HR: 15:10h
AN: S23C-06    [Abstracts]
TI: When it happens again: impact of future San Francisco Bay area earthquakes
AU: * Zoback, M
EM: zoback@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025
AU: Boatwright, J
EM: boat@usgs.gov
AF: USGS, 345 Middlefield Rd., Menlo Park, CA 94025
AU: Kornfield, L
EM: laurence.kornfield@sfgov.org
AF: Dept. Building Inspection, 1660 Mission, San Francisco, CA 94103
AU: Scawthorn, C
EM: cscawthorn@worldnet.att.net
AF: Dept. Urban Management, Kyoto Univ., Kyoto, 606 Japan
AU: Rojahn, C
EM: crojahn@atcouncil.org
AF: Applied Tech. Council, 201 Redwood Shores, Redwood City, CA 94065
AB: San Francisco Bay area earthquakes, like major floods and hurricanes, have the potential for massive damage to dense urban population centers concentrated in vulnerable zones-along active faults, in coastal regions, and along major river arteries. The recent destruction of Hurricane Katrina does have precedent in the destruction following the 1906 "San Francisco" earthquake and fire in which more than 3000 people were killed and 225,000 were left homeless in San Francisco alone, a city of 400,000 at the time. Analysis of a comprehensive set of damage reports from the magnitude (M) 7.9 1906 earthquake indicates a region of ~ 18,000 km² was subjected to shaking of Modified Mercalli Intensity of VIII or more - motions capable of damaging even modern, well-built structures; more than 60,000 km² was subjected to shaking of Intensity VII or greater - the threshold for damage to masonry and poorly designed structures. By comparison, Katrina's hurricane force winds and intense rainfall impacted an area of ~100,000 km² on the Gulf Coast. Thus, the anticipated effects of a future major Bay Area quake to lives, property, and infrastructure are comparable in scale to Katrina. Secondary hazards (levee failure and flooding in the case of Katrina and fire following the 1906 earthquake) greatly compounded the devastation in both disasters. A recent USGS-led study concluded there is a 62% chance of one or more damaging (M6.7 or greater) earthquakes striking the greater San Francisco Bay area over the next 30 years. The USGS prepared HAZUS loss estimates for the 10 most likely forecast earthquakes which range in size from a M6.7 event on a blind thrust to the largest anticipated event, a M7.9 repeat of the 1906 earthquake. The largest economic loss is expected for a repeat of the 1906 quake. Losses in the Bay region for this event are nearly double those predicted for a M6.9 rupture of the entire Hayward Fault in the East Bay. However, because of high density of population along the Hayward Fault, an Association of Bay Area Governments study concluded that the two quakes would produce similar numbers of displaced households, between 155,000 to 160,000 in the 9-county Bay area (www.abag.ca.gov/bayarea/eqmaps/eqhouse.html). A recent vulnerability analysis for the city and county of San Francisco by the Applied Technology Council found that a repeat of a 1906-size quake and subsequent fires could completely destroy 35% of the privately-owned buildings (~45,000 buildings out of a total of ~122,000). These losses in the City are comparable to those in 1906. This CAPSS (Community Action Plan for Seismic Safety) analysis was conducted using HAZUS modified for detailed ground motion inputs and a building inventory at neighborhood scale and of unprecedented detail. It concluded the most serious impact of future quakes in San Francisco would be damage to and loss of residential housing, due largely to construction style and age of housing stock. More than 122,000 displaced households were estimated for a repeat of 1906 (out of a total of ~329,000; 42%). Defining the scope of the earthquake risk and exposure is a necessary step in developing long-term mitigation plans including criteria or the evaluation and repair of damaged buildings, incentives, and education. As Katrina taught us, recovery from disasters producing massive loss of housing and personal property is a formidable challenge.
DE: 6300 POLICY SCIENCES (7964)
DE: 6334 Regional planning (1880)
DE: 7200 SEISMOLOGY
DE: 7212 Earthquake ground motions and engineering seismology
SC: Seismology [S]
MN: Fall Meeting 2005