Press Release

Earthquake Studies: Fault Moving Faster Than Believed

By SpaceRef Editor
November 1, 2001
Filed under , ,

Scientists at NASA’s Jet Propulsion Laboratory, Pasadena,
Calif., and the University of California, Los Angeles, have
concluded that earthquake fault zones in California’s eastern
Mojave Desert are moving in different ways than they expected.

For years researchers were aware that movement in the
southern California shear zone was distributed over a 100-
kilometer (60-mile) wide area. However, they assumed that deep
below the surface the Blackwater Little Lake and the Garlock
faults were creeping steadily, something that the new study
seems to contradict.

New findings indicate that more than half of the right-
lateral motion of the Eastern California shear zone is sharply
concentrated along the Blackwater Little Lake fault system.
The rapid strain accumulation observed along the fault system
indicates that the fault is building up stress in the shallow
crust at a rate three times faster than the rate inferred from
geological observations. This may be the manifestation of
stress transfer between the Garlock fault and other faults in
the Mojave area, in particular those that produced the
magnitude 7.3 Landers earthquake in 1992 and the magnitude 7.8
Owens Valley earthquake in 1872.

Scientists arrived at the conclusion after studying radar
interferometry data collected by satellites over the last
eight years. Radar interferometry is a method to map the
topography and displacement of the Earth’s surface with
extreme accuracy.

A paper with the findings is in the Nov. 1, 2001, issue
of the journal Geology.

“The most exciting thing is we discovered something we
didn’t expect. We were looking for deformation on the Garlock
fault, but we saw in the image a concentration of shear along
the Blackwater Little Lake fault, which cuts the Garlock fault
at a right angle,” said Dr. Gilles Peltzer, a UCLA professor
and JPL research scientist who is the lead author of the
study. “Radar interferometry has been applied previously to
the study of earthquakes, and what we are imaging here is the
surface strain field produced by the slow creep occurring at
depth on active faults between earthquakes.”

Operated by the European Space Agency, the European
Remote Sensing satellites use interaction of radar waves to
measure distances and angles precisely. The satellites look at
Earth in a slanted angle at 23 degrees. The only other way to
gain such accurate information on fault displacement would be
to place Global Positioning System receivers every 50 meters
(about 165 feet).

JPL is a division of the California Institute of
Technology in Pasadena.

SpaceRef staff editor.