This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Office of News Services
University of Colorado-Boulder
3100 Marine Street, 5th Floor
584 UCB
Boulder, Colorado 80309-0584
(303) 492-6431

Contact:
Kristine Larson, (303) 492-6583, Kristine.Larson{at}colorado.edu
Jim Scott, (303) 492-3114

May 14, 2003

GPS SATELLITE RECEIVERS FOUND TO BE NEW TOOL FOR EARTHQUAKE STUDIES

Note to Editors: Contents embargoed until 2 p.m. EDT on Thursday,
May 15.

A serendipitous discovery by a University of Colorado at Boulder-led 
team has shown for the first time that satellite signals from the
Global Positioning System are a valuable new tool for studying
earthquakes. 

CU-Boulder Associate Professor Kristine Larson of aerospace
engineering sciences said seismic waves from a 7.9 magnitude
earthquake in Alaska's Denali National Park in November 2002 were
detected using Global Positioning Satellite, or GPS, receivers as far
away as 2,350 miles from the event. The quake also was picked up by
scores of GPS receivers in Canada and the United States.

GPS is a constellation of satellites originally designed by the U.S. 
military to provide precise positions of ships, tanks, airplanes,
other military equipment and even people. Currently there are 27 GPS
satellites orbiting Earth at roughly 12,500 miles above the planet.

"This is the first time GPS has been used to track seismic waves," 
Larson said. "The signals were large enough to be recorded by GPS 
receivers as far away as Colorado Springs, Colorado."

A paper on the subject will be published electronically by Science 
magazine on Science Express May 15. In addition to Larson, co-authors 
include Paul Bodin from the University of Memphis and Joan Gomberg
from the U.S. Geological Survey's Memphis office.

"The nice thing about GPS is it's great versatility," said Larson.
"In this study we were able to track seismic waves that traveled from
Alaska through Canada to Washington, Montana and Colorado."

GPS also has a number of other scientific uses, like measuring ice
sheet movements, the inflation of magma under volcanoes and plate
tectonics, Larson said. More practical uses of GPS include navigating
aircraft, boats and cars, as well as helping lost hikers find their
way to safety. 

GPS users -- like hikers, boaters and car drivers -- decide how 
frequently their position determination is needed. For measuring
seismic waves from Denali, Larson's team used GPS receivers that were
set to measure positions once each second, or 1 Hertz.

Ordinarily, she said, scientists study earthquakes with seismometers, 
but these often are set for a particular sensitivity range. Because
the earthquake in Alaska was so big, however, many seismometers in
the United States and Canada were not able to measure it. "But GPS
researchers love very big signals," Larson said. "The bigger the
better for us."

The Denali quake ruptured almost 200 miles, causing surface 
displacements of more than 25 feet in some places, she said. "This is 
permanent deformation. The deformations we observed with GPS in the 
lower 48 states also were large, but were caused by the seismic waves 
and did not cause permanent displacement."

For a sense of how big the seismic waves were, a GPS receiver in
eastern Washington moved nine inches horizontally in just 10 seconds,
even though it was 1,500 miles from the Denali earthquake.

There are many continuously operating GPS receivers in the United 
States, she said, and scientists use them primarily to monitor small 
motions on faults. Roughly 250 GPS receivers are operating in Los 
Angeles County, for example, installed in response to the 6.7
magnitude Northridge earthquake in 1994.

The National Science Foundation recently funded a research project
known as Earthscope to study the structure and evolution of the North
American continent, Larson said. Earthscope also is designed to
decipher what causes earthquakes and volcanic eruptions and as part
of that effort, Earthscope engineers will soon be installing 800
additional GPS receivers in the western United States.

 - END OF FILE -
==========

@Message posted automagically by IMTHINGS POST 1.30
---