Scientists have begun installing a network of 250 Global Positioning System (GPS) receivers that will continuously measure the constant, yet physically imperceptible, movements of earthquake faults throughout Southern California. This information, which in many cases will be gathered and analyzed with the help of local students, should help researchers forecast future earthquake hazards in the greater Los Angeles area.
NASA Administrator Daniel S. Goldin dedicated a new site in the Southern California Integrated GPS Network (SCIGN) today at Rialto High School, before a demonstration of the technology to science students from the school. Goldin was accompanied by U.S. Rep. George Brown (D-Calif.), the ranking minority leader of the House Science Committee, and representatives from the National Science Foundation and the U.S. Geological Survey.
"This network is a tremendous example of how technology developed for space benefits life on Earth. This interagency project will give us detailed information never before available to track the invisible geologic strains and stresses that lie beneath the California landscape," Goldin said. "Such data should give us fresh insight into the forces that produce earthquakes, and could one day help reduce the loss of life and property from such disasters."
GPS uses data transmitted from a constellation of 24 Earth- orbiting satellites that are jointly governed by the departments of Defense and Transportation. The satellites are arranged so that several of them are "visible" from any point on the surface of the Earth at any time. A user on the ground using a GPS receiver can determine the site's precise location by coordinating the signals from the satellites.
"The surface of the Earth is constantly moving and Southern California is being squeezed in the process. The GPS network will continuously measure movements of the Earth's crust with a precision of one millimeter per year, which will show us where strain is building up," said Dr. Andrea Donnellan, a member of the SCIGN coordinating committee at NASA's Jet Propulsion Laboratory (JPL), Pasadena, CA.
"GPS is the most important new technology to emerge for the study of earthquakes in decades. This information will permit us to improve our estimates of the regional earthquake hazard in Southern California and to prioritize earthquake mitigation activities, including emergency preparedness and retrofit strategies," said Dr. Tom Henyey, director of the USGS-NSF Southern California Earthquake Center (SCEC) in Los Angeles. "Continuous GPS measurements will also allow for more rapid regional damage assessment following large earthquakes."
The earthquake network began in 1990 with only four GPS receivers as a prototype project funded by NASA. It detected very small motions of the Earth's crust in Southern California associated with the June 1992 Landers and the January 1994 Northridge earthquakes. "The GPS receivers operating during the Landers earthquake were able to detect for the first time a subtle change in the regional deformation pattern, which is potentially of great importance for studying the physics of earthquakes and hazards mitigation," said Dr. Yehuda Bock, a SCIGN executive board member from Scripps Institution of Oceanography, University of California, San Diego.
Currently, the SCIGN has 40 GPS receivers up and running, with the remaining receivers scheduled to be installed over the next three years.
"With data from the 40 receivers, we have determined that Southern California has continued to move since the Northridge quake in 1994. This may mean that stress is being relieved in part without earthquakes, which may reduce the overall earthquake hazard," JPL's Donnellan said. "We will try to determine if other faults have been loaded as a result of the earthquake."
"The survey data are particularly important for identifying active buried faults that do not reach the ground surface. Such faults may be common in the Los Angeles metropolitan region," said Dr. David Jackson, science director of SCEC.
The GPS measurements will also be useful to characterize earthquake damage. "The network will help agencies monitor important structures. GPS receivers placed on or near dams, bridges and buildings would allow off-site detection of probable damage to those structures. We are collaborating with Los Angeles County in a pilot study of continuous GPS monitoring of Pacoima Dam," said Dr. Ken Hudnut, SCIGN executive board member at the U.S. Geological Survey in Pasadena.
Many of the receivers are being placed at schools so that students can be involved in the experiment. SCEC's "Global Science Classroom" at the University of Southern California has formed a partnership with JPL, several school districts and educators' groups to develop a science unit for use in schools. The unit, titled "The Elastic Planet," will give students access to the data being gathered by the network.
"This network is a model of interagency cooperation between NASA, the U.S. Geological Survey and the National Science Foundation, as well as with local governments and schools," Goldin said. "Students will get hands-on science experience in using real data. It should ignite their enthusiasm for science while providing a genuine public service."
SCIGN is a consortium of institutions with a common interest in using GPS for earthquake research and mitigation. The consortium is coordinated by the Southern California Earthquake Center (SCEC), a National Science Foundation Science and Technology Center headquartered at the University of Southern California. The lead institutions in the installation and operation of SCIGN are: JPL, the Institute of Geophysics and Planetary Physics-Scripps Institution of Oceanography at the University of California, San Diego, the United States Geological Survey, the University of California, Los Angeles and the University of Southern California.
Mary Hardin, JPL, Pasadena, CA
October 28, 1996
NASA Headquarters, Washington, DC
National Science Foundation, Arlington, VA
U.S. Geological Survey, Reston, VA
For more information, visit the Global Positioning System home page.
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