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A POTENTIALLY CATASTROPHIC earthquake inthe heart of the San Francisco Bay area isincreasing likely. Geologic studies along thesouthern Hayward Fault in the East Bay indicatethat this fault has generated 12 major earth-quakes in the last 1900 years, most recently in1868. These earthquakes were powerfulenough to offset the ground surface, indicatingthat they had magnitudes greater than 6.3. Theaverage interval between these earthquakes is160 ± 65 years (one standard deviation uncer-tainties) based on radiocarbon dating of thesoils they disturbed. The last five earthquakesseem to have occurred more frequently,however. They are separated by an averageinterval of only 140 ± 60 years, as JamesLienkaemper of the US Geological Survey(USGS) and others have written in an article tobe published shortly.

This year marks the 140th anniversary of theMagnitude 6.8 earthquake which broke asection of the Hayward Fault from the locationof present-day Fremont to probably just northof Oakland on 21 October 1868. Known until1906 as “the great San Francisco earthquake”for the damage it caused to the major popula-tion centre of the time, the 1868 earthquakeresulted in the strongest shaking the whole BayArea had experienced since its settlement byEuropeans. Unreinforced masonry walls camedown in San Francisco, Oakland and San Jose, areport published by the Carnegie Institutefollowing the 1906 San Francisco earthquakerecounts.

Huge societal exposures to the next 1868 earthquake Along most of its length, the Hayward Faultruns through Alameda County where the citiesof Berkeley, Oakland, Alameda, Hayward and

Fremont lie either on or directly adjacent to thefault’s trace. A repeat of the 1868 earthquaketoday would have enormous consequences. Itwould affect property worth more than $500billion and approximately 5 million people insix surrounding counties. The populationtoday is more than 19 times what it was in 1868.

According to a 2008 report for the USDepartment of Labor’s Bureau of LaborStatistics, the exposure of employers, employ-ees and wages to an earthquake along theHayward Fault ($25 billion in quarterly wages)greatly exceeds those that were at risk toHurricane Katrina ($3 billion to $4.7 billion) in2005. Approximately 87,000 employerssupporting 1.5 million jobs are located in areaswhere very strong shaking is expected.

The report stated that that the industriesmost affected would include health care andsocial assistance, educational services (includ-ing the largest employer in the East Bay,University of California Berkeley with its 20,000employees and 30,000 students), as well asmanufacturing and the retail trade. Oldercommercial districts with vulnerable buildingsare expected to be closed for months.

Severe effects of a repeat of the 1868 earthquake Preliminary estimates by catastrophe modellerRisk Management Solutions (RMS) of total resi-dential and commercial economic losses,including damage to private buildings andcontents, business interruption and additionalliving expenses, due to shaking alone exceed$120 billion for a repeat of an 1868 earth-quake. Damage to infrastructure, the effects offires following the earthquake and post-eventamplification, such as economic demandsurge, claims inflation, repair cost delay infla-

tion and coverage expansion, may substan-tially increase the loss total.

Predicted losses will be concentrated (>95%)in five Bay Area counties: Alameda, Santa Clara,San Francisco, Contra Costa and San Mateo.Alameda and Santa Clara counties account formore than 75% of the forecast insured residen-tial loss and slightly less than 70% of theinsured commercial loss. Few homeowners orbusinesses buy earthquake insurance.Presently more than 90% of residential lossesand around 85-90% of commercial losses willbe uninsured, although loss amplification andpost-event fires can impact this.

The primary drivers of Bay Area economy,white collar jobs and tourism, are likely tosuffer severely. Studies conducted by theAssociation of Bay Area Governments (ABAG)and published in 2003 indicate that land, seaand air transportation networks will all bestrongly disrupted and probably temporarilyshut down. Interstate 580, one of two majoreast-west arteries into the Bay Area, could beoffset horizontally as much as 1.8m (6 feet).Seismically robust bridges and tunnels arecurrently replacing or upgrading major trans-

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A repeat of the 1868 Hayward fault California earthquake todaywould have enormous consequences. Property worth more than$500 billion and approximately 5 million people in six surroundingcounties would suffer badly from such a quake. By Thomas Brocher and other members of the 1868 Hayward Earthquake Alliance

The Hayward Fault:Is It America’sMost Dangerous?

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portation links between Oakland and SanFrancisco, including the Bay Bridge and theBART tunnel beneath the bay. Until thisconstruction is completed several years fromnow, however, it is likely that the more than180,000 daily commuters using these trans-portation links will have to seek overtaxedalternate routes for months.

The Oakland and San Francisco internationalairports and nearly all the region’s port facili-ties are built on landfill over very young andsoft materials strongly susceptible to damageby liquefaction and strong shaking, a scenariostudy on a Magnitude 7.0 earthquake,published in 1996 by the EarthquakeEngineering Research Institute (EERI), found.As a result, the capacity to deliver the goodsneeded to support recovery will be signifi-cantly diminished.

Disruption will not be limited to only majortransportation routes. In 2003, ABAG esti-mated that a repeat of the 1868 earthquakecould result in approximately 1,100 roadclosures, including 900 in Alameda Countyalone. Expected common causes of these shortterm closures are damage to bridge abut-

ments, surface cracking and offset by the faultdisplacement in the quake, land slides in thehills, liquefaction in areas of landfill, andextensive collapse or leaning of major build-ings into roads.

Water delivery to much of the region will beinterrupted. In 2002, the Bay Area EconomicForum reported around $17 billion of poten-tial economic losses due to the rupture of theHetch Hetchy aqueduct, which crosses thesouthern Hayward Fault and provides waterfor more than 2.4 million Bay Area residents.More than half of the losses would be tocommercial and industrial facilities thatdepend on this water.

The forum attributed roughly 30% of theprojected loss to the lack of adequate watersupply to suppress post-quake fires. East Baywater customers may fare better. The East BayMunicipal Utility District conducted majorseismic retrofits and upgrades after the 1989Loma Prieta earthquake. The San FranciscoPublic Utilities Commission, which operatesthe Hetchy Hetchy dam and aqueduct system,is in the process of seismically retrofitting this70 year old water delivery system.

Ominous comparisons The fault that ruptured in the Magnitude 6.9Kobe, Japan, earthquake in 1995 is a closeanalogue to the Hayward Fault. The geographyof Kobe, a port city built along the Nojima Faulton Osaka Bay, is strikingly similar to the EastBay, with a large population living on the plainsbetween the mountains and the shore. TheNojima Fault, like the Hayward Fault, is a strike-slip fault, and it has a similar length.

The 1995 Kobe earthquake caused more than5,000 fatalities and widespread damage tobuildings and infrastructure. Fire was a majorcontributor to the death toll. Ground failure,especially liquefaction, damaged the port facil-ities in Kobe, resulting in a permanent loss ofbusiness as shipping companies permanentlyrelocated to undamaged ports in Japan. Largesegments of Kobe and nearby communitiespreviously populated by low income residentshave not yet been rebuilt.

In general, residences and commercial build-ings built in Japan before 1995 were not asresilient as those constructed in the last 30 to40 years in the San Francisco Bay area, and theKobe area may not have been as prepared for

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San Francisco Bay area

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earthquakes as the Bay Area is today. None-theless, a 1996 ABAG study suggested that arepeat of the 1868 earthquake would result inabout 90,000 uninhabitable units, displacingapproximately 220,000 residents and resultingin 60,000 to 70,000 of them seeking temporarypublic shelter.

Two-thirds of this impact is forecast to occurin Alameda County where 62% of the popula-tion is ethnic or minority, according to the2005 Communities Survey by the US CensusBureau. Census data from 2000 indicates that27% speak a first language other than English,and 11% of the country’s population haveincomes below the poverty line. These residents tend to work and reside in relativelyold buildings predating modern buildingcodes.

Hurricane Katrina demonstrated theprofound impact on the local economy whenlarge numbers of residents are displaced fromtheir homes. In the San Francisco Bay area thosedisplaced residents are also likely to speak amyriad of foreign languages. Dealing with thisdisplacement, as well as the physical damageand disruption, is likely to take years.

Pay now or pay later? According to estimates from USGS, SanFrancisco Bay Area businesses and govern-ments have invested or are committed to investmore than $30 billion in strengthening impor-tant infrastructure since the 1989 Loma Prietaearthquake. Residents have repeatedlysupported bond measures to cover the costs ofretrofitting key lifelines. The CaliforniaDepartment of Transportation (Caltrans) hasinvested at least $10 billion in retrofitting andreplacing toll bridges in the Bay Area, as well asall the elevated sections of state owned roads.

As a result of the 1994 California State SenateBill 1953, hospitals throughout the Bay Areaare being seismically strengthened or replaced,although the deadline for such work has nowbeen postponed until 2030. Since 1989, thePacific Gas & Electric Company has investedover $2 billion to replace old cast iron gas pipeswith flexible plastic pipes in liquefiableregions, and strengthened key elements of itselectrical transmission and distributionnetwork. The BART District is retrofitting itstunnel beneath San Francisco Bay and itselevated tracks. Many cities have replaced orseismically strengthened vulnerable city hallsand emergency response centres.

The relatively low rate of earthquake insur-ance coverage in both the residential andcommercial markets is troubling. In contrast toHurricane Katrina where insured losses werebetween about 33% and 50% of total economiclosses, according to RMS, only about 10% of thetotal projected Hayward Fault earthquakelosses will be covered by insurance.

Major strides have been made since 1989 inimproving the resilience of the San Francisco

Bay area to earthquakes. Still, a large HaywardFault earthquake is likely to be a super catastro-phe that would dramatically change East Baycommunities for decades.

As the 1868 Hayward Earthquake Alliance,we are exploring the extent and ramificationsof such a catastrophe by investigating ques-tions such as: (1) What is the potential forcascading failures of utilities and transporta-tion systems that depend on each other inrecovery? (2) How will the large number ofpredominantly residential-use multi-storybuildings weakened at ground floor by largenumbers of openings for garages or windowsperform? (3) What will be the long term post-earthquake economic climate and will busi-nesses leave the area?

We intend that our results will be directlyapplicable in proactive decision making bycommunity leaders. To help raise awareness ofthese hazards, the 1868 Hayward EarthquakeAlliance, which is a private-public consortium,is planning many activities and events tocommemorate the 140th anniversary (seewww.1868alliance.org) including publicforums, conferences, publications, websites,videos and public service announcements.

The authors are members of the 1868 HaywardEarthquake Alliance. Thomas Brocher, US Geological Survey, Menlo Park,brocher@usgs.gov Keith Knudsen, California Geological Survey,keith_knudsen@urscorp.com Mary Lou Zoback, Risk Management Solutions,marylou.zoback@rms.com Jeanne Perkins, Association of Bay AreaGovernments, jeannep@abag.ca.gov Margaret Hellweg, University of California, Berkeley,peggy@seismo.berkeley.edu William Savage, US Geological Survey, Menlo Park,wusavage@usgs.gov Kathy Bailey, California Governor’s Office ofEmergency Services, kathleen_bailey@oes.ca.gov www.1868alliance.orgReferences: ABAG, Southern Hayward Earthquake – 1,138road closures, 2003,(http://quake.abag.ca.gov/eqtrans/hasm_rslt.html). ABAG, Shaken Awake! Report Summary, 1996(http://www.abag.ca.gov/bayarea/eqmaps/shelpop/summary.html). Bay Area Economic Forum, 2002, Hetch Hetchy Water andthe Bay Area Economy, located on line at:http://www.bayeconfor.org/pdf/hetchhetchyfinal2.pdf Earthquake Engineering Research Institute, Scenario for amagnitude 7.0 earthquake on the Hayward Fault, HF-96,1996 (http://haywardfault.eeri.org/index.php). Holden, R. J., D. Bahls, and C. Real, Estimating economiclosses in the Bay Area from a magnitude-.69 earthquake,Bureau of Labor Statistics, Monthly Labor Review, Vol. 130,No. 2, Jan. 10, 2008(http://www.bls.gov/opub/mlr/2007/12/art2abs.htm). Lawson Report on the California Earthquake of April 18,1906, Carnegie Institution of Washington, Pub. 87, Vol. 1,1908. Lienkaemper, J., P. Williams, and T. P. Guilderson, Newevidence for 12 Southern Hayward Fault earthquakes inpast 1900 years, Seismological Res. Lett., vol. 79, in press,[abstract], 2008.

The fault that rupturedin the Magnitude 6.9 Kobe, Japan,earthquake in 1995 is a close analogue to theHayward Fault

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Kobe, Japan, earthquake in 1995

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WEBLINKS visit: www.cat-risk.comInsurers to pay $6.5bn in 2007 catastrophe claims

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