NSF PR 97-9 - February 10, 1997
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World's Most Innovative GPS Network to Monitor Southern
California's Earthquake Faults
Southern California may soon be the best-surveyed
area on the planet, thanks to powerful tools used
by scientists seeking to understand the region's earthquake
potential.
The National Science Foundation (NSF) Southern California
Earthquake Center (SCEC) at the University of Southern
California is installing 250 ground-based "monuments"
to electronically track satellites of the Global Positioning
System (GPS).
The resulting network -- the densest of its kind on
the planet -- will enable scientists to follow, in
unprecedented detail, movements of the Earth's crust
in one of the world's most seismically active and
highly populated areas.
"The Southern California scientific community can
now pioneer the use of the most promising new tool
in seismology since the invention of the seismometer,"
says SCEC director Thomas Henyey. "Eventual completion
of the 250-station array will put the full potential
of GPS technology to work in an earthquake-prone region
particularly suited to the task."
GPS makes it possible to locate geophysical monuments
with extraordinary precision. Such monuments, located
at specific key points on the Earth's surface, are
equipped with special electronic units to receive
signals, around the clock, from the 24 GPS satellites
orbiting the earth. Although the monuments may be
separated by scores of miles, a change in their relative
position -- even by no more than a single millimeter,
or about one twenty-fifth of an inch -- can be detected
by the GPS system.
In seismically active areas such as Southern California,
where plate tectonic forces are at work, substantial
earth movements of millimeters to centimeters occur
continuously each year and are readily measurable
by the state-of-the-art GPS technology.
These movements give scientists indications of how
fast strain is building up, where it's concentrated,
and where earthquakes might occur in the near future.
Before and after the January, 1994, Northridge earthquake,
the few GPS monuments then in service revealed important
scientific clues about processes taking place far
underground. GPS technology is particularly valuable
for studying hidden faults, like the one that caused
the Northridge earthquake, according to Henyey. Faults
located far underground are more difficult to study
by other methods.
According to Henyey, SCEC is rapidly expanding a current
network of 40 monument receiver stations. In addition
to providing coverage for the 25,000-square-mile area
extending from the Tehachapi Mountains south to the
Mexican border, and from the Pacific Ocean to the
Colorado River, stations will be concentrated along
a tectonically critical corridor extending through
the Los Angeles basin. Each station will be monitored
daily.
Funding for the project comes from NSF and the W.M.
Keck Foundation.
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