GPS, a constellation of 24 navigation satellites operated by the U.S. Department of Defense, permits points on the Earth's surface to be located with high precision. The resulting monument network 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 array, which started with only four sites in 1990, has already detected very small motions of the Earth's crust in Southern California associated with the 1992 Landers and 1994 Northridge earthquakes. The GPS receivers operating during the Landers earthquake were able to detect, for the first time, subtle changes in the regional deformation pattern. GPS technology is particularly valuable for studying hidden faults, like the one that caused the Northridge earthquake.
Faults located far underground are more difficult to study by other methods.
The current network was funded by earlier grants from NASA, NSF and USGS to the Jet Propulsion Laboratory and the Scripps Institution of Oceanography. They in turn will make the processed data available to the entire scientific community, where it will be combined with data from other sources to create the most accurate and detailed picture ever of the earthquake hazard in Southern California.