NR 2004-08
April 16, 2004

Contact: Anita Gore
Ed Wilson
Mark Oldfield
Don Drysdale
(916) 323-1886


SAN FRANCISCO – The California Department of Conservation has just completed installing a group of sensitive instruments on the western portion of the Bay Bridge … instruments it hopes will never be used.

The 88 seismic sensors – 79 on the bridge itself and nine in a subsurface array at the foot of the bridge -- provide engineers with information about the ground shaking and structural response in the event of a major earthquake. That data can be used to assess the immediate safety of the bridge and to design more quake-resistant structures in the future. Also, combined with readings from other sites in the Bay Area, the data can help guide emergency response personnel to the hardest-hit areas in the region after a quake.

“Obviously, we would prefer to collect no data from these instruments,” DOC Director Darryl Young said. “However, the best information science can provide indicates that there will be a major earthquake in our lifetime – perhaps not as destructive as the Great San Francisco Earthquake, but something very significant.”

The 98th anniversary of the magnitude 7.8 earthquake that killed about 3,000 people and leveled much of San Francisco is April 18.

The sensors are part of a California Department of Transportation-funded project by DOC’s Strong Motion Instrumentation Program (SMIP) to instrument all toll bridges in California.

Northern California hasn’t experienced a damaging earthquake since the magnitude 6.9 Loma Prieta of 1989, which caused part of the Bay Bridge, as well as the Cypress Structure on the Nimitz Freeway, to collapse.

“Damaging earthquakes don’t happen every day, so the public tends to forget about the risk,” Young said. “But earthquakes are an everyday concern to the Department of Conservation and the California Geological Survey. The instrumentation of the Bay Bridge is just one example of the work being done to ensure public safety.”

DOC’s California Geological Survey is also doing extensive Seismic Hazard Zone mapping work in the Bay Area, identifying areas more likely to experience liquefaction (ground temporarily behaving like quicksand) and landslides during major earthquakes.

The instrumentation of the Bay Bridge has taken place as Caltrans' retrofitting work has progressed over the last two years. Instrumentation is complete on the San Mateo, Benicia-Martinez, eastbound Carquinez, and Golden Gate bridges, and is ongoing on the Richmond-San Rafael Bridge, the new Benicia bridge, and the new east span of the Bay Bridge.

Part of DOC's California Geological Survey, SMIP is the largest program of its kind in the world. SMIP was established following the 1971 San Fernando earthquake and has sensors at more than 900 locations throughout the state. The SMIP instruments on the Bay Bridge automatically dial up a central computer when strong earth motion -- generally from a magnitude 4.0 or greater temblor -- is recorded.

SMIP is a member of the California Integrated Seismic Network, along with the U.S. Geological Survey, the California Institute of Technology and the University of California at Berkeley. SMIP installs seismic monitors on high-rise buildings, dams, hospitals and industrial facilities around the state. The instruments are also placed in open land to measure the effects of earthquakes on soils.

Data from SMIP and other network stations produce a ShakeMap of ground shaking right after an earthquake. The ShakeMap identifies areas of the greatest potential damage and is used by the Office of Emergency Services and other emergency response agencies to immediately direct resources.

“The data these instruments produce gives a clear picture of where to concentrate initial response efforts, saving lives and property damage,” acting State Geologist Michael Reichle said. “In the bigger picture, it improves the building codes and practices that make California better prepared than anywhere else in the world for earthquakes.”

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