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NR 2006-25
October 11, 2006

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

CALIFORNIA GEOLOGICAL SURVEY
TO INSTALL ADDITIONAL SEISMIC MONITORS IN SANTA ROSA

SACRAMENTO – The California Geological Survey (CGS) is expanding its inventory of seismic instruments in Santa Rosa, an area that has experienced significant shaking during past earthquakes. These “accelerographs” are not an early warning system, but instead collect data about the response of buildings and structures to ground motion. That information can improve public safety, and help emergency responders and local planners.

“We have relatively few instruments around Santa Rosa, given the population and the shaking we’d anticipate there in the event of a large earthquake in the Bay Area,” said State Geologist Dr. John Parrish, chief of CGS. “The information we gather with these instruments ultimately can help make buildings better able to withstand large earthquakes, which are infrequent but inevitable in California.”

CGS, part of the California Department of Conservation, established the Strong Motion Instrumentation Program (SMIP) in 1971 after the damaging San Fernando earthquake. SMIP has installed and maintains recording instruments at more than 1,000 locations statewide, including the city halls of Los Angeles, San Francisco and Oakland, and the state capitol. A number of high-rises, dams and all major bridges are instrumented.

In Santa Rosa, SMIP currently has instruments in a bank, a hospital, a retirement home, and in an open field. The ongoing work will add instruments at four fire stations in the city and one in nearby Sebastopol.

“We place quite a few instruments in fire stations, for a few reasons,” explained Supervising Geologist Dr. Anthony Shakal, who heads SMIP. “For one thing, it’s a protected environment. Also, fire departments are in a state of readiness at all times in case of emergency, so they understand our mission and are very cooperative with us. Finally, fire departments tend to follow the pattern of population density in a community, which is important in monitoring the shaking where people and buildings are.”

The accelerographs measure the vertical and horizontal response of buildings and soils. When activated by earthquake shaking, the devices produce a digital record from which the critical characteristics (acceleration, velocity, displacement) of ground motion can be calculated. The information gathered by SMIP is processed and disseminated to seismologists, engineers, building officials, local governments and emergency response personnel throughout the state.

SMIP data has verified the performance of new types of earthquake-resistant construction, and has resulted in improved formulas in the Uniform Building Code for calculating building vibration periods, which is vital in earthquake-resistant design.

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.

Within a few minutes of a large earthquake, data from the SMIP and CISN seismic instruments is used to create a “ShakeMap.” 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.

Santa Rosa suffered severe damage during the Great San Francisco Earthquake of 1906. While the last major earthquake in the Bay Area – the magnitude 6.9 Loma Prieta of October 17, 1989 – registered on SMIP’s instruments in Santa Rosa, the epicenter was too far away (about 110 miles) to do any damage in the community.

Two moderate earthquakes – magnitude 5.6 and 5.7 – centered two miles north of Santa Rosa on the Rodgers Creek fault system occurred on October 1, 1969 and caused significant damage. There were no instruments in or near Santa Rosa at the time, so relatively little is known about the ground shaking that occurred.

“Santa Rosa tends to have significant shaking because of the underlying geology,” Shakal said. “There are very deep sediments under the city, and the Rodgers Creek and Maacama fault systems are nearby. With more instruments there, we will gain understanding of how the structures and the ground there perform in earthquakes. The more we know, the better prepared we’ll be.”

SMIP data is available at the Department of Conservation's Web site, www.conservation.ca.gov, and at quake.ca.gov. Data from many earthquakes can be viewed and downloaded conveniently for use in engineering and scientific applications. There is also information about how the public can prepare for future earthquakes.

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