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 should help researchers forecast future earthquake hazards in the greater Los Angeles area.
"GPS is the most important new technology to emerge for the study of earthquakes in decades," says Tom Henyey, director of the Southern California Earthquake Center (SCEC) in Los Angeles, a National Science Foundation Science and Technology Center. "This information will allow 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. Continuous GPS measurements will also allow for more rapid regional damage assessment after large earthquakes."
GPS is a constellation of 24 Earth-orbiting satellites, arranged so that several are "visible" from any point on the surface of the Earth at any time. A user on the ground with a GPS receiver can determine his or her precise location by measuring signals from the GPS satellites.
The continuous, earthquake-related measurements from the GPS network will allow scientists to make a high-precision survey of the southern California terrain. Information from the network of receivers will be used to create maps of strain accumulation along fault lines that will enable scientists to evaluate future probabilities of regional earthquake hazards, and develop earthquake scenarios for specific faults.
Currently, the network has 40 GPS receivers up and running, with the remaining 210 receivers scheduled to be installed over the next three years. The receivers are placed about six miles (10 kilometers) apart, usually in open fields. With data from the 40 receivers, scientists have determined that the Earth has continued to move, mostly in quiet and without us feeling it, since the Northridge quake in 1994. "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," says David Jackson, science director of SCEC.
The GPS measurements will also be useful during and after earthquakes. Scientists can measure ground motions from earthquakes, and identify the fault that ruptured and help evaluate regional deformation and stress changes in near-real-time with an automated system. The network will also help in monitoring important structures. GPS receivers placed on or near dams, bridges, and buildings will allow off-site detection of probable damage to those structures.
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 NASA's Jet Propulsion Laboratory in Pasadena, California, several school districts, and educators' groups to develop a science unit for use in schools. "The Elastic Planet" will give students access to the data being gathered by the network.