largest yet collected for an event of this size, was ob- region ............................................................. 5 General conclusions ..................................................... 5 tained from sites on various geologic deposits, including References cited ......................................................... 6 a unique set on "soft soil" deposits (artificial fill and bay mud). These exceptional ground-motion data are used by the authors of the papers in this chapter to infer radiation characteristics of the earthquake source, identify domi- nant propagation characteristics of the Earth's crust, INTRODUCTION quantify amplification characteristics of near-surface geologic deposits, develop general amplification factors Strong ground motion generated by the Loma Prieta, for site-dependent building-code provisions, and revise Calif., earthquake (Mp-7.1) of October 17, 1989, re- earthquake-hazard assessments for the San Francisco sulted in at least 63 deaths, more than 3,757 injuries, and Bay region. Interpretations of additional data recorded in damage estimated to exceed $5.9 billion. Strong ground well-instrumented buildings, dams, and freeway over- motion severely damaged critical lifelines (freeway over- passes are provided in other chapters of this report. passes, bridges, and pipelines), caused severe damage to poorly constructed buildings, and induced a significant number of ground failures associated with liquefaction and landsliding. It also caused a significant proportion of EARTHQUAKE RUPTURE AND the damage and loss of life at distances as far as 100 km CRUSTAL-PROPAGATION EFFECTS from the epicenter. Consequently, understanding the characteristics of the strong ground motion associated Numerous models have been inferred regarding the with the earthquake is fundamental to understanding the characteristics and distribution of earthquake rupture re- earthquake's devastating impact on society. The papers sponsible for generating the dominant features of the assembled in this chapter address this problem. earthquake's seismic radiation field. Details of these Damage to vulnerable structures from the earthquake models differ, but their general features, derived from varied substantially with the distance from the causative both teleseismic and strong-motion data, are consistent. fault and the type of underlying geologic deposits. Most The models imply that (1) fault rupture initiated near the of the damage and loss of life occurred in areas under- bottom (16-18-km depth) of a seismogenic zone in the lain by "soft soil." Quantifying these effects is important San Andreas fault; (2) rupture propagated bilaterally at for understanding the tragic concentrations of damage about 80 percent of the local shear velocity over an area in such areas as Santa Cruz and the Marina and Embar- extending about 15 km northwestward and 20 km south- cadero Districts of San Francisco, and the failures of the eastward along the fault and to within 2 to 3 km of the San Francisco-Oakland Bay Bridge and the Interstate Earth's surface; and (3) slip was irregular but concen- Highway 880 overpass. Most importantly, understanding trated in two regions, with maximums exceeding 4 m these effects is a necessary prerequisite for improving and centered about 6 to 7 km on each side of rupture A2 STRONG GROUND MOTION AND GROUND FAILURE initiation and at a depth ranging from 10 to 14 km (Choy evidence that the shaking in San Francisco and Oakland and Boatwright, 1990; Hartzell and others, 1991 ; Beroza, was dominated by shear (SH)-wave energy reflected in press; Steidl and others, in press; Wald and others, in from the base of a relatively shallow Earth's crust (25 press). km thick) in the region (see Borcherdt and Glassmoyer, An especially important characteristic of the rupture this chapter; Somerville and others, this chapter; Stevens process is that the rupture proceeded bilaterally from its and Day, this chapter; McGarr and others, 1991). Calcu- point of initiation. As a result, the rupture process was lations suggest peak amplitudes for reflected waves as relatively brief, lasting only 6 to 8 s; waveforms of the much as 2.5 times larger than for direct waves (see dominant radiated energy are quite simple and of short Somerville and others, this chapter). duration, consistent with a relatively simple rupture pro- The direction of dominant shaking observed at sites in cess (for example, Beroza, in press, figs. 5, 6; see Bor- San Francisco and Oakland was perpendicular to the cherdt and Glassmoyer, this chapter, fig. 2). Damage strike of the San Andreas fault. This direction is readily could have been substantially greater had a unilateral or apparent from ground motions inferred for this direction more complex rupture process occurred to increase the (see Borcherdt and Glassmoyer, this chapter, fig. 2) and duration of shaking by at least 50 percent (see Som- from particle-motion plots for ground motions at periods erville and others, this chapter). Kanamori and Satake longer than 1 s (see Vidale and Bonamassa,
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