Using GPS to Monitor the Earth’s Movement

Caitlin Dempsey



Earlier this month, a network of research stations located across Southern California and Baja California was dedicated in order to detect minute movements of the earth.

On July2, 2001, the 250th station was installed. Each of the 250 stations in the Southern California Integrated GPS Network (SCIGN), is linked to a Global Positioning System (GPS).

Using a network of GPS to detect tectonic activity

The goal is to detect any tectonic shift in the Earth’s crust in an attempt to factors leading to earthquakes. Many of these processes are still poorly understood and scientists hope that analyzing data gathered before and after earth movements will improve their knowledge base.

Most of what is known about earthquakes has not been supported by direct observation. This new network will change that.

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A seismically active region of the world

A black and white map showing "Earthquakes in Southern California 1981-1993".
Earthquakes in Southern California 1981-1993.

The Southern California region is one of the most populated and seismically active regions of the world. According to Bock, contraction of the Los Angeles Basin is occurring at a rate of 7-8mm per year (Southern California Earthquake Center Quarterly Newsletter, Vol. 5, No. 2, 2000):

“Is all the strain accumulating underneath downtown L.A., or is it being distributed among small strike-slip faults over the basin? What is the role of thrust faulting? Is most of the contraction taken up by vertical thrust faults, some of which you can’t see? Is some of it taken up by the squeezing out to the sides on strike-slip faulting? Where is that 7 mm/yr?”

Through data gathered by the research stations, the stress allocation of this movement will be studied.

Measuring the underlying stress that creates earthquakes

Most of the stations are located on public property such as schools. One of the criteria was a clear view of the sky in order to receive signals from the GPS satellites.

Until now, most earthquake centers around the region have mostly measure amplitude and location of tremblers.   These stations seek to measure the underlying stress that causes the earth to shake.

The network will be able to measure the earth’s movement along tectonic plate boundaries within a precision of 1 millimeter.

A multi-agency effort to study earthquakes

SCIGN was designed and will be managed by the Southern California Earthquake Center.   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) will also be contributing to the research effort. NASA, the W.M. Keck Foundation, the National Science Foundation (NSF) and the U.S. Geological Survey (USGS) are providing funding for this project.

Solving an earthbound problem Ken Hudnut, the current chair of SCIGN states, “Southern California is the premiere place in the world where significant tectonic problems exist and have been solved in large part by GPS.” (Southern California Earthquake Center Quarterly Newsletter, Vol. 5, No. 2, 2000).

A map showing the location of GPS stations that will be used to study earthquakes.
Current GPS permanent station network in Southern California, showing movement of locations throughout the region because of the large scale movement of the Pacific Plate relative to the North American Plate.


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About the author
Caitlin Dempsey
Caitlin Dempsey is the editor of Geography Realm and holds a master's degree in Geography from UCLA as well as a Master of Library and Information Science (MLIS) from SJSU.