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Stanford Report, September 6, 2000

San Andreas Fault subject of three-day conference


Few forces of nature are as destructive as the earthquakes generated by the San Andreas Fault.

Just ask residents of California's Napa Valley wine country who were jolted from their beds by a 5.2 earthquake Sunday morning. According to the U.S. Geological Survey (USGS), the quake was produced by a new fault previously unknown to scientists that is probably an offshoot of the larger San Andreas system. The world's most closely watched earthquake zone is indeed full of surprises. Beginning today, the San Andreas fault system will be the subject of a long-planned conference at Stanford and the USGS in Menlo Park.

Experts from around the world will present their findings at the Third Conference on Tectonic Problems of the San Andreas Fault System today through Friday.

The first two days will be held in the B-01 Auditorium of the Gates Computer Science Building on campus. On Friday, the conference will move several miles from Stanford to Building 3 of the USGS, 345 Middlefield Road in Menlo Park.

The event is co-sponsored by the Stanford School of Earth Sciences and the USGS Earthquake Hazards Program.

Stanford hosted the first conference in 1968 and the second in 1973.

"What we are trying to do with this conference is bring together people who are interested in the dynamics of fault systems," says Goetz Bokelmann, visiting associate professor of geophysics from the University of Bochum in Germany.

"Nearly 30 years have passed since the last conference," he notes. "We understand much more about the behavior of the fault zone now, but many problems are still around."

The conference will feature leading geological researchers from Stanford, USGS, Caltech, Princeton, Hebrew University, Lawrence Berkeley National Laboratory, the Geological Survey of Japan and several other institutions.

The presentations will focus on the San Andreas fault system ­ a giant fracture in the Earth at least 10 miles deep and more than 800 miles long that stretches from Northern California into Mexico.

The San Andreas fault system marks the boundary between the massive North American and Pacific plates, which continually grind together producing underground stresses that sometimes trigger earthquakes.

This continual grinding process, known as plate tectonics, is responsible for the 1906 and 1989 earthquakes that caused widespread destruction in the San Francisco area.

Researchers at this week's conference will describe many of the technological advances that have transformed earthquake science in the past three decades.

Stanford geophysicists Howard Zebker and Paul Segall will explain the use of satellite radar analysis to measure subtle changes in the Earth's crust following the 1999 Hector Mine earthquake in California.

USGS scientists Ross Stein and Tom Parsons, along with Shinji Toda of the University of Tokyo, will present new findings on the relationship between geological stress and earthquake frequency in the aftermath of California's 1983 Coalinga and 1989 Loma Prieta earthquakes.

Ruth Harris of the USGS Earthquake Hazards Team will compare San Andreas seismic activity with the 1999 earthquake that struck Izmit, Turkey, in a talk titled "What Stops Earthquakes?"

Stanford geophysicist Robert Kovach will welcome conference attendees this morning and will be followed immediately by colleague Amos Nur, who will present a brief, historical overview of earthquake theories dating back to the early Greeks.

Also this morning, Bokelmann and Stanford geophysicist Gregory Beroza will discuss seismic activity along Northern California's Calaveras Fault. Felix Waldhauser and William Ellsworth then will analyze activity along the Hayward Fault, which runs through Oakland and other East Bay cities.

"Seismology has developed a lot since the last conference in 1973," says Bokelmann. "There are now hundreds of seismological stations along the San Andreas fault system providing data that are routinely available on the Internet."

He points out that, despite technological improvements, earthquake prediction remains elusive.

"We really haven't made as much progress on that as we had hoped," Bokelmann observes.

Here is a summary of the conference schedule:

Sept. 6 (Wednesday), 9 a.m. to 5 p.m.: "Seismicity and Fault-Related Experiments"

Sept. 7 (Thursday), 8 a.m. to noon: "The Big Picture and Deformation"; 1:30 to 6 p.m.: "Stress, Stress Triggering and Fault Zone Strength"

Sept. 8 (Friday), 8:15 to 10:10 a.m.: "Paleoseismology"

A ceremony honoring retired USGS geologist Bob Wallace will take place at the USGS in Menlo Park on Friday from 10:30 a.m. until noon. Geologists Kerry Sieh of Caltech and Steve Wesnousky of the University of Nevada-Reno will describe Wallace's many contributions to San Andreas Fault research. Following their remarks, the USGS Robert E. Wallace Earthquake Center will be dedicated in his honor. SR