SEISMIC HAZARD ZONE REPORT 081

SEISMIC HAZARD ZONE REPORT FOR THE

OAKLAND WEST 7.5-MINUTE QUADRANGLE,

ALAMEDA COUNTY, CALIFORNIA

DEPARTMENT OF CONSERVATION

California Geological Survey

STATE OF CALIFORNIA

GRAY DAVIS

GOVERNOR

THE RESOURCES AGENCY

MARY D. NICHOLS

SECRETARY FOR RESOURCES

DEPARTMENT OF CONSERVATION

DARRYL YOUNG

DIRECTOR

CALIFORNIA GEOLOGICAL SURVEY

JAMES F. DAVIS, STATE GEOLOGIST

Copyright © 2003 by the California Department of Conservation. All rights reserved. No part of this publication may be reproduced without written consent of the Department of Conservation.

“The Department of Conservation makes no warrantees as to the suitability of this product for any particular purpose.”

SEISMIC HAZARD ZONE REPORT 081

SEISMIC HAZARD ZONE REPORT FOR THE

OAKLAND WEST 7.5-MINUTE QUADRANGLE,

ALAMEDA COUNTY, CALIFORNIA

CALIFORNIA GEOLOGICAL SURVEY'S PUBLICATION SALES OFFICES:

Southern California Regional Office 655 S. Hope Street, Suite 700 Los Angeles, CA 90017

(213) 239-0878

Publications and Information Office 801 K Street, MS 14-31 Sacramento, CA 95814-3531

(916) 445-5716

Bay Area Regional Office 185 Berry Street, Suite 210 San Francisco, CA 94107-1728

(415) 904-7707

List of Revisions – Oakland West SHZR 081

9/1/05 BPS address corrected and web links updated

10/10/05 Bay Area Regional Office and Southern California Regional Office addresses updated

CONTENTS

EXECUTIVE SUMMARY .......................................................................................................... vii

INTRODUCTION

SECTION 1 LIQUEFACTION EVALUATION REPORT Liquefaction Zones in the Oakland West 7.5-Minute Quadrangle, Alameda County, California

PURPOSE

BACKGROUND

METHODS SUMMARY

SCOPE AND LIMITATIONS

PART I

PHYSIOGRAPHY

GEOLOGY

ENGINEERING GEOLOGY

GROUND WATER

PART II

LIQUEFACTION POTENTIAL

LIQUEFACTION SUSCEPTIBILITY

LIQUEFACTION OPPORTUNITY

LIQUEFACTION ZONES

ACKNOWLEDGMENTS

REFERENCES

iii

SECTION 2 EARTHQUAKE-INDUCED LANDSLIDE EVALUATION REPORT Earthquake- Induced Landslide Zones in the Alameda County Part of the Oakland West 7.5-Minute Quadrangle, California

PURPOSE

BACKGROUND

METHODS SUMMARY

SCOPE AND LIMITATIONS

PART I

PHYSIOGRAPHY

GEOLOGY

ENGINEERING GEOLOGY

PART II

EARTHQUAKE-INDUCED LANDSLIDE HAZARD POTENTIAL

EARTHQUAKE-INDUCED LANDSLIDE HAZARD ZONE

ACKNOWLEDGMENTS

REFERENCES

AIR PHOTOS

APPENDIX A Source of Rock Strength Data

SECTION 3 GROUND SHAKING EVALUATION REPORT Potential Ground Shaking in the Oakland West 7.5-Minute Quadrangle, Alameda County, California

PURPOSE

EARTHQUAKE HAZARD MODEL

APPLICATIONS FOR LIQUEFACTION AND LANDSLIDE HAZARD ASSESSMENTS 50

USE AND LIMITATIONS

REFERENCES

iv

ILLUSTRATIONS

Figure 2.1. Yield Acceleration vs. Newmark Displacement for the Southern California Edison Lucerne Record

Figure 3.1. Oakland West 7.5-Minute Quadrangle and portions of adjacent quadrangles, 10 percent exceedance in 50 years peak ground acceleration (g)—Firm rock conditions

Figure 3.2. Oakland West 7.5-Minute Quadrangle and portions of adjacent quadrangles, 10 percent exceedance in 50 years peak ground acceleration (g)—Soft rock conditions

Figure 3.3. Oakland West 7.5-Minute Quadrangle and portions of adjacent quadrangles, 10 percent exceedance in 50 years peak ground acceleration (g)—Alluvium conditions

Figure 3.4. Oakland West 7.5-Minute Quadrangle and portions of adjacent quadrangles, 10 percent exceedance in 50 years peak ground acceleration—Predominant earthquake

Figure 3.5. Oakland West 7.5-Minute Quadrangle and portions of adjacent quadrangles, 10 percent exceedance in 50 years magnitude-weighted pseudo-peak acceleration for alluvium - Liquefaction opportunity

Table 1.1. Correlation of Quaternary Stratigraphic Nomenclatures Used within the Oakland West Quadrangle

Table 1.2. Geotechnical Characteristics for Quaternary Geological Units in the Oakland West 7.5-Minute Quadrangle

Table 1.3. Liquefaction Susceptibility for Quaternary Map Units within the Oakland West 7.5-Minute Quadrangle

Table 2.1. Summary of the Shear Strength Statistics for the Oakland West Quadrangle

Table 2.2. Summary of Shear Strength Groups for Geologic Formations that Occur within the Oakland West Quadrangle

Table 2.3. Hazard Potential Matrix for Earthquake-Induced Landslides in the Oakland West Quadrangle

Plate 1.1. Quaternary geologic map of the Oakland West 7.5-Minute Quadrangle, California 56

Plate 1.2. Historical liquefaction sites, depth to historically highest ground water, and location of boreholes used in this study, Oakland West 7.5-Minute Quadrangle, California

Plate 2.1. Shear test sample locations, Oakland West 7.5-Minute Quadrangle v

EXECUTIVE SUMMARY

This report summarizes the methods and sources of information used to prepare the Seismic Hazard Zone Map for the Alameda County portion of the Oakland West 7.5-Minute Quadrangle.

This map and report replace the map released in 2000 that covers only the City of Oakland. The map displays the boundaries of zones of required investigation for liquefaction and earthquake-induced landslides over an area of approximately 25 square miles at a scale of 1 inch = 2,000 feet.

The quadrangle includes Yerba Buena Island and part of Treasure Island on the west where land within the city and county of San Francisco was zoned in 2000. The boundary between Alameda and San Francisco counties trends northwesterly through the center of San Francisco Bay across the quadrangle. On the eastern side of the quadrangle, Official Seismic Hazard Zone maps covering the cities of Oakland and Piedmont were released in 2000. The current study completes seismic zoning within the Alameda County part of the quadrangle and includes the cities of Berkeley, Oakland, Emeryville and Alameda. The flatland areas in these cities are heavily developed for residential and commercial use. Most of the hilly areas in Oakland and Berkeley also have been developed for residential use. Hillside areas are accessed by a system of steep, winding roads.

The map is prepared by employing geographic information system (GIS) technology, which allows the manipulation of three-dimensional data. Information considered includes topography, surface and subsurface geology, borehole data, historical ground-water levels, existing landslide features, slope gradient, rock-strength measurements, geologic structure, and probabilistic earthquake shaking estimates. The shaking inputs are based upon probabilistic seismic hazard maps that depict peak ground acceleration, mode magnitude, and mode distance with a 10 percent probability of exceedance in 50 years.

In the Oakland West Quadrangle the liquefaction zone covers most of the Alameda County land except for some of the higher elevation terrain in Berkeley and near the eastern boundary in Oakland. The scarcity of hilly terrain within the quadrangle results in less than one percent of the land area in the Oakland West Quadrangle lying within the earthquake-induced landslide hazard zone.

vii

How to view or obtain the map

Seismic Hazard Zone Maps, Seismic Hazard Zone Reports and additional information on seismic hazard zone mapping in California are available on the California Geological Survey's Internet page: http://www.conservation.ca.gov/CGS/index.htm

Paper copies of Official Seismic Hazard Zone Maps, released by CGS, which depict zones of required investigation for liquefaction and/or earthquake-induced landslides, are available for purchase from:

BPS Reprographic Services 945 Bryant Street San Francisco, California 94105

(415) 512-6550

Seismic Hazard Zone Reports (SHZR) summarize the development of the hazard zone map for each area and contain background documentation for use by site investigators and local government reviewers. These reports are available for reference at CGS offices in Sacramento, San Francisco, and Los Angeles. NOTE: The reports are not available through BPS Reprographic Services.

http://www.conservation.ca.gov/CGS/index.htm

INTRODUCTION

The Seismic Hazards Mapping Act (the Act) of 1990 (Public Resources Code, Chapter 7.8, Division 2) directs the California Department of Conservation (DOC), Division of Mines and Geology (DMG) [now called California Geological Survey (CGS)] to delineate seismic hazard zones. The purpose of the Act is to reduce the threat to public health and safety and to minimize the loss of life and property by identifying and mitigating seismic hazards. Cities, counties, and state agencies are directed to use the seismic hazard zone maps in their land-use planning and permitting processes. They must withhold development permits for a site within a zone until the geologic and soil conditions of the project site are investigated and appropriate mitigation measures, if any, are incorporated into development plans. The Act also requires sellers (and their agents) of real property within a mapped hazard zone to disclose at the time of sale that the property lies within such a zone. Evaluation and mitigation of seismic hazards are to be conducted under guidelines adopted by the California State Mining and Geology Board (SMGB) (DOC, 1997). The text of this report is on the Internet at http://gmw.consrv.ca.gov/shmp/webdocs/sp117.pdf

The Act also directs SMGB to appoint and consult with the Seismic Hazards Mapping Act Advisory Committee (SHMAAC) in developing criteria for the preparation of the seismic hazard zone maps. SHMAAC consists of geologists, seismologists, civil and structural engineers, representatives of city and county governments, the state insurance commissioner and the insurance industry. In 1991 SMGB adopted initial criteria for delineating seismic hazard zones to promote uniform and effective statewide implementation of the Act. These initial criteria provide detailed standards for mapping regional liquefaction hazards. They also directed CGS to develop a set of probabilistic seismic maps for California and to research methods that might be appropriate for mapping earthquake-induced landslide hazards.

In 1996, working groups established by SHMAAC reviewed the prototype maps and the techniques used to create them. The reviews resulted in recommendations that 1) the process for zoning liquefaction hazards remain unchanged and 2) earthquake-induced landslide zones be delineated using a modified Newmark analysis.

This Seismic Hazard Zone Report summarizes the development of the hazard zone map.

The process of zoning for liquefaction uses a combination of Quaternary geologic mapping, historical ground-water information, and subsurface geotechnical data. The process for zoning earthquake-induced landslides incorporates earthquake loading, existing landslide features, slope gradient, rock strength, and geologic structure.

Probabilistic seismic hazard maps, which are the underpinning for delineating seismic hazard zones, have been prepared for peak ground acceleration, mode magnitude, and mode distance with a 10 percent probability of exceedance in 50 years (Petersen and others, 1996) in accordance with the mapping criteria.

http://gmw.consrv.ca.gov/shmp/webdocs/sp117.pdf

This report summarizes seismic hazard zone mapping for potentially liquefiable soils and earthquake-induced landslides in the Oakland West 7.5-Minute Quadrangle.

SECTION 1

LIQUEFACTION EVALUATION REPORT

Liquefaction Zones in the Oakland West 7.5-Minute Quadrangle, Alameda County, California

By Kevin B. Clahan, M. Elise Mattison, Anne M. Rosinski, Jacqueline D. J. Bott, Wayne D. Haydon, and Keith L. Knudsen

California Department of Conservation California Geological Survey

PURPOSE

The Seismic Hazards Mapping Act (the Act) of 1990 (Public Resources Code, Chapter 7.8, Division 2) directs the California Department of Conservation (DOC), Division of Mines and Geology (DMG) [now called California Geological Survey (CGS)] to delineate Seismic Hazard Zones. The purpose of the Act is to reduce the threat to public health and safety and to minimize the loss of life and property by identifying and mitigating seismic hazards. Cities, counties, and state agencies are directed to use seismic hazard zone maps developed by CGS in their land-use planning and permitting processes. The Act requires that site-specific geotechnical investigations be performed prior to permitting most urban development projects within seismic hazard zones.

Evaluation and mitigation of seismic hazards are to be conducted under guidelines adopted by the California State Mining and Geology Board (SMGB) (DOC, 1997). The text of this report is on the Internet at http://gmw.consrv.ca.gov/shmp/webdocs/sp117.pdf

Following the release of DMG Special Publication 117 (DOC, 1997), agencies in the Los Angeles metropolitan region sought more definitive guidance in the review of geotechnical investigations addressing liquefaction hazards. The agencies made their request through the Geotechnical Engineering Group of the Los Angeles Section of the American Society of Civil Engineers (ASCE). This group convened an implementation

CALIFORNIA GEOLOGICAL SURVEY SHZR 081 4

committee under the auspices of the Southern California Earthquake Center (SCEC).

The committee, which consisted of practicing geotechnical engineers and engineering geologists, released an overview of the practice of liquefaction analysis, evaluation, and mitigation techniques (SCEC, 1999). This text is also on the Internet at:

http://www.scec.org/

This section of the evaluation report summarizes seismic hazard zone mapping for liquefaction in the cities of Berkeley, Oakland and Alameda in the Oakland West 7.5-Minute Quadrangle. Seismic hazard zone mapping on Treasure Island and Yerba Buena Island, which are in the city and county of San Francisco, is summarized in CGS Open File Report (DOC 2000b). Official Seismic Hazard Zone maps covering the cities of Oakland and Piedmont were prepared in 1999 and released in March 2000 (DOC, 1999). The release of this new map and report includes the remaining areas within Alameda County on the Oakland West Quadrangle. The liquefaction zones of required investigation within the city of Oakland have been modified slightly, primarily because of the availability of new, more detailed Quaternary geologic mapping, new shallow ground-water data and a revised method of mapping the margins of the liquefaction zone of required investigation.

This section of the evaluation report summarizes seismic hazard zone mapping for potentially liquefiable soils in the Oakland West 7.5-Minute Quadrangle. Section 2 (addressing earthquake-induced landslides) and Section 3 (addressing potential ground shaking) complete the report, which is one of a series that summarizes production of similar seismic hazard zone maps within the state (Smith, 1996). Additional information on seismic hazards zone mapping in California is on CGS’s Internet web page:

http://www.conservation.ca.gov/CGS/index.htm

BACKGROUND

Liquefaction-induced ground failure historically has been a major cause of earthquake damage in northern California. During the 1989 Loma Prieta and 1906 San Francisco earthquakes, significant damage to roads, utility pipelines, buildings, and other structures in the San Francisco Bay Area was caused by liquefaction-induced ground displacement.

Localities most susceptible to liquefaction-induced damage are underlain by loose, water-saturated, granular sediment within 40 feet of the ground surface. These geological and ground-water conditions are widespread in the San Francisco Bay Area, most notably in alluviated valley floodplains and around the margin of the bay. In addition, the potential for strong earthquake ground shaking is high because of the many nearby active faults.

The combination of these factors constitutes a significant seismic hazard in the San Francisco Bay Area, including areas in the Oakland West Quadrangle.

http://www.scec.org

2003 SEISMIC HAZARD ZONE REPORT FOR THE OAKLAND WEST QUADRANGLE 5

METHODS SUMMARY

Characterization of liquefaction hazard presented in this report requires preparation of maps that delineate areas underlain by potentially liquefiable sediment. The following were collected or generated for this evaluation:

• Existing geologic maps were used to provide an accurate representation of the spatial distribution of Quaternary deposits in the study area. Geologic units that generally are susceptible to liquefaction include late Quaternary alluvial and fluvial sedimentary deposits and artificial fill

• Construction of shallow ground-water maps showing the historically highest known ground-water levels

• Quantitative analysis of geotechnical data to evaluate liquefaction potential of deposits

• Information on potential ground shaking intensity based on CGS probabilistic shaking maps

The data collected for this evaluation were processed into a series of geographic information system (GIS) layers using commercially available software. The liquefaction zone map was derived from a synthesis of these data and according to criteria adopted by the SMGB (DOC, 2000a).

SCOPE AND LIMITATIONS

Evaluation for potentially liquefiable soils generally is confined to areas covered by Quaternary (less than about 1.6 million years) sedimentary deposits. Such areas within the Oakland West Quadrangle consist mainly of gently sloping alluvial fans and areas bordering larger streams, low-lying shoreline regions, alluviated valleys, floodplains, and canyons. CGS’s liquefaction hazard evaluations are based on information on earthquake ground shaking, surface and subsurface lithology, geotechnical soil properties, and ground-water depth, which is gathered from various sources. Although selection of data used in this evaluation was rigorous, the quality of the data used varies. The State of California and the Department of Conservation make no representations or warranties regarding the accuracy of the data obtained from outside sources.

Liquefaction zone maps are intended to prompt more detailed, site-specific geotechnical investigations, as required by the Act. As such, liquefaction zone maps identify areas where the potential for liquefaction is relatively high. They do not predict the amount or direction of liquefaction-related ground displacements, or the amount of damage to facilities that may result from liquefaction. Factors that control liquefaction-induced ground failure are the extent, depth, density, and thickness of liquefiable materials, depth to ground water, rate of drainage, slope gradient, proximity to free faces, and intensity

CALIFORNIA GEOLOGICAL SURVEY SHZR 081 6

and duration of ground shaking. These factors must be evaluated on a site-specific basis to assess the potential for ground failure at any given project site.

Information developed in the study is presented in two parts: physiographic, geologic, and hydrologic conditions in PART I, and liquefaction and zoning evaluations in PART

II.

PART I

PHYSIOGRAPHY

Study Area Location and Physiography

The Oakland West 7.5-Minute Quadrangle covers approximately 60 square miles in Alameda and San Francisco counties on the east and west sides of San Francisco Bay, respectively. The boundary between Alameda and San Francisco counties trends northwesterly through the center of San Francisco Bay. Approximately 16 square miles (27 percent of the quadrangle) is within San Francisco County. The parts of the quadrangle in San Francisco have not been reevaluated and were previously released in November of 2000 (DOC, 2000b).

Parts of the cities of Oakland, Berkeley, Emeryville, and Alameda lie within the map area. Oakland, Emeryville, and Berkeley are contiguous and lie within the flatlands along the margin of the bay. Oakland and Berkeley also extend into the steep, hilly areas in the Berkeley Hills. Alameda is on an island in San Francisco Bay that is separated from Oakland by a tidal channel.

The flatland areas in Oakland, Berkeley, Emeryville, and Alameda are heavily developed for residential and commercial use. Most of the hilly areas in Oakland and Berkeley have also been developed for residential use. Hillside areas are accessed by a system of steep, winding roads.

Elevations in the map area range from sea level along the shore of San Francisco Bay to more than 660 feet in the northeastern corner of the quadrangle. The Berkeley Hills are drained by numerous creeks, which flow westward across the alluvial plain to San Francisco Bay. Strawberry Creek flows through Strawberry Gulch, where Berkeley’s University of California, Memorial Stadium is located. Temescal Creek flows out of Lake Temescal in the adjacent Oakland East Quadrangle. Glen Echo Creek flows into Lake Merritt within the Oakland West Quadrangle

Major highways include northwest-trending Interstate 880 that extends along the shoreline of San Francisco Bay from the southern quadrangle border to the San Francisco Oakland Bay Bridge. Interstate 80 extends from the San Francisco Oakland Bay Bridge northward along the shoreline to the northern quadrangle border. Interstate 580 extends southeast from the San Francisco Oakland Bay Bridge into the foothills and to the

2003 SEISMIC HAZARD ZONE REPORT FOR THE OAKLAND WEST QUADRANGLE 7

southern quadrangle border. Interstate Highway 980 and State Highway 24 trend northeast-southwest and intersect at Interstate 580 north of downtown Oakland. A network of secondary roads links these major highways. Bay Area Rapid Transit (BART) extends roughly north-south through the quadrangle, through the cities of Oakland and Berkeley.

GEOLOGY

Bedrock and Surficial Geology

Geologic units that generally are susceptible to liquefaction include late Quaternary alluvial and fluvial sedimentary deposits and artificial fill. To evaluate the areal and vertical distribution of shallow Quaternary deposits and to provide information on subsurface geologic, lithologic and engineering properties of the units in the Oakland West Quadrangle, digital maps were obtained from the U.S. Geological Survey. These include unpublished Quaternary mapping by Robert C. Witter (unpublished) and a published map of part of the Oakland metropolitan area (Graymer, 2000). These GIS maps were combined, with minor modifications along the bedrock/Quaternary contact, to form a single, 1:24,000-scale geologic map of the Oakland West Quadrangle. The distribution of Quaternary deposits on this map (summarized on Plate 1.1) was used in combination with other data, discussed below, to evaluate liquefaction potential and develop the Seismic Hazard Zone Map.

In the Oakland West Quadrangle, Witter (unpublished) mapped 14 Quaternary units. The methods used by Witter in his mapping of the Oakland West Quadrangle are the same as those described by Knudsen and others (2000b). These methods consist of interpretation of topographic maps, aerial photographs, and soil surveys, as well as compiled published and unpublished geologic maps. The ages of deposits are estimated using landform shape, relative geomorphic position, cross-cutting relationships, superposition, depth and degree of surface dissection, and relative degree of soil profile development. Table 1.1 compares stratigraphic nomenclature used in Knudsen and others (2000b) and the CGS GIS database, with that of several previous studies performed in northern California.

The eastern half of the quadrangle is covered by late Quaternary deposits with a small area of bedrock in the Berkeley Hills located in the northeastern corner of the quadrangle.

Topographically higher southeast-sloping Pleistocene alluvial fan surfaces (Qpf, Qof) at the base of the Berkeley Hills have Holocene alluvial deposits (Qhf, Qha) inset into them that extend toward the historical shoreline of San Francisco Bay. The Pleistocene surfaces have been uplifted and are west of the active Hayward Fault zone. Latest Pleistocene to Holocene alluvial fan deposits (Qf) are mapped in the northeast corner of the quadrangle within the city of Berkeley. Witter (unpublished) also mapped Pleistocene bay terrace deposits (Qbt) at the base of early to late Pleistocene alluvial fan deposits (Qof) in the southeast corner of the quadrangle, along the shore of Lake Merritt.

Latest Pleistocene to Holocene dune sand (Qds), locally referred to as the Merritt Sand, underlies much of downtown Oakland. Artificial fill over Bay Mud (afbm) deposits

CALIFORNIA GEOLOGICAL SURVEY SHZR 081 8

extend from the historical shoreline to the present bay margin along most of the coastline in the southeastern portion of the Oakland West Quadrangle.

The southeastern portion of Alameda Island within the quadrangle is mapped as primarily latest Pleistocene to Holocene dune sand (Qds). This unit makes up the core of Alameda Island, which is then ringed by up to 11,000 horizontal feet of artificial fill over Bay Mud (afbm). The northern third of Alameda Island is mapped as afbm.

Some artificial fill (af) has been placed along the lower reaches of several creeks, including Strawberry and Temescal, when the streams were channelized or culverted.

Holocene alluvial fan deposits have been subdivided into the following units: Qhc, Qhf, Qha, and Qf. Qhc are modern channel deposits and are found within the banks of creeks.

Qhf are alluvial fan deposits that are mapped along much of the west-southwest sloping East Bay Plain. Qha are undifferentiated alluvial deposits generally mapped within upland drainages and canyons. Qf are alluvial fan deposits, with typically a thin (0- to 5-foot) mantle of Holocene deposits over Pleistocene material.

The bedrock geology of the area is associated with a series of oceanic crust and volcanic arc terranes that were accreted to the continent during Mesozoic and Cenozoic time, and further deformed by transpression along the Hayward Fault Zone during the Cenozoic.

The oldest mapped geologic units are rocks from the Jurassic Coast Range Ophiolite (Graymer and others, 1996). Additional units include the Late Jurassic-Early Cretaceous Franciscan Complex, the Late Jurassic-Early Cretaceous Knoxville Formation, the Late Cretaceous Great Valley Sequence, and numerous Tertiary sedimentary and volcanic units. See the earthquake-induced landslide portion (Section 2) of this report for additional description of bedrock geology.

2003 SEISMIC HAZARD ZONE REPORT FOR THE OAKLAND WEST QUADRANGLE 9

UNIT Witter (unpublished)

Knudsen and others (2000b)

Helley and Graymer (1997)

Helley and others (1979)

CGS GIS

database

Artificial fill af af af af Artificial fill over Bay Mud afbm afbm afbm

Artificial stream channel ac ac Qhasc ac Modern stream channel deposits Qhc Qhc Qhsc Qhsc Qhc

Latest Holocene beach sand Qhbs Qhbs Qhbs

Holocene San Francisco Bay Mud(1) Qhbm Qhbm Qhbm Qhbm Qhbm

Holocene alluvial fan deposits Qhf Qhf Qhaf Qham, Qhac Qhf

Holocene alluvial fan levee deposits Qhl Qhl Qhl Qhl

Holocene alluvium, undifferentiated Qha Qha Qhaf Qha

Latest Pleistocene to Holocene dune sand Qds Qds Qms,Qhms Qps Qds

Latest Pleistocene to Holocene alluvial fan deposits

Qf Qf Qf

Latest Pleistocene alluvial fan deposits Qpf Qpf Qpaf Qpf

Pleistocene bay terrace deposits Qbt Qmt Qmt Qbt

Late Pleistocene San Francisco Bay Mud(1) Qpbm

Early to late Pleistocene pediment deposits Qop Qop Qop

Early to late Pleistocene alluvial fan deposits Qof Qof Qpaf, Qpoaf Qof

Notes:

(1) Not mapped at surface but unit interpreted in the subsurface.

Table 1.1. Correlation of Quaternary Stratigraphic Nomenclatures Used within the Oakland West Quadrangle. For this study, CGS has adopted the nomenclature of Knudsen and others (2000a).

CALIFORNIA GEOLOGICAL SURVEY SHZR 081 10

Structural Geology

The Oakland West Quadrangle is within the active San Andreas Fault system, which distributes shearing across a complex system of primarily northwest-trending, right-lateral, strike-slip faults that include the San Andreas, Hayward, and Calaveras faults.

The Hayward Fault extends northwestward through the northeasternmost corner of the quadrangle passing beneath U.C. Berkeley Memorial Stadium. The Calaveras Fault is approximately 14 miles east of the eastern border of the quadrangle, and the San Andreas Fault is about 12.5 miles to the southwest. Historical ground-surface rupturing earthquakes have occurred on all of these faults (Lawson, 1908; Keefer and others, 1980;

Hart, 1984). In addition, the Concord-Green Valley, Mt. Diablo Thrust, and Greenville faults will contribute, over the long term, to the release of almost all of the seismic moment in the San Francisco Bay Area (WGCEP, 1999). The Concord-Green Valley, Mt. Diablo Thrust, and Greenville faults are approximately 15, 16, and 30 miles east of the eastern border of the quadrangle, respectively.

ENGINEERING GEOLOGY

Information on subsurface geology and engineering characteristics of unconsolidated deposits was obtained from borehole logs collected from reports on geotechnical and environmental projects. For this investigation, 255 borehole logs were collected from the files of the California Department of Transportation (CalTrans), BART, City of Oakland Public Works Department, URS Greiner Woodward Clyde, William Lettis and Associates, Alan Kropp and Associates, and Alameda County Water District. Data from 246 borehole logs were entered into a CGS geotechnical GIS database (see Plate 1.2).

Thirteen cone penetrometer (CPT) soundings were obtained from the U.S. Geological Survey, which collected the data under the direction of Tom Holzer and Mike Bennett.

Standard Penetration Tests (SPTs) provide a standardized measure of the penetration resistance of geologic deposits and are commonly used as an index of soil density. This in-field test consists of counting the number of blows required to drive a split-spoon sampler (1.375-inch inside diameter) one foot into the soil at the bottom of a borehole at chosen intervals while drilling. The driving force is provided by dropping a 140-pound hammer weight 30 inches. The SPT method is formally defined and specified by the American Society for Testing and Materials in test method D1586 (ASTM, 1999).

Recorded blow counts for non-SPT geotechnical sampling where the sampler diameter, hammer weight or drop distance differ from those specified for an SPT (ASTM D1586), are converted to SPT-equivalent blow counts. The actual and converted SPT blow counts are normalized to a common-reference, effective-overburden pressure of one atmosphere (approximately one ton per square foot) and a hammer efficiency of 60 percent using a method described by Seed and Idriss (1982) and Seed and others (1985). This normalized blow count is referred to as (N1)60.

Geotechnical borehole logs provided information on lithologic and engineering characteristics of 4,452 feet of Holocene materials and 9,623 feet of Pleistocene materials penetrated by boreholes analyzed for this study. Geotechnical characteristics of the Quaternary map units are summarized in Tables 1.2 and 1.3. Analysis of these data leads

2003 SEISMIC HAZARD ZONE REPORT FOR THE OAKLAND WEST QUADRANGLE 11

to recognition of certain characteristics and relationships among the units, including: 1) median values for penetration resistance suggest Holocene materials are less dense and more readily penetrated than Pleistocene materials; 2) penetration resistance values measured from the same map unit can vary considerably, the standard deviation is often 50 to 100 percent of the mean; 3) Holocene units consist of both fine and coarse-grained materials, but have sand lenses throughout that have the potential to liquefy; and 4) late Pleistocene to Holocene dune sand (Qds) is primarily coarse grained with a wide range of penetration resistance values. Not shown in Tables 1.2 and 1.3 is the frequent occurrence of gravel within units generally of Pleistocene age.

GEOLOGIC

MAP UNIT

DRY DENSITY

(pounds per cubic foot)

STANDARD PENETRATION RESISTANCE

(blows per foot, (N1)60)

Unit (1)

Texture (2)

Number of Tests

(3) Mean CV

(4) Median Min Max Number of Tests

(3) Mean CV

(4) Median Min Max

Fine 24 97.8 0.13 99.2 74.0 124 62 20.8 0.83 15.5 1.9 75.2 Af & afbm Coarse 37 98.7 0.15 102.0 56 119 113 21.8 0.85 16.6 0.9 >99

Fine 69 72.0 0.31 64.0 38.0 132 111 7.2 1.22 3.2 0.6 51.4 Qhbm Coarse 5 103.6 0.11 97.0 94.0 120.0 15 12.1 1.14 7.1 1.2 50.2 Fine 46 101.9 0.08 100.0 87.0 126.0 216 19.0 0.64 16.4 1.7 83.3 Qhf Coarse 12 98.3 0.17 102.5 49.0 113.0 101 21.1 0.51 19.8 3.1 58.5 Fine 10 110.2 0.04 110.5 102.3 116.0 17 20.9 0.7 20.3 0.76 47.8 Qds Coarse 150 110.5 0.04 110.0 99.0 128.0 365 49.0 0.75 40.1 1.3 >99 Fine 16 103.7 0.07 105.6 92.7 113.7 19 19.5 0.70 14.5 5.9 54.8 Qf Coarse 2 102.0 0.07 102.0 97.0 107.0 - - - - - - Fine 152 104.5 0.07 105.0 82.0 121.0 284 23.2 0.59 20.2 2.0 93.6 Qpf Coarse 57 110.3 0.08 112.0 85.0 134.0 101 31.9 0.58 27.3 4.8 >99 Fine 140 105.3 0.11 106.5 76.0 117 19 23.6 0.49 21.3 4.7 48.5 Qbt Coarse 3 104.7 0.12 98.0 97.0 119.0 4 45.3 0.42 41.0 27.7 71.3 Fine 92 97.5 0.13 100.0 52.0 119.0 27 25.9 0.50 21.3 10.6 58.0 Qpbm Coarse 15 104.3 0.13 103.0 73.0 125.0 4 38.3 0.47 21.6 13.9 53.9 Fine 29 104.1 0.11 104.0 79.0 129.0 25 23.7 0.45 22.1 10.0 45.6 Qof Coarse 5 104.2 0.09 103.0 92.0 115.0 8 28.4 0.22 28.1 20.1 36.9

(1) See Table 1.3 for names of the geologic map units listed here.

(2) Fine soils (silt and clay) contain a greater percentage passing the #200 sieve (<0.074 mm); coarse soils (sand and gravel) contain a greater percentage retained by the #200 sieve.

(3) Number of laboratory samples or field penetration resistance measurements.

(4) CV = coefficient of variation (standard deviation divided by the mean).

Table 1.2. Geotechnical Characteristics for Quaternary Geological Units in the Oakland West 7.5-Minute Quadrangle.

dwang Oval dwang Oval dwang Oval

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Geologic Map

Unit (1)

Description

Length of borings penetrating map unit

(feet)

Composition by Soil Type (2)

(Percent of total sediment column logged)

Depth to ground water (feet) and liquefaction susceptibility category assigned to geologic unit (3)

<10 10 to 30 30 to 40 >40 af Artificial fill (4) 1144 SP 22; CL 22; SM 13;

other 22 VH-L H-L M-L VL afbm Artificial fill over Bay Mud 0 n/a VH H M VL ac Artificial stream channel 0 n/a VH-L H M VL

Qhc Modern stream channel deposits 0 n/a VH H M VL

Qhbs Latest Holocene beach sand 0 n/a VH H M VL

Qhbm Holocene San Francisco Bay Mud 1767 CH 47; CL 40; other 13 H M L VL

Qhf Holocene alluvial fan deposits 1534 CL 49; ML 15; SM 13;

other 23 H M L VL

Qhl Holocene alluvial fan levee deposits 7 CL 70; SM 30 H M L VL

Qha Holocene alluvial fan levee deposits 0 n/a M M L VL

Qds Latest Pleistocene to Holocene dune sand 2443 SP 42; SM 26; SC 24;

CL 4; other 4 M L L VL

Qf Latest Pleistocene to Holocene alluvial fan deposits 163 CL 56; ML 33; other 11 M L L VL

Qpf Latest Pleistocene alluvial fan deposits 4144 CL 58; SC 12; ML 10;

other 20 L L VL VL

Qbt Pleistocene bay terrace deposits 129 CL 60; SC 22; ML 10;

SM 8 L L VL VL

Qpbm Latest Pleistocene San Francisco Bay Mud 1918 CL 55; CH 15; ML 11;

other 19 L L VL VL

Qop Early to late Pleistocene pediment deposits 0 n/a L L VL VL

Qof Early to late Pleistocene alluvial fan deposits 826 CL 69; SM 7; other 24 L L VL VL

(1) Susceptibility assignments are specific to the materials within the Oakland West 7.5-Minute Quadrangle.

(2) Unified Soil Classification System.

(3) Based on the Simplified Procedure (Seed and Idriss, 1971; Youd and Idriss, 1997) and a small number of borehole analyses for some units.

(4) The liquefaction susceptibility of artificial fill ranges widely, depending largely on the nature of the fill, its age, and whether it was compacted during emplacement.

(5) n/a = not applicable

Table 1.3. Liquefaction Susceptibility for Quaternary Map Units within the Oakland West 7.5-Minute Quadrangle. Units indicate relative

2003 SEISMIC HAZARD ZONE REPORT FOR THE OAKLAND WEST QUADRANGLE 13

susceptibility of deposits to liquefaction as a function of material type and ground water depth within that deposit. VH = very high, H = high, M = moderate, L = low, and VL = very low to none.

GROUND WATER

Liquefaction hazard may exist in areas where depth to ground water is 40 feet or less.

CGS uses the highest known ground-water levels because water levels during an earthquake cannot be anticipated because of the unpredictable fluctuations caused by natural processes and human activities. A historical-high ground-water map differs from most ground-water maps, which show the actual water table at a particular time. Plate

1.2 depicts a hypothetical ground-water table within alluviated areas.

Ground-water conditions were investigated in the Oakland West Quadrangle to evaluate the depth to saturated materials. Saturated conditions reduce the effective normal stress, thereby increasing the likelihood of earthquake-induced liquefaction (Youd, 1973). The evaluation was based on first-encountered water noted in geotechnical borehole logs acquired from Alameda County Water District, City of Oakland, City of Alameda, Alameda County Public Works Department, and the State Water Resources Control Board. The depths to first-encountered unconfined ground water were plotted on a map of the project area, interpreted, and contoured. Water depths from boreholes known to penetrate confined aquifers were not utilized.

Regional ground-water contours on Plate 1.2 show historical-high water depths, as interpreted from borehole logs from investigations between the 1950’s and 1999. Depths to first-encountered water range from 0 to greater than 20 feet below the ground surface (Plate 1.2). In general, ground-water levels are close to the ground surface in the Oakland West Quadrangle. They are shallowest close to the San Francisco Bay margins and deepest (greater than 10 feet) along the Berkeley Hills range front (Plate 1.2).

Boreholes within Alameda Island indicate an area of depressed (deeper than 10 feet) ground water in the center of the island, but depths to ground water are commonly less than 10 feet.

PART II

LIQUEFACTION POTENTIAL

Liquefaction may occur in water-saturated sediment during moderate to great earthquakes. Liquefied sediment loses strength and may fail, causing damage to buildings, bridges, and other structures. Many methods for mapping liquefaction hazard have been proposed. Youd (1991) highlights the principal developments and notes some of the widely used criteria. Youd and Perkins (1978) demonstrate the use of geologic

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criteria as a qualitative characterization of liquefaction susceptibility and introduce the mapping technique of combining a liquefaction susceptibility map and a liquefaction opportunity map to produce a liquefaction potential map. Liquefaction susceptibility is a function of the capacity of sediment to resist liquefaction. Liquefaction opportunity is a function of the potential seismic ground shaking intensity.

The method applied in this study for evaluating liquefaction potential is similar to that of Tinsley and others (1985). Tinsley and others (1985) applied a combination of the techniques used by Seed and others (1983) and Youd and Perkins (1978) for their mapping of liquefaction hazards in the Los Angeles region. CGS’s method combines geotechnical analyses, geologic and hydrologic mapping, and probabilistic earthquake shaking estimates, but follows criteria adopted by the SMGB (DOC, 2000a).

LIQUEFACTION SUSCEPTIBILITY

Liquefaction susceptibility reflects the relative resistance of a soil to loss of strength when subjected to ground shaking. Physical properties of soil such as sediment grain-size distribution, compaction, cementation, saturation, and depth govern the degree of resistance to liquefaction. Some of these properties can be correlated to the geologic age of a deposit and the environment of deposition. With increasing age, relative density may increase through cementation of the particles or compaction caused by the weight of the overlying sediment. Grain-size characteristics of a soil also influence susceptibility to liquefaction. Sand is more susceptible than silt or gravel, although silt of low plasticity is treated as liquefiable in this investigation. Cohesive soils generally are not considered susceptible to liquefaction. Such soils may be vulnerable to strength loss with remolding and represent a hazard that is not addressed in this investigation. Soil characteristics and processes that result in higher measured penetration resistances generally indicate lower liquefaction susceptibility. Thus, blow count and cone penetrometer values are useful indicators of liquefaction susceptibility.

Saturation is required for liquefaction, and the liquefaction susceptibility of a soil varies with the depth to ground water. Very shallow ground water increases the susceptibility to liquefaction (soil is more likely to liquefy). Soils that lack resistance (susceptible soils) typically are saturated, loose and sandy. Soils resistant to liquefaction include all soil types that are dry, cohesive, or sufficiently dense.

CGS’s map inventory of areas containing soils susceptible to liquefaction begins with evaluation of geologic maps and historical occurrences, cross-sections, geotechnical test data, geomorphology, and ground-water hydrology. Soil properties and soil conditions such as type, age, texture, color, and consistency, along with historical depths to ground water are used to identify, characterize, and correlate susceptible soils. Because Quaternary geologic mapping is based on similar soil observations, liquefaction susceptibility maps typically are similar to Quaternary geologic maps. CGS’s qualitative relations among susceptibility, geologic map unit and depth to ground water are summarized in Table 1.3.

2003 SEISMIC HAZARD ZONE REPORT FOR THE OAKLAND WEST QUADRANGLE 15

Most Holocene materials where water levels are within 30 feet of the ground surface have susceptibility assignments of high (H) to very high (VH) (Table 1.3). Undifferentiated Holocene alluvium (Qha) primarily is composed of fine-grained material and is assigned moderate susceptibility. However, this unit may contain lenses of material with higher liquefaction susceptibility. All latest Pleistocene and older deposits within 30 feet of the ground surface have low (L) susceptibility assignments except late Pleistocene to Holocene alluvial fan deposits (Qf) and latest Pleistocene to Holocene dune sand (Qds).

The Qf unit is relatively dense in the Oakland West Quadrangle but may have low densities along with lenses of potentially liquefiable material that could liquefy if saturated (Table 1.3). It is therefore assigned moderate susceptibility. Latest Pleistocene to Holocene dune sand (Qds) is relatively dense in the area of downtown Oakland but has variable density elsewhere in the quadrangle. It is therefore generally assigned moderate

(M) susceptibility where it is saturated above 10 feet. All other units have low (L) to (VL) susceptibility assignments within 40 feet of the ground surface.

LIQUEFACTION OPPORTUNITY

Liquefaction opportunity is a measure, expressed in probabilistic terms, of the potential for strong ground shaking. Analyses of in-situ liquefaction resistance require assessment of liquefaction opportunity. The minimum level of seismic excitation to be used for such purposes is the level of peak ground acceleration (PGA) with a 10 percent probability of exceedance over a 50-year period (DOC, 2000a). The earthquake magnitude used in CGS’s analysis is the magnitude that contributes most to the calculated PGA for an area.

For the Oakland West Quadrangle, PGAs of 0.52 g to 0.79 g, resulting from earthquakes of magnitude 7.1 to 7.9, were used for liquefaction analyses. The PGA and magnitude values were based on de-aggregation of the probabilistic hazard at the 10 percent in 50-year hazard level (Petersen and others, 1996). See the ground motion section (3) of this report for further details.

Quantitative Liquefaction Analysis

CGS performs quantitative analysis of geotechnical data to evaluate liquefaction potential using the Seed-Idriss Simplified Procedure (Seed and Idriss, 1971; Seed and others, 1983;

National Research Council, 1985; Seed and others, 1985; Seed and Harder, 1990; Youd and Idriss, 1997; Youd and others, 2001). Using the Seed-Idriss Simplified Procedure one can calculate soil resistance to liquefaction, expressed in terms of cyclic resistance ratio (CRR), based on SPT results, ground-water level, soil density, moisture content, soil type, and sample depth. CRR values are then compared to calculated earthquake-generated shear stresses expressed in terms of cyclic stress ratio (CSR). The Seed-Idriss Simplified Procedure requires normalizing earthquake loading relative to a M7.5 event for the liquefaction analysis. To accomplish this, CGS’s analysis uses the Idriss magnitude-scaling factor (MSF) (Youd and Idriss, 1997). It is convenient to think in terms of a factor of safety (FS) relative to liquefaction, where: FS = (CRR / CSR) * MSF.

FS, therefore, is a quantitative measure of liquefaction potential. CGS uses a factor of safety of 1.0 or less, where CSR equals or exceeds CRR, to indicate the presence of potentially liquefiable soil. While an FS of 1.0 is considered the “trigger” for

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liquefaction, for a site specific analysis an FS of as much as 1.5 may be appropriate depending on the vulnerability of the site and related structures.

The CGS liquefaction analysis program calculates an FS for each geotechnical sample where blow counts were collected. Typically, multiple samples are collected for each borehole. The program then independently calculates an FS for each non-clay layer that includes at least one penetration test using the minimum (N1)60 value for that layer. The minimum FS value of the layers penetrated by the borehole is used to determine the liquefaction potential for each borehole location. The reliability of FS values varies according to the quality of the geotechnical data. FS, as well as other considerations such as slope, presence of free faces, and thickness and depth of potentially liquefiable soil, are evaluated in order to construct liquefaction potential maps, which are then used to make a map showing zones of required investigation.

Of the 256 geotechnical borehole logs reviewed in this study (Plate 1.2), most include blow-count data from SPTs or from penetration tests that allow reasonable blow count translations to SPT-equivalent values. Non-SPT values, such as those resulting from the use of 2-inch or 2½-inch inside-diameter ring samplers, were translated to SPT-equivalent values if reasonable factors could be used in conversion calculations. The reliability of the SPT-equivalent values varies. Therefore, they are weighted and used in a more qualitative manner. Few borehole logs, however, include all of the information (e.g. soil density, moisture content, sieve analysis, etc.) required for an ideal Seed-Idriss Simplified Procedure. For boreholes having acceptable penetration tests, liquefaction analysis is performed using recorded density, moisture, and sieve test values or using averaged test values of similar materials.

The Seed-Idriss Simplified Procedure for liquefaction evaluation was developed primarily for clean sand and silty sand. As described above, results depend greatly on accurate evaluation of in-situ soil density as measured by the number of soil penetration blow counts using an SPT sampler. However, many of the Holocene alluvial deposits in the study area contain a significant amount of gravel. In the past, gravelly soils were considered not to be susceptible to liquefaction because the high permeability of these soils presumably would allow the dissipation of pore pressures before liquefaction could occur. However, liquefaction in gravelly soils has been observed during earthquakes, and recent laboratory studies have shown that gravelly soils are susceptible to liquefaction (Ishihara, 1985; Harder and Seed, 1986; Budiman and Mohammadi, 1995; Evans and Zhou, 1995; and Sy and others, 1995). SPT-derived density measurements in gravelly soils are unreliable and generally too high. They are likely to lead to overestimation of the density of the soil and, therefore, result in an underestimation of the liquefaction susceptibility. To identify potentially liquefiable units where the N values appear to have been affected by gravel content, correlations were made with boreholes in the same unit where the N values do not appear to have been affected by gravel content.

2003 SEISMIC HAZARD ZONE REPORT FOR THE OAKLAND WEST QUADRANGLE 17

LIQUEFACTION ZONES

Criteria for Zoning

Areas underlain by materials susceptible to liquefaction during an earthquake were included in liquefaction zones using criteria developed by the Seismic Hazards Mapping Act Advisory Committee and adopted by the SMGB (DOC, 2000a). Under those guideline criteria, liquefaction zones are areas meeting one or more of the following:

1. Areas known to have experienced liquefaction during historical earthquakes

2. All areas of uncompacted artificial fill containing liquefaction-susceptible material that are saturated, nearly saturated, or may be expected to become saturated

3. Areas where sufficient existing geotechnical data and analyses indicate that the soils are potentially liquefiable

4. Areas where existing geotechnical data are insufficient

In areas of limited or no geotechnical data, susceptibility zones may be identified by geologic criteria as follows:

a) Areas containing soil deposits of late Holocene age (current river channels and their historic floodplains, marshes and estuaries), where the M7.5-weighted peak acceleration that has a 10 percent probability of being exceeded in 50 years is greater than or equal to 0.10 g and the water table is less than 40 feet below the ground surface; or

b) Areas containing soil deposits of Holocene age (less than 11,000 years), where the M7.5-weighted peak acceleration that has a 10 percent probability of being exceeded in 50 years is greater than or equal to 0.20 g and the historical high water table is less than or equal to 30 feet below the ground surface; or

c) Areas containing soil deposits of latest Pleistocene age (11,000 to 15,000 years), where the M7.5-weighted peak acceleration that has a 10 percent probability of being…