World Wide Seismic Event..., page 2

Study: SF Bay area likely to face destructive earthquake by 2032
By BETH FOUHY, Associated Press Writer
Last Updated 4:25 p.m. PDT Tuesday, April 22, 2003
BERKELEY, Calif. (AP) - The San Francisco Bay area has a 62 percent chance of being struck by a major earthquake in the next 30 years, and the populous Interstate 880 corridor in the East Bay is particularly vulnerable to a catastrophe, according to a federal study released Tuesday.
The study, commissioned by the U.S. Geological Survey, found that the Bay Area has a 62 percent chance of being struck by a magnitude 6.7 or greater quake by 2032. That's down from the 70 percent chance researchers estimated in 1999, the last time the study was conducted.

But the apparent decrease shouldn't set residents at ease, cautioned David Schwartz, the study's co-author, noting that area residents face a greater chance of experiencing a significant quake than coming into contact with an "Anxiety of the Week" such as anthrax.

"The things we face every day--when we turn on the TV, or read the newspaper-- in many ways will never touch us," Schwartz, head of the USGS San Francisco Bay Area Earthquake Hazards project. "But living in this region, earthqakes will affect us. Earthqakes are going to happen."

Schwartz presented the research results in a public lecture at the University of California, Berkeley.

The Bay Area's last major earthquake was the magnitude 6.9-Loma Prieta quake of 1989. Centered in a mountainous region 50 miles south of San Francisco, the quake killed 40 people and caused about $6 billion dollars in structural damage. Researchers cautioned that the devastation would have been much worse if the quake's epicenter had been closer to the region's urban center.

Today, the most potentially hazardous of the region's seven major faults is the combined Hayward-Rodgers Creek system, which has a 27 percent chance of producing a large earthquake in the next 30 years, according to the study. The Hayward fault roughly parallels the densely populated Interstate 880 corridor, while the Rodgers Creek fault extends north of San Francisco into the city of Santa Rosa.

In general, Schwartz said, the East Bay region has a greater chance of being struck by a quake than the Peninsula and other areas west of the Bay because of a greater number of active faults in that region. He said researchers are paying particular attention to the Northern Calavaras fault, stretching from Danville to San Jose.

Between November and February, an "earthquake swarm"--hundreds of earthquakes measuring magnitude 3.9 or less-- occurred along the fault, shaking homes and rattling residents' nerves.

"We are very, very concerned that we could be setting up for a larger earthquake," Schwartz said, "and we are watching this area very closely."

There study contained some findings, however, that could help reassure the earthquake-phobic. The region has just a 10 percent chance of seeing an earthquake of magnitude 7.5 or greater, because only two faults - the San Andreas, which bisects the Peninsula, and the San Gregorio, which runs along the Pacific shore - are large enough to produce a quake of that size.

The most significant seismic event in the Bay Area in the last century--the magnitude 7.9 San Francisco quake of 1906-- was caused by a 300 mile rupture along the San Andreas fault.

On the other hand, the study suggested the region has an 80 percent chance being hit by at least one quake of magnitude 6.0 or greater.

Schwartz said the message Bay Area residents should take from the study is that strengthening homes and structures-- in the form of earthquake retrofitting-- is essential to minimizing the potential damage of a significant quake. Public agencies have spent about $12 billion on retrofitting since the Loma Prieta earthquake, Schwartz said, but more needs to be done to ensure safety.

The USGS has produced a web site featuring "shake maps" that area residents can use after an earthquake strikes. The maps show the impact of quakes in specific regions throughout the Bay area almost immediately after they occur.