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PD0RDD > NASA 07.11.98 00:48l 94 Lines 4610 Bytes #-9817 (0) @ WW
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Subj: Nasa Information 243
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Sent: 981106/1918Z @:PI8WNO.#UTR.NLD.EU #:37657 [DeMeern] FBB5.15c $:37657_PI8W
From: PD0RDD@PI8WNO.#UTR.NLD.EU
To : NASA@WW
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 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
south of the high San Gabriel Mountains.
The results come from the Southern California Integrated Global
Positioning System (GPS) Network, an array of 60 GPS receivers
that continuously measures the constant, 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 thatÕs being squeezed. Specifically, downtown and West
L.A. appear to be moving toward the San Gabriel Mountains at
about one-fifth of an inch (half a centimeter) per year."
Argus is presenting his findings 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 24 Earth-orbiting satellites 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 0.4 inch (1 centimeter).
"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 about 60 GPS receivers on the ground around
Southern California. Two new sites are being added every week
with plans for a total of 250 more. The earthquake network
began in 1990 with only four GPS receivers as a prototype funded
by NASA. It detected very small motions of EarthÕs 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 at the
University of Southern California (USC). 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.
The JPL research is part of NASAÕs Earth Sciences
enterprise, which 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.
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Greetings from Hans at Maarssenbroek ³~ The Netherlands
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