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Los Angeles Squeeze

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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.