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NR 2003-29
October 16, 2003

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

NEW BRIDGE TO BE OUTFITTED WITH SEISMIC MONITORS

VALLEJO – A new bridge over the Carquinez Straits on westbound Interstate 80 will include instruments that can help emergency responders evaluate the safety of the bridge after a devastating earthquake and provide engineers the information they need to design more earthquake-resistant structures.

Ultimately, there will be about 103 instruments on the bridge, which opens November 15, plus about 27 on the south approach. The sensors, called accelerometers, are part of a Caltrans-funded project by the Department of Conservation’s Strong Motion Instrumentation Program (SMIP) to instrument all toll bridges in California.

Data from such instruments went into the design of the new Al Zampa Memorial Bridge -- the first suspension span built in the country in nearly four decades - to make it as resistant as possible to earthquake shaking. Zampa was an ironworker who survived a fall from the Golden Gate Bridge during its construction.

Northern California hasn’t experienced a damaging earthquake since the Loma Prieta temblor, 14 years ago tomorrow. That 6.9 quake, centered in the Santa Cruz Mountains, caused part of the Bay Bridge and the Cypress Structure on the Nimitz Freeway to collapse.

“Some scientists think we’re overdue for a significant earthquake in the Bay Area, so it’s important to keep preparing,” DOC Director Darryl Young said. “This instrumentation is a key part of being ready for the next big quake.”

Seismic instrumentation of Bay Area bridges has taken place as Caltrans' retrofitting work has progressed over the last five 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 and the Bay Bridge, among others.

The westbound span across the Carquinez Straits opened in 1927 and does not meet current seismic design or traffic safety standards. Caltrans determined the structure could not be repaired without closing it for an extended period to the 109,000 cars that use it daily. The new bridge, which will cost about $200 million, will provide four lanes of traffic -- including a carpool lane -- and a pedestrian/bicycle path.

“After the 1994 Northridge earthquake, we analyzed the westbound Carquinez bridge and decided that replacing it was the best option,” said Robert Stott, Chief of Structure Design Services and Earthquake Engineering for Caltrans. “The seismic instrumentation on the new bridge is an important tool our engineers will use to protect public safety in future construction projects.”

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 that will be installed on the new bridge automatically dial up a central computer when strong earth motion -- generally from a magnitude 4.0 or greater temblor -- is recorded.

SMIP data from the new Carquinez bridge and other sites can be used in three ways. First, it can be analyzed in the minutes following a quake to allow Caltrans engineers to assess the integrity and safety of the bridge or structure. Second, it can be used to guide emergency response personnel to the hardest-hit areas in the region. Third, it shows how structures react to the shaking, and is applied to engineering principles that are incorporated into new design codes for better earthquake-resistant construction.

The closest major fault to the Al Zampa Memorial Bridge is the Concord Fault, approximately 6.5 miles to the east. A magnitude 5.4 earthquake was centered between Walnut Creek and Concord on or near that fault on October 23, 1955. There are several major faults in the greater Bay Area.

The Strong Motion Instrumentation Program is a member of the California Integrated Seismic Network (CISN), 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 CISN 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 to these areas.

“This information is critical both immediately after an earthquake and in the long term because it can save lives and minimize property damage,” Young said. “Earthquakes are inevitable in California, and this SMIP data fortifies the building codes that keep us safe.”

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