October 12, 2009
Contact: Don Drysdale
SACRAMENTO – To help gather vital earthquake data, the California Geological Survey (CGS) is installing data-collecting seismic instruments on the new span of the Bay Bridge. The installations come as the 20th anniversary of the October 17, 1989 Loma Prieta quake approaches. The instruments are not an early warning system, but instead collect data about how buildings and structures respond to ground motion.
“By placing instruments along the new eastern span of the Bay Bridge we are able to gather important information about how earthquakes impact structures and transportation infrastructure,” said Dr. John Parrish, California’s State Geologist and head of CGS. “Ultimately this data will enhance our response to quakes and allow us to better prepare for expected damages.”
CGS’ Strong Motion Instrumentation Program (SMIP) will place 73 instruments called “accelerographs” on a 1.2-mile span of the bridge known as the “Skyway,” a stretch crossing from Oakland to Yerba Buena and Treasure Island.
When instrumentation is complete, a total of 200 strong motion sensors will sit on the bridge’s east span, more than any other bridge in the United States and in most other countries. The self-anchored suspension portion of the bridge will have nearly 90 sensors, with locations ranging from the very top of the tower to inside the piles bored into the rock of the foundation. The west span of the Bay Bridge was brought up to modern seismic standards several years ago and was instrumented with 80 strong motion sensors.
Immediately after an earthquake, the information is transmitted from the instruments to a central computer at headquarters in Sacramento for computer processing and the production of a digital “ShakeMap” of the intensity of shaking in the area. Among other things, the ShakeMap helps emergency responders determine where the highest levels of shaking have occurred and thus where critical infrastructure – such as transportation corridors and water lines – is most likely to be damaged. In the long term, however, SMIP’s data is even more valuable for its influence on building codes and practices.
“Over the years, our partnership with Caltrans has produced a great deal of information beneficial to the
scientific and engineering communities,” said Dr. Anthony Shakal, head of SMIP. “California’s seismic codes and construction practices are the most effective in the world in guiding structural design to help ensure critical infrastructure will not fail in the event of a large earthquake. The experience of the Loma Prieta earthquake, and the data and knowledge gained through our program and others, has prompted government and the private sector to do a tremendous amount of retrofitting work to protect public safety while avoiding unnecessary costs due to overdesign.”
CGS, which celebrates its 150th anniversary next year, established SMIP in 1971 after the damaging San Fernando earthquake. SMIP has installed and maintains more than 5,000 recording instruments at more than 1,100 locations statewide, including the city halls of San Francisco and Oakland. Since the Loma Prieta quake, monitors have been placed on 80 bridges and more than 200 buildings around the state. The Applied Technology Council in 2006 honored SMIP as one of the top seismic programs of the 20th century.
SMIP recently installed 18 sensors on berths 35 and 37 at the Port of Oakland, as well as three instruments on the ground. In the near future, installations are planned at the Dumbarton (Highway 84 between Fremont and Menlo Park) and Antioch (Highway 160 between Antioch and Sacramento County) bridges, which will have instruments added while they’re being strengthened. Another noteworthy project in the planning stages is the instrumentation of the BART tube under the San Francisco Bay between Oakland and San Francisco. It is being retrofitted as part of system-wide BART effort.
The goal of SMIP and its partners in the California Integrated Seismic Network (CISN) – the California Institute of Technology, UC Berkeley, and the U.S. Geological Survey – is to have at least one instrument in every ZIP code in the state.
SMIP data is available online viat the California Department of Conservation and at www.strongmotioncenter.org.