The Lorna Prieta, California, Earthquake of 

October 17, 1989-Marina District 

THOMAS D. O'ROURKE, Editor 

STRONG GROUND MOTION AND GROUND FAILURE 

THOMAS L. HOLZER, Coordinator 

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1551-F 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1992 

Collapsed four-story wood-frame building at southwest comer of Divisadero and Jefferson Streets. Local subsidence caused by soil liquefaction is visible at street comer. Heaved and fractured pavement is oriented perpendicular to direction of strongest seismic shaking. 

Underground water, gas, and wastewater pipelines were considerably damaged at this site. View southward; photograph courtesy of 

T.D. O'Rourke. 
CONTENTS 

By M.G. Bonilla 

Ground-motion amplification --------- ......................... 

By John Boatwright, Linda C. Seekins, Thomas E. Fumal, 

Hsi-Ping Liu, and Charles S. Mueller 

Observation of local site effects at a downhole-andsurface station -------------- ----------------- --------------- 

By Hsi-Ping Liu, Richard E. Warrick, Robert E. Westerlund, 

Eugene D. Sembera, and Leif Wennerberg 

Determination of the dynamic shear modulus of 

Holocene bay mud for site-response analysis --------- 

By Harry E. Stewart and Ashraf K. Hussein 

Behavior of the seawalls and shoreline during the 

earthquake ------------------- ------------- ------------------- 

By H.T. Taylor, J.T. Cameron, S. Vahdani, and H. Yap 

Lifeline performance and ground deformation during 

the earthquake ------- - ----- - ----------------- --------------- 

By Thomas D. O'Rourke, Jonathan W. Pease, and 

Harry E. Stewart 

Effects of ground conditions on the damage to fourstory comer apartment buildings ........................ 

By Stephen K. Harris and John A. Egan 

Performance of emergency-response services after 

the earthquake --------------- ------------- ------------------ 

By Charles R. Scawthom, Keith A. Porter, and 

Frank T. Blackburn 

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THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND FAILURE 

CONTENTS 

MARINA DISTRICT 

INTRODUCTION 

By Thomas D. O'Rourke, 

Cornell University 

Page 

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2 

4 

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5 

5 

INTRODUCTION 

During the earthquake, a total land area of about 4,300 

km2 was shaken with seismic intensities that can cause 

significant damage to structures (Plafker and Galloway, 

1989; McNutt and Toppazada, 1990). The area of the Marina District of San Francisco is only 4.0 km2-less than 

0.1 percent of the area most strongly affected by the earthquake-but its significance with respect to engineering, 

seismology, and planning far outstrips its proportion of 

shaken terrain and makes it a centerpiece for lessons 

learned from the earthquake. 

The Marina District provides perhaps the most comprehensive case history of seismic effects at a specific site 

developed for any earthquake. The reports assembled in 

this chapter, which provide an account of these seismic 

effects, constitute a unique collection of studies on site, as 

well as infrastructure and societal, response that cover virtually all aspects of the earthquake, ranging from incoming ground waves to the outgoing airwaves used for 

emergency communication. 

An aerial view and map of the Marina District are presented in figure 1. The Marina District encompasses the 

area bounded by San Francisco Bay on the north, the Presidio on the west, and Lombard Street and Van Ness Avenue on the south and east, respectively. Nearly all of the 

earthquake damage in the Marina District, however, occurred within a considerably smaller area of about 0.75 

km2, bounded by San Francisco Bay and Baker, Chestnut, 

and Buchanan Streets. 

At least five major aspects .lake response in th 

Marina District are covered by the reports in this chapter: 

(1) dynamic site response, (2) soil liquefaction, (3) lifeline 

performance, (4) building performance, and (5) emergency 

services. 

DYNAMIC SITE RESPONSE 

One of the most important response characteristics of the 

Marina District was the amplification of earthquake motion, with notably stronger shaking in the Marina District 

than in surrounding areas on bedrock and firmer soils. In 

this chapter, several studies are focused on evaluating subsurface conditions and assessing the factors contributing to 

site amplification. 

Bonilla reviews the historical development of the Marina 

District and delineates in considerable detail the locations 

of natural-sand deposits, fill associated with tipping from 

shore and seawall construction, and hydraulic fill placed in 

preparation for the 19 15 Panama-Pacific International Exposition. Bonilla, Bardet and others, Taylor and others, and 

O'Rourke and others provide a comprehensive view of 

subsurface conditions, based on an examination of hundreds of soil borings and soundings. The three-dimensional 

picture that emerges from these studies shows that the Marina District is underlain by a bedrock basin, approximately 

100 m deep, filled with alluvial and marine sedimentary 

deposits on which loose sandy fills have been placed to 

develop new land next to the bay. The remarkable degree 

of resolution with which the subsurface conditions have 

been characterized is unusual for any site and, in this instance, provides an excellent framework within which to 

evaluate site response. 

Boatwright and others evaluate the amplification of 

+ground motion with the records of seismographs deployed 

after the earthquake to measure aftershocks. These records 

show a relatively high amplification for the central part of 

the Marina District, with ground motion in the bedrock 

magnified by a factor of 6 to 10 in the frequency range 

0.7-1.5 Hz, corresponding to the predominant response 
F2 MARINA DISTRICT 

frequencies of many Marina District buildings. On the basis of the aftershock data, Boatwright and others estimate 

that ground motions from the main shock may have been 

equivalent to those at the Outer Harbor Wharf in Oakland, 

where a peak ground acceleration of 0.29 g was recorded. + Liu and others report that ground-motion amplification 

during aftershocks in the Marina District depended on 

both ground-motion direction and earthquake location. 

Their data show significant three-dimensional characteristics. Upon first arrival, ground motion was aligned with 

the direction of the incoming wave, after which a widely 

varying path of horizontal motion can be traced, indicating 

multiple reflections and wave scattering. Liu and others also show that the highest spectral-ratio peaks are associated 

with ground-motion components parallel to the major axis 

of the underlying bedrock basin, thereby demonstrating a 

relation between bedrock topography and the amplification 

of surface relative to bedrock waves. 

Bardet and others compare the results of one- and twodimensional analytical models of site response in the 

Marina District, showing clearly the importance of twodimensional simulations in accounting for the amplification of seismic shaking. Their two-dimensional analyses 

show peak acceleration at the ground surface as high as 

0.23 g, approximately twice as large as that calculated 

from their one-dimensional model. The two-dimensional 

effects resulted mainly from the geometry of the bedrock 

basin and stiff soil layers, an outcome consistent with the 

ground-motion data presented by Liu and others. 

Stewart and Hussein evaluate the nonlinear dynamicresponse properties of soft clay and silt, typical of the deposits underlying the Marina District. Their laboratory data and proposed model of soil behavior provide a sound 

experimental basis for the analytical modeling of nonlinear 

site response. 

SOIL LIQUEFACTION 

Liquefaction is the temporary loss of soil strength 

caused by high water pressures generated in the soil as a 

Figure 1.-Marina District of San Francisco. A, Marina District 2 days after the earthquake, showing areas of conspicuous damage and earthquake 

effects. Photograph den fiom a height of 2,000 m; courtesy of Pacific Aerial Surveysl Oaklandl Calif. B, Sketch maps showing locations of the Marina 

District within San Francisco and of areas of figure 1A. 
result of earthquake shaking. Under conditions of severe 

shaking, the strength loss may be so large that the ground 

behaves as a liquid, with consequent foundation failures, 

damage to utilities, settlement, and lateral deformation. 

The reason for the liquefaction hazard is shown clearly 

by the geologic and historical development of the Marina 

District, as described by Bonilla. Much of the liquefaction 

hazard is related to how soils were placed to develop the 

areas adjacent to San Francisco Bay. From 1851 to 1912, 

both marsh and bay were filled in a piecemeal fashion by 

loosely dumping natural sand, much of which was excavated from dunes and beaches in the vicinity of the old 

shoreline. In 191 2, hydraulic fill was placed principally in 

an artificial lagoon enclosed by a seawall, which still provides support and horizontal stability for parts of the Marina District. This hydraulic fill consists of sand and silt, 

dredged and pumped into the lagoon. The Marina District, 

therefore, is built on three types of sandy soils, including 

natural sand, loose sand placed by tipping from the shoreline and seawall, and hydraulic fill. 

The properties and liquefaction behavior of these different soils are an important aspect of our investigations and 

are directly relevant to other places where these types of 

soils exist. Bardet and others show that liquefaction, in the 

form of sand boils, was most conspicuous throughout areas underlain by hydraulic fill. O'Rourke and others explore the postliquefaction consolidation of the different 

deposits. (Postliquefaction consolidation is the volume loss 

and settlement that result as soils densify during the dissipation of high water pressures triggered by an earthquake.) 

These researchers show that the most widely used methods of site exploration, utilizing the standard penetration 

test, are not sufficiently refined for predicting the 

postliquefaction consolidation of hydraulic fill. Instead, 

other methods of site exploration, such as the cone penetration test, are required to evaluate properly the stratification of hydraulic fill and thus to identify more accurately 

the sandy layers that actually liquefy. 

Taylor and others describe the behavior of the Marina 

District's seawalls and waterfront during the earthquake. 

Lateral displacements and settlements as high as 600 mm 

were observed near the St. Francis Yacht Club. Deformation analysis of the main seawall in the Marina District 

shows approximately 150 mm of lateral movement, which 

is consistent with the observed performance of the seawall. This type of validation and refinement of analytical 

Area of 

figure IA - 

Lombard St. 

Figure 1 .-Continued. 
F4 MARINA DISTRICT 

models on the basis of observations is an important step in 

forecasting the seawall and shoreline response in the Marina District during a larger earthquake. 

LIFELINE PERF'ORMANCE 

Lifelines are systems for the distribution of critical resources, such as water supplies, transportation arteries, gas 

and liquid-fuel complexes, telecommunication and electric-power systems, and wastewater-conveyance networks. 

These facilities are important for life support and the restoration of community and economic activity after an 

earthquake. 

In the Marina District, there were 123 repairs to pipelines of the Municipal Water Supply System (MWSS) of 

San Francisco, more than three times the number of repairs throughout the rest of the city. The loss of water 

from this system severely hampered firefighting efforts in 

the district. Approximately 13.6 km of gas-distribution 

piping was replaced, and more than 20 percent of the 

wastewater-collector lines were repaired or replaced. 

09Rourke and others report on the damage to lifelines in 

the Marina District and show that damage to the MWSS 

and wastewater-conveyance system was caused primarily 

by soil deformation associated with postliquefaction consolidation. The remarkable correlation between pipeline 

damage and surface settlement, both with respect to magnitude and spatial distribution, is perhaps the clearest demonstration in any earthquake of pipeline-network 

vulnerability to liquefaction-induced ground deformation. 

BUILDING PERFORMANCE 

Earthquake effects in the Marina District provide a 

graphic illustration of the damage that can occur to certain 

types of buildings, particularly those constructed before 

the adoption of appropriate seismic codes and for which 

retrofitting has not been implemented. The most severe 

damage occurred in four-story, wood-frame corner buildings, which are the subject of the report by Harris and 

Egan, focusing on ground conditions and structural damage. Their study shows that the highest concentration of 

most heavily damaged buildings correlates with the areas 

of fill placed by tipping from the former shorelines and 

seawall, with somewhat less damage in areas of hydraulic 

fill. Building damage is shown to be related closely to the 

fundamental frequency of the structure. The most heavily 

damaged buildings had fundamental frequencies of approximately 0.8 to 1.2 Hz, which corresponds to the frequency range of greatest site amplification reported by 

Boatwright and others. Dynamic analyses indicate displacements of about 300 mm for heavily damaged buildings, which is consistent with the permanent deformation 

actually observed in many of these structures. 

A particularly interesting aspect of Harris and Egan's 

work is the difference in the response of wood-frame corner buildings from that of buildings which had unreinforced-masonry or concrete first stories but were otherwise 

similar in construction. The buildings with masonry and 

concrete first stories, which had fundamental frequencies 

of about 3 Hz, were damaged on average about 10 times 

less severely than their wood-frame counterparts. Such observations emphasize the importance of fundamental frequency and the substantial improvements in structural 

response associated with stiffening structures at soft-soil 

sites. 

EMERGENCY SERVICES 

Scawthorn and others describe the emergency-response 

services of the police and fire departments, ambulance 

crews, and Marina District residents. Their study brings 

into focus some of the most important lessons learned in 

the Marina District. 

San Francisco is served by two in-ground water-supply 

systems, the MWSS and the Auxiliary Water Supply System (AWSS); the AWSS is operated exclusively for firefighting purposes. Water was available from neither of 

these systems after the earthquake. As previously mentioned, the MWSS was severely disrupted by the effects of 

liquefaction in the Marina District. The AWSS had likewise been damaged by liquefaction nearly 5 km away, and 

water was completely lost from a reservoir supplying city 

areas adjacent to the bay. 

Of critical importance in controlling and suppressing the 

fire in the Marina District were the fireboat, which was 

dispatched to the St. Francis Yacht Club Harbor, and the 

Portable Water Supply System (PWSS). The PWSS consists of special hose tenders, with 1,600 m of 125-mmdiameter hose and associated equipment, which can draw 

water from the bay and underground cisterns. This system 

was responsible for stopping the fire in the Marina District, thereby saving the community from considerably 

more severe fire damage. The acquisition of the PWSS, as 

well as the planning and training for its use under emergency conditions, proved to be of inestimable value in reducing earthquake-related losses. 

Scawthorn and others draw attention to the congested 

radio traffic between firefighters and the central communications center. This traffic, which far exceeded the capacity of the allotted channels, underscores a need for 

additional channels and improved oversight by means of 

aerial reconnaissance. These investigators also point out 

the important role played by Marina District residents in 

assisting emergency-service personnel. 
CONCLUDING Rl3MARKS 

The Marina District has been a focal point of media 

coverage, postearthquake investiga+ions, and rehabilitation 

efforts. In the first few months after the earthquake, special studies were undertaken by geotechnical staff at the 

University of California, Berkeley (Mitchell and others, 

1990), the 1J.S. Geological Survey (1990), and the National Center for Earthquake Engineering Research (09Rourke 

and others, 1990). These initial studies were used to acquire data and evaluate site conditions for use by city and 

district residents in the rehabilitation and seismic remediation of the area. Additional studies sponsored by the National Science Foundation, the U.S. Geological Survey, 

and the National Center for Earthquake Engineering Research helped to establish a detailed and vigorous program 

for the assessment of earthquake effects in the Marina 

District. Many of the reports in this chapter are the result 

of research sponsored by these national organizations. 

Studies commissioned by the city of San Francisco (Harding Lawson Associates and others, 1991) have focused on 

liquefaction hazards, with a first-time, systematic review 

of the sites vulnerable to liquefaction-induced ground deformation and their potential effect on lifeline systems. 

These studies have involved an engineering evaluation of 

liquefaction and lifeline hazards in the Marina District, 

with recommendations for retrofitting, site stabilization, 

and infrastructure planning. 

The investigations and studies stimulated by the Marina District have important ramifications not only for 

local residents but also for the larger community of people living in places vulnerable to earthquakes. Lessons 

learned regarding the pattern of ground deformation 

relative to subsurface conditions and its effect on lifelines and buildings will help in the mapping of hazard 

zones as part of a statewide effort engendered by the 

Seismic Hazards Mapping Act passed by the California 

Legislature (1990). Lessons learned about dynamic site 

response, liquefaction, lifeline performance, and emergency services are relevant to a11 seismically vulnerable 

areas and help to achieve the goals of earthquake-damage mitigation embodied in the National Earthquake 

Hazards Reduction Program. 

The Marina District is a microcosm of the type of site 

response and damage patterns that can be sustained not 

only in the San Francisco Bay area but also at locations of 

reclaimed land and soft sedimentary deposits' throughout 

the world. The findings reported in this chapter, therefore, 

contribute to improved engineering and planning practices 

for sites most vulnerable to earthquakes and most in need 

of assistance to reduce existing hazards. 

Acknowledgment.-I thank Laurie Mayes of Cornell 

University for helping in the organization and coordination 

of this publication. 

REFERENCES CITED 

California State Legislature, 1990, Public Resources Code, chap. 1168, 

sec. 2690 ff. 

Harding Lawson Associates, Dames & Moore, KennedylJenkslChilton, 

and EQE Engineering, 1991, Liquefaction study, Marina District 

and Sullivan Marsh area, San Francisco, California; final report prepared for San Francisco Department of Public Works: San Francisco, 144 p. 

McNutt, S.R., and Toppazada, T.R., 1990, Seismological aspects of the 

17 October 1989 earthquake, in The earthquake, sec. 1 of McNutt, 

S.R.- and Sydnor, R.H., eds., The Loma Prieta (Santa Cruz Mountains), California, earthquake of 17 October 1989: California Division of Mines and Geology Special Publication 104, p. 11-27. 

Mitchell, J.K., Tahir, M., Kayen, R.E., and Seed, R.B., 1990, Soil conditions and earthquake hazard mitigation in the Marina District of San 

Francisco: report to the mayor of San Francisco. 

O'Rourke, T.D., Stewart, H.E., Blackburn, F.T., and Dickerman, T.S., 

1990, Geotechnical and lifeline aspects of the October 17, 1989 

Lorna Meta earthquake in San Francisco: Buffalo, N.Y., National 

Center for Earthquake Engineering Research Technical Report 

NCEER-90-0001 49 p. 

Plafker, George, and Galloway, J.P., eds., 1989, Lessons learned from the 

Loma Prieta, California earthquake of October 17, 1989: U.S. Geological Survey Circular 1045, 48 p. 

U.S. Geological Survey, 1990, Effects of the Lorna Prieta earthquake on 

the Marina District, San Francisco, California: Open-File Report 

90-253. 
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND F'AILUm 

MARINA DISTFUCT 

GEOLOGIC AND HISTORICAL FACTORS 

AFFECTING EARTHQUAKE DAMAGE 

CONTENTS 

Fable I follows wfemnces] 

By M.G. Bonilla, 

U.S. Geological Survey 

Ground-water levels ............................................... Discussion and conclusions ----- - ....................... ---------------- Acknowledgments .................................................... ---- References ~it& ......................................................... 

Page 

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26 

ABSTRACT 

A northwest-trending valley in the bedrock surface is 

buried by firm Pleistocene bay clay, dense to very dense 

Pleistocene sand, soft Holocene bay deposits, loose to 

dense Holocene beach and dune sands, and artificial fill 

that have an aggregate maximum thickness of about 90 m. 

Depth to the ground-water table is generally less than 2.7 

m (9 ft) except in one area of thick dune sand; the groundwater table is quite shallow in some places where no surface effects of liquefaction related to the earthquake were 

reported. 

Artificial filling of a cove at the site of the Marina District proceeded gradually from the late 1860's to 1912, 

when major hydraulic filling was done for the PanamaPacific International Exposition. The remains of thousands 

of piles driven for the exposition probably still exist and 

may have affected long-term ground settlement and earthquake-related ground displacements. 

Previous studies suggest that ground motion was amplified on both natural and artificially filled ground because 

of the configuration of the bedrock surface and the position 

and thickness of various clay and sand deposits underlying 

the fill, but that most of the settlement, liquefaction, and 

damage to pipelines* building foundations, streets, sidewalks, and curbs occurred in areas of artificial fill consisting mainly of loose sand. 

INTRODUCTION 

During the earthquake, substantial damage occurred in 

the Marina District of San Francisco, even though it was 

100 km (60 mi) from the epicenter. Factors that influenced 

the damage included liquefaction, differential settlement, 

amplification of ground motion, and the types and conditions of the buildings. To understand the reasons for the 

damage and to anticipate the effects of future earthquakes, 

various studies have been conducted and described, among 

them a preliminary report on the geology and the artificial 

fills that underlie the Marina District (Bonilla, 19901, and a 

report that discussed the relations of the geology, historical 

development7 and earthquake effects (Bonilla, 1991). The 

present study is a summary and expansion of the cited reports, including information about the historical development of the Marina District and the composition and 

distribution of bedrock, unconsolidated Pleistocene and 

Holocene deposits, and artificial fills. Its purpose is to provide background information for current and future scientific and geotechnical investigations of the Marina District, 

and its emphasis is on those aspects of the geology and 

historical development that are pertinent to understanding 

past and future earthquake effects. 
F8 MARINA DISTRICT 

Both customary and metric units are used in this report, 

because many of the anticipated geotechnical users prefer 

customary units; furthermore, the original data for some 

illustrations are in customary units and cannot be conveniently or accurately shown in metric units. Dual units are 

given in the text and, where practical, in the illustrations 

also. 

Although much information is available about the Marina District, much still remains unknown. Where necessary, 

I have made interpretations even if the information is 

scanty. The bases for my interpretations are described in 

the text or shown on the maps and cross sections, to allow 

the reader to judge the reliability of the interpretations. 

The location of the Marina District and of streets and 

localities referred to in the text are shown in figure 1. For 

brevity, the Marina District is referred to as "the Marina" 

in the following text. 

GEOLOGY 

SOURCES OF INFORMATION 

The geologic map of the Marina District (fig. 2) is derived from old maps, photographs, boreholes, and previously published geologic maps. The positions of shorelines and 

marsh areas are from U.S. Coast Survey maps dated 1851 

through 1869. Areas of dune sand, beach sand, and beach 

sand covered by dune sand were interpreted on the basis of 

(1) the sand patterns shown on the maps, (2) areas of higher 

ground shown by hachures or contours on the maps, and (3) 

other historical information including photographs taken in 

1856 through 1887. The area of undivided Quaternary sedimentary deposits shown near Chestnut and Scott Streets is 

inferred from hachures and sand patterns shown on the 

185 1 map. The areas of undivided Quaternary and Franciscan bedrock are slightly modified from the maps by Schlocker (1974, pi. 1) and Schlocker and others (1958). The 

areas of artificial fill were delineated primarily from topographic and planimetric maps, including those by the U.S. 

Coast Survey dated 1851 through 1895, Lawson (1 908, 

map 17), and Leurey (1914, fig. 3). The information on 

these maps was supplemented by a photograph taken in 

1 9 12, historical accounts, and boreholes. 

The boreholes used in this study are identified by an alphanumeric code related to a grid that is referenced to the 

Marina street pattern (fig. 3); for example, the borehole in 

the northwest comer of figure 3 is referred to as 3A1. The 

last number in the code was assigned serially according to 

the date of drilling, if known. The sources, dates, and other pertinent information about the boreholes are listed in 

table 1. Many of the borehole logs are considered proprietary information by landowners, and readers interested in 

copies of these logs should contact the listed sources for 

the owners' names. 

The locations of many of the boreholes drilled for the 

Panama Pacific International Exposition are uncertain, and 

so their locations as shown in figure 3 may differ from 

locations used by other workers. Whitworth (1932, pi. 24) 

showed the boreholes on a small-scale (approx 1:90,000) 

map, and described their locations in relation to both 

streets and exposition buildings, but some of his descripSan Francisco Bay 1 STUDY AREA 

Base from U.S. Geological Survey San Francisco North 7.5' quadrangle, photorevised in 1973 

Figure 1.-Marina District of San Francisco, showing locations of features mentioned in text. 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE F9 

tions are in conflict with his map. Furthermore, some of 

Whitworth's descriptions are clearly wrong, such as giving 

distance west of an east-west-trending street; other distances and directions place a borehole in a different part of 

a given building than his text states. The map by Leurey 

(1914) accurately shows a few boreholes in relation to exposition buildings, and he stated that boreholes were 

drilled at the comers of the buildings; Whitworth's locations in relation to exposition buildings, if not incongruous 

with other information, are accepted here. The locations of 

exposition buildings as shown by Todd (1921) were plotted in relation to present-day streets by using as controls 

the Palace of Fine Arts and the centerline of Scott Street, 

the only exposition street that was centered on existing 

San Francisco streets (Markwart, 19 15a, p. 75). 

BEDROCK 

The bedrock underlying the Marina consists of Franciscan assemblage and serpentine. Nearby outcrops consist of 

sandstone and shale except to the west, where serpentine 

is also exposed (Schlocker, 1974). The locations of outcrops of Franciscan sandstone and shale in Fort Mason are 

shown in figure 2. A borehole near the south end of the 

Palace of Fine Arts (2G1, fig. 3) penetrated shale, but a 

U.S. Geological Survey (USGS) borehole (5E3) southeast 

of the intersection of Divisadero and Beach. Streets penetrated serpentine. 

Several maps show the configuration of the bedrock surface beneath the Marina. The map by Whitworth (1932, 

pi. 33) shows the surface at an elevation of 75 m (250 ft) 

below sea level in the southern and southeastern parts of 

the Marina. The maps by Schlocker (1962, 1974) and 

Schlocker and others (1954) show similar depths except in 

the western part of the Marina where they show elevations 

of 0 to -15 m (0 to -50 ft). The map by Schlocker and 

others (1954) relied on the boreholes reported by Whitworth (1932), but included a precautionary note: "Bedrock 

may be considerably deeper than shown; contours drawn 

on top of 'yellow hardpan' of drillers log." This note, 

however, was omitted from the later bedrock-surface maps 

by Schlocker (1962; 1974, pi. 3). Various post-1932 borehole logs show that the bedrock is indeed deeper than the 

EXPLANATION 

ARTIFICIAL FILLS NATURAL DEPOSITS 

191 2--17 1912) [,,1 ~e~~h sand 

1906-12 Beach sand with th~n cover of dune sand 

a 1895-1906 Dune sand 

1869-95 Quaternary sedimentary deposits, undivided 

1851-69 Bedrock--Franciscan assemblage 

Fills, undivided 

Figure 2.Ã‘Geologi map of the Marina District, showing locations of major artificial fills and cross sections A-A' through C-C' (see figs 5-7). 

Northwest-trending dashed curve on left designates part of 1851 shoreline. Undated fill near the Fort Mason docks was placed about 1910, and fills 

north of yacht harbor are post-1914. See text ("General Distribution, Age, and Composition of Artificial Fills") regarding accuracy of map. 
F10 MARINA DISTRICT 

yellow hardpan. A map showing the bedrock surface under 

part of the Marina and San Francisco Bay (Carlson and 

McCulloch, 1970) is based on the map by Schlocker 

(1962) and interpretation of offshore continuous subbottom acoustic profiling. 

My interpretation of the configuration of the bedrock 

surface is shown in figure 4. Although more than 200 

boreholes have been drilled in the Marina, few reach the 

bedrock surface; mapping of this bedrock surface therefore 

requires many inferences and interpretations. In preparing 

figure 4, I assumed that the bedrock surface was shaped 

by stream erosion rather than tectonic deformation and 

that the stream had its outlet through the Golden Gate, 

where bedrock is about 120 m (400 ft) below sea level 

(Carlson and McCulloch, 1970). The maps by Carlson and 

McCulloch (1978) and Schlocker (1974) show a bedrock 

basin in the Marina that opens to the north just west of 

Fort Mason. However, two boreholes considerably farther 

west (5E3, 2G1, fig. 3) that penetrated bedrock at elevations of -77 m (-252 ft) and -23 m (-75 ft) indicate that 

the bedrock basin may open to the northwest rather than 

the north. A stream flowing northwest would have a shorter path to the Golden Gate than one flowing northward 

and then westward, and so a northwest-flowing drainage 

was assumed. Using this basic model, the surface drainage 

shown on the old topographic maps was extrapolated, and 

contours were inferred from borehole data, outcrops, and 

the offshore geophysical survey of Carlson and McCulloch 

(1978). 

The bedrock surface shown in the northwest comer of 

figure 4 is deeper than the onshore and near-offshore contours shown by Carlson and McCulloch (1970). Their interpretations onshore in the western part of the Marina were 

influenced by the erroneous contours on the yellow hardpan 

(Schlocker, 1962), and so they are discounted here. Offshore, Carlson and McCulloch show a -75-m (-250 ft) 

bedrock elevation where figure 4 shows an elevation of -90 

m (-300 ft). Straight-line extrapolations of the bedrock surface between boreholes or between outcrops and boreholes 

indicate bedrock elevations of at least -90 m (-300 ft) well 

inland under the Marina, and so, if the stream-erosion model is correct, bedrock elevation must be less than -90 m in 

the northwest comer of figure 4. Owing to difficulty in 

identifying bedrock in the reflection profiles and unknown 

velocities in firm materials above bedrock, the bedrock surface may well be lower than shown on Carlson and McCulloch's map (P.R. Carlson, oral cornrnun., 1990). Van 

Reenan (1966) also stated that identification of the bedrock 

surface by reflection methods is difficult in some places, 

and he noted on his profiles that refraction data locally 

show greater depths than do reflection data. 

O'Rourke and others (1991, fig. 12; see O'Rourke and 

others, this chapter, fig. 14) independently prepared a map 

showing contours on the bedrock surface beneath the MaFigure 3.-Marina District, showing locations of boreholes (numbered dots). See text for explanation. 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE Fll 

rina. They used bedrock outcrops farther to the southwest, 

south, and east than I did, but not Anita Rock or the offshore geophysical surveys. Their map, generated by computer software that uses a method called kriging, is similar 

to figure 4 in showing a northwest-trending valley in the 

bedrock surface, but differs in that the valley is about 15 

m (50 ft) shallower and does not extend as far to the 

southeast. 

UNCONSOLIDATED 

NATURAL SEDIMENTARY DEPOSITS 

sea levels during glacial periods resulted in erosion of valleys in the then-existing sedimentary deposits. Exposure of 

these deposits resulted in near-surface desiccation and oxidation, which made the sediment firmer and produced the 

brown colors commonly reported in boreholes. This geologic history produced various geologic units in the Marina and surrounding area, including bay, marsh, beach, and 

dune deposits. 

PLEISTOCENE BAY DEPOSITS 

The bedrock in the Marina is buried by a sequence of 

unconsolidated sedimentary deposits. The term "unconsolidated" is used here in the geologic sense (that is, not hard 

rock) rather than in the geotechnical sense. The complexity of these deposits can be partially understood by reviewing the recent geologic history of the San Francisco Bay 

estuary. During the past million years, at least four periods 

of deposition occurred in San Francisco Bay, separated by 

periods when sea level was lower because ocean water 

was incorporated into glaciers (Atwater, 1979). The lower 

Several boreholes in the Marina penetrated silty to sandy 

clay at considerable depth. In USGS borehole WSS (5E3, 

fig. 3), south of Beach Street and east of Divisadero Street 

(Kayen and others, 1990), the clay is 58 m (189 ft) thick 

and extends from an elevation of -19 m (-63 ft) to the 

bedrock surface at an elevation of -77 m (-252 ft). The 

clay is probably correlative with one or more of the three 

pre-Holocene bay deposits that formed in San Francisco 

Bay during the past million years (Atwater, 1979). During 

the latest interglacial sea-level highstand about 100 ka, an 

extensive bay deposit formed in San Francisco Bay (AtwaFigure 4.-Marina District, showing inferred contours on bedrock surface, ocp, data points at rock outcrops. Acoustic-profile tracklines from Carlson 

and McCulloch (1970). 
F12 MARINA DISTRICT 

ter and others, 1977; Atwater, 1979, fig. 3). The upper part 

of the thick clay penetrated in USGS borehole WSS (5E3, 

fig. 3) is probably this approximately 100,000-year-old bay 

deposit, but the lower part may be still-older bay deposits. 

The Pleistocene bay deposits are not exposed at the surface 

in the Marina, but their inferred extent and thickness in the 

area of figure 2 is shown on cross sections A-A', B-B', and 

C-C' (figs. 5, 6, and 7, respectively). When a plan-view 

sketch was made of the upper surface of the Pleistocene 

bay deposits, using the few borehole data, it became apparent that this surface has a broad depression, represented in 

figures 5 through 7, that apparently trends northeast. 

Treasher (1963) reported that valleys eroded into the older 

bay deposits are common in various parts of San Francisco 

Bay, and Atwater and others (1977) also recognized a major unconformity at that stratigraphic level. Whether this 

depression in the surface of the Pleistocene bay deposits in 

the Marina is a result of erosion is unclear. 

PLEISTOCENE SAND ZONE 

Many boreholes penetrated a sand zone overlying the 

Pleistocene bay silty clay. Its thickness, as measured on 

the cross sections (figs. 5-7), ranges from 3 to 38 m. Two 

samples of the sand zone, from USGS borehole WSS 

(5E3, fig. 3) contain only 1 to 4 weight percent silt and 

clay (Kayen and others, 1990), suggesting a dune or beach 

origin. A third sample contains 26 weight percent silt and 

clay and could be of stream or estuarine origin. In some 

borehole logs, the sand zone is described as sand, silty 

sand, or clayey sand. Thick interbeds of clay (fig. 7) are 

probably estuarine, suggesting that the sand zone has had 

a varied history. A sand zone in the southeastern part of 

San Francisco has a similar stratigraphic position-under 

the Holocene bay clay and above the older bay clay-and 

in that area the lower part of the sand is interbedded with 

the older clay (Radbruch and Schlocker, 1958). The sand 

zone in the Marina is probably less than 100,000 years old 

because it overlies the Pleistocene bay deposits thought to 

be about 100,000 years old. As discussed in the next section, the upper part of this sand zone was apparently eroded by streams near the end of the latest glaciation, and so 

the zone is interpreted to be of Pleistocene age. 

The sand zone lithologically resembles the Colma Formation and may be correlative with that formation. The 

Colma Formation, commonly a weathered sand, is thought 

to have originated primarily as a beach deposit (Schlocker, 

1974). Information on the age of an ash bed in marine 

deposits beneath the Colma in the southwestern part of 

San Francisco (Meyer and others, 1980, 1991; SarnaWojcicki and others, 1985) indicates that the Colma must 

be considerably less than 400,000 years old and may correlate with one of the latest sea-level highstands between 

about 130 and 70 ka (Clifton and others, 1988). 

HOLOCENE BAY DEPOSITS 

Sea level during the latest (Wisconsin) glaciation was 90 

to 120 m (300-400 ft) lower than at present and the ocean 

shoreline was probably seaward of the Farallon Islands, 

about 50 krn (30 mi) west of San Francisco. The Holocene 

bay deposits in the Marina accumulated during the sealevel rise that followed the latest glaciation. The rising sea 

is estimated to have entered the Golden Gate 11-10 ka 

(Helley and Lajoie, 1979, p. 18). The bay deposits in the 

Marina are generally soft silty clay or clayey silt, but locally they include fine sand. These deposits have been referred to by the term "bay mud and clay" (for example, 

Schlocker and others, 1958; Schlocker, 1974), but for 

brevity and in keeping with more common usage they are 

here referred to as "bay mud." 

The bay mud formed the bottom of Marina Cove (see 

fig. 10) and underlies much of the Marina. This bay mud 

is not exposed at the ground surface, and so its extent 

must be inferred (fig. 8). The northern margin shown in 

figure 8 is based on a few borehole data on the west and 

on predevelopment lagoon-bottom contours, inferring that 

the edge of the estuarine mud coincides with the steep 

slope indicated by the contours in figure 9. The swift tidal 

currents in the deeper water do not permit deposition of 

mud, and sand is known to cover the bay bottom north of 

the Marina (Carlson and others, 1970, p. 106). These considerations and three boreholes to the west (3A1, 3A2, 

4A1, fig. 3), each of which penetrated silty sand, are the 

basis for the inferred north contact of bay mud and silty 

sand shown in figure 6. Whether this contact is gradational 

or interfingering is unknown; the position of the margin of 

the bay mud west of the area of figure 8 is also unknown. 

The configuration of the bottom of Marina Cove and of 

the surface of the bay mud in 1873 is shown in figure 9, 

EXPLANATION FOR FIGURES 5 THROUGH 7 

1912 hydraulic fill Miscellaneous artificial fill 

[j Sand F] Sand and clayey sand ( smd and silty sand :..-.. j^te .=. 

p^j clay Rj Silty clay and clayey silt Sandy clay 

^^J Silty clay and sandy clay 0 Gravel 

Inferred Pleistocene-Holocene boundary 

T I Borehole 

M.S.L., mean sea level datum 

C.D., San Francisco city datum 

Explanation for figures 5 through 7. 
C.D. 

- 50 ft 

- 0 

- -50 

- -100 

- -150 

- -200 

- -250 

-2"" 

1w 15.00 2000 3000 3500 4000 45.00 5000 55.00 6000 feet 

0 500 1000 15.00 2000 3000 35.00 4000 4500 5000 5500 6000 feet t . 1 I I I I I I I I I I I I I I I I I I 

0 500 1000 1500 1800 meteis SECTION A-A' WITH NO VERTICAL EXAGGERATION 

Figure 5.-East-west cross section A-A' along Beach Street (see fig. 2 for location). Sand fill, difficult to distinguish from natural sand, may locally overlie beach and dune deposits near Baker Street. 

Marsh deposits below artificial fills in western part of the cross section are too thin to be delineated. Queries indicate uncertainty in location. Interfingering of Pleistocene clay and Pleistocene sand in 

eastern part of cross section is schematic. 
F14 MARINA DISTRICT 

based on an 1873 map by the U.S. Coast Survey (register a late Pleistocene erosional surface, a condition that ac1214a, scale 1:20,000), that shows soundings in feet below counts for its irregular bottom. 

mean lower low water and contours of 6-, 12-, and 18-ft A layer of green sand and clay, commonly described as 

depth. These soundings and contours were transferred to a hard, was penetrated at the bottom or near the base of the 

l:10,000-scale base map, and the contours shown in figure bay mud in 70 percent of the boreholes made for the 1915 

9 were drawn, interpolating between soundings and using Panama-Pacific International Exposition, and most of the 

the old shoreline and the three depth contours shown on exposition piles were founded in this layer. A layer rethe 1873 map as guides. The 1873 rather than earlier maps 

was used for contouring because the earlier maps are more 

difficult to match with modem maps and soundings are 

sparser. Both the top of the bay mud in 1873 and its 

present surface, modified by application of artificial fill 

(see O'Rourke and others, this chapter, fig. 16), show 

much less relief than its bottom does (see figs. 5-7). As 

discussed below, the bay mud was apparently deposited on 

ferred to in the borehole logs as "yellow hardpan" lies beneath the hard green sand and clay, and was reached by 85 

percent of the exposition boreholes. Although descriptions 

vary, several 1989 and 1990 boreholes penetrated a similar 

zone containing hard or firm layers that produced high 

peaks on the cone-penetrometer-test records. The "yellow 

hardpan" is probably a soil zone that formed on an erosional surface developed during the low sea level of the 

SOUTH 

B 

M.S.L. C.D. 

NORTH 

B' 

M.S.L. C.D. 

o 500 1000 m SECTION B-B' WITH NO VERTICAL EXAGGERATION 

Figure 6.-North-south cross section B-B' along Divisadero Street (see fig. 2 for location). Sand fill, difficult to distinguish from natural sand, may 

locally overlie beach and dune deposits. 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE F15 

latest glaciation, and the green layer (sand and clay) 

formed during the early stages of bay deposition. Inclusion 

of the green layer within the bay deposits is supported by 

the fact that it is locally interbedded with bay deposits 

(Whitworth, 1932, boreholes 2, 11, and probably 14A). If 

this interpretation is correct, the hard zone (that is, the 

"yellow hardpan" and the hard green sand and clay) is 

near the local boundary between the Pleistocene and Holocene. In figures 5 through 7 the inferred Pleistocene-Holocene boundary is shown as a heavy line drawn above the 

yellow hardpan, where so identified in the borehole logs, 

or where hard zones of yellow or brown color are indicated in the logs. This boundary is at the top of the Pleistocene sand zone (described above), as shown in figures 5 

through 7. 

General descriptions of the bay mud were given by 

Schlocker (1974) and Helley and Lajoie (1979), and some 

of the geotechnical properties of the bay mud in the Marina were described by Kayen and others (1990) and are 

given in other reports in this chapter. 

HOLOCENE BEACH AND DUNE SAND 

Holocene beach sand underlies the northwestern part of 

the Marina and forms a narrow strip in the southeastern 

SOUTH 5' . x0 Is^ 

NORTH 

C' 

M.S.L. C.D. 

ft 

-50 

- 

-0 

- 

-50 

ISECTION C-C' WITH NO VERTICAL EXAGGERATION 

Figure 7.-North-south cross section C-C' along Fillmore Street (see fig. 2 for location). 
F16 MARINA DISTRICT 

EXPLANATION 

-^ 

Margin of Holocene bay mud; 

queried where uncertain + 

Control point 

Figure 8.-Schematic map of the Marina District, showing areal extent of Holocene bay mud (dotted pattern) in subsurface. Small areas of thin marsh 

deposits lie outside boundary shown in southwestern part of the map area. 

EXPLANATION 

8 

Sounding, MLLW, ft 

stk S.M. 

Character of bottom 

~t.6 ftjContour, MLLW 

Figure 9.-Marina District, showing bottom of Marina Cove in 1873. Soundings from U.S. Coast Survey map 1214a, 1873, scale 1:20,000. MLLW, 

mean lower low water, approximately 0.9 m (3 ft) below mean sea level datum. Character of bottom: stk, sticky; S., sand; M., mud. 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE 

part (fig. 2). The sand deposits in the northwest form a 

spit formerly called Strawberry Island; comparison of 

maps dated 185 1 and 1869 show that this spit was growing eastward before placement of artificial fill. On the basis of line patterns on old maps, and photographs taken in 

1876, much of the beach sand had a thin, discontinuous 

cover of dune sand. The 1851 map shows a symbol that 

indicates "sand hills or dunes" (U.S. Coast and Geodetic 

Survey, 1942, fig. 189) for most of Strawberry Island and 

a small area southeast of Marina Cove (see fig. 10); these 

areas are shown in figure 2. Old maps, photographs, and 

historical accounts show that dune sand (wind-deposited 

sand) underlies the eastern and southeastern parts of the 

Marina. 

The bulk of both the beach and dune deposits consists of 

clean, well-sorted sand. Detailed descriptions and analyses 

of the beach and dune sands were given by Schlocker 

(1 974). 

HOLOCENE MARSH DEPOSITS 

Tidal marsh deposits, now covered by artificial fill, underlie an area in the southwestern part of the Marina and 

continue westward into the Presidio; their original extent 

is shown on an 185 1 map (fig. 10). A small part of the 

marsh was evidently covered by dune sand between 185 1 

and 1869; the marsh area east of the longest of the northsouth segments of the tidal channel shown in figure 10 is 

indicated as sand on the 1869 map (fig. 11) and on the 

geologic map of Lawson (1908, map 17). This area is near 

the north central part of the block bounded by Bay, Divisadero, Francisco, and Broderick Streets. 

The marsh deposits consist of clay and silt containing 

small amounts of marsh vegetation. They grade into the 

bay deposits that underlie the Marina, and in places interfinger with beach sand. General descriptions of the marsh 

deposits around San Francisco Bay were given by Helley 

and Lajoie (1979) and Atwater and others (1979). 

UNDIVIDED QUATERNARY SEDIMENTARY DEPOSITS 

Small areas of undivided Quaternary sedimentary deposits are shown in the southwestern, southeastern, and northeastern parts of figure 2. In the southwest, near Chestnut 

and Scott Streets, figure 10 shows areas with map symbols 

that indicate bluffs, and "sand and gravel" or "stones and 

gravel" (U.S. Coast and Geodetic Survey, 1942, fig. 189). 

The origin of these deposits is unknown, but they could 

have been formed by storm waves. The undivided Quaternary sedimentary deposits shown in the southwest, southeast, and northeast comers of figure 2 are from Schlocker 

and others (1958) and Schlocker (1974). In the northeast 

Figure 10.-Part of U.S. Coast Survey chart 314, dated 1851. Diagonal-lined area, marsh areas. Bracketed labels are not on original map, which is at 

1 : 10,000 scale. 
F18 MARINA DISTRICT 

comer of figure 2, these deposits are primarily colluvium, 

and rest directly on bedrock. 

ARTIFICIAL FILLS 

Human modification of the natural environment of the 

Marina, particularly by the emplacement of artificial fill, 

has had important effects on subsurface conditions there. 

To better understand both the environmental changes and 

the content of the fills, the development of the Marina is 

outlined. 

HISTORICAL DEVELOPMENT OF THE MARINA 

The earliest accurate map of the Marina, dated 185 1 (fig. 

lo), shows a small embayment (Marina Cove) west of the 

bedrock headland now occupied by Fort Mason, as well as 

a meandering tidal slough draining a marsh that extended 

west of the Marina. North of this principal slough was a 

broad sand spit, covered discontinuously by dune sand, referred to as Strawberry Island (Dow, 1973). The north 

edge of Strawberry Island is labeled "Sand Point" on the 

1851 map. A narrow waterway extended northwestward of 

the mouth of the principal slough, just reaching the present 

position of Beach Street. Another small waterway, trending northeast, lay east of the principal slough. A narrow 

strip of beach sand was to the north, and a broad area of 

dune sand to the east of this waterway. The features shown 

on an 1857 U.S. Coast Survey map are almost the same, 

except for shortening of the narrow, northwest-trending 

waterway and an eastward shift in the positions of the 

mouth of the principal tidal slough and associated sand 

spits at the south end of Marina Cove. These changes 

were likely natural because no roads or structures are 

shown near the shoreline. 

By 1869 (fig. 1 I), the mouth of the principal slough had 

shifted westward, probably by natural processes, and the 

narrow, northwest- and northeast-trending waterways mentioned above no longer existed. Probably both of these 

narrow waterways were artificially filled, at least in part, 

because roads are shown crossing their former sites. A 

roadway, evidently on fill, is shown partly crossing the 

principal slough along the present position of Divisadero 

Street at Francisco Street. The Fillmore Street wharf, built 

in 1863 and 120 m (400 ft) long (Dow, 1973, p. 95), is 

shown extending into Marina Cove north of the present 

Figure 11.-Part of U.S. Coast Survey map 3055, dated 1869. Black Point is now part of Fort Mason. Intersection of Fillmore Street wharf and shoreline is 

approximately at present position of Bay Street-Fillmore Street intersection. Dotted patterns, sand areas; ruled pattern, marsh; ruled pattern with black 

borders, lake. Original map is at 1 :40,000 scale and has a 204 contour interval. Surveys for this map were performed in 1850-57 and 1867-68. 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE F19 

position of Bay Street at Fillmore Street; presumably, this 

wharf was built on piles. East of the Fillmore Street wharf 

is an artificial fill, perhaps 30 m (100 ft) long, along the 

east side of the present position of Webster Street and 

south of the present position of North Point Street. The 

symbol used on the 1869 map suggests that this fill was of 

sand. 

In the 1860's a hotel, shooting gallery, and other structures were built north of the present site of the Palace of 

Fine Arts. The Santa Cruz Power Co. had a small wharf in 

the same vicinity (Dow, 1973), probably one of the two 

wharves shown in figure 11 northwest of Marina Cove at a 

site north of the present-day Marina Boulevard. The 

Phelps Manufacturing plant, which made bolts, heavy 

forgings, railroad cars, and cable was built in 1882 in a 

triangular area bounded by present-day Fillmore, Bay, and 

Buchanan Streets (Dow, 1973, p. 95). 

In 1891, the San Francisco Gas Light Co. Constructed a 

wharf extending 300 m (1,000 ft) north of Bay Street at its 

property east of the Phelps plant (fig. 12; Dow, 1973, 

p. 97). This wharf, which is referred to as an "earthen 

mole" on the map by the Sanbom Ferris Map Co. (1899), 

had a rock retaining wall around it (Olmsted and others, 

1977, p. 667). 

In the late 1800's, a seawall was built around property 

owned by J.G. Fair; it was built of rock dumped from cable-drawn railroad cars operating on a pile trestle (Olmsted and others, 1977, p. 716, pi. 20). According to Dow 

(1973, p. 96-101), this seawall was built in 1894, retained 

the hydraulic fill placed for the 1915 Panama-Pacific International Exposition, and was at or near the present seawall 

north of Marina Boulevard. The date of construction of 

Fair's seawall is problematic because it is not shown on 

the large-scale map of wharflines and pierheads surveyed 

in 1895 (fig. 12). The "seawall(?)" shown on the 1895 

map only partly coincides with the present seawall and 

does not reach the east or west shores of the lagoon; however, an 1899 map shows the seawall reaching both shores 

(Sanbom Ferris Map Co., 1899). 

At the time of the 1906 earthquake Marina Cove was 

enclosed by a rim of artificial fill except for a narrow 

opening to the north (fig. 13). Little historical information 

Figure 12.-Part of U.S. Coast and Geodetic Survey register 2205, surveyed in 1895. The intersection of North Point and Buchanan Streets is in 

center of San Francisco Gas Light Co. buildings. Building at southeast comer of intersection still exists and is called the Pacific Union Co. 

building. "Cal. Pressed Brick Works" is northeast of intersection of Jefferson and Broderick Streets. Dot-dashed line, boundary of the Presidio, 

which now curves to exclude the Palace of Fine Arts. Bracketed labels are not on original map, which is at 1:10,000 scale and is titled "Re-Survey 

of San Francisco Bay; City Water-Front Wharf-Lines and Pier-Heads." 
F20 MARINA DISTRICT 

is at hand as to the method of placement or composition 

of this fill, but segments of the assumed seawalls shown 

on the 1895 map and Fair's seawall must have been incorporated into it. Two boreholes drilled through the fill in 

1975 penetrated sand containing some rock fragments, 

brick, and other rubble (Dames & Moore, 1976). Artificial 

fill had also been placed over the eastern part of the principal slough as far west as the present location of Lyon 

Street. A photograph of Marina Cove taken in 19 12 before 

hydraulic filling (fig. 14) shows conditions similar to those 

shown on the 1908 map (fig. 13), except that the photograph shows a broader area of fill on the east side of the 

cove. The general outline of the west edge of this 1906- 

12 fill, as shown in figure 2, was interpreted from figure 3 

of Leurey (1914) (fig. 15), which shows a contour line 

near mean high water, the conventional shoreline for most 

maps. How much debris from the 1906 earthquake and 

fire was incorporated into fills in the Marina is unknown, 

and, as described in the subsection below entitled "General Distribution, Age, and Composition of Artificial Fills," 

1906 debris would be difficult to distinguish from the 

Panama-Pacific International Exposition debris. There was 

a refuse dump at the foot of Webster and Bay Streets in 

the 1900's (Khorsand, 1973, p. 35); from the context of 

the description, this dump probably predated the 1906 

earthquake. Two historical accounts that cover the Marina 

(Dow, 1973; Khorsand, 1973) made no mention of any 

dumping of 1906 debris at Harbor View (present-day Marina). Two general reports on the 1906 earthquake stated 

that debris from the main part of San Francisco was 

dumped in Mission Bay (in the eastern part of San Francisco) and that some was hauled by barges to the vicinity 

of Mile Rock, west of the Golden Gate (Bronson, 1959, p. 

170; Sutherland, 1959, p. 197). Considering its age, however, the 1906-12 fill could include debris from the 1906 

earthquake. Logs of four boreholes (Whitworth, 1932, 

feet 

0 500 I I I I 

meters 

[Artificial 

fill1 

Figure 13.-Part of a geologic map published in the report on the 1906 earthquake (Lawson, 1908, map 17); original scale, 1:40,000. Bracketed label is 

not on original map, which identified by color the area of artificial fill surrounding Marina Cove. 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE F2 1 

boreholes 10A, 14A, 14B, 15) within this fill area do not 

mention debris, although the ambiguous term "fill" is used 

in one log. Another borehole, 9E3, on the border of the 

fill, penetrated a railroad tie and gravel in the upper 1 m 

(3 ft), and a boulder at a depth of 3 m (9.8 ft) (Bennett, 

1990, p. D-34, borehole Marina 5). Probably, at least a 

small amount of 1906 debris is in the fills. 

Large changes were made in the Marina in connection 

with the 1915 Panama-Pacific International Exposition. In 

1912, large hydraulic fills were placed in the central part 

of the Marina and in adjacent parts of the Presidio. Smaller hydraulic and other fills were placed through 1917, during restoration of the site of the exposition; these changes 

are described in detail in the subsections that follow. 

After restoration of the exposition site, the land was unused until about 1924, when sale of the land to developers 

quickly led to residential construction (Dow, 1973, p. 103- 

108). Various modifications were made in the yacht-harbor 

area, north of Marina Boulevard, including enlargement of 

the harbor, changes in breakwaters and seawalls, and the 

addition of some small fills. 

ARTIFICIAL FILLS RELATED TO THE 

PANAMA-PACIFIC INTERNATIONAL EXPOSITION 

Changes made in the Marina in connection with the 

19 15 Panama-Pacific International Exposition were important, and so these changes are here described in detail. 

Hydraulic filling of what remained of Marina Cove was 

done from April 13 to September 7, 1912. The cove was 

"* * * 12 feet in depth to the mud at mean high tide, 

formed by a seawall running east and west along the line 

of what became the northern boundary of the grounds" 

(Markwart, 1915a, p. 63). A suction dredge was positioned about 90 m (300 ft) offshore and generally moved 

parallel to the shore. If the discharge contained too much 

fine material, the dredge was moved to get a larger proportion of sand. Marina Cove, which was being filled, 

contained semifluid sludge. A gate was left in the old seawall so that the sand, discharged on the landward side, 

would displace as much as possible of the soft material 

into the bay. To help remove mud from the bottom of the 

original basin, "* * * at times water was pumped instead 

of sand, and this carried out considerable mud in solution 

through the waste gate" (Markwart, 1915a, p. 64-65). 

The fill was about 70 percent sand and 30 percent mud 

(Todd, 1921, v. 1, p. 300). 

Hydraulic fill was also placed west of Lyon Street in a 

low-lying area along the old marsh and tidal channel 

shown in figure 10. This fill did not exceed 1.8 m (6 ft) in 

depth, and was "* * * mostly sand with a slight percentage of mud and frequently large boulders * * *" (Markwart, 1915b). 

Locally, nonhydraulic fill was placed for the exposition. 

"Six or eight acres, on part of which lay the eastern half 

Figure 14.-Marina area in April(?) 1912. Shortly after this photograph was taken, cove in right center was hydraulically filled for the Panama-Pacific 

International Exposition. Sand was pumped from the bottom of the bay, transported by pipeline, and discharged into the cove. Pond to left is now part 

of lagoon at the Palace of Fine Arts. Next to pond is Baker Street and then Broderick Street. Photograph courtesy of Archives, San Francisco Main 

Library. 
F22 MARINA DISTRICT 

of the Court of the Four Seasons, had to be filled by 

scrapers to bring it up to grade" (Todd, 1921, v. 1, p. 162). 

The center of this court was southeast of the intersection 

of Beach and Broderick Streets, on the old sand spit formerly called Strawberry Island. The northwest-trending 

waterway mentioned above in connection with the 1851 

map was in this area and may account for the need for a 

special fill. The east half of this court would cover only 

about 1 acre; this is probably the same fill described by 

Dow (1973, p. 101) as covering 12 acres. Dow logically 

inferred that the source of this fill was dune sand from the 

undeveloped land at the east end of the exposition grounds 

(Dow, 1973, p. 101-102). 

The method of placement of the 1912-17 fill (fig. 2) in 

the zone half a block wide between the 1895-1906 fill and 

the 1891 San Francisco Gas Light Co.'s wharf is uncertain. The 1908 map (Lawson, 1908, map 17) shows a sand 

pattern without a definite boundary to the north, suggesting that natural sedimentation was taking place there. This 

strip was filled by the time of the Panama-Pacific International Exposition and evidently was filled for the exposition, but the information at hand does not indicate the 

method of filling. 

EXPOSITION PILES 

Numerous wooden piles from the Panama-Pacific International Exposition probably still exist in the Marina. 

Whether these piles provided some resistance to long-term 

ground settlement and to earthquake-related liquefaction 

and vertical or horizontal ground displacements is unclear 

(Bonilla, 1990, 1991). More than 15,000 piles were used 

to support the principal buildings (Leurey, 1914), and piles 

supported some buildings not included in that total (Leurey, 1914, p. 254). The locations of buildings with pile 

Figure 15.Ã‘Contour on bottom of Marina Cove in 1912, before modifications for the Panama-Pacific International Exposition, in relation to 

modem streets. Contours in feet, based on San Francisco city datum, 

which is approximately 8.6 ft above mean sea level datum. After Leurey 

(1914, fig. 3). 

foundations are shown in figure 16, and the number and 

average lengths of piles are listed in table 2. 

The spacing of the piles can be judged from specific'ations for the Mines Building and Varied Industries Building, which called for structural piles to be clustered in 

groups of 2 to 10, and the clusters to be about 9 m (28 ft) 

apart from north to south and 25 m (82 ft) apart from east I 

to west (Markwart, 1915a, app. B). In addition to supporting structural frames of buildings, piles were used to support floors and to support columns for concrete firewalls 

(Markwart, 1913, 1915b; Leurey, 1914). 

Piles were as much as 23 m (75 ft) long, and many were 

to be driven into the layer of green sand and clay (Markwart, 1913) described above in the subsection entitled 

"Holocene Bay Deposits." However, sand of preexposition 

artificial fill provided suitable support for piles of the Education Building (Leurey, 1914, p. 254). Figures 2 and 16 

show that the Education Building site is underlain by fill 

placed in 1895-1906. One reason for the extensive use of 

piles for exposition buildings was greater safety in case of 

earthquakes (Markwart, 1913, p. 902; Leurey, 1914, 

p. 254). 

Specifications for dismantling of the exposition include 

the statement that piles "* * * shall be cut off two (2) 

feet below the surface of the ground as it existed at the 

time the site was taken over" (Todd, 1921, v. 5, app. p. 

134). However, the position of the ground surface referred to by Todd is unknown; as discussed below, the 

former exposition ground surface now has 1.5 m (5 ft) of 

artificial fill above it in some places. The exposition 

structures were designed for a lifespan of only a few 

years, and the piles were probably not treated with creosote. Thus, the parts of the piles above the water table 

may have deteriorated because of decay and termite action, but wooden piles that are submerged-that is, below the water table in the case of the Marina-last a 

long time. Borehole data indicate that the depth to the 

water table at exposition building sites ranges from about 

2 to 3 m (7-10 ft). 

Two boreholes drilled in 1923 encountered timbers, 

and the borehole sites had to be shifted to complete the 

holes; the reported timbers may have been remnants of 

piles. One borehole (10E2, fig. 3) was within the perimeter of the Machinery Building, and the other (9G2, fig. 

3) was near but outside the perimeters of the Machinery 

and Varied Arts Buildings. I am not aware of any post1923 boreholes or excavations that may have found pile 

remnants. 

DEMOLITION OF EXPOSITION BUILDINGS AND 

RESTORATION OF THE SITE 

After the exposition closed in December of 1915, dynamite was used to bring down buildings and other struc- 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE 

tures, most of which were of wood. Wood that could not 

be economically salvaged was burned on the site on a daily basis by the fire department (Todd, 1921, v. 5, p. 246- 

247). Reinforced-concrete firewalls, foundations, and 

transformer vaults were dynamited and broken up by a 

pile hammer (Todd, 1921, v. 5, p. 246). As previously stated, piles were not removed, but foundation obstructions 

were removed to some unknown depth (Todd, 1921, v. 5, 

p. 247). Postexposition filling was also done, described as 

follows: "Some of the lands had not been filled up to the 

terms of the leases when they were built upon, and it was 

now necessary to carry out this part of the exposition's 

obligations. They were filled partly by the public dump 

method, but by September 1916, a suction dredge went to 

work pumping mud over them, and finished by January 

1917" (Todd, 1921, v. 5, p. 247). One public dump was at 

Lobos Square, now the site of the Marina Junior High 

School and Moscone Recreation Center, southeast of the 

intersection of Bay and Webster Streets. The locations of 

other dumps were not given. The hydraulic fills in the 

postexposition period required construction of retaining 

levees, but their thickness and areal extent are unknown. 

CHANGES AFTER 1917 

The land on which the exposition stood was unused until 

1924, when residential construction began (Dow, 1973, 

p. 103-108). Any fills related to residential construction 

are probably very small. Some modifications have also 

been made in the yacht-harbor area, including enlargement 

of the harbor, changes in breakwaters and seawalls, addition of some small fills, and construction of a major sewerline under Marina Boulevard during the late 1970's. 

GENERAL DISTRIBUTION, AGE, AND COMPOSITION OF 

ARTIFICIAL FILLS 

The areas of artificial fills of various ages are shown in 

figure 2. The fill boundaries are based on superimposing, 

on a 1973 map, shorelines shown on the maps of 1851, 

1869, 1895, and 1908, supplemented by descriptions of 

the Panama-Pacific International Exposition fills. Shorelines and other features on the old maps cannot be precisely related to modem maps because the positions of many 

EXPLANATION 

Miscellaneous 

artificial fills 

Natural 

sedimentary 

deposits 

Figure 16.-Principal buildings of the 1915 Panama-Pacific International Exposition (letters; see table 2 for names), in relation to modem streets and 

simplified geology. Locations of exposition buildings from Todd (1921). Locations of buildings with respect to modem streets are based on location of 

Scott Street, the only exposition street that was centered on existing San Francisco streets (Markwart, 1915a, p. 75), and on location of the Palace of 

Fine Arts. 
MARINA DISTRICT 

Table 2.-Panama-Pacific International Exposition buildings and piles 

[Average length is below cutoff (from Leurey, 

1914, table 1). which would have been at some 

unspecified height above the ground surface at 

that time] 

S yrnbol Building Number Average 

(fig. 16) of piles length (ft) 

Fine Arts - - - - - - 1,051 

Food Products- - - 665 

Agriculture - - - - - 1,374 

Transportation - - - 4,541 

Mines - - - - - - - - 2,026 

Machinery- - - - - - 1,577 

Education - - - - - - 634 

Liberal Arts- - - - - 75 1 

Manufactures- - - - 1.59 1 

Varied Industries 1,444 

Horticulture- - - - - (1) 

Festival Hall - - - - (2) 

Tower of Jewels - (2) 

Tower of Progress (2) 

1 Unknown; under dome at east end. 

2 Unknown. 

natural and cultural landmarks are shown differently on 

the old and new maps, and so a best-fit compromise must 

be made by superimposing the maps at a common scale. 

Thus, the fill boundaries and other features shown may be 

in error by 30 m (100 ft) or more. The northeast-trending 

line in the southwestern part of the map separating the 

1869-95 fill from the 1895-1906 fill is from the 1899 edition of a 1:62,500-scale topographic map that was surveyed in 1892-94 (Lawson, 1914); this line is less 

accurate than other boundaries. The major timespans during which the fills were emplaced are shown in figure 2, 

but each of the outlined areas may contain small fills 

younger than the designated ages. Some artificial fill also 

lies outside the fills delineated in figure 2. The shorelines 

on the maps, used to outline the fill, represent mean high 

water. Artificial fills were placed landward of the mapped 

shorelines to prevent flooding during higher tides, and so 

figure 2 shows only the minimum extent of the fills. Local 

fills were also placed at low points on land, such as in 

local drainageways and areas between sand dunes. Outside 

the principal fill areas, borehole data show fill thicknesses 

that generally range from 0 to 4.3 m (0-14 ft), but at a site 

on the east side of Pierce Street south of Chestnut Street, 

broken glass and other debris was penetrated at a depth of 

7.6 m (25 ft). 

Part of the 1851 shoreline is shown in figure 2 by a 

dashed curve that trends generally northwest. This shoreline is not shown as a fill boundary because the area between this line and the edge of the 1869-95 fill probably 

grew by natural sedimentation. The narrow, northwestand northeast-trending 1851-69 fills may include naturally 

deposited material along waterways, as mentioned 

previously. 

A general indication of the lower surface of the artificial 

fills is shown in figure 9. Only very minor fills had been 

placed in the cove by 1873: Except for a possible fill extending from near Chestnut Street along or just east of 

Scott Street as far north as Capra Way, the 1873 map 

shows no marked change in shoreline in comparison with 

the 1869 map, which shows essentially natural conditions. 

The artificial fills in the Marina probably sank only a short 

way into the soft upper surface of the bay mud shown in 

figure 9, which provides a good approximation of the minimum level of the bottom of the artificial fills. Even in the 

last remnant of Marina Cove, where the level of soft mud 

as indicated by bottom contours in 1912 (fig. 15) was several decimeters (feet) above the 1873 level, boreholes 

show that the hydraulic filling displaced or removed the 

softest mud down to approximately the 1873 level. 

The 1869-95 fill probably consists mostly of sand, 

which was locally available from nearby beach and dune 

deposits. Levinsohn (1976, p. 34) stated that in filling the 

tidelands north of Lombard and Chestnut Streets during 

the 1890's, sand from the eastern sand hills (dune sand) 

was loaded by bucket conveyors to railroad cars which ran 

along tracks to the shoreline. In places, the 1869-95 fill 

contains riprap (large blocks of stone) placed for protection from wave action. For example, the rectangular, 

north-trending area in the northeastern part of the 1869-95 

fill (fig. 2) is the site of the 1891 San Francisco Gas Light 

Co.'s wharf, which had a rim of riprap. The following description probably applies to the San Francisco Gas Light 

Co.'s mole: "A retaining wall was being built with rock 

brought to this site on barges and unloaded by a derrick 

barge around the three sides of this area. When the wall 

was completed, the interior was filled with earth and surfaced with a hard paving." (recollection of Howard Livingston, 1964, in Olmsted and others, 1977, p. 716). 

Locally, debris from factories and other sources probably 

is contained in the 1869-95 fill also. 

The source and method of emplacement of the 1895- 

1906 fill are largely unknown. The fill evidently contains 

remnants of the assumed seawalls shown on the 1895 

map, and Fair's seawall. As previously stated, Fair's seawall was built of rock dumped from railroad cars operating on a pile trestle. The 1906-1912 fill probably contains 

debris from the 1906 earthquake and fire, but exactly how 

much is problematical. 

The 191 2-17 fills were emplaced principally in 19 12 for 

the Panama-Pacific International Exposition, using the hydraulic fill methods previously described. The general level of the top of the 1912 hydraulic fill before construction 

of the principal Panama-Pacific International exposition 

buildings was at an elevation of about -0.85 m (-2.75 ft) 

in relation to the San Francisco city datum (Leurey, 19 14, 

p. 250). Its level can also be obtained from the elevations 

of boreholes that Leurey stated were drilled at the comers 

of the main buildings after the fill had settled somewhat, 

and those elevations were considered in drawing the upper 

surface of the hydraulic fill in figures 5 and 7. 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE F25 

The position of the bottom of the hydraulic fill is probably irregular and is poorly known. A map showing the approximate elevation of the lagoon bottom about 1912, 

before the filling (fig. 15; Leurey, 1914, fig. 3), indicates 

only its general position because Leurey (1914, p. 250) 

stated that the fill pushed its way 0.6 to 1.5 m (2-5 ft) into 

the soft ooze of the lagoon bottom, and postexposition 

borehole logs also show artificial fills extending below the 

1912 bottom. As noted before, the area of 1912-17 fills 

also includes scraper fill, post-1915 hydraulic fill of unknown dimensions, and public dumps, all related to the 

exposition. 

Several boreholes shown in figures 5 through 7 support 

the historical data indicating that fill was placed after the 

1912 hydraulic fill. These boreholes were drilled in 1912, 

after placement of the main hydraulic fill. Since then about 

1.5 m (5 ft) of fill has been placed above the 1912 surface 

at the sites of these boreholes, probably during restoration 

of the 1915 exposition site. The apparent fill over the 

borehole near 330 m (1,085 ft) on the horizontal scale of 

figure 5 (borehole 54 of Leurey, 1914) is unexplained; an 

unrecorded small fill may exist there. 

A small body of artificial fill in the western part of cross 

section A-A' (fig. 5) was placed on a marsh area near the 

Palace of Fine Arts. Some of this fill was probably placed 

by hydraulic methods in 1912 for the exposition. 

The artificial fills in the Marina are principally sand obtained from nearby sites on land or offshore. However, the 

varied history of development of the area, both cultural 

and physical, implies that a great variety of materials are 

locally incorporated into the fills. Borehole logs mention 

small amounts of timber, brick, pottery, glass, large rocks, 

coal, and wire rope. 

GROUND-WATER LEVELS 

Depth to ground water is shown in figure 17. Because 

data are scarce, some water depths measured as long ago 

as 1923 are included; however, where both pre- and post1980 depths are close together, they do not differ greatly, 

suggesting that water levels have changed very little. Pre1980 measurements are identified in figure 17, which 

shows that ground-water depths are generally less than 2.7 

m (9 ft) except in the southeastern part of the map area 

and a few other isolated areas. 

DISCUSSION AND CONCLUSIONS 

Knowledge of site conditions is necessary for understanding the effects of past and future earthquakes. The 

Marina is worthy of study because much information is 

available on both site conditions and earthquake effects 

there. Site conditions vary. A deep, northwest-trending valley cut into bedrock is filled mostly by thick Pleistocene 

bay deposits overlain by an extensive Pleistocene sand 

zone. Above these are Holocene bay deposits, covered by 

Holocene sand in some places and various artificial fills in 

other places. The ground-water table in unconsolidated deposits is generally less than 2.7 m (9 ft) below the ground 

surface except in the dune-sand area, where it is generally 

more than 3 m (10 ft) deep. Liquefaction during the 1989 

earthquake, as reported by Bennett (1990) and Benuska 

(1990), did not occur in some areas of very shallow ground 

water, illustrating again that suitable deposits as well as 

shallow ground water are necessary for liquefaction. 

The effects of geology and historical development on 

earthquake damage in the Marina have been discussed by 

various authors, including Bonilla (1991). Although the 

damage in the Marina during the 1906 earthquake was 

high relative to nearby areas, not all of it was clearly related to fill (Lawson, 1908; Bonilla, 1991). High amplification of ground motion and severe damage to buildings in 

the 1989 earthquake sequence occurred on natural ground 

as well as on artificial fills (U.S. Geological Survey staff, 

1990; Boatwright and others, 1990, 1991; Bonilla, 1991; 

Boatwright and others, 1991; Boatwright and others, this 

chapter). These facts suggest that the configuration, thickness, and composition of the natural materials had a strong 

influence on shaking. Liquefaction, settlement, and damage to foundations, streets, curbs, sidewalks, and pipelines 

during the 1989 earthquake, however, were largely confined to areas underlain by artificial fills (Bennett, 1990; 

Benuska, 1990, p. 89-1 14; O'Rourke and Roth, 1990; see 

O'Rourke and others, this chapter). Thus, the natural geologic conditions apparently were responsible for the greater shaking in the Marina relative to adjacent areas, but 

behavior of the artificial fills increased particular types of 

damage. More complete analysis of the available data and 

of new data should provide insights that can be used in 

anticipating and moderating the effects of inevitable future 

earthquakes, not only in the Marina but also in other places with similar conditions. 

ACKNOWLEDGMENTS 

Substantial help in finding sources of information was 

provided by Jackie Freeberg of the U.S. Geological Survey's Library in Men10 Park, Calif.; by Roger Bonilla of 

the Palo Alto City Library; by Nicole Bouche of the University of California's Bancroft Library in Berkeley; and 

by Gladys Hanson and Patricia Akre of the San Francisco 

Archives, San Francisco Main Library. Jane Wegge of the 

California State Lands Commission, Sacramento, expedited the selection and duplication of out-of-print maps. F.L. 

Rollo of Treadwell Associates, Inc., San Francisco; Diane 

Sarmiento of Harding Lawson Associates, San Francisco; 

Don Fowler of Fowler and Associates; and Charles Ng, 
F26 MARINA DISTRICT 

City of San Francisco, provided access to unpublished da- T.J., Leviton, A.E., and Berson, Margaret, eds., 1979, San Francisco . * 

ta. R.V. Allen provided information on water depth at the Bay; the urbanized estuary: American Association for the Advanceyacht harbor, and Julius Schlocker identified the rock in ment of Science, Pacific Division Annual Meeting, 58th, San Francisco, 1977, Proceedings, p. 31-45. 

USGS borehole WSS. Atwater, B.F., Hedel, C.W., and Helley, E.J., 1977, Late Quaternary depositional history, Holocene sea-level changes, and vertical crustal 

movement, southern San Francisco Bay, California: U.S. Geological 

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R.L., and Savage, Wayne, 1979, History, landforms, and vegetation 

Atwater, B.F., 1979, Ancient processes at the site of southern San Francis- of the estuary's tidal marshes, in Conomos, T.J., Leviton, A.E., and 

co Bay; movement of the crust and changes in sea level, in Conomos, Berson, Margaret, eds., 1979, San Francisco Bay; the urbanized estu- 

-- 

EXPLANATION 

Water- tabledepth contours, 

in feet 

1-1 Principal 19 12 

" hydraulic fill 

A 7.5 

Water-table depth, 

in feet 

Miscellaneous 

artificial fills 

Figure 17.-Marina District, showing depth to water table. Depths measured before 1980 are in smaller type, with last two digits of year of measurement following hyphen. 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE F27 

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Division Annual Meeting, 58th, San Francisco, 1977, Proceedings, 

p. 347-385. 

Bennett, M.J., 1990, Ground deformation and liquefaction of soil in the 

Marina District, chap. D of Effects of the Loma Prieta earthquake on 

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Bronson, William, 1959, The earth shook, the sky burned: Garden City, 

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of the flatland deposits, in Helley, E.J., Lajoie, K.R., Spangle, W.E., 

and Blair, M.L., 1979, Flatland deposits of the San Francisco Bay 

Region, California-their geology and engineering properties, and 

their importance to comprehensive planning: U.S. Geological Survey 

Professional Paper 943, p. 14-68. 

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of Effects of the Loma Prieta earthquake on the Marina District, San 

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1906; report of the State Earthquake Investigation Commission: Carnegie Institution of Washington Publication 87.2 v. 

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Washington, D.C., U.S. Geological Survey, 24 p. 

Leurey, L.F., 1914, Soft-ground foundations, Panama-Pacific International 

Exposition: Engineering News, v. 72, no. 5, p. 250-254. 

Levinsohn, J.L., 1976, Cow Hollow; early days of a San Francisco neighborhood from 1776: San Francisco, Calif., San Francisco Yesterday, 

46 p. 

Markwart, A.H., 1913, The Panama-Pacific Exposition: Engineering 

News, v. 70, no. 19, p. 895-904. 

1915a, Building an exposition-report of the activities of the Division of Works of the Panama-Pacific International Exposition, covering the pre-exposition period, i.e., the period ending February 20, 

1915: San Francisco, Panama-Pacific International Exposition, 75 1 p. 

[copy, without illustrations, in San Francisco Library Archives, Main 

Library; appendixes, also without illustrations, at Bancroft Library, 

University of California, Berkeley, bound volume 1401. 

1915b, Engineering problems of the Panama-Pacific Exposition: 

Engineering News, v. 73, no. 7, p. 329-336. 

Meyer, C.E., Sama-Wojcicki, A.M., Hillhouse, J.W., Woodward, M.J., 

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Proceedings, v. 2, p. 1601-1612. 

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F28 MARINA DISTRICT 

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TABLE 1 
F30 MARINA DISTRICT 

Table 1.-Data on boreholes drilled in the Marina District of San Francisco 

[Where the date of drilling was not given in the log, another date, such as that of the accompanying report or the date when water level was measured, is listed as an 

approximation. Source firms have offices in San Francisco unless otherwise noted. PPIE, Panama-Pacific International Exposition; bldg, building; do., ditto] 

Borehole Original Location Date Source Job 

No. No. 

1 E.ofBroderickSt.,N.sideBaySt.------------- 

6 NW. comer Agriculture bldg, PPIE, S. of Marina 

Blvd., W. of Divisadero St. 

5 8 N. center Agriculture bldg, PPIE; E. of Divisadero 

St., S. of Marina Blvd. 

HSA-6 N. side Marina Blvd., E. of Divisadero St. - - - - - - - - HSA-5 N. side Marina Blvd., W. of Divisadero St.- - - - - - - - HSA-24 N. side Marina Blvd., E. of Divisadero St. - - - - - - - - HSA-26 N. side Marina Blvd.. W. of Divisadero St.- - - -. - - - - HSA-25 N. side Marina Blvd.. E. of Divisadero St. - - - - - - - - HSA-7 do------------------------------------ 

C.H. Hartsog & Associates, --- Mountain View, Calif. 

Treadwell & Associates - - - - - - 1070A 

whitworth (1932) - - - - - - - - - - - - - - - - - - - - - - - ' 
GEOLOGIC AND HISTORICAL FACTORS AFFECTING EARTHQUAKE DAMAGE F3 1 

Table 1.-Data on boreholes drilled in the Marina District of San Francisco-Continued 

Borehole Original 

No. 

Location Date source Job 

No. 

- - - SW. corner Divisadem St. & Marina B1vd.- - - - - - - - 

1 S. side Marina Blvd., W. of Divisadero St.- - - - - - - - 2 W. side Divisadero St., S. of Marina B1vd.- - - - - - - - 1 E. sidewalk of Divisadero St., S. of Jefferson St. - - - 2 S. sidewalk Jefferson St., E. of Divisadem St. - - - - - 1 N. side Jefferson St., W. of Divisadero St. - - - - - - - - B-1 S. of Jefferson St., W. of Divisadem St.- - - - - - - - - - B-2 &------------------------------------ 

B-2 &------------------------------------ 

5 0 SE. comer Agriculture bldg, PPIE; Beach St. 

E. of Divisadem St. 

1 NE. side of W*eld Scott School b1dg.- - - - - - - - - - wss &------------------------------------ 

1 W. side Divisadero St., S. of Beach St. - - - - - - - - - - 2 S. sidewalk of Beach St., W. of Divisa&ro St. - - - - - 1 Property at NW. comer Beach St. & Divisadero St. 

2 &------------------------------------ 

3 b------------------------------------ 

4 &------------------------------------ 

Marina 3 W. curb of Divisadem St., 60 ft S. of Beach St.- - - - - 1 NE. of Beach St. & Divisadero St. 

3 &------------------------------------ 

7A NE. side Liberal Arts bldg PPIE; E. of Divisadem St., 

N. of N. Point St. 

2 Winfield Scott School bldg, E. side near center- - - - - B-1 N. sidewalk of North Point St., W. of Divisadero St. 

75 SW. comer Liberal Arts bldg, PPIE; N. of Bay St., 

w. of Divisadem st. 

B-1 W.ofDivisdemSt.,N.ofBaySt.-------------- 

1 W. side Divisadem St., &tween Chestnut St. 

& Francisco st. 

2 N. side Marina Blvd., E. side Smtt St .- - - - - - - - - - - HSA-9 N. side Marina Blvd., Em of Scott St. - - - - - - - - - - - - 

HSA-8 N. side Marina Blvd., We of Scott St.- - - - - - - - - - - - HSA-23 N. side Marina Blvd., E. side of Scott St.- - - - - - - - - HSA-30 N. side Marina Blvd., W. of Scott St. - - - - - - - - - - - - 2 W. side Scott St., N. of Jefferson St. - - - - - - - - - - - - 8 SW. comer Transportation bldg, PPIE - - - - - - - - - - - 1 ScottSt.,N.ofJeffasonSt.------------------- 

1 N. side Jefferson St., W. of Scott St. - - - - - - - - - - - - 1 W.si&AvaaSt.,N.ofBwhSt.---------- ---- 7 E.sideLiberalArtsbldg,PPIE ---------- ------ 9A NW. side Manufactures Bldg, PPE, W. side Avila 

St., N. of Capra Way. 

1 W.si&ScottSt.,N.ofCapraWay- ------------- 2 &------------------------------------ 

1 W.sideScottSt.,N.ofNorthPointSt. ---------- 2 W. side Scott St., N. of North Point St. - - - - - - - - - - 

42 SW. comer Manufactures Bldg. PPIE; E. of ~vila 

St., S. of Capra Way. 

1 N.si&BaySt.,W.ofScoaSt.---------------- 

1 S.sideCapaWay,E.ofScottSt.-------------- 

B-1 N.ofAlhambraSt.,E.ofScottSt. ------------- 104 N. center Transportation bldg. PPE, NW. of 

Avila St., S. of Marina Blvd. 

C.H. Hartsog & Associates, --- 

Mountain View, Calif. 

Don Hillebrandt Associates - - - 2015-2 

&-------------------- 2015-2 

Harlan Tait Associates - - - - - - 964.01 

Harlan Tait Associates - - - - - - - 964.01 

Treadwell & Associates - - - - - - 1063A 

Harding Lawson Associates - - - 19870001 .04 

&-------------------- 19870001 -04 

19856001.04 

bwey (1914) - - - - - - - - - - - - - - - - - - - - - - - - - - 

Harding Lawson Associates - - - 19738001.04 

Don Hillebrandt Associates - - - 2025 - 1 

Treadwell & Associates 1047A 

HermgAssociates---------- 2813.01 .OO.l 

Harding Lawson Associates - - - 89 2316.04 

bwey (1914) - - - - - - - - - - - - - - - - - - - - - - - - - - 
F32 MARINA DISTRICT 

Table 1 .-Data on boreholes drilled in the Marina District of San Francisco-Continued 

Borehole Original 

No. 

Location Date Job 

No. 

3 S. side Marina Blvd. at Avila St. & Casa Way- - - - - - 

HSA-10 N. side Marina Blvd., W. of Avila St.- - - - - - - - - - - - HsA-11 &------------------------------------ 

Marina 9 Marina Green, N. of Avila St.-Casa Way intersection 

1 S. side Beach St. , W. of Mallorca Way - - - - - - - - - - 

B-1 N. side Beach St. , W. of Cervantes B1vd.- - - - - - - - - B-2 &------------------------------------ 

Marina 4 NW. pint Beach St. & Cervantes Blvd. - - - - - - - - - 

B-1 SW. side Cervantes Blvd., SE. of Pra& St. - - - - - - - 7 6 NE. comer Manufactures Bldg, PPIE; E. of Pierce 

St., S. of Beach St. 

9 SE. comer Manufactures Bldg, PPIE - - - - - - - - - - - - 

1 N. side Alhambra St., W. of Pierce St. - - - - - - - - - - - 2 SE.ofRerceSt.&ChesmutSt.---------------- 

4 &------------------------------------ 

1 NW.ofPierc43St.&ChesmutSt.--------------- 

2 &------------------------------------ 

1 SE.ofRerceSt.&ChesmutSt.---------------- 

3 &------------------------------------ 

8A NE.comer Transportation bldg PPIE; SW. of 

Casa Way, SE. of Avila St. 

HSA-12 N. side Marina Blvd., E. of Casa Way- - - - - - - - - - - - HsA-13 &------------------------------------ 

64 SW. comer Mines bldg, PPIE; S. side Rim Way, 

W. of Retiro Way. 

1 1 NW. comer Varied Industries bldg, PPIE - - - - - - - - - B-1 NW. side Alhambra St., SW. side Mallorca Way- - - - 

1 E. side Mallorca Way, SE. of Alhambra St.- - - - - - - - S-A SE. side steiner St. & Lombard St.- - - - - - - - - - - - - - 

S-B &------------------------------------ 

s-c &------------------------------------ 

S-D &------------------------------------ 

S-E &------------------------------------ 

S-F &------------------------------------ 

SMW-1 &------------------------------------ 

SMW-2 &------------------------------------ 

SMW-3 b------------------------------------ 

MW-4 E. side Steiner St., S. of Lombard St. - - - - - - - - - - - - MW-5 SE.cornerSteinerSt.&LombardSt.------------ 

MW-6 S. side Lombard St. E. of Steiner St. - - - - - - - - - - - - 

MW-7 SW.si&SteinerSt.&LombardSt.------------- 

MW-8 NW.cmerStehrSt.&LomhdSt.----------- 

MW-9 S. side Lombard St. E. of Steiner St.- - - - - - - - - - - - - 10 NE. comer Mines bldg, PPIE; W. side Fillmore St., 

S. of Retiro Way. 

4 S. side Marina Blvd., E. side Fillmore St - - - - - - - - - 

HSA-14 N. side Marina Blvd., W. of Fillmore St. projected 

HSA-15 NE. comer Fillmore St. & Marina Blvd. - - - - - - - - - - 

Marina 7 Marina Green, N. of Marina Blvd., 

opposite Fillmore St. 

14B Jefferson St., E. of Fillmore St.; NW. corner 

Machinery bldg. bldg, PPIE. 

10A SE. comer Mines bldg, PPIE; W. side Fillmore St., 

N. of Beach St. 

15 S.ofBachSt.,E.ofFillmoreSt,-------------- 

Marina 5 FillmoreSt.,dueE.of S.curbBeachSt.---- - -- --- 

&-------------------------------

M.J. Bennett (written commun., 1991) - - - - - - - 
GEOLOGIC AND HISTORICL FACTORS AFFECTING EARTHQUAKE DAMAGE 

Table 1 .-Data on boreholes drilled in the Marina District of San Francisco-Continued 

- 

Borehole Original 

No. 

Location Date source Job 

No. 

9F 1 11 A Varied Industries bldg, PPIE; SW. of Divisadero St. 

& Beach st. 

9F2 14A SW. comer Machinery bldg., PPIE; S. of North 

Point St. 

9F3 16 NorthPointSt.E.ofFihoreSt. -------------- 9F4 B-1 NE. of Cervantes Blvd. opposite Alhambra St.- - - - - 9F5 B-2 NE. of Cervantes Blvd., NW. of Alhambra St. 

w*d 

9F6 B-1 W. of Fillmore St., N. of North Point St. projected 

9Gl 11B Varied Industries bldg, PPIE; W. side Fillmore St., 

N. of Bay St. 

902 17 E.ofFillmoreSt.,N.ofBaySt. --------------- 9Hl Marina6 FillmoreSt.,N.ofChesmutSt.---------------- 

18 

12 

13 

5A 

HSA-16 

HSA-18 

HSA- 17 

101 

14C 

5 

HSA-19 

14D 

19 

2 

1 

14 

20 

22 

1 

1 

2 

3 

4 

5 

6 

1 

2 

2 1 

N. of Chestnut St. , E. of Fillmore St. - - - - - - - - - - - N.ofL,ombardSt.,W.ofFihoreSt. ----------- W. of Fillmore St., N. of Lombard St. - - - - - - - - - - - N.si&MhBlvd.atWebsterS~------------- 

N. side Marina Blvd., W. of Webster St.- - - - - - - - - - N. side Marina Blvd., E. of Webster St.- - - - - - - - - - N. side Marina Blvd., at Webster St. - - - - - - - - - - - - S. side Marina Blvd. between Fillmore St. & 

Webster St, 

NE. comer Machinery bldg. PPE Jefferson St. 

at Webster St. 

S. side Marina Blvd. at Webster St. - - - - - - - - - - - - - N. side Marina Blvd., E. of Webster St. - - - - - - - - - - Center Machinery bldg. PPB, W. of Webster St., 

S. of Beach St. 

S.sideBe~hSt.atWebstaSt.---------------- 

W. side Webster St., N. of Beach St.- - - - - - - - - - - - - N. of North Point St., W. side Webster St, - - - - - - - - SE. comer Machinery bldg., PPIE; W. of Webster St., 

S. of North Point St. 

WebterS~&NorthPointSt.----------------- 

E. of Webster St., N. of North Point St. - - - - - - - - - - W. of Websta St., S. of North Point St. - - - - - - - - - S. of North Point St., W. of Webster St. - - - - - - - - - &--------------.--------------------- 

&------------------------------------ 

ha-------------.--------------------- 

&------------------------------------ 

&-me--------------------------------- 

N. side North Point St., W. of Webster St. - - - - - - - - W. side Webster St., N. of North Point St. - - - - - - - - N. side Bay St. at Buchanan St. - - - - - - - - - - - - - - - - HSA-20 N. side ~kna Blvd., W. of Buchanan St. - - - - - - - - 23 S.ofBeachSt.,W.ofBuchananSt. ------------ HSA-21 N. side Marina Blvd., W. of Buchman St. - - - - - - - - HSA-22 N. side Marina Blvd., E. of Buchanan St. - - - - - - - - - 2 N. of North Point St., W. side Buchanan St. - - - - - - - --- S. of Marina Blvd., W. of Buchanan St. - - - - - - - - - - 1 S. side Beach St. , W. of Buchanan St. - - - - - - - - - - - 2 &------------------------------------ 

B-1 &------------------------------------ 

B-2 &------------------------------------ 

24 S.~fN~rthP~intSt., W.~fB~~hanmSt. --- ----- 25 North Point St., W. of Buchman St. - - - - - - - - - - - - 12 N.ofNorthPointSt.,W.~fhg~St.---------- 

1 W. of Laguna St., S. of North Point St. - - - - - - - - - - 
F34 MARINA DISTRICT 

Table 1.-Data on boreholes drilled in the Marina District of San Francisco-Continued 

Borehole Original 

No. 

Location Date source Job 

No. 

N.ofNorthPointSt. atBuchananSt. - ----- -- --- 12/9/80 

S. side Bay St. opposite Buchanan St. - - - - - - - - - - - pre-1913 

N.ofBaySt.,W.ofBuchmanSt. -------------- 1124123 

W.ofLagunaSt., N.ofBaySt.---------------- 9/23/66 

W.ofBwhmSt.&BaySt.---------------- 5129187 

&------------------------------------ 5/29/87 

&------------------------------------ 5/29/87 

&------------------------------------ 5/26/88 

&------------------------------------ 5/26/88 

&------------------------------------ 5/26/88 

&------------------------------------ 5/26/88 

~t aso on, pim 1 - - - - - - - - - - - - - - - - - - - - - - - - - - 811949-111950 

&------------------------------------ 811949-1/1950 

&------------------------------------ 811949-111950 

&------------------------------------ 811949-111950 

N.si&BeachSt.atLagunaSt. ---------------- 6110175 

W.ofNorthPointSt.&hmaS~------------ 3130165 

&------------------------------------ 3130165 

&------------------------------------ 3130165 

&------------------------------------ 3130165 

SW. of North Point St. & Lagma St. - - - - - - - - - - - - 9/23/66 

W.ofLagmaSt.,N.ofBaySt.---------------- 9/23/66 

SW.wmaLagunaSt.&BaySt.--------------- 6/13/75 

FtMmn,Rm3--------------------------- 811949-111950 

FtMason,Ea2--------------------------- 811949-111950 

&------------------------------------ 811949-111950 

FtMmn,Ea3--------------------------- 811949-111950 

&------------------------------------ 811949-111950 

&------------------------------------ 811949-111950 

&------------------------------------ 811949-111950 

FtMmn,Rm2--------------------------- 811949-111950 

FtMmn,Ra3--------------------------- 811949-111950 

Ft Mason, S. of Beach St. & W. of 6/12/75 

Octavia St. projected. 

Ft Mason, N. of Beach St. projected, E. of Laguna St. 10120175 

Ft Mason, S. of Beach St. & E. of Octavia St. 10121175 

pro*ted. 

S. of Francisco St., W. of Octavia St. - - - - - - - - - - - 11/1/89 

8 Ft Mason, S. of Beach St. & W. of Gough St. 6/13/75 

projected. 

18 N.si&BaySt.atGoughSt. ------------------ 611 7175 

30 SE.ofhbardSt.&Gou&St,--------------- 1912 

9 Ft Mason, S. of Beach St. & W. of Franklin St. 611 1175 

projected. 
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND FAILURE 

MARINA DISTRICT 

GROUND-MOTION AMPLIFICATION 

By John Boa .twright, Linda C. Seekins, Thomas E. Fumal, Hsi-Ping Liu, and Charles S. Mueller, 

U.S. Geological Survey 

CONTENTS 

Abstract .................................................................. Introduction ------------ --------- ----------------- --------- ----------------- Instrument locations ---- a ---- - ..................... -- ..................... Aftershock recordings .......................... ----- ..................... Decomposition for source and site spectra ........................... Relative site mplifications ------------------- -- ---- - ------------------- One-dimensional model for the ground-motion amplification 

in the Marina District ---------- -------------- ........................ Extrapolating min-shock ground motions ------------ --------------- Conclusions ----------- ------------- -------------- ---------- ---------------- Acknowledgments ------ ---- - ------------------- -------- ------------------ References ~it& -------------------------------a ------- ------------------- 

Page 

F35 

35 

36 

39 

40 

41 

44 

44 

48 

48 

49 

ABSTRACT 

After the earthquake, event-triggered seismographs 

were deployed in and around the Marina District to investigate site amplification. During the 3 weeks after the main 

shock, 23 aftershocks were recorded by two or more of 

these stations; two other stations, deployed in April 1990, 

recorded three earthquakes that occurred in Contra Costa 

County. By recasting the method of spectral ratios into a 

generalized inverse problem, we combine the shear-wave 

spectra from these 19 aftershocks to estimate the relative 

site amplification as a function of frequency. Ground motion at all five stations located in the central part of the 

Marina District were amplified by factors of 6 to 10 at 1 

Hz and 2 to 4 at 3 Hz relative to a station located on 

Franciscan sandstone at Fort Mason, irrespective of 

whether they are sited on artificial fill or beach sand. Stations located on dune sand and Quaternary sedimentary 

deposits outside the central part of the Marina District 

were amplified by a factor of 2 to 4 at frequencies above 1 

Hz. Four stations located on Franciscan sandstone in Pacific Heights, Nob Hill, Rincon Hill, and Diamond Heights 

show little amplification relative to Fort Mason. 

Conditional estimates of the main-shock spectra can 

be determined at stations that recorded only aftershocks, if 

they can be linked to stations that recorded the main 

shock. These estimates are predicated on the assumption 

that the ground behaved linearly during the main shock, an 

assumption that is clearly violated for those sites where 

ground failure occurred. Using this method of extrapolation 

for a site in the Marina District that showed no evidence of 

ground failure yields an estimated main-shock spectrum 

that is slightly greater than the spectrum from the Outer 

Harbor Wharf in Oakland and that significantly exceeds the 

spectra from the free-field accelerograms located in San 

Francisco. 

INTRODUCTION 

The extensive damage in the Marina District caused by 

the earthquake, as detailed in figure 1, suggests that the 

ground motion was significantly amplified relative to that 

in such nearby areas as Pacific Heights or Russian Hill. To 

investigate this amplification, the U.S. Geological Survey 

deployed seismometers with General Earthquake Observation System (GEOS) event recorders (Borcherdt and others, 

1985) at 12 sites inside and just outside the Marina District 

for 3 weeks after the main shock. Despite the large epicentral distances (-100 km) and the relatively noisy urban environment, 14 aftershocks ranging in local magnitude (ML) 

from 3 to 5 were recorded in the Marina Disect; two 

smaller earthquakes were recorded at epicentral distances 

of 20 and 35 km. 

This report analyzes these aftershock recordings to determine the relative site response as a function of frequency 

in the Marina District. By suitably combining the spectra 

of the recorded shear waves, we estimate the seismic amplification for five sites within the central part of the Marina District and for two sites outside this area, relative to a 

hard-rock site in Fort Mason. Our results indicate that 

ground motions within the central part of the Marina District are amplified by factors ranging from 6 to 10 for periods of about l s; the relative amplification decreases 

gradually to a factor of 3 for periods of about 0.3 s and to 

a factor of 2 for periods of about 0.2 s. We note that this 

amplification spans the approximate range of the fundamental periods (0.3-0.4 s) for three- to four-story wood- 
F36 MARINA DISTRICT 

frame structures (International Conference of Building Officials, 1985, p. 117), suggesting that seismic amplification 

contributed significantly to the earthquake damage in the 

Marina District. 

No accelerographs were located in the Marina District 

before the earthquake. The extensive building damage and 

ground failure in the Marina District, however, encourage 

estimates of the main-shock ground motions. Conditional 

estimates or extrapolations of these ground motions can be 

made by using aftershock spectra from sites within the 

Marina District, together with aftershock and main-shock 

spectra from nearby sites in San Francisco that recorded 

the main shock. The closest site that recorded both mainshock and aftershock accelerograms was located at a fire 

station on Pacific Heights, approximately 1.5 km south of 

the Marina District. 

The relative amplifications determined from aftershock 

recordings are explicitly appropriate only for weak levels 

of ground motion. Using these amplifications to estimate 

the strong ground motions in the Marina District during 

the main shock is problematic. The ground failure and liquefaction of hydraulic fill that occurred in parts of the Marina District conclusively demonstrate that the ground 

behaved nonlinearly and that the aftershock site amplifications cannot be used to estimate strong ground motions. In 

these areas, the extrapolated ground motions can be considered only as upper bounds for the main-shock ground 

motions. 

One of our sites in the Marina District, however, lies 

outside the area of ground failure but within the concentration of building damage west of Divisadero Street (fig. 

1). Although the absence of ground failure does not prove 

that the beach sand and older bay deposits underlying this 

site behaved linearly, the assumption of linearity is more 

reasonable for this station. Extrapolating the main-shock 

ground motions for this site yields spectral accelerations 

that are similar to those for the main shock recorded at the 

Outer Harbor Wharf in Oakland and that exceed those for 

the main shock recorded by all the free-field accelerographs in San Francisco. 

INSTRUMENT LOCATIONS 

The locations of the six instruments deployed within the 

central Marina District are shown in figure 2A. In general, 

I 

0 500 EXPLANATION 

I I I I J Buildings 

meters with Red Tags 

Buildings with Yellow Tags 

Figure 1.-Marina District of San Francisco, showing locations of red (unsafe for occupancy)- and yellow (dangerous)-tagged buildings. The set of 

tagged buildings was revised and updated by the City and County of San Francisco in fall 1990. Many red and yellow tags were originally issued to 

buildings for perceived danger from broken gas mains, asbestos, or possible collapse of a nearby building and were later upgraded; these buildings are 

plotted using the later tags. Red- and yellow-tagged buildings that were upgraded to yellow or green (no restriction on use) after repair work are plotted 

as originally tagged. A few demolished buildings are also included as red-taggedbuildings. 
GROUND-MOTION AMPLIFICATION 

Table 1 .-Afiershocks recorded at stations in San Francisco 

[Events are listed as arrival times by Julian day (first three digits) and Greenwich mean time (hours and minutes, last four digits); thus, the main 

shock, which occurred at 5:04 p.m. P.d.t. October 17, would be listed as event 2910004. Magnitudes from U.S. Geological Survey preliminary 

listing. Letters denote second when recording began: A, 0-2 s; B, 3-5 s; C, 6-8 s; and so on] 

Event Magnitude Station-LET NPT BEA LMS DEM PUC CAL HHS MAS LEA RIN DIA 

the site names are abbreviations for the street or building 

where the instruments were located; for example, stations 

NPT and BEA were located on North Point and Beach 

Streets, whereas station PUC was located at the Pacific 

Union Co. building, also known as the "Gas Light Building." Figure 2A also shows the location of station MAS, 

deployed on the knoll at Fort Mason. 

The locations of other stations whose recordings are analyzed here are shown in figure 25. Stations CAL and 

RIN, on Pacific Heights and Rincon Hill, respectively, 

were colocated with strong-motion accelerographs that recorded the main shock. A third station, DIA, was colocated with a strong-motion accelerograph on Diamond 

Heights, south of the map area. Station LEA is located on 

Nob Hill. These four stations, together with station MAS 

at Fort Mason, constitute a set of "hard rock" sites located 

on Franciscan sandstone in areas that sustained little or no 

damage during the main shock. Station CAL, colocated 

with a strong-motion accelerograph on Pacific Heights, is 

critical for estimating the main-shock ground motions in 

the Marina District. The 11 aftershocks recorded by both 

stations CAL and MAS ensure that the relative amplification at these two sites is well determined. 

The aftershocks recorded at the various stations are listed in table 1. Station MAS recorded the largest number of 

aftershocks, probably as a result of its isolation from vehicular traffic and the relatively hard rock of its site. This 

instrument was deployed in a concrete ammunition bunker 

poured onto Franciscan sandstone. Station MAS provides 

a linchpin for comparing site amplifications throughout the 

city. The instruments that were deployed within the Marina District had to be retrieved about 2 weeks after the 

earthquake because the seismic noise from work of replacing the gas and water mains made it impossible to record 

aftershocks. 

In April 1990, 5 months after the main shock, two additional stations, HHS and LET, were deployed at sites outside the central part of the Marina District. Station HHS 

was deployed on dune sand two blocks east of station 

PUC, and station LET was located in Letterrnan Army 

Medical Center within the Presidio, built on undivided 

Quaternary surficial deposits. Station LET was colocated 
F38 MARINA DISTRICT . 

LEA 

0 

CAL 

0 
GROUND-MOTION AMPLIFICATION F39 

with an accelerograph that recorded a peak acceleration of 

0.14 g during the main shock. However, we were unable 

to obtain a digitizable copy of the main-shock accelerogram from the U.S. Army Corps of Engineers. 

AFTERSHOCK RECORDINGS 

The east-west seismograms recorded at five stations during an ML=3.6 aftershock are plotted in figure 3. This afFigure 2.-Marina District (A) and northeastern part of San Francisco 

(B), showing locations of recording stations. In figure 2A, note that stations BEA and LMS lie within area of 1912 hydraulic fill (see Bonilla, 

this chapter) but stations NPT, DEM, and PUC lie outside it; station 

MAS is sited on an outcrop of Franciscan sandstone at Fort Mason. Cir- 

& labeled "borehole" indicates location of borehole described by Kayen 

and others (1990). In figure 25, stations CAL and RIN were cosited with 

SMA-1 instruments that recorded the main shock on Pacific Heights and 

Rincon Hill, respectively; station LEA was sited at a fire station on Nob 

Hill. Unlabeled circles indicate temporary seismograph stations within 

the city whose recordings are not analyzed in this report. 

tershock, which occurred 8 days after the main shock, was 

well recorded in the Marina District, largely because it occurred at 2:01 a.m. P.s.t. A cursory glance at the ground 

velocities indicates the severity of the ground amplification within the Marina District. At stations NPT, BEA. and 

LMS, located in the Marina District, the peak velocities 

range from 0.04 to 0.05 cmls. whereas at stations MAS 

and CAL, located at relatively hard-rock sites, the peak 

velocities are 0.02 and 0.01 cmls, respectively. The hypocentral distances to these stations range from only 97 to 99 

km, and so we can reasonably assume that the wavefield 

incident at depth below these stations is the same. 

The spectral amplitudes of the shear waves are plotted in 

figure 4. The relative seismic amplification apparent in figure 3 is clearly delineated in the frequency domain. In particular, the spectral amplitudes of the shear waves 

recorded at station CAL are consistently the smallest 

among the five stations. Station MAS exhibits spectral amplitudes intermediate to those at station CAL on Pacific 

Heights and at stations in the Marina District. Station BEA 

NPT 

Time (8) 

Figure 3.-East-west (EW) ground velocity for an ML=3.6 aftershock (event 2990901, table 1) recorded at stations in the 

Marina District. S waves are strongest on east-west component, whereas P waves are weakest. Spectral amplitudes plotted in 

figure 4 are determined from 20-s samples starting approximately 2 s before 5-wave arrival. 
F40 MARINA DISTRICT 

has a marked spectral peak at 2.2 Hz, whereas stations 

NPT and LMS have spectral peaks near 4.0 Hz, which is 

approximately the fundamental frequency for a three-story 

building with a wood frame. 

In general, the relative spectral amplitudes recorded at 

these stations vary among events, depending on the component of ground motion, hypocentral distance, hypocentral depth, and the focal mechanism of the aftershock. To 

ensure that we obtained the least biased estimate of the 

seismic amplification, we used all the aftershock recordings together. We briefly describe this analysis in the next 

section. 

DECOMPOSITION 

FOR SOURCE AND SITE SPECTRA 

where the subscripts k, i, and j refer to the recording, the 

station, and the earthquake, respectively; SRi( f) is the siteresponse spectrum for the ith station; and ESj(f) is the 

source spectrum for the jth earthquake. The geometric 

spreading factors ri=x,,/2 are set equal to half the 

hypocentral distance between the station and the earthquake; the factor of 2 compensates for the amplification of 

the free surface. Note that the decomposition in equation 1 

does not explicitly describe attenuation as a function of 

distance and frequency, that is, ri(io). This description is 

unnecessary for the present data set because most of the 

aftershocks were recorded at similar epicentral distances. 

This system of equations can be linearized by taking 

logarithms and solved by minimizing the error in the k=l, 

K equations: 

[In Rk (j) + ln rk - ln SRi (./) 

Following Andrews (1986), we assume that each record -In ES~(~) ] /a: IJ) = 0 a (2) 

spectrum is the product of a site-response spectrum and a 

source spectrum and may be written as 

The record spectra R:( f) are determined by summing the 

squares of the spectral amplitudes of the two horizontal 

1 components of the shear wave. The spectral amplitudes 

RkW - rsRiy)EsjY), (1) were resampled logarithmically to save space, with the 

1 .o 10. 

Frequency (HZ) 

Figure 4.-Spectral amplitudes of shear waves plotted in figure 3. Note that the spectra from the Marina District stations (NPT, 

BEA, LMS) are similar in overall amplitude, as the relative amplitudes of the recorded velocities suggest. For this event and this 

component, station MAS is amplified by a factor of 3 at 3 Hz relative to station CAL. 
GROUND-MOTION AMPLIFICATION F4 1 

frequencies from 0.1 to 100 Hz divided into 40 frequency 

bands that each span a factor of 2''4=l.189 in frequency. 

This resampling effectively smooths the spectra at high 

frequencies. 

The variances o 3 f) were determined by taking small 

samples of the P-wave coda before the shear-wave arrivals. Summing the squares of the noise spectra from the 

two horizontal components of ground motion yields the 

noise functions N:( f). The variances are constrained as 

(Andrews, 1986) 

site responses for the 1-1 other stations are determined relative to this station (Bonamassa and Mueller, 1989). We 

use MAS as a reference station both because it recorded 

the most aftershocks and it has the most nearly "average" 

response among the hard-rock stations. This station constraint is simply written as In SR( f)=O. Inverting the 

resulting system of equations 2 yields the constrained 

"site" and "source" spectra, 

which limits the signal-to-noise ratio of the data to less 

than a factor of 2. This conditioning is necessary because 

equation 1 represents an approximate decomposition and 

the P-wave-coda noise samples provide only weak estimates of the variation in the data. 

For K recordings, I stations, and J earthquakes, equation 

2 describes a system of K equations to determine I+J unknowns. There is one undetermined degree of freedom associated with this system of equations. Physically, this 

undetermined degree of freedom means that we can estimate relative, but not absolute, site response and source 

spectra. 

As a first constraint for the inversion, we set the site 

response for one station identically equal to 1 so that the 

SRi 0 

for i = 1,I SRMAS 0 

and SRMAS (/) ES, (/) for j= 1,J 

Dividing these constrained "source" spectra by the appropriate geometric spreading factors (that is, xMASj/2) yields 

spectral estimates for the ground motion recorded at station MAS from the jth earthquake. 

RELATIVE SITE AMPLIFICATIONS 

The site response at station NPT relative to station MAS 

is plotted in figure 5; station NPT is located within an area 

Frequency (Hz) 

Figure 5.-Average site-response spectrum for shear waves at station NPT, relative to station MAS. Vertical 

bars show 68-percent-confidence interval for spectral estimates. Relative site response is well determined 

from 0.7 to 15 Hz. At low frequencies, relative amplification is slightly larger than a factor of 2; it peaks 

around 1 Hz and decreases gradually with increasing frequency up to 15 Hz, where there is little relative 

amplification. 
F42 MARINA DISTRICT 

that was heavily damaged during the main shock (fig. 1). 

The relative site response, which is well determined within 

the frequency band from 0.6 Hz (1.6 s) to 15 Hz, is amplified by a factor of 7 near 1 Hz and decreases gradually 

with increasing frequency up to 15 Hz. At the lowest frequencies, the amplification is approximately a factor of 2 

but is poorly resolved. 

The relative site response at all five stations located in 

the central part of the Marina District is plotted in figure 

6. Although there is some variation among these five stations, the overall behavior is remarkably similar: a rapid 

increase to a peak amplification of 6 to 10 near 1 Hz, 

followed by a gradual decrease with increasing frequency 

up to 15 Hz. The frequency band from 0.7 to 3.0 Hz is 

significantly amplified for all the Marina District stations 

relative to station MAS. The logarithmic resampling interpolates, but does not smooth, the input record spectra; the 

absence of a marked peak-and-trough structure indicative 

of a modal site resonance is a consistent characteristic of 

these site-response spectra. 

There is a slight variation among the site responses at 

high frequencies, where station PUC is more strongly amplified than the rest of the Marina District stations. The 

amplification at station PUC relative to station MAS is approximately a factor of 3 within the frequency band from 

2.5 to 25 Hz. We note that station PUC is located to the 

east of the hydraulic fill (see Bonilla, this chapter); the 

thin (-6 m thick) layer of hydraulic fill may attenuate the 

high-frequency motion at stations BEA and LMS. 

The site response at the hard-rock stations (fig. 7) indicates the significance of the seismic amplification in the 

Marina District. On average, these stations show no relative amplification within the frequency band from 0.3 to 

20 Hz. At 5.0 to 15 Hz, the amplification at station LEA 

increases to a factor of 2, whereas the amplification at station CAI, is approximately half that at station MAS at 2.0 

to 20 Hz. Overall, the median amplification at these five 

stations is remarkably close to 1, justifying the description 

of station MAS as an "average" hard-rock station. The increase in the relative site response at low frequencies at 

station DIA is the result of a malfunctioning recorder: 

Gary Glassmoyer (oral commun., 1990) identified, but 

could not correct, a baseline offset in the recording of 

event 31 12342 (table 1). 

The site response at stations HHS and LET is plotted 

in figure 8. Comparison with figure 6 indicates a pronounced difference in the response between these stations and the five stations in the central part of the 

Marina District: Stations HHS and LET, located on dune 

sand and sediment, respectively, show little relative 

amplification at low frequencies; the amplification increases to 2-4 above 1 Hz. We note that the difference in 

0.1 1 I 

1 10 

Frequency (Hz) 

Figure 6.-Site-response spectra for shear waves at five stations in central part of the Marina District, relative 

to station MAS. Dotted line shows site response for station NPT. Although there is some variation between 

stations, the overall amplification is remarkably consistent, with a peak amplification of a factor of 7 to 10 

near 1.0 Hz that gradually decreases with increasing frequency. Station PUC has the most amplification, and 

station LMS the least amplification, at high frequencies. 
GROUND-MOTION AMPLIFICATION 

DIA 

LEA 

Frequency (Hz) 

Figure 7.-Site-response spectra for shear waves at five hard-rock stations in San Francisco, relative to station 

MAS. Constraining station MAS yields a flat amplification of 1.0 (dotted line), close to the median site 

response for the other stations. Station CAL has the least amplification, and stations RIN and LEA the most 

amplification, reaching 2. Apparent amplification at low frequencies for station DIA is due to a malfunctioning recorder. 

1 10 

Frequency (Hz) 

Figure 8.Ã‘Site-respons spectra relative to station MAS for shear waves at two stations sited on dune sand 

and undivided sedimentary deposits inside and just outside the Marina District. Station LET is located at 

Letterman Army Medical Center in the Presidio, and station HHS in eastern part of the Marina District. 

Bedrock contours drawn by Bonilla (this chapter) indicate that the sedimentary basin underlying the Marina 

District is about 35 m thick beneath station HHS but does not extend westward beneath station LET. 
F44 MARINA DISTRICT 

relative amplification between stations HHS and LET 

correlates with the relative amount of damage in these 

two areas. There was little damage in the Presidio (LET), 

whereas the area near the Heritage House (HHS) sustained moderate damage (see fig. 1). Because Letterman 

Army Medical Center is a large (six story) building, the 

relative site response plotted in figure 8 is also conditioned by the building response. 

ONE-DIMENSIONAL MODEL FOR THE 

GROUND-MOTION AMPLIFICATION 

IN THE MARINA DISTRICT 

The shear-wave velocities in the sedimentary deposits 

underlying the Marina District were determined by Kayen 

and others (1990) from a 9 1 -m-deep borehole located near 

station NPT (see fig. 2A). The sedimentary column is 

largely made up of older bay mud, with a shear-wave velocity of approximately 300 mls, overlying Franciscan serpentine. We investigate the amplification due solely to the 

vertical velocity structure, using the one-dimensional model of Haskell (1960) for the propagation of SH waves. The 

distributions of shear-wave velocity, density, and Q are 

plotted in figure 9A. The estimated densities are assumed 

from results obtained in similar rock types, as are the 

shear-wave velocities for depths below 25 m (Fumal, 

1991). 

To model the amplification at station NPT relative to 

station MAS, we calculate the one-dimensional amplification for the velocity structure shown in figure 9A as the 

site amplification at station NPT, and use the velocity 

structure for depths below 80 m to calculate the site amplification at station MAS. Dividing the amplification at 

station NPT by the amplification at station MAS yields the 

model spectral ratio. The observed and model spectral ratios are plotted in figure 95. 

The one-dimensional model for the central part of the 

Marina District fits the observed amplification for frequencies above 2.5 Hz. Basically, this high-frequency fit 

is derived from the cumulative Q structure shown in figure 9A. For frequencies between 1 and 2.5 Hz, however, 

the one-dimensional model substantially underestimates 

the observed amplification. In particular, the width of the 

low-frequency peak is poorly modeled. To first order, this 

peak represents the lowest mode of a quarter-wave resonance: The average shear-wave velocity of 300 rnls for 80 

m of sediment yields a travel time of 0.27 s, a quarter of 

the period of the lowest resonance peak. The misfit of 

both the width of the spectral peak and the trough near 2 

Hz (shaded area, fig. 95) suggests that this quarter-wave 

resonance is modified by seismic-focusing effects. At 

these frequencies, the shape of the sedimentary basin underlying the Marina District (see Bonilla, this chapter, 

figs. 4, 5) may contribute significantly to the observed site 

amplification. 

EXTRAPOLATING MAIN-SHOCK 

GROUND MOTIONS 

If we include the accelerograph recordings of the main 

shock in the record set that is decomposed into source and 

site spectra, equation 2 can be constrained to yield linear 

extrapolations of the main-shock ground motions at stations that recorded only aftershocks. Setting the source 

spectra of the main shock identically equal to 1 (that is, In 

ESo( f) =0, where "o" indicates the main shock) is mathematically similar to constraining one of the site spectra. 

Inverting the resulting set of equations yields the reconstrained "site" and "source" spectra 

SRi 0 ESO 0 for i = \,I 

and ESj 0 

for j = 1,J 

ESO 0 

Dividing these reconstrained "site" spectra by the geometric spreading factors (xio/2) yields spectral estimates of the 

main-shock ground motions at the Z stations that recorded 

aftershocks. This method of reconstraining the inversion of 

equation 2 to extrapolate ground motion is more readily 

implemented than the explicit averaging 

determined from the N main-shock recordings RÃ£Ã f) and 

the relative site responses SRi( f )/SRn( f) obtained through 

the constraints described in equation 4. 

To test this procedure, we incorporate the main-shock 

spectrum at station CAL into the data set and extrapolate 

for station RIN. The recorded spectrum and the 68-percent-confidence limits for the extrapolated spectrum are 

plotted in figure 10. The recorded main-shock spectrum 

falls well within the confidence interval for this extrapolation, as determined from the variance defined in equation 

3 and the number of main-shock accelerograms. 

To extrapolate the ground motions in the central part of 

the Marina District for the main shock, we incorporate the 

main-shock spectra at stations CAL and RIN into the data 

set and extrapolate for station NPT. The extrapolated acceleration spectrum is plotted in figure 11. As shown in 

figure 5, the amplification at station NPT has a broad peak 

at 1 Hz and a "side lobe" at 2.3 Hz; these peaks are similarly evident in the extrapolated acceleration spectrum. 

Two main-shock acceleration spectra are also plotted in 

figure 11. The spectrum labeled "GGB" was obtained at a 

station located 2 krn west of the Marina District, sited on 

Franciscan serpentine below the Toll Plaza of the Golden 

Gate Bridge. Station GGB recorded a peak ground acceleration of 0.25 g. The main-shock spectrum at station 
GROUND-MOTION AMPLIFICATION 

NPT 

Density (gIcrn3) 

10.0 observations 

Frequency (Hz) 

Figure 9.-One-dimensional model for ground-motion amplification. A, Distributions of shear-wave velocity, density, and Q 

values inferred for station NPT. Shear-wave velocity was logged by Kayen and others (1990) to a depth of 25 m, then extrapolated to Franciscan serpentine at 80 m, assuming a velocity of 300 m/s. Stepped increase in shear-wave velocity in the basement 

rock was chosen arbitrarily, as were the densities. Q structure was adjusted to fit observed spectral ratio at high frequencies. 

Velocity, density, and Q structure used to model station MAS were obtained by stripping the upper 80 m of structure used for 

station NPT. B, Observed spectral ratio compared to predicted amplification at station NPT, relative to station MAS. Fit at 

frequencies above 2.5 Hz was obtained by adjusting cumulative attenuation in the sedimentary deposits. Misfit between 1 and 

2.5 Hz (shaded area) could be caused by seismic-focusing effects due to the shape of sedimentary basin; varying the velocity 

structure below 80-m depth does not improve this misfit. 
MARINA DISTRICT 

"1 I 

n 

03 

a " 100 

cd 

f-1 

4' 

u 

CD 

A 

CQ 

. 

0 IÃ‘ 

4' 10 

f-1 

CD 

d 

CD 

0 

1 

1 10 

Frequency (Hz) 

Figure 10.-Extrapolated acceleration spectrum, plotted as a 68-percent-confidence interval (shaded area), 

compared to acceleration spectrum for main shock from station RIN (heavy curve). Extrapolation was obtained using only the main-shock recording from station CAL, together with the set of aftershock recordings. 

u 

w 

cd 

f-1 

4' 

u 

CD 

A 

0) 

IÃ‘ 

0 

4' 

cd 

f-1 

0) 

d 

d> 

u 

2 

for Station NPT 

1 10 

Frequency (Hz) 

Figure 11.-Extrapolated acceleration spectrum, plotted as 68-percent-confidence interval (shaded area), for 

main shock at station NPT, compared to acceleration spectra from two accelerograph sites that recorded the 

main shock. Station GGB is sited on Franciscan serpentine below the Toll Plaza of the Golden Gate Bridge; 

station OHW is sited on older bay clay and sand at the Outer Harbor Wharf in Oakland. These two stations 

recorded peak accelerations of 0.25 and 0.29 g, respectively. 
GROUND-MOTION AMPLIFICATION F47 

GGB is a factor of 3 smaller than the extrapolated spectrum for station NPT near 1 Hz, and a factor of 2 smaller 

at most other frequencies. The spectrum labeled "OHW" 

was obtained at a station sited on sand and older bay deposits near the Outer Harbor Wharf in Oakland. Station 

OWH recorded a peak ground acceleration of 0.29 g, the 

largest acceleration of any station north of the San Francisco Airport. The extrapolated spectrum for station NPT 

exceeds the main-shock spectrum for station OHW at 1 

and 2 to 3 Hz; the two spectra are similar at frequencies 

above 4 Hz. 

Although the spectral decomposition does not incorporate the phase information necessary for synthesizing acceleration time histories, the comparison of spectral 

amplitudes suggests a range 20.25 g in the extrapolated 

peak acceleration at station NPT, if the underlying sedimentary deposits responded linearly. This suggested range 

exceeds all the free-field peak accelerations recorded in 

San Francisco. Clearly, the assumption of linearity is critical: The extrapolated spectrum should be considered as an 

upper bound for the main-shock ground motion. The difference between the main-shock spectrum for station 

OWH and the extrapolated spectrum for station NPT 

could represent the nonlinearity of the response of the sedimentary deposits below station OHW. Station NPT lies 

one block outside the 1912 hydraulic fill (see Bonilla, this 

chapter). The ground settlement in this area was minimal, 

about 14 mm (Bennett, 1990). It cannot be determined after the fact whether nonlinear sediment response damped 

the main-shock ground motion near station NPT. 

The suggested range in peak acceleration is commensurate, however, with modified Mercalli intensities (MMI's) 

of VIII and IX (Evernden and Thompson, 1985). An MMI 

of IX was assigned to the Marina District (Benuska, 1990, 

p. 69). It is useful to compare the damage in the Marina 

District with that in the Richmond District, which shares 

similar architectural styles and construction practices. The 

peak ground accelerations for the main shock recorded at 

the nearest stations, sited on undivided sedimentary deposits at Letterman Army Medical Center (0.14 g), on dune 

sand at Veterans' Administration Hospital (0.16 g), and on 

Franciscan serpentine at the Presidio (0.21 g), suggest that 

the peak ground acceleration in the Richmond District, underlain by dune sand, ranged from 0.10 to 0.20 g. The 

MMI assigned to the Richmond District ranged from VI to 

VII. 

Extrapolating main-shock ground motions for areas that 

sustained ground failure generally overestimates the actual 

ground motions. Other than the two most northern blocks 

east of Scott Street, which sustained the largest ground 

1 10 

Frequency (Hz) 

Figure 12.-Extrapolated acceleration spectra, plotted as 68-percent-confidence intervals (shaded area), for 

two sites within 1912 hydraulic fill, compared to recorded and extrapolated acceleration spectra at station TRI 

(dashed curve), located on hydraulic fill at Treasure Island. Extrapolation for station TRI was determined from 

relative amplification of north-south component of motion for seven aftershocks and from main-shock recording at station YBI on Yerba Buena Island. The recorded acceleration spectrum at station TRI is about a factor 

of 3 less than the extrapolated spectra, a difference due to nonlinearity of ground response. 
F48 MARINA DISTRICT 

settlement (Bennett, 1990), the area underlain by the 1912 

hydraulic fill was less severely damaged than the blocks to 

the west and south (see fig. 1). This damage pattern contradicts the uniformity of relative amplification plotted in 

figure 6, which shows all the central Marina District stations to be similarly amplified in the frequency band 1-5 

Hz, suggesting that the ground motions were smaller inside the area underlain by the 1912 hydraulic fill because 

the ground behaved nonlinearly during the main shock. 

The extrapolated spectra for the main-shock ground motions at two stations underlain by the 19 12 hydraulic fill in 

the Marina District are shown in figure 12. As in figures 

10 and 11, these extrapolations are plotted using 68-percent-confidence intervals. The spectrum labeled "TRI" was 

obtained at the station on Treasure Island, which recorded 

a peak ground acceleration of 0.16 g at a site that sustained liquefaction. The dashed curve is an extrapolation 

of the main-shock spectrum at Treasure Island, obtained 

by multiplying the amplification at station TRI relative to 

the Yerba Buena Island station (YBI), determined from recordings of seven aftershocks by Jarpe and others (1990), 

by the main-shock spectrum at station YBI, according to 

equation 6. 

The extrapolated spectrum for station TRI is similar to 

those for stations BEA and LMS, particularly at frequencies above 2 Hz. This comparison confirms one hypothesis 

of Hanks and Brady (1991), who suggested that the similarity of the geometric and geologic relations between stations TRI and YBI and stations CAL and BEA is 

indicative of a corresponding similarity of the relative amplification between these pairs of stations. We note, however, that the extrapolated spectrum overestimates the 

recorded spectrum at station TRI by a factor of 3 within 

the frequency band from 1 to 10 Hz. Hanks and Brady 

(1991) argued that the accelerogram recorded at station 

TRI approximates the ground acceleration in the area of 

the Marina District underlain by the 1912 hydraulic fill, 

although this assertion cannot be tested. 

CONCLUSIONS 

Recordings of aftershocks indicate that weak ground 

motions in the Marina District were significantly amplified 

relative to sites in Fort Mason and Pacific Heights within 

the frequency band from 1 to 5 Hz. This frequency band 

spans the approximate range in the fundamental frequencies for two- to four-story wood-frame buildings. A onedimensional model of the sedimentary structure in the 

Marina District yields an adequate fit to the amplification 

observed above 2.5 Hz but markedly underestimates the 

amplification observed from 1 to 2.5 Hz. This "additional" 

amplification may be associated with focusing of shear 

waves derived from the three-dimensional shape of the 

sedimentary basin underlying the Marina District. 

The extensive shaking damage in the central part of the 

Marina District-that is, damage not directly associated 

with ground failure and liquefaction-suggests that the 

, strong ground motions in parts of the Marina District were 

amplified during the main shock. Using the relative amplification obtained from aftershock recordings to extrapolate 

to main-shock spectra for the Marina District yields spectral estimates that exceed the spectra recorded at all other 

San Francisco sites. Both damage estimates and spectral 

extrapolations suggest that the peak accelerations in the 

Marina District reached or exceeded 0.25 g. This range is 

similar to the range of peak accelerations recorded at stations sited on sand and older bay deposits in Emeryville 

and Oakland (0.25-0.29 g). 

The liquefaction of the hydraulic fill emplaced in 1912 

in the Marina District can be reasonably expected to have 

attenuated the ground motions on the fill. The peak ground 

acceleration of 0.16 g recorded at Treasure Island, which 

also sustained liquefaction, appears markedly damped relative to both extrapolations and recordings at stations sited 

on older bay deposits that did not sustain ground failure. 

The distribution of damage shown in figure 1 indicates 

that the blocks to the west of the 1912 hydraulic fill sustained greater damage than the area within the 1912 fill, 

suggesting that the main-shock accelerations varied spatially within the Marina District. In contrast, there was relatively little variation in amplification of the weaker 

aftershock motions between the five sites in the central 

part of the Marina District. 

ACKNOWLEDGMENTS 

We are indebted to Robert Bowen, Joseph Machi, David 

Katz, A1 De Martini, the Pacific Union Co., the Heritage 

House, the Presidio of San Francisco, Jayne Shaeffer of 

the National Park Service, and Capts. John Herrington, 

James Groshong, and Douglas Goodin of the San Francisco Fire Department for allowing us to deploy GEOS recorders at the sites necessary to carry out this study. 

Thomas Hanks organized the deployment of seismographs 

in the Marina District. Christopher Deitel, Eugene Sembera, James Gibbs, Thomas Hanks, Thomas Noce, and 

Roger Borcherdt deployed and maintained the instruments, 

and Gary Glassmoyer was responsible for data playbacks 

and the consequent organization of the data (Mueller and 

Glassmoyer, 1990). The accelerograms from stations CAL, 

RIN, PRS, DIA, TRI, YBI, and OHW were gathered, 

processed, and distributed by the California Strong Motion 

Instrumentation Program of the California Division of 

Mines and Geology. The accelerogram from station GGB 

was gathered and processed by the National Strong Motion Network of the U.S. Geological Survey in Men10 

Park, Calif. William Joyner, Robert Brown, Thomas 

Hanks, Gary Glassmoyer, Manuel Bonilla, and Tom 
GROUND-MOTION AMPLIFICATION F49 

O'Rourke provided useful reviews of the manuscript; Carol Sullivan retyped it after the original file had been lost. 

REFERENCES CITED 

Andrews, D.J., 1986, Objective determination of source parameters and 

similarity of earthquakes of different size, in Das, Shamita, Boatwright, John, and Scholz, C.H., Earthquake source mechanics: 

American Geophysical Union Monograph 37 (Maurice Ewing series, v. 6), p. 259-268. 

Bennett, M.J., 1990, Ground deformation and liquefaction of soil in the 

Marina District, chap. D of Effects of the Lorna Prieta earthquake 

on the Marina District, San Francisco, California: U.S. Geological 

Survey Open-File Report 90-253, p. Dl-D36. 

Benuska, Lee, ed., 1990, Loma Prieta earthquake reconnaissance report: 

Earthquake Spectra, v. 6, supp. 9041,448 p. 

Bonamassa, Ornella, and Mueller, C.S., 1989, Source and site-response 

spectra from aftershock seismograms of the 1987 Whittier Narrows, 

California, earthquake [abs.]: Seismological Research Letters, v. 59, 

no. 1, p. 23. 

Borcherdt, R.D., Fletcher, J.B., Jensen, E.G., Maxwell, G.L., Vanschaack, 

J.R., Warrick, R.E., Cranswick, Edward, Johnston, M.J.S., and McClem, Robert, 1985, A general earthquake-observation system 

(GEOS): Seismological Society of America Bulletin, v. 75, no. 6, p. 

1783-1 825. 

Evemden, J.F., and Thomson, J.M., 1985, Predicting seismic intensities, 

in Ziony, J.I., ed., Evaluating earthquake hazards in the Los Angeles 

region-an earth-science perspective: U.S. Geological Survey Professional Paper 1360, p. 151-202. 

Fumal, T.E., 1991, Preliminary report on the geology and shear wave 

velocities at strong motion sites that recorded the Lorna Prieta, California, earthquake: U.S. Geological Survey Open-File Report 91- 

311, 163 p. 

Hanks, T.C., and Brady, A.G., 1991, The Lorna Prieta earthquake, ground 

motion, and damage in Oakland, Treasure Island, and San Francisco: Seismological Society of America Bulletin, v. 81, no. 5, p. 

20 19-2047. 

Haskell, N.A., 1960, Crustal reflections of plane SH waves: Journal of 

Geophysical Research, v. 65, no. 12, p. 4147-4150. 

International Conference of Building Officials, 1985, Uniform building 

code: Whittier, Calif., 817 p. 

Jarpe, S.P., Hutchings, L.J., Hauk, T.F., and Shakal, A.F., 1990, Selected 

strong- and weak-motion data from the Loma Prieta earthquake sequence: Seismological Research Letters, v. 60, no. 4, p. 167-176. 

Kayen, RE., Lui, H.-P., Fumal, T.E., Westerlund, R.E., Warrick, R.E., 

Gibbs, J.F., and Lee, H.J., 1990, Engineering and seismic properties 

of the soil column at Winfield Scott School, San Francisco, chap. G 

of Effects of the Loma Prieta earthquake on the Marina District, San 

Francisco, California: U.S. Geological Survey Open-File Report 90- 

253, p. Gl-Gl8. 

Mueller, C.S., and Glassmoyer, Gary, 1990, Digital recordings of aftershocks of the 17 October 1989 Lorna Prieta, California, earthquake: 

U.S. Geological Survey Open-File Report 90-503, 147 p. 
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND FAILURE 

MARINA DISTRICT 

OBSERVATION OF LOCAL SITE EFFECTS 

AT A DOWNHOLE-AND-SURFACE STATION 

By Hsi-Ping Liu, Richard E. Warrick, Robert E. Westerlund, Eugene D. Sembera, and Leif Wennerberg, 

U .S . Geological Survey 

CONTENTS 

[Figures 1 1-1 8 follow references] 

Page 

F5 1 

5 1 

52 

52 

52 

52 

53 

53 

53 

53 

53 

57 

57 

61 

62 

63 

ABSTRACT 

After the earthquake, the U.S. Geological Survey 

drilled a borehole at Winfield Scott School at Beach and 

Divisadero Streets; the borehole intersected bedrock surface at 79.5-m depth. Two three-component seismometers, one in bedrock at 88-m depth and one located at 

the surface, were installed at the site; each seismometer 

consists of one vertical and two orthogonally oriented 

horizontal geophones with a natural period of 0.5 s. Between August 1990 and January 1991, more than 50 

earthquakes were recorded digitally; 8 of these earthquakes, ranging in magnitude from 2.8 to 3.6 and 

originating on the Calaveras, Franklin, Greenville, and 

Hayward Faults and on faults parallel and close to the 

San Andreas Fault, generated seismograms with high 

signal-to-noise ratios. Horizontal ground-motion amplification, expressed as spectral ratios between ground 

motions at the surface and in bedrock, was calculated 

for motions in two orthogonal directions (along Divisadero and Beach Streets), using entire seismograms. 

Except for the lowest-frequency spectral-ratio peak at 

about 1 Hz, the frequency of other peaks depends on 

earthquake location. The earthquakes were divided into 

two groups, comprising those with epicenters located 

east and south of San Francisco Bay. Within each group, 

spectral-ratio peaks from different earthquakes align with 

each other, thus showing consistency in spectral-ratio 

peaks as a function of earthquake location. The amplitude of spectral-ratio peaks varies, depending on groundmotion direction and earthquake location; for example, 

the amplitude of the 1-Hz spectral-ratio peak ranges 

from 7.2 to 12.7. The surface/downhole spectral ratio 

therefore provides only partial information on how 

ground motions are amplified by sedimentary deposits. If 

we use this ratio for earthquake engineering applications, 

the ratios for the eight earthquakes indicate the variation 

in spectral ratio to be expected from earthquakes with 

similar magnitudes and epicentral distances on various 

bay-area faults. Also noteworthy are observations that 

the two horizontal-component seismograms recorded by 

each seismometer have a similar coda amplitude and duration regardless of earthquake location, and that particle-motion polarization becomes complex shortly after 

the P- and S-wave onsets. This complex particle-motion 

polarization indicates that incident wavefields in the bedrock and at the surface are three dimensional; the bedrock topography underlying the site has been delineated 

previously to be three dimensional from drill-hole information. We suggest that three-dimensional effects need 

to be considered when modeling site amplification in the 

Marina District. 

INTRODUCTION 

In comparison with other sites where the effects of nearsurface sedimentary deposits on earthquake ground motions have been studied (for example, Seed and Idriss, 

1970; Joyner and others, 1976; Johnson and Silva, 198 1; 

Seale and Archuleta, 1989; Blakeslee and Malin, 1991), the 
F52 MARINA DISTRICT 

Marina District of San Francisco has several distinguishing features: (1) owing to a combination of liquefaction, 

differential ground settlement, and ground-motion amplification, extensive damage occurred during the earthquake 

(U.S. Geological Survey, 1990); (2) the soil column consists of a thick sequence of low-shear-wave-velocity clay 

and sand with a total depth of 79.5 m overlying bedrock; 

and (3) the three-dimensional bedrock topography underlying the site has been delineated from drill-hole and other 

information (Bonilla, 199 1 ; O'Rourke and others, 199 1). 

After the earthquake, the U.S. Geological Survey 

(USGS) drilled a borehole (WSS, fig. 1) to 91-m depth on 

the Winfield Scott School playground at Beach and Divisadero Streets to obtain a detailed stratigraphy of the 

sedimentary deposits and to install a three-component seismometer below bedrock. Scientists could then study the 

three-dimensional characteristics of site amplification by 

comparing seismographic readings recorded below the 

bedrock with those recorded at the surface. 

METHODS 

SITE CHARACTERIZATION 

A detailed description of the geology and history of artificial fill in the Marina District was given by Bonilla 

(1991). On the basis of borehole data and the assumption 

that the bedrock surface was shaped by stream erosion, the 

gross shape of this bedrock surface is inferred to be a halfbasin deepening northwestward. Bonilla (1991, fig. 4) 

showed an east-west cross section of the Marina District 

intersecting USGS borehole WSS, located on the southwest side of the half-basin axis (lat 37'48'13" N., long 

122026'301' W.). Engineering and seismic properties of the 

soil column at the site were reported by Kayen and others 

(1990). To summarize, the soil column consists of 4.3 m of 

filled sand overlying another 3.3 m of natural-sand deposits 

near the surface. Below these deposits is an interbedded 

sequence of clayey sand and clay to a depth of 11.6 m 

interpreted to be the base of Holocene bay clay. A layer of 

dense sand between 11.6- and 22.9-m depth is characterized by a distinct yellow-brown color and high penetration 

resistance. The lower 56.6 m of the soil column consists of 

Pleistocene bay clay overlying hydrothermally altered serpentine bedrock. The shear-wave velocities are 130 m/s for 

the filled sand, 175 m/s for the natural sand, 145 m/s for 

the Holocene clay, 285 m/s for the upper section of dense 

sand, 435 m/s for the lower section of dense sand, and 260 

m/s for the Pleistocene bay clay. 

TEST EQUIPMENT 

SEISMOMETERS 

The surface seismometer, placed at a distance of 2 m 

from the borehole, is a Mark Products L-22-3D seismometer consisting of three orthogonally oriented Mark Products L-22D geophones, each with a natural period of 0.5 

s. The horizontal components are designated "inline" and 

"perpendicular." Using a Brunton compass, the "inline" 

component is measured to orient at azimuth 353' after emplacement. The borehole seismometer, housed in a pressure-tight container, incorporates one vertical1 and two 

orthogonally oriented horizontal Mark Products L-22D 

geophones with the same specifications as those of the 

surface seismometer. The horizontal components of the 

borehole seismometer, designated "HG1" and "HG2," are 

leveled to within 0.1' after emplacement, using an internal 

gimbal device (Liu and others, 1991). The orientation of 

component "HG 1 " is determined to be 205.7Â±7.2' using 

the nearly linearly polarized (linearity, 20.94) first-P-wavearrival particle motions of eight earthquakes whose epicenLOMBARD 

Figure 1.-Marina District of San Francisco, showing location of USGS borehole WSS. 
OBSERVATION OF LOCAL SITE EFFECTS AT A DOWNHOLE-AND-SURFACE STATION 

ters were located by the USGS central California network 

(see supplementary section below entitled "Determination 

of Borehole Horizontal-Geophone Orientation"). The geophone amplitude and phase responses are calibrated by using the geophone-release test (Asten, 1977) and the phaseellipse test (Liu and Peselnick, 1986). All geophones are 

adjusted to 0.7 of critical damping by shunt resistors. The 

effects on geophone response of the cable linking each 

seismometer to its recording instrument were analyzed and 

found to be negligible (Liu and others, 1991). 

RECORDING INSTRUMENT 

One General Earthquake Observation System (GEOS) 

recorder (Borcherdt and others, 1985), set for six-channel 

digitization using 16-bit analog-to-digital conversion at a 

rate of 200 samples per second per channel, was used to 

record the earthquakes; the cutoff frequency of the antialiasing filter was set at 100 Hz. The gains were set at 18 

dB for the' surface seismometer and at 42 dB for the borehole seismometer. To reduce the possibility of false triggering by artificial noise, the recorder was triggered by a 

horizontal component of the borehole seismometer. 

SPECTRAL COMPUTATION 

Horizontal ground-motion amplification, expressed as 

the spectral ratio between motion at the surface and that in 

the bedrock, was calculated from seismograms of high signal-to-noise ratio for two orthogonal directions. The spectra used in the spectral-ratio calculations were computed 

from the entire records, including preevent data. For example, the entire 45-s duration of the records shown in 

figure 4 was used for spectral computation, applying a fast 

Fourier transform (FFT) algorithm. One practical reason 

for using the entire record is that buildings and other 

structures respond to horizontal ground shaking regardless 

of wave type; another reason is that, by using the entire 

seismogram, accurate spectral estimates can be obtained. 

For low-noise seismograms, and for data windows that begin before the signal onset and end at the end of coda 

waves, the spectral-leakage problem associated with data 

truncation does not arise; only the possibility of aliasing 

error needs to be considered. 

Corresponding to a sampling interval of 5 ms, the Nyquist frequency is 100 Hz. As shown by Papoulis (1977), 

the aliasing error is negligible if the spectral amplitude at 

frequencies above the Nyquist frequency is negligible in 

comparison with the peak spectral amplitude. This condition is, indeed, satisfied for all the seismograms analyzed 

in this report (see fig. 5). 

Fluctuations in the FFT spectra were smoothed by using 

a truncated Gaussian window 0.61 Hz wide; the window 

decreases in height from 1 at the center to 0.21 at the edge. 

RESULTS 

DATA 

Between August 1990 and January 1991, the station was 

maintained continuously, and more than 50 bay-area earthquakes were recorded during this period. 

Seismograms generated by an ML=3.4 earthquake on 

the San Andreas fault (epicentral distance, 74.2 km; 

backazimuth, 153.43O) are shown in figure 2. Because 

this earthquake occurred at 2:24 p.m. P.d.t., the first-Pwave-arrival ground motions at the surface seismometer 

were over-whelmed by artificial noise in the Marina District. In contrast, because surface-wave amplitude decreased exponentially with depth, this artificial noise was 

reduced considerably at 88-m depth, such that the impulsive first P-wave arrival was clearly recorded by the 

borehole seismometer. 

Eight of the recorded earthquakes, however, occurred 

between 7 p.m. and 7 a.m. P.d.t.; both surface and bedrock 

ground motions were recorded with a high signal-to-noise 

ratio. These eight earthquakes, whose epicenters are plotted in figure 3 and whose parameters are listed in table 1, 

were analyzed for local ground-motion site amplification. 

Seismograms generated by the ML=3.1 August 25, 1990, 

Berkeley, Calif., earthquake (2, table 1) are shown in figure 4. For all the seismograms analyzed for site amplification, the spectral amplitude at 50 Hz is negligible in 

comparison with the peak spectral amplitude. Smoothed 

FFT spectra of the horizontal-component seismograms in 

figure 4 are shown in figure 5. Spectral details differ for 

seismograms generated by different earthquakes. Seismograms generated by the ML=3.0 September 23, 1990, Felt 

Lake, Calif., earthquake (3, table 1) are shown in figure 6, 

and smoothed FFT spectra of the horizontal-component 

seismograms are shown in figure 7. In comparison with 

the Berkeley earthquake, the Felt Lake earthquake generated higher frequency ground motions. 

SPECTRAL RATIO OF HORIZONTAL MOTIONS 

ALONG STREET DIRECTIONS 

Because building response is strongly influenced by horizontal motions in an earthquake, and because most buildings in the Marina District respond differently to motions 

parallel and perpendicular to the street to which they front 

(Celebi, 1990), we calculated spectral ratios of horizontal 

motions parallel to Divisadero and Beach Streets by using 

the equation 
F54 MARINA DISTRICT 

where Xw and Xpf are the Fourier transforms of the entire 

inline and perpendicular components, respectively, of the 

surface seismometer; Xw and Xu are the Fourier transforms of components HG1 and HG2, respectively, of the 

borehole seismometer; Iy, Ip,, IW and I,/ are the corresponding geophone responses; and A,, Ap, Ay, and AL are 

the azimuthal directions of positive movement of the geophone coils. For the surface seismometer, A,=353O and 

AP=083O; and for the borehole seismometer, AU=205.7O 

and AL=115.70. The spectral ratio for motions parallel to 

Divisadero Street is calculated by substituting AS=350.7O 

in the equation on the previous page, and for motions parallel to Beach Street by substituting As=080.70. 

The spectral ratios Rs calculated for the eight earthquakes listed in table 1 are plotted in figure 8. The lowest 

frequency spectral-ratio peak, calculated for all eight 

earthquakes and for motions parallel to both Beach and 

Divisadero Streets, occurs coherently at about 1 Hz; the 

higher frequency spectral-ratio peaks are spread wider 

apart. 

Two spectral ratios, one for motion parallel to Divisadero Street and the other for motion parallel to Beach Street, 

generated by earthquake 3 in table 1 are compared in figure 9. The peaks generally differ in position and amplitude; for example, both spectral ratios have a peak at 1.0 

Hz, but the amplitude is 9.8 for motion parallel to Beach 

Street and 7.2 for motion parallel to Divisadero Street. 

The spectral ratios for motions in two orthogonal directions generated by earthquake 7 in table 1 are compared in 

figure 10. 

The spectral ratios for motions generated by earthquakes 

1 and 5 in table 1, which occurred close to each other on 

the Calaveras Fault (see fig. 3), are compared in figure 11. 

The spectral ratios for motion parallel to Beach Street (fig. 

- I 

fn - 11 ill, I 

Figure 2.-Seismograms generated by an earthquake (ML=3.4) on the San Andreas Fault and recorded by vertical 

component (A), inline horizontal component (B), and perpendicular horizontal component (Q of surface seismometer and by vertical component (D), horizontal component HG1 (Â£) and horizontal component HG2 (F) of 

borehole seismometer. Earthquake parameters: origin time, 1990:234:2124:5.62 G.m.t.; focal depth, 11.69 km; 

epicenter, lat 37'12.4' N., long 122'4.01' W.; epicentral distance, 74.2 km; backazimuth, 153.43'. 
OBSERVATION OF LOCAL SITE EFFECTS AT A DOWNHOLE-AND-SURFACE STATION 

Table 1.-7990 earthquakes used in analysis 

[Backazimuth is the angle measured from north to the line connecting the seismometer station and earthquake epicenter] 

Earth- Julian Time Latitude Longitude Epicentral Back- Depth ML Fault 

quake day (G.m.L) (O N.) (Â W.) distance azimuth (km) 

(km) 0 

Calaveras 

Hayward 

Near San 

Andreas 

Near San 

Andreas 

Calaveras 

Greenville 

Franklin 

Hayward 

Figure 3.-Sketch map of San Francisco Bay area, showing locations of major faults and epicenters of earthquakes listed in table 1 (squares). Four earthquakes south of Men10 Park are grouped as "south bay"; other 

four earthquakes are grouped as "east bay." 
F56 MARINA DISTRICT 

11B) agree fairly well with each other, in that the first 

three major peaks at 1.0, 2.7, and 3.5 Hz are similar in 

amplitude; the agreement is less satisfactory for motions 

parallel to Divisadero Street (fig. 11A). Two spectral-ratio 

peaks, at 3.9 and 4.9 Hz, in response to the ML=2.8 earthquake are missing from the spectral ratio in response to 

the ML=3.6 earthquake; this discrepancy can be traced to 

differences in the spectra of the inline component of the 

surface seismometer, as shown in figure 12A. (The inline 

component of the surface seismometer, oriented at azimuth 

353', is nearly parallel to the orientation of Divisadero 

Street at azimuth 350.7O.) Smoothed FFT spectra of the 

perpendicular component of the surface seismometer, and 

of the two horizontal components of the borehole seismometer, generated by these two earthquakes are shown in 

figures 125 through 12D. 

The eight earthquakes listed in table 1 can be divided 

into two groups by backazimuth. The four earthquakes (2, 

6, 7, 8) whose backazimuths range from 025.07O to 

089.48' can be grouped as "east bay" earthquakes; the 

other four earthquakes, whose backazimuths range from 

129.46' to 155.29', can be grouped as "south bay" earthquakes (see fig. 3). The epicentral distances of the southbay earthquakes range from 20.1 to 59.9 km, and those of 

the east-bay earthquakes from 52.7 to 89.7 km. Spectral 

ratios in response to the four east-bay earthquakes are 

plotted in figures 13A and 135. In contrast to figure 8, the 

second-lowest-frequency peak becomes coherent at 2.2 Hz 

for motions parallel to Divisadero Street (fig. 13A); and 

for motions parallel to Beach Street, the second- and thirdlowest-frequency peaks become coherent at 2.4 and 3.4 

Hz, respectively. In the plots of spectral ratios in response 

0 10 2 0 3 0 40 50 0 10 20 30 4 0 50 

T I M E (seconds) T I M E (seconds) 

Figure 4.-Seismograms generated by August 25, 1990, Berkeley, Calif., earthquake (ML=3.1), recorded by vertical 

component (A), inline horizontal component (B), and perpendicular horizontal component (C) of surface seismometer, 

and by vertical component (D), horizontal component HG1 (Q, and horizontal component HG2 (F) of borehole seismometer. Earthquake parameters: origin time, 1990:237:1147:29.71 G.m.t.; focal depth, 8.72 km; epicenter, lat 

37'52.42' N., long 122'13.78' W.; epicentral distance, 20.06 km; backazimuth, 067.17'. 
OBSERVATION OF LOCAL SITE EFFECTS AT A DOWNHOLE-AND-SURFACE STATION F57 

to the four south-bay earthquakes (figs. 13C, 13D), the 

second-lowest-frequency peak becomes coherent at 2.7 Hz 

for motions parallel to Beach Street (fig. 13D). The locations and amplitudes of spectral-ratio peaks in response to 

an east-bay earthquake (fig. 10) and a south-bay earthquake (fig. 9) are listed in tables 2 and 3, respectively. 

PARTICLE MOTIONS 

Comparison of two surface or downhole horizontal-component seismograms generated by any one of the eight 

earthquakes listed in table 1 (figs. 4B and 4C, 4E and 4F, 

6A and 65, and 6C and 6D) indicates that the two seismograms have similar coda amplitude and duration, an observation that holds true regardless of earthquake location. A 

reasonable conjecture for this similarity is that, in propagating from earthquake source to receiver, wave motions 

are randomized considerably by multiple reflections and 

scattering. To investigate this conjecture, surface particle 

motions, projected onto a horizontal plane as constructed 

from the horizontal-component seismograms in figures 4B 

and 4C, are plotted for successive 3-s intervals in figure 

14. The first P-wave arrival (1, fig. 14A) is linearly polarized and aligns to within 011' of the earthquake backazimuth; however, this linear polarization is lost after half a 

cycle. Particle motions of the onset of a large-amplitude 

secondary arrival (fig. 14B), presumably of shear waves, 

are nearly linearly polarized and at an angle of about 117' 

to the earthquake backazimuth; again, linearity of secondary-arrival particle motions is lost after half a cycle. The 

other two particle-motion plots (figs. 14C, 1423) show an 

inconsistency in particle-motion polarization. Similar observations of short-period P waves propagating in the 

shallow crust of the Adirondack Mountains in New York 

State were reported by Menke and Lerner-Lam (1991). 

DISCUSSION AND CONCLUSIONS 

Horizontal ground-motion amplification, expressed as 

the spectral ratio between motion at the surface and that 

directly below in the bedrock, Xy lXIf, was calculated for 

ground motions in two orthogonal directions, using entire 

seismograms. One reason for using the entire seismogram 

is that structures respond to all horizontal ground motions, 

regardless of wave type. As shown in figure 8, these spectral ratios are generally greater than 1 in the frequency interval of interest (0.5-20 Hz). The observed spectral 

ratios, however, provide only partial information on how 

ground motions are amplified by sedimentary deposits, as 

evidenced by variation in these ratios. For example, although the location of the lowest frequency spectral-ratio 

peak (at approx 1 Hz) is common to motions in two orthogonal directions (parallel to Divisadero and Beach 

Table 2.-Spectral-ratio peaks (below 10 HZ) in response to an east-bay 

(ML=3.3 October 14, 1990, Martinez, Calif.) earthquake 

[Directions of motion: B, parallel to Beach Street; D, parallel to Divisadero Street] 

Direction of motion Peak location Peak spectral-ratio 

(Hz) amplitude 

B 0.92 7.8 

D 1.09 10.6 

D 2.23 6.8 

B 2.51 6.1 

D 2.94 4.7 

B 3.41 6.9 

D 3.64 5.3 

B 4.39 3.2 

D 5.03 2.9 

B 5.97 3.5 

D 6.68 1.6 

D 7.42 2.4 

D 8.64 2.8 

D 9.48 3.8 

B 9.57 3.3 

Table 3.-Spectral-ratio peaks (below 10 Hz) in response to a south-bay 

(ML=3.0 September 23, 1990, Felt Lake, Calif.) earthquake 

[Directions of motion: B, parallel to Beach Street; D, parallel to Divisadero Street] 

Direction of motion Peak location Peak spectral-ratio 

(Hz) amplitude 

D 0.96 7.2 

B 98 9.8 

D 1.78 7.5 

D 2.37 7.5 

B 2.70 8.5 

D 2.98 6.0 

D 3.67 4.5 

B 3.72 10.0 

B 4.88 5.8 

D 5.00 6.6 

B 5.86 2.5 

D 6.02 3.6 

B 6.97 2.4 

D 7.53 2.8 

B 8.53 1.9 

D 8.83 6.7 

D 9.63 4.4 

B 9.78 2.7 

Streets, respectively), its amplitude ranges from 7.2 to 

12.7. At higher frequencies, XylXIf depends on direction of 

ground motion as well as earthquake location. An analogy 

with a causal system in which Xlf is the input, Xy is the 
F58 MARINA DISTRICT 

output, and Hf=Xy/Xifis the system transfer function of the 

sedimentary deposits cannot be made because (1) upgoing 

as well as downgoing waves were recorded by the borehole seismometer, and only upgoing waves can be considered as input when investigating how site amplification is 

affected by sedimentary deposits overlying bedrock; (2) 

entire seismograms were used for spectral-ratio calculation, and some phases recorded by the surface seismometer-for example, higher frequency surface waves-may 

not be causally related to wave motions recorded by the 

borehole seismometer; and (3) the bedrock surface is 

curved, and so the input excitation must be characterized 

by bedrock motion at more than one point. 

Boatwright and others (1991) calculated a model onedimensional site amplification, using the shear-wave velocities determined at USGS borehole WSS by Kayen and 

others (1990), and estimated the shear-wave velocities of 

bedrock, as well as the density and shear-wave-absorption 

parameters of sedimentary deposits and bedrock. Their results agree qualitatively with our observations; in particular, the lowest frequency spectral-ratio peak is located at 

about 1 Hz. 

The most interesting result of our study is establishment 

of the dependence of spectral ratio on earthquake location 

(fig. 13). Specifically, the coherency of some spectral-ratio 

peaks from different earthquakes is markedly improved 

when the earthquakes are broadly separated into two 

groups, east bay and south bay, in spite of the difference 

in epicentral distances within each group. (For example, 

the epicentral distances of the four east-bay earthquakes 2, 

6, 7, and 8 are 20.1, 59.9, 33.0, and 21.0 km, respectively.) Other evidence that indicates an independence of spectral-ratio peaks from epicentral distance is shown in figure 

15, which compares the spectral-ratio peaks of a south-bay 

earthquake (3, table 1; epicentral distance, 52.7 krn) with 

those of an east-bay earthquake with a similar epicentral 

distance (6, table 1; epicentral distance, 59.9 km): The 

second- and third-lowest-frequency peaks from these two 

earthquakes do not align with each other. 

Another significant result of our study is that the amplitude of spectral-ratio peaks varies with ground-motion direction. The surface/downhole spectral ratio therefore 

provides only partial information on how ground motions 

are amplified by sedimentary deposits. The spectral ratios 

from these eight earthquakes also indicate the variation in 

ground-motion amplification to be expected from earthquakes with similar magnitudes and epicentral distances 

on various bay-area faults. 

FREQUENCY (Hz) FREQUENCY (Hz) 

Figure 5.-Smoothed FFT spectra of horizontal-component seismograms in figure 4 for inline (A), and perpendicular (B) components of surface seismometer, and for components HG1 (C) and HG2 (D) of borehole seismometer. Spectral amplitude at 50 Hz is negligible in comparison with peak value in each plot. 
OBSERVATION OF LOCAL SITE EFFECTS AT A DOWNHOLE-AND-SURFACE STATION 

Figure 6.-Seismogrqms generated by September 23, 1990, Felt Lake, Calif., earthquake (ML=3.0), as recorded 

by inline horizontal component (A), and perpendicular horizontal component (B) of surface seismometer, and by 

horizontal components HG1 (Q and HG2 (D) of borehole seismometer. Earthquake parameters: origin time, 

1990:266:1335:47.15 G.m.t.; focal depth, 7.88 km; epicenter, lat 37'22.50' N., long 122'11.23' W.; epicentral 

distance, 52.71 km; backazimuth, 154.76'. 

0 1- 

,< FREQUENCY 10 (HZ) 15 20 !/v:i:!:\ 0 FREQUENCY 10 (HZ) 15 20 

Figure 7.-Smoothed FFT spectra of horizontal-component seismograms in figure 6 for inline (A), and perpendicular (B) components of surface seismometer, and for components HG1 (0 and HG2 (D) of borehole seismometer. 
MARINA DISTRICT 

5 10 15 20 

FREQUENCY (Hz) 

Figure 8.-Spectral ratios of horizontal motions at surface to those in bedrock in direction 

parallel to Divisadero Street (A) and Beach Street (B), calculated for eight earthquakes listed 

in table 1. 
OBSERVATION OF LOCAL SITE EFFECTS AT A DOWNHOLE-AND-SURFACE STATION F6 1 

The observation that particle-motion polarization changes from linear to complex shortly after P- and 5-wave onsets indicates that the incident wavefields in the bedrock 

and at the surface are three dimensional. The bedrock topography underlying the site has been delineated previously to be three dimensional from drill-hole information 

(Bonilla, 1991; O'Rourke and others, 1991). We suggest 

that such three-dimensional effects need to be considered 

when modeling site amplification in the Marina District. 

To evaluate further the influence of bedrock topography 

on site response, we calculated spectral ratios for orthogonal-motion components parallel to the major and minor 

axes of the bedrock basin underlying the site using Bonilla's (1991) map. A notable difference in these results from 

those calculated for motions parallel to the street grid is 

that for a component of motion parallel to the major axis 

of the bedrock basin, spectral-ratio peaks are higher. 

Otherwise, the results (figs. 16, 17) are similar to those 

calculated for components of motion parallel to the main 

street-grid directions, in that except for the lowest frequency peak at about 1 Hz, the frequency of other peaks depends on earthquake location, and for east- or south-bay 

earthquakes, spectral-ratio peaks from different earthquakes align with each other. A quantitative understanding 

of the influence of bedrock topography on site amplification requires further numeric modeling. 

The ground motions that generated the spectral ratios 

calculated in this study were small (peak acceleration, approx 0.002 g). Soil nonlinear effects, especially those associated with damping and shear-modulus degradation of 

Holocene bay clay and liquefaction in sand, are outside 

the scope of this report. 

ACKNOWLEDGMENTS 

We thank Thomas Sammon and Claudia C. Jeung of the 

San Francisco Unified School District, who facilitated our 

work at Winfield Scott School; F.W. Lester, who provided 

us with the earthquake parameters determined by the U.S. 

Geological Survey's central California seismic network; 

and J.C. Savage, for helpful discussions. - 

5 10 15 

FREQUENCY (Hz) 

Figure 9.-Site response for motions parallel to Divisadero Street (dashed curve) and Beach Street (solid curve) 

generated by September 23, 1990, Felt Lake, Calif., earthquake (ML=3.0). See figure 6 for seismograms. 
F62 MARINA DISTRICT 

SUPPLEMENTARY INFORMATION: horizontal-geophone orientation are listed in table 4; four 

DETERMINATION OF BOREHOLE of these earthquakes are also listed in table I. Following 

HOMZONTAL-GEOPHONE Aster and Shearer (1991) and using the variance-tensor 

ORIENTATION method, we fit an ellipse to the first half-cycle of P-wavearrival particle motions projected onto the horizontal 

The orientation of the surface horizontal geophone was 

determined with a Brunton compass. Because no remotereading compass was included in the borehole-seismometer package, the orientation of its horizontal geophones 

must be inferred indirectly. Using the nearly linearly polarized (linearity, 20.94) first-P-w ave-arrival particle motions of eight earthquakes whose epicenters were located 

by the USGS' central California network, the orientation 

of horizontal component HGl is determined to be 

205.7k7.2O. Three criteria were used in selecting seismograms for borehole horizontal-geophone orientation: (1) 

the first-P-wave-arrival motion must be recorded with high 

signal-to-noise ratio, (2) the first half-cycle of first-Pwave-arrival particle motion must be nearly linearly polarized, and (3) the epicenter distribution of earthquakes that 

generated the seismograms should cover a wide range of 

backazimuths. The eight earthquakes used for borehole 

plane. Orientations of the horizontal-component geophones 

can be determined to within *180Â if we assume that 

the semimajor axis of the ellipse aligns with the backazimuth. The ambiguity of 180' arises because it cannot be 

determined whether the first-P-wave-arrival motion is 

away from or toward the source by studying only borehole-seismometer data. Using seismograms recorded by 

the surface seismometer, the sense of the first-p-wavearrival motion can be ascertained, thus eliminating this 

ambiguity. By averaging the results obtained from earthquakes whose epicenters cover a wide range of backazimuths, Aster and Shearer (1991) were able to determine 

the horizontal-geophone orientation of a surface seismometer in the San Jacinto fault zone to within 5.7'. (Because 

of the high surface noise in a city environment, we were 

unable to conduct a similar test on our surface seismometer.) To assess the uncertainty in the borehole horizontalgeophone orientation on spectral-ratio calculations, some 

Figure 10.-site response for motions parallel to Divisadero Street (dashed curve) and Beach Street (solid curve) 

generated by October 14, 1990, Martinez, Calif., earthquake (Mp3.3) (earthquake 7, table 1). 
OBSERVATION OF LOCAL SITE EFFECTS AT A DOWNHOLE-AND-SUWACE STATION 

Table 4.-1990 earthquahs used in orienting borehole horizontal-component geophones 

[Backazimuth is the angle measured from north to the line connecting the seismometer station and earthquake epicenter] 

Julian Time Latitude Longitude Epicentral Back- Depth ML 

&Y (G.m.t.) (" N.) (OW.) Distance azimuth (km) 

(W (") 

11.7 3.4 (Los 

Gatos) 

8.7 3.1 

(Berkeley) 

11.0 2.1 

(Berkeley) 

7.9 3.O(Felt 

Lake) 

15.8 3.0 (N. of 

Livermore) 

6.1 2.8 (San 

Pablo) 

13.0 5.7 (Mono 

Lake) 

11.4 1.7 (W. of 

Golden 

Gate Park) 

of the results plotted in figure 11 were calculated again for 

AFl98S0 and AF2l2.g0. The results (fig. 18) show that 

such uncertainty mainly affects the amplitude, not the position, of spectral-ratio peaks. 

REFERENCES CITED 

Asten, M.W., 1977, Theory and practice of geophone calibration in-situ 

using a modified step method: Institute of Electrical and Electronic 

Engineers Transactions on Geoscience Electronics, v. GE-15, no. 4, 

p. 208-214. 

Aster, R.C., and Shearer, P.M., 1991, High-frequency borehole seismograms recorded in, the San Jacinto fault zone, southern California: 

Seismological Society of America Bulletin, v. 81, no. 4, p. 1057-1 100. 

Blakeslee, Sam, and Malin, Peter, 1991, High-frequency site effects at 

two Parkfield downhole and surface stations: Seismological Society 

of America Bulletin, v. 81, no. 2, p. 332-345. 

Boatwright, John, Fumal, T.E., Liu, H.-P., Mueller, C.S., and Seekins, 

L.C., 1991, Ground motion amplification in the Marina District: Seismological Society of America Bulletin, v. 81, no. 5, p. 1980-1997. 

Bonilla, M.G., 1991, Geology and historical development of the Marina 

District, San Francisco, California: Seismological Society of America Bulletin, v. 81, no. 5, p, 1958-1979. 

Borcherdt, R.D., Fletcher, J.B., Jensen, E.G,, Maxwell, G.L., VanSchaack, J.R., Warrick, R.E., Cranswick, Edward, Johnston, M.J.S., 

and McClearn, Robert, 1985, A general earthquake-obsewation system (GEOS): Seismological Society of America Bulletin, v. 75, 

no. 6, p. 1783-1825. 

Celebi, Mehmet, 1990, 'Qpes of structural damage, chap. B of Effects of 

the Loma Prieta earthquake on the Marina District, San Francisco, 

California: U.S. Geological Society Open-File Report 90-253, 

p. Bl-B6. 

Johnson, L.R., and Silva, Walt, 1981, Effects of unconsolidated sediments upon the ground motion during local earthquakes: Seismological Society of America Bulletin, v. 71, no. 1, p. 127-142. 

Joyner, W.B., Wamck, R.E., and Oliver, A.A., 1976, Analysis of seismograms from a downhole array in sediments near San Francisco 

Bay: Seismological Society of America Bulletin, v. 66, no. 3, p. 

937-958. 

Kayen, R.E., Liu, H.-P,, Fumal, T.E., Westerlund, R.E., Warrick, R.E., 

Gibbs, J.F., and Lee, H.J., 1990, Engineering and seismic properties 

of the soil column at Winfield Scott School, San Francisco, chap. G 

of Effects of the Loma Prieta earthquake on the Marina District, San 

Francisco, California: U.S. Geological Suwey Open-File Report 90- 

253, p. Gl-Gl8. 

Liu, He-P., and Peselnick, Louis, 1986, Improved phase-ellipse method 

for in situ geophone calibration: Geophysical Prospecting, v. 34, 

no. 4, p. 537-544. 

Liu, H.-P., Warrick, R.E., Westerlund, R.E., and Fletcher, JAB., 1991, A 

three-component borehole seismometer for earthquake seismology: 

Seismological Society of America Bulletin, v, 81, no. 6, p. 2458- 

2485. 

Menke, William, and Lerner-Lam, Arthur, 1991, Observations of the 

transition from linear polarization to complex polarization in shortperiod compressional waves: Seismological Society of America 

Bulletin, v. 81, no. 2, p. 611-621. 

O'Rourke, T.D., Gowdy, T.E., Stewart, H.E., and Pease, J.W., 1991, Life 

line and geotechnical aspects of the 1989 Loma Prieta earthquake: 

International Conference on Recent Advances in Geotechnical Engineering and Soil Dynamics, 2d, St. Louis, Mo., 1991, Proceedings, 

V. 2, p. 1601-1612. 

Papoulis, Athanasios, 1977, Signal analysis: New York, McGraw-Hill, 

431 p. 

Seale, S.H., and Archuleta, R.J., 1989, Site amplification and attenuation 

of strong ground motion: Seismological Society of America Bulletin, v. 79, no. 6, p, 1673-1696. 

Seed, H.B., and Idriss, I.M., 1970, Analyses of ground motions at 

Union Bay, Seattle, during the earthquakes and distant nuclear 

blasts: Seismological Society of America Bulletin, v. 60, no. 1. p. 

125-136. 

U.S. Geological Survey, 1990, Effects of the Loma Prieta earthquake on 

the Marina District, San Francisco, California: Open-File Report 

90-253. 
FIGURES 11-18 
SPECTRAL RATIO SPECTRAL RATIO 
MARINA DISTRICT 

FREQUENCY (Hz) 

Figure 12.-rn spectra of ground motion generated by two earthquakes (1, 5, table 1) that occurred close to 

each other for inline horizontal component (A) and perpendicular horizontal component (B) of surface seismometer, and for horizontal components HGl (C) and HG2 (D) of borehole seismometer. Dashed curves, earthquake 1; 

solid curves, earthquake 5. 
OBSERVATION OF LOCAL SITE EFFECTS AT A DOWNHOLE-AND-SURFACE STATION 

Figure 13.-Spectral ratios in response to east-bay (A, B) and south-bay (C, D) earthquakes for motions parallel 

to Divisadero Street (A, C) and Beach Street (B, D). 
MARINA DISTRICT 

I I 

0.05 cmls 

Figure 14.-Surface panicle motions projected onto a horizontal plane, as constructed from horizontal-component 

seismograms in Figures 3B and 3C. A, 0 to 3 s. 1, onset of P-wave arrival; 2, maximum of P-wave arrival. B, 3 

to 6 s. 1, onset of 5-wave arrival; 2, maximum of S-wave arrival. C, 6 to 9 s. D, 9 to12 s. 
OBSERVATION OF LOCAL SITE EFFECTS AT A DOWNHOLE-AND-SURFACE STATION 

FREQUENCY (Hz) 

Figure 15.-Spectral ratios calculated for an east-bay earthquake (6, table 1) and a south-bay 

earthquake (3, table 1) for motions parallel to Divisadero Street (A) and Beach Street (B). 

Dashed curves, earthquake 3; solid curves, earthquake 6. 
MARINA DISTRICT 

5 10 15 20 

FREQUENCY (Hz) 

Figure 16.-Spectral ratios of horizontal motions at surface to those in bedrock parallel to 

major (A) and minor (B) axes of bedrock basin underlying the Marina District, calculated for 

eight earthquakes listed in table 1. 
OBSERVATION OF LOCAL SITE EFFECTS AT A DOWNHOLE-AND-SURFACE STATION 

OO 

: 5 10 15 20 

FREQUENCY (Hz) 

Figure 17.-Spectral ratios in response to east-bay (A, B) and south-bay (C, D) earthquakes for motions 

parallel to major (A, Q and minor (B, D) axes of bedrock basin underlying the Marina District. 
MARINA DISTRICT 

5 10 15 

FREQUENCY (Hz) 

Figure 18.Ã‘Sit response for motions parallel to Divisadero Street (A) and Beach Street (B) generated 

by earthquake 1 in table 1, showing effects of uncertainty in borehole horizontal-geophone orientation 

An on calculated site response. 
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND FAILURE 

MARINA DISTRICT 

DETERMINATION OF' THE DYNAMIC SHEAR MODULUS 

OF HOLOCENE BAY MUD FOR SITE-RESPONSE ANALYSIS 

CONTENTS 

By Harry E. Stewart and Ashraf K. Hussein, 

Cornell University 

Page 

m5 

75 

76 

76 

7 8 

78 

79 

80 

80 

8 1 

82 

82 

82 

ABSTRACT 

The earthquake caused severe damage in many parts 

of San Francisco that are underlain by deposits of soft 

Holocene bay mud. The damage was partly due to the amplification of bedrock motions through the soft deposits. 

Site-response analyses can be used as aids in understanding the interactions between local site conditions and 

earthquake motions, but such analyses depend on an accurate characterization of the dynamic soil properties. One of 

the critical aspects of soil modeling is the relation between 

dynamic shear modulus and shear strain. 

We performed a series of laboratory tests on specimens of Holocene bay mud recovered from depths of approximately 10 to 20 m below the ground surface, near the 

intersection of Mission Street and the Embarcadero Skyway. We conducted one-dimensional consolidation tests, 

using instrumented lateral-stress membranes to determine 

the relationship between the coefficient of horizontal soil 

stress (KO) and overconsolidation ratio (OCR), so that 

specimens later could be consolidated anisotropically in a 

resonant-column/torsional-shem (RCflS) system while 

maintaining zero lateral strain. Large specimens of bay 

mud then were consolidated anisotropically in the RCRS 

system to OCR's of 1, 2, and 4. The stress ratios used to 

maintain zero lateral strain were determined from the KOOCR relation. The shear moduli then were evaluated, using 

both RC methods for small strains and TS methods for 

larger strains. We present data for evaluating the low-amplitude shear modulus (Gmm) on the basis of void ratio (e), 

OCR, and mean effective stress. The shear-modulus-reduction curves obtained in this study agree reasonably well 

with previously reported results for OCR=l and OCR=2; 

shear moduli were found to decrease more rapidly for 

OCR=4. 

INTRODUCTION 

The aim of this study is to develop relations for the normalized shear modulus of Holocene bay mud for stress 

states representative of those in situ. Specimens of bay 

mud were consolidated one-dimensionally to determine the 

overconsolidation ratio (OCR), and to evaluate the coefficient of horizontal soil stress (KO) as a function of the 

OCR. Specimens were KO-consolidated over a range of 

OCR's, and the dynamic shear moduli were determined, 

using a resonant-colum/torsional-shear (RCflS) system. 

The KO-OCR relation for Holocene bay mud is presented 

here, along with laboratory values of the small-strain shear 

modulus (Gmm). Simplified relations are presented to estimate Gmax on the basis of readily obtainable soil and site 

properties. Finally, modulus-reduction curves are presented 

for bay mud. The shear-modulus-reduction curves are compared with those obtained by other workers. 

The Holocene bay mud used in this study was recovered 

from a boring made near the intersection of Mission Street 

and the Embarcadero Skyway near the northeast end of 

Market Street. The samples were obtained from 76.2-mmdiameter Shelby tubes with an Osterberg sampler. The soil 

tested is classified as clay of low plasticity (CL) in the 

Unified Soil Classification System, with a liquid limit of 35 

percent, a plastic limit of 22 percent, and a plasticity index 

of 13 percent. The average natural water content (by 
MARINA DISTEUCT 

weight) was 47 percent. The average bulk unit weight was 

17.08 kN/m3, and the specific gravity was 2.70. 

EVALUATION OF KO 

The in sit^ coefficient of horizontal soil stress, KO, depends on the loading and unloading sequences, or stress 

history9 that the soil has undergone. In general, KO is difficult to determine in situ because the stress history of the 

soil may be unknown or complex. For level ground, the 

effective vertical stress (Ev) is equal to the total overburden stress minus the pore pressure. This Zv value can be 

quite easily and accurately determined from in situ measurements of density and level of the water table. However, 

the effective horizontal stress (Gh) depends on the stress 

history of the deposit and cannot be measured directly 

without special field equipment or laboratory testing. 

The variation in effective vertical and horizontal stresses 

for soil beneath level ground subjected to a simplified 

stress history that includes primary loading, primary unloading, and primary reloading is illustrated in figure 1. 

For primary or virgin loading, the soil is normally consolidated, and Ko=Konc. This KO value generally is assumed to 

be constant over a wide range of stresses, represented by 

the segment 0-A-B. Unloading from the normally consolidated state, termed "primary unloading," is represented by 

the concave-downward segment B-C-D. Upon unloading, 

both Sv and E,, decrease, and the soil becomes increasingly 

overconsolidated. However, since the soil element is confined laterally by the surrounding soil, these stresses do 

not decrease in direct proportion to each other, or by the 

same ratio, as in primary loading. For primary unloading 

Ko=Kopu, and KO increases with increasing overconsolidation. Upon reloading, 5" and Eh increase again, and the 

soil approaches a normally consolidated state. Reloading 

from the minimum stress state, termed "primary reloading," is represented by the concave-upward segment D-E. 

Figure 1.-Effective horizontal stress (Gh) versus effective vertical stress 

(ZV)* showing stress paths for simple stress histories (after Mayne and 

Kulhawy* 1982). See text for explanation. 

Table 1 .-Characteristics of wire-reinforced membranes 

Membrane : 

Wire reinforcement: 

Wire diameter (m)----------------------------O 15 

Center-to-center spacing between wires (m)---0.5 

Height of wire windings (nun)------------------30 

Youngf s modulus of Constantan (kPa) - - - - - - - - - - -1.52~10~ 

Tensile strength of Constantan (kPa) - - - - - - - - - - 5.7x105 

Instrumentation: 

Electrical resistance (n)-------------------- -=I38 

Maximum excitation voltage (V)----------------2 

For primary reloading, Ko=Kopr, and KO decreases with decreasing overconsolidation. Beyond point B, the soil becomes normally consolidated again, and Ko=Konc. The 

reloading, curve is expected to join the virgin-loading 

curve at point B. 

KO TESTING OF' HOLOCENE BAY MUD 

Horizontal stresses are directly measurable in the laboratory with a direct-simple-shear (DSS) device, using a calibrated, wire-reinforced rubber membrane that acts on a 

strain-gage principle. This method was used by Dyvik and 

others (1981) to measure horizontal stresses in soft marine 

clays. The measurements of horizontal stress obtained during consolidation loading and unloading were used to determine the KO-OCR relation. 

In this procedure, a Constantan wire-reinforced membrane was calibrated by applying known air pressures to 

the instrumented membrane and measuring the resulting 

change in the electrical resistance of the wires. The specifications for the calibrated wire-reinforced membranes 

used with the Norwegian Geotechnical Institute (NGI) 

DSS device are listed in table 1. The radial stiffness of the 

membranes generally is regarded as high enough that lateral expansion can be ignored, although it has been argued 

(Saada, 1984) that the reinforcement is insufficient to 

maintain a KO condition. The pressure was applied to the 

membrane through an aluminum cylinder surrounded by a 

rubber bladder that was used to disperse the concentrated 

flow of air released from the holes. The membrane was 

secured to the rubber bladder and cylinder with rubber 

strips and hose clamps placed adjacent to the wire reinforcement. A mechanical air-pressure regulator was used 

to manually cycle the pressure over a 5-minute timespan; 

the pressure was cycled between ambient pressure and ap- 
DETERMINATION OF THE DYNAMIC SEAR MODULUS OF HOLOCENE BAY MUD FOR SITE-RESPONSE ANALYSIS F77 

proximately 140 kPa several times to define any difference 

in behavior due to unloading or reloading. 

The amplifier system used was a Measurements Group, 

Inc., model 2130 strain-gage-conditioning amplifier. The 

bridge system included a two-arm Wheatstone bridge 

composed of an active membrane, a passive membrane, 

and two precision resistors (within the amplifier) to complete the bridge, as shown in figure 2. The membrane used 

to measure horizontal stress is the active membrane; the 

passive membrane is an identical membrane used to complete the circuit and provide temperature compensation. A 

typical membrane-calibration curve is shown in figure 3. 

The curve is nearly a straight line, but the zero-pressure 

reading does not coincide with the origin, as shown by the 

intercept, because an initial pressure is required to seat the 

bladder against the membrane. The slope, not the intercept, is important for the calibration; the slope was determined by linear regression. 

Each calibration consisted of a loading followed by at 

least one unloading-reloading cycle. The difference between the slopes of the unloading and reloading segments 

was less than 1 percent. However, the slope of the loading 

Precision 

resistors1 

Excitation 

voltage 

(max 2V) 

Active 

membrane 

-138A-l 

Amplifier 

Figure 2.-Schematic diagram of bridge amplifier system. 

Passive 

membrane 

-138A-l 

0 20 40 60 80 I00 I20 I40 

Applied Air Pressure (kPa) 

Figure 3,-Membrane output voltage versus applied air pressure, showing calibration curve. 

portion differed slightly; this behavior during initial loading was attributed to seating of the membrane. The calibration value used for the consolidation tests, called KO 

tests, was the average value between the curves. 

Additional calibrations were performed after KO tests to 

identify any change in membrane performance due to testing. No significant differences were observed. In addition, 

there was no evidence of creep or drift in the horizontal 

stress measurements over time. To minimize temperature 

effects, the passive membrane was placed within a few 

centimeters of the specimen, a temperature-compensating 

circuit was used, and constant laboratory temperature was 

maintained, 

A specimen was trimmed from a 76.2-mm-diameter 

Shelby tube sample recovered from a depth of 10.7 to 11.4 

m. The specimen was then consolidated incrementally. Beyond the maximum past pressure (&,,), unload-reload-unload cycles were applied. The variations in effective 

horizontal and vertical stresses measured during a KO test 

are plotted in figure 4. When the soil was removed from 

the ground, the confining stresses were released, and the 

soil underwent unloading. Recompression occurred during 

the initial stages of consolidation until the preconsolidation pressure was reached. This recompression is shown in 

figure 4 by the concave-upward segment from the origin 

to point A. Beyond the preconsolidation pressure, segment 

A-B represents primary loading. Along this stress path, 

the soil is normally consolidated (OCR=l), and the horizontal-stress coefficient is KOnc. Along segment B-C, 

which represents primary unloading, the OCR is increasing, and the horizontal-stress coefficient is Kopu. Along 

segment C-B', which represents primary reloading, the 

OCR is decreasing, and the horizontal-stress coefficient is 

Vertical Stress, 6" (kPa) 

Figure 4,-Effective horizontal versus effective vertical stress during KO 

loading and unloading. See text for explanation. 
F78 MARINA DISTRICT 

Kopr. Note that Kopu and Kopr are changing continuously as 

the OCR changes. After point B', segment B1-D followed 

the primary-loading curve. The specimen finally was unloaded to point E. 

The relation between the effective horizontal and vertical stresses for primary loading during a KO test is shown 

in figure 5. Using linear regression through the origin, the 

equation of the curve is: 

where zh is^ the effective horizontal stress and Ev is the 

effective vertical stress. Equation 1 indicates that KO,,== 

0.62. 

The Kopu-OCR relation (fig. 6) can be expressed by 

The general form of equation 2 has been used frequently 

by other workers (for example, Schmidt, 1966). 

The regression intercept in equation 2 represents the KO 

value for OCR=l. The agreement between the two fitted 

data sets for OCR=l indicates that KonC=0.62 for Holocene 

bay mud and that equation 2 is reasonable for evaluating 

KO for primary unloading. The tests conducted in this 

study did not generate sufficient data to develop equations 

for Kopr. 

OEDOMETER TESTS 

The purpose of the oedometer tests was to determine the 

maximum past pressure (Gv,,,) for a specimen before testing in the RCRS system, to ensure that the RCRS specimens would be consolidated to stresses greater than Gvm 

I00 200 300 

Vertical Stress, eV (kPa) 

and then rebounded to controlled 0CR7s. The oedometer 

specimens were trimmed from the tube sample directly 

above the RCRS specimen. The original plan was to perform an oedometer test for each RCRS specimen; however, the results from six oedometer tests indicated little 

variation in the results, and so additional testing was discontinued. Specimen depth, initial void ratio (eo), OCR, 

compression ratio (CR), and recompression ratio (RR) 

from these oedometer tests are listed in table 2. 

=SONANT-COLUMN1 

TORSIONAL-SHEAR APPARATUS 

RCRS tests were conducted separately to measure the 

dynamic soil properties over a wide range of shear strain. 

The use of two types of equipment requires two different 

specimens, which may have different properties. When using two separate systems, it may be difficult to obtain 

overlap between the results from the low-strain RC tests 

and the higher strain TS tests. This limitation is significant 

when investigating the reduction in shear modulus as a 

function of strain amplitude, or in determining the strain 

level at which pore pressure begins to build up. These 

drawbacks led to the design of a hybrid device, combining 

RC and TS, that allows the determination of dynamic 

properties over the entire range of shear strain that is of 

engineering interest. 

The RCRS apparatus used in this study was designed by 

Soil Dynamics Instruments, Inc. This apparatus, shown 

schematically in figure 7, can test solid or hollow speci- 

= 0.62 OCR 0.58 

OCR 

Figure 5.-Effective horizontal versus effective vertical stress for primary 

loading. See text for explanation. 

Figure 6.-KO versus overconsolidation ratio (OCR) for primary 

unloading. 
DETERMINATION OF THE DYNAMIC SHEAR MODULUS OF HOLOCENE BAY MUD FOR SITE-RESPONSE ANALYSIS F79 

Table 2.-Results of oedometer tests on Holocene bay mud 

[CR, compression ratio; eo; initial void ratio; OCR, overconsolidation ratio; RR, recompression ratio; Zvm, 

maximum past pressure; Eva, in situ effective vertical stress] 

Sample %o %I 

depth (m) 1 !? o (kPa) OCR CR RR 

 average-------^-------------------------------- -0,207 

Coefficient of variation (percent)--------:----- 3.7 

mens, consolidated either isotropically or anisotropically. 

The dynamic and quasi-static loadings are controlled independently and may be applied simultaneously, Quasi-static 

loading may be monotonic or cyclic, using strain or stress 

control. The pneumatic axial loader was added so that anisotropic consolidation stresses could be controlled more 

accurately. 

A Hardin oscillator was used to apply sinusoidal torsional vibrations. The large inertia mass of the oscillator provides a fixed reaction. The maximum shear strain that can 

be generated in the RC is approximately 1.5~ percent, 

I depending on specimen geometry. 

Displacement 

transducer 

Axial loader 

Stepper-motor Piston-adjusment yoke 

A quasi-static torsional load can be applied to the specimen by a torque motor system mounted on the pressurechamber lid. The motor system consists of a stepper 

motor, rotary table, and sprockets located on the top of the 

rotary table and on the piston, which are linked by two 

plastic-coated wire chains. The piston passes through the 

chamber lid and is fixed rigidly to the Hardin oscillator, 

which is fastened to the top platen by a special coupling. 

The applied torsion passes through a cam assembly, the 

upper platen, the specimen, and axial-load transducer, and 

is measured with a torque transducer mounted under the 

pressure-chamber base. The relative rotation between the 

bottom and top of the specimen is measured by two noncontacting displacement transducers located on a cylindrical platform. The maximum rotation is approximately 30' 

in either direction. 

TESTING PROCEDURES 

system 

Proximity 

transducers 

Pressure 

chamber - 

Load shaft 

Hardin oscillata 

Cams 

Platform 

Specimen 

Load cell 

8 4 ..., 1 

Torque transducer Differential pressure 

transducer I I I 

Base plate 

-Concrete block 

Figure 7.-Schematic diagram showing resonant-column/torsional-shear 

apparatus. 

Undrained RCRS KO tests were performed to study the 

dynamic properties of Holocene bay mud. A total of 18 

RC and 24 TS tests were carried out on undisturbed specimens for this study. Typical testing procedures were as 

folIows. 

1. Undisturbed specimens were trimmed from the Shelby 

tubes. 

2. Backpressure was used to ensure full saturation of the 

specimens. While maintaining the 'effective confining 

pressure at 50 kPa, both cell pressure and backpressure 

were increased in 35-kPa increments, allowing time for 

equalization at each stage. Full saturation was assumed 

to be achieved when the value of Skempton's B parameter was at least 0.96 or greater; a backpressure in the 

range 300-400 kPa generally was required to satisfy 

this condition. - - 3- After saturation at ov=o,,=50 Wa, the specimens were 

consolidated anisotropically to the required effective 

vertical stress (Gv) and effective horizontal stress (E,,) 
F80 MARINA DISTRICT 

(effective confining pressure). Each specimen initially 

was normally consolidated (OCR=l), with $Ov=0.62. 

During this consolidation phase, the axial loads were 

adjusted by using the pneumatic loader mounted above 

the load shaft. Overconsolidation was achieved by increasing Gv and 6 with Ko=0.62 (OCR=l) and then reducing these stresses to achieve the desired OCR. The 

results from the KO tests were used to determine o., and - 

(Jh during unloading to the desired OCR's. A value of - (Jh/o=0.93 was used for unloading to OCR=2, and of - ohhv=l .40 for further unloading to OCR=4; these values were determined from the test results given by 

equation 2. The stress paths used for obtaining different 

OCR's under KO conditions are shown in figure 8. 

4. The changes in the axial length and the volume of the 

specimens were monitored during consolidation. During 

consolidation and rebound, and 5 were adjusted to 

the KO values for primary loading and primary unloading determined from the tests made with the lateralstress membranes in the DSS device. If the true KO 

values were achieved in the RC/TS system, then the axial strains should equal the volumetric strains. The axial 

and volumetric strains measured from the RCITS consolidation and rebound phases are shown in figure 9. 

The excellent agreement of the results indicates that the 

KO-OCR relation determined by using the lateral-stress 

membranes is appropriate. 

5. After the end of primary consolidation, the drainage 

lines were closed, and the shear modulus was determined by using the RC. These tests provided shear 

moduli at single-amplitude shear strains ranging from 

2~10-~ to 7~10-~ percent. 

Vertical Stress, 5-,, (kPa) 

Figure 8.-Effective horizontal versus effective vertical stress for various OCR's in resonant-column/torsional-shear tests. 

6. After the RC tests, one cycle of strain-controlled TS 

testing was carried out at a higher strain level, with a 

constant strain rate of 0.3 percent/min. The data from 

this test were used to determine the shear modulus at 

this higher shear-strain level. 

7. Finally, the apparatus was disassembled, final specimen 

dimensions were measured, and the water content was 

determined. 

TEST RESULTS 

The test results are summarized in table 3. The data 

were reduced using the equations recommended by Chen 

and Stokoe (1979) and Isenhower and others (1987), 

which take into account nonlinear stress-strain behavior. In 

table 3, Gmax is the modulus for a shear strain of about104 

percent. 

DETERMINATION OF GmÃ§ 

Hardin and Drnevich (1972) proposed the following 

equation to calculate the low-amplitude shear modulus, 

Gmm, for cohesive soils: 

where K is a parameter related to the plasticity index, 

OCR is the overconsolidation ratio, 5 is the effective 

mean stress, e is the void ratio (not to exceed 2), and pa is 

atmospheric pressure. However, the shear moduli calculated from this equation with K=0.13 (plasticity index, 13 

5 6 7 8 9 10 I I 

Volumetric Strain (percent) 

Figure 9.-Axial and volumetric strain from consolidation and rebound. 
DETERMINATION OF THE DYNAMIC SHEAR MODULUS OF HOLOCENE BAY MUD FOR SITE-RESPONSE ANALYSIS F8 1 

Table 3.-Results of resonant-column/torsional-shear tests 

[e, void ratio; G, shear modulus; Gmax, low-amplitude shear modulus; OCR, overconsolidation ratio; ycy cyclic shear strain; 

Oh, effective horizontal stress; o,,, effective vertical stress] 

^v Bh %ax ^CY G 

Test OCR (kPa) - e (Mpa) (percent) (~ia) 

percent) were found to be 30 to 40 percent higher than 

those measured in the RC tests. Regression was used to fit 

an empirical equation to the measured values. The general 

form of the predictive equation was kept the same so that 

comparisons between the two equations would be clearer. 

The results of this regression on the Holocene bay mud 

data are given by 

The coefficient of determination (r2) for this regression is 

0.95, indicating that this equation fits the measured values 

very well. The relation between the backcalculated values 

of Gmax for bay mud, using equation 4 and the measured 

values of GmaX, isplotted in figure 10. 

In equation 4, is the mean effective stress, which can 

be written as 

By substituting the relations for KO presented previously, 

equation 4 can be expressed as 

Note that equations 4 and 6 represent laboratory test results. In the field, the effects of secondary compression or 

aging must be taken into consideration, as explained by 

Anderson and Stokoe (1978). 

SHEAR-MODULUS REDUCTION 

The relation between the normalized shear modulus, 

GIGmax, from the RC/TS tests and the cyclic shear strain 

Test number 

gcFJ 

0 I 

0 2 

Measured Emax (kPo) 

Figure 10.Ã‘Calculate versus measured Gmax value. 
F82 MARINA DISTRICT 

(y) is shown in figure 11. For OCR=l and OCR=2, 

GIGmax-1.0 until the cyclic shear strain exceeds 0.001 percent. At OCR=4, the apparent threshold cyclic-shear-strain 

level is approximately 0.0001 percent. 

The normalized shear moduli are nearly the same for 

OCR=l and OCR=2, but lower for OCR=4. This increased 

degradation for OCR=4 is at variance with the results for 

the effects of stress history obtained by Kokusho and others (1982) and Dobry and Vucetic (1987), possibly because of the differences in material structure and 

composition of the other soils. 

For purposes of comparison, Isenhower and Stokoe's 

(1 98 1) normalized shear-modulus-reduction curve for San 

Francisco bay mud at Hamilton Air Force Base, and that 

of Stokoe and Lodde (1978) at the Dumbarton Bridge, are 

plotted along with the curves obtained in this study in figure 12. The results of this study indicate smaller threshold 

strain limits than those reported by other workers. 

shear modulus increases with increasing effective mean 

stress. However, the effective mean stress has a negligible 

effect on the GIGmax-strain relation. For tests in which the 

effective mean stress was approximately the same, the 

shear modulus increased with increasing OCR. The laboratory test results were compared with the frequently used 

formulation of Hardin and Drnevich (1972) for cohesive 

soils, which predicts shear moduli about 30 to 40 percent 

higher than the measured values. An empirical relation for 

bay mud was developed that accounts for stress-history effects by including KO as dependent on the OCR. The Gmax 

value determined from these laboratory tests will be substantially smaller than the in situ value because of aging 

effects, which were not evaluated in this study, but are 

recognized as significant for San Francisco bay mud (Lodde, 1979). The modulus-reduction curves obtained in this 

study agree reasonably well with previously reported results for bay mud but indicate that the effects of the OCR 

may be significant. 

CONCLUDING REMARKS 

We have presented laboratory test data on the values of 

KO, Gmax, and GIGmax for Holocene bay mud. The KO 

values are consistent with trends identified for general 

stress-history effects. The specific KO values determined 

for various OCR's were used to control the anisotropicconsolidation stresses in the RC7TS tests. Measurements 

of axial and volumetric strains during primary loading and 

unloading confirmed that the KO values determined from 

the calibrated lateral-stress membranes are reasonable. 

Laboratory measurements of Gm, using RC/TS techniques, indicate that, for a given strain level and OCR, the 

ACKNOWLEDGMENTS 

This study was sponsored in part by National Science 

Foundation grant BCS-90 1 1458. A. Avcisoy and K.J. Stewart, who prepared the drawings and manuscript, respectively, are duly recognized for their skills and contributions. 

REFERENCES CITED 

Anderson, D.G., and Stokoe, K.H., 11, 1978, Shear modulus; a time-dependent soil property, in Dynamic geotechnical testing: American 

Cyclic Shear Strain (percent) 

Figure 11.-Normalized shear modulus versus cyclic shear strain. 

Dumbarton Bridge 

(Stokoe and Lodde, 1978) 

Figure 12.-Curves of normalized shear modulus versus cyclic shear 

strain obtained in this study in comparison with those from previous 

studies. 

0 

z 

0 

- 

a~~~~J n~~~J a n*laJ I t~~~~J laa*L 

0.00001 0.0001 0.001 0.01 0. I I 

Cyclic Shear Strain (percent) 
DETERMINATION OF THE DYNAMIC SHEAR MODULUS OF HOLOCENE BAY MUD FOR SITE-RESPONSE ANALYSIS F83 

Society for Testing and Materials Special Technical Publication 654, 

p. 66-90. 

Chen, A.T.F., and Stokoe, K.H., 11, 1979, Interpretation of strain-dependent modulus and damping from torsional soil tests: Men10 Park, 

Calif., U.S. Geological Survey Report USGS-GD-79-002 (NTISPB-298749/AS), 45 p. 

Dobry, Ricardo, and Vucetic, Mladen, 1987, State-of-the-art report; dynamic properties and response of soft clays: International Symposium on Geotechnical Engineering of Soft Soils, 1987, Proceedings, 

v. 2, p. 51-87. 

Dyvik, Rune, Zimmie, T.F., and Floess, C.H.L., 1981, Lateral stress 

measurements in direct simple shear device, in Laboratory shear 

strength of soil: American Society for Testing and Materials Special 

Technical Publication 740, p. 191-206. 

Hardin, B.O., and Drnevich, V.P., 1972, Shear modulus and damping in 

soils: design equations and curves: American Society of Civil Engineers Proceedings, Soil Mechanics and Foundations Division Journal, v. 98, no. SM7, p. 667-692. 

Isenhower, W.M., and Stokoe, K.H., 11, 1981, Strain rate-dependent modulus of San Francisco Bay Mud: International Conference on Recent 

Advances in Geotechnical Earthquake Engineering and Soil Dynamics, St. Louis, Mo., 1981, Proceedings, v. 2, p. 597-602. 

Isenhower, W.M., Stokoe, K.H., 11, and Allen, J.C., 1987, Instrumentation for torsional shearlresonant column measurements under 

anisotropic stresses: Geotechnical Testing Journal, v. 10, no. 4, 

p. 183-191. 

Kokusho, Takeji, Yoshida, Yasuo, and Esashi, Ysuyuki, 1982, Dynamic 

properties of soft clay for wide strain range: Soils and Foundations, 

v. 22, no. 4, p. 1-18. 

Lodde, P.F., 1979, Shear moduli and material damping of San Francisco 

Bay Mud: Austin, University of Texas, M.S. thesis. 

Mayne, P.W., and Kulhawy, F.H., 1982, KO-OCR relationships in 

soil: American Society of Civil Engineers Proceedings, Geotechnical Engineering Division Journal, v. 108, no. GT6, p. 

85 1-872. 

Saada, A.S., 1984, Discussion; specimen size effect in simple shear test: 

Journal of Geotechnical Engineering, v. 110, no. 3, p. 445-447. 

Schmidt, Birger, 1966, Discussion; earth pressures at rest related to 

stress history: Canadian Geotechnical Journal, v. 3, no. 4, p. 

239-242. 

Stokoe, K.H., 11, and Lodde, P.F., 1978, Dynamic response of San Francisco Bay Mud: American Society of Civil Engineers Conference on 

Earthquake Engineering and Soil Dynamics, Pasadena, Calif., 1978, 

Proceedings, v. 2, p. 940-959. 
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND FAILURE 

MARINA DISTRICT 

SITE-RESPONSE ANALYSES 

By J.-P. Bardet, M. Kapuskar, G.R. Martin, and J. Proubet, 

University of Southern California 

CONTENTS 

[Figures 19-23, 28-35, and 38-53 follow references] 

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104 

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112 

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113 

ABSTRACT 

We have analyzed the site response of the Marina District of San Francisco during the earthquake, using numerical-modeling techniques that encompass the conventional 

methods used in engineering practice, as well as advanced 

techniques capable of accounting for three-dimensional geometry and wave propagation. Our models are based on a 

synthesis of the geology of the Marina District with data 

from various site investigations. 

Nonlinear one-dimensional analyses with the computer 

programs DETRAN and LINOS predict peak ground-surface accelerations of 0.12 and 0.15 g in the Marina District 

for the Yerba Buena accelerogram with bedrock peak accelerations of 0.067 g (original) and 0.15 g (scaled), respectively. The program SHAKE predicts a larger 

amplification, reflecting the use of an equivalent linear material model that does not consider complete failure. The 

Yerba Buena Island accelerogram was assumed to be the 

most realistic input record because its peak acceleration of 

0.067 g agrees with the accelerations recorded on bedrock 

sites in the San Francisco Bay area. The amplification of 

bedrock acceleration resulted mainly from deep deposits of 

older bay mud. The accelerations reaching the layer of yellow hardpan were truncated by yielding of the overlying 

layers composed of artificial fills and younger bay mud. A 

F85 
F86 MARINA DISTRICT 

simplified liquefaction analysis clearly indicated that the 

artificial fills would liquefy during the earthquake. 

For comparison with the one-dimensional analyses, we 

also performed two types of two-dimensional site-response 

analyses using numerical methods that are not commonly 

used in engineering practice. The first type assumed a uniform input for the ground motion along the model boundary, whereas the second type assumed nonuniform inputs 

along the model boundary in an attempt to account for the 

effects of wave propagation on the dynamic response of the 

Marina District. These two-dimensional analyses predicted 

peak ground-surface accelerations of 0.20 and 0.23 g for 

peak bedrock accelerations of 0.067 and 0.15 g, respectively. The two-dimensional analyses predicted larger peak accelerations than the one-dimensional analyses, indicating 

that the one-dimensional site-response analyses used in engineering practice may not necessarily be conservative. 

Our analyses indicate that two-dimensional effects are 

important in the site response of the Marina District. 

These two-dimensional effects resulted mainly from the irregular geometry of the bedrock and the yellow hardpan. 

Inclusion of wave-propagation effects into the site-response analyses substantially complicates the dynamic-response analyses; however, these effects were more 

noticeable in linear than in nonlinear analyses. The present 

study shows the complexity of site-response analyses for 

three-dimensional geologic structures and clearly indicates 

that future research is needed on this topic. 

INTRODUCTION 

The 1989 earthquake was the largest to occur in the San 

Francisco Bay area since the catastrophic San Francisco 

1 

EXPLANATION 

Liquefaction sand boils 

- Tension crack Landfill Volume< 1 m3 

- Buckling of sidewalk 0 Volume > 1 m3 

[ZI3 Building destroyed 1 Lagoon in 1906 0 Data of Bennett, 1990 

Figure 1.-Sketch map of study area in the Marina District, showing results of field investigation of October 

1989. 
SITE-RESPONSE ANALYSES F87 

earthquake of 1906. About 40 buildings were destroyed or 

condemned in the Marina District, 108 km away from the 

epicenter. Disruption of the ground underlying the Marina 

District caused vertical settlement and lateral displacement 

of most buildings, as well as buckling of sidewalks, cracking of asphalt pavements, and breakage of underground 

pipes (Bardet and Kapuskar, 1991c and in press). 

This report investigates the site response of the Marina 

District during the 1989 earthquake by using numericalmodeling techniques of site response, including conventional analyses and advanced nonlinear finite-element 

methods. Our objectives are to describe the dynamic response of the Marina District by applying the site-response analyses used in engineering practice, and to 

complete these analyses by using advanced techniques capable of accounting for two- and three-dimensional geometry and wave-propagation effects. 

OBSERVATIONS ON SAND BOILS 

AND STRUCTURAL DAMAGE 

Besides structural collapse, one of the most striking 

phenomena recorded in the Marina District during the 

earthquake was the abundant ejection of water and finegrained sand from the ground. These observations are only 

briefly described here; a more complete description was 

given by Bardet (1990a) and Bardet and Kapuskar (1991c 

and in press). 

A few days after the earthquake, a reconnaissance team 

from the University of Southern California (USC) visited 

the Marina District and collected data on sand boils. The 

study area (fig. 1) is bounded by Baker Street, Fillmore 

Street, Marina Boulevard, and Lombard Street. Sand boils 

were highly visible on the concrete floors of buildings and 

on sidewalks. A few days after the main shock, access to 

the study area was still limited, a circumstance that was 

unintentionally beneficial to our research: The police protection preserved perishable sand boils that otherwise 

would have been cleaned up by Marina District residents. 

One of the largest sand boils covered a 29-m2 area (fig. 

2). It emerged through a backyard lawn, flowed through a 

wooden fence, and completely covered a neighboring backyard. The sand-water mixture, which emerged through two 

large craters, must have been under high pressure to have 

created such large orifices. A large volume of water also 

was evidently expelled from the ground so as to transport 

the large amount of deposited sediment. Abundant mud and 

silt littered the periphery of the sand volcanoes. 

We recorded a total of 74 sand boils in the study area 

(fig. 1). Bennett (1990) reported 10 additional sand boils 

north of the study area (squares, fig. 1); 42 percent of 

Figure 2.-Large sand boils that covered two backyards in the Marina District during the earthquake (approx 

scale, 1 in.=2 m). 
F88 MARINA DISTRICT 

these sand boils were smaller than 0.2 m3 in volume. The 

cumulative volume of sand ejected during the earthquake 

exceeded 37 m3. The largest sand boil (3.5-m3 volume) 

completely flooded the backyard of an apartment building; 

the ejected sand was fine, dark gray, odorless, and accompanied by bay mud. In some places, sand seeped through 

the lawn and littered the grass and flowerbeds. Contrary to 

common belief, the sand boils were not caused by breakage of waterpipes or sewerpipes but by liquefaction of underlying soils. 

The sand boils did not completely cover the Marina District but surfaced mainly in the northeastern part, over a 

350- by 600-m area near the comer of Fillmore Street and 

Marina Boulevard (fig. 1). Without exception, all of the 

sand boils occurred over the site of a 1906 lagoon that was 

filled in 1915 to host the Panama-Pacific International Exposition. Lawson (1908, p. 404-405) reported severe 

ground shaking around this lagoon during the 1906 earthquake, even before the Marina District was built. In addition to sand boils, our survey also mapped evidence of 

superficial ground displacements, such as buckling of concrete sidewalks, rupture of curbs, and tension cracks in asphalt pavement. Our observations of ground displacements 

and major structural damage to buildings are summarized 

in figure 1. 

A superficial crack about 300 m long was observed in 

the middle of the Marina District, along the southeast side 

of the liquefied area. The lateral ground displacement was 

estimated to reach 30 cm, according to our measurements. 

Along this superficial crack, a major fire was ignited, and 

three apartment buildings located at street comers collapsed. Surprisingly, the collapsed buildings and large 

ground displacement were not close to the sand boils but 

about 100 m away (fig. 1). The damage was not directly 

caused by liquefaction of the sand underlying the foundation of the buildings, as was observed during the 1964 Niigata, Japan, earthquake (Seed, 1970). The ripples and 

undulations in the ground surface suggest that the liquefied sandy fills of the Marina District spread laterally and 

were forced down a gentle slope by gravity. The most severe structural damage took place along the edges of the 

liquefied area and resulted from differential displacements 

between the liquefied and nonliquefied soils (Bardet and 

Kapuskar, 1991c and in press). 

GEOLOGY OF THE MARINA DISTRICT 

We first summarize the geology of the Marina District 

because it is used to construct the model for site-response 

analysis (see Bonilla, this chapter, for details). The Marina 

District is located on the north waterfront of San Francisco, 

1 mi east of the Golden Gate Bridge, between the Presidio 

and Fort Mason (see fig. 1). The soils beneath the Marina 

District are divided into natural deposits and artificial fills. 

NATURAL DEPOSITS 

During the last 1 m.y. of the late Cenozoic glacial episode (3,500-15 ka), at least three glacial-interglacial cycles occurred in San Francisco Bay, each marked by a 

period of material deposition during high sea levels, followed by a period of desiccation and erosion due to lower 

sea levels (W.H. Hensolt, written comrnun., 1988). 

Between 1.8 and 0.7 Ma, when sea level was more than 

90 m lower than today, the Golden Gate channel was 

formed, and San Francisco Bay came into existence. As 

suggested by Schlocker (1974), the bedrock underlying the 

Marina District is composed of Franciscan assemblage 

eroded by waters of the ancient Sacramento and San Joaquin Rivers flowing through the Golden Gate channel 

about 1.5 Ma. 

The earliest stage of development of the Golden Gate 

channel and San Francisco Bay took place during the glacial-interglacial cycle that occurred between 1.0 and 0.5 

Ma, when unconsolidated estuarine sandy materials were 

deposited during high sea levels. These older materials 

consist of firm, orange to light-brown sand. 

During the most recent interglacial interval, the Sangamon stage of the Pleistocene Epoch (125-75 ka), thick, 

gray estuarine clay deposits containing interbeds of sand 

and shells were formed (Schlocker, 1974; Bonilla, 1990). 

These materials (also referred to as the older bay mud) 

cover virtually all of the deep soils and bedrock underlying the Marina District. 

Borehole logs from as early as 1912 (Schlocker, 1961) 

and more recent investigations (for example, Bennett, 

1990) have indicated that beds of dense sand cover the 

older clay deposits under the Marina District. These firm 

materials, the uppermost part of which are called the yellow hardpan, are assumed to be eolian deposits formed 

during the early part of the Altonian Glaciation (40-30 ka) 

that were subjected to surface erosion during the low sea 

level of the Wisconsin Glaciation. These hard strata, referred to as Pleistocene sand zones (Bonilla, 1990), are 

considered to be at least 10 ka old. 

After the Wisconsin Glaciation that ended some 10 ka, 

deposition of estuarine materials began on the site of the 

Marina District, owing to high sea levels flooding the 

Golden Gate channel. These materials (commonly referred 

to as the younger bay mud) consist of semiconsolidated, 

olive-gray, fine sand and clay that cover most the Marina 

District. 

ARTIFICIAL FILLS 

The shoreline of the Marina District is shown in figure 

1. By 1906, Marina Cove was enclosed by a seawall. The 

Panama-Pacific International Exposition of 19 15 had the 

largest environmental impact on the Marina District. A.H. 
SITE-RESPONSE ANALYSES F89 

Markwart, assistant director of works for the exposition, 

wrote in 1915 that the filling started on April 13, 19 12, 

along the shoreline to create solid land for the exhibition. 

The filling of the tidelands continued for 5 months, and by 

September 1915, 1 million m3 of sand and mud had been 

pumped into the area. Sand containing silt, gravel, debris, 

and organic waste mainly composed the material used for 

fill. According to Markwart, the fill was about 70 volume 

percent sand and 30 volume percent mud. A total of 46 ha 

(114 acres) of marshlands on the grounds of the Presidio 

were also filled for the exposition. "The fills proved satisfactory," Markwart wrote, "as the installation of roads and 

gardens, the work of pile driving, and construction of the 

Exhibition Palaces took place immediately upon completion of the fill, a procedure which was unusual (in 1912) 

in the case of many new fills." After the exposition closed, 

the area remained unused until the 1920's, when real estate development began in the Marina District. 

THREE-DIMENSIONAL SOIL MODEL 

The study area covers about 1.2 km2 between Lyon, 

Lombard, and Laguna Streets and the northern waterfront, 

including the St. Francis Yacht Club Harbor (fig. 3). 

Data on stratigraphy and soil properties were compiled 

to construct a three-dimensional soil model of the Marina 

District. On the basis of data compiled from 86 borehole 

logs, 10 geologic units were distinguished: Franciscan assemblage, serpentine (of the Franciscan assemblage), Colma Formation, late Pleistocene bay clay, Holocene bay 

clay, shells, beach sand, dune sand, tidal-marsh deposits, 

WEST-EAST X COORDINATE ON GREENWICH ST. (m) 

Figure 3.-Marina District, showing location of study area (box) and orientation of cross sections A-A' through D-D' in three-dimensional soil model. 
F90 MARINA DISTRICT 

and artificial fills. These units were grouped into four layers: (1) the late Pleistocene bay clay, above a bedrock surface of Franciscan assemblage; (2) the yellow hardpan; (3) 

Holocene bay clay, with traces of Holocene green sand; 

and (4) an upper layer of mixed silt-sand-gravel, beach 

sand, and dune sand. 

SITE INVESTIGATION IN SEPTEMBER 1990 

Deep-borehole logs were too scarce to provide sufficient 

information on the depth, thickness, and soil properties of 

the yellow hardpan and older bay mud, and so the purpose 

of the site investigation was to collect additional soil profiles and soil properties. The investigation included nine 

cone penetration tests (CPT's) and three downhole seismic 

CPT's. The CPT investigation was performed in September 

1990 by Earth Technology Corp. (1990), using a 20-ton 

system. 

To delineate the subsurface strata to the north of the 

study area, two CPT soundings were located on the Marina waterfront (boreholes C-1, C-5, fig. 4). Two downhole 

u SAN FRANCISCO BAY // 

seismic CPT's were performed in borehole C-1. To aid 

interpretation of the CPT results, an additional CPT 

sounding C-2 was performed in borehole C-2 in the center of the old Marina Cove, next to U.S. Geological Survey (USGS) borehole M4. The third seismic CPT, in 

borehole C-17, was located on the 1857 shoreline, where 

surficial dune sand occurs. 

Six soil columns interpreted from the CPT results are 

illustrated in figure 5. These columns were obtained after 

comparing the CPT results obtained in borehole C-2 

against the soil column in USGS borehole M4 (U.S. Geological Survey, 1990). Our interpreted soil columns in other places were found to match the borehole logs obtained 

by Dames & Moore (1977) and Harding Lawson Associates (written commun., 1990). 

The yellow hardpan was penetrated in boreholes C-1 

and C-5, where it was found to be less than 1.2 m thick. It 

was penetrated in borehole C-1 at a depth of 31 m, and in 

borehole C-3 at a depth of 27.7 m, 5 m below the depth 

predicted by Dames & Moore (1977). 

During the CPT investigation, problems arose with the 

sticky older bay mud. At borehole C-1, the CPT was terEXPLANATION 

A USC seismic CPT 

A USCCPT 

UCD and USGS boreholes 

St. Francis 

Yacht Club I 1 

Harbor Marina Green 

Fort 

Mason 

Figure 4.-Marina District, showing locations of boreholes and CPT soundings during site investigation of September 1990. 
SITE-RESPONSE ANALYSES 

minated 12 m below the yellow hardpan, owing to excessive sleeve friction; and in boreholes C-2, C-8, and C-12, 

penetration failed owing to rod buckling and high tip bearing resistance. In all the other boreholes, the dense sand 

layer was not reached, owing to sleeve friction in the hydraulic fill and (or) excessive probe inclination. 

UNDRAINED SHEAR STRENGTH 

The undrained shear strength Su in the older and younger bay muds was calculated from the tip resistance measured from the CPT soundings of the site investigation, 

using the method of Schmertmann (1975) with a bearingcapacity factor of 6, based on shear-strength correlations 

between CPT and vane shear tests (Denby, 1961; Martin 

and Tsai, 1981). The calculated Su values (fig. 6) were correlated with additional data from Schlocker (1974), Dames 

and Moore (1977), Denby (1978), Bonaparte and Mitchell 

(1979), Seed and Sun (1989), and Kayen and others 

(1990). The calculated profile of un-drained shear strength 

(fig. 6) is complex and varying; the Su value tends to increase with depth and jumps abruptly in the yellow hardpan and in the top 5 m, owing to the presence of debris. A 

highly simplified shear-strength profile was used in the 

site-response analyses (fig. 6) to reduce the number of elements required in the two-dimensional models. For nonlinear site-response analyses, the Su values plotted in figure 6 

were increased to account for rapid-loading effects. The 

values of undrained shear strength T~~ in dynamic analyses were assumed to be 40 percent greater than the Su values in all soil layers except the top layer. An average Su 

value of 20 kPa was assumed for the saturated cohesionless fill and the younger bay mud above the yellow 

hardpan. Su was set to 160 kPa in the yellow hardpan, as 

in the deeper layers of the older bay mud, and to 100 kPa 

in the 30-m-thick layer of late Pleistocene bay clay underlying the yellow hardpan. 

3481 Pierce St. 

Hole 78 

(Schlocker, 

1961) 

Figure 5.-Soil columns interpreted from CPT results in boreholes, with references used for comparison. Soils are identified by 

symbols in Unified Soil Classification. 

3495 Divisadero 

St. 

Job 19738,001.04 

(Harding Lawson 

Associates) 

Marina Green 

Drive (extension 

of Fillmore St.) 

HSA-15 (Dames 

& Moore, 1977) 

701 Marina ~lvd 

(Broderick st.) 

HSA-3 (Dames & 

Moore, 1977) 

101 Cervantes 

M4 (USGS.90) 

BH-3A (UCD.90) 

location 

soil-column 

calibration 

3899 Scott St. 

HSA-23 (Dames 

& Moore, 1977) 
F92 MARINA DISTRICT 

WAVE VELOCITY 

Shear- and compressional-wave velocities were determined from three seismic CPT's performed in boreholes C1, C-5, and C-17. As plotted in figure 7, four zones can be 

distinguished from the interpreted shear-wave velocities. 

1. In the loose, unsaturated and unconsolidated, sandy and 

gravelly artificial fill, the velocities of shear and compressional waves are vs=290-415 m/s and vp=580-870 

m/s, respectively. The large variation in these velocities 

is attributed to the inhomogeneity of the artificial fill, 

which ranges widely in composition from silty sand and 

debris (borehole C-17, fig. 4), through clayey sand and 

scattered rock fragments near Fair's seawall (boreholes 

C-1, C-5, fig. 4), to wooden piles left over from the 

exposition. 

2. In the saturated, sandy artificial fill, the natural-sand deposits, and the Holocene bay clay, vS=120-225 m/s and 

vp=l,520-1,650 m/s. The lower range is confirmed by 

measurements (Kayen and others, 1990) in USGS borehole WSS (fig. 4), where vS=128-160 m/s. The higher vS 

value applies to more consolidated Holocene bay clay. 

3. In the yellow hardpan, vs=290-460 m/s. These velocities 

were measured in USGS borehole WSS in a layer of the 

EXPLANATION 

CPT, borehole C-1 

CPT, borehole C-3 

Shear strength 

used in analyses 

0 100 200 300 400 

Undrained shear strength, Su (kPa) 

yellow hardpan 11 m thick. The average vS value of 366 

m/s is similar to the values of 335 and 365 m/s selected 

in the dynamic analyses of Seed and Sun (1989). 

4. Below the yellow hardpan, vS>225 m/s and vP=l,740 

m/s. In borehole C-1, seismic CPT's were performed 

down to a depth of 43 m, about 10 m into the late 

Pleistocene bay clay. The vS values were found to be 

identical to those in the lowest parts of the Holocene 

bay clay. In the absence of other deep measurements of 

vS in the Marina District, the shear-wave velocities were 

supplemented by measurements in three other places: 

USGS borehole WSS (fig. 4), the Southern Pacific 

Building (approx 1.5 km southeast of the Marina District), and the Embarcadero Center (Seed and Sun, 

1989). In USGS borehole WSS, vS =265 m/s. At the 

Southern Pacific Building, where soil conditions are 

similar to those in the Marina District; vs was estimated 

at 335 m/s for a layer of stiff, consolidated (Pleistocene) clay 30 m thick. 

The shear-wave velocities measured in these other places and the velocity profile selected in our analysis are plotted in figure 7. This velocity profile was used to calculate 

the low-strain elastic-shear modulus Gmax in the site-response analyses. 

-w- Borehole C-1 

- Borehole C-5 

-.- Borehole C-17 

---*--- Southern Pacific 

Building 

----A --- Embarcadero site 

----A--- USGS borehole 

wss 

This analysis 

0 100 2 0 0 300 400 500 

Shear-wave velocity (mls) 

Figure 6.-Depth versus undrained shear strength in the study area. Figure 7.-Depth versus shear-wave velocity in the study area. 
SITE-RESPONSE ANALYSES 

'CONSTRUCTION OF 

THREE-DIMENSIONAL SOIL MODEL 

On the basis of a compilation of the borehole data, a 

four-layer model was constructed to represent the soils in 

the Marina District. Later, these basic material layers are 

further divided into elements when defining the finite-element meshes. This degree of accuracy is believed to be 

adequate for evaluating site-response characteristics. 

The three-dimensional model was developed from discrete borehole logs. It covers a horizontal area 1,500 by 

1,100 m and is composed of 1,152 nodes. It was constructed by identifying the top and bottom surfaces and three 

interfaces-that is, five surfaces-in all the available borehole logs. Each surface was generated by the elevation of 

nodes on a uniform grid of 16 by 12 nodes. Delaunay triangulation was used to interpolate the elevations of these 

evenly spaced nodes from the scattered data of borehole 

logs. In the process, erroneous identifications of soils were 

filtered, and the interface positions were smoothed. The 

layers were stacked in sandwich fashion without intersecting one another. The elevation of gridpoints was slightly 

adjusted by trial and error until interfaces stopped intersecting. Each surface and layer in the model are described 

below. 

GROUND SURFACE 

The ground surface constitutes the upper surface of the 

three-dimensional model. It was defined by 650 scattered 

elevation points digitized from USGS topographic maps 

(U.S. Geological Survey, 1973) inside a rectangular 4,000- 

by 3,000-m frame. A thre~e-dimensional model of the Marina District and its surroundings is shown in figure 8. 

BEDROCK SURFACE 

The bedrock surface constitutes the lower surface of the 

three-dimensional model. In geotechnical engineering, the 

definition of bedrock is generally subjective, closely dependent on the particular problems to be solved. In the 

Marina District, the bedrock was rather easily identified 

because a significant discontinuity could be located between superficial and deep sedimentary deposits. The bedrock underlying the Marina District is made up of 

serpentine and of sandstone and weathered shale of the 

Franciscan assemblage. A bedrock depression was inferred 

from (1) the distribution, size, and shape of nearby outcrops; (2) a few reliable deep boreholes; and (3) geologic 

considerations. 

Figure 8.-Three-dimensional model of ground surface in the study area. Short vertical segments represents boreholes used to generate model. 
F94 MARINA DISTRICT 

Our construction of the three-dimensional bedrock surface was made difficult by the absence of deep borehole 

data. At this date, only three boreholes have reached bedrock. High-resolution profiling based on geophysical seismic reflection would have been an appropriate technique 

to define the exact position of the bedrock; however, the 

limitations of this type of investigation in the presence of 

deep sedimentary deposits in a heavily urbanized area 

ruled out its use. 

Construction of the bedrock surface was also complicated by the presence of a layer of yellow hardpan 60 m 

above the true bedrock. This hard layer was misinterpreted 

as bedrock by several investigators (for example, Schlocker, 1961) who based their definition of bedrock on available geotechnical soundings. The error was discovered in 

the USGS map (Schlocker, 1974) after noting the anomaly 

in the bedrock contours east of Webster Street. 

The outcrops noted on the geologic map of Schlocker 

(1961) were useful in reconstructing the bedrock surface 

in the Marina District (fig. 9). The following bedrock outcrops surrounding the Marina District were included: at 

Fort Mason, on Russian Hill, on Nob Hill, around Lafayette Square (Fillmore Hill), at the intersection of Scott and 

Greenwich Streets, at Alta Plaza east of the Presidio, in 

the central part of the Presidio, and at Crissy Field. The 

bedrock depths determined in USGS borehole WSS and in 

UCD borehole BH-3A (at USGS borehole M4, fig. 4) 

were extremely useful to calibrate the bedrock depth. Old 

drillholes at the center of Funston Playground (fig. 3; U.S. 

Geological Survey, 1990) and south of the Palace of Fine 

Arts (fig. 3; Dames & Moore, 1962) were also included. 

Bedrock-elevation contours were obtained by interpolating (with a Delaunay triangulation) the scattered data of 

130 known and about 20 hypothetical elevations. The hypothetical elevations were obtained on the basis of geologic considerations, such as the gradients of bedrock 

drainage paths toward the Golden Gate channel, as shown 

in figure 9 (Schlocker, 1974; W.H. Hensolt, written commun., 1990). The bedrock surface is assumed to be a halfbasin surrounded by bedrock outcrops; it opens toward the 

bay on a northwestward trend. Under the Marina waterfront, the depression is bounded by the bedrock outcrops 

WEST-EAST X COORDINATE ON GREENWICH ST. (m) 

Figure 9.-Estimated bedrock contours and drainage paths in the Marina District. Coordinate system is defined in figure 3. Asterisks represent points 

(hypothetical or measured) used to draw contour lines. 
SITE-RESPONSE ANALYSES F95 

at Forts Mason and Scott. The depression is assumed to 

reach 87-m depth under Marina Boulevard. Offshore, the 

basin is bounded by the outcrop of Alcatraz Island to the 

far northeast (Schlocker, 1961), which is less than 2 mi 

from the Marina District, and by an underwater outcrop 

called Anita Rock (fig. 3; Carlson and McCulloch, 1970). 

during the 1980's. These deposits, which underlie the 

western part of the Marina District, formed old Strawberry 

Island, a sand spit in the northwest comer of the district. A 

small band of beach sand is situated south of Alhambra 

Street (fig. 4). Dune sand that probably covered the western beach deposits occurs mainly between Webster Street 

and Fort Mason. 

LATE PLEISTOCENE BAY CLAY (OLDER BAY MUD) 

THREE-DIMENSIONAL MODEL 

The late Pleistocene bay clay covers the bedrock under 

the Marina District; it reaches a thickness of about 60 m 

under Marina Boulevard between Scott and Fillmore 

Streets. Only a few deep boreholes were available to yield 

reliable information on this layer, which is assumed to be 

continuous and overlain by the yellow hardpan throughout 

the Marina District. 

YELLOW HARDPAN 

The top of the yellow hardpan was modeled on the basis 

of 74 borehole logs, and its bottom from 35 borehole logs; 

39 boreholes did not penetrate this layer. The yellow hardpan deepens toward the waterfront and rapidly dips down 

to below 28-m depth at borehole C-3 and to below 31-m 

depth at borehole C-1 (fig. 4). In comparison with other 

layers, the yellow hardpan generally is very thin (0.3-1.2 

m thick), although it thickens considerably (11 m) under 

the Palace of Fine Arts (fig. 3; Dames & Moore, 1962). 

HOLOCENE BAY CLAY (YOUNGER BAY MUD) 

The layer of Holocene bay clay was constructed from 87 

borehole logs. It extends landward past the 1869 shoreline 

from Fort Mason across Funston Playground (fig. 3) and 

under Lombard Street toward the Presidio. This layer has a 

fairly smooth top that could be explained by the absence of 

erosion since its deposition. A layer of hard green sand 

underlies the Holocene bay clay under most of the Marina 

District. 

TOP LAYER 

The top layer is composed of tidal-marsh deposits, beach 

sand, dune sand, and artificial fills. A band of tidal-marsh 

deposits occurs under the Presidio (at Crissy Field, fig. 3) 

and southwest of the Marina District between Scott and 

Fillmore Streets as far south as Lombard Street. These deposits contain organic clay and silt and some Holocene 

materials, such as bay mud and beach sand. The naturalsand deposits along the present shoreline east of the Golden Gate between Fort Point and Telegraph Hill are now 

overlain by artificial materials that were used for landfill 

A three-dimensional model of the ground and bedrock 

surfaces as seen from the waterfront is shown in figure 10. 

The elevation of the ground surface rises from 0 to about 

15 m (San Francisco city datum) near the shoreline in the 

southwestern part of the Marina District; southeast of the 

Presidio, the bedrock surface meets the ground surface. 

Soil profiles along four cross sections through the threedimensional model of figure 10 are shown in figure 11. 

Cross sections A-A' and B-B', which run north-south, have 

not been extended northward because of the absence of 

borehole logs in San Francisco Bay. The northern part of 

the three-dimensional model is therefore only approximately defined. Cross section C-C', which contains Beach 

Street, is used in a two-dimensional analysis of the site 

response. The bedrock eventually emerges at the ground 

surface if the widths of cross sections C-C' and D-D' are 

extended. 

Our three-dimensional soil model of the Marina District 

reveals that the bedrock and soil layers are not horizontal 

and uniform but have a complex three-dimensional configuration. Because the methods for treating multidimensional site response are still in a relatively early stage of 

development and evaluation, the three-dimensional model 

was not directly analyzed. However, two one-dimensional 

soil columns (in boreholes M4 and WSS, fig. 4) and one 

two-dimensional cross section (C-C', fig. 11) were extracted from the three-dimensional model and subjected to several types of site-response analyses. 

ONE-DIMENSIONAL 

SITE-RESPONSE ANALYSES 

We first examine the site response of the Marina District 

by using conventional one-dimensional analyses. 

PROGRAMS FOR ONE-DIMENSIONAL ANALYSIS 

Several computer programs for one-dimensional analysis 

of the effects of local soil conditions on ground response 

during earthquakes are presently available, for example, 

SHAKE (Schnabel and others, 1972), DETRAN (Chen 

and Joyner, 1974), DYSAC2 (Muraleetharan and others, 
F96 MARINA DISTRICT 

1990), DYNAlD (Prevost, 1989), LASS I1 (Ghaboussi 

and Dikmen, 1977), DESRA2 (Lee and Finn, 1978), and 

LINOS (Bardet, 1989). Some of these computer programs 

were described by the National Research Council (1985). 

The numerical methods are based on the assumption that 

the soil deposits are homogeneous layers of infinite horizontal extent and that earthquake response arises from upward propagation of shear waves from the underlying rock 

formations. Analytical procedures based on this concept 

and the inclusion of nonlinear soil behavior are being increasingly used in earthquake engineering for predicting 

site response and the characteristics of ground-surface motions. We used the programs SHAKE, DETRAN, and LINOS in this study. 

The program SHAKE (Schnabel and others, 1972) is 

based on a one-dimensional lumped-mass model of the 

soil-layer system connected by linear shear springs and 

dashpot elements. The nonlinearity of the shear modulus is 

accounted for by the use of equivalent linear soil properties (Seed and Idriss, 1970). An iterative procedure is used 

to obtain. values for modulus and damping compatible 

with the effective shear strains in each soil layer. 

The program DETRAN (a version of NONLI3, developed by Chen and Joyner, 1974) is based on a one-dimensional lumped-mass model of the soil-layer system 

connected by multilinear shear springs and dashpot elements. The multilinear springs are made of a series of linear springs in parallel with frictional elements (Iwan, 

1967). In contrast to SHAKE, the program DETRAN uses 

a true hysteretic formulation of the stress-strain relation 

and can therefore handle nonlinear strain-softening material with hysteretic damping. The stress-strain behavior of 

the springs satisfies Masing's (1926) criterion. 

The program LINOS (Bardet, 1989) is a three-dimensional, nonlinear, finite-element code that includes dynamic capabilities and a library of various nonlinear material 

models. The program may also be used to simulate oneand two-dimensional problems. The material models may 

be formulated in terms of either total or effective stress. 

INPUT MOTION 

As summarized in table 1, 11 strong-motion accelerograms were recorded (Shakal and others, 1989) within 7 

km of the Marina District. The peak acceleration ranges 

from 0.05 to 0.21 g in the horizontal direction; these extremes were measured in Pacific Heights and the Presidio, 

respectively 1.7 and 2.2 km from the Marina District. Surprisingly, both extremes were in the records closest to the 

CE OF 

ARTS 

BAY VIEW 

^ 

NORTH 

Figure 10.-Isometric view of three-dimensional soil model. 
SITE-RESPONSE ANALYSES 

Table 1.-Accelerograms recorded during the earthquake in the vicinity of the Marina District 

Maximum acceleration 

Accelero- Distance Site 

@-am Location (km) Horizontal Vertical subsoils te) te) 

47-story office building ----- Rincon Hill ------------------- 

6-story building, 

University of California, 

San Francisco. 

Diamond Heights ------------ Treasure island --------------- 

Yerba Buena Island---------- 

Artificial fill. 

Franciscan assemblage 

(sandstone, shale). 

Artificial fill over 

bay muds. 

Franciscan assemblage 

(sandstone, shale). 

Franciscan assemblage (shale, sandstone). 

Serpentine. 

Franciscan assemblage (sandstone, shale). 

Franciscan (chert). Artificial fill. 

Franciscan assemblage (sands tone). 

district. Among the accelerograms listed in table 1, the 

record from Yerba Buena Island, 7 km east of the Marina 

District, was thought to be best representative of the accelerations that probably took place in the bedrock of the 

Marina District during the earthquake. The original record 

has a peak acceleration of 0.067 g and a duration of 39.8 s 

in an east-west direction. Yerba Buena Island is primarily 

built on sandstone of the Franciscan assemblage. The peak 

acceleration on bedrock sites versus epicentral distance d 

is plotted in figure 12. The peak accelerations corresponding to d=80 km (Marina District) range from 0.03 to 0.15 

g. The peak acceleration of 0.067 g on the original Yerba 

Buena accelerogram is a mean of the peak accelerations 

plotted in figure 12. Those accelerograms listed in table 1 

that were recorded in the basements of buildings were not 

considered in this study because they were influenced by 

building structural responses. The accelerograms recorded 

on Treasure Island and in the Presidio also were not considered: The Treasure Island station is located on soft 

soils, and the strong motion recorded in the Presidio, although this station is located on serpentine bedrock, was 

much higher than the average recorded on bedrock in the 

San Francisco Bay area. The accelerograms recorded on 

Treasure Island and in the Presidio, although they correspond to the same distance d as the Marina District, fall 

outside the range of bedrock accelerations plotted in figure 

12. A similar conclusion may be drawn from the response 

spectra of five accelerograms recorded in the vicinity of 

the Marina District (fig. 13). All of these response spectra 

were calculated by assuming 5-percent critical damping. 

The Telegraph Hill, Pacific Heights, and Yerba Buena Island accelerograms, which were recorded on bedrock, 

clearly differ from the Treasure Island and Presidio accelerograms recorded on soft soils. 

Two input acceleration-time histories were considered 

in the one- and two-dimensional analyses: the original 

Yerba Buena Island accelerogram (east-west and vertical 

components) and a scaled Yerba Buena Island accelerogram. The scaled horizontal acceleration has a peak of 

0.15 g, which corresponds to the upper bound of peak acceleration for d=80 krn in figure 12. The scaled vertical 

acceleration has a peak of 0.061 g, which preserves the 

ratio between the horizontal and vertical components of 

the original motion. The east-west and vertical components of the original Yerba Buena Island accelerogram are 

plotted in figures 14A and 145, respectively. As shown in 

the response spectra (fig. 140, the dominant period of 

bedrock acceleration is about 0.6 s. 

ONE-DIMENSIONAL LINOS MODEL 

The soil column used in the one-dimensional analyses 

represents the soil profile at the center of the liquefaction 

zone shown in figure 1. This soil column consists of five 

layers, including four clay layers and a 1-m-thick layer of 

the yellow hardpan at the transition between the older and 

younger bay muds (fig. 15). The finite-element model consists of plane-strain, four-noded, isoparametric elements 

with two degrees of freedom per node. The analyses were 

carried out by assuming that the deformation remained 

undrained during earthquake shaking. The term "undrained" refers to zero volume change. This incompressibility, which was ensured by using a penalty formulation, 
F98 MARINA DISTRICT , 

to evaluate the shear strength. The variations in normalized shear modulus GIGmm versus shear strain y and in 

equivalent viscous damping ratio D versus y were known 

from a previous laboratory study of the older and younger 

bay muds (Isenhower, 1979). 

The results of laboratory and site investigations were 

combined in a two-step calibration procedure. In the first 

step, nonlinear backbone curves (assuming Masing behavior) were generated to reproduce the curves of GIGmm and 

D versus y for the older and younger bay muds. In the 

is justified in view of the low permeability coefficient of 

the older and younger bay muds, which prevents rapid 

consolidation. This assumption does not significantly influence the numerical model because the material model used 

in the analyses does not depend on the mean effective 

pressure. 

MODELING OF' NONLINEAR SOIL PROPERTIES 

The parameters required for the nonlinear material model in the numerical analysis could not be calibrated directly from laboratory test results, owing to the absence of 

data. The model parameters were calibrated from the siteinvestigation data and from independent studies on the 

older and younger bay muds. The only field measurements 

during the site investigation were shear-wave velocity and 

CPT results. The shear-wave velocity measurements were 

used to derive the distribution of initial low-strain shear 

modulus versus depth, whereas the CPT results were used 

Accelerations 

used in analvsis 

BAY MUDp 

A ' 

\ 

c 

LATE PLEISTOCENE BAY CLAY 

BEDROCK , -- 125m 

10 100 

Distance (km) 

Figure 12.-Peak acceleration versus distance for accelerograms recorded at bedrock sites during the earthquake (data from Housner and Pen- * 

zien, 1990). 

BEDROCK 125m 

ARTIFICIAL FILL AND NATURAL --- OEPOSiTS 

--- 

- YELLOW HARDPAN -HOLOCENE BAY CLAYLATE PLEISTOCENE BY' 

,I 1 

. 11 Yerba Buena Island 11 -- - Treasure Island :, ; I\ - -. Telegraph Hlll Ill \ Presidio -;I\; 1 

I I,; I, 

- Pacific Helghts 

'\ ; 1; ', 1 \ 

'. 

- .-.7.. 

1 2 3 4 5 

- 

BEDROCK 

D1 

ARTIFICIAL FILL AND NATUQAL OE?OSl-5 - . - HOLOCENE BAY CLAY 

---..-. YELLOW - HARDPAN a=--- / 

LATE PLEISTOCENE BAY CLAY 

BEOROCK 

Period (s) 

Figure 1 l.-Cross sections A-A' through D-D' in three-dimensional soil 

model (see fig, 3 for locations). Vertical exaggeration, 2x. 

Figure 13.-Response spectra of accelerograms from five stations in the 

vicinity of the Marina District. 
SITE-rnSP0NSE ANALYSES F99 

second step, these synthesized backbone curves were used 

to calibrate the material parameters of a three-dimensional 

constitutive model for soils. An elastoplastic model with 

multiple yield surfaces (Prevost, 1978) was selected to 

=present the soil behavior in the one- and two-dimensional analyses. 

GENERATION OF BACKBONE CURVES 

l~,,,l,,,,l,t,, 

10 2 0 3 0 4 0 

Time (s) 

Time (s) 

Horizontal - 

..--... Vertical 

0 1 2 3 4 

Period (s) 

Figure 14.-Acceleration-time history of horizontal (A) and vertical (B) 

components of ground motion, with corresponding response spectra (0, 

for original Yerba Buena Island accelerogram (peak acceleration, 0.M7 g). 

The stress-strain response of soils during cyclic simpleshear tests is commonly described by using a backbone 

curve and the Masing effect. The best known and most 

widely used backbone curve is of the hyperbolic type 

(Hardin and Drnevich, 1972). Backbone curves were generated by three models in this study: a bilinear model, a 

modified hyperbolic model, and a power-law model. 

BILImAR MODEL 

The stress-strain response in the bilinear model during 

simple shear is given by 

where T is the shear stress, Tmax is the maximum allowable 

shear stress, Gmax is the elastic initial shear modulus, and 

17.6 40.5 19.4 

.: 

BAY CUY 

207 

YELLOW HMDPAN 20.8 345.0 225.0 

213 

HOLOCENE AND 230 

AE REI~T~ENE 17.9 175.0 140.0 .6 

BAY CLAY 245 

ATE PLEISTOCENE 

BAY CLAY .6 

WITH INTERBEDS 18'4 287'5 225'0 

OF SHELLS 300 

LATE 

PLEISTOCENE 18.4 345.0 225.0 335 .6 

BAY CLAY 

Figure 15.-Soil column near borehole M4 (fig. 41, showing corresponding soil properties. ysa,, saturated unit weight; G, shear modulus; T,,,~, 

undrained shear strength; vs, shear-wave velocity; n, porosity. 
Floe MARINA DISTRICT 

yr=~max/Gmm is the shear strain at failure. The secant 

shear modulus, G, is given by 

where Gmax, ymax, TI, and m are all real, positive material 

parameters. Equation 7 ensures that The equivalent viscous damping, D, is given by 

a~ 

T = 0 and = Gmax at y = 0 

and 

where the work Wl is defined as the area under the stressstrain curve 

and W2 is the work under the secant line: 

Power-law model 

- - Bilinear model .-.- Modified hyperbolic model 

* Experimental data 

In the bilinear model, equations 4 and 5 become (lsenhrxer, 1979) 

Wl = W2 for y < yr 

1 

The bilinear model was applied to reproduce the curves 

of GIGmax and D versus y for the older bay mud at 28-m 

depth. At this depth, we selected -cmm=Su=l40 kPa and 

Gmm=175,000 kPa on the basis of the results of the site 

investigation plotted in figures 6 and 7. As shown in figure 

16, the bilinear model predicts that G=Gmax until y=0.08 

percent, and then GcGmax as y increases. The bilinear 

model cannot simulate hysteretic damping at low strain 

(ycyr) and overestimates D for p0.1 percent. This model 

is of only limited interest for site-response analyses; it 

does not provide any flexibility to fit the experimental data 

plotted in figure 16 because it has only two parameters, 

Tmm and Gmax- Shear strain (percent) 

MODIFED HYPERBOLIC MODEL Figure 16.-Normalized shear modulus (A) and damping ratio (B) versus 

shear strain for older and younger bay muds (modified from Isenhower, 

1979), fitted to curves generated by power-law, bilinear, and modified 

hyperbolic models. 

The stress-strain response in modified hyperbolic model 

(Prevost, 1989) is given by 
SITE-RESPONSE ANaYSES Flol 

T=T~= at y=ymawhen the following relation is satisfied: where n is the material parameter. After integrating equation 12, the backbone curve becomes 

where ymax=~m~/(Gmaxymax). Equation 7 is calibrated 

from experimental data by fitting only two material parameters, m and ymax, since Gmax and zmaX are given from 

experimental results. The secant shear modulus G is computed by dividing T in equation 7 by y. The equivalent 

damping ratio D is calculated by using equation 3 specified in the following expressions for Wl and W2: 

where X=Y lyma and y =~~l(G~~~y~~). 

The experimental curves of GIGma versus y and D versus y were fitted by choosing m=5 and ymax=0.0015 (fig. 

16). G is simulated accurately, whereas D is underestimated for small values of y and overestimated for y>O.l percent. The discrepancy between experimental and simulated 

results at small values of y is expected because the material model generates only structural damping and neglects 

viscous damping. 

POWER-LAW MODEL 

As an alternative to the modified hyperbolic model, a 

simpler, power-law model was also used (Bardet, 1990~). 

In this model, the tangent shear modulus Gt varies as a 

power function of the distance between T and the line 

T = Tmax: 

where ~~=~~~l[G~~(l-n)]. The secant shear modulus G 

is computed by dividing T in equation 13 by y. The equivalent damping ratio D is calculated by using equation 3 

specified in the following expressions for Wl and W2: 

max Wl= TmaXY - Gmax (2 - n) for Y >Yr 

In contrast to the modified hyperbolic model, the powerlaw model has only one material parameter n, which was 

set equal to 0.6 to fit the experimental data on the older 

and younger bay muds. As shown in figure 16, both the 

modified hyperbolic and power-law models are capable of 

describing the experimental points, whereas the bilinear 

model is too approximate. Therefore, we selected the power-law model to generate the backbone curves of the older 

and younger bay muds because its formulation and calibration are simpler than those of the modified hyperbolic 

model. 

ELASTOPLASTIC MODELING OF THE BEHAVIOR OF 

THE OLDER AND YOUNGER BAY MUDS 

The backbone curves describe soil behavior only for 

one-dimensional loading and cannot be directly used for 

generalized multidimensional loadings, such as those used 

in two-dimensional analyses or even one-dimensional 

site-response analyses allowing for vertical motion. In the 

LINOS analyses, the elastoplastic constitutive equation 

for multiple yield surfaces (Prevost, 1978) was used to 

simulate the nonlinear behavior of the older and younger 

bay muds under generalized loadings. This elastoplastic 

model, which was available within the program LINOS, 

provided a piecewise linear simulation of the power-law 

model (assuming Masing behavior) fitted to the experimental data. 
F102 MARINA DISTRICT 

ELASTOPLASTIC MODEL 

The pressure-independent elastoplastic model was used 

successfully to simulate the hysteretic response of clays 

during cyclic loading (Prevost, 1978). The yield surfaces 

may be expressed by the equation 

where T~ is the ordinate of the mth point on the stressstrain curve in figure 17. The elastic-shear modulus G is 

the initial slope of the stress-strain curve: 

where ar is the center of the mth yield surface, km is the 

size of the mth yield surface, and so is the deviatoric 

stress, given by 

where ou is the effective stress tensor, p=%okk is the effective mean pressure, and 6u is Kronecker's delta. The 

yield-surface evolution is controlled by kinematic hardening; the yield surfaces may translate, but they do not 

change in size. The largest yield surface is fixed in stress 

space and defines the failure surface. 

CAL,IBRATION OF MATERIAL CONSTANTS 

The elastoplastic model predicts that the stress-strain response is piecewise linear. If the initial values of all the 

coefficients a7 are assumed to be zero, then the increments 

of shear stress d~ and shear strain dy during simple shear 

with an initially isotropic stress are linearly related through 

where Hm is the plastic modulus associated with the 

mth yield surface. 17 applies, provided that 

km/ fi < T < km + T is inside the smallest 

yield surface-that is, when T < kl / ,b -equation 17 becomes 

As shown in figure 17, the continuous backbone curves 

may be fitted by piecewise linear curves defined by discrete points (ym, T~). Three to seven points were found to 

be sufficient to accurately fit the continuous backbone 

curves for the older and younger bay muds. Once these 

discrete points have been selected, the surface radius km is 

related to xm by 

The elastoplastic modulus H& associated with the mth 

yield surface is given by 

where H& is related to the plastic modulus Hm through 

The plastic modulus associated with the largest yield surface is set equal to zero. The material parameters calibrated for the four layers of the older and younger bay muds 

and the yellow hardpan are listed in table 2. 

The layer of yellow hardpan was modeled by using the 

same type of model as for the older and younger bay 

muds. On the basis of the CPT results, the yellow hardpan 

was assigned a large shear strength, 160 kPa, equal to the 

largest shear strength selected for the older bay mud. Because no laboratory data were available on the yellow 

hardpan, this layer was assigned the same material properties as the older bay mud at 70-m depth. Because the thin 

EXPIANATION 

- 

- - 5-m depth 

28-m depth 

. . . . . . . 

50-m depth 

70-m depth 

Shear strain (percent) 

Figure 17.-Stress-strain relation during simple shear, as predicted by 

multiple-yield-surfaces model at various depths for older and younger 

bay muds and yellow hardpan. 
SITE-RESPONSE ANALYSES F103 

Table 2.-Material parameters of multiple-yield-surfaces model 

[G, shear modulus; n, Poisson ratio; m, number of yield surface; k, size of yield 

surface; H', elastoplastic modulus] 

of fit depends on the depth because the backbone curve 

(eq. 13) predicted by the power-law model depends on 

Gmax and tmax, which vary with depth. 

5 33.6 0.00 

layer 2 (depth, 13 m) 

309.4 0.3 1 123.2 472.5 

layer 3 (depth, 28 m) 

157.7 0.3 1 73.7 253.0 

6 242.5 0.00 

layer 4 (depth, 50 m) 

259.5 0.3 1 1 16.9 410.4 

7 389.7 0.00 

layer 5 (depth, 70 m) 

309.4 0.3 1 123.2 472.5 

layer of surficial sand was not expected to significantly influence the overall site response, its behavior was not simulated with accuracy. Instead, it was modeled by using the 

same elastoplastic model as for clay, but calibrated with 

the 20-kPa shear strength estimated from the CPT results. 

The backbone curves generated by the power-law model 

for the older and younger bay muds at four depths ranging 

from 5 to 70 m are plotted in figure 17. The initial shear 

modulus Gmax and maximum stress T~~~ were computed 

based on results of field investigation. The power law 

model provides a smooth and gradual change of slope 

from elastic to perfectly plastic behavior. 

The curves of GIGmav versus y and D versus y generated 

by the elastoplastic model at four different depths are plotted in figure 18. As in figure 15, this model accounts well 

for the shear modulus, although it slightly overestimates 

the damping properties at larger strain amplitudes. The 

damping ratio is also underestimated at low strain because 

RESULTS OF 

ONE-DIMENSIONAL LINOS ANALYSES 

The one-dimensional analyses were carried out, first, by 

assuming elastic properties for the underlying soils and, 

second, by using the elastoplastic model. The linear analysis, though of limited interest in practice, was carried out 

first to provide a means of qualitatively assessing the effect of material nonlinearity on the dynamic response of 

the Marina District. Only the scaled Yerba Buena Island 

accelerogram was used in the elastic one- or two-dimensional analyses. The results of linear analyses at 0.15 g 

can be scaled linearly down to 0.067 g for the original 

Yerba Buena Island accelerogram. The damping, which 

was of the Rayleigh stiffness type, was adjusted to provide 

a 1-percent critical damping ratio at the fundamental periEXPLANATION 

5-m depth - - - - 28-m depth 

---- 50-m depth 

. . - - - . . 70-m depth 

Experimental data 

(lsenhower, 1979) 

Shear strain (percent) 

Figure 18.-Normalized shear modulus (A) and damping ratio (B) versus 

the material model neglects viscous damping. The quality shear strain at various depths for older and younger bay muds. 
F104 MARINA DISTRICT 

od. This damping ratio, which is slightly smaller than the 

value of 2 percent observable in the low-strain laboratory 

test results of Isenhower (1979), corresponds to the damping ratio predicted by the power law at 0.01-percent shear 

strain. 

The elastic response of the ground surface to the scaled 

bedrock input motion on Yerba Buena Island is plotted in 

figure 19. The peak acceleration is 0.4 and 0.07 g in the 

horizontal and vertical directions, respectively. The acceleration is practically unchanged in the vertical direction 

(fig. 19A), whereas it is amplified 2.6 times in the horizontal direction (fig. 195). 

The acceleration-time history and response spectra of 

ground-surface acceleration at borehole M4 (fig. 4), as 

predicted by linear and nonlinear analyses for the scaled 

Yerba Buena Island accelerogram (peak acceleration, 0.15 

g) are plotted in figure 20. The predicted peak acceleration 

is not amplified; it is about 0.15 g in the horizontal direction and 0.06 g in the vertical direction. As shown in figure 20A, the peak horizontal acceleration is truncated, 

owing to yielding of the soft top layer (fig. 20E) that 

reaches a maximum shear strength of 19.4 kPa (as specified in fig. 15). The response spectrum of horizontal acceleration shows two distinct peaks at 0.6 and 1 s; the second 

peak corresponds to the fundamental mode of the elastic 

soil deposit. The structural damping, as illustrated by the 

hysteretic stress-strain curve in figure 20E, lowers the 

spectral peaks obtained in the linear analysis. The response spectra in the vertical direction are almost identical 

in the nonlinear and linear analyses. 

The acceleration-time history and response spectra of 

ground-surface acceleration at borehole M4 (fig. 4), as 

predicted by nonlinear and linear analyses for the original 

Yerba Buena accelerogram (peak acceleration, 0.067 g), 

are plotted in figure 21. In contrast to the figure 20, the 

predicted peak acceleration (0.12 g) is amplified by a factor of 2 in the horizontal direction. The stress-strain curves 

at 9- and 6-m depth are plotted in figures 21E and 21F, 

respectively. The soft top layer does not yield as much as 

in figure 20E; however, the yielding at 9-m depth controls 

the peak acceleration at the ground surface, which is the 

same as that predicted for 0.15 g in figure 20E. The vertical accelerations predicted in the linear and nonlinear analyses coincide. The lower accelerations and reduced 

yielding also account for the greater similarity of the response spectra in the nonlinear and linear analyses. 

The acceleration-time history at the ground surface, at 4- 

m depth, and at the top of the yellow hardpan is plotted in 

figure 22. The yellow hardpan sustained the same acceleration as the ground surface. The soft layers just above the 

yellow hardpan did not amplify the acceleration further 

because they yielded at this acceleration level. Figure 22 

suggests that most of the site amplification in the Marina 

District during the earthquake was caused by the thick layers of older bay mud underlying the yellow hardpan. 

RESULTS FROM THE PROGRAMS 

SHAKE AND DETRAN 

The site response at borehole M4 (fig. 4) was analyzed 

by using the programs DETRAN and SHAKE. The same 

geometry and backbone curves were defined for the soil 

layers (see figs. 15, 16). The ground motion in the 

SHAKE and DETRAN analyses is limited to the horizontal east-west component of the Yerba Buena Island accelerogram. In the SHAKE analysis, we used the curves of 

GIGmax versus y and D versus y of Isenhower (1979) for 

the older and younger bay muds. The 40-percent increase 

in undrained shear strength Sn was not considered in the 

SHAKE analysis. A 1-percent viscous damping was also 

considered in the DETRAN analysis in addition to the 

hysteretic structural damping. 

The response spectra of the horizontal component of the 

ground motion at borehole M4 (fig. 4) calculated by using 

the programs DETRAN, SHAKE, and LINOS are plotted 

in figure 23. All the response spectra are similar in shape 

but differ in amplitude; they predict similar dominant periods but different amplifications. The spectral amplitude 

calculated by using the program LINOS falls between 

those predicted by the programs DETRAN and SHAKE. 

The DETRAN analysis predicts the lowest amplitude because it includes a 1-percent viscous damping in addition 

to the same structural damping, as in the LINOS analysis. 

The SHAKE analysis predicts the highest spectral amplitudes, reflecting the use of an equivalent material model 

that does not include complete failure. Similar conclusions 

were drawn by Arulanandan and Yogachandran (1990) after comparing the results of the programs SHAKE and 

DYSAC2. Provided with the same input ground motion, 

soil-layer geometry, and properties for the Marina District, 

the programs DETRAN and LINOS gave comparable results, whereas the program SHAKE tends to give higher 

spectral amplifications. 

SIMPLIFIED LIQUEFACTION ANALYSIS 

OF ARTIFICIAL FILL 

Equivalent SPT blow counts were determined from the 

CPT results, on the basis of correlations with normalized 

tip bearings and friction ratios (Douglas and Olsen, 1981; 

Earth Technology Corp., 1990; Martin, 1991). Within the 

bounds of Marina Cove, the equivalent SPT blow count 

Nl was found to range from 5 to 20 in the artificial fill 

(top 2.75 m) and to average 5 for the lower natural-sand 

deposits (Bardet and Kapuskar, 199 1 b). The properties of 

the soils above the yellow hardpan at borehole M4 are listed in figure 24A. The average earthquake-induced shear 

stress in the hydraulic fill was obtained by the simplified method of Seed and Idriss (1971 ; see Seed and others, 

1983): 
SITE-RESPONSE ANALYSES F105 

where ama is the peak ground acceleration, g is the acceleration due to gravity, y is the soil unit density, h is the 

height of soil shaken, and rd is a depth factor that accounts 

for the variation in ground acceleration with depth. In view 

of the shallow thickness h of the column considered in 

figure 24A, no depth correction was considered (rd=l). The 

estimated average stress ratio ~~~~/o~~ (where otV is the effective overburden pressure) calculated for a peak acceleration of 0.15 g is listed in table 3. Because ground 

accelerations were not measured in the Marina District, the 

value of 0.15 g was chosen to represent a reasonable estimate on the basis of the results of site-response analyses. 

The liquefaction potential of the sand above the yellow 

hardpan was assessed by using the empirical procedure of 

Seed and others (1983) that is commonly used in engineering practice today. From field correlations between SPT 

tests and the observed liquefaction characteristics of sand 

over a range of earthquake magnitudes, cyclic liquefactionstrength curves (tcycIotv versus number of cycles NL to 

cause liquefaction) were derived. The liquefaction-strength 

curves obtained for Ni=5, 10, and 20 by using this procedure are plotted in figure 24B. qyc is the average stress 

Table 3.-Summary of liquefaction analyses for sands at borehole M4 

(fig. 4) by a simplified evaluation procedure 

(4 SAND (kNJrn3) (MPa) (k~/rn~) (mls) -- (blowslft) 1 ARTIFICIAL FILL 18.5 167.6 .. 305 .. 5-20 2.75 

HOU3C8SE 17.3 40.6 17.2 152 -- -- 

BAY CLAY 17.6 76.6 26.3 207 -- -- 

12:; YELLOWHARDPAN 20.4 -- 366 -- 65 -- 

HOLOCENEAND -- 81.4 27.7 213 -- -- LATE PLEISTOCENE 

BAY CLAY 

EXPLANATION 

Number of cycles to cause liquefaction (NL) 

Figure 24.-Soil column in borehole M4 (fig. 4) (A) and liquefaction 

strength curve (B) for artificial fill, as estimated from CPT results. ySap 

saturated unit weight; Sy, undrained shear strength; G, shear modulus; us, 

shear-wave velocity; n, porosity; New, SPT blow count. 

Parameter (Units) Compacted sandy fill Sand deposit 

(depth, 2.75 m) (depth, 7.5 m) 

max (g) 0.15 0.15 

7 (kNIm3) 18.5 17.6 

^ave 5.0 12.87 

o'~~ (kpa) 12.0 29.2 

1 (blowslft) 10 5 

tave/o'vo applied 0.4 0.44 

tcyc/o'vo required .2 06 

to withstand liquefaction 

for N= 10 

ratio to achieve liquefaction after a representative "significant" number of cycles associated with a given earthquake 

magnitude. The average shear-stress ratios fy,&otV listed in 

table 3 fall well above the liquefaction-strength curves, indicating that the sand deposits in the Marina District should 

liquefy under the acceleration predicted at borehole M4. 

Using the liquefaction-strength curves in figure 24B, a 

DESRA2 analysis (Lee and Finn, 1978) could have been 

performed to demonstrate the acceleration-time histories of 

pore-pressure buildup in the layers of saturated sand. However, this additional analysis would not have contributed 

significantly to our understanding of the site response of the 

Marina District. In view of the relative proportion of clay 

and sand in the subsoils of the Marina District, the site 

response (leading to liquefaction of the saturated sand) was 

largely controlled by the underlying older and younger bay 

muds. 

TWO-DIMENSIONAL 

SITE-RESPONSE ANALYSES 

TWO-DIMENSIONAL MODEL 

A cross section of the three-dimensional model in figure 

10 that is used hereafter in two-dimensional analyses of 

the Marina District is shown in figure 25. This east-west 

cross section contains Beach Street (see fig. 3) and intersects the liquefied zone. The cross section is 1,500 m long 

and as much as 90 m high: It is discretized into 250 planestrain elements, arranged in 50 columns of five elements 

each. The model has five layers: The top layer is composed of surficial materials that are either the younger bay 

mud or artificial fill; the second layer from the top represents the thin, dense sand layer at the transition between 

the surficial layer and the older bay mud; and the underly- 
F106 MARINA DISTRICT 

ing layers are composed of overconsolidated older bay 

mud. As shown in figure 25, the thickness and depth of 

these layers are not constant but vary in an east-west direction. The lateral boundaries of the two-dimensional 

model were defined sufficiently far away from the region 

of interest to attenuate undesirable boundary effects. The 

optimal model width was defined by eigenvalue analysis. 

EIGENVALUE ANALYSIS 

The 10 vibrational modes of the selected cross section, 

which correspond to the lowest natural frequencies ranging from 1.16 to 1.93 Hz, are illustrated in figure 26. The 

elastic properties of the one-dimensional analyses were assumed in these eigenvalue calculations. The first mode, 

with a natural frequency of 1.16 Hz, is essentially similar 

to the first mode of a shear beam. The vertical columns 

lean in the same direction and have a maximum amplitude 

at the center and zero amplitude on the extremities; there 

is a slight surface wave, the wavelength of which is equal 

to the model width. The second mode has a natural frequency (1.23 Hz) close to the fundamental frequency. In 

the second mode, the vertical columns do not lean in the 

same direction, and the surface wave has a wavelength 

equal to half the model width. The soil elements in the 

center of the model do not undergo cycles of simple shear 

loading but are subjected to cycles of lateral tension-compression. The other modes display an increasing importance of the surface modes. Starting from the third mode, 

the surface modes exhibit a common focal point on the 

east side of the Marina District; the ninth mode exhibits 

the strongest surface amplification in the vicinity of this 

focal point. This particular mode should, however, be interpreted with some caution because the wavelength has 

reached the spacing of the discretized systems. The common focal point is located east of the region where the 

yellow hardpan layer is thinnest. 

A wider model was constructed to estimate lateral 

boundary effects. This larger model included bedrock that 

crops out on the east at Nob Hill (approx 1,500 m east) 

WEST 

and is very shallow in the west under the Presidio. Because its eigenvalues and eigenvectors were found to coincide approximately with those of the model in figure 26, 

we concluded that this first model was wide enough for 

the purposes of our analysis. 

To compare the natural modes of the one- and two-dimensional analyses, the natural modes of a one-dimensional model selected at the center of the two-dimensional 

model are plotted in figure 27. The first five modes range 

in natural frequency from 1.12 to 7.95 Hz. The lowest frequency of the one-dimensional model is slightly smaller 

than that of the two-dimensional model. The corresponding mode shapes coincide in the one- and two-dimensional 

analyses; however, the second natural frequency (2.87 Hz) 

of the one-dimensional model is higher than the 10th natural frequency of the two-dimensional model. The compressional modes are not plotted in figure 27 because the 

column was assumed to be composed of incompressible 

material. In contrast to the soil elements of the two-dimensional model that may undergo tension-compression, the 

soil elements of the one-dimensional model undergo only 

simple shear loading. 

From this comparison, it is apparent that two-dimensional effects could significantly influence the dynamic response of the Marina District. These effects are caused by 

thinning of the hard sand layer and the slope of the 

bedrock surface. The modal deformations in the two-dimensional analyses are also more complex than in the 

one-dimensional analyses. The soils undergo not only simple shear versus depth but also much more complex loadings involving tension-compression and combined 

shearlnormal-loading cycles. These complex loadings observed in linear mode shapes may be also influenced by 

nonlinear soil behavior. 

INPUT MOTIONS 

As in the one-dimensional analyses, the earthquake motion was characterized by two input accelerations: from 

the original (0.067 g) and the scaled (0.15 g) Yerba Buena 

EAST 

Palace of Scott St. Boreholes M4 and C-2 Fine Arts 

Bedrock 100 200m 

O___I 

Figure 25.-Two-dimensional model of the Marina District (cross sec. C-C', fig. 3). 
SITE-RESPONSE ANALYSES F107 

Mode No. 1 Freq = 1.157 Hz 

Mode No.2 Freq = 1.228 Hz 

Mode NO. 3 Freq = 1.337 Hz 

Mode No. 4 

Mode No. 5 Freq = 1.552 Hz 

Mode No. 7 Freq = 1.753 HZ 

Mode NO. 8 Freq = 1.842 Hz 

Mode No. 10 Freq = 1.926 Hz 

0 

u 

100 200 meters 

Figure 26.-Eigenmodes of two-dimensional model (fig. 25). 
F108 MARINA DISTRICT 

Island accelerograms. The bedrock and the lateral bound- RESULTS 

aries are assumed to behave as a rigid body, and so the 

input motion is applied simultaneously to all the boundary The two-dimensional analyses were carried out, first, by 

nodes. The effects of wave propagation on site response assuming elastic properties for the underlying soils and, 

are neglected in this analysis but are considered in a sub- second, by using the elastoplastic model that was calibratsequent section. ed in the one-dimensional analyses. Like the one-dimenordinate scale iÃ‘Ã‘Ã 7.7446 

Mode No. 1 Freq = 1.124 Hz Mode No. 2 Freq = 2.87 Hz 

Mode No. 3 Freq = 4.256 Hz Mode No. 4 Freq = 6.1 13 Hz Mode No.5 Freq = 7.947 Hz 

Figure 27.-Eigenmodes of one-dimensional model at borehole M4 (fig. 4). 
SITE-RESPONSE ANALYSES F109 

sional analyses, linear two-dimensional analyses are of 

limited interest in practice. They were carried out mainly 

to evaluate the effects of material nonlinearity on the dynamic response of the Marina District and to compare 

two- versus one-dimensional elastic response. 

LINEAR ANALYSES 

Only the scaled Yerba Buena Island accelerogram was 

used in the elastic two-dimensional analyses. The results 

of the linear analyses were scaled down linearly to give 

results corresponding to the original Yerba Buena Island 

accelerogram. The acceleration-time history and response 

spectra at borehole M4 (fig. 4), in the center of the artificially filled Marina Cove that liquefied in 1989, are plotted 

in figure 28. The peak horizontal acceleration reaches 0.58 

g in the two-dimensional analyses, in comparison with 

0.40 g in the one-dimensional analyses. The accelerationtime histories are comparable in both analyses but show a 

larger amplitude in the two-dimensional analyses. In both 

analyses, the dominant period is 0.7 s; the corresponding 

frequency (1.43 Hz) is close to the fourth natural frequency (1.45 Hz) of the two-dimensional model shown in figure 26. 

The response spectra of predicted ground motion at 

boreholes M4 and WSS (fig. 4) in comparison with those 

of bedrock motions are shown in figure 29. The bedrock 

motion exhibits a small peak acceleration at a period of 

0.6 s; this peak is amplified about 5 times at borehole M4, 

whereas it is amplified about 4 times at borehole WSS. 

The amplification of ground motion at 0.6 and 0.7 s results 

from the presence of 0.6- to 0.7-s motion in the input bedrock motion that activates the fourth and fifth modes 

shown in figure 26 (1.45 and 1.55 Hz, respectively). 

NONLINEAR ANALYSES 

The acceleration-time history and response spectra of 

predicted ground motion at boreholes M4 and WSS (fig. 

4) for the scaled Yerba Buena Island accelerogram are 

shown in figures 30 and 31, respectively. In the nonlinear 

analyses, the peak accelerations at boreholes M4 and WSS 

are identically equal to 0.23 g, in comparison with 0.58 g 

in the linear analyses. The peak acceleration is amplified 

1.5 times for the horizontal component and 1.6 times for 

the vertical component. The response spectra emphasize 

the difference in response between boreholes M4 and 

WSS: The peak at borehole M4 is smaller and broader 

than at borehole WSS. Wider peaks in the response spectra 

are generally attributable to material nonlinearity because 

material softening shifts the fundamental period. This nonlinear effect is observed by comparing the response spectra in the linear and nonlinear analyses plotted in figures 

30C and 31C. The wide peak in figure 30C implies that 

the soils at borehole M4 underwent larger strain than at 

borehole WSS, as corroborated by comparison of the 

stress-strain curves in figure 30E and 31E. The energy dissipated, which corresponds to the area underneath the 

stress-strain curve, is larger at borehole M4 than at borehole WSS. The peak acceleration at borehole M4 predicted 

in the two-dimensional analyses (0.23 g, fig. 30A) is larger 

than that predicted in the one-dimensional analyses (0.12 

g, fig. 20A). As shown in figure 30F, in the two-dimensional analyses, the soil elements in the upper layer undergo not only cyclic simple-shear loading but also cycles of 

tension-compression. These changes in loading direction 

cause an increase in acceleration that may be transmitted 

through soils. The stress states in the two-dimensional 

analyses, however, are more complex than in the one-dimensional analyses, ruling out a calculation of peak acceleration from shear strength by using relations similar to 

equation 23. 

Similarly, the acceleration-time history and response 

spectra of predicted ground motion at boreholes M4 and 

WSS (fig. 4) for the original Yerba Buena Island accelerogram are shown in figures 32 and 33, respectively. The 

peak acceleration is 0.20 g at both boreholes in the twodimensional analyses, larger than the peak acceleration of 

0.12 g predicted at borehole M4 by the one-dimensional 

analyses but agreeing well with the peak acceleration of 

0.21 g measured in the Presidio, 2 km from the Marina 

District (see table 1). The stress-strain curves at 9-m depth 

indicate that the soft top layer failed at borehole M4 but 

barely yielded at borehole WSS, an observation that is 

corroborated by comparing figures 32C and 33C: The peak 

of spectral acceleration in figure 32C is wider and lower 

than that in figure 33C, implying larger material 

nonlinearity. 

The bedrock accelerations are amplified 3 times on the 

original Yerba Buena Island accelerogram, in comparison 

with 1.5 times on the scaled accelerogram. The stressstrain curves for the soft top layer plotted in figures 32E 

and 33E show less yield that those in figures 30E and 3 1 E, 

implying that the accelerations in the yellow hardpan are 

not truncated by the soft top layer on the original Yerba 

Buena Island accelerogram. The response spectra in figures 30C and 32C clearly indicate the contribution of the 

fundamental mode (1.15 Hz) to the ground motion at borehole M4 (fig. 4). 

The amplification of the horizontal and vertical components of ground motion along the surface of the two-dimensional model is plotted in figures 34 and 35, 

respectively. The linear results are for the scaled Yerba 

Buena Island accelerogram (peak acceleration, 0.067 g), 

whereas the nonlinear results are for both the original and 

scaled accelerograms (peak acceleration, 0.067 and 0.15 g, 

respectively). In the linear analyses, the amplification of 

ground motion reaches a maximum of 4 between points H 
F110 MARINA DISTRICT 

and I and is constant at 2.5 between points B and G. Modal deformation was observed to be concentrated within 

segment HI (see fig. 26). The nonlinear analyses for the 

original accelerogram predict the same amplification as 

does the linear analyses between points B and G; however, 

between points H and I, the nonlinear analyses predict a 

minimum, whereas the linear analyses predict a maximum. 

The nonlinear analyses for the scaled accelerogram predict 

an amplification lower in value but similar in shape to that 

for the original accelerogram. This decrease in amplification for the scaled accelerogram results from nonlinear effects. The nonlinear analyses predict a minimum 

amplification between points H and I as a result of the 

concentration of deformation and nonlinear effects. The 

vertical component (fig. 34) follows trends similar to those 

of the horizontal component (fig. 35). 

The importance of two-dimensional effects on the siteresponse of the Marina District is clearly shown in figures 

28 through 35. These two-dimensional effects were characterized for a particular type of stress-strain relation 

derived from conventional dynamic testing. The two-dimensional analyses predict an overall-stronger horizontal 

component of ground motion. Comparison of the one- and 

two-dimensional analyses at boreholes M4 and WSS in the 

Marina District indicates that the one-dimensional analyses give acceptable, but not necessarily conservative, predictions for the acceleration at the ground surface. 

WAVE-PROPAGATION ANALYSIS 

OF SITE RESPONSE 

In the preceding section, we studied the response of the 

Marina District by assuming a uniform acceleration on the 

boundary nodes, therefore neglecting the influence of 

wave propagation on site response, as well as the effects 

of the overlying soil layers on bedrock motion. However, 

the model is 1,500 m long; that is, shear waves traveling 

horizontally at a velocity of 3 kmls in the underlying bedrock take 0.5 s to cross the model. Thus, the assumption 

of constant in-phase input acceleration needs to be investigated. The previous analyses also neglected the refraction 

of waves at the soil-bedrock interface. This assumption is 

reasonably justifiable because the overconsolidated older 

bay mud is much softer than the underlying bedrock, and 

so the wave energy may be expected to remain trapped 

inside the soil layer without dissipation through refraction. 

CALCULATION OF INPUT ACCELERATION 

The inclusion of wave-propagation effects in finite-element analysis complicates the problems of site response. 

The influence of wave propagation has been investigated 

for elongate structures, such as suspended cable bridges, 

but has received little attention for earth structures and soil 

deposits. 

We accounted for the influence of wave propagation on 

the dynamic response of the Marina District by prescribing nonuniform acceleration-time histories along the bedrock. Joyner (1975) adopted a similar approach to account 

for wave propagation in two-dimensional problems. However, our calculation of the prescribed acceleration used a 

more rigorous method developed by X. Wu and V.W. Lee 

(unpub. data, 1991). A simpler method had earlier been 

proposed by Mooeen-Vaziri and Trifunac (1988), and similar methods were also used by Todorovska and Lee (in 

press) in analyzing the site response of valleys. 

First, Wu and Lee calculated fast Fourier transforms 

(FFT's) of the free-field-accelerogram data in the horizontal and vertical directions. These FFT's were then considered as incident waves to the arbitrary-shape canyon. They 

were multiplied by the corresponding transfer functions at 

each point of the canyon in the frequency domain to obtain FFT's of the resulting waves after scattering and diffraction from the canyon. An inverse FFT was then taken 

to calculate the resulting wave in the time domain. At each 

frequency and point of the canyon, the value of the complex transfer function is calculated as the solution of a 

boundary condition involving zero stress at the surface of 

the canyon and half-space: 

0 = 0, = 0, (24) 

where (~n~ and Q are the normal and tangential components of stress, respectively, at the surface of the canyon 

and half-space. The resulting waves are the sum of the incident and scattered waves. The scattered waves are composed of both longitudinal (P) and shear (5) waves 

satisfying Sommerfeld's radiation conditions. Scattering 

accelerograms 6 

Recording 

Canyon instrument - 

I - I 

R 

Nodes where 

accelerations earthquake 

are calculated waves 

/ 

Figure 36.Ã‘Calculatio of input acceleration from free-field input in 

two-dimensional model (fig. 25). 
SITE-RESPONSE ANALYSES Fill 

and diffraction will cause the resulting waves to differ in 

both amplitude and phase at each point of the canyon, 

which is no longer undergoing uniform motion. 

The calculation of bedrock accelerations is illustrated in 

figure 36. Station R (Yerba Buena Island) measures the 

free-field accelerogram at the surface of the half-space 

composed of bedrock. The acceleration at station R, which 

results from the incoming and reflected earthquake waves, 

is assumed not to be influenced by surface geometry, such 

as valleys or soft-soil layers. On the basis of the free-field 

accelerogram, this method gives the acceleration along 

points located on the surface of the canyon. 

Three types of earthquake waves are independently considered in the wave-propagation analysis: longitudinal (P), 

vertical shear (SV), and Rayleigh (R). The free-field accelerogram is assumed to result from only one type of wave, 

either P, SV, or R. This assumption is simplistic, however, 

because earthquake accelerations result from a combination of P, SV, and R waves. As yet, no method exists to 

combine these various types of R waves. 

The wave-propagation analysis assumes that free stress 

conditions exist along the bedrock surface; it therefore neglects the weight of soils above bedrock and any interaction between soils and bedrock. This assumption may be 

justified by the relatively small thickness of the soil deposits and the difference between wave velocity in soils and 

bedrock. 

INPUT MOTIONS 

In a rigorous sense, the boundary nodes should undergo 

different accelerations due to the effects of wave propagation. Because each digitized input-acceleration record has 

a duration of 40 s and a time increment of 0.02 s, there 

are 2,000 data points for each component of acceleration. 

If all the nodes were independent, 244,000 data points 

would be required to specify the acceleration on the model 

boundary. For practical reasons, the boundary nodes were 

assembled into 11 groups labeled A through K (fig. 37), 

reducing the input from 244,000 to 44,000 data points. 

The inclusion of wave-propagation effects in the site-response analysis also raises the problem of specifying the 

direction and type of waves that hit the Marina District. 

Because this more complete determination is not yet possible, only a few wave types and orientations are considered 

here. These types include a P wave traveling vertically or at 

a 20' inclination to the vertical, an SV wave traveling vertically or at a 20' inclination, an R wave, and, finally, an 

arbitrary combination of P, SV, and waves. 

The record used to generate the acceleration along the 

boundary is the original Yerba Buena Island accelerogram 

(peak acceleration, 0.067 g). The input accelerations at the 

model boundary resulting from P, SV, and R waves are 

plotted in figures 38 through 46. 

The acceleration-time history of the horizontal and vertical components of ground motion in groups A through K 

for a vertical P wave is plotted in figures 38 and 39, respectively, and the corresponding response spectra in figure 40. In comparison with the Yerba Buena Island 

accelerogram (fig. 14), the vertical component varies 

slightly along the model boundary and is practically equal 

to the original vertical component, whereas the horizontal 

component varies spatially, reaching a minimum at the 

center of the model and a maximum at the extremities. 

The response spectra indicate that the dominant period 

(initially 0.6 s in fig. 14) decreases to 0.4 s in groups B 

through E and remains constant at 0.6 s in group A. Because the P wave travels vertically in the far field, only the 

vertical component influences the acceleration in the model boundary, explaining the presence of the dominant period of 0.4 s noticed in the vertical component on the 

original Yerba Buena Island accelerogram. 

The acceleration-time history of the horizontal and vertical components of ground motion in groups A through K 

for a vertical SV wave is plotted in figures 41 and 42, respectively, and the corresponding response spectra in figure 43. The horizontal component is practically uniform 

along the model boundary and is equal to the original horizontal component, whereas the vertical component is 

smaller and varies spatially, increasing with the inclination 

of the boundary. The response spectra indicate that the 

horizontal component along the model boundary has the 

same dominant period as on the original accelerogram, 

whereas the vertical component displays two dominant periods, at 0.5 and 0.9 s. 

WEST EAST 

c I-lLLJ ~Llll,~ 

D E F G H I 

0 

u 

100 200 meters 

Figure 37.Ã‘Group (A-K, fig. 36) of boundary nodes in two-dimensional model (fig. 25) assembled for inclusion of wavepropagation effects. 
F112 MARINA DISTRICT 

Four additional sets of input acceleration, not shown 

here, were also calculated. Two of these sets correspond to 

the cases of a P wave and an SV wave traveling at an 

inclination of 20Â° an angle arbitrarily chosen to represent 

a deviation from the vertical propagation assumed in the 

one-dimensional analyses. No seismologic data were available on wave paths from the earthquake epicenter to the 

Marina District. The third set corresponds to the case of an 

R wave traveling horizontally from east to west. The 

fourth set corresponds to an arbitrary weighted sum of the 

accelerations caused by P-, SV-, and R-wave motions; the 

weighting coefficients were set to 20, 70, and 10 percent, 

respectively. 

RESULTS 

Most of the wave-propagation analyses of site response 

were carried out by assuming elastic properties for the underlying soils. Only two nonlinear analyses were carried 

out, by using an SV wave inclined at 20'. 

LINEAR ANALYSES 

The response spectra of the horizontal and vertical components of ground motion predicted at borehole M4 for 

various types of waves are plotted in figure 44. The input 

accelerations along the model boundary were generated 

by using the scaled Yerba Buena Island accelerogram 

(peak acceleration, 0.15 g). These response spectra may 

be compared to those in figure 28 for the case of uniform 

acceleration. The dominant period is 0.7 s in both directions, independent of wave type and propagation direction. However, the peak of the spectral amplitude depends 

strongly on wave type and propagation direction. The 

largest amplitude, obtained for a P wave inclined at 20Â° 

is almost twice that obtained with uniform input acceleration. The other types of waves and inclinations produce 

smaller amplitudes. Both SV and R waves have similar 

response spectra. Vertical SV waves produce the same response as uniform input acceleration. The lowest amplitude is obtained for a vertical P wave, underlining the 

importance of P-wave inclination on the response spectra. 

This effect is emphasized in figure 45, which compares 

the response spectra for two P-wave inclinations of 20' 

and -20'. 

The amplification of the horizontal and vertical components of ground motion along the surface of the two-dimensional model is plotted in figures 46 and 47, 

respectively. The amplification is a maximum (approx 7) 

at point H for a P wave traveling at 20Â° and a minimum 

(0.4) at point F for a vertical P wave. The other types of 

waves produce an amplification ranging from 2 to 4, always with a maximum amplification in the segment HI, 

where modal deformations were concentrated. Except for 

a P wave inclined at 20Â° uniform input acceleration produces an upper bound for site-response amplification. 

As shown in figure 47, the vertical component is not so 

strongly influenced by wave type: The vertical component 

is amplified by a factor ranging from 1 to 3, with a peak 

of 5 at point I for a P wave inclined at 20'. 

NONLINEAR ANALYSES 

The acceleration-time history and response spectra of the 

horizontal and vertical components of ground motion at 

borehole M4 and the stress-strain relation at 9-m depth, as 

predicted by two-dimensional nonlinear analyses for uniform input acceleration and an SV wave inclined at 20Â° 

are plotted in figure 48. The stress-strain relation predicted 

by the analyses with uniform input acceleration and with 

an inclined SV wave are similar (fig. 480. In both analyses, the peak acceleration is truncated at 0.12 g, owing to 

yielding of the soft top layer. 

The amplification of the horizontal and vertical components of ground motion along the surface of the two-dimensional model for the scaled Yerba Buena Island 

accelerogram is plotted in figures 49 and 50, respectively. 

The amplification factors coincide perfectly in the nonlinear analyses, whereas they differ in the linear analyses. 

From figures 48 through 50, we conclude that nonlinear 

behavior decreases the influence of wave propagation on 

the site amplification. 

Results similar to those in figures 48 through 50 for the 

original Yerba Buena Island accelerogram are shown in 

figures 51 through 53, respectively. The similarity of response with uniform input acceleration and with wavepropagation effects included shows that the influence of 

wave propagation is unimportant in this nonlinear analysis. Future research is needed to establish the effects of 

wave propagation in the presence of material nonlinearity. 

CONCLUSIONS 

We have analyzed the site response of the Marina District during the earthquake by using numerical modeling 

techniques, which encompass the conventional analyses 

used in engineering practice and advanced techniques capable of accounting for three-dimensional geometry and 

wave propagation. 

The one-dimensional analyses predict peak ground-surface accelerations of 0.12 and 0.15 g, for peak bedrock 

accelerations of 0.067 and 0.15 g, respectively. The amplification of bedrock acceleration resulted mainly from thick 

deposits of the older bay mud. The acceleration reaching 

the yellow hardpan was truncated by yielding of the soft 

top layer composed of artificial fill and the younger bay 

mud. The programs SHAKE and DETRAN, which are 

used to analyze one-dimensional site response in engineer- 
SITE-RESPONSE ANALYSES 

ing practice, yielded results in agreement with those of the 

program LINOS. However, the program SHAKE predicted 

a larger amplification, reflecting the limitation of an equivalent linear material model that does not consider complete failure. A simplified liquefaction analysis based on 

these acceleration values clearly indicates that the artificial 

fills liquefied during the earthquake. The Marina District 

was constructed in 1915 on landfill that was predisposed 

to ground amplification. Liquefaction of the sand filling 

the 1906 lagoon was therefore triggered by amplification 

of (he earthquake motion by natural deposits of the older 

bay mud. 

Two types of two-dimensional analyses were performed 

to complete the one-dimensional analyses. The first type 

assumed uniform input ground motion on the model 

boundary, whereas the second type attempted to account 

for the effects of wave propagation on the site response of 

the Marina District. The two-dimensional analyses predicted peak ground-surface accelerations of 0.20 and 0.23 g 

for peak bedrock accelerations of 0.067 and 0.15 g, respectively. The two-dimensional analyses therefore predicted a larger peak acceleration than did the onedimensional analyses, indicating that the one-dimensional 

site-response analyses used in engineering practice are not 

necessarily conservative. 

The two-dimensional analyses indicated that two-dimensional effects are important in modeling the site response 

of the Marina District. These two-dimensional effects, 

which resulted mainly from the irregular geometry of the 

bedrock surface and the layer of yellow hardpan, provide a 

better understanding of the deformational modes of the 

Marina District. The effects of wave propagation were 

found to be important but could not be completely characterized. The complex input acceleration generated along 

the model boundary tends to excite many other vibrational 

modes within the soft-soil deposits than the first fundamental mode used in one-dimensional models. Inclusion 

of wave-propagation effects in the site-response analysis 

substantially complicates the dynamic response of the soft 

soils. Material nonlinearity was observed to decrease these 

effects. The present study shows the complexity of siteresponse analyses for three-dimensional geologic structures and clearly indicates the need for future research in 

seismic site-response analysis. 

ACKNOWLEDGMENTS 

We thank V.W. Lee and his graduate research assistant 

X. Wu of the Department of Civil Engineering of the University of Southern California, Los Angeles, for their contribution to the wave-propagation analysis, and T.D. 

O'Rourke of Cornell University, Ithaca, N.Y., for sharing / his site-investigation data. This research was supported by 

National Science Foundation grant BCS9003656. 

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Martin, G.R., and Tsai, C.F., 1981, Nonlinear response of soft clay sediments to high-strain earthquake ground motions: Long Beach, Calif., Earth Mechanics Corp. report on contract USGS-14-08-0001- 

19106, p. 29-46. 

Masing, G., 1926, Eigenspannungen und Verfestigung beim Messing 

[Fundamental stresses and strengthening with brass]: Inter-national 

Congress of Applied Mechanics, 2d, Zurich, 1926, Proceedings. 

Mooeen-Vaziri, Nasser, and Trifunac, M.D., 1988, Scattering and diffraction of plane P and SV waves by two-dimensional inhomogeneities; 

part 11: Soil Dynamics and Earthquake Engineering, v. 7, no. 4, 

p. 189-200. 

Muraleetharan, K.K., Mish, K., and Arulanandan, K.K., 1990, DYSAC2; 

user's manual: Davis, University of California, Department of Civil 

Engineering. 

National Research Council, 1985, Liquefaction of soils during earthquakes: Washington, D.C., National Academy Press, p. 137-143. 

Prevost, J.H., 1978, Anisotropic undrained stress-strain behavior of clays: 

American Society of Civil Engineers Proceedings, Geotechnical Engineering Division Journal, v. 104, no. GT8, p. 1075-1090. 

1989, DYNAlD; a computer program for nonlinear seismic site 

response analysis-technical documentation: Buffalo, N.Y., National 

Center for Earthquake Engineering Research Technical Report 

NCEER-89-0025, p. 6-1 to 6-13. 

Schlocker, Julius, 1961, Geological topographic bedrock map of the San 

Francisco North quadrangle, California: U.S. Geological Survey 

Open File Map, scale 1 :3 1,680. 

1974, Geology of the San Francisco North quadrangle, California: 

U.S. Geological Survey Professional Paper 782, 109 p. 

Schmertman, J.H., 1975, Measurement of in situ shear strength: ASCE 

Conference on In Situ Measurement of Soil Properties, Raleigh, 

N.C., 1975, Proceedings, v. 2, p. 79-99. 

Schnabel, P.B., Lysmer, J., and Seed, H.B., 1972, SHAKE-a computer 

program for earthquake response analysis of horizontally layered 

sites: Berkeley, University of California, Earthquake Engineering 

Research Center Report EERC 72-12. 

Seed, H.B., 1970, Soil problems and soil behavior, in Wiegel, R.L., ed., 

Earthquake engineering: Englewood Cliffs, N.J., Prentice-Hall, 

D. 227-252. 

Seed, H.B. and ~driss, I.M., 1971, Simplified procedure for evaluation of 

soil liquefaction potential: American Society of Civil Engineers Proceedings, Soil Mechanics and Foundations Division Journal, v. 97, 

no. SM9, p. 1249-1273. 

Seed, H.B., Idriss, I.M., and Arango, Ignacio, 1983, Evaluation of liquefaction potential using field performance data: Journal of Geotechnical Engineering, v. 109, no. 3, p. 458-482. 

Seed, H.B., and Idriss, I.M., 1970, Soil moduli and damping factors for 

dynamic response analysis: Berkeley, University of California, 

Earthquake Engineering Research Center Report EERC 70-10. 

Seed, H.B. and Sun, J.I., 1989, Implications of site effects in the Mexico 

City earthquake of Sept. 19, 1985 for earthquake-resistant design 

criteria in the San Francisco Bay area of California: Berkeley, University of California, Earthquake Engineering Research Center Report UCB/EERC-89-03, p. 27-40. 

Shakal, A., Huang, M., Reichle, M., Ventura, C., Cao, T., Sherbume, R., 

Savage, M., Darragh, R., and, Petersen, C., 1989, CSMIP strongmotions records from the Santa Cruz Mountains (Loma Prieta), California earthquake of 17 October 1989: California Division of 

Mines and Geology, Office of Strong Motion Studies Report OSMS 

89-06, 196 p. 

Todorovska, M.L., and Lee, V.W., in press, Surface motion of circular alluvial valleys of variable depth for incident plane Pwaves-analytical solution: Royal Astronomical Society Geophysical Journal. 

U.S. Geological Survey, 1973, San Francisco North quadrangle, California: special topographic map, scale 1: 24,000. 

1990, Effects of the Lorna Prieta earthquake on the Marina District, San Francisco, California: Open-File Report 90-253. 

MARINA DISTRICT 

Time (s) 

Horizontal ---.-.- Vertical I 1 

1 

Period (s) 

Figure 19.-Acceleration-time history of horizontal (A) and vertical (B) 

components of ground motion, with response spectra (C) of horizontal 

(solid curve) and vertical (dashed curve) components, at borehole M4 

(fig. 4), as predicted by one-dimensional linear analyses for scaled Yerba 

Buena Island accelerogram (peak acceleration, 0.15 g). Curves in figure 

19C are plotted with 5-percent damping. 
SITE-RESPONSE ANALYSES 

0. 1 0. 20. 30. 40. 

Time (s) n. in. 

0. 1 0. 20. 30. 40. 

Time (s) 

Period (s) Period (s) 

- , -L-.-a-. L L 

-0. 04 -0.02 0. 0.02 0.04 

Shear strain (percent) 

Figure 20.-Acceleration-time history of horizontal (A) and vertical (B) components of ground motion, with corresponding response spectra (C, D), at 

borehole M4 (fig. 4), and stress-strain relation (Â£ at 6-m depth, as predicted by nonlinear (solid curves) and linear (dashed curves) one-dimensional 

analyses for scaled Yerba Buena Island accelerograrn (peak acceleration, 0.15 g). Curves in figures 20C and 200 are plotted with 5-percent damping. 
F118 MARINA DISTRICT 

Time (s) Time (s) 

Period (s) Period (s) 

$1 

-0. 4 -0.2 0. 0.2 0.4 

Shear strain (percent) Strain ell (percent) 

Figure 21.-Acceleration-time history of horizontal (A) and vertical (B) components of ground motion, with corresponding response spectra (C, D) at 

borehole M4 (fig. 4), and stress-strain relation at 9 (0- and 6 (0-m depth, as predicted by nonlinear (solid curves) and linear (dashed curves) onedimensional analyses for original Yerba Buena Island accelerogram (peak acceleration, 0.067 g). Curves in figures 21C and 21D are plotted with 5- 

percent damping. 
SITE-RESPONSE ANALYSES F119 

EXPLANATION 

- LINOS 

DETRAN 

........ SHAKE 

Period (s) 

Figure 23.-Response spectra of horizontal acceleration at borehole M4 

(fig. 4), calculated by using three computer programs of site-response 

analysis for scaled (A; peak acceleration, 0.15 g) and original (B; peak 

acceleration, 0.067 g) Yerba Buena Island accelerograms. 

Figure 22.-Acceleration-time history of horizontal (A, B) and vertical 

(C) components of ground motion at surface (solid curves), at top of 

yellow hardpan (dashed curves, figs. 22A, 22C), and at 4-m depth 

(dashed curve, fig 22B) at borehole M4 (fig. 4), as predicted by nonlinear 

one-dimensional analyses for original Yerba Buena Island accelerogram 

(peak acceleration, 0.067 g). 

SITE-RESPONSE AN 

8 r--~---l ' a a 1 

Period (s) 

Figure 29.-Response spectra of horizontal (A) and vertical (B) components of ground motion at borehole M4 (solid curves), at borehole WSS 

(dashed curves), and on bedrock (dot-dashed curves), as predicted by line two-dimensional analyses for scaled Yerba Buena Island accelerogram (peak acceleration, 0.15 g). 
F122 MARINA DISTRICT 

Time (s) Time (s) 

Period (s) Period (s) 

Shear strain (percent) Strain Ell (percent) 

Figure 30.-Acceleration-time history of horizontal (A) and vertical (B) components of ground motion, with corresponding response spectra (C, D), at 

borehole M4 (fig. 4), and stress-strain relation (E, F) at 9-m depth, as predicted by two-dimensional (solid curves) and one-dimensional (dashed curves) 

nonlinear analyses, using the program LINOS, for scaled Yerba Buena Island accelerogram (peak acceleration, 0.15 g). 
SITE-RESPONSE ANALYSES F123 

0. 10. 20. 30. 10. 20. 30. 40. 

n 

nJ 

Time (s) Time (s) 

0. 1. 2. 3. 4. 5. 0 0. 1. 2. 3. 4. 5. 

Period (s) Period (s) 

-0. 1 0. 0. 1 0.2 0.3 0.4 -0. 04 -0.02 0. 0.02 0.04 

Shear strain (percent) Strain ell (percent) 

Figure 31.-Acceleration-time history of horizontal (A) and vertical (B) components of ground motion, with corresponding response spectra (C, D), at 

borehole WSS (fig. 4). and stress-strain relation (E, F) at 9-m depth, as predicted by two-dimensional (solid curves) and one-dimensional (dashed 

curves) nonlinear analyses, using the program LINOS, for scaled Yerba Buena Island accelerogram (peak acceleration, 0.15 g). 
F124 MARINA DISTRICT 

Shear strain (percent) 

Time (s) 

Period (s) 

I I I., , -- 

I 1 I I 

-0. 04 -0.02 0. 0.02 0.04 

Strain cl1 (percent) 

Figure 32.-Acceleration-time history of horizontal (A) and vertical (B) components of ground motion, with corresponding response spectra (C, D), at 

borehole M4 (fig. 4), and stress-strain relation (E, F) at 9-m depth, as predicted by two-dimensional (solid curves) and one-dimensional (dashed curves) 

nonlinear analyses, using the program LINOS, for original Yerba Buena Island accelerogram (peak acceleration, 0.067 g). 
SITE-RESPONSE ANALYSES F125 

0. 10. 20. 30. 40. 

Time (s) 

n. 

Period (s) 

-, -pT , 1'- 

Shear strain (percent) 

0. 10. 20. 30. 40. 

Time (s) 

Period (s) 

-A& I 

-0. 04 -0.02 0. 0.02 0.04 

Strain (percent) 

Figure 33.-Acceleration-time history of horizontal (A) and vertical (B) components of ground motion, with corresponding response spectra (C, D), at 

borehole WSS (fig. 4), and stress-strain relation (E, F) at 9-m depth, as predicted by two-dimensional (solid curves) and one-dimensional (dashed 

curves) nonlinear analyses. using the LINOS, for orkina1 Yerba Buena Island accelerogram (peak acceleration, 0.067 g). 
MARINA DISTRICT 

8 

EXPLANATION 

-- Ã‘Ã‘Â Linear analysis (0.1 5 g ) 

t Â¥Nonlinea analysis (0.067 g ) 

Â Nonlinear analysis (0.1 5 Q ) 

B C D E F G H I J 

Location at surface 

Figure 34.-Amplification of horizontal component of ground motion along surface of two-dimensional model (fig. 25), as 

predicted by two-dimensional nonlinear and linear analyses. Letters refer to groups of boundary nodes in figure 37. 
SITE-RESPONSE ANALYSES 

EXPLANATION 

Â Linear analysis (0.1 5 g ) 

Â¥Nonlinea analysis (0.067 g ) 

Nonlinear analysis (0.15 Q ) 

B C D E F G H I J 

Location at surface 

Figure 35.-Amplification of vertical component of ground motion along surface of two-dimensional model (fig. 25), as predicted by two-dimensional nonlinear and linear analyses. Letters refer to groups of boundary nodes in figure 37. 
F128 MARINA DISTRICT 

l l Group C 

Figure 38.-Acceleration-time history of horizontal component of ground motion in bedrock for a vertical P wave (groups A, C, E, and F, fig. 37). 
SITE-RESPONSE ANALYSES F129 

Group A 

Group E 1 

Ill 

I 

Time (s) 

Group C 

e 

Group F 

20. 30. 

Time (s) 

Figure 39.-Acceleration-time history of vertical component of ground motion in bedrock for a vertical P wave (groups A, C, E, and F, fig. 37). 
MARINA DISTRICT 

EXPLANATION + - Group A 

---- Group B 

. - - - Group C 

.....-. Group D m - - ...- Group E 

0 1 2 3 4 5 

0 2 3 4 5 

Period (s) 

Figure 40.-Response spectra of horizontal (A) and vertical (B) components of ground motion in bedrock for a vertical P wave on original 

Yerba Buena Island accelerogram (peak acceleration, 0.067 g). 
SITE-RESPONSE ANALYSES F131 

Group E I 

n ^ ...,,..,,,,,,, ,,,, ,,,, ,,, 

Time (s) 

(M 

2 

sÃ‘ 

,"". 

GroupA . - 

Time (s) 

P 

Figure 41 .-Acceleration-time history of horizontal component of ground motion in bedrock for a vertical SV wave (groups A, C, E, and F, fig. 37). 

""~"~'~"'~~""~""l""~""l"' 

Group F I 
F132 MARINA DISTRICT 

Group A I 

Group E I 

Group C 

Group F I 

0. 10. 20. 30. 40. 

Time (s) 

Figure 42.-Acceleration-time history of vertical component of ground motion in bedrock for a vertical SV wave (groups A, C. E, and F, fig. 37). 
SITE-RESPONSE ANALYSES F133 

i~'~~l~'~~l.'~~l'~~. 

A 

EXPLANATION 

Group F - - - - Groups G and .E - - - - Groups H and D .-.-0.- Groups 1 and C - ...- Groups J and B 

Period (s) 

Figure 43.-Response spectra of horizontal (A) and vertical (B) components of ground motion in bedrock for a vertical SV wave on original 

Yerba Buena Island accelerogram (peak acceleration, 0.067 g). 

EXPLANATION 

P wave, vertical - - - - P wave, 20Â . -. - SV wave, vertical . - . . . . . SV wave, 20Â - ...- R wave 

Period (s) 

Figure 44.-Response spectra of horizontal (A) and vertical (B) components of ground motion at borehole M4 (fig. 4), as predicted by linear 

analyses for different types of waves on scaled Yerba Buena Island accelerograrn (peak acceleration, 0.15 g). 
Period (s) 

Figure 45.-Response spectra of horizontal (A) and vertical (B) components of ground motion at borehole M4 (fig. 4). as predicted by linear 

analyses for P waves traveling at 20' (solid curves) and -20Â (dashed 

curves). 
SITE-RESPONSE ANALYSES 

8. - 

EXPLANATION -B- Uniform acceleration 

7. -- 

Â Vertical P wave 

6. ---*- 

Â 

Inclined P wave (20' ) 

Vertical SV wave 

03 Â R wave 

4. -- .- -- Combined waves 

B C D E F G H I J 

Location at surface 

Figure 46.-Amplification of horizontal component of ground motion along surface of two-dimensional model (fig. 25), as 

predicted by linear analyses for different types of waves. Letters refer to groups of boundary nodes in figure 37. 
MARINA DISTRICT 

EXPLANATION 

-m- Uniform acceleration 

Â Vertical P wave 

-- Inclined P wave (20" ) 

Â 

- 

Vertical W wave 

Inclined SV wave (20" ) 

Â R wave 

X- Combined waves Â 

Location at surface 

Figure 47.-Amplification of vertical component of ground motion along surface of two-dimensional model (fig. 25). as predicted by linear analyses for different types of waves. Letters refer to groups of boundary nodes in figure 37. 
SITE-RESPONSE ANALYSES F137 

Time (s) Time (s) 

Period (s) -- 7' ------- I 

-1- - ., -u - . - -3 

-0. 4 -0.2 0. 0.2 0.4 

Shear strain (percent) 

Period (s) 

-0. 04 -0.02 0. 0.02 0.04 

Strain en (percent) 

Figure 48.-Acceleration-time history of horizontal (A) and vertical (B) components of ground motion, with corresponding response spectra (C, D), at 

borehole M4 (fig. 4). and stress-strain relation (E, F) at 9-m depth, as predicted by two-dimensional nonlinear analyses for SV waves inclined at 20' 

(solid curves) and uniform acceleration (dashed curves) on scaled Yerba Buena Island accelerogram (peak acceleration, 0.15 g). 
MARINA DISTRICT 

I EXPLANATION 

7. - Inclined SV wave (nonlinear analysis) 

Ã‘Ã‘n Inclined SV wave (linear analysis) 

Uniform acceleration (nonlinear analysis) 

. 5. +J Uniform acceleration (linear analysis) u 

B C D E F G H I J 

Location at surface 

Figure 49.-Amplification of horizontal component of ground motion along surface of two-dimensional model (fig. 25), as 

predicted by two-dimensional nonlinear analyses with wave-propagation effects included for scaled Yerba Buena Island accelerogram (peak acceleration, 0.15 g). Letters refer to groups of boundary nodes in figure 37. 

- EXPLANATION Inclined W wave (nonlinear analysis) 

t - Inclined SV wave (linear analysis) 

Uniform acceleration (nonlinear analysis) 

t * Uniform acceleration (linear analysis) 

B C D E F G H I J 

Location at surface 

Figure 50.-Amplification of vertical component of ground motion along surface of two-dimensional model (fig. 25), as predicted by two-dimensional nonlinear analyses with wave-propagation effects included for scaled Yerba Buena Island accelerogram 

(peak acceleration, 0.15 g). Letters refer to groups of boundary nodes in figure 37. 
SITE-RESPONSE ANALYSES F139 

. - )I' f 8- 4 1 

s ^ lib^ 'I^ ' ,; 111' - u\ 

u (8 S 0 * , 1 , ,1 I I, I(,;; '11 11, $1 Ill I I!#^,^- III I ,I / Bt I ( t i, !I I 

,, ;;y 1 

Time (s) Time (s) 

0. 1. 2. 3. 4. 5. 

Period (s) Period (s) 

Shear Strain ~11 (percent) strain (percent) 

Figure 51.-Acceleration-time history of horizontal (A) and vertical (B) components of ground motion, with corresponding response spectra (C, D), at 

borehole M4 (fig. 4), and stress-strain relation (E, F) at 9-m depth, as predicted by two-dimensional nonlinear analyses for SV wiiyes inclined at 20' 

(solid curves) and uniform acceleration (dashed curves) on original Yerba Buena Island accelerogram (peak acceleration, 0.067 g). 
MARINA DISTRICT 

- Inclined W wave (linear analysis) 

Uniform acceleration (nonlinear analysis) 

8. -> 

' - Uniform acceleration (linear analysis) 0 

7- 

B C D E F G H I J 

Location at surface 

EXPLANATION 

-- Inclined W wave (nonlinear analysis) 

Figure 52.-Amplification of horizontal component of ground motion along surface of two-dimensional model (fig. 25), as 

predicted by two-dimensional nonlinear analyses with wave-propagation effects included for original Yerba Buena Island accelerogram (peak acceleration, 0.067 g). Letters refer to groups of boundary nodes in figure 37. 

t - Inclined W wave (linear analysis) 

Uniform acceleration (nonlinear analysis) 

8. 

'- t Uniform acceleration (linear analysis) 

7. 

1 II I I I I 1 I 

B C D E F G H I J 

Location at surface 

EXPLANATION 

-- - Inclined W wave (nonlinear analysis) 

Figure 53.-Amplification of vertical component of ground motion along surface of two-dimensional model (fig. 25), as predicted by two-dimensional nonlinear analyses with wave-propagation effects included for original Yerba Buena Island accelerogram 

(peak acceleration, 0.067 g). Letters refer to groups of boundary nodes in figure 37. 
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND FAILURE 

MARINA DISTRICT 

BEHAVIOR OF THE SEAWALLS AND SHORELINE 

DURING THE EARTHQUAKE 

By H.T. Taylor, J.T. Cameron, S. Vahdani, and H. Yap, 

Harding Lawson Associates 

CONTENTS 

Page 

F141 

14 1 

141 

141 

142 

143 

143 

143 

144 

144 

144 

149 

151 

152 

152 

ABSTRACT 

I 

Deformations resulting from the earthquake occurred 

in the seawalls that surround the St. Francis Yacht Club 

Harbor, in the seawall north of the St. Francis Yacht Club 

along the shore of San Francisco Bay, and in the seawall 

north of the Marina Green. Although the deformations 

were as great as 2 ft, damage to the walls was relatively 

light. This report describes the subsurface conditions, including the history of filling this reclaimed land; records 

the approximate deformations; and estimates the magnitude of ground shaking. The study area is north of Marina 

Boulevard, east of the Presidio, and includes Fort Mason. 

INTRODUCTION 

This study records the earthquake-related deformations 

(both settlement and lateral displacement) that were observed, reported, and measured in the area north of Marina 

Boulevard. The study area includes the Marina Green, Fort 

Mason, Gas House Cove, and the St. Francis Yacht Club 

Harbor (fig. 1). 

We first describe the fill history and subsurface conditions; then the major structures, including Fair's seawall, 

the Marina Boulevard seawall, and the Marina Boulevard 

box sewer; and finally, the estimated ground shaking during the earthquake. 

SUBSURFACE CONDITIONS 

FILL HISTORY 

Most of the present Marina District is founded on fills of 

various types that were constructed to provide greater land 

area above water. 

A map by the U.S. Coast Survey dated 185 1 shows a 

small bay, herein referred to as Marina Cove, and a tidal 

slough draining a marsh that extended westward from the 

present location of Scott Street into the Presidio. A broad 

area of beach sand, perhaps with some discontinuous cover 

of dune sand, that existed west of Marina Cove is referred 

to as Strawberry Island. 

By 1894, a seawall known as Fair's seawall had been 

built along the alignment shown in figure 1. This seawall 

was reportedly built of rock from (he San Bruno Mountain 

quarry (Olmstead and others, 1977); the rock was dumped 

from a pile-supported trestle. A narrow band of fill was 

placed by 1906 behind Fair's seawall; this seawall was later used to retain the hydraulic fill that formed the land for 

the Panama-Pacific International Exposition of 19 15. 

The area east of Webster Street and one arm of Fair's 

seawall had been filled for a gas plant before 1903. This 

filled area was described as "earthen fill surrounded by a 

rock retaining wall.'' A pile-supported bulkhead and transport docks were constructed at Fort Mason in 1910; the 

area behind this bulkhead was filled with sand. In 1962, 

the Gashouse Cove Yacht Harbor was created, and a driven 

concrete-sheet-pile wave barrier was installed. 

A small boat harbor was created by the Fulton Shipbuilding Works in the area of St. Francis Spit before 

1900. This harbor was utilized during the 1915 exposition; 
MARINA DISTRICT 

the California Building was supported on fill that occupied the west end of what is now the St. Francis Yacht 

Club Harbor. After the San Francisco Port Commissioners acquired these properties, the yacht harbor was improved about 1920; improvements included dredging the 

fill that had formerly supported the California Building. 

The original St. Francis Yacht Club building was constructed on a pier about 1928 and was accessible by a 

road. The filling of this spit area continued during the 

1930's' and a wall was built in 1935 by the Works 

Progress Administration. In 1958, the yacht-harbor entrance was moved from the north side to the east side, 

and the spit was further extended. Repairs and maintenance were performed on the seawalls surrounding the 

yacht harbor during the period from 1952 through the 

1980's. There is no evidence that the existing seawalls on 

either side of the spit are pile supported. 

SITE CONDITIONS 

The ground surface in the Marina District slopes downward very gently toward the bay, at an average grade of 

about 0.4 percent. 

The soil profile along Divisadero Street (fig. 2) shows 

that (1) the fill thickness is 20 to 30 ft and (2) the bay 

mud is as much as 80 ft thick near Marina Boulevard. 

However, bay mud was not present in the boreholes 

drilled near the St. Francis Yacht Club, where the subsurface consists of about 20 ft of medium-dense sand fill, 20 

ft of medium-dense beach sand underlain by loose to medium-dense silty sand to a depth of 80 ft, and dense silty 

sand to a depth of 90 ft. The ground-water level is approximately 8 ft below the ground surface. 

The subsurface beneath Fort Mason (fig. 1) consists of 0 

to 35 ft of loose to medium-dense sandy fill containing a 

few silt and clay zones. Below the sandy fill is 0 to 10 ft 

of bay mud consisting of soft to medium-stiff silt and clay. 

This bay mud is underlain by medium-dense to dense sand 

and silty sand that extends to bedrock at a depth of about 

100 ft. The hydraulically placed sand fill is generally fine 

grained, with a mean grain size of 0.15 to 0.20 mm (Bennett, 1990). It is generally loose to medium dense, with 

blow counts generally less than 10 (O'Rourke and others, 

1990a) and a fines content of 3 to 21 percent' (Bennett, 

 ore hole data indicate that the fines content is a high as 35 percent. 

ST. FRANCIS SPIT ~~&!#&\ ST. FRANCIS YACHT CLUB HARBOR 

\/ &A BOULEVARD SEAWALL / GASHOUSE COVE YACHT HARBOR 

LIMIT OF STUDY AREA' LWATO ST. 

Base from U.S. Geological Survey San Francisco North 7.5' quadrangle, photorevlsed In 1973 

EXPLANATION 

-Approximate Alignment of Fair's Seawall 

. . . . . . . . Approximate Alignment of Marina Boulevard Seawall 

.- .- .- Approximate Alignment of Marina Boulevard Box Sewer 

Figure 1.-Marina District of San Francisco, showing locations of features referred to in text. Base from U.S. Geological Survey (1990). 
BEHAVIOR OF THE SEAWALLS AND SHORELINFi DURING THE EARTHQUAKE 

1990). The bay mud is generally soft to medium stiff and 

is normally consolidated (09Rourke and others, 1990b); 

the old bay clay underlying the bay mud is generally stiff 

to very stiff. 

The slopes along the shoreline typically range from 3:l 

to 6:l (horizontal to vertical). 

FAIR'S SEAWALL 

Olmstead and others (1977) descad the construction 

of Fair's seawall (fig. I), which was built about 1894 by 

James G. Fair to fill approximately 15 blocks of tidelands 

and 21 blocks of shoreline property for commercial and 

industrial development. The seawall (of undocumented 

height) was built of rock that was brought to the site in 

cars on barges from the San Bruno Mountain quarry. The 

cars were unloaded from the barges by hoisting engines 

onto a pile-supported trestle constructed approximately 

parallel to the proposed alignment of the seawall, The rock 

was then dumped from the cars at various points along the 

alignment, to construct the seawall. A masonry seawall 

was built on top of Fair's seawall in 1935. 

(VERY LOOSE TO MEDIUM DENSE) FILL 7- 

BEACH (AND DUNE) SAND 

(MEDIUM DENSE TO DENSE) 

BAY MUD 

(WFT TO MEDIUM STIFF) 

(VERY DENSE) 

BAY MUD 

(SOFT TO 

MEDIUM 

STIFF) 

I Notes: 1 

1. Elevations referenced to San Francisco City Datum. 

-120 A 2. MSL denotes Mean Sea Level. 

3.3 denotes groundwater level. 

MARINA BOULEVARD SEAWALL 

The Marina Boulevard seawall (fig. 1) was built between 

1933 and 1934 through collaborative efforts of the San 

Francisco Board of Supervisors and the State Emergency 

Relief Administration. The Marina Boulevard seawall is a 

cantilever concrete wall with basalt block facing supported 

by wood piles. This seawall is about 30 ft north of the 

Marina Boulevard box sewer. The seawall is 5 ft wide at 

the base and approximately 9.5 ft high. 

MARINA BOULEVARD BOX SEWER 

The Marina Boulevard box sewer (fig. 1) is part of the 

Northshore Outfalls Consolidation Project, a high-capacity, 

gravity-flow, consolidating sewer designed to collect the 

dry- and wet-weather flows from all existing outfall sewers in the northshore area. The box sewer runs along the 

northern curbline. It was constructed in the late 1970's by 

open-cut techniques, and the excavation was temporarily 

shored by sheet piles, which we understand were removed 

at the end of construction. 

NORTH \ 

' iT. FRANCIS ST. FRANCIS 3 , 

YACHT CLUB HARBOR , SPIT , 

CONCRETE HU-2 

(MEDIUM DENSE) 

9------7----e8 

BOX SEWER 

0 2 00 

SCALE: Horizontal U 

Vertical: As Shown 

Scale in Feet 

4. HLA-2 denotes Boring No. 2 drilled 

by Harding Lawson Associates in 1977. 

Figure 2.-Subsurface profile along Divisadero Street. 
F144 MARINA DISTRICT 

The top of the box sewer is approximately 2 ft below 

the ground surface. The dimensions of the box sewer increase from west to east, from approximately 11 ft wide 

by 12 ft high at Baker Street to approximately 21 ft wide 

by 23 ft high at Buchanan Street. The box sewer is underlain by a 1-ft-thick layer of drain rock, and the 1-ft-wide 

space between the sheet pile and its sides was also filled 

with drain rock. The drain-rock backfill was intended to 

reduce any uplift pressure that may develop below the box 

sewer, should the underlying fills liquefy during a major 

earthquake. 

DEFORMATION OF THE MARINA 

SHORELINE 

SETTLEMENT 

Ground-surface settlement of the Marina shoreline resulting from the earthquake was determined by comparing 

a November 1987 topographic map (1:600 scale) of the 

San Francisco Marina with surveying information obtained 

between October and December 1990. Although some minor consolidation settlement may have occurred within 

this period, we can reasonably assume that any differences 

in elevation between these two surveys indicate the 

amount of settlement caused by the earthquake. 

The approximate amounts of settlement along the shoreline between the two surveys are shown in figures 3 and 4. 

From 0.5 to almost 2 ft of settlement seems to have occurred in the vicinity of the St. Francis Yacht Club. On the 

basis of information obtained from the contractors who 

repaired the St. Francis Yacht Club, the maximum settlement of the ground at the yacht club was 0.5 to 1.0 ft. The 

pile-supported building, however, settled less than 1 in. In 

addition, visual inspection of those areas where large settlement is indicated does not appear to correlate with these 

high values. We cannot explain the discrepancies between 

the observed and calculated amounts of settlement in the 

vicinity of the St. Francis Yacht Club. 

From 0.5 to 0.7 ft of settlement occurred along the sidewalk immediately north of Marina Boulevard between 

Baker and Scott Streets. This amount of settlement appears to be consistent with that reported by Bennett (1990) 

for settlements measured along the south side of Marina 

Boulevard. 

The survey information indicates that 1 to 2 ft of settlement occurred in the vicinity of the Harbor Master building near the north end of Scott Street (fig. 1). The 

pavement surface slumped approximately 0.6 to 1.0 ft immediately north of a buried concrete box culvert near the 

bayward tip of Scott Street. In addition, it appears that approximately 1 ft of slumping occurred at the south edge of 

the pavement surf'ace in the seawall that runs east-west 

immediately south of the Harbor Master building. The seawalls and the Harbor Master building itself appear to have 

undergone little or no differential settlement. As with the 

relatively large amounts of settlement calculated near the 

St. Francis Yacht Club, those calculated near the Harbor 

Master building do not appear consistent with visual inspection. 

Approximately 0.5 to 1 ft of settlement occurred at the 

northeast corner of the Marina shoreline (fig. 4). The calculated settlements in this part of the Marina District are 

consistent with estimates made by visual inspection. 

Measurements near the outfall location of the pile-supported sewerline that is aligned with the projection of 

Pierce Street (fig. 1) indicate that approximately 6 to 8 in. 

of differential settlement occurred between the sewer and 

the surrounding soils. Figure 4 does not include settlements calculated for this area because it was not included 

in the 1990 survey. Similar measurements at the outfall 

location of the pile-supported sewerline that exits near the 

west edge of the St. Francis Yacht Club indicate approximately 0.8 ft of differential settlement between the sewer 

and the surrounding soil surface (fig. 5). These measurements are consistent with the amount of settlement indicated by comparison of the survey data obtained in 1987 

and 1990. 

Fort Mason (fig. I), immediately east of the Marina 

Green, is composed of a combination of three pile-supported piers and five adjacent pile-supported buildings 

with slab-on-grade floors. Each of the buildings is 200 to 

370 ft long by 50 ft wide and oriented lengthwise in a 

north-south direction. Four of the five buildings have perimeter loading docks supported on shallow footings that 

extend 3 to 5 ft away from the building face. The loading 

docks range from 1.5 to 3.5 ft in height, with a concrete 

slab-on-grade at the dock surface. As a result of the earthquake, the loading docks settled differentially with respect 

to the buildings by as much as 0.6 ft. Similar amounts of 

differential settlement occurred between the floor slabs 

and the building walls inside the buildings. The greater 

amount of settlement occurred at the north end of the 

buildings, where the underlying fill and bay mud are thickest. In addition to settling of the loading docks, the buildings also underwent separation of exterior metal stairways 

from the tops of the loading dock and some separation of 

utility lines that were connected to the outside of the 

buildings. There were no noticeable signs of differential 

movement between the base of the loading docks and the 

adjacent pavement; they appear to have settled together. 

LATERAL SPREADING 

The 1987 topographic map, which was obtained by aerial photography before the earthquake, is not sufficiently 

accurate to measure the lateral movements that occurred 

as a result of the earthquake. Therefore, lateral spreading 
Figure 3.4omputed settlements of west side of Marina shoreline (in feet) between November 1987 and December 1989 surveys. 
Figure 4.4omputed settlements of east side of Marina shoreline (in feet) between November 1987 and December 1989 surveys. 
BEHAVIOR OF THE SENWALLS AND SHORELINE DURING THE EARTHQUAKE F147 

was determined by visual inspection or by discussing cisco Yacht Club Harbor to the south, whereas the separamovements with knowledgeable people present immedi- tions in the masonry landscape wall perpendicular to the 

ately after the earthquake. The greatest apparent lateral shore and west of the St. Francis Yacht Club indicate a 

spreading was in the parking area and seawall west of the total displacement of about 1 ft (fig. 7). Lateral moveSt. Francis Yacht Club (fig. 6). Summing up the cracks in ments of the seawall and parking area east of the St. Franthe pavement indicates a movement of approximately 2 ft cis Yacht Club appeared to be somewhat smaller. 

between San Francisco Bay to the north and the San Fran- Deformation in the seawalls directly north and south of 

Figure 5.-Storm sewer outlet immediately west of the St. Francis Yacht Club. Photograph taken in October 

1989. 

Figure 6.-Cracks in asphalt pavement southwest of the St, Francis Yacht Club. Photograph taken in October 

1989. 
F148 MARINA DISTRICT 

the St. Francis Yacht Club is discussed in the next section. 

No evidence exists that any of the seawalls are supported 

on pilings instead of on spread footings on sand fill. The 

cobblestone seawall located at the west end of the St. 

Francis Yacht Club Harbor was considerably damaged, 

owing to both lateral movement and settlement (fig. 8). 

The pile-supported seawall located along the south side of 

the St. Francis Yacht Club Harbor just north of Marina 

Boulevard showed no evidence of any significant horizontal movement. The masonry seawall along San Francisco 

Bay just north of the Marina Green is believed to be supported on spread-footing foundations on top of Fair's seawall. This masonry seawall showed no evidence of 

uneven lateral movement or settlement (fig. 9), but there 

was a crack a few inches wide parallel to, and about 30 to 

50 ft behind, the seawall. There was no evidence of lateral 

Figure 7.-Earthquake-caused cracks in masonry wall on west side of the St. Francis Yacht Club. Photograph 

taken in 1991. 

Figure 8.-Seawall at west end of the St. Francis Yacht Club Harbor. Photograph taken in 1991. 
BEHAVIOR OF THE SEAWALLS AND SHORELINE DURING THE EARTHQUAKE F149 

movement of the seawalls around Gashouse Cove or in 

the Fort Mason area. 

ST. FRANCIS YACHT CLUB 

Because most of the St. Francis Yacht Club building is a 

relatively new structure supported on long concrete pilings, it is a reference point for judging both lateral spreading and vertical settlement. Observed movements are 

mapped in figure 10 and detailed below: 

Location 

(fig. 10) 

Comments 

A ----- Paved parking lot (fig. 6). Horizontal movement 

toward San Francisco Bay, about 2 ft; vertical 

settlement, generally less than 1 ft. 

B------ Masonry wall separated into 12 segments, 8 to 

12 ft long, with gaps of as much as 2 in; total 

of gaps, about 12 in. (fig. 7). 

C------ Open deck supported on wood piles reportedly 

less than 60 ft long moved northward away 

from west wing 3 in. and settled about 8 in. 

D ----- Open deck supported on wood piles moved 

northward 12 in. and settled about 8 in. sloping 

down toward north. Upper 2 ft of piles under 

east wing visible, with slight lean toward north. 

Soil craters around piles (fig. 11). 

E------ Concrete-block wall on spread footings settled 

and shifted toward San Francisco Bay (fig. 12). 

F------ Parking lot and seawall settled and shifted toward San Francisco Bay (fig. 13). 

G------ West wing built in 1977 after original building 

was destroyed by fire. New 16-in.-square prestressed piles 85 to 90 ft long were driven. 

Floor slab was poured on top of old wood-pilesupported deck, leaving about 2 ft of 

clearspace above ground surface. Moderate 

damage to utilities supported on ground. Building within 1 in. of level but estimated to have 

shifted northward 2 to 4 in. 

H------ East wing built in 1985 on 90-ft-long, 16-in.- 

square prestressed piles, including courtyard. 

No visible signs of movement in building but 

extensive damage to underground utilities. 

Utilities were embedded in fill, which had been 

used as a form to pour floor slab. Underground 

tunnels dug to repair utilities. About 6 in. of 

settlement observed in ground surface, and 

pipes displaced that same amount (fig. 14). 

I ------ South wing built in 1929 and survived 1977 fire, 

so it was not rebuilt; was either supported on 

short wood piles or on spread footings. Settled 

6 to 12 in. with structural damage. A 4-in. gap 

between south wing and 1977 west wing 

caused by lateral spreading. Demolished; new 

two-story building built on new 90-ft-long, 16- 

in.-square prestressed piles. 

J ------ Slabs on ground settled about 4 in. more than 

adjacent building and moved southward from 

building 4 to 6 in. 

K ------ Soil adjacent to pile-supported entrance slab indicated 6 to 8 in. of vertical and lateral movement. 

Figure 9.-Masonry wall above Fair's seawall. Note storm-sewer outfall in foreground. Photograph taken in 

1991. 
MARINA DISTRICT 

SAN FRANCISCO BAY 

A A RIPRAPSLOPE A A 

1 DECK \ 

WEST WING, 1977 

@ 

< 

s 

>- 

r SOUTH WING, 

z 1929 

$ 

s 

REBUILT, 

1990 

\ BLOCK 

FENCE 

- 

EAST WING, 1985 

COURTYARD I@ 

Figure 10.Ã‘Sketc plan of the St. Francis Yacht Club. Letters denote locations referred to in text. 

Figure 11.-Approximate 8-in. gap between concrete pile and adjacent soil caused by ground settlement 

below the St. Francis Yacht Club. Photograph taken in October 1989. 
BEHAVIOR OF THE SEAWALLS AND SHORELINE DURING THE EARTHQUAKE F15 1 

Figure 12.-Separation between concrete-block wall and east building 

wall of the St. Francis Yacht Club. View westward; photograph taken in 

October 1989. 

L ------ Yacht-harbor edge about 130 ft south of St. Francis Yacht Club is masonry wall, not pile supported, and is at top of riprapped 4:l 

(horizontal to vertical) slope about 15 ft high. 

No visible cracking or displacement of masonry wall. Short wood piles that support hoist 

platform and guide floats leaned toward south. 

Piles under hoist also settled a few inches. 

SEISMIC GROUND SHAKING 

Because there were no accelerographs in the Marina 

District at the time of the main shock, recorded motions 

are not available for the area. The extensive building damage Aid ground failure in the Marina District suggest a 

significant amplification of bedrock motion in that area 

relative to such nearby undamaged areas as Pacific 

Heights or Russian Hill. Because of the collapse and widespread structural damage to buildings in the Marina District, and because some of these structures were severely 

damaged with no apparent evidence of ground failure, a 

modified Mercalli intensity of IX has been assigned to this 

area (Benuska, 1990) 

The closest accelerograph that recorded the main shock 

was located at a fire station in Pacific Heights, approximately 1.5 km south of the Marina District. The recorded 

motions at this station and on Telegraph Hill, about 2 km 

east of the Marina District indicate that the average of the 

two horizontal components of peak bedrock acceleration 

in the Marina District was about 0.07 g. The frequency 

content of average bedrock motions recorded in the San 

Francisco Bay area, including those recorded at Pacific 

Figure 13.-Parking-lot deformation east of the St. Francis Yacht Club. Photograph taken in 1991. 
F152 MARINA DISTRICT 

Heights and on Telegraph Hill, indicate that bedrock motion had significant energy in the period range 0.25-1.0 s 

(Office of Strong Motion Studies, 1989; Housner and Penzien, 1990). Also, recordings of aftershocks in the Marina 

District, including data from stations immediately south of 

the Marina Green, indicate that ground motions were significantly amplified (relative to bedrock sites) in the same 

period range (see Boatright and others, this chapter). 

The subsurface along Fair's seawall (north of the Marina Green) in the Marina District consists of an average of 

about 25 ft of sand fill and dune sand, 55 ft of Holocene 

bay mud, 4 ft of dense sand (hardpan), and 180 ft of old 

bay clay, with estimated low-strain shear-wave velocities 

of 600, 550, 1,200, and 1,000 ft/s, respectively (Kayen 

and others, 1990; Bardet and others, 1991). The site period, estimated from a weighted-average shear-wave velocity of 870 ft/s and a depth to bedrock of 270 ft, was about 

1.25 s. 

On the basis of a one-dimensional wave-propagation 

analysis (Bardet and others, 1991; Dickenson and Seed, 

1991) and the recorded motion at Treasure Island under 

similar soil conditions, the average of the two horizontal 

ground-surface accelerations during the earthquake is estimated at 0.17 g. At the St. Francis Yacht Club, where sand 

fill is underlain by natural sand, the amplification factor is 

estimated to be less than along Fair's seawall. Neglecting 

the effects of liquefaction on ground-motion parameters, 

the average of the two horizontal ground-surface accelerations near the St. Francis Yacht Club during the earthquake is estimated at 0.12 g. 

CONCLUSIONS 

The hydraulically placed sand fill and loose natural-sand 

deposits near the shoreline of the Marina District in San 

Francisco underwent liquefaction during the earthquake, 

resulting in ground settlements and lateral spreading of as 

much as 2 ft. Earlier studies (John A. Blume & Associates, 

1974) predicted that liquefaction could occur in the Marina District. The greatest apparent lateral spreading was in 

the parking area and seawall west of the St. Francis Yacht 

Club. 

The pile-supported Marina Boulevard seawall showed 

no evidence of any significant lateral movement. Fair's 

seawall, a rock dike with a masonry seawall on top, 

moved a few inches. 

We performed a deformation analysis of Fair's seawall, 

using the method of Newmark (1965), the accelerationtime history recorded on Treasure Island (with peak acceleration scaled to 0.17 g), and a yield acceleration of 0.05 g 

(Harding Lawson Associates and others, 1991). The results 

of this analysis indicate movement of Fair's seawall by 

about 6 in., which agrees with the observed movement. 

REFERENCES CITED 

Bardet, M.K., Martin, G.R., and Proubet, J., 1991, Preliminary results of 

the dynamic response of the Marina District of San Francisco during the Loma Prieta earthquake: Japan-U.S. Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures 

Figure 14.Ã‘Separate 3-in.-diameter utility line beneath the St. Francis Yacht Club. Bottom of slab-on-grade 

is at top. Photograph taken in 1990. 
BEHAVIOR OF THE SEAWALLS AND SHORELINE DURING THE EARTHQUAKE F153 

for Soil Liquefaction, 3d, San Francisco, 1990, Proceedings, p. 

109-128. 

Bennett, M.J., 1990, Ground deformation and liquefaction of soil in the 

Marina District, chap. D of Effects of the Loma Prieta earthquake 

on the Marina District, San Francisco,, California: U.S. Geological 

Survey Open-File Report 90-253, p. Dl-D36. 

Benuska, Lee, ed., 1990, Loma Prieta earthquake reconnaissance report: 

Earthquake Spectra, v. 6, supp. 9041,448 p. 

Dickenson, S.E., and Seed, R.B., 1991, Correlations of shear wave velocity and engineering properties for soft soil deposits in the San Francisco Bay Region: Berkeley, University of California, Earthquake 

Engineering Research Center Report UCBiEERC-ALIXX, 105 p. 

Harding Lawson Associates, Dames & Moore, Kennedy/Jenks/Chilton, 

and EQE Engineering, 1991, Liquefaction study, Marina District and 

Sullivan Marsh area, San Francisco, California; final report prepared 

for San Francisco Department of Public Works: San Francisco, 144 p. 

Housner, G.W., and Penzien, J., 1990, Competing against time; report of 

the Governor's Board of Inquiry on the 1989 Loma Prieta Earthquake: Sacramento, Calif., 264 p. 

John A. Blume & Associates, 1974, San Francisco seismic safety investigation; report prepared for San Francisco Department of City Planning: San Francisco, 124 p. 

Kayen, R.E., Liu, H.-P., Fumal, T.E., Westerlund, R.E., Warrick, R.E., 

Gibbs, J.F., and Lee, H.J., 1990, Engineering and seismic properties 

of the soil column at Winfield Scott School, San Francisco, chap. G 

of Effects of the Loma Prieta earthquake on the Marina District, San 

Francisco, California: U.S. Geological Survey Open-File Report 90- 

253, p. Gl-Gl8. 

Newmark, N.M., 1965, Effects of earthquakes on dams and embankments: Geotechnique, no. 2, p. 139-160. 

Office of Strong Motion Studies, 1989, Plots of the processed data for 

the interim set of 14 records from the Santa Cruz Mountains earthquake of October 17, 1989: Sacramento, California Division of 

Mines and Geology, 133 p. 

Olmstead, R., Olmstead, N., and Pastron, A., 1977, San Francisco Waterfront; report on historical cultural resources for the north shore and 

channel outfalls consolidation projects: San Francisco, Wastewater 

Management Program, 728 p. 

O'Rourke, T.D., Gowdy, T.E., Stewart, H.E., and Peese, J.W., 1990a, 

Lifeline performance and ground deformations in the Marina during 

the 1989 Loma Prieta Earthquake: U.S.-Japan Workshop on Earthquake Resistant Design of Lifeline Facilities and Countermeasures 

for Soil Liquefaction, 3d, San Francisco, 1990, Proceedings, p. 

129-146. 

O'Rourke, T.D., Stewart, H.E., Blackburn, F.T., and Dickerman, T.S., 

1990b, Geotechnical and lifeline aspects of the October 17, 1989 

Loma Prieta earthquake in San Francisco: Buffalo, N.Y., National 

Center for Earthquake Engineering Research Technical Report 90- 

001. 

U.S. Geological Survey, 1990, Effects of the Loma Prieta earthquake on 

the Marina District, San Francisco, California: Open-File Report 

90-253. 
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND FAILURE 

MARINA DISTRICT 

LIFELINE PERFORMANCE AND GROUND DEFORMATION 

DURING THE EARTHQUAKE 

By Thomas D. O'Rourke, Jonathan W. Pease, and Harry E. Stewart, 

Cornell University 

CONTENTS 

Page 

F155 

155 

156 

156 

159 

159 

161 

163 

165 

166 

167 

176 

177 

178 

178 

ABSTRACT 

We describe the subsurface conditions and settlements 

associated with soil liquefaction in the Marina District as a 

result of the earthquake, and evaluate the earthquake performance of the water-supply, gas-distribution, and wastewater-conveyance systems. The response of the Municipal 

Water Supply System depended strongly on pipe diameter; 

moreover, strong correlations exist for each diameter of 

pipe between the repair rate per unit length of pipe and the 

angular distortion, a measure of the local slope of the settlement profile. The close correspondence between the settlement distribution and the pattern of damage to buried 

utilities emphasizes the critical role of subsurface conditions in the performance of lifeline systems. 

The vertical strains inferred from surface settlements 

in various sandy soils agree closely with the strains predicted by means of existing simplified procedures, provided that the presence of nonliquefiable soils is accounted 

for properly. The postliquefaction consolidation of hydraulic fill in the Marina District apparently was influenced by 

layers of fine-grained sedimentary deposits. The resolution 

in delineating subsurface conditions with cone-penetrationtest measurements is important for estimating the magnitude and extent of postliquefaction consolidation in the hydraulic fill. Hydraulic fill, because it may be interstratified 

with fine-grained soils, is likely to require a more detailed 

evaluation for assessing postliquefaction settlement than 

can be supplied by the widely used standard penetration 

test and split-spoon sampling. 

INTRODUCTION 

The Marina District is a micro~osm of the types of site 

response and damage patterns that can be sustained in the 

most vulnerable settings of the San Francisco Bay area. 

During the earthquake, the deep alluvial basin and thick 

deposits of Holocene bay mud underlying the Marina District amplified accelerations and altered the natural period 

of ground motions transmitted from bedrock to surface 

structures. Liquefaction of loose sandy fill led to settlement 

and lateral movement of the grou d. Especially important 

was the influence of ground defo 4 ation on buried utilities. 

Damage to the water-distributiori system in the Marina 

District cut off critical water resources that were needed 

during the outbreak of fire which followed the earthquake. 

Various reports have already been written about the 

earthquake in the Marina District (for example, U.S. Geological Survey, 1990; Mitchell and others, 1990; O'Rourke 

and others, 199la, b; Bardet and others, 1991; Bonilla, 

1991). In addition, a detailed study of geotechnical conditions and underground public facilities in areas of potential 

ground deformation from liquefaction, including the Marina District, has been performed for the city of San Francisco (Harding Lawson Associates and others, 1991). 

This report concentrates on two aspects of earthquake response in the Marina District. First, we summarize the 

damage to buried lifeline systems and evaluate it in the 

context of the historical and geotechnical factors contributing to the disruption of these systems. Second, we examine 

the soil characteristics affecting postliquefaction consolidation, and draw conclusions with respect to the ground deformations that occurred in natural and fill materials. We 
F156 MARINA DISTRICT 

show that postliquefaction consolidation played a critical 

role in lifeline performance, and we develop relations between the magnitude of settlement and the proportion of 

pipeline system damaged. 

HISTORICAL DEVELOPMENT 

OF THE MARINA DISTRICT 

The Marina District is bounded by San Francisco Bay 

on the north, the Presidio on the west, and Lombard Street 

and Van Ness Avenue on the south and east, respectively. 

In this report, we focus on that part of the district to the 

west of Laguna Street. As discussed by Bonilla (this chapter), this area overlies the deepest part of an underlying 

bedrock basin and includes loose fills. Furthermore, the area includes virtually all locations of lifeline damage and 

pipeline replacements as a result of the earthquake. 

Like several other sites in the San Francisco Bay area, 

the Marina District has been developed by placing sandy 

fills on soft clay and silt. A plan view of the Marina District on which is superimposed the 1857 shoreline, as 

mapped by the U.S. Coast Survey (1857), is shown in figure 1. Along its west boundary was a narrow sand spit 

known as Strawberry Island, with adjacent saltwater 

marshes. Sand dunes, 6 to 12 m high, were situated south 

of the shoreline in the southeastern part of the area. 

To aid in the construction of industrial facilities, a seawall 

was built during the 1890's (Olmsted and others, 1977). 

The seawall was constructed by dumping rock, which had 

been hauled to the site on barges, and backfilling in places 

behind the rock embankment with sand taken primarily 

from the dunes. Similar construction was performed by the 

San Francisco Gas and Light Co. to establish an earthen 

mole. The locations of the seawall and earthen mole (Sanborn Ferris Map Co., 1905), which represent the waterfront 

and extent of filling at the time of the 1906 earthquake, are 

shown in figure 2. This configuration of seawall, embankment, and artificial fill remained essentially unchanged until 

1912, when construction on the site was started for the 

19 15 Panama-Pacific International Exposition. 

Although the Marina District was not developed extensively in 1906, there are nevertheless several historical accounts of damage in this area (Jones, 1906; Gilbert and 

others, 1907; Lawson, 1908), some of which are summarized in figure 2. Lawson (1908), for example, drew attention to evidence of severe ground shaking in the area 

extending from North Point Street between Lyon and 

Broderick Streets to the shoreline (diagonal-lined area, fig. 

2). In this area, timber structures were thrown out of vertical, reminiscent of the shear deformation sustained by 

four-story timber buildings during the 1989 earthquake. 

Moreover, damage to the Baker Street sewer implies that 

permanent ground deformation occurred in this area. 

The most comprehensive observations of damage are associated with the coal-gasification plants that were located 

in the southeastern part of the Marina District in 1906. 

Gilbert and others (1907) reported that all the buildings at 

the San Francisco Gas and Electric (renamed from the 

original San Francisco Gas Light Co.) plant sustained 

damage and that the ground settled "very considerably" in 

this place. Jones (1906) reported from 600 to 900 mm of 

settlement adjacent to the principal gas holder at the North 

Beach Station. The settlement ruptured the 600-mm-diameter outlet connections of the holder, causing all the stored 

gas to escape. 

In 1912, the lagoon enclosed by the seawall was filled 

with dredged soil pumped from bay deposits approximately 90 m offshore. Pumping of the fill material was relatively strictly controlled. The opening along the north line 

of the seawall was used to sluice out fine-grained and organic materials during hydraulic filling. An estimated 70 

percent of the fill placed in this way was sand (Olmsted 

and others, 1977). 

In summary, the placement of fill and development in 

the Marina District may be simplified as having occurred 

in two stages. The first stage was associated with the 

placement of land-tipped, or end-dumped, fills. Most of 

these soils were placed until about 1900 adjacent to both 

the original shoreline and Strawberry Island, and as part of 

the seawall. The second stage was in 1912, when sandy 

deposits were dredged and pumped into the lagoon bounded by the old seawall. On the basis of historical development, three general types of soils are distinguishable in the 

Marina District: (1) natural soils associated with the original beach and sand spit deposits, (2) land- and bargetipped fills, and (3) hydraulic fill. Areas underlain by each 

of these soil types behaved differently during the 1989 

earthquake, as analyzed below. 

WATER-SUPPLY SYSTEM 

Water to the Marina District is supplied by two systems 

of pipelines: the Municipal Water Supply System (MWSS) 

and the Auxiliary Water Supply System (AWSS). The 

MWSS supplies potable water for domestic and commercial uses, as well as for firefighting via hydrant and sprinkler systems; the AWSS supplies water exclusively for 

firefighting purposes. 

Within the Marina District, in an area bounded by the 

1857 shoreline on the south (U.S. Coast Survey, 1857) and 

the current shoreline on the north, there is approximately 

11,300 m of pipelines belonging to the MWSS and 2,300 

m of pipelines belonging to the AWSS. The MWSS mains 

are 100, 150, 200, and 300 mm in diameter, whereas the 

AWSS mains are predominantly 250 and 300 mm in diameter. The pipelines in both systems are composed of pitcast iron, and many were installed between late 1924 and 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F157 

1925. The MWSS pipelines were built predominantly with 

cement-caulked, bell-and-spigot couplings, whereas the 

AWSS pipelines were built with special couplings, as described below. All the pipelines were buried at nominal 

depths to top of pipe between 0.9 and 1.2 m. 

The locations of MWSS pipelines and repairs relative to 

the current street system, 1906 waterfront, and 1857 

shoreline are shown in figure 3. Repairs were made at 

points of sheared or disengaged service connections with 

mains, flexural round cracks in mains, and longitudinally 

split sections of mains. In some places, damage was concentrated at or near gate valves, which tend to anchor the 

pipelines and therefore may contribute to locally pronounced deformation and stresses. 

The locations of the MWSS mains that were replaced 

after initial repair are shown in figure 4. These mains were 

most heavily damaged in areas of greatest surface settlement and so are most likely to be subject to continuing 

rupture and maintenance difficulties in the future. Approximately 2.7 km of mains was replaced, primarily in or immediately adjacent to areas underlain by hydraulic fill. 

Even though the MWSS was substantially damaged in 

the Marina District, the AWSS was repaired at only one 

place, at a leaking joint at Scott and Beach Streets (fig. 5). 

The MWSS pipeline damage reported by the San Francisco Water Department as of November 1, 1989, is summarized in table 1. Service connections typically are made 

with pipe substantially smaller than the main, and in many 

places, the performance of service connections cannot be 

linked directly with the diameter of the main. Thus, the 

service repairs listed in table 1 are omitted from the repair 

rate based on pipe diameter but are included in the total 

. , . . -. . 

EXPLANATION 

ccj Saltwater Marsh - 1857 Shoreline Contour Interval: 6 m 

Figure 1 .-Marina District, showing location of 1857 shoreline. 
F158 MARINA DISTRICT 

Table 1 .-Municipal Water Supply System pipeline damage 

Pipeline Main Repairs Service- Length of Repair rate 

diameter repairs at or near line pipe (per kilometer) 

(m) gate valves repairs (m) 

- 

TOTAL--------57 12 54 11,350 '10.84 

l1ncludes mains and service lines. 

repair rate, because they contribute to an overall assessment of system damage. The repair statistics pertain to the 

area of MWSS pipeline damage bounded by Baker Street, 

Marina Boulevard, and Buchanan Street on the west, 

north, and east, respectively, and by Bay and Chestnut 

Streets on the south. 

A total of 123 repairs were made to the MWSS mains 

and service lines in the Marina District, more than three 

times the number in the entire MWSS elsewhere. A total 

of 69 repairs were made to mains, including those at or 

near gate valves; more than 80 percent of these repairs 

were attributed to flexural round cracks. In contrast, only 

one leaking joint was found in a 300-mm-diameter AWSS 

pipeline out of 2,290 m of 250- and 300-mm-diameter 

pipelines within the area of MWSS damage described 

above, resulting in a repair rate of only 0.43 per kilometer. 

The repair rates for MWSS and AWSS pipelines are 

plotted on a logarithmic scale as a function of nominal 

pipe diameter in figure 6. The slope of the linear regression is approximately -3, implying that pipeline repair 

was inversely proportional to the cube of the pipe diameter. Because the moment of inertia of a given pipe is a 

function of the cube of its diameter, the regression analysis indicates that damage was influenced strongly by the 

longitudinal bending resistance of the pipelines. Thus, it 

appears that bending stress caused by differential settlement of the underlying soil was the main cause of pipe 

failure and that resistance to such stress, resulting from 

Earthen 

6 Waterfront Mole of 

San Francisa 

er was damaged. 

wson and others, 1908) Jones, 1906) ; differential 

ettlement of buildings 

Gilbert and others, 1907) 

Figure 2,-Marina District, showing locations of 1906 waterfront and of damage and ground movements observed after 1906 San Francisco earthquake. 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F159 

flexible AWSS joints and increasing pipe diameter, was responsible for the lowest repair rates. 

GAS-DISTRIBUTION SYSTEM 

The high pressure gas-distribution lines in the Marina 

District were damaged in only one place, at a miter joint 

near the boundary of hydraulic fill and the 1857 shoreline. 

The high-pressure mains were constructed mostly of 

Grade B steel with electric-arc girth welds. 

In contrast to the high-pressure (approx 200 kPa) lines, 

the low-pressure (approx 2 kPa) gas-distribution mains 

were substantially damaged. Approximately 13.6 km of 

steel and cast-iron mains, ranging from 100 to 300 mm in 

diameter, was replaced within the area bounded by Laguna, Lombard, and Lyon Streets and San Francisco Bay 

(Phillips and Virostek, 1990). A little more than half this 

length was replaced with medium-density polyethylene 

(MDPE) piping inserted within existing steel and cast-iron 

pipes; the rest was replaced by direct burial of MDPE piping. The replacement pipes ranged from 50 to 150 mm 

in nominal diameter; about 90 percent were 50 mm in 

diameter. 

WASTEWATER-CONVEYANCE SYSTEM 

In San Francisco, wastewater is collected, transported, 

and treated under the Clean Water Program. The wastewater-conveyance system consists of 1,159 krn of collector 

sewers, ranging in diameter from 200 to 600 mm; 241 km 

of transport sewers, ranging in diameter from 0.9 to 2.3 m; 

and a series of storage culverts to hold water during heavy 

runoff for later transport and treatment. Approximately 77 

percent of the collection and transport sewers are more 

than 50 years old. 

Three types of sewage conduit in the Marina District 

were affected by the earthquake: (1) collector sewers, 

ranging in diameter from 200 to 600 mm; (2) outfall sewers, ranging in diameter from 1.5 to 2.3 m; and (3) a 3- to 

5-m-wide reinforced-concrete box sewer along Marina 

Boulevard. The collector sewers are composed mainly of 

vitrified-clay pipe in sections nominally 1.5 to 1.8 m long, 

Earthen 

Service repair 

W Main repair 

Repair at or near gate valve . :Z 

Pipeline, with diameter 

(in millimeters) 

Figure 3.-Marina District, showing locations of repairs to MWSS mains, service lines, and sections at or near gate valves as of November 1, 1989. 
F160 MARINA DISTRICT 

with mortared joints. This type of pipe is relatively weak 

and brittle. Since about 1960, the Clean Water Program 

has been installing stronger vitrified-clay pipe, equipped 

with polyethylene gaskets at the joints to promote 

flexibility. 

The locations of damage to the wastewater-conveyance 

system are shown in figure 7. Damage at the outfall sewers occurred primarily because of broken connections between the pile-supported outfalls and collector sewers, 

which settled differentially relative to the outfalls. The 

outfall sewer along Pierce Street was a circular reinforced-concrete structure, ranging in diameter from 1.8 to 

2.3 m, supported on timber piles, with an invert depth 

about 3 m below the ground surface. It was heavily damaged north of the seawall on the Marina Green. The 1.5- 

m-diameter Baker Street outfall, of similar construction, 

was cracked and fractured at a turning point (triangle, fig. 

7) where a joint connects it to an overflow weir. Minor 

cracking was observed along the invert of the Marina 

Boulevard sewer. 

Within the area bounded by Marina Boulevard and Baker, Chestnut, and Buchanan Streets is 9.8 km of vitrifiedclay-pipe collector sewers, of which approximately 2 km 

were replaced or repaired as a result of the earthquake. 

The lengths of pipeline in which repairs and replacements 

were made are shown in figure 7 on the basis of records 

provided by the Clean Water Program. Much of the damage was in the form of cracked and crushed joints. Approximately 1.4 km of vitrified-clay pipe was replaced 

with stronger clay pipe, utilizing gasketed joints. Nearly 

73 percent of the replaced or repaired pipes were located 

in or immediately adjacent to (within half a block of) areas of hydraulic fill. 

The repair-and-replacement statistics for collector sewers 

are summarized in table 2. In contrast to the MWSS damage, the collector-sewer damage does not correlate with 

nominal pipe diameter. Except for the 250- and 600-mmdiameter pipes, from 15 to 28 percent of the collector 

sewers were replaced; overall, 20 percent of the collector 

sewers within the area of damage were replaced. 

Figure 4.-Marina District, showing locations of MWSS pipelines replaced about 6 months after initial repairs illustrated in figure 3. 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F161 

Table 2.-Repair-and-replacement statistics for collector sewers 

Diameter Length Length replaced Percentage 

(mm) (m) or repaired (m) replaced or repaired 

GROUND DEFORMATION 

AND PIPELINE REPAIR 

Settlement caused by the earthquake was evaluated on 

the basis of survey data collected in 1961, 1974, and 1989 

and published by Bennett (1990), and a detailed evaluation 

of subsurface conditions in the Marina District was presented by O'Rourke and others (1991b). Settlement data 

were confined to street intersections. 

It was assumed that the settlement from 1961 to 1974 

was caused principally by secondary compression of Holocene bay mud. From the survey data base, the incremental 

secondary compression, AS, was regressed relative to the 

thickness of Holocene bay mud, H, to obtain the best linear fit of the data with slope AS/H=0.0011, which is related 

to soil properties in the form 

where Cac is the coefficient of secondary compression, defined as the ratio of the change in one-dimensional vertical 

strain to the change in the logarithm of time since the end 

of primary consolidation; and t, and t, are the times since 

the of hydraulic fill in 1974 and 1912-61, respectively. 

A value of Ca=O.O1l was calculated with equation 1, 

which compares favorably with the Cat value determined 

Figure 5.-Marina District, showing locations of damage to AWSS and high-pressure gas-distribution system. Approximately 13.6 lun of low-pressure 

gas-distribution mains that were replaced after the earthquake is omitted for simplicity. 
F162 MARINA DISTRICT 

for Holocene bay mud on the basis of one-dimensional 

consolidation tests (Dames & Moore, 1989). On the basis 

of 42 test results with stress increments to levels of 1.2 to 

2.5 times the preconsolidation pressure, the mean Cue value was 0.011, with a standard deviation of 0.004. 

The value of Cae=O.O1l was used to calculate the incremental secondary compression for each survey point between 1974 and 1989. These values were subtracted from 

the difference in actual survey measurements to yield 

"corrected" settlements that would best represent the 

amount of vertical movement caused by liquefactionassociated consolidation of the fills underlying the Marina 

District. Settlement contours were calculated from these 

corrected measurements with Golden Software, Inc.'s 

computer program bbSurfer," using a procedure referred to 

as kriging, in which contours are computed with minimal 

estimation variance froma statistical evaluation of the input data (Ripley, 1981). 

The resulting settlement contours are mapped in figure 

8. The maximum settlements occurred in the hydraulic fill, 

with decreasing amounts of vertical deformation in the 

land- and barge-tipped fills and in areas underlain by natural beach and sand-bar deposits. 

EXPLANATION 

- \ MWSS cast-iron 

pi pe 

100 200300 

Pipe Diometer, mm 

Figure 6.-Linear regression of repair rate versus nominal pipe diameter 

for MWSS and AWSS mains in the Marina District. Only repairs to 

MWSS mains, including sections at or near gate valves, were used in 

regression analysis. 

To represent the distribution of MWSS damage, the Marina District was divided into a grid of approximately 40 

cells, and the number of repairs in each cell was counted. 

The repairs then were normalized with respect to a reference length of 300 m to provide a consistent basis for 

evaluation. Contours of equal repair rates were drawn and 

superimposed on the street system and previous shorelines, as shown in figure 9. These repair-rate contours are 

closely related to the settlement contours and to the locations of hydraulic fill and the 1857 shoreline. Inspection of 

figures 8 and 9 shows that the closely spaced settlement 

contours, indicating the largest local settlement slopes, 

correspond to the highest repair-rate contours. High concentrations of pipeline repair fall within the area of hydraulic fill. The heaviest repair concentration occurs at the 

junction of the hydraulic fill, seawall, and 1857 shoreline, 

except for an isolated area on Rico Way, where unusual 

stresses were generated as a result of pipeline construction 

along the curved street. 

We note that settlement before the earthquake, caused by 

primary consolidation and secondary compression of Holocene bay mud, could have affected the vulnerability of 

existing pipelines. Because such settlement would have 

been largest over the thickest parts of bay mud, we would 

expect pipeline damage to be locally high near these places. The relative absence of concentrated pipeline damage 

in places of thick Holocene bay mud implies that any vulnerability caused by preearthquake consolidation was not 

sufficiently pronounced to influence damage when other 

factors, such as postliquefaction consolidation, were 

involved. 

To explore further the relation between pipeline damage 

and settlement pattern, MWSS repair rates were correlated 

with both the magnitude of settlement and the slope of the 

local settlement profile. The MWSS pipeline repairs within 

half a block in all street directions from each intersection 

were divided by the total length of pipe within this area 

and correlated with the settlement measured at each intersection. In addition, the MWSS pipeline repairs along 

each block were divided by the total length of pipeline 

along the block and correlated with the angular distortion, 

defined as the differential settlement across each block divided by the block length, or the local slope of the settlement profile. In geotechnical engineering practice, angular 

distortion is the parameter most commonly used to evaluate potential damage to buildings from differential foundation settlement (Tomlinson, 1986). 

In calculating the correlations, the pipelines on Rico 

Way and Pierce Street were deleted from the data base. 

Because the water main on Rico Way had been laid along 

a relatively sharp curve in the street, it is believed to have 

been especially vulnerable to damage because of installation stresses and constraints imposed by such construction. 

The water main along Pierce Street was underlain by a 

pile-supported sewer. 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F163 

Only a weak correlation was found between repair rate 

and the magnitude of settlement. Relatively good correlations were found between repair rate and angular distortion. The relation between the MWSS repair rate per 300 

m of pipe and the angular distortion is plotted in figure 10. 

Note that the data in figure 10 do not include damage to 

service lines and connections but only to mains. Because 

of the strong correlation between repair rate and nominal 

pipe diameter illustrated in figure 6, regressions were developed for each diameter of cast-iron main. An equation 

and coefficient of determination, r2, are given for each regression curve in figure 10. The slopes of these curves increase in inverse proportion to the nominal pipe diameter. 

For 200-mm-diameter mains, a bilinear plot (dashed curve, 

fig. 100 also conforms with the data. 

The spatial patterns of damage mapped in figures 7 and 

9 and their close relation to the pattern of settlement 

mapped in figure 8 indicate a strong link between pipeline 

damage and differential movement that is corroborated 

further by the correlations plotted in figure 10. Differential 

movement and angular distortion were most heavily concentrated at the boundaries among the fills, natural soils, 

and old seawalls. Note that damage to the relatively large, 

300-mm-diameter MWSS main (see fig. 3) and 300-mmdiameter gas pipeline (see fig. 5) both occurred very close 

to the boundary between hydraulic fill and the 1857 shoreline, where there was substantial differential settlement 

and angular distortion. 

The amount of differential settlement also depends on 

the properties and relative thickness of the soil susceptible 

to liquefaction, as discussed in the following sections. 

SOIL CONDITIONS 

The locations of boreholes and soundings for which data 

were collected to evaluate subsurface conditions in the 

Marina District are shown in figure 11. The boreholes 

were drilled for engineering projects both before and after 

the earthquake, although most were drilled to clarify foundation conditions beneath buildings during repair and reconstruction after the earthquake (O'Rourke and others, 

Figure 7.-Marina District, showing locations of damage to wastewater-conveyance pipelines. 
F164 MARINA DISTRICT 

1991a; Bonilla, this chapter). A total of 144 conventional 

boreholes and 14 cone-penetration-test soundings were 

used in the evaluation. 

On the basis of borehole and sounding data, two cross 

sections (A-A', B-B', fig. 11) providing information about 

the type of soil, water level, fines content, plasticity, and 

approximate undrained shear strength of soft to medium 

clays. Standard penetration tests (SPT) were performed in 

conjunction with many of the conventional borings, and 

selected uncorrected SPT values are given. 

Cross section A-A' (fig. 12) shows loose fill extending 

along Marina Boulevard from approximately Baker Street 

to Buchanan Street, with a maximum depth of about 9 m. 

This distance correlates well with the distance between locations of the 1857 shoreline shown in figures 1 and ll. 

The depth to water table is approximately 2.5 m. Underlying the loose fills and natural-sand deposits is Holocene 

bay mud, which ranges in thickness along Marina Boulevard from 9 to 32 m. Underlying the Holocene bay mud 

are dense sand and stiff to hard clay. 

Cross section B-B' (fig. 13) trends northwest through the 

hydraulic fill, which is characterized by low SPT values. 

Holocene bay mud increases rapidly in thickness toward 

the bay from about two blocks from the Marina waterfront. 

Borehole and outcrop information were analyzed with a 

geostatistics procedure, embodied in Golden Software, 

Inc.'s computer program "Surfer." This method of analysis 

is the same as that employed for generating the contours 

of surface settlement in figure 8. Contours of the bedrock 

surface and the bottom and top of the Holocene bay mud 

underlying the Marina District are shown in figures 14 

through 16. Similar subsurface-contour plots have been 

discussed elsewhere (0' Rourke and others, 199 1 a), and so 

they are only briefly described here. 

Figure 14 shows that the Marina District is underlain by 

an oblong bedrock basin, with its long axis oriented west 

by northwest. The basin is more than 75 m deep below 

Marina Boulevard. 

Figure 15 shows that the Holocene bay mud thickens 

rapidly toward the bay and that its steepest bottom surface 

Ear then 

1 857 Shoreline 

contour Interval: 20 mm - - ,-----, - 1-1 ,-- 

Figure 8.-Marina District, showing contours of settlement caused by the earthquake, calculated from 1961, 1974, and 1989 survey data reported by 

Bennett (1990). Settlements were adjusted for secondary compression between 1974 and 1989 of underlying Holocene bay mud, as inferred from 1961- 

74 settlement measurements. Hachures indicate area of closed low. 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F165 

extends from Broderick Street to Scott Street between Marina Boulevard and Jefferson Street. Slopes of the bottom 

of the bay mud in this area are locally as steep as 10'. 

Figure 16 shows that the underlying surface of the fills is 

irregular, especially beneath the hydraulic fill, and that it 

takes the form of a hummocky surface with mounds and 

depressions. Such an irregular surface is consistent with the 

method of filling whereby sand was pumped into various 

parts of the lagoon, causing local bearing failures and associated mounding of displaced fine-grained sedimentary deposits. Across the rest of the area, the top of the Holocene 

bay mud is in contact with natural sand and does not show 

disturbed features. Note that the contours of the top of the 

Holocene bay mud are a good representation of the fill 

thickness because the elevation of the ground surface is 

relatively uniform throughout much of the Marina District. 

A three-dimensional view of the Marina District in 

which the street surface, fill and natural-sand deposits, and 

Holocene bay mud are superimposed on the underlying 

bedrock basin is shown in figure 17. 

LIQUEFACTION POTENTIAL 

FROM SPT MEASUREMENTS 

Given a general understanding of the bedrock and soil 

conditions in the Marina District, we next examine the 

various soil deposits with respect to their liquefaction potential. It is well known that contraction of loose granular 

soils is associated with liquefaction, resulting in volume 

reduction and settlement. Differential settlement in the 

Marina (District significantly affected buried-lifeline response. Accordingly, the liquefaction characteristics of the 

Marina District soils and their contribution to ground 

movement are of critical importance in evaluating and 

planning for future lifeline performance. 

As mentioned previously, the Marina District provides 

an excellent opportunity to examine the characteristics and 

liquefaction response of three different soil types: (1) hydraulic fill, (2) land-tipped fills, and (3) natural-sand deposits. The locations of these deposits in the Marina 

District can be delineated with reasonable accuracy on the 

- - -- - 

Earthen 

1 Mole of 906 Waterfront 

EXPLANATION - 

per 300 m 

Q Contour of repairs1 

1---1-1r 

Figure 9.-Marina District, showing contours of MWSS repair rates per 300 m, including damage to mains, service lines, and sections at or near gate 

valves. Anomolously high contour of 22 per 300 m represents a pipeline installed along a relatively sharp curve on Rico Way, thus vulnerable to 

earthquake effects because of installation stresses and constraints imposed at joints. 
F166 MARINA DISTRICT 

basis of historical records and many boreholes and 

soundings. 

Liquefaction-potential analyses were performed for each 

soil type, using the empirical relation between cyclicstress ratio and corrected SPT value developed by Seed 

and others (1983, 1985). The SPT values were obtained 

from 75 boreholes in which tests were performed in accordance with the specifications of the American Society 

for Testing and Materials (199la). The SPT values were 

corrected for such factors as in situ confining stress and 

energy losses, according to the recommendations of Seed 

and others (1983, 1985). The cyclic-stress ratio for various 

depths was calculated by assuming a peak acceleration of 

0.2 g, a value consistent with the peak horizontal component of acceleration recorded at the nearby Presidio (Benuska, 1990). The results are plotted in figure 18. 

The most striking feature of the plots in figure 18 is the 

relatively high liquefaction potential of the hydraulic fill. 

The corrected SPT values for at least half of the measurements in the sample are less than 6, implying that the hydraulic fill would have a very low undrained residual shear 

strength, perhaps lower than 5 kPa, based on the empirical 

relations suggested by Seed (1987). In contrast, both the 

land-tipped fills and natural-sand deposits show increasing 

y=(1.0xlo4) 8- 0.3 

regression, r2=0.52 

4-6- 

10 20 '30 40 50 60 

Angular Distortion x 10 ( 8) 

Figure 10.-Linear regressions of MWSS repair rate versus angular distortion (local slope of settlement profile) for water mains 100 (A), 150 

(B), and 200 mm in diameter (0. 

resistance to liquefaction, as well as a successively wider 

range of in situ densities, as reflected by the SPT values. 

About half the data for land-tipped fills plot to the left of 

the 5-percent-fines curve, whereas only about 15 percent 

of the data for natural-sand deposits plot in the same zone. 

The land-tipped fills show the widest variation with respect to corrected SPT values, with a coefficient of variation of 0.65 for (NI)rn. 

The relation between depth and corrected SPT value for 

the hydraulic fill, land-tipped fills, and natural-sand deposits with regard to liquefaction potential is plotted in figure 

19. Although these plots provide only a general picture of 

subsurface conditions because they lump all the data into a 

single cross section, they nevertheless show some interesting trends. A relatively uniform distribution of low in situ 

density with depth is indicated for the hydraulic fill, 

whereas density tends to increase markedly with depth for 

areas underlain by land-tipped fills. The natural-sand deposits vary widely in in situ density with depth; most densities fall outside the range of susceptibility to liquefaction 

during the earthquake. 

LIQUEFACTION POTENTIAL 

FROM CPT MEASUREMENTS 

As illustrated in figure 11, 14 CPT soundings were used 

in this study of the Marina District, most of which had 

been reported by Bennett (1990) and Bardet and Kapuskar 

(1991). The CPT measurements were performed in accordance with the specifications of the American Society for 

Testing and Materials (1 99 1 b). CPT soundings can resolve 

subsurface conditions in considerably more detail than 

SPT measurements, and so they provide a more accurate 

picture of the variations in in situ density and soil type. 

Liquefaction-potential analyses were performed for all 

CPT soundings in areas of hydraulic fill, using the empirical correlations between cyclic-stress ratio and modified 

cone-tip resistance, qcl, proposed by Seed and de Alba 

(1986). Calculation of the modified cone-tip resistance involves normalizing the measured tip resistance with respect to an effective overburden stress of about 100 kPa, 

according to the recommendations of Seed and de Alba 

(1986). The cyclic-stress ratios for various depths were 

calculated similarly to those for the corrected SPT values 

by assuming a peak acceleration of 0.2 g. 

As an illustration of this analysis, consider the normalized CPT profiles shown in figure 20, in which liquefaction-potential curves are plotted for three combinations of 

fines content and mean grain size chosen to be consistent 

with the composition of the fills and natural-sand deposits 

in the Marina District. The CPT data for each sounding 

were first analyzed to identify the soil type at each depth, 

according to the recommendations of Robertson and 

Campenella (1983) and Olsen and Fan- (1986). On the 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F167 

basis of this soil identification, the appropriate liquefaction-potential curve was used to evaluate whether the soil 

type at a given depth was susceptible to liquefaction during the earthquake. 

The CPT profiles for three soundings in the hydraulic 

fill, from north to south designated as C-8, C-4, and C-15 

(see fig. ll), are shown in figures 205 through 20D, respectively. For example, sounding C-8 indicates liquefiable sand and silty sand between depths of 3 and 4.5 m 

and again at 5.5 to 6.5 m. Between 4.5 and 5.5 m, the 

cone penetrated silt and silty clay, which can be interpreted as not susceptible to liquefaction, and so no heavy 

curve is drawn for this depth interval. Sounding C-4 (fig. 

200 shows liquefiable sand and silty sand generally between depths of 2.6 to 7 m, with thin intervening layers of 

clayey silt that can be interpreted as not susceptible to liquefaction. Sounding C-15 (fig. 20D) shows only a few 

thin seams of sand and silty sand that are clearly susceptible to liquefaction. 

In general, the liquefaction potential deduced from CPT 

measurements corroborates the average trends shown by 

the SPT measurements for hydraulic fill, land-tipped fills, 

and natural-sand deposits. The advantage of the CPT 

soundings is the precision to which potentially liquefiable 

and nonliquefiable layers can be delineated. This precision 

permits an additional degree of detail in evaluating the 

postliquefaction consolidation at various places in the Marina District, as discussed in the next section. 

VERTICAL STRAINS AND SETTLEMENT 

Simplified methods for predicting the vertical strain 

caused by postliquefaction consolidation were proposed by 

Tokimatsu and Seed (1987) and Ishihara and Yoshimine 

(1990). These methods permit an estimation of the vertical 

strain, given either corrected SPT values or relative densities. This approach is similar to that used for evaluating 

liquefaction potential, in that the cyclic-stress ratio is required as an input parameter. Ishihara and Yoshimine's 

method requires an estimation of the factor of safety 

against liquefaction, FSL, defined as the ratio of the cyclicEarthen 

1906 Waterfront ~~l~ of 

San Francisco 

Figure 11.-Marina District, showing locations of conventional boreholes (dots), cone-penetration-test soundings (triangles), and cross sections A-A', BB ', and C-C' (figs. 12, 13, 22). 
F168 MARINA DISTRICT 

stress ratio required to initiate liquefaction, CSRL, to the 

cyclic-stress ratio that actually affects the soil layer of 

interest, CSR (FSL=CSRL/CSR). We evaluate the cyclicstress ratio to initiate liquefaction, according to the liquefaction-potential curves in figure 18, as the intercept 

between the appropriate curve and the average corrected 

SPT value for the soil. Once the vertical strain has been 

estimated, we multiply it by the thickness of soil below 

the water table to estimate the magnitude of settlement. 

Although it is beyond the scope of this report to discuss 

strain-estimation methods in detail, it is nonetheless instructive to illustrate the application of at least one method. The 

relation between the cyclic-stress ratio and the corrected 

SPT value for the various soil types in the Marina District 

relative to the simplified estimation of earthquake-induced 

vertical strain in saturated sand proposed by Tokimatsu and 

Seed (1 987) is plotted in figure 21. The predicted strains are 

lowest for natural-sand deposits, with strains of about 0.1 to 

0.2 percent corresponding to the average corrected SPT value. Likewise, strains of about 2 and 4 percent are associated 

with the average corrected SPT values of land-tipped fills 

and hydraulic fill, respectively. 

Vertical strains were estimated from the observed settlements at different sites above land-tipped fills and hydraubarge- tipped fill 

EXPLANATION 

X. Water level in borehole Loose silty fine sand/ Soft lo medium stiff clay 

3. Mean sea level soft silt, where differentiated (Holocene boy mud) 

21 Uncorrected SPT value m Medium-dense fine sand/ Stiff to hard clay 

(l5) Fines content (weight percent) :: silty fine sand (old bay mud) 

Plasticity index Includes gravel and cobbles/ 

brick and rubble Dense green sand and clay 

(50) Undroined shear strength 

JL. (MPa) from Torvane or correloted Dense fine sand la Very dense fine sand/ 

.. . dense sandy clay 

Sandy clay or clayey sand . ~. . Weathered bedrock 

Figure 12.Ã‘Cros section A-A' along Marina Boulevard. Elevation refers to San Francisco city datum. See figure 11 for location. 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE 

Elevation . b5? 

EXPLANATION 

Water level in borehole 

3. Mean sea level 

21 Uncorrected SPT value 

@ Fines content (weight percent) 

Plasticity index 

(50) Undrained shear strenath 

(MPa) from Torvane or correlated 

SURFACE 

Loose silty fine sand / Soft to medium stiff clay 

soft silt, where differentiated (Holocene boy mud 

Medium-dense fine sand/ Stiff to hard clay 

silty fine sand (old bay mud) 

Includes gravel and cobbles/ 

brick and rubble 

Dense fine sand .. . 

Sandy clay or' clayey sand . . 

Dense green sand and clay 

Very dense fine sand/ 

dense sandy clay 

Weathered bedrock 

Figure 13.-Cross section B-B' trending northwest through hydraulic fill. Elevation refers to San Francisco city 

datum. See figure 11 for location. 
F170 MARINA DISTRICT 

lie fill. At each site, the settlement was divided by the 

thickness of fill below the water table to give the vertical 

strain. The data for land-tipped fills and hydraulic fill are 

summarized in tables 3 and 4, respectively. The weightedaverage vertical strain is 2.1 percent for land-tipped fills 

and hydraulic fill. 

Areas of the Marina District where little damage occurred were not explored extensively. As a result, more 

detailed information about the subsurface stratigraphy at 

sites of measured settlement is available for land-tipped 

fills and hydraulic fill than for natural-sand deposits. Data 

from a few sites, summarized in table 5, indicate that vertical strains of about 0.1 to 0.2 percent occurred in naturalsand deposits. Note that the sites included in table 5 were 

selected in part because of their proximity to the areas of 

strongest ground shaking. 

Strains were evaluated on the basis of the data listed in 

tables 3 through 5 by assuming that surface settlements 

were caused by postliquefaction consolidation throughout 

the entire depth of fill or natural sand below the water 

table. The natural-sand deposits and land-tipped fills are 

relatively consistent in composition with depth; their fines 

content is less than 5 percent, and their median grain size 

ranges from 0.2 to 0.4 mm. Because silty and clayey layers are scarce or absent, it seems reasonable to estimate 

Table 3.-Average settlement and vertical strain for land-tipped fills 

Average Number Average Average depth Vertical 

settlement of depth of of fill below strain 

(nun ) locations fill (m) water table (m) (percent) 

Table 4.-Average settlement and vertical strain for hydraulic fill 

Average Number Average Average depth Vertical 

settlement o f depth of of fill below strain 

(mm) locations fill (m) water table (m) (percent) 

strains in these materials directly from the submerged 

thickness. Such is not the case with hydraulic fill, however, whose average fines content has been shown to be 

Figure 14.Ã‘Contour of equal elevation, relative to San Francisco city datum, of bedrock surface underlying the Marina District. Diagonal-lined areas, 

bedrock-outcrops from Schlocker (1974). 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F171 

Table 5.-Settlement and vertical strain for natural-sand deposits 

Settlement Location Thickness of natural Vertical 

(mm) sand below water strain 

table (m) (percent) 

11 Divisadero Street 4.5 0.2 

between Beach and 

North Point Streets 

(2 locations) 

7 Bay Street near Baker 4.2 .2 

Street. 

5 Fillmore Street near 8.7 .1 

Chestnut Street. 

generally at least 15 percent (O'Rourke and others, 

1991b). 

O'Rourke and others (1991b) suggested that the average 

fines content of the hydraulic fill results in soil conditions 

not fully consistent with those for relatively clean sand 

and the median grain sizes of soils on which the simplified 

strain-estimation procedures of Tokimatsu and Seed (1987) 

are based. They suggested that an increase in the corrected 

SPT values would account for the influence of fines content on diminishing the vertical strains resulting from 

postliquefaction consolidation. These increased SPT values could then be used in Tokimatsu and Seed's diagram 

(fig. 21) to estimate the vertical strain. Their reasoning, 

however, was based on the assumption that the hydraulic 

fill has a relatively consistent, silty-sand composition. This 

type of soil characterization emerges from an evaluation of 

borehole data that utilize SPT measurements and splitspoon sampling. 

We examined the characteristics of the hydraulic fill in 

greater detail by means of the CPT soundings. As explained previously, CPT measurements can be used to distinguish relatively thin layers of silty and clayey soils that 

would not be expected to liquefy. Moreover, in soil types 

that are susceptible to liquefaction, the modified cone-tip 

resistance, qd, can be used to assess the liquefaction potential. 

The settlements observed near five CPT soundings in 

hydraulic fill are summarized in table 6. The net liquefiable thickness was determined by subtracting the cumulative thickness of silty and clayey soils as well as soils with 

then 

e of 

Franc 

Light 

iscc 

C o< 

JS horeline- -7r 

0 

0 200 m 

Area filled before 1912 w 

(see Bonillo, this chapter) -, ,-, ,--I ,, 7, ,--- 

0 600ft 

Figure 15.Ã‘Contour of equal elevation, relative to San Francisco city datum, of bottom of Holocene bay mud. 
F172 MARINA DISTRICT 

Table 6.-Settlement and vertical strain deduced from CPT soundings 

CPT Settlement Fill thickness Net Vertical 

sounding (mm) below water liquefiable strain 

(fig. 11) table (m) thickness (m) (percent) 

a high q,, value relative to their liquefaction threshold 

from the total submerged thickness. For some soundings, 

such as C-10, there was uncertainty regarding the soil 

composition at a particular depth. At these sites, the net 

liquefiable thickness was estimated as an upper and lower 

bound. The vertical strain was computed by dividing the 

settlement by the net liquefiable thickness. 

The observed and predicted vertical strains for the various soil types in the Marina District are compared in table 

7. Predictions were made on the basis of corrected SPT 

Table 7.-Comparison of observed and predicted vertical strains 

Soil type Observed vertical strain Predicted vertical strain 

(percent) (percent) 

With CPT Without CPT Tokimatsu and Ishihara and 

adjustment adjustment and Seed (1987) and Yoshimine 

(1992) 

Natural - - - - 0.2 0.3 0.2 

sand 

deposits. 

Land-tipped 

fill: 

<3.5 m deep - - - 2.2 2.2 2.7 

>3.5 m deep --- 2.1 1.3 . 1.8 

Hydraulic 3.5 2.1 3.7 4.5 

fill. 

values, using the techniques of Tokimatsu and Seed (1987) 

and Ishihara and Yoshimine (1992). Because of the increase in in situ density with depth for the land-tipped fills 

(see fig. 19), the vertical strains in these soils were evaluated for depths less than and greater than 3.5 m. The predicted and observed vertical strains agree closely for 

natural-sand deposits and land-tipped fills, whereas the 

1--- 

(see Bonilla, this chapter) I-, ,-, ,-, ,-- 

Figure 16.Ã‘Contour of equal elevation, relative to San Francisco city datum, of top of Holocene bay mud. 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE 

EXPLANATION 

F 

drock Basin and Marina I I and Natural- Sand Deposits 

Recent Boy Mud 

ck Contour Interval = 12.5 m 

............... 

........................ 

................. 

Street Surface 

Top of Holocene 

Bay Mud - 0 

- 20 

Expanded 

Vertical 

Scale 

Bottom of Holocene 

Bay Mud - 10 

- 20 

-30 

Figure 17.-Block diagram of the Marina District, generated by computer on the basis of borehole and CPT logs. View southeastward. 
MARINA DISTRICT 

0.5 I I I I 

- 35 percent T - B. 

percent 

percent 

0.5 - I I 

- 35 percent x 

30 I 

Natural-Sond Deposits 

I I 

c - 

0.2 Corrected SPT, blows/ft 

0. I 

/ 

0 l I I I I I 

0 20 40 60 

Corrected SPT Value, (Dl Igo, blows /ft 

Figure 18.-Cyclic-stress ratio versus corrected SPT value at different fines contents for hydraulic fill (A), land-tipped fills (B), and natural-sand deposits (0. Fines content is defined as 

proportion (in weight percent) of soil that is silt size or smaller (sO.075 mm). Curves show 

boundaries of liquefaction potential for an M=7.1 earthquake, according to procedure of Seed 

and others (1985); data points to left of curves indicate increasing susceptibility to liquefaction. 

Histograms, showing normal and gamma frequency distributions of corrected SPT values, provide a measure of variation in soil density. 5, mean; a, standard deviation. 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F175 

predicted strains are from 75 to 114 percent higher than 

those observed for the hydraulic fill, using the total fill 

thickness. When the net liquefiable thickness is adjusted 

on the basis of CPT measurements, the vertical strains inferred from observed settlements compare quite favorably 

with the predicted strains. 

Note that the vertical strains in the hydraulic fill predicted solely on the basis of corrected SPT values will be influenced by the relatively low SPT values associated with 

layers of silt and clay. Even though these fine-grained layers are discounted when estimating the net liquefiable 

thickness, there is no direct way to remove the associated 

SPT values from data on the hydraulic fill. An alternative 

approach for predicting the vertical strain is to use CPT 

measurements directly in conjunction with the technique 

of Ishihara and Yoshirnine (1992). The potential vertical 

strain for each increment of cone penetration can be 

determined from charts developed by Ishihara and Yoshimine, using the qd value to estimate the relative density 

and the FSL value. The vertical strains determined in this 

way for each increment of thickness can be averaged to 

provide an average strain, or integrated over the full 

Corrected SPT Value, (fj Icol bows/ft Corrected SPT Value, (Ill Iso, blows/ft 

Corrected SPT Value, (hJ1 Iso, blowslft 

Figure 19.-Depth versus corrected SPT value at different fines contents for hydraulic fill (A), land-tipped 

fills (B), and natural-sand deposits (0. Fines content is defined as proportion (in weight percent) of soil that 

is silt size or smaller (~0.075 mm). Curves show boundaries of liquefaction potential for an M=7.1 earthquake, according to procedure of Seed and others (1985); data points to left of curves indicate increasing 

susceptibility to liquefaction. Inverted triangles denote depth to water table. 
F176 MARINA DISTRICT 

thickness to yield an estimated settlement. Although the 

details are beyond the scope of this report, this approach 

nonetheless represents a potentially useful area for further 

study and evaluation. 

Strong evidence exists that the liquefaction behavior of 

the hydraulic fill is influenced by the presence of finegrained soil layers. When the net thickness of sand and 

silty sand most susceptible to liquefaction is assessed, the 

agreement between the observed and predicted vertical 

strains is good. This result indicates that the resolution 

provided by CPT measurements is an important factor in 

estimating the magnitude and extent of postliquefaction 

consolidation for these and similar soils. Investigations by 

35 percent or Dso=O.I mm 

15 percent or ~50=0.2mm 

55 percent or llwO.3mm 

(after Seed and de Alba, 

1986) 

LAND-TIPPED FILL 

+ silty to clean SAND 

SILT seam- 4 

slightly silty SAND 

clayey SILTslightly silty SAND 

sondy SILT 

35 percent 

15 percent silty SAND5 Percent clayey SILT 

silty SANDSILT 

silty SAND I 

Martin and others (1991) on the practical assessment of 

liquefaction effects also emphasize the importance of CPT 

characterization. The hydraulic fill, because it may contain 

relatively thin fine-grained soil layers, is likely to require 

more detailed evaluation for assessing postliquefaction settlement than can be supplied by SPT measurements. 

DISTRIBUTION OF SETTLEMENT 

As discussed above, the highest concentrations of differential settlement and, thus, of damage to buried utilities 

depend on the boundaries among the fills, natural-sand deLAND-TIPPED FIL .L 

slightly silty 

SAND 

! i%, clean SAND 

Normalized Tip Resistance (q ), MPa 

SILT seom- J 

silty SAND \ 

slightly silty 

SAND - 

clayey to sandySILT 

clean SAND i 

Normalized Tip Resistance (gel), MPa 

Figure 20.-Depth versus normalized tip resistance at different fines contents for hydraulic fill (A) and for 

CPT soundings C-8 (B), C-4 (Q, and C-15 (D) (see fig. 11 for locations). Fines content is defined as 

proportion (in weight percent) of soil that is silt size or smaller (50.075 mm). Profiles in figure 20A were 

calculated for an M=7.1 earthquake, according to procedure of Seed and others (1985); profiles in figures 205 

through 20D were plotted according to procedure of Seed and de Alba (1986). In figures 20B through 20D, 

solid curves denote appropriate liquefaction potential for specific depths and soil types, and dashed curves are 

shown for reference. Data points to left of curves indicate increasing susceptibility to liquefaction; breaks in 

curves indicate that a particular soil layer is not readily susceptible to liquefaction. Inverted triangles denote 

depth to water table. 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F177 

posits, and old seawalls, as well as on the properties and 

thicknesses of soils susceptible to liquefaction. Given that 

existing simplified methods provide reasonably good estimates of the vertical strain from postliquefaction consolidation, accurate prediction of buried-lifeline damage will 

also require an assessment of differential settlement and, 

thus, a knowledge of the variation in fill thickness. 

The relation between settlement and fill thickness is illustrated in figure 22, which shows a simplified cross section along Divisadero Street (C-C', fig. 11). Note that 

some of the most extensive damage to pipelines and the 

heaviest concentration of building damage were on Divisadero Street, primarily in the area from Beach Street to Marina Boulevard. 

Cross section C-C' shows that the settlement profile 

along Divisadero Street is closely related to the thickness 

of land-tipped fills. The locations of maximum settlement 

coincide with increasing fill thickness from Beach Street 

to Marina Boulevard, as well as with increasing fill thickness in a zone once occupied by a tidal marsh south of old 

Strawberry Island. The zone of minimum settlement coincides with Strawberry Island and its associated naturalsand deposits. As shown in figures 3 and 7, the locations 

of maximum settlement and angular distortion between 

Beach Street and Marina Boulevard and near Francisco 

Street are also the locations of greatest damage to MWSS 

pipelines and collector sewers along Divisadero Street. 

CONCLUDING REMARKS 

Information obtained from our investigations in the Marina District has provided insight critically important for the 

design and planning of lifeline systems in relation to local 

geology and soil conditions. Because the historical development of the Marina District is well understood, at least 

three different local soil types can be identified with reasonable accuracy: (1) hydraulic fill; (2) fills tipped from the 

shoreline or during seawall construction, herein referred to 

as land-tipped fills; and (3) natural beach, dune, and sandspit deposits. Comparisons of the observed vertical strains 

in each of these three soil types with those predicted on the 

basis of simplified procedures indicate that the predicted 

and observed vertical strains agree closely for the naturalsand deposits and land-tipped fills, whereas the predicted 

strains are substantially higher than the observed strains in 

hydraulic fill, using only SPT measurements. When the net 

liquefiable thickness is adjusted on the basis of CPT measurements, the vertical strains inferred from observed settlements compare quite favorably with the predicted strains. 

Vertical Strain (percent) 

0543 2 I 0.5 

Soil 

type 

Natural 

sand 

Landtipped 

fills 

Hydraulic 

fill 

* Normal 

""I'~O 1 Symbol 1 x* I cov 

distribution 

Corrected SPT Value, (N1 blows/f t 

Figure 21.-Cyclic-stress ratio versus corrected standard-penetration-test value for hydraulic fill, land-tipped 

fills, and natural-sand deposits, superimposed on chart of Tokimatsu and Seed (1987) for estimating vertical 

strain caused by postliquefaction consolidation. COV, coefficient of variation; Z, mean. 
F178 MARINA DISTRICT 

The liquefaction behavior of the hydraulic fill in the Marina District was apparently influenced by the presence of 

fine-grained soil layers. The resolution in delineating subsurface conditions by CPT measurements is shown to be 

an important factor in estimating the magnitude and extent 

of postliquefaction consolidation in the hydraulic fill. Hydraulic fill, because it may be interstratified with finegrained soils, is likely to require more detailed evaluation 

for assessing postliquefaction settlement than can be supplied by the widely used methods of SPT measurements 

and split-spoon sampling. 

This study was sponsored by the National Center for 

Earthquake Engineering Research, Buffalo, N.Y., under 

project 893008, and by the National Science Foundation 

grant BCS-90 11458. We especially thank T. Dickerman of 

the San Francisco Water Department, F. Blackburn and A. 

Nielsen of the San Francisco Fire Department, J. Clark of 

the Pacific Gas and Electric Co., and P.T. Law and S. Yu of 

the Clean Water Program, all for their help in gathering 

lifeline data; and T.L. Holzer and M.J. Bennett of the U.S. 

Geological Survey, R. Darragh and D. Koutsoftas of 

Dames & Moore, H. Taylor of Harding Lawson Associates, 

and M. Power of Geomatrix for their help in gathering 

geotechnical data. We appreciate the assistance of Ted 

Gowdy, who helped prepare data bases and performed 

three-dimensional computer analyses, A. Avcisoy, who 

drafted the illustrations, and L. Mayes and K.J. Stewart, 

who typed the manuscript. 

REFERENCES CITED 

American Society for Testing and Materials, 1991a, Standard test method 

for deep, quasi-static, cone and friction-cone penetration tests of 

soil, in 1991 annual book of standards: Philadelphia, v. 4.08, 

p. 439-444. 

tlement, mm 

0- 

/@- 

100 

/ a-â 

LAND-TIPPED FILL 

v 

0' 

NATURAL- SAND DEPOSITS 

- - 

I 

I 

EXPLANATION 

Observed water M 

level 100m 

3. Mean sea level 

Figure 22.-Cross section C-C' along Divisadero Street, showing settlement profile, water table, and stratification of underlying soils. See figure 11 for 

location. 
LIFELINE PERFORMANCE AND GROUND DEFORMATION DURING THE EARTHQUAKE F179 

1991b, Standard test method for penetration test and split-barrel 

sampling of soils, in 1991 annual book of ASTM standards: Philadelphia, v. 4.08, p. 232-239. 

Bardet, J.P., and Kapuskar, M., 1991, Site investigation of the Marina 

District of San Francisco in September 1990, in report to National 

Science Foundation: Los Angeles, University of Southern California, Civil Engineering Department, 93 p. 

Bardet, JP., Kapuskar, M., and Martin, G.R., 1991, Dynamic response of 

the Marina District of San Francisco during the 1989 Loma Prieta 

earthquake, in Japan-U.S. Workshop on Earthquake-Resistant Design of Lifeline Facilities and Countermeasures for Soil Liquefaction, 3d, San Francisco, 1991, Proceedings: Buffalo, N.Y., National 

Center for Earthquake Engineering Research, Report NCEER-91- 

0001, p. 109-128. 

Bennett, M.J., 1990, Ground deformation and liquefaction of soil in the 

Marina District, in Effects of the Loma Prieta earthquake on the 

Marina District, San Francisco, California: U.S. Geological Survey 

Open-File Report 90-253, p. Dl-D36. 

Benuska, Lee, ed., 1990, Loma Prieta earthquake reconnaissance report: 

Earthquake Spectra, v. 6, supp. 9041,448 p. 

Bonilla, M.G., 1991, The Marina District, San Francisco, Californiageology, history, and earthquake effects: Seismological Society of 

America Bulletin, v. 81, no. 5, p. 1958-1979. 

Dames & Moore, 1989, Factual report, site investigation for completion 

of preliminary design-phase I, Muni Metro Turnaround Facility; 

report for Bechtel National, Inc., Job 185-215-03: San Francisco, 

v. 2. 

Gilbert, G.K., Humphrey, R.L., Sewell, J.S., and Soul6, F., 1907, The 

San Francisco earthquake and fire of April 18, 1906, and their effects on structures and structural materials: U.S. Geological Survey 

Bulletin 324, 170 p. 

Harding Lawson Associates, Dames & Moore, KennedyIJenkslChilton, 

and EQE Engineering, 1991, Liquefaction study, Marina District 

and Sullivan Marsh area, San Francisco, California: final report prepared for San Francisco Department of Public Works: San Francisco, 144 p. 

Ishihara, Kenji, and Yoshimine, M., 1992, Evaluation of settlements in 

sand deposits following liquefaction during earthquakes: Soils and 

Foundations, v. 32, no. 1, p. 1-22. 

Jones, E.C., 1906, The story of the restoration of the gas supply in San 

Francisco after the fire, in Pacific Gas Association Annual Meeting, 

14th, San Francisco, 1906, Proceedings, p. 350-364. 

Lawson, A.C., chairman, 1908, The California earthquake of April 18, 

1906; report of the California State Earthquake Investigation Commission: Carnegie Institution of Washington Publication 87, 2 v. 

Martin, G.R., Tsai, C.-F., and Arulmoli, K., 1991, A practical assessment 

of soil liquefaction effects and remediation needs: International 

Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, 2d, St. Louis, Mo., 1991, Proceedings, 

v. 1, p. 411-418. 

Mitchell, J.K., Tahir, M., Kayen, R.E., and Seed, R.B., 1990, Soil conditions and earthquake hazard mitigation in the Marina District of 

San Francisco; report to mayor of San Francisco: San Francisco, 

59 p. 

Olmsted, R., Olmsted, N., and Pastron, A., 1977, San Francisco waterfront-report on historical cultural resources for the north shore and 

channel outfalls consolidation projects: San Francisco, Wastewater 

Management Program, 728 p. 

Olsen, R.S., and Fan, J.V., 1986, Site characterization using the cone 

penetrometer test, Clemence, S.P,, ed., in Use of in-situ tests in geotechnical engineering: American Society of Civil Engineers Geotechnical Special Publication 6, p. 854-868. 

O'Rourke, T.D., Gowdy, T.E., Stewart, H.E., and Pease, J.W., 1991a, 

Lifeline and geotechnical aspects of the 1989 Loma Prieta earthquake: International Conference on Recent Advances in Geotechnical Earthquake Engineering and Soil Dynamics, 2d, St. Louis, Mo., 

1991, Proceedings, v. 2, p. 1601-1612. 

1991 b, Lifeline performance and ground deformation in the Marina during 1989 Loma Prieta earthquake, in Japan-U.S. Workshop on 

Earthquake-Resistant Design of Lifeline Facilities and Countermeasures for Soil Liquefaction, 3d, San Francisco, 1991, Proceedings: Buffalo, N.Y., National Center for Earthquake Engineering 

Research, Report NCEER-9 1-0001, p. 129-146. 

Phillips, S.H., and Virostek, J.K., 1990, Natural gas disaster planning and 

recovery-the Loma Prieta earthquake: San Francisco, Pacific Gas 

and Electric Co., 39 p. 

Ripley, B.D., 1981, Spatial statistics: New York. Wiley, 252 p. 

Robertson, P.K., and Campanella, R.G., 1983, Interpretation of cone penetration tests, part I-sand: Canadian Geotechnical Journal, v. 20, 

no. 4, p. 718-733. 

Sanborn Ferris Map Co., 1899 [1905], Insurance maps: San Francisco, 

4 v. 

Schlocker, Julius, 1974, Geology of the San Francisco North quadrangle, 

California: U.S. Geological Survey Professional Paper 782, 109 p. 

Seed, H.B., 1987, Design problems in soil liquefaction: Journal of Geotechnical Engineering, v. 113, no. 8, p. 827-845. 

Seed, H.B., and de Alba, Pedro, 1986, Use of SPT and CPT tests for 

evaluating the liquefaction resistance of sands, in Clemence, S.R, 

ed., Use of in situ tests in geotechnical engineering: American Society of Civil Engineers Geotechnical Special Publication 6, p. 281- 

302. 

Seed, H.B., Idriss, I.M., and Arango, Ignacio, 1983, Evaluation of liquefaction potential using field performance data: Journal of Geotechnical Engineering, v. 109, no. 3, p. 458-482. 

Seed, H.B., Tokimatsu, Kohji, Harder, L.F., and Chung, R.M., 1985, Influence of SPT procedures in soil liquefaction resistance evaluations: Journal of Geotechnical Engineering, v. 11 1, no. 12, p. 1425- 

1445. 

Tokimatsu, Kohji, and Seed, H.B., 1987, Evaluation of settlements in 

sands due to earthquake shaking: Journal of Geotechnical Engineering, v. 113, no. 8, p. 861-878. 

Tomlinson, M.J., 1986, Foundation design and construction (5th ed.): 

Harlow, U.K., Longman, 842 p. 

U.S. Coast Survey, 1857, Topographic map of city of San Francisco and 

its vicinity, California: scale 1: 10,000. 

U.S. Geological Survey, 1990, Effects of the Loma Prieta earthquake on 

the Marina District, San Francisco, California: Open-File Report 

90-253. 
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND FAILURE 

MARINA DISTRICT 

EFFECTS OF GROUND CONDITIONS ON THE DAMAGE 

TO FOUR-STORY CORNER APARTMENT BUILDINGS 

By Stephen K. Harris, EQE Engineering and Design; and 

John A. Egan, Geomatrix Consultants 

CONTENTS 

ABSTRACT 

Damage in the Marina District from the earthquake 

was concentrated in one class of building: four-story, 

wood-frame comer apartment buildings, which accounted 

for six of the seven building collapses. Construction in the 

district is quite uniform in configuration and material; 

however, ground conditions vary widely, from firm, competent sand, through soft natural clay and silt, to liquefaction-susceptible hydraulic fill. 

On the basis of postearthquake observations of 

ground-failure phenomena and borehole data, the Marina 

District was divided into three soil-profile zones: a 

ground-failure zone, bayward of the old (1851) shoreline 

and characterized by thick recent (post- 1906) fill underlain 

by deep bay mud, within which substantial ground-failure 

effects were observed; a "soft"-soil-profile zone, also bayward of the old shoreline, characterized by older (pre1906) fill underlain by dense natural-sand deposits and 

deep, old bay mud; and a "firm9'-soil-profile zone, landward of the old shoreline, characterized by competent natural-sand deposits overlying relatively thin or no bay mud. 

We expect that ground shaking in the Marina District varied considerably among these three zones. 

Page 

F181 

181 

182 

182 

186 

188 

188 

189 

191 

191 

193 

193 

194 

Estimated response spectra indicating amplified spectral ordinates of approximately 5 for the "soft7'-soil-profile 

zone were calculated from ground motions recorded on 

bedrock in Pacific Heights. Using these response spectra, a 

simplified, single-degree-of-freedom dynamic analysis of 

the comer buildings was undertaken. Building weights 

ranging from 400 to 500 kips (1,800-2,200 kN), and wall 

stiffnesses of 0.67 kipsiin. per foot of wall (385 kN/m per 

meter of wall), were estimated. Building periods ranging 

from 0.8 to 1.25 s were computed. Correlations were made 

between spectral displacement and observed damage, indicating a maximum spectral displacement for the heavily 

damaged buildings approximately equal to the observed 

permanent lateral deformation, and between structural base 

shear and observed damage, suggesting a damage threshold 

of approximately 15 to 20 kipsift (225-300 kN/m). Results 

indicate that the severe damage to this class of buildings in 

the Marina District was due to a combination of factors, 

particularly the near-coincidence of the fundamental building period with the maximum spectral displacement. 

INTRODUCTION 

The Marina District of San Francisco was one of the 

most heavily damaged areas in the earthquake. Damage included building collapse, underground-pipe breakage, and 

road and sidewalk damage due to ground shaking and liquefaction-related ground failure. Of the more than 1,400 

buildings in the Marina District, 7 collapsed, and another 

65 were moderately to severely damaged. Damage was 

concentrated in one class of building: four-story, woodframe comer apartment buildings; the 74 buildings in this 

class accounted for 6 of the 7 collapses. Because of the 

great uniformity in construction of these buildings, it is 

reasonable to question the nonuniformity in their apparent 

damage. Ground conditions throughout the district vary 

widely, from firm, competent sand, through soft natural 

clay and silt, to liquefaction-susceptible hydraulic fill. This 

report discusses the effects of ground conditions on the response and performance of these buildings. 
F182 MARINA DISTRICT 

DESCRIPTION OF BUILDINGS 

The Marina District was built in the late 1920's and early l93O's, after the 19 15 Panama-Pacific International Exposition. Construction until 1930 was all wood frame; 

after 1930, the large garages under apartment buildings 

were built of noncombustible materials (masonry or concrete) instead of wood frame. Most of the buildings are 

single-family dwellings or flats. About 5 percent of the total Marina District building stock consists of pre-1930, 

wood-frame comer apartment buildings (Harris and others, 

1990), which are the focus of this report. 

All the comer buildings are four-story structures, with 

three residential levels over a parking garage. Although 

several of these buildings were built on acute-angle corners and are triangular in plan, most (50 of 74) are rectangular, with plan dimensions of approximately 50 by 75 ft 

(15 by 23 m). Of these buildings, nearly all are oriented 

with their 50-ft (15 m) dimension oriented north-south. 

The distribution of years of construction (79 percent of the 

buildings were built between 1926 and 1928; Real Estate 

Data, Inc., 1991) is plotted in figure 1 and the distribution 

of building area (68 percent of the buildings are from 

10,000 to 14,000 ft2 [900 and 1,300 m2] in area; Real Estate Data, Inc., 1991) is plotted in figure 2. 

Because of the garages at their bottom levels, the comer 

buildings have many garage-door openings on both street 

sides. In general, the two street sides of the buildings are 

completely open, except for 10 to 20 ft (3-6 m) on one 

side near the comer. A typical garage-level building plan 

is shown in figure 3. 

GEOTECHNICAL ASPECTS 

The land of the present Marina District consists of areas 

of native soil deposits (beach, dune, and older alluvium) 

and artificial fills created during several periods of filling 

from about 185 1 to 1917. Areas adjacent to the original 

shoreline (U.S. Coast Survey, 1851) and sloughs that meandered inland from the old shoreline were filled before 

1894. At that time, a seawall was constructed that partly 

enclosed the Marina lagoon and, over the next decade, 

small amounts of fill were placed adjacent to the seawall. 

After the great 1906 San Francisco earthquake, principally 

in 1912, the enclosed lagoon area was hydraulically filled 

with sand and silt in preparation for the Panama-Pacific 

International Exposition held in 19 15; this hydraulically 

filled area is now the central part of the Marina District. 

Minor filling, grading, and leveling were performed after 

the exposition, but in general the land in the Marina District was little modified between 1917 and 1989. (See 

Bonilla, this chapter, for a more detailed account of the 

Marina District's development. 

1926 1927 1928 1929 1930 

Year of Construction 

Figure 1.-Number of buildings in the Marina District versus year of construction. Numbers at top of bars 

indicate percentage of total. 
EFFECTS OF GROUND CONDITIONS ON THE DAMAGE TO FOUR-STORY CORNER APARTMENT BUILDINGS F183 

After the 1989 earthquake, effects of strong ground soil; areal subsidence; settlement; distortion of residential 

shaking and liquefaction could be observed throughout the buildings; compressional buckling of sidewalks and curbs; 

Marina District. Liquefaction and ground failure were and utility-line breaks. Street-by-street mapping of geomanifested by sand boils; subsurface voids; horizontal and technical effects was conducted, and the more significant 

vertical spreading cracks in pavements, sidewalks, and of these observations are summarized in figure 4, with the 

Building Area (ftA2) 

Figure 2.-Number of buildings in the Marina District versus building area. Numbers at top of bars indicate 

percentage of total. 

- ONE-STORY PORTION PLASTER-SHEATHED 

WALLS AT ENTRY 

ENTRY SOLID WALL 

\ / 1 

THREE STORIES OVER GARAGE 

LIGHTWELL 

GARAGE-DOOR - OPENING 

Figure 3.-Typical garage-level building plan, showing solid-wall construction of brick veneer or stucco over 

straight wood sheathing over wood studs. Not to scale. 
F184 MARINA DISTRICT 

location of the original shoreline (U.S. Coast Survey, 

185 1) drawn for reference. Examination of the pattern of 

observations shown in figure 4 indicates that the areas of 

lateral-spreading cracks, liquefaction sand boils, settlement, and buckling coincide well and define what may be 

considered as the ground-failure zone. This zone lies bayward of the old shoreline, extending about 3,000 ft (900 

m) along Marina Boulevard between Webster and Broderick Streets and inland as far as about the intersection of 

Alhambra and Avila Streets. Note that a close spatial 

correlation exists between the ground-failure zone identified in figure 4 and the area of fill placed after 1906. Geotechnical effects did occur outside of the postulated 

ground-failure zone but appeared to consist primarily of 

differential building settlements and local subsidence near 

the old shoreline and in the filled slough channel (fig. 4). 

For example, a house on Francisco Street near Divisadero 

Street sustained 1.7 ft (0.5 m) of differential settlement; 

and farther west along Francisco Street, near Broderick 

Street, sidewalks and backyard soils exhibited cracks with 

horizontal widths as large as half an inch (0.01 m) and 

vertical offsets as large as 1.25 in. (0.03 m). In areas landward of the old shoreline and former slough boundaries, 

negligible geotechnical effects were observed. 

No ground-motion recordings were obtained in the Marina District during the main shock, and so actual ground 

motions there are unknown. Peak horizontal ground accelerations at nearby bedrock strong-motion-recording stations in Pacific Heights and on Telegraph Hill were 0.06 

and 0.08 g, respectively, but liquefaction and ground-failure observations indicate that higher levels of ground motion were probably sustained in the Marina District. 

Sand boils erupted throughout the ground-failure zone. 

In most places, ejected sand was dark gray, indicative of 

the sandy fill dredged from the bay bottom. Results of liquefaction analyses using simplified procedures (Seed and 

others, 1985) indicate that liquefaction during the main 

shock was confined primarily to the loose hydraulic fill. 

Settlement damage to buildings occurred in many places, mainly along Marina Boulevard. Between Broderick 

and Scott Streets, several houses settled as much as 6 to 

12 in. (0.15-0.3 m), as manifested by unclosable garage 

doors, buckling of downspouts, and distortion of walls, as 

well as by cracking of garage slabs. Between Fillmore and 

Webster Streets, at the other end of the ground-failure 

zone, houses settled differentially, listing against each other in their final positions. Bearing deformation (punching) 

of column footings and wall foundations was observed in 

many places. Lateral spreading was most evident in the 

vicinity of Winfield Scott School, where movements of as 

much as 8 in. (0.2 m) were observed. Spreading could be 

traced easily across the schoolyard to North Point Street 

near Scott Street, and through the garage of the comer 

building at Scott and North Point Streets. Several houses 

EST. FRANCIS 

SAN FRANCISCO BAY 

. 8 \ YACHTCLUB 

0 I 200 ft EXPLANATION 

- Notes 1851 shoreline (after U.S. Coast Survey, 1851) 1. Lateral-spreading cracks, settlement, and buckling; 50 m - Lateral-spreading cracks mapping by J.A. Egan (Geomatrix Consultants). 

2. Sand boils, mapping by J.A. Egan (Geomatrix : Building settlement Consultants), R.B. Seed (University of California, 

\\\x\x\-w Pavernent/curb/sidewalk buckling Berkeley), and M.J. Bennett (U.S. Geological Survey) 

Sand boil 

Figure 4.-Marina District, showing locations of earthquake-related liquefaction and ground failure and of 

185 1 shoreline. 
EFFECTS OF GROUND CONDITIONS ON THE DAMAGE TO FOUR-STORY CORNER APARTMENT BUILDINGS F185 

in this area were racked by settlement and lateral movement. Horizontal displacement was also evident along 

Beach and North Point Streets near Webster Street, where 

cracks as much as 3 in. (0.08 m) wide opened in the 

street, and separations between curb and street pavement 

as great as 5 in. (0.15 m) developed. Several inches of 

areal subsidence occurred within the ground-failure zone. 

Subsidence of as much as 5 in. (0.15 m) was observed 

around a 60-ft (18 m)-diameter inground pump station on 

the Marina Green near Avila Street. Such vertical and lateral displacements caused broken waterlines and fractured 

manholes throughout the Marina District; near the seawall 

and at the St. Francis Yacht Club, lateral-spreading cracks 

and deformation were quite evident. At the yacht club, differential settlement of 8 in. (0.2 m) was observed between 

the pile-supported part of the structure and that part supported on spread footings. Finally, a phenomenon observed throughout the ground-failure zone was buckling of 

sidewalks and curbs, including heave and override of 

driveway and sidewalk slabs. Although some of this buckling was associated with lateral spreading, we believe that 

much of it was caused by large, spatially nonuniform 

displacements. 

In examining the ground performance mapped in figure 

4, three soil-profile zones can be defined (fig. 5): first, the 

ground-failure zone; second, a zone between the groundfailure zone and the old shoreline within which relatively 

minor ground-failure effects were observed; and third, a 

zone landward of the old shoreline within which groundfailure effects were essentially absent. Ground conditions 

in these three zones were evaluated by examining the logs 

of numerous boreholes drilled throughout the Marina District both before and after the earthquake. 

The first soil-profile zone is generally characterized by 

approximately 25 to 30 ft (7.6-9.1 m) of loose to very 

loose hydraulic fill (sand and silt) overlying Holocene natural sand and soft bay sedimentary deposits, hardpan (older sand), and deep, old bay clay. After the earthquake, the 

U.S. Geological Survey drilled an exploratory borehole in 

the Winfield Scott School yard near Beach and Divisadero 

Streets (within this first soil-profile zone) to investigate 

subsurface geologic/geotechnical conditions (Kayen and 

others, 1990). The borehole penetrated about 25 ft (7.6 m) 

of loose sandy fill overlying Holocene bay mud and natural sand to a depth of about 40 ft (12 m), where a firm 

material described as "hardpan" was penetrated. Bedrockcontour maps by Schlocker (1974) indicate bedrock at approximately this depth. The borehole continued into and 

through the hardpan and penetrated clay at a depth of 

about 75 ft (23 m). The clay stiffens with depth until bedrock is penetrated at a depth of 265 ft (81 m). 

The second soil-profile zone is generally characterized 

by older, medium-dense, surficial fill materials overlying 

generally dense natural beach sand and, in turn, deep, old 

bay clay. Given the deep, relatively soft conditions in the 

ground-failure zone and this "soft"-soil-profile zone, site 

amplification of ground motions in the Marina District 

during the main shock may have occurred analogously to 

that at similar sites of deep, soft sedimentary deposits 

around the margins of San Francisco Bay, notably 

SAN FRANCISCO BAY 

NORTH 

Figure 5.-Marina District, showing locations of three soil-profile zones differentiating relative ground performance during the earthquake. Numbers shown are city block numbers, which are referenced in table 2. 
F186 MARINA DISTRICT 

Treasure Island, Emeryville, and Oakland. Aftershock recordings obtained at temporary stations established in the 

Marina District indicate significant site-amplification effects for low-amplitude bedrock motions nearby (see Boatwright and others and Liu and others, this chapter). 

The third soil-profile zone is generally characterized by 

firm, competent natural beach and (or) dune sand underlain by a considerably lesser thickness or even absence of 

bay clay. Thus, the ground motions during the earthquake 

in this "firm9'-soil-profile zone landward of the old shoreline are not expected to have been as great as in the 

"soft"-soil-profile zone bayward of the old shoreline. 

OBSERVED PERFORMANCE 

Given their eccentric building plan, we expected that the 

comer buildings would behave in a highly torsional manner. In general, however, torsion was not exhibited by the 

damaged buildings: They were seen to lean at the first story, parallel to the street (some leaned in two directions). 

This nontorsional behavior may be explained by the presence of short, plaster-sheathed walls on each side of the 

buildings' main-entry doors (see fig. 3); these stiff but 

brittle walls were able to resist some of the forces generated by the eccentricity. The lightwell walls opposite the 

main entry also contributed to the buildings' torsional 

resistance. 

The Marina District buildings are built immediately adjacent to each other, without space to allow for lateral 

drift. Thus, pounding has been identified as one of the 

main causes of damage to the comer buildings. (The 

thinking is that the last building in a line gets pushed 

over.) Although pounding must have been a contributing 

factor, at least one comer apartment building (1801 Beach 

Street) failed that was not immediately adjacent to another 

building, suggesting that pounding was not everywhere required for comer-building failure. 

Damage to the wood-frame, comer apartment buildings 

in the Marina District varied; the average damage to these 

buildings was more than 3 times higher than for any other 

building type. However, more than 50 percent of these 

comer buildings were assessed during a postearthquake 

survey as having sustained a maximum of 10 percent damage (Harris and others, 1990). Clearly, then, there was a 

great deal of disparity in the damage within a fairly uniform class of buildings. Some differences exist in construction between the comer buildings, but not so much as 

to explain the variation in damage observed. The distribution of damage to comer buildings in the three soil-profile 

zones described above is plotted in figures 6 through 8; 

the damage states are defined in table 1. 

Damage State 

Figure 6.-Number of buildings in "soft"-soil-profile zone versus damage state. Most (64 percent of) buildings 

were assigned to damage states 5 (heavy) through 7 (destroyed). Numbers at top of bars indicate percentage of 

total. 
EFFECTS OF GROUND CONDITIONS ON THE DAMAGE TO FOUR-STORY CORNER APARTMENT BUILDINGS 

1 2 3 4 5 6 7 

Damage State 

Figure 7.-Number of buildings in "firm9'-soil-profile zone versus damage state. All buildings except one 

were assigned to damage states 4 (moderate) and below. Numbers at top of bars indicate percentage of total. 

1 2 3 4 5 6 7 

Damage State 

Figure 8.-Number of buildings in ground-failure zones versus damage state. Buildings are spread across all 

damage states but are concentrated at lower end. Numbers at top of bars indicate percentage of total. 
F188 MARINA DISTRICT 

Table 1 .-Definition of damage states 

[From Applied Technology Council (1986)] 

Central 

Damage Description Damage damage 

state of damage factor factor 

(percent) (percent) 

Damage states for each building were estimated by engineers during an extensive field survey immediately after 

the earthquake (Harris and others, 1990). Figures 6 

through 8 indicate a definite correlation of damage state 

with soil-profile zone. Only one of the buildings on firm, 

native soil (albeit marshland) was damaged beyond state 

4. Buildings on soft soil, however, were damaged more 

severely; 64 percent of these buildings were assigned to 

damage states 5 through 7. The buildings in the groundfailure zone showed a mixed performance: 73 percent 

were assigned to damage states 1 through 4, and the rest 

to damage states 5 through 7. 

ANALYSIS AND METHODOLOGY 

To quantify further the correlation of damage state with 

soil-profile zone, a simplified dynamic structural analysis 

was performed on the comer buildings, as described 

below. 

RESPONSE SPECTRA 

As mentioned previously, no ground-motion recordings 

of the main shock were obtained in the Marina District. 

The closest strong-motion data were recorded by the Califomia Division of Mines and Geology (Shakal and others, 

1989) in Pacific Heights (sta. 58 13 l), approximately 1.5 

mi (2.5 km) south of the Marina District. The Pacific 

Heights station is founded on bedrock. To estimate the 

ground motions in the Marina District, we decided to 

relate the recorded Pacific Heights bedrock motions to 

Marina District ground motions through simple period-dependent amplification-transfer functions. For the "soft"- 

soil-profile zone, we considered that the pair of stations on 

Treasure Island (sta. 581 17) and Yerba Buena Island (sta. 

58163), both islands in San Francisco Bay, would provide 

an appropriate transfer function, given their similarity in 

distance and azimuth from the fault rupture, their subsurface site conditions and depth to bedrock, and their site 

geometry. To account for possible differences between direction of shaking, north-south and east-west amplification-transfer functions were evaluated separately. These 

functions were then used to scale the respective directional 

components of the Pacific Heights record to calculate 

ground motions for the 'bsoft"-soil-profile zone. The resulting spectra are plotted in figure 9, with components of the 

Pacific Heights bedrock record shown for comparison. 

For the "firm"-soil-profile zone, no similar soil-bedrock 

site pairs existed within reasonable proximity to the Marina District, and so an amplification-transfer function was 

developed from the soil and bedrock attenuation relation 

of Sadigh and others (1986). Because this attenuation relation does not differentiate shaking direction, only an average function was utilized to scale the Pacific Heights 

bedrock record, and an average bedrock spectrum was calExp Lanation 

- - - - Rock, 360' Pacific Heights - - Rock, 

- Soft soil, 360- Marina District - + soft 

.04 .1 .2 5 1 2 5 10 20 

Period (s) 

Figure 9.-Estimated bbsoft"-soil-profile-zone tripartite response spectra 

of orthogonal horizontal north-south (360') and east-west (90') groundmotion components in the Marina District derived from respective 

components recorded at bedrock station in Pacific Heights (California 

Division of Mines and Geology sta. 58131), which are shown for comparison. 
EFFECTS OF GROUND CONDITIONS ON THE DAMAGE TO FOUR-STORY CORNER APARTMENT BUILDINGS F189 

culated from components of this record. The resulting 

spectrum is plotted in figure 10, with the corresponding 

Pacific Heights bedrock spectrum shown for comparison. 

BUILDING MODELS 

Earthquake deformations in the comer buildings were 

concentrated in the weak first stories. Even heavily damaged buildings commonly showed little evidence of deformation above the first story, and so the buildings were 

assumed to behave essentially as structures with a single 

degree of freedom in each major axis, and to be rigid 

above the first story. Using these assumptions, the estimation of building response becomes a straightforward task. 

(For simplicity, buildings with irregular plans were omitted from the analysis.) The steps involved were (1) estimation of the total building mass tributary to the first story 

and above, (2) estimation of the stiffness of the first story 

in the building's two principal directions, (3) calculation 

Exp Lanation 

Pacific Heights ---- ~ock, average 

Marina District - Firm soil 

,04 .1 .2 5 1 2 5 10 20 

Period (s) 

Figure 10.-Estimated "firm"-soil-profile-zone tripartite response spectrum of average horizontal-motion component in the Marina District, derived from average of horizontal components recorded at bedrock station 

in Pacific Heights (California Division of Mines and Geology sta. 

58131), which is shown for comparison. 

of the building's fundamental period of vibration in its two 

principal directions, and (4) application of the appropriate 

response spectra to the fundamental periods to determine 

spectral amplitudes. 

Building mass was estimated by using average unit 

weights based on construction typical of the 1920's, as indicated below: 

Part of building Unit weight 

flb~f^iWal) 

Using these unit weights, total building weights were calculated, mostly in the range 400-500 kips (1,800-2,200 

kN). The estimated building weights and building dimensions are listed in table 2. 

Building stiffnesses in each principal direction were estimated by using a unit shear stiffness derived from testing 

of wood-sheathed diaphragms (ABK Joint Venture, 1981). 

One of the diaphragms tested was an unchorded, straightsheathed diaphragm intended to represent the roof of a 

typical unreinforced-masonry (URM) building; this construction is quite similar to the exterior walls of the comer 

buildings. Because the diaphragm was unchorded, it deformed almost exclusively in shear, not in flexure. The 

same shear deformation (mostly due to nail slip) was evident in damaged Marina District buildings. The absence of 

flexural stiffness in the building walls also allows the addition of wall-pier stiffnesses along a line without regard 

to the piers' relative flexural rigidity. Total wall stiffness 

was based on the total length of available wall. 

From the results of these tests, a unit shear stiffness of 

0.67 kipslin. per foot of wall (385 kN/m per meter of 

wall) was calculated on the basis of the preyield stiffness 

of the test diaphragm. Postyield tests show that considerable softening occurs after repeated load cycles. However, 

since the building periods under consideration are quite 

long and the earthquake was of short duration, the number 

of postyield cycles that any building underwent is likely to 

have been small, and so only the preyield stiffness was 

used in our analyses. 

The distribution of building stiffnesses, as represented 

by the fundamental period of vibration, in east-west and 

north-south directions is plotted in figure 11. Note that the 

buildings are generally stiffer in the east-west direction, 

because most of them are oriented with their longest dimension oriented east-west. 
MARINA DISTRICT 

Table 2.-Data on comer buildings 

N-S N-S EW E W 

Area Dimension Walls Dimension Walls Weight 

Location Block Year fft2) Units fft1 fft1 fft) (ft1 Facade fki~s) 

2 Alhambra Street 

90 Alhambra Street 

190 Alhambra Street 

200 Alhambra Street 

290 Alhambra Street 

400 Avila Street 

2100 Bay Street 

2101 Bay Street 

2185 Bay Street 

2190 Bay Street 

2285 Bay Street 

2300 Bay Street 

2301 Bay Street 

1700 Beach Street 

1701 Beach Street 

1740 Beach Street 

1750 Beach Street 

1801 Beach Street 

1901 Beach Street 

2000 Beach Street 

2090 Beach Street 

2101 Beach Street 

2190 Beach Street 

2195 Beach Street 

3255 Broderick Street 

3301 Broderick Street 

3465 Broderick Street 

3555 Broderick Street 

3650 Broderick Street 

10 Capra Way 

50 Capra Way 

75 CapraWay 

101 Capra Way 

2 Casa Way 

2 Cervantes Boulevard 

25 Cervantes Boulevard 

95 Cervantes Boulevard 

98 Cervantes Boulevard 

101 Cervantes Boulevard 

2050 Chestnut Street 

2390 Chestnut Street 

2490 Chestnut Street 

2500 Chestnut Street 

3459 Divisadero Street 

3501 Divisadero Street 

3560 Divisadero Street 

3701 Divisadero Street 

3755 Divisadero Street 

3789 Fillmore Street 

2200 Francisco Street 

2201 Francisco Street 

2290 Francisco Street 

2295 Francisco Street 

2300 Francisco Street 

2301 Francisco Street 

2395 Francisco Street 

1801 Jefferson Street 

1895 Jefferson Street 

180 Mallorca Way 

201 Mallorca Way 

225 Mallorca Way 

2100 North Point Street 

2101 North Point Street 

2200 North Point Street 

5 Rico Way 

3360 Scott Street 

3490 Scott Street 

3636 Scott Street 

3750 Scott Street 

3800 Scott Street 

3825 Scott Street 

1 Toledo Way 

2 Toledo Way 

96 Toledo Way 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Brick 

Stucco 

Stucco 

Brick 

Stucco 

Brick 

Brick 

Brick 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Brick 

Stucco 

Stucco 

Stucco 

Brick 

Brick 

Brick 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Stucco 

Brick 

Stucco 

Stucco 

Stucco 

Stucco 

Brick 
EFFECTS OF GROUND CONDITIONS ON THE DAMAGE TO FOUR-STORY CORNER APARTMENT BUILDINGS F191 

On the basis of the soil-profile-zone map (fig. 5), each 

building was assigned to either the "soft"-soil-profile response spectrum or the "firm"-soil-profile response spectrum. Response parameters in each of the buildings' 

principal directions were calculated and are discussed in 

the next section. 

RESULTS AND DISCUSSION 

SPECTRAL DISPLACEMENT 

VERSUS DAMAGE RATIO 

Using the simplified dynamic analysis described above, 

correlations were made between the damage ratio, defined 

as the repair cost divided by the replacement cost, and the 

estimated maximum spectral displacement for comer 

buildings in all three soil-profile zones (fig. 12) and for 

only those outside the ground-failure zone (fig. 13). Although the data in figure 13 do not show a strong correlation, they do illustrate the following points. 

1. The maximum spectral displacement for buildings 80 

percent damaged (which leaned over but did not collapse) is about 1 ft (0.3 m). The buildings 100 percent 

damaged show similar, if slightly more varied, results. 

Note that because these buildings collapsed, such detailed dimensions as wall length were only estimated. 

A spectral displacement of 1 ft (0.3 m) is approximately equal to the permanent lateral deformation observed 

in these buildings. 

2. The data in figure 13 appear to suggest an upper bound 

for the damage ratio, given the spectral displacement, 

that may indicate the presence (in some buildings) of 

structural attributes invisible from the exterior, such as 

diagonal wall sheathing or first-story walls with interior 

stucco, that would significantly increase building 

strength and stiffness. 

Examination of the "soft9'-soil-profile response spectra in 

figure 9 indicates that the maximum spectral displacements occur in the period between 1.5 and 2.5 s, whereas 

the calculated fundamental building periods are in the 

range 0.8-1.25 s. Thus, if some decrease in building stiffness occurred during hysteresis, there would have been an 

accompanying increase in spectral displacement. Although 

this effect cannot be quantified at this time, some of the 

uncertainty evident in figure 13 may be due to decreases 

in building stiffness. 

We also note the contrast in the response of the woodframe comer buildings to that of the comer buildings with 

URM or concrete first stories. Harris and others (1990) 

EXPLANATION 

Figure 11,-Number of buildings versus estimated fundamental building period. Periods are spread across a 

narrow band from 0.8 to 1.25 s. East-west periods are generally shorter than north-south periods, owing to 

building orientation. Periods plotted are preyield estimates; actual periods may be somewhat longer because 

of postyield hysteresis. 
MARINA DISTRICT 

100 - u 

Estimated Maximum Spectral Displacement (in.) 

EXPLANATION 

0 "Soft" Soil-Profile + "Firm" Soil-Profile ^ Ground Failure Zone 

Figure 12.-Damage ratio versus estimated maximum spectral displacement for all comer buildings studied. 

01 +- I -b&L-l- m I I I I I I 

3 4 5 6 7 8 9 10 11 12 13 

Estimated Maximum Spectral Displacement (in.) 

EXPLANATION 

1 0 oft oil-profile + oil-profile 1 

Figure 13.-Damage ratio versus estimated maximum spectral displacement for all comer buildings studied 

except those within ground-failure zone. Spectral displacements of buildings 80 to 100 percent damaged are 

about 1 ft (0.3 m), approximately equal to permanent lateral deformation observed in heavily damaged buildings that did not collapse. 
EFFECTS OF GROUND CONDITIONS ON THE DAMAGE TO FOUR-STORY CORNER APARTMENT BUILDINGS F193 

reported that these buildings were damaged, on average, 

10 times less severely than the (otherwise similar) woodframe buildings. In addition, none of the URM- or concrete-first-story buildings was damaged beyond state 4 

(moderate). The fundamental building periods of these 

stiffer structures may be estimated at about 0.3 s. Applied 

to the bbsoft"-soil-profile response spectra in figure 9, this 

building period results in a spectral displacement of approximately 0.4 in. (0.01 m). The decrease in response 

helps to explain the surprisingly good performance of 

URM construction in the Marina District, where the soft 

soils may be considered to have isolated these stiff but 

brittle buildings from damaging, high-frequency ground 

motions. 

BASE SHEAR VERSUS DAMAGE RATIO 

Correlations were also made between the damage ratio 

and the estimated maximum structural base shear per foot 

of exterior wall (fig. 14). Again, owing to the approximations in these analyses, a well-defined correlation is not 

apparent, although a general positive slope is indicated for 

the bbsoft"-soil-profile zone. The following observations 

can be made. 

1. The buildings in the "firm"-soil-profile zone generally 

indicate base shears less than about 15 to 20 kips/ft 

(225-300 kNIm), whereas those in the b'soft"-soil-profile zone generally indicate a higher shear that appears 

to be an approximate lower bound for the large perrnanent lateral deformation observed in the heavily damaged comer buildings. 

2. This correlation is somewhat clearer than that between 

damage ratio and maximum spectral displacement, indicating that the length of wall available for shear resistance is also an important factor affecting damage, 

as would be expected. 

SUMMARY AND CONCLUSIONS 

The extremely poor performance of many of the woodframe comer apartment buildings in the Marina District 

during the earthquake appears to be due to an infortuitous 

combination of factors, among the most important of 

which is the near-coincidence of the fundamental building 

period with the maximum spectral displacement. The 

ground failure in the central part of the filled area appears 

to have mitigated much of the potential damage by 

dissipating seismic energy through liquefaction. From 

these and the above observations, we draw two main 

conclusions. 

First, in future large earthquakes that affect the Marina 

District, the energy dissipation from ground failure may 

Estimated Maximum Structural Base Shear (kips/ft of wall) 

EXPLANATION 1 0 "Soft Soil-Profile + "Finn" Soil-Profile 

Figure 14.-Damage ratio versus estimated maximum structural base shear for all comer buildings studied 

except those within ground-failure zone. Base shear of about 15 to 20 kipsift (225-300 kN/m) appears to be 

approximate lower bound of permanent lateral deformation observed in heavily damaged buildings. 
F194 MARINA DISTRICT 

not be so apparent. Longer durations, such as those expected from a repeat of the 1906 event, would be expected 

to cause severe damage or collapse to many comer buildings that were not severely damaged in the 1989 event. 

We note that San Francisco's recent postearthquake building-strengthening ordinance applied only to buildings with 

damage ratios of at least 10 percent; that is, lightly damaged buildings were not required to be strengthened. 

Second, buildings similar to the comer buildings in the 

Marina District exist in several other San Francisco neighborhoods (including the Richmond and Mission Districts). 

Most of these buildings are not located on soft soils or 

fills and were not seriously affected by the 1989 earthquake. However, a repeat of the 1906 event could cause 

serious damage to these structures. Using the unreduced 

lateral-force formula (34-1) from the "Uniform Building 

Code" (International Conference of Building Officials, 

1991, chap. 23), 

where V is the base shear, Z=0.4, I=1.0, C=2.75, W is the 

building weight, and Rw=l.O. The spectral acceleration, Sa, 

defined as V/W, would be approximately 1.1 g (425 in/s2 

[10.79 m/s2]); this acceleration is intended to correspond 

to a 475-year event. Using this acceleration and a firstmode period of 0.9 s, the spectral displacement, Sd, may 

be computed from the standard formula 

where T is the (first) modal period. This computation results in a spectral displacement of 9 in. (0.22 m), approximately equal to the lower bound for severe damage shown 

in figure 13, from which we may conclude that the damage observed in the "soft"-soil-profile zone of the Marina 

District would be possible in similar buildings on firmer 

ground in a much larger earthquake. 

Finally, building damage in the Marina District was 

highly sensitive to ground conditions, as well as to building construction. Accordingly, any conclusions drawn 

from performance data in the Marina District should be 

used with the knowledge that the observed building damage was a result of the coincidence of many factors, including seismologic, geologic, and structural parameters. 

Future earthquakes affecting the Marina District and other 

areas are likely to cause markedly different effects. 

REFERENCES CITED 

ABK Joint Venture, 1981, Methodology for mitigation of seismic hazards 

in existing unreinforced masonry buildings; diaphragm testing: Report ABK-TR-03,424 p. 

Applied Technology Council, 1985, Earthquake damage evaluation data 

for California: Redwood City, Calif., 472 p. 

Harris, S.K., Scawthorn, C.R., and Egan, J.A., 1990, Damage in the 

Marina District of San Francisco in the October 17, 1989 Loma 

Prieta earthquake: Japan Earthquake Engineering Symposium, 1990, 

Proceedings. 

International Conference of Building Officials, 1991, Uniform building 

code: Whittier, Calif., 1050 p. 

Kayen, R.E., Liu, H.-P., Fumal, T.E., Westerlund, R.E., Warrick, R.E., 

Gibbs, J.F., and Lee, H.J., 1990, Engineering and seismic properties 

of the soil column at Winfield Scott School, San Francisco, chap. G 

of Effects of the Loma Prieta earthquake on the Marina District, San 

Francisco, California: U.S. Geological Survey Open-File Report 90- 

253, p. GI-G18. 

Real Estate Data, Inc., 1991, REALDEX real estate atlas of the county of 

San Francisco: San Francisco, 2,260 p. 

Sadigh, K., Egan, J.A., and Youngs, R.R., 1986, Specification of ground 

motions for seismic design of long period structures: Earthquake 

Notes, v. 57, no. 1, p. 13. 

Schlocker, Julius, 1974, Geology of the San Francisco North quadrangle, 

California: U.S. Geological Survey Professional Paper 782, 109 p. 

Seed, H.B., Tokimatsu, K., Harder, L.F., and Chung, R.M., 1985, 

Influence of SPT procedures in soil liquefaction resistance 

evaluations: Journal of Geotechnical Engineering, v. Ill, no. 12, 

p. 1425-1445. 

Shakal, A., Huang, M., Reichle, M., Ventura, C., Cao, T., Sherburne, R., 

Savage, M., Darragh, R., and Petersen, C., 1989, CSMIP strongmotion records from the Santa Cruz Mountains (Loma Prieta), California earthquake of 17 October 1989: California Division of Mines 

and Geology, Office of Strong Motion Studies Report OSMS 89-06, 

196 p. 

U.S. Coast Survey, 1851, South shore Golden Gate from Point Lobos to 

San Francisco, California: scale 1 : 10,000. 
THE LOMA PRIETA, CALIFORNIA, EARTHQUAKE OF OCTOBER 17,1989: 

STRONG GROUND MOTION AND GROUND FAILURE 

MARINA DISTRICT 

PERFORMANCE OF EMERGENCY-RESPONSE SERVICES 

AFTER THE EARTHQUAKE 

By Charles R. Scawthom and Keith A. Porter, EQE Engineering and Design; and 

Frank T. Blackbum, PWSS Co., Ltd. 

CONTENTS 

Intr&uction ................................................................ The Marina District before the earthquake ........................... San Francisco Police Department ...................................... San Francisco Fire Department ......................................... 

San Francisco Department of Public Health, Paramedic 

Earthquake damage in the Marina District ........................... SmD response -------- A ................................................... SFFD response ............................................................ First response: Building collapse at 2 Cervantes 

Concluding remarks ...................................................... 

References cited .......................................................... 

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209 

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213 

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214 

ABSTRACT 

Building collapses, gas leaks, and a large fire made 

the Marina District the primary focus of emergency response in the city of San Francisco. A total of 7 Marina 

District buildings collapsed, and 63 more were declared 

unsafe to enter or occupy. Police and emergency medical 

services were not generally overwhelmed, despite temporary loss of computer-aided dispatch. A fire that grew to 

near-conflagration proportions demonstrated both the 

strengths and weaknesses of emergency response. The fireboat Phoenix, the San Francisco Fire Department's Portable Water Supply System, and the tactics and training for 

using them were critical in controlling the fire. In contrast, 

the city's Auxiliary Water Supply System was poorly utilized because of overwhelmed procedures for emergency 

operations, communication, and command and control. 

INTRODUCTION 

The earthquake severely tested the preparedness of emergency-response services throughout the San Francisco Bay 

area. San Francisco itself sustained moderate to strong 

ground shaking, with intensities ranging from VI to IX on 

the modified Mercalli intensity (MMI) scale (Benuska, 

1990). The most severe damage occurred in the Marina 

District, an area of approximately % mi2 with 14,000 residents at the end of the San Francisco peninsula. This area, 

assigned an MMI of IX by the U.S. Geological Survey, 

became the focus of the city's most intensive police and 

fire-service involvement. This report discusses the effectiveness of police, fire, and ambulance emergency services 

in the Marina District during the early hours after the 

earthquake. We first briefly review the setting of the Marina District and San Francisco's emergency-response capabilities before the earthquake, and we then describe police, 

ambulance, and, especially, fire-service response. We conclude with a summary of the lessons learned. 

THE MARINA DISTRICT 

BEFORE THE EARTHQUAKE 

San Francisco's Marina District, located at the north end 

of the San Francisco peninsula (fig. l), is primarily a residential neighborhood, bounded on the north by San Francisco Bay; on the south by Lombard Street, a major transit 

corridor; on the east by Fort Mason; and on the west by 

the Palace of Fine Arts and the Presidio of San Francisco 
F196 MARINA DISTRICT 

(figs. 1, 2). The land that composes the Marina District 

was reclaimed from San Francisco Bay, filled in stages 

during the years 1869 to 1917 (Bonilla, 1990). The 1915 

Panama-Pacific International Exposition was held on the 

site of the Marina District; afterward, streets and lifeline 

services were installed, and the land was auctioned for 

housing. A typical Marina District apartment building is a 

1920's-era wood-frame structure of one to three stories 

above a ground-level garage. Walls are typically constructed of stucco over straight wood sheathing, although some 

buildings have unreinforced-masonry or reinforced-conCrete first stories. 

SAN FRANCISCO POLICE DEPARTMENT 

On October 17, 1989, the San Francisco Police Department (SFPD) employed 1,768 officers, of whom approximately a third were on duty at 5:04 p.m. P.d.t. (Lt. Harper, 

oral commun., 1991). Officers operate out of nine police 

stations, or districts (fig. 3). Above the district level are 

three commanders, each in charge of three police districts; 

the Marina District is contained within the SFPD's Northern District. 

The SFPD is responsible for emergency telephone (or 

9 1 1) service. All calls to the 9 1 1 exchange are received at 

the Hall of Justice (fig. 1) at 6th and Bryant Streets. A 

dispatch officer determines whether the emergency is police related; if not, the call is routed to the appropriate 

municipal unit, such as the fire department or the paramedics, using a transfer line routed through Pacific Bell's 

central office on McCoppin Street. If the emergency is police related, the dispatch officer uses a computer-aided-dispatch (CAD) system to order the appropriate police 

district to respond. 

SAN FRANCISCO FIRE DEPARTMENT 

On October 17, 1989, the San Francisco Fire Department (SFFD) employed approximately 1,300 firefighters 

and officers, not including staff at headquarters, training 

Fort Mason 

Figure 1.-Sketch maps of San Francisco Bay area and city of San Francisco, showing location of the Marina 

District (shaded area). CFAS, Central Fire Alarm Station. 
PERFORMANCE OF EMERGENCY-RESPONSE SERVICES AFTER THE EARTHQUAKE F197 

center, and other support services. San Francisco's 41 fire 

stations are divided among 10 battalions of three to five 

stations each (fig. 4); each battalion is commanded by a 

battalion chief. The 10 battalions are organized into four 

divisions under the command of a division chief: three 

within the city of San Francisco and one at San Francisco 

International Airport. Department Chief Frederick Postel 

was out of town at the time of the earthquake. Three deputy chiefs, Michael Farrell, John Boscacci, and Frank 

Scales, report to Chief Postel; Deputy Chief Farrell was 

the acting chief in Chief Postel's absence. The units in service at 5:04 p.m. included 41 engine companies, 18 truck 

companies, 2 rescue companies, 1 air-service company, 1 

fireboat company, and 1 equipment unit. 

The SFFD typically responds to a 911 call as follows. 

When the call is received, the caller speaks first to a police 

dispatch officer. If the emergency is within the purview of 

the SFFD, the call is transferred to the SFFD's communications center at the Central Fire Alarm Station (CFAS, 

fig. 1) in Jefferson Square Park, on Turk Street between 

Gough and Laguna Streets. The caller then speaks to an 

SFFD dispatcher, who directly contacts the appropriate responding units. In an emergency such as an earthquake, 

the SFFD's communications center is designated the city's 

LOMBARD ST 

Figure 2.-Marina District, showing street grid. 
MARINA DISTRICT 

0 

RICHMOND 2% 

PARK 

TARAVAL 

Figure 3.-Sketch map of San Francisco, showing locations of SFPD districts and areas of most extensive 

damage (shading). Map courtesy of SFPD. 

Figure 4.-Sketch map of San Francisco, showing locations of SFPD battalions and fire stations. 
PERFORMANCE OF EMERGENCY-RESPONSE SERVICES AFTER THE EARTHQUAKE F199 

Emergency Operations Center (EOC), where the mayor, 

city-department heads, and all command and control are 

based. 

Within minutes of the earthquake, 27 fires had broken 

out throughout the city, and the SFFD would turn out for 

more than 400 incidents in the next 4 hours (San Francisco Fire Fighters Local 798, 1990), the most significant of 

which were the fire and building collapses in the Marina 

District. 

Normally, the SFFD has three available systems of water 

supply: the Municipal Water Supply System (MWSS), the 

Auxiliary Water Supply System (AWSS), and the Portable 

Water Supply System (PWSS). The MWSS serves the dual 

purpose of supplying potable water and providing water to 

fire hydrants. The AWSS is intended solely to ensure adequate water flow and pressure for firefighting purposes; it 

is separate and redundant to the MWSS, and is owned and 

controlled by the SFFD. Built in the decade after the 1906 

earthquake and fire, the AWSS is concentrated primarily in 

the urbanized part of the city of 1906, still the central 

business district (fig. 5). It has been gradually extended to 

other parts of the city, although the original part still constitutes most of the AWSS. The AWSS network in the Marina District is mapped in figure 6. 

The AWSS has been described in detail elsewhere 

(Scawthorn and others, 1990a, b). Briefly, it consists of 

several components: 

Static supplies: The 10-million-gal reservoir at Twin 

Peaks, the 750,000-gal Jones Street Tank, and the 

500,000-gal Ashbury Tank (fig. 5). 

Pump stations: Two stations, each capable of pumping 

water from San Francisco Bay into the undergroundpipe system at 10,000 gallmin and 300-lb/ft2 pressure. 

Pipe network: 129 mi of cast-iron and ductile-iron pipe 

serving approximately 1,500 dedicated high-pressure 

hydrants. The pipe network is divided into three pressure zones: Twin Peaks, upper, and lower. 

Fireboats: At the time of the earthquake, San Francisco possessed only one fireboat, the Phoenix, whose 

pump capacity is 9,600 gallmin at 150-lb/ft2 pressure. 

Fireboats may hook into the AWSS and pump seawater into the pipe network at any of five manifolds. 

Cisterns: In addition to the above components, San 

Francisco has 151 underground cisterns, again largely 

in the northeast quadrant of the city. These cisterns are 

generally of concrete construction, with a 75,000-gal 

capacity, about 1-hour supply for a typical SFFD 

pumper. 

Control of the AWSS is centered at the Jones Street 

tankhouse, where gages provide pressure readings at a 

limited number of points in the network. A few gate 

valves can be operated remotely from this tankhouse by a 

signal transmitted over land lines. The water pressure in 

the lower pressure zone can be increased by opening 

valves at the tankhouse, and the Twin Peaks pressure zone 

can be "cut in" by remotely operating valves located at the 

Ashbury Tank. Remotely operable valves are presently 

powered by Pacific Gas & Electric Co. (PG&E), the local 

electric utility, but are being converted to a backup emergency battery system. 

.^Pump Station No. 2 

- Lower Zone 

--- Upper Zone 

---- Son Francisco Contour Line 

City Line- Contour 

..-..A 

Interval: 30 m = 100 f t 

I .0 mile 

-I 

1.6 km 

Figure 5.-Sketch map of San Francisco, showing location of AWSS pipe network. After Scawthorn and 

others (1990). 
F200 MARINA DISTRICT 

Although the AWSS provides high assurance of firefighting water supply in the northeast quadrant of the city, major fires can and do occur far from the AWSS pipe 

network. Experience in the 1906 earthquake, as well as in 

subsequent California earthquakes in 197 1 (San Fernando) 

and 1983 (Coalinga), had also taught that earthquakes can 

damage piped water supply. In recognition of this fact, and 

to provide additional flexibility in deployment and to extend further the "reach" of the AWSS, since 1985 the 

SFFD has developed the PWSS. Its basic components are: 

Hosetenders, trucks capable of carrying 5,000 ft of 

large (5 in. diam) hose, with a high-pressure monitor 

for a master stream. 

Hose ramps, which allow vehicles to cross the hose 

when it is charged. 

Gated inlet Wye, allowing water supply into large-diameter from standard-diameter fire hose. 

Gleeson valve, a pressure-reducing valve connected to 

portable hydrants to draw water from the portable 

main at usable pressure. 

Portable hydrants, which allow water to be distributed 

from large-diameter hose. 

Hosetenders, which carry all the hose, hydrants, valves, 

and other fittings, are capable of laying 5,000 ft of hose in 

about 20 minutes. Hose lengths are intermittently fitted 

with portable hydrants, permitting water supply at many 

locations along the hose. Hose can thus be gridded and, in 

effect, provide a system of above-ground water mains. At 

the time of the earthquake, the SFFD had four PWSS 

hosetenders. 

SAN FRANCISCO DEPARTMENT OF 

PUBLIC HEALTH, PARAMEDIC DIVISION 

Emergency medical calls to the 91 1 exchange are routed 

to the Paramedic Division's Centralized Medical Dispatch 

Center (CMED) for response. Ambulances and crews are 

located at a staging area in Golden Gate Park (fig. 1) near 

Stanyan and Haight Streets. Normally, 15 ambulances are 

stationed there, and crews are available for 11 or 12 ambulances, with the others held in reserve. At the time of the 

earthquake, 11 ambulance crews were scheduled for duty. 

EARTHQUAKE DAMAGE 

IN THE MARINA DISTRICT 

The earthquake caused severe damage and widespread 

liquefaction-induced, permanent ground displacements in 

the Marina District. Seven buildings in the Marina District 

collapsed; their locations are shown in figure 7. These 

were the only buildings in San Francisco or Oakland that 

collapsed in the earthquake, although several structures in 

Figure 6.-Marina District, showing location of AWSS pipe network (heavy lines). Map courtesy of SFFD. 
PERFORMANCE OF EMERGENCY-RESPONSE SERVICES AFTER THE EARTHQUAKE F20 1 

San Francisco and Oakland (fig. I), outside the Marina 

District, sustained the loss of upper-story facades. At one 

brick building in downtown San Francisco, an upper-story 

facade collapsed, killing five people. Several other Marina 

District structures were on the verge of collapse. Eventually, 63 Marina District structures that had not collapsed 

were declared unsafe (red tagged), and many more were 

declared damaged and of questionable safety (yellow 

tagged); the locations of these structures are shown in 

figure 8. 

The earthquake also caused widespread damage to underground facilities and other utilities. Electric power failed, 

and traffic signals went dark at a time when commuters 

were driving home, resulting in heavy, slow traffic in many 

places. The MWSS immediately sustained 123 main and 

service-line breaks within the Marina District, and 35 others outside the district (O'Rourke and others, 1990). The 

result in the Marina District was a total loss of flow to 

customers and to MWSS fire hydrants. The AWSS was undamaged in the Marina District. Elsewhere, however, the 

LOMBARD ST. 

Figure 7.-Marina District, showing locations of collapsed buildings (dark areas). Base map from U.S. Geological Survey (1990). 

H Buildings with Red Tags 0 Buildin s with both Red 

and demolished structures and Ye ? low Tags 

Buildings with Yellow Tags 

Figure 8.-Marina District, showing locations of damaged buildings. From Seekins and others (1990). 
F202 MARINA DISTRICT 

AWSS sustained one main break, one hydrant-branch 

break, and five hydrant-elbow breaks that soon made it ineffective (though not inoperative) in the Marina District. 

Long delays in getting a dial tone led many users to believe 

that the telephones were not working (Benuska, 1990). 

PG&E's low-pressure gas-distribution system sustained numerous breaks in the Marina District; soon after the earthquake, the smell of natural gas pervaded the district. 

In summary, this was the situation confronting SFPD 

and SFFD personnel responding to the Marina District immediately after the earthquake: Traffic was stopped or severely congested at several key points in the city; people 

frightened by the earthquake were filling the streets; 7 

structures had collapsed; 63 more structures were severely 

damaged, some of which threatened to collapse; building 

occupants were trapped, injured, or both; the odor of escaping gas filled the air, raising fears of fire; and, although 

the SFFD did not know it yet, MWSS fire hydrants in the 

Marina District lacked all pressure, and the high-pressure 

AWSS zone serving the Marina District was rapidly draining through breaks south of Market Street. 

SFPD RESPONSE 

Damage to lifelines immediately reduced SFPD telecommunication and data-processing capabilities. The loss of 

commercial power and water, and limited interruption of 

telephone service, combined to force a temporary shutdown of the SFPD's computerized dispatch, and disrupted 

communications with the SFFD and the Paramedics Division. According to the SFPD's earthquake report: 

Mainframe equipment was physically shifted by the force of the earthquake, there was some minor failure of ancillary equipment, and the 

emergency power source failed because the generator's cooling system 

uses water (which was unavailable when the main was broken). . . . When emergency generator power failed, the mainframe went down, and 

so did the Computer Aided Dispatch (CAD) system. The 911 transfer 

line to other municipal units such as the fire department and paramedics 

was not operational, due to Pacific Bell's McCoppin Street switch failure. 

Nonetheless, the emergency did not overwhelm the SFPD's ability to respond. The SFPD estimated that "police 

resources could have dealt successfully with twice the affected area and one additional major perimeter if other 

conditions (e.g., no major aftershocks, lack of looting, few 

reported offenses) remained the same." 

Soon after the earthquake, the SFPD transmitted by local 

broadcast media an order recalling all offduty police officers and canceling all leaves. Many officers returned to 

duty on their own initiative, before the recall order was 

announced. 

SFPD involvement was most extensive in their Northern 

District, which contains the Marina District, where activities focused on crowd and access control. A Marina Command Perimeter was established to control access into the 

more severely damaged part of the Marina District between Marina Boulevard, Chestnut Street, Baker Street, 

and Fillmore Street (fig. 9). The SFPD had some difficulty 

maintaining access control in the days after the earthquake. According to the SFPD's earthquake report: 

Reports of "tourists," tour buses, residents, interested third parties, and 

others attempting to enter affected areas and buildings are numerous. . . . changes in "policy" were made with enough frequency that maintaining 

access control became difficult; and many citizens were angered by the 

resulting delays and miscommunications. The authority of Parking Control Officers was often challenged when they were used to man the Marina perimeter. . . . This began to occur on October 18 and may have been 

largely due to confusion and the use of non-sworn personnel to man barricades. 

SFFD RESPONSE 

FIRST RESPONSE: BUILDING COLLAPSE 

AT 2 CERVANTES BOULEVARD 

The SFFD's first recorded dispatch after the earthquake 

was at 5:06 p.m. P.d.t., according to official SFFD tape 

transcripts. The first response to the Marina District was at 

5: 11 p.m., when the communications center dispatched 

Engine 16 in reply to a report of people trapped at Fillmore Street and Cervantes Boulevard. Engine 16 arrived 

at the site by 5:14 p.m.; its crew reported finding the fourstory structure at Fillmore Street and Cervantes Boulevard 

collapsed, with people trapped inside. The death toll from 

this collapse would turn out to be three, including Diane 

Laufer, 40, Paul Hams, 48, and 3%-month-old Scott Dickinson. Engine 16 also reported discovering a ruptured gas 

main nearby, and they asked the communications center to 

call PG&E, the owner of the main, to send crews to deal 

with the break. The communications center ordered Engine 16 to handle it themselves. Just 3 minutes later, at 

5: 17 p.m., they reported, "Get PG&E . . . gas all over the 

place." 

The Battalion 4 chief on duty, Victor Shannon, heard 

Engine 16's initial report to the communications center regarding the collapsed building. Shannon signaled that he 

was going to respond to the scene, and he ordered that a 

rescue squad be dispatched as well. Rescue Squad 2 arrived 6 minutes later, at 520 p.m. 

A MAJOR GAS LEAK 

At 5:23 p.m., Chief Shannon reported a major gas leak 

at Mallorca Way and Alhambra Street, that police were on 

the scene, and that PG&E was needed to deal with the gas 

leak right away. This leak turned out to be a cracked miter 

joint in a 12-in.-diameter steel feeder main, the only leak 

in the high-pressure steel feeder system in the Marina District;numerous other leaks in the district were in the low- 
PERFORMANCE OF EMERGENCY-RESPONSE SERVICES AFTER THE EARTHQUAKE F203 

pressure cast-iron and steel system. Then, 3 minutes later 

at 5:26 p.m., Shannon requested more trucks at the scene; 

Truck 5 responded. 

COMMUNICATION PROBLEMS 

At 5:28 p.m., Station 16 called the communications center, reporting "the collapse on Beach Street; there's a fire 

now in the collapse at Beach, between Divisadero and 

Broderick." This was the first indication of a fire in the 

Marina District on the SFFD's tape transcripts. 

The communications center, however, did not acknowledge the message. Immense radio traffic was making contact extremely difficult. After analyzing the tape transcripts 

of radio communications between the communications 

center and field units, SFFD analysts later concluded: 

Throughout this time [from 5:04 until 7:30 p.m.], field units and the 

communications center interfered with one another on the radio. Units 

were cut off, and many messages were not acknowledged. Some field 

units failed to wait 1 second for the radio repeaters to open; thus, the first 

parts of their messages were not heard. Radio traffic was so heavy that 

units could not get through to the communications center. When they did, 

they were often not heard. 

FIRE, COLLAPSE, AND TRAPPED VICTIMS 

AT BEACH AND DIVISADERO STREETS 

As Station 16 had reported, two four-story apartment 

buildings had collapsed at Beach and Divisadero Streets 

(fig. 10). The building on the northeast comer had collapsed onto Beach Street, covering an MWSS fire hydrant. 

Of its south facade, only one story remained; two stories 

remained at its rear on the north side (fig. 11). Sherra Cox, 

who was trapped in the rear of this building, would become the object of a difficult and dangerous rescue. Of the 

building on the northwest comer, two stories remained upright, leaning forward over an AWSS fire hydrant on the 

comer (fig. 12). This was the structure where the fire, 

which would eventually consume four buildings, began. 

As this building smoldered, a husband and wife, William 

and Janet Ray, lay trapped in a lower floor. 

At about 5:30 p.m., Chief Shannon ordered Engine 38 to 

Cervantes Boulevard and Fillmore Street to assist with the 

rescue. He then requested an ambulance and another truck 

company, and he reported that a baby had been found in 

the collapsed building. The communications center dispatched both Truck 9 and Engine 41 to the scene. 

m = vetucle ana redesman Access 

Figure 9.-Western part of the Marina District, showing location of SFPD North District's Marina Command 

Perimeter (outline). Map courtesy of SFPD. 
F204 MARINA DISTRICT 

At 5:35 p.m., Engine 10 reported a gas leak in front of At 5:37 p.m., the first unit to report from the fire scene 

2359 Francisco Street, near Broderick Street. The crew of was Truck 16, commanded by Capt. Robert Jabs. AccordEngine 10 spent the next 20 minutes closing gas shutoff ing to his report, Truck 16 had been on the way to the 

valves on Francisco Street while the fire three blocks to building collapse at Fillmore Street and Cervantes Boulethe north smoldered and grew. vard when they were stopped by two offduty police offiFigure 10.-Two collapsed apartment buildings at Beach and Divisadero Streets. Building in foreground is 

3701 Divisadero, where fire started; building in background is 2090 Beach Street, where Sherra Cox was 

trapped. Photograph taken at about 5:20 p.m. P.d.t. October 17, 1989, from Beach Street; view northeastward. 

Figure 11 .-Collapsed building at 2090 Beach Street, after fire was much advanced. Note firefighter directing 

water onto exposed side of building. Photograph by S.P. Harris, taken at about 7:00 p.m. P.d.t. October 17, 

1989. 
PERFORMANCE OF EMERGENCY-RESPONSE SERVICES AFTER THE EARTHQUAKE F205 

cers and told that buildings had collapsed, trapping people 

inside. Capt. Jabs ordered Truck 16 to Divisadero and 

Beach Streets, where they found the collapsed buildings. 

He radioed the communications center of Truck 16's location and of the situation: "We're at Divisadero and [garbled]. We've got 10 or 12 buildings collapsed. There's one 

starting on fire. We've got people trapped. We're going to 

need an engine company." The SFFD's tape transcripts indicate that the communications center mistook Truck 16 

for Engine 16 and ordered Truck 10 to respond to the fire 

scene to assist Engine 16. As late as 5:47 p.m., the communications center believed that Engine 16 was at the fire. 

RESCUE AT 3701 DIVISADERO STREET 

Capt. Jabs could see some of the trapped occupants of the 

northeast comer building at 2090 Beach Street. Civilians 

had been first on the scene and heard voices coming from 

inside this building. Because both comer buildings were in 

danger of further collapse, Capt. Jabs split his company of 

five and attempted both rescues. He sent firefighters 

Howard Cross and Wayne Martin into the northeast corner 

building, while he and the two remaining firefighters, John 

Reed and Thomas Bailon, began to search the burning 

building. Reed and Bailon went inside, while Capt. Jabs, 

aided by several civilians, tried to reach the trapped occupants from the side of the building, but they found the task 

impossible. Meanwhile, Reed and Bailon used axes to cut 

open the floor, and found the two trapped occupants, Janet 

Ray and her husband, William Ray. Capt. Jabs recorded, 

"They were trapped beneath debris from the collapsed 

building. I entered the building with four or five civilians to 

begin extraction." The building was on fire. 

An explosion shook the building, and Capt. Jabs ordered 

the civilians out. He later wrote: 

Smoke was now starting to fill the floor ... and I could see flames 

coming from the front of the building. We could not free the trapped 

victims from the debris, so I had power saws and jacks brought into the 

building. We were racing against time, as the fire was spreading rapidly, 

and the only defense we had was a lV2-inch hose line working under 

reduced pressure. Voices from outside the building called, saying, "The 

building is going to collapse!" I looked out the window and saw that the 

top floor of the building was fully involved with fire. At this point, we 

chose to continue rescue attempts. Heat and smoke drove us from the 

building, but the male victim had crawled out through the hole we cut in 

the floor. Myself and a male civilian carried the victim across the partially collapsed roof to safety and awaited an ambulance. 

Janet Ray, 28, perished. 

PG&E ARRIVES 

By 552 p.m., two PG&E workers had arrived at Alhambra Street and Mallorca Way, determined that the gas leak 

was in the high-pressure system, and had Chief Shannon 

radio the communications center to ask for an additional 

PG&E crew. 

Figure 12.-Collapsed building at 3701 Divisadero shortly after the earthquake. SFFD units had not yet 

arrived. Note dust or smoke from incipient fire at right. Photograph taken at about 520 p.m. October 17, 1989, 

from intersection of Beach and Divisadero Streets; view northwestward. 
F206 MARINA DISTRICT 

ENGINE 41 ARRIVES AT THE FIRE 

Firefighters Reed and Bailon were still attempting to cut 

through the floor of 3701 Divisadero Street when the first 

engine to report from the fire, Engine 41, arrived at 552 

p.m. It had been ordered to report to Cervantes Boulevard 

and Fillmore Street to assist there, but when it arrived, a 

column of smoke was visible over the rooftops, and so 

Chief Shannon ordered Engine 41 to continue on to the 

fire. According to a report by Lt. Peter Cornyn of Engine 

41, when Engine 41 reached Beach and Divisadero 

Streets, the fire was still small. Firefighters Baker and 

Fitzpatrick hooked up to the AWSS hydrant immediately 

in front of the burning building, leading a line from the 

hydrant to Engine 41. The engine was positioned on 

Beach Street to utilize its deck gun. Three large lines were 

led from the engine: one to the west end of the building, a 

second to the middle, and a third to Divisadero Street. 

Firefighters manned and charged the lines, but they found 

that the system pressure was inadequate to supply all 

three. According to Lt. Cornyn's report: 

Two large lines were left charged, but the hose stream didn't reach the 

fire. The fire was starting to escalate. Both ready lines were lead to the 

fire and charged, but there wasn't enough pressure to slow the fire down. 

At this point, Engine 41 was moved to Divisadero Street to escape the 

heat from the escalating fire. 

Engine 41 withdrew to Divisadero Street, ripping the 

hose still connected to the hydrant in front of the burning 

building. While Engine 41 was still attacking the fire from 

Beach Street, Engine 2 from the Presidio Fire Department 

(PFD) arrived by way of Marina Boulevard. They attempted to draw water from an MWSS hydrant on the north 

side of the building, but they found the hydrant dry. They 

positioned their apparatus on Divisadero Street to the 

north of the burning building and, using water from their 

tank, provided protection for Capt. Jabs and the firefighters in 3701 Divisadero Street until the rescuers were 

forced from the building. When its water tank was empty, 

PFD Engine 2 was repositioned on Jefferson Street. 

At 555 p.m., the communications center ordered Engine 

14 to respond to Beach and Divisadero Streets, but then 

reversed the order, saying that a unit would be called from 

the PFD. 

At 556 p.m., Engine 10 reported discovering another 

gas leak at 2240 Francisco Street. They asked whether 

they should ignore it and respond to the fire, which was 

only three blocks away. The communications center misunderstood this signal and believed that Engine 10 was 

going to the fire. Radio communication was confused; 3 

minutes later, Engine 10 reported that they were available. 

At about 5:55 p.m., Chief Shannon arrived at the fire 

and found the building in flames. At 5:58 p.m., he ordered 

Engine 16 to assist with the fire. The communications center reported to Shannon that a PFD unit was coming to the 

fire. 

AWSS WATER PRESSURE LOW 

At 6:01 p.m., Chief Shannon reported that the fire crews 

were putting water on the fire but that system pressure was 

very low. This is the first recorded report that pressure in 

the AWSS system was low in the Marina District. The 

pressure had dropped because of breaks sustained by the 

AWSS in the lower pressure zone south of Market Street. 

At 6:09 p.m., Truck 10 reported that two buildings 

were now on fire and were burning out of control. They 

requested at least one, preferably two, additional engines. 

The communications center dispatched Engine 14 to the 

fire. At the time, Engine 14 was 4 mi away at 25th Avenue and Geary Boulevard. Engine 10 again reported that 

they were at Scott and Alhambra Streets, four blocks 

from the fire, and asked whether they should report to 

the fire. They received no response and eventually informed the communications center that they were responding to the fire. From the previous communication 

with Engine 10, the communications center seemed to 

think that there was a fire at Scott and Alhambra Streets, 

and at 6: 15 p.m. they ordered Engine 3 1 to a fire at that 

intersection. 

AWSS WATER SUPPLY NEVER EXHAUSTED 

At 6:13 p.m., Engine 10 arrived at the fire and drove to 

Beach and Broderick Streets. The crew tested the lowpressure hydrant on the southeast comer and found it 

almost dry. They then hooked up Engine 10 to the AWSS 

hydrant on the northeast comer. The crew led two 3- 

in.-diameter hoses from the hydrant to the building 

immediately west of the fire, 2130 Beach Street. They 

found they had enough water to operate both leads, but 

only at reduced pressures. According to firefighter William 

Koenig of Engine 10, the pressure in the AWSS system 

ranged from 0 to 40 lb/in2 at the engine. Somewhat later, 

Koenig reported: 

Both big lines were receiving 50 to 60 psi, certainly not the best. . . . It was necessary to prime No. 10 on about five to six occasions; however, most of the time water was there. . . . As the water supply fluctuated 

during this period, it was necessary to close down a line or two, depending on the fire situation. 

Radiated heat began to ignite window casings on the 

building directly opposite the fire on Beach Street. In response, Koenig reported, "All lines were shut down to allow Lt. Donham [Truck 51 to have increased pressure to 

enable him to reach the third-floor window to extinguish 

this fire." 

At 6:16 p.m., Engine 21 reported from the Marina District. Chief Shannon ordered Engine 21's crew to attack 

the fire from the west along Beach Street. They tried the 

AWSS hydrant at Beach and Broderick Streets, which was 

supplying lines, but they saw that the lines were limp, as 
PERFORMANCE OF EMERGENCY-RESPONSE SERVICES AFTER THE EARTHQUAKE F207 

if the capacity of the hydrant were being exceeded. Its 

crew moved Engine 21 to the southeast comer of Beach 

and Baker Streets, tested the AWSS hydrant there, and 

found that it appeared to have enough water. They placed 

two Gleeson valves on the hydrant, led two lines to Beach 

and Broderick Streets, and charged the lines. According to 

the report by Capt. Guido Costella of Engine 21, "After 

charging both lines, the water supply went to zero." 

DRAFTING FROM THE LAGOON 

Engine 21 abandoned the AWSS hydrant and fixed on 

another source of water: the lagoon at the Palace of Fine 

Arts, just two blocks to the west (fig. 13). According to 

Capt. Costella's report: 

We broke the lines at Beach and Broderick, connected both lines into 

El4 [Engine 141, and proceeded with E21 back to Baker and Beach. Our 

. . . plan was to draft from Palace of Fine Arts lagoon. All access to the 

lagoon was blocked. We found a car with the owner able to move it, and 

we were able to drive down the pathway. 

Figure 13.-Western part of Marina District, showing location of fire relative to lagoon at the Palace of Fine Arts. Photograph taken October 18, 

1989. 

We used one length of 6-inch suction [a rigid hose that does not collapse under vacuum from the engine's pump] to draft. We were supplying two 3-inch hose leads to El4 at Beach and Broderick and one supply 

lead to E3 that was working on Beach Street. 

"Once the relay was established," recorded firefighter 

Koenig, "water was no problem, with both big lines now 

receiving 100 psi and the big multiversal in operation continuously." The fire by now had advanced westward to the 

three-story building at 2130 Beach Street. Before long, according to Koenig, "without warning, the second building, 

now 75 percent in flames from east to west, collapsed . . . into the first fire building and out into the street." 

FIREBOAT PHOENIX DISPATCHED 

At 6: 16 p.m., Chief Shannon reported that the AWSS in 

the Marina District was running out of water, and he requested the fireboat Phoenix to respond to the fire. About 

this time, offduty Battalion 4 chief, Greg Abell, arrived in 

the Marina District. Water pressure in the AWSS hydrants 

in the district had been low since the first fire crews had 

arrived, and there was no pressure in the MWSS hydrants. 

In response, Chief Abell called for a PWSS hosetender, 

carrying portable water-supply equipment, to lay an 

aboveground water main supplied with seawater pumped 

from the St. Francis Yacht Club Harbor by the Phoenix. 

The communications center immediately dispatched Engine 22 and Hosetender 22 to the Marina, informing them 

they would lead from the fireboat. At 6: 19 p.m., Chief Abell 

informed the communications center that the fire was five 

alarm. The communications center informed Chief Abell: 

"The fireboat's responding. They don't have a [firefighting] 

crew." This situation was normal. At the time of the earthquake, the fireboat Phoenix was assigned only its officer, Lt. 

Robert Banchero, Pilot Arvid Hanneras, and Engineer Nate 

Hardy. Lt. Banchero, when later questioned on what, in his 

opinion, could be done in the future to improve response, 

replied, "A: Have crew assigned to the fireboat. We couldn't 

wait for a cover co[mpany] the night of the quake." 

Also at 6:19 p.m., Truck 2 reported that it was responding to the Marina District, and Truck 5 left the collapse at 

Fillmore and Cervantes Streets to respond to the fire. 

TWIN PEAKS RESERVOIR HELD IN RESERVE, 

PWSS ARRIVES 

By 6:24 p.m., Engine 21 was asking the communications center about extra water supply to the AWSS. They 

were at the AWSS hydrant at Beach and Baker Streets, 

and were requesting water. The communications center did 

not know whether extra pressure had been cut in from the 

Twin Peaks Reservoir, and they informed Engine 21 that 

the Jones Street Tank had detected a leak. Within a few 

minutes, the communications center informed Chief Shan- 
F208 MARINA DISTRICT 

non that the Twin Peaks Reservoir had not been cut in and 

was being held in reserve. 

About this time, Hosetender 25 arrived at Marina Boulevard and Divisadero Street, having been dispatched by 

telephone. This was the first PWSS equipment to arrive in 

the Marina District; its use would turn out to be critical. 

Normally, a hosetender and its engine travel together; one 

firefighter drives the hosetender, while two firefighters and 

the officer travel in the engine. Hosetender 25, however, 

had been dispatched alone to the Marina District, and carried only the driver. 

By coincidence, Hosetender 25 arrived just as two 

offduty firefighters, Tom Kuhn and Steve Jones, returned 

to duty from their homes in Marin County. On their way 

into the city, the two firefighters had seen the fire and reported directly to the Marina District; they also saw PWSS 

Hosetender 25. Both firefighters Kuhn and Jones were normally assigned to Station 8, which houses another PWSS 

hosetender, No. 8. The two were assigned to assist 

Hosetender 25. 

The now-complete crew of Hosetender 25 began immediately to make the initial 5-in.-diameter hose lead. It ran 

from Marina Boulevard up Divisadero Street to Beach 

Street and included two portable hydrants, with 900 ft of 

5-in.-diameter hose. Hosetender 25 was then positioned on 

the east flank of the fire (fig. 14); from this position, they 

would be able to protect the buildings across, and farther 

north on, Divisadero Street. 

By 6:27 p.m., the Division 2 chief, Assistant Chief Harry Brophy, had arrived in the Marina District, becoming 

the incident commander. He repeated the request for additional PG&E crews: "Send the PG&E out here to the 

area of Cervantes and Fillmore. You've got major gas in 

that area. Major gas leak . . . There's gas all over the 

place . . . You're gonna have a major one if we do not 

get it now." 

By 6:41 p.m., Engine 21 was attempting to draft water 

from the lagoon at the Palace of Fine Arts, but its crew 

was having trouble getting the engine to the water because 

all access was blocked by parked cars. Engines 22 and 31 

had attempted to draft water directly from the bay at the 

foot of Divisadero Street, but because of low tide, they 

were unable to find adequate access to the water over the 

harbor-bank riprap. 

At 6:46 p.m., the second PWSS truck, Hosetender 22, 

arrived at the fire, along with Engine 22. It was ordered to 

lead hose up from Divisadero Street and Marina Boulevard one block south to Jefferson Street, along Jefferson 

Street one block west to Broderick Street, on Broderick 

Street one block south to Beach Street, and down Beach 

Street to the south flank of thehfire. This hose lead was 

3,000 ft long and had three portable hydrants. Chief Brophy had set it out to provide water all around the perimeter of the fire, preparing to make a stand on Jefferson 

Street to the north with aerial ladders and hand lines. 

Hosetender 22 was positioned on Beach Street to open up 

its own monitor on the fire's south flank. 

THE PHOENIX ARRIVES AT THE FIRE 

About the same time as Hosetender 22 began to lay its 

hose, the Phoenix was arriving at the yacht harbor. It had 

trouble getting into position at the foot of Divisadero 

Street because of the outgoing tide. The water was so low 

that the Phoenix was dragging bottom, its screws churning mud. After the Phoenix was in position, the tide continued to drop, grounding the fireboat on the harbor 

bottom. 

Engine 36, which had led hose from the high-pressure 

hydrant at Chestnut and Divisadero Streets, found that 

they had run out of hose half a block from the fire. Chief 

Brophy was still urgently calling for more hose. 

Figure 14.-Northwestern part of Marina District, showing location of 

the St. Francis Yacht Club Harbor. Hosetender 25 was located immediately to right of fire. PWSS hose leads from yacht harbor are visible on 

Divisadero and Broderick Streets. Photograph taken October 18, 1989. 
PERFORMANCE OF EMERGENCY-RESPONSE SERVICES AFTER THE EARTHQUAKE F209 

At 657 p.m., Chief Abell reported that the fireboat had 

been hooked up and was ready to pump water. This was a 

turning point. Chief Brophy recorded, "Upon the arrival of 

the Fireboat . . . we changed from a defensive mode to 

offensive." Despite being aground, the Phoenix was able 

to pump because its intake sea chests were off the bottom 

and still under water. The fireboat's first lines had been put 

into the gated inlet Wye supplying Hosetender 25's 5-in.- 

diameter hose leads. Hosetender 25 had already been set 

up for some 10 minutes before receiving water from the 

Phoenix. The fire's radiant heat burnt the paint on the side 

of the truck but did not force it to withdraw as it waited 

for water. As soon as the Phoenix was hooked up, Chief 

Brophy ordered the line charged. 

Hosetender 25 now had water and immediately opened 

up its high-pressure battery monitor on the fire's east 

flank. The effect was immediate and dramatic. Flowing 

900 gal (3 tons) of water per minute, with 90 lb/in2 of tip 

pressure and a 150-ft horizontal reach, Hosetender 25's 

monitor issued a powerful stream that knocked down the 

tremendous radiant heat threatening the exposure buildings 

on the east side of Divisadero Street. The fire in the buildings burning to the north began to darken. 

THREAT OF A CONFLAGRATION ENDED 

At 7:00 p.m., Hosetender 8 was the last of the PWSS to 

arrive, 3 minutes after Hosetender 25 opened its monitor 

on the fire. Chief Brophy ordered it to make a lead from 

the fireboat, up Marina Boulevard to Broderick Street, 

south to Jefferson Street, and then east to Divisadero 

Street. This route provided an additional portable water 

main on the north flank, with three more portable hydrants 

and 2,400 ft of 5-in.-diameter hose supplying pumpers and 

aerial trucks on this side of the fire. 

At 7:17 p.m., Chief Shannon reported that headway was 

being made against the fire. Then, 7 minutes later, a second aboveground main from the fireboat was ready to be 

charged. The fire was still out of control by 7:29 p.m., 

when the transcript ends. Half a block was still ablaze, 

but Chief Shannon was by then confident that the fire 

would go out, recording, "The threat of a big conflagration is over." About 9:30 p.m., the fire was brought under 

control. 

RESCUE OF SHERRA COX 

Even while the Phoenix was still maneuvering into the 

yacht harbor, firefighter Gerald Shannon of Truck 9, Capt. 

Robert Boudoures of Truck 10, and firefighter Jerome Polizzi of Truck 2 had been working for some time on the 

difficult rescue of Sherra Cox. She was trapped in a lower 

floor of the collapsed four-story building at 2090 Beach 

Street, on the northeast comer of Divisadero and Beach 

Streets, directly across Divisadero Street from the fire. The 

heat of the fire was causing the buildings facing it to 

smoke, and igniting curtains inside their windows. The 

building containing Shannon, Boudoures, and Cox caught 

fire several times during the rescue; each time, the firefighters outside extinguished the flames. The heat was intense, but Shannon did not retreat; he had promised Cox 

that he would not leave until he brought her out. "After I 

saw her," he stated, "I just couldn't leave.'' 

The rescue of Sherra Cox took 2 hours. Relief from the 

heat came when Hosetender 25's monitor opened up; all 

the crew of Truck 9 could feel the cooling effect of the 

water being put on the fire. Cox was pulled out on a backboard and taken to San Francisco General Hospital (see 

fig. 1). She later underwent surgery for a fractured pelvis 

(New York Times, 1989). 

Relief began to come for the initial responders late into 

the night. Engine 41 was relieved around 11:30 p.m., and 

Engine 10 around midnight. Firefighters continued mopping-up operations for several days (fig. 15). The fire damaged seven structures, destroying four buildings containing 

33 apartments and flats (Sanborn Map Co., 1988): 3701 

Divisadero (2 1 apartments), 21 30 Beach (1 2 apartments), 

3717-19 Divisadero (2 flats), and 3723-25 Divisadero (2 

flats). SFFD estimates place the losses from this fire at 

$7.4 million (fig. 16). 

SIGHTSEERS AND VOLUNTEERS 

Civilians had been the first on the scene at 3701 Divisadero Street, and they remained long into the battle with 

the fire, some helping, some hindering. By 6:30 p.m., 

sightseers were becoming a problem, and Chief Abell instructed the communications center to notify the media to 

ask people to stay off the highways. Chief Brophy was 

becoming concerned about civilians as well; in a fragmented transmission recorded on the tape transcripts he 

said: ". . . people off to Marina Greens and Chestnut to the 

other. We have major, major damage. Buildings down everywhere. Gas leaks everywhere. Police Department seal 

off the area. Get civilians out." 

At 6:33 a.m., the fire was still out of control (fig. 17), 

and the police were having trouble evacuating civilians. At 

6:35 p.m., Chief Brophy radioed the communications center. Again, the transmission is fragmented, but its urgency 

is apparent: "The situation down here in the Marina is 

devastating. We've 20 or 30 buildings here off their foundations . . . this is a national . . . police cannot handle the 

sit. . . ." 

EMERGENT VOLUNTEERS 

At 6:40 p.m., Chief Brophy requested all available 

hosetenders to the scene: 
F210 MARINA DISTRICT 

Get me all the hosetenders with the 5-inch hose that you can afford. Indeed, there were plenty of volunteers (fig. 18). An 

Have them report in on Jefferson right where the yacht harbor is down offduty police officer at home in his apartment on Divisathere . . . Divisadero. We're going to have to take water from the bay. . . . We have three blocks that are going to be involved. We'll have to give dero Street near Beach Street felt the earthquake, took his 

awav some houses to make a S~OD. but we need the hose. We have the daughter out Of the went back inside to get his *, 

manpower to pull it; we've got a lot of volunteers, but get it here. shield, and emerged again to take control of the area. CivilFigure 15.-Mopping-up operations on fire. Photograph taken October 18, 1989, from southeast comer of 

Beach and Divisadero Streets. 

Figure 16.-Northwestern part of Marina District, showing area near Beach and Divisadero Streets. Fire 

destroyed comer building, another immediately to west, and two more immediately to north. 
PERFORMANCE OF EMERGENCY-RESPONSE SERVICES AFTER THE EARTHQUAKE F211 

ians in the Marina District took it upon themselves to go unteers helped lead hose to the fire from the AWSS hydrant 

from house to house, shutting off gas. Engine 41, while at Divisadero and Bay Streets, two blocks south; volunteers 

setting up at Divisadero and Beach Streets, was assisted by then manned the hoses (fig. 19). Lt. Peter Cornyn, in his 

civilian men and women, offduty police officers, and retired report to Chief Postel, wrote of ". . . [Tlhirty civilians, 

firefighter Bill Koehler, formerly of Engine 41. These vol- whose names I did not get, . . . manned lines attempting to 

Figure 17.-Fire in the Marina District. Photograph by Martin Klimek, Marin Independent Journal, taken 

shortly after sunset October 17, 1989; view southeastward. 

Figure 18.-Volunteers assisted SFFD at fire. Note firefighter at right. Photograph by C.R. Scawthorn. 
F212 MARINA DISTRICT 

stop the Marina fire. Both men and women manned the lines 

with total disregard to their own safety and well-being." 

Engine 36 employed volunteers relaying messages about 

charging the hoses, and keeping people out of the way. The 

crew of Engine 10, while closing street gas valves on Francisco Street, was assisted by civilians who formed a human 

barricade to close the street to all traffic. Perhaps most 

striking were the civilians who assisted Capt. Robert Jabs 

and firefighters Bailon and Reed of Truck 16 as they tried 

to rescue the two trapped occupants of 3701 Divisa-dero 

Street while the building burned overhead. In his report to 

Chief Postel, Chief Shannon wrote: "The citizens did everything possible to assist. I will not forget the acts or faces of our heroic citizens, but I do not know the names." 

PARAMEDIC DIVISION RESPONSE 

Paramedics responded to three Marina District locations. 

At 2 Cervantes Boulevard and 3701 Divisadero Street, 

Figure 19.Ã‘Civilian helped to lead hoses and then man them at fire. 

Photograph by C.R. Scawthom. 

paramedics treated the injured and examined the dead. In 

addition, they set up an incident command post half a 

block from the fire, with an ambulance and a multicasualty 

unit standing by throughout the night. 

CMED dispatched an ambulance to the Marina District 

shortly after the earthquake. Charles Saunders, medical director of the San Francisco Department of Public Health's 

Paramedic Division, indicated that the initial response occurred within 5 or 6 minutes of the earthquake; a second 

ambulance was dispatched shortly afterward. Firefighters 

had discovered four occupants trapped within the building 

at 2 Cervantes Boulevard by the time paramedics arrived: 

Carol Dickinson, Scott Dickinson, Diane Laufer, and Paul 

Harris. 

Moments before the earthquake, Carol Dickinson waved 

goodbye to her husband Walter as he left for a bicycle ride. 

She returned to apartment 104, 2 Cervantes Boulevard, just 

as the earthquake occurred. Carol tried to escape from the 

building, carrying her 3%-month-old infant Scott in her 

arms, but they were caught when the stairway collapsed. 

She was trapped, and the baby was underneath her. She 

recalled that the baby was breathing at first, but then it 

became difficult for her to breathe, and she realized that the 

baby had stopped breathing. Despite the danger of further 

collapse, firefighters and paramedics successfully extracted 

the mother and child, and an ambulance transported them to 

Pacific Medical Center, with paramedic Eberle in attendance. Paramedic Eberle attempted to revive the baby but 

was unsuccessful. Scott Dickinson was pronounced dead on 

arrival at Pacific Medical Center at 8:15 p.m. Carol Dickinson survived (Medical Examiner1 Coroner's Register 1303). 

The other two victims, Diane Laufer and Paul Harris, 

were pronounced dead on arrival by a San Francisco Medical Examiner investigative team. The building had been 

pronounced structurally unsound, and the dead occupants 

were trapped beneath the debris; they were not extracted 

until the next day, after the building had been carefully 

disassembled. They were found lying amongst the rubble, 

partly pinned beneath a door jamb; Paul Harris appeared 

to be cradling Diane Laufer in his arms (Medical Examinerlcoroner's Registers 1306, 1307). 

Paramedics were dispatched to treat William Ray when 

he was extracted from 3701 Divisadero Street, and, later, 

to treat Sherra Cox was she was removed from 2090 

Beach Street. Both were taken to the hospital. 

Throughout the night, paramedics manned the multicasualty unit and an ambulance standing by at the incident 

command post, half a block from the fire. The multicasualty unit was equipped with medical supplies, basic medical equipment, and communications equipment. 

Injured Marina District residents generally were unable 

to communicate with the Paramedic Division because long 

delays getting a dial tone made it appear that telephone 

service within the district was inoperative. The Paramedic 

Division found that most earthquake victims near the dis- 
PERFORMANCE OF EMERGENCY-RESPONSE SERVICES AFTER THE EARTHQUAKE F213 

trict self-reported to nearby Letterman Army Medical Center and St. Francis Hospital. Of 70 who arrived at these 

two hospitals, only about 12 were brought by Emergency 

Medical Services. 

CONCLUDING REMARKS 

When examining the events related here, it is worthwhile 

contrasting San Francisco's experience in the 1989 earthquake with those in the 1906 earthquake. This section 

briefly summarizes observations and lessons learned, based 

on police, fire, and paramedic response in the Marina District, with reference to the record of the 1906 earthquake. 

1. The city's fireboat Phoenix and the use of the PWSS 

proved crucial in stopping the blaze at 3701 Divisadero 

Street. The fire had burned out of control until PWSS 

equipment was deployed and supplied with water by the 

vast pumping capacity of the Phoenix. Without the fireboat 

Phoenix or the PWSS, the damage in the Marina District 

probably would have been substantially greater. Some firefighters also credit the limited damage to the unusual lack 

of wind. Estimates vary on the extent to which the fire 

might have burned, had winds been more typical of an 

October evening in the Marina District. One firefighter, in 

responding to a questionnaire by San Francisco Fire Fighters Local 798, noted, "Marina not in ashes because of (1) 

no wind, (2) fire boat, (3) portable hydrants and hose" 

(San Francisco Fire Fighter's Local 798, 1990). 

In 1906, saltwater from the bay was the only source of 

water available to firefighters protecting buildings near the 

Embarcadero waterfront, the South Beach waterfront, and 

the channel. Pumping the saltwater were several military 

and private vessels, including the U.S. Navy destroyer 

U.S.S. Preble, the fireboat Leslie, the tugboats Active and 

Fortune, the U.S. Navy tugboat Sotoyomo, the two California fireboats Governor Irwin and Governor Markham, 

the Revenue cutter Golden Gate, and others (Hansen and 

Condon, 1989). 

2. Planning and training in the use of the PWSS and the 

Phoenix worked. The strategies used with the PWSS had 

been carefully developed by SFFD staff, in anticipation of 

major events. When the time came to employ them, the 

plans proved well thought out and effective, and the time 

training PWSS crews proved well spent. We note that just 

3 weeks before the earthquake, Chief Brophy had conducted a major training exercise at San Francisco's Pier 32, 

using the fireboat Phoenix to supply the PWSS. Firefighters interviewed after the earthquake remarked on how the 

use of the PWSS in the actual fire situation went just like 

the drill. This lesson demonstrates the effectiveness of 

thorough training and of tactics using high-pressure battery monitors to control large fires. 

In 1906, SFFD leadership was centralized in Chief Dennis Sullivan. When he was incapacitated in the earthquake, 

the absence of institutionalized preparedness planning is 

generally thought to have contributed to the inability of 

SFFD to contain the fire. 

3. Inadequate communications capacity and procedures 

aggravated the SFFD's difficulty in identifying the number 

and location of fires, advising incident commanders of inservice-unit location and status, and employing the AWSS. 

From the start of the emergency response, radio traffic between SFFD units and the communications center far exceeded the capacity of allotted channels. Additional radio 

channels would likely have made a substantial difference 

in the SFFD's response in the Marina District. 

As congested as radio traffic was in 1989, it represented 

a vast improvement over conditions in 1906, when the 

Central Fire Alarm Station at 15 Brenham Place was badly 

damaged, making the city's fire-alarm system inoperative 

(Hansen and Condon, 1989). 

4. Significant numbers of volunteers emerged to assist in 

the Marina District response. This pattern of emergent volunteers assisting emergency-service personnel during crises has been observed in past earthquakes as well. After 

the September 19, 1985, Mexico City earthquake, volunteer rescue teams worked around the clock searching for 

trapped victims of building collapse (EQE Engineering, 

1986). In the May 2, 1983, Coalinga, Calif., earthquake, 

citizen volunteers manned firefighting hose lines and shut 

off their own and neighbors' gas (Scawthorn and Donelan, 

1984). Lechat (1989) reported, "In Japan, it was observed 

that within half an hour after an earthquake (Niigata, 

1964), 75 percent of the non-affected survivors were engaged in some kind of rescue activity." Emergency-response planning for fire and search and rescue should 

consider how best to employ emergent response. At a minimum, substantial supplies of clothing and equipment for 

volunteers should be cached or prearranged. 

5. The value of preevent planning and standard operating procedures (SOP'S) was demonstrated by the success 

of the PWSS and by the short-term ineffectiveness of the 

AWSS. Faced with the loss of water pressure, the SFFD 

had three options to increase AWSS water supply to the 

Marina District: 

(a) Start the pumps at Pump Stations 1 and 2. Each station has a pumping capacity of 10,000 gallmin at 300- 

lb/in2 pressure. Pump Station 2 alone could supply enough 

water flow and pressure for the fire (M. Khater, oral commun., 1991). The extent of damage to the AWSS pipe network, and potential flooding and washout, made this 

option problematic in the first hours after the earthquake. 

(b) Order the fireboat Phoenix to the fireboat manifold at 

Fort Mason's Pier 1. Once attached to the fireboat manifold, the Phoenix could pump 9,600 gallmin at 150-lb/in2 

pressure directly into AWSS mains near the fire, thereby 

supplying similar flows to those from Pump Station 2. We 

note that the fireboat was dispatched directly to the Marina 

District, rather than to a manifold. In hindsight, this deci- 
F214 MARINA DISTRICT 

sion can be seen as proper because AWSS damage was 

unknown at the time and the fire's proximity to the shoreline permitted the fireboat to supply the PWSS directly. 

(c) Cut the Twin Peaks Reservoir into the lower pressure 

zone. This option would have briefly prevented the Jones 

Street Tank from draining, but it would also have resulted 

in drawing down the Twin Peaks Reservoir within several 

hours, leaving the upper pressure zone unprotected by the 

AWSS. 

In the end, no decision was made. Lacking SOP'S, operators at the Jones Street Tank waited for instructions that 

they never received, leading to a temporary loss of water 

within the AWSS' lower pressure zone. 

6. The SFFD and the local geotechnical- and earthquake-engineering communities had long been aware of 

the potential for liquefaction in the Marina District. The 

earthquake vulnerability of structures on made ground had 

been evident as early as 1868, after the Hayward earthquake of that year and the San Francisco earthquake of 

1865. Nonetheless, the old City Hall, completed in 1896, 

was built on filled land and subsequently destroyed in the 

1906 earthquake (Hansen and Condon, 1989). 

Despite this past experience, the area's seismic vulnerability was not well known by residents in 1989, nor was it 

reflected in the city's emergency planning for earthquakes. 

Since the earthquake, the city of San Francisco has sponsored studies of several areas where a high potential for 

liquefaction is known to exist, including the Marina District (Harding Lawson Associates and others, 199la, b). 

This type of study represents a bridge of knowledge between the engineering community and city officials. The 

conclusions of these studies should be integrated into future emergency plans. 

7. Immediately after the earthquake, although the building collapse at 2 Cervantes Boulevard was known, surrounding areas in the Marina District were not 

reconnoitered for similar damage, allowing precious time 

for the fire to grow. Indeed, personnel at the SFFD's communications center (the City's EOC) long lacked a clear 

picture of the damage in the Marina District. They did not 

realize the magnitude of the emergency until they saw it 

on television, broadcast nationwide by the blimp that was 

on hand for the World Series. 

After an earthquake, television and radio helicopters 

should be employed immediately for rapid reconnaissance. 

Their reports could be integrated within a disaster-information-management system, to transmit this data rapidly, 

effectively, and without unnecessary repetition to emergency-response authorities at the EOC. With a clear picture of 

the situation, these authorities can maximize scarce resources and respond effectively to the emergency. 

The foregoing observations and lessons can provide the 

basis for improved disaster mitigation. However, some of 

these observations have been made before and not acted 

upon (for example, those regarding construction on made 

ground). Perhaps the most useful lesson is to observe a 

case in which recommendations based on "lessons learned 

were implemented. Before 1906, SFFD officials and insurance underwriters had recognized that the city's water-supply system was inadequate to protect against conflagration. 

A design for the AWSS had been proposed but not implemented until after the 1906 disaster provided the final impetus. The AWSS has served San Francisco well, providing 

copious amounts of water for numerous large fires. 

Earthquake losses were reduced only where responsible 

experts anticipated problems and communicated them effectively to appropriate authorities, who saw to it that solutions were promptly developed, implemented, and 

institutionalized with training and SOP'S. 

ACKNOWLEDGMENTS 

We gratefully appreciate the ongoing assistance and encouragement of Thomas D. O'Rourke of Cornell University, Ithaca, N.Y. Data were provided by Charles Saunders 

(San Francisco Department of Health, Paramedic Division), Ron Kramer (San Francisco Police Department), 

Tom Dickerrnan (San Francisco Water Department), and 

Andrew Nielsen and Steve Van Dyke (San Francisco Fire 

Department). This study was funded by research grants 

from the National Center for Earthquake Engineering Research, State University of New York, Buffalo. 

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