by Robert Sanders
Six years ago the deadly Loma Prieta earthquake struck the Bay Area without warning, collapsing freeways, damaging the Bay Bridge and igniting San Francisco's Marina district.
Now, thanks to a grant from Pacific Bell's CalREN program, Berkeley's Seismographic Station is upgrading its seismic network to bring closer the time when Northern and Central California will have critical early warning of quakes like that.
In the case of distant quakes such as Loma Prieta, which struck near Santa Cruz Oct. 17, 1989, strong ground shaking can take from 30 seconds to more than a minute to reach the Bay Area. Early warning would give authorities a brief period in which to respond.
"If you could get 20 to 30 seconds advance warning of a dangerous shock, you could stop potentially hazardous equipment, like electrical generators," says Berkeley seismologist Lind Gee. "With 30 seconds to a minute warning you can begin to think about human response issues, like evacuation."
The $85,000 CalREN grant will subsidize installation of high-capacity communication lines linking outlying earthquake detectors with the campus, and linking the campus with the U.S. Geological Survey in Menlo Park.
Six of a planned 21 lines have been installed so far, and one detector is already connected to the Seismographic Station to feed seismic data day and night.
Gee estimates that with the new high capacity lines funneling "real-time" data from detectors directly into the station, their computers eventually will be able to analyze and spit out a preliminary magnitude and location within seconds of a quake.
Seismographic Station director Barbara Romanowicz, professor of geophysics, cautions that an early warning system would be of limited use to cities near the epicenter of a quake.
"Most of the quake sources are in the Bay Area, so warning would be short," she says.
Cities farther from the epicenter could benefit, though. San Jose and Santa Cruz, for example, could be warned of quakes at the north end of San Francisco Bay, and vice versa.
Already the Seismographic Station has developed a program called REDI, for Rapid Earthquake Data Integration, that alerts emergency preparedness agencies, power and telephone companies and transportation agencies of an earthquake as quickly as possible--typically within six to nine minutes of a temblor. Operated in cooperation with the USGS, REDI delivers information via pager after analysis at Berkeley and is made available to the public through the World Wide Web at http://www.seismo.berkeley. edu/seismo/Homepage.html.
Berkeley, Lawrence Livermore National Laboratory and the USGS are now working on an improved system that would provide warning within seconds.
"We are now at the point of developing equipment to see if it's feasible," Gee says.
Essential to this goal is quick, reliable transmission of data from the field. In Southern California the networks operated by the California Institute of Technology and the USGS were set up with high capacity lines earlier this year, thanks to a $98,000 grant from CalREN.
Berkeley's network, however, currently relies on old fashioned phone lines, plus a few microwave relays and radio links, to get the information to Berkeley.
These links can fail and block transmission of critical data, or can introduce noise or glitches.
"The new network will provide more reliable and cleaner data," Gee says. "Glitches can be mistaken for even big earthquakes, and now a lot of our analysis time is spent trying to tell the difference between glitches and real signals."
CalREN's grant will enable Berkeley to hook up 21 high resolution seismic detectors scattered around Northern and Central California to the campus via Pacific Bell's "frame relay" system.
The system has the ability to route information around damaged parts of the phone network, ensuring reliable, real time delivery. The system also can transmit 56,000 bits of information per second.
An even faster link will be built between Berkeley and the USGS to carry 1.5 million bits of data per second, allowing the Seismographic Station and the USGS to share earthquake data.
The high speed communication lines will also help seismologists collect other types of geophysical data, such as position information needed to track earth movement. The Seismographic Station operates a network of continuously recording GPS (global positioning system) receivers in northern California to monitor fault movement in cooperation with the USGS.
"Now we dial up once a day to get the data," Romanowicz says.
"With a continual connection we could do real time geodetic processing, providing complementary information to the seismological data."
Berkeley also has nearly completed an expensive program to improve its 21 seismic detectors.
Soon each will have both a state-of-the-art strong motion detector designed to record accurately during even the most violent shaking, plus detectors tuned for sensitive monitoring of smaller quakes.
The USGS also has plans to upgrade its seismic network in the near future.
"The USGS network is denser, providing a more accurate and rapid position for a quake, but with the dynamic range and accuracy of our instruments we can make a more robust estimate of a quake's magnitude and rupture characteristics," Romanowicz says.
"In that sense our networks are complementary."
CalREN (California Research and Education Network) is a $25 million program set up by Pacific Bell in 1993 to stimulate practical applications for emerging communications technologies.