Understanding Earthquake Hazards in the San Francisco Bay Region The Hayward Fault—Is It Due for a Repeat of the Powerful 1868 Earthquake?

n October 21, 1868, a magnitude 6.8 Oearthquake struck the San Fran- cisco Bay area. Although the region was sparsely populated, the quake on the Hay- ward Fault was one of the most destruc- tive in California’s history. U.S. Geological Survey (USGS) studies show that similar Hayward Fault quakes have repeatedly jolted the region in the past and that the Strong shaking fault may be ready to produce another during the 1868 magnitude 6.8 to 7.0 earthquake. Such an Hayward Fault earthquake could unexpectedly change earthquake caused people’s lives and impact the Bay Area’s the second story of the Alameda County infrastructure and economy, but updated Courthouse in San building codes and retrofits, as well as Leandro to collapse (photo courtesy of the Bancroft Library, University of California). The inset planning, community training, and pre- photo shows the courthouse before the quake (photo courtesy of San Leandro Public Library). paredness, will help reduce the effects of The 1868 earthquake devastated several East Bay towns and caused widespread damage in a future Hayward Fault earthquake. the San Francisco Bay region.

In the early morning of October 21, serious damage in Napa and Hollister. Numer- Santa RODGERS Rosa CREEK 80 1868, seismic waves from a power- ous witnesses reported seeing the ground AREA N OF MAP ful earthquake raced through the fog- move in waves. Shaking was felt as far away Napa shrouded San Francisco Bay area. as Nevada, and aftershocks rattled the Bay CALIF Frightened people ran out of their homes, Area for weeks. Even though the region was San Francisco Oakland and cattle and even fire-engine horses only sparsely populated at the time, the 1868 San Leandro panicked and bolted. Strong shaking quake killed about 30 people and caused great HAARDHayward lasted more than 40 seconds, devastating property damage. It still ranks as one of the Fremont S A 1868 several East Bay towns. Brick build- most destructive earthquakes in California’s N

G San Jose R CAAERAS ings, walls, and chimneys were also history, but this is not the end of the story. The E G O R SAN ANDREAS I shaken down in Oakland, San Francisco, Hayward Fault will rupture violently again, O

Santa Rosa, and San Jose, and there was and perhaps soon. Major faults Hollister 0 20 MILES 101

Major earthquake faults in the San Francisco N Stadium Bay region. The section of the Hayward Fault Gulch that produced the 1868 Hayward earthquake is highlighted in yellow. Dot size indicates the present 0 500 1,000 FEET Hamilton relative population sizes of cities. 0 100 200 300 METERS

A filtered vertical laser image, taken using a technique called light detection and ranging (LIDAR), of part of the Hayward Fault (red lines) in the City of Berkeley. The fault passes through the University of California Berkeley football stadium (left), and past earthquake movements have significantly offset Hamilton Gulch (center). Arrows show relative movement on the fault.

U.S. Department of the Interior Fact Sheet 2018–3052, August 2018 U.S. Geological Survey Supersedes Fact Sheet 2008–3019 The Hayward Fault is Creeping The Hayward Fault is a near-vertical surface that allows two huge blocks of bedrock to move past each other in the eastern San Francisco Bay region. It is one of a number of “creeping” earthquake faults in the region, meaning the two sides of the fault are constantly moving past each other at a slow rate. Ample evidence for the creep of the fault is provided by roads, curbs, and buildings that are being progressively offset. U.S. Geological Survey and other scientists have shown that the rate of movement is about 1/5 inch (5 millimeters) per year. Creep gener- ally appears to be limited to the topmost 3 miles (5 km) of a fault plane, and below that depth, the fault is locked and building up stress. Creep and small earthquakes account for only about one-third of the long-term (thousands of years) movement on Creep (slow, steady movement) on the the Hayward Fault, and the remaining two-thirds must be released in large earth- Hayward Fault has offset this curb in the quakes like the 1868 event. city of Hayward.

Scientists at the University of Interferometric satellite California, Berkeley, are using aperture radar, or InSAR, a technique called interfero- N uses repeated passes metric satellite aperture radar by satellites to record (InSAR), which uses repeat the change in distance satellite radar surveys of the between the satellite and Earth’s surface to monitor HAARD FAUT recognizable points on the creep along the Hayward ground (dots). This InSAR image of part of the East Fault. Comparing radar returns Fremont Bay clearly shows creep from the same points on the on the Hayward Fault. In ground over time reveals general, warm colors mean how rapidly the points are the points are moving to moving. This technique allows the southeast (closer to the scientists to determine which satellite), and cool colors parts of a fault are creeping mean the points are moving and at what rates, and which to the northwest (farther parts are locked all the way away). The color scale indicates the rate of this to the surface and thus may 0 1 2 3 MILES –10 0 10 movement in millimeters be capable of producing even per year (1 millimeter = 0 1 2 3 KILOMETERS stronger quakes. Millimeters per year 0.04 inch).

The Earthquake of 1868 people were killed and property losses mission buildings were heavily damaged. were significant. Many brick walls, Oakland, a town of about 12,000 and The 1868 earthquake on the Hayward cornices, and other heavy architectural mainly wood-frame buildings, was much Fault capped a decade-long sequence of elements of buildings in the city fell, less heavily damaged than San Leandro seven increasingly strong quakes in the and the U.S. Custom House and several and Hayward. San Jose, a town of about Bay Area. Ground cracking caused by this other structures built on land reclaimed 9,000 that lies several miles south and earthquake was traced for 20 miles along from the former Yerba Buena Cove west of the fault trace, had few wrecked the Hayward Fault, from Warm Springs (today’s Financial District) sustained buildings but many fallen chimneys. in Fremont north to San Leandro. Histori- severe damage. However, as in 1906, cal land-survey data suggest that the fault well-constructed buildings on firm ground Understanding the 1868 Quake broke as far north as Berkeley, with an sustained much less damage. average horizontal offset of about 6 feet Towns in the East Bay suffered the Because seismographs had not yet (2 meters). most severe damage. Almost every build- been invented, there are no recordings Shaking from the 1868 quake was the ing in Hayward, then a town with about of the 1868 earthquake. Much of what strongest that the new towns and growing 500 residents, was wrecked or severely we know about the 1868 quake is docu- cities of the Bay Area had ever experi- damaged—few places have paid so dearly mented in a chapter of an important report enced. Until it was eclipsed by the great to have a fault named after them. At San on the 1906 San Francisco earthquake, 1906 earthquake, the 1868 earthquake Leandro, with a population of about 400, which was published in 1908. The chapter was known as the “great San Francisco the second floor of the Alameda County reviewed the descriptions of surface fault- quake.” The area of strongest shaking Courthouse collapsed, and many other ing, collected damage and felt reports, and covered about 1,000 square miles. In San buildings were destroyed. At Mission interviewed survivors of the earthquake. Francisco, the largest city on the west San Jose, in southern Fremont, the USGS and other scientists have used coast with a population of 150,000, five adobe church built in 1809 and other the 1908 report, as well as historical Similarity to the 1995 Kobe Earthquake

Studies of past earthquakes allow scientists to fore- Tokushima N cast the effects of future quakes. A quake similar to allejo the anticipated next large Hayward Fault earthquake N may be the magnitude 6.9 earthquake that struck Richmond Concord Kobe, Japan, in 1995. The geography of Kobe, a port 1868 Rupture city built along the Nojima Fault on Osaka Bay, is strik- Sumoto Oakland ingly similar to that of the East Bay, and the Nojima San Francisco 1995 Rupture and the Hayward Faults have similar lengths and San Akashi types of movement. The 1995 Kobe quake and subse- Francisco quent fires caused more than 5,000 deaths. Shaking Bay Hayward akayama Osaka Bay

and ground failures, including liquefaction (in which Kobe Fremont shaken sandy soils behave like a liquid and cannot support the weight of structures), devastated resi- dences and infrastructure. Damage to the port facili- 0 10 20 MILES 0 10 20 MILES San ose ties in Kobe resulted in a permanent loss of business, 0 10 20 KILOMETERS 0 10 20 KILOMETERS Osaka because some shipping companies relocated to other 15 miles above undamaged ports in Japan. Many lower income areas The urban geographic settings of the Nojima Fault of Kobe, Japan, and the of Kobe were not rebuilt for more than a decade. Hayward Fault, California, are very similar, as were the lengths of rupture in their most recent strong earthquakes. The 1995 Kobe earthquake caused more than Although construction codes and practices for 5,000 deaths and widespread devastation (satellite images from Google Earth). residential buildings in Japan were not as stringent in 1995 as those now in use, and Kobe was not as likely that a repeat of the 1868 Hayward earthquake will also produce prepared for earthquakes as the Bay Area is now, it is significant loss of life and high levels of damage. newspaper accounts, photographs, pioneer estimates with current knowledge of San Leandro, and weaker but damaging diaries, and letters, to understand the earthquake effects and geology allows in Oakland, San Francisco, and San Jose. shaking effects and gauge the size of the researchers to create a “ShakeMap” that Scientists estimate that the magnitude of 1868 earthquake. To estimate the shaking depicts the inferred intensity of shaking the 1868 quake was 6.8. Comparing the intensity, it is necessary to consider the throughout the region in 1868 and can ShakeMaps from the 1868 Hayward and construction of the damaged buildings, also be used to predict damage to modern the 1989 (magnitude 6.9) Loma Prieta that is, whether they were adobe, brick, buildings. The map shows that shaking earthquakes shows that a repeat of the or wood. Combining these intensity was strongest in Hayward, Fremont, and 1868 quake would produce much higher levels of shaking and damage in the East 1868 N 1989 N Bay than the 1989 quake. Benicia Benicia Impact of the 1868 Hayward Quake Antioch Antioch on Building Practice alnut alnut Berkeley Creek Berkeley Creek After the 1868 quake, and a previous San Francisco Oakland San Francisco Oakland one in 1865, damaged San Francisco, San eandro San eandro ivermore ivermore engineers worked to strengthen buildings Hayward MMI Damage Hayward throughout the Bay Area. They retrofit San X+ ery heavy San Fremont Fremont masonry buildings with iron tie-rods and Pacific Ocean Mateo Pacific Ocean Mateo IX Heavy anchors between floors and walls, and Palo Palo Moderate Alto VIII Alto San they designed and implemented systems San Heavy ose ose to make new buildings more resistant to Moderate VII shaking. Innovations included a stronger VI ight course of brick-laying, incorporating Epicenter of V ery light 1989 quake iron binders into brick walls, and interior iron framing. But the most significant 0 10 20 MILES Santa 0 10 20 MILES Cruz Santa improvement in shaking resistance was Cruz 0 10 20 KILOMETERS 0 10 20 KILOMETERS the advent of steel-frame buildings in 1885. These measures combined to ensure A ShakeMap showing the inferred intensity of ground shaking in the 1868 earthquake (measured that buildings built in San Francisco as MMI, or Modified Mercalli Intensity), compared to a ShakeMap for the 1989 magnitude 6.9 between 1868 and 1906 survived the Loma Prieta earthquake. Red lines are major earthquake faults; black line shows the portion of powerful shaking of the 1906 San Fran- the Hayward Fault that ruptured in 1868; diamonds show locations of damage reports (1868) and cisco quake, with the exception of the San seismic recordings (1989). Francisco City Hall. Interval 183 158 153 97 12 150 years and (years) 113 1317 175 1629 1725 1868 counting More Information: uakes Magnitude 6.8 October 21, 1868, Magna Black Columbus California 1906 Hayward Fault Earthquake Carta plague reaches missions San Francisco in Europe New orld founded earthquake http://earthquake.usgs.gov/regional/ nca/1868 The HayWired Earthquake Scenario— We Can Outsmart Disaster: USGS 1200 1400 1600 1800 2000 Fact Sheet 2018–3016, at https://doi. ear org/10.3133/fs20183016 Study of excavations across the Hayward Fault has provided a record of strong earthquakes, all The 1868 Hayward Earthquake: estimated at magnitude of 6.3 or greater, going back hundreds of years—some historical events 145-Year Retrospective, Risk are shown for reference. The dates for earthquakes before 1868 are based on radiocarbon dating. Management Solutions, Inc. White Note that the interval between successive quakes has varied from 95 to 183 years, averaging Paper, at https://forms2.rms.com/ 150 years, and it is now more than 150 years since the 1868 earthquake.... rs/729-DJX-565/images/eq_1868_ hayward_eq_retrospective.pdf Other important engineering lessons Hayward Fault during the past 1,900 years. from the 1868 earthquake, though actively Notably, the last six quakes (in 1134, 1317, Putting Down Roots in Earthquake discussed at the time, were not heeded. 1475, 1629, 1725, and 1868) occurred Country, USGS General Information The hazard of building on landfill in San at intervals of 95 to 183 years, with an Products 15, 41, and 42, at Francisco Bay (called “made land” at the average interval of about 150 years. http://www.earthquakecountry.org/ time) and the admonition to “build no more booklets/. cornices” were largely forgotten by the time The Next Major Hayward Fault Earthquake Country Alliance, of the 1906 quake. Earthquake Bay Area, https://www. earthquakecountry.org/bayarea/ Is the Hayward Fault the Nation’s The 150th anniversary of the 1868 Most Dangerous Fault? quake was observed in 2018; scientists are convinced that the Hayward Fault in a densely populated urban region. The Two factors combine to make the has reached the point where a powerful, population at greatest risk from a Hayward Hayward Fault very dangerous. The damaging earthquake can be expected at Fault earthquake is 100 times greater than first is its location in the urban heart of any time. According to a 1996 Earthquake in 1868. The urban infrastructure in the Bay the Bay Area. The Hayward Fault is the Engineering Research Institute report, the Area has been tested only by the relatively single most urbanized earthquake fault next major Hayward Fault earthquake is remote, 1989 magnitude 6.9 Loma Prieta in the United States—in 1868 there expected to produce extensive damage to earthquake, and the smaller 2014 magnitude were only 24,000 residents living in residences, businesses, and to transportation 6.0 South Napa earthquake. USGS Alameda County; now there are more than and public utility infrastructure. Several earthquake science tells us that it’s now 2.4 million people. Hundreds of homes hundred thousand people are likely to be urgent to prepare for the next magnitude and other structures are built along the homeless after the quake. 7 quake on the Hayward Fault. Preparing fault trace, and mass transit corridors, As demonstrated by the aftermath of now can significantly reduce loss of life and major freeways, and many roadways Hurricanes Katrina, Sandy, and Maria, property from that coming quake. cross it at numerous locations. Also, recovery from catastrophic events can critical regional gas and water pipelines take years. According to a 2013 study and electrical transmission lines cross (see “More Information” box), a repeat Thomas M. Brocher, Jack Boatwright, James J. Lienkaemper, Carol S. Prentice, the fault. In 2018, the USGS released of the 1868 earthquake could cause David P. Schwartz, and Howard Bundock the HayWired earthquake scenario (see extensive economic losses (including “More Information” box), which included damage to buildings and contents, business Edited by Claire Landowski Graphic design by Suzanne Roberts updated forecasts of major impacts of a interruption, and living expenses) exceeding Banner photograph of the Bay Bridge and large earthquake on the Hayward Fault, $100 billion, with 85 percent or more of San Francisco skyline by Scott Haefner. including the loss of housing resulting both residential and commercial losses Seismogram from 1906 San Francisco earthquake, from the shaking and fires caused by the being uninsured. Damage to infrastructure, courtesy of IRIS Data Management Center. quake and long-term outages of drinking such as transportation and utilities, and COOPERATING ORGANIZATIONS water. Ongoing slip and aftershocks along other long-term economic effects could Earthquake Country Alliance the Hayward Fault may last for months, substantially increase the losses. University of California at Berkeley further damaging buildings and infrastruc- The 1868 Hayward Fault earthquake https://twitter.com/USGS ture that straddle the fault. is a reminder of the tremendous power https://www.facebook.com/USGeologicalSurvey A second factor making the Hayward that lurks beneath the Earth’s surface in Fault so dangerous is that its most recent the San Francisco Bay region. Other large damaging earthquake was more than quakes, like the damaging 1995 Kobe ISSN 2327-6916 (print) ISSN 2327-6932 (online) 150 years ago. USGS scientists have found earthquake in Japan, offer realistic visions https://doi.org/10.3133/fs20183052 evidence for 12 quakes on the southern of the destruction that such events can inflict Supersedes USGS Fact Sheet 2008–3019