San Andreas Fault subject
of three-day conference
BY MARK SHWARTZ
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
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