Earthquake scientists today unveiled the Southern California Integrated GPS Network (SCIGN), a new type of ground motion monitoring network. Unlike other instrument networks that record shaking, SCIGN tracks the slow motion of the Earth's plates by using the Global Positioning System (GPS) -- a constellation of satellites, originally designed for military navigation, that are used to determine precise locations on the ground. With SCIGN, the link between the motions of the plates that make up the Earth's crust and the resulting earthquakes is now being observed by an array of GPS stations operating in southern California and Baja California -- one of the world's most seismically active and highly populated areas. On July 2, 2001, the 250th SCIGN station was installed.

Using SCIGN data to measure deformation of the Earth's crust, which can occur as movement on faults or as slow distortion of the ground, scientists can determine how strain builds up slowly over time before being released suddenly during earthquakes. The accumulated strain is directly related to earthquake potential, and measurement of it contributes to earthquake hazard assessments that help motivate people to prepare for earthquakes. "We have in southern California over half of the nation's earthquake risk, and we are applying GPS technology in new ways to assess this risk," said SCIGN chairman Ken Hudnut of the U.S. Geological Survey.

Scientists of the Southern California Earthquake Center (SCEC) designed and manage SCIGN. NASA's Jet Propulsion Laboratory (JPL), the Scripps Institution of Oceanography (SIO) at the University of California at San Diego, and the U.S. Geological Survey (USGS) are the main participants in SCIGN. Funding for SCIGN is provided by NASA, the W.M. Keck Foundation, the National Science Foundation (NSF) and the U.S. Geological Survey (USGS).

"Thanks to SCIGN's sponsors, the southern California scientific community can pioneer the use of the most promising new tool in geophysics since the invention of the seismometer," said SCEC director Tom Henyey, a professor of earth sciences at the University of Southern California.

Yehuda Bock of the Scripps Institution of Oceanography recalled the history of SCIGN. "The initial sites went into ground in the early 1990s," he said. "The Northridge earthquake gave us a tremendous boost in interest and funding in the project, expanding the network to 50 sites. Since about 1996 we have been working on adding an additional 200 sites in the area. So today is the culmination of 10 years of work to complete the project. But since the network has been designed to last at least 50 years, SCIGN is just beginning."

Frank Webb of the Jet Propulsion Laboratory added, "Decades ago NASA began looking at the plate motions by using large radio telescopes around the world. Since then the ground systems and processing capability have improved such that we can measure movement as small as a few millimeters a year with very portable GPS instruments."

Such small changes are significant. Ghassem Asrar, associate administrator for earth science at NASA said, "NASA's Earth Science Enterprise is dedicated to understanding how the Earth is changing and what the consequences of those changes are to our daily lives, the economy and the environment. Today we make a great stride forward in this endeavor with the development of a new tool, based upon space technology. SCIGN will provide us with the ability to study the development of earthquake potential at the boundary between two of the Earth's great tectonic plates. Research using SCIGN data will provide other government agencies, states, and local communities with new knowledge of these dangerous events."

Edward Stone, chairman of the science, engineering, and liberal arts grant program committee of the W.M. Keck Foundation summarized the value of the new network-- "the SCIGN array offers an important new way to observe the steady deformation that shapes the Earth's crust around us. The W. M. Keck Foundation of Los Angeles is especially pleased to have helped SCEC realize this new capability, one that should benefit all who live here."

"SCEC, an NSF Science and Technology Center, has been very effective in developing interagency partnerships and incubating large-scale innovative experiments such as SCIGN," said Margaret Leinen, assistant director for geosciences at the National Science Foundation. "With the help of our partners, NSF will continue to support such facilities and research that translate into concrete benefits to society."

John Filson, national program coordinator, Earthquake Hazards Office of the USGS said, "precise measurement of deformation, to assess earthquake hazards, was pioneered by USGS scientists using lasers from the early 1970s through the late 1980s -- when GPS came along. Now with SCIGN, southern California is "wired" like no place else in the U. S. Never before has a network like SCIGN been built. It is unique in the world, and other countries are learning from SCIGN as they attempt to understand and cope with their earthquake risks."

SCIGN has already begun to provide valuable earthquake-related data to scientists, surveyors, utilities, emergency planners, government agencies and commercial photogrammetry and imagery companies and others. SCIGN data are freely available to anyone over the Internet (www.scign.org). Each month, people retrieve more than 50,000 SCIGN data files, and this number continues to increase. The majority of the hundreds of SCIGN data users are scientists working in universities and government agencies around the world.

The other major use of SCIGN data is by land surveyors and engineers in southern California. According to William Young of the California Spatial Reference Center, "the new GPS stations replace survey markers that surveyors have customarily used to determine property boundaries and infrastructure locations. Continual movement of the ground moves the survey markers and continually changes their location, affecting the accuracy of surveys. With GPS we know daily how much a particular monument may be moving."

The California Department of Transportation is also working with SCIGN. Doug Failing, chief deputy of District 7, said, "not one major freeway structure collapsed during the Northridge earthquake of 1994 that had been seismically retrofitted prior to this earthquake. 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 underway at the time. Knowledge derived from SCIGN will allow Caltrans to focus on which structures are most likely to be shaken in earthquakes, and apply future advancements in seismic strengthening to these structures."

Another new earthquake monitoring device being installed is a laser strainmeter along the east side of the Glendale Freeway, made possible with the support of Caltrans. Here a laser beam will travel back and forth inside a 2000-foot long pipe to precisely measure the distance between the endpoints of the pipe. Any change indicates deformation of the Earth's crust. The laser strainmeter complements the GPS measurements by making observations of strain that are approximately 100 - 1000 times more sensitive. "The strainmeter is so sensitive that if we were to take the LA 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 of Oceanography.

For more information about the Southern California Earthquake Center and SCIGN visit www.scec.org and www.scign.org.

EDITOR:

Publication-quality photos can be found at http://www.scec.org/scign/images.html.

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