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NR 2001-41
April 27, 2001

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

EARTHQUAKE MONITORS INSTALLED
AT SAN FRANCISCO CITY HALL

Sensors Will Provide Emergency Data,
Determine Effectiveness of Retrofitting

SAN FRANCISCO -- It has beauty and a brain. Inside beautiful San Francisco City Hall, an electronic brain with an army of sensors is ready to respond to the next Bay Area earthquake.

State officials today demonstrated the new seismic monitoring system at the historic structure as part of an extensive earthquake retrofitting project.

The California Department of Conservation has installed 18 sensors. Divided among the four levels and dome of City Hall, the devices measure seismic waves shaking the building. During an earthquake, these "accelerometers" report to a central computer the shaking that occurs at several key points in the structure from the foundation to the top of the dome. The instruments provide valuable data about earthquake shaking and the building's response.

"We can't stop earthquakes from happening, but we can better prepare ourselves by improving the way we build new structures and retrofit older ones," said Darryl Young, director of the Department of Conservation. "These strong-motion sensors provide the latest technology to help us do that."

The installation project conducted by DOC's Strong Motion Instrumentation Program (SMIP) began in 1999 as part of the mammoth earthquake retrofit of City Hall.

The sensors also serve as watchdogs, automatically phoning an alert to computers at SMIP headquarters in Sacramento when strong ground motion occurs (generally magnitude 3.5 or greater in the San Francisco Bay Area.)

In addition to City Hall, accelerometers have been installed on other structures in the San Francisco area, such as the Golden Gate Bridge and San Mateo Bridge. In the event of a large earthquake, information gathered by the sensors can be analyzed by DOC

computers and seismologists and help emergency crews determine the hardest-hit areas within minutes after the quake. During the 1989 Loma Prieta earthquake, the City Hall dome twisted like a bottle cap, moving two inches. Walls and concrete floor slabs cracked on all levels.

In 1995 engineers began a "base isolation" retrofit of the entire building. Base isolation helps buffer a building from seismic waves. There are 590 rubber cylinders at the base of City Hall's support columns that dampen the effect of the seismic waves. Base isolation also allows the building to move more than two feet in any direction during an earthquake, further minimizing quake damage.

Data gathered by SMIP sensors on how structures react to temblors is being applied by engineers to create stronger, safer building plans for new construction and retrofits.

The Strong Motion Instrumentation Program is part of the DOC's Division of Mines and Geology, which is California's State Geological Survey. SMIP instruments, in combination with sensors from the U.S. Geological Survey, California Institute of Technology and UC Berkeley, are the backbone of a developing integrated seismic network that will cover most of the state's earthquake-prone areas. This consortium of institutions will jointly produce maps of the shaking to help guide emergency response. With more than 800 stations in place, the state's Strong Motion Instrument Program, established in 1971 following the San Fernando earthquake, is one of the largest of its kind in the world.

In addition to studying and mapping earthquakes and other geologic phenomena, the Department of Conservation maps and classifies areas containing mineral deposits; ensures reclamation of land used for mining; regulates oil, gas and geothermal wells; administers agricultural and open-space land conservation programs; and promotes beverage container recycling.

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