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Sensors may aid quake predictions

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LOS ANGELES — Scientists installed the last of 250 satellite monitoring stations Friday that will track minuscule ground movements in Southern California — a step they hope eventually will allow them to predict earthquakes.

More than seven years after seismologists were jolted into action by the 1994 Northridge quake, scientists will be able to record as little as a millimeter of movement in the Earth's crust using the Southern California Integrated Global Positioning System Network.

Scientists unveiled one of the space-age spindly legged white domes at the Glendale Civic Auditorium. They said someday they hope the system — called SCIGN — will allow them to predict earthquakes.

"Over the long term, we believe, we can get to a place of understanding where we can ultimately forecast these events," said Ghassem Asrar, associate administrator for earth science at NASA.

"It will allow us to predict future earthquakes with much greater accuracy, as well as study in much greater detail the fundamental processes of distortion that are the causes of earthquakes," said Tom Jordan, director of the Southern California Earthquake Center, which will oversee the project.

Earlier this week, the 250th SCIGN station was placed at Joshua Tree National Park. The initial stations were drilled into the ground in the early 1990s, but the Northridge Earthquake prompted greater interest and funding for the $20 million project.

The 6.7-magnitude Northridge Earthquake left 57 dead, 1,500 seriously injured, more than 24,000 buildings vacated and has now cost nearly $50 billion, Asrar said.

"The impact of this disaster, which was one of the worst natural disasters in U.S. history, convinced NASA that it was time to apply years of research and development to study the reduction of earthquake risk," Asrar said.

After the earthquake, the network was expanded to 50 sites. Since 1996, 200 additional sites have been installed. The stations are located on private property, along freeways, atop dams and on an oil drilling platform.

Scientists at the Southern California Earthquake Center designed and will manage the system. NASA's Jet Propulsion Laboratory; the Scripps Institution of Oceanography at the University of California, San Diego; and the U.S. Geological Survey also participated in the project.

Linked to an orbiting cluster of satellites, the GPS stations will provide continuous data for 50 years or more about otherwise imperceptible shifts in the Earth's crust.

"With this technology, signals from the GPS system are used to measure changes as small as one millimeter, or one-25th of an inch, over distances that are tens of miles apart," said Ed Stone, chairman of the Science, Engineering and Liberal Arts Grant Program Committee at the W.M. Keck Foundation.

With more than 200 faults in Southern California that can produce earthquakes above magnitude 6, SCIGN greatly improves scientists' ability to assess seismic hazards and quickly measure plate movements that occur during and immediately after earthquakes.

Scientists hope SCIGN will allow them to understand the interaction between Southern California's 10 major faults, including the mighty San Andreas Fault.

"That is, how an earthquake can trigger another sometimes even larger event at nearby faults," said Ken Hudnut, chairman of the SCIGN Executive Committee for the U.S. Geological Survey. "We have in Southern California over half of the nation's earthquake risk, and we are applying SCIGN to mitigate the risk of this threat."

SCIGN has already begun to provide valuable earthquake-related data to scientists, surveyors, utilities, emergency planners, government agencies, and commercial photogrammetry and imagery companies. SCIGN data is available on the Internet at www.scign.org.

The California Department of Transportation uses SCIGN data to focus on which structures are most likely to be shaken in earthquakes and seismically retrofit the facilities.

Caltrans Chief Deputy Doug Failing said last year Caltrans retrofitted 671 freeway bridges in Southern California.

"Not one major freeway structure collapsed during the Northridge Earthquake of 1994 that had been seismically retrofitted prior to this earthquake," Failing said. "The damage we did sustain to those seven freeway structures that did collapse was the result of seismic retrofit work not being complete or not yet under way at the time."

Another new earthquake monitoring device being installed is a laser strain-meter along the east side of the Glendale Freeway that will travel back and forth inside a 2,000-foot-long pipe to precisely measure the distance between the end points of the pipe.

"The strain-meter is so sensitive that if we were to take the L.A. Basin and squeeze it over its entire breadth by no thicker than a human hair, the change would be easily detected," said Frank Wyatt of the Scripps Institution for Oceanography.