MEDIA RELATIONS OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA 91109. TELEPHONE (818) 354-5011
http://www.jpl.nasa.gov
Contact: Mary Hardin, (818) 354-0344
FOR IMMEDIATE RELEASE
October 28, 1998
METROPOLITAN L.A. UNDER A SLOW SQUEEZE
Downtown and West Los Angeles are moving toward the San
Gabriel Mountains and the metropolitan area in between is being
and will be squeezed slowly over the next several thousand years,
according to researchers using precise satellite surveying
techniques at NASA's Jet Propulsion Laboratory (JPL), Pasadena,
CA.
The measurements suggest that new mountains may be forming
to the south of the high San Gabriel Mountains.
The results come from the Southern California Integrated
Global Positioning System (GPS) Network, an array of 60 current
and 250 planned GPS receivers that continuously measures the
constant, yet tiny, movements of earthquake faults throughout
Southern California.
"We've known for some time that the area between the
coastline and the Mojave Desert is being squeezed together by the
constant movement of Earth's crust," said Dr. Donald Argus, a
geophysicist at JPL. "This new research helps pinpoint the area
that's being squeezed. Specifically, downtown and West L.A.
appear to be moving toward the San Gabriel Mountains at about
half a centimeter (one-fifth of an inch) per year."
Argus is presenting his finding Oct. 29 at the annual
meeting of the Geological Society of America in Toronto, Canada.
"While this research does not mean that an earthquake in Los
Angeles is imminent, one possible conclusion is that the
earthquakes that occur in Los Angeles might be concentrated in
the northern part of the basin," Argus said.
The GPS surveying system uses radio signals transmitted from
a constellation of 24 Earth-orbiting satellites that are jointly
operated by the U.S. Departments of Defense and Transportation.
Equipment on the ground receives signals from several satellites
at a time, allowing scientists to pinpoint the position of a
receiver to better than 1 centimeter (0.4 inch).
"The regional project is designed for exactly this kind of
study. Our goal is to observe and monitor the slow, small
motion, called strain, of the ground in greater Los Angeles,"
said JPL's Dr. Frank Webb, chair of the Southern California
network. "This research helps us learn where earthquakes are
more likely to happen, and helps with estimating the regional
earthquake hazard in Southern California. It enables other
agencies to make priorities about earthquake mitigation
activities, including emergency preparedness and retrofit
strategies."
There are now about 60 GPS receivers on the ground around
Southern California with two new sites being added every week.
The earthquake network began in 1990 with only four GPS receivers
as a prototype project funded by NASA. It detected very small
motions of Earth's crust in Southern California associated with
other California earthquakes in June 1992 in the town of Landers
and in January 1994 in Northridge.
The Southern California network includes a number of
institutions using GPS for earthquake research. The consortium is
coordinated by the Southern California Earthquake Center, a
National Science Foundation science and technology center
headquartered at the University of Southern California. The array
is operated by JPL, USC, the U.S. Geological Survey and the
Institute of Geophysics and Planetary Physics at the University
of California at San Diego's Scripps Institution of Oceanography.
More information about SCIGN is available at:
http://milhouse.jpl.nasa.gov/
The JPL research is part of NASA's Earth Sciences Enterprise
that seeks to understand the total Earth system and the effects
of natural and human-induced changes on the global environment.
JPL is a division of the California Institute of Technology.
#####
#98107
mah 10/28/98