The Next Bay Area Earthquake This morning I would like to summarize what the recent UCERF2 Probability Report says about the risk of large earthquakes in the Bay Area Show you what the ground shaking and damages might be like for an earthquake on the Hayward fault What to expect Where? When? How Large? Dr. John Boatwright, Bay Area Earthquake Alliance Co-Chair Co-Regional Coordinator for Northern California US Geological Survey

40 mm/yr Farallons-Sierra Nevada 2 5 7 9 6 15 North American plate 17 24 The Bay Area is underlain by a complex web of faults. This means that the 40 mm/yr motion of the Pacific Plate past the North American Plate is spread across many faults. The San Andreas has half of the motion in the north Bay and only a third of the motion along the Peninsula. The seismic hazard does not simply lie along the San Andreas fault, but spreads across the entire Bay Area as far east as Livermore and Fairfield. Pacific plate

What is the History of Large Earthquakes in the Bay Area? 1989 Loma Prieta (M6.9) 1906 San Francisco (M7.8) 1868 Hayward (M6.8) 1838 Peninsula (M7?) Paleoseismic Earthquakes (pre-1776) identified by trenching active faults The historic record of earthquakes in the Bay Area consists of 4 large events in 230 years. The paleoseismic record of earthquakes contains 7-8 large events in the century preceding the Spanish exploration and settlement.

Hayward Earthquake 1868 “We need to correct our style of architecture … to work a savings of untold sums of money in the future” - San Jose Mercury News October 29, 1868 Note types of building damage

1906 San Francisco 20 foot fence offset in 1906 near Pt. Reyes “Mole track” is a common surface expression of an earthquake fault in soil Arnold Genthe’s famous photograph down Sacramento Street

Moment Accumulation in the SF Bay Region Cumulative M0, dyne-cm Stress Shadow

One characteristic of recent large earthquakes in California is the damage to freeways and bridges. The Cypress freeway was torn down and replaced by a ground level freeway. The eastern span of the Bay Bridge is being replaced by a new bridge. Loma Prieta 1989

Written history in the Bay Area dates back to the founding of Mission Dolores in San Francisco, about 10 days before the Declaration of Independence was signed. Remarkably there were no earthquakes recorded in the first 32 years of mission records.

Bay Area Earthquake History Four large earthquakes have occurred in the historic record: the 1838, 1868, 1906, and 1989. But before the Spanish arrived in Baja California, there was a century of large earthquakes that geologists have found by trenching the active faults in the Bay Area. These paleo-earthquakes are indicated by the yellow lines. Note that this is a temporally bunched but spatially diffused release of stress. The east Bay was extremely active, starting with an event on the Greenville fault and ending with an event on the northern Calaveras. 1600-2000 A.D.

2007-2036 63% In the next 30 years, there is a 63% prob- ability, nearly a 2/3rds chance, of an M6.7 or larger earthquake in the greater Bay Area. Hazard is highest in the East Bay due to the larger number of faults there, including the Hayward fault. (UCERF2 Report, 2007) 3% 1% 31% 21% 6% 7% 11% The USGS started making Probability Reports after the 1989 Loma Prieta earthquake. This figure shows the result for the third iteration for the Bay Area, which was published in 2007. These probabilities are derived from the slip rate and the recurrence interval on each fault segment. 63% 2007-2036

M ≥ 6.7 Hazard is highest in the East Bay due to the larger number of faults including the Hayward Fault. Remarkably, there is more hazard in the east Bay than in the west Bay along the San Andreas.

So if you’re really lucky with your trench, and the sedimentation rate and your dates, youo can determine chronology of earthquakes. This slide shows the dates of eleven events in 180 years.

1868 Hayward Earthquake Near-Field MMI Intensities are strong from San Leandro south through Hayward towards Alvarado (MMI 8-9 & 9) But they appear moderate in both Oakland and Milpitas (MMI 7-8 & 8) 38° This is the ShakeMap or isoseismal map that Howard Bundock and I determiined for the 1868 earthquke. It is very sparse through large sections of the east and south Bay. At the time of the 1868 earthquake, there were 260,000 people living in the Bay Area. Much of the east Bay was still ranchos. The strongest shaking occurred in Hayward and San Leandro, near the middle of the fault. 37.5° -122.5° -122°

Hayward Fault Earthquake: The Infrastructure Earthquake In the 140 years since the last Hayward fault earthquake, the east Bay has become densely populated, and many lifelines and much infrastructure directly crosses the Hayward fault. 14

Animation of Shaking from a M7.0 on the Hayward Fault Fremont Epicenter To end the talk, I’d like to show a movie that Brad Aagaard showed you last year. This movie shows a rupture starting at the southeastern end of the Hayward fault, near Mission San Jose, and rupturing towards Berkeley and Emeryville. http://earthquake.usgs.gov/regional/nca/simulations/hayward/

Losses by county - M7.0 scenario Sonoma Solano Santa Clara Santa Mateo The predicted economic losses vary strongly depending on which direction the fault ruptures. A rupture from San Pablo Bay to the southeast produces the greatest damage, not only in Santa Clara but also in Alameda and Contra Costa. San Francisco Marin Contra Costa Alameda $0 $40B $80 $100 Economic Loss ($Billions) 16

Soft-Story Damage & Failures Fire Following Earthquake What can happen in the urban neighborhoods of the Bay Area in next large earthquake? I would like to highlight two critical hazards for future earthquakes in the Bay Area Soft-Story Damage & Failures Fire Following Earthquake

Soft-Story Buildings One of the most vulnerable building type is soft-story buildings. The weight of these buildings is greater than the strength of the (open) first story. The building shown in the upper-right is criminal, if it is in a seismically active area. soft-story retrofits in San Francisco are still voluntary rather than mandatory 18

This photo shows the vulnerability that the Loma Prieta earthquake exposed This is an “action” photo from the heart of the Marina district, following the 1989 earthquake. In the foreground, you can see the wreckage of two soft story buildings, 2090 Beach, from which Sherra Cox was rescued, and 3701 Divisadero, in which there were two fatalities and where the Marina fire started.

We Were Very Fortunate in 1989 We were lucky in 1989: there was no wind to drive the fire through the Marina. I live on the flank of Russian Hill, just to the left of this picture. It was really eerie watching the fire and all that night smelling the bay water that had been used to put it out. Marina fire To Have Favorable Fire Conditions

google: cisn shakemap nc 38° google: cisn shakemap nc http://www.cisn.org/shakemap/nc/shake/ 37.5° Within 10 minutes of a M > 3.5 earthquake anywhere in northern California, we post a ShakeMap that shows the recorded ground motions, plotted as intensities. Yellow is MMI 6, the threshold for damage. Orange is MMI7, which can damage chimneys and masonry. Orange-red is MMI 8, which can damage wood-frame buildings. Google “cisn shakemap nc” & bookmark it! 37° 123° 122° 121°