NSF PR 96-67 - October 30, 1996
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New Technology to Help Measurement and Study of Earthquakes
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.
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