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August
2, 2007
2006
PLATE MOTION REVERSAL UNLIKELY TO HAVE EASED
SEISMIC STRAIN, EARTHQUAKE ANTICIPATION NEAR ACAPULCO, SAYS
CU STUDY
A reversal of tectonic plate motion between Acapulco
and Mexico City in
the last half of 2006 probably didn’t ease seismic strain in
the region or the
specter of a major earthquake anticipated there in the coming decades,
says a University
of Colorado
at Boulder
professor.
Instead of creeping toward Mexico City at about one inch per year
– the
expected speed from plate tectonic theory – the region near
Acapulco moved in
the opposite direction for six months and sped up by four times, said
CU-Boulder aerospace engineering Professor Kristine Larson. The changes
in
motion were detected by analyzing data from GPS satellite receivers set
up in Guerrero,
Mexico,
that were installed by the National Autonomous University of Mexico
(UNAM)
under the direction of UNAM geophysicist Vladimir Kostoglodov and
augmented by
CU-Boulder.
“The million-dollar question is whether the event makes a
major earthquake in
the region less likely or more likely,” said Larson, whose
research is funded
in part by the National Science Foundation. “So far, it does
not appear to be reducing
the earthquake hazard.”
A paper on the subject by Larson, the University of Tokyo’s
Shin’ichi Miyazaki and UNAM’s Kostoglodov and
José Antonio Santiago was
published Aug. 1 in Geophysical Research
Letters.
Scientists use GPS satellite receivers to record laser pulses from
spacecraft
to measure tiny movements in Earth’s crust.
The question of earthquake hazard is particularly important for
Guerrero, since
it is located 175 miles southwest of Mexico City,
Larson said. “A very large earthquake in
Guerrero would produce seismic waves that would travel quickly to the
Mexican
capital, and since Mexico City
is built on water-saturated lakebed deposits that amplify seismic
energy, the
results would be catastrophic,” she said.
In 1985, a magnitude 8.1 earthquake triggered by the Cocos Plate
dipping under
the North American Plate off the west coast of southern Mexico struck
along the
coast north of Guerrero and killed 10,000 people in Mexico City,
injured about
50,000 and caused an estimated $5 billion in property damage.
Since the last major earthquake in northwest Guerrero was a 7.6
magnitude event
in 1911, many scientists think the area is ripe for a much larger
earthquake,
likely in the range of 8.1 to 8.4, Larson said. Geophysicists refer to
the impending
earthquake as the “Guerrero Gap,” she said.
“Before GPS we thought the ground moved at a constant speed
between
earthquakes,” Larson said. “The recognition of
these transient events where the
plate reverses direction is arguably the most important geophysical
discovery
that has stemmed from the introduction of GPS measurements.”
The Guerrero slip events recorded by Larson and Kostoglodov’s
research team in
2006 are the largest ever reported in the world.
Studies of the Guerrero Gap are helping scientists better understand
other
subduction zones around the world, including the Cascadia region off
the coast
of Washington and Oregon, Larson said. Smaller but much faster
backwards slip
events have occurred there, as have very large earthquakes in previous
centuries.
##
Contact:
Kristine
Larson
University of
Colorado at
Boulder
303-492-6583
Kristinem.larson@gmail.com
This
text derived from:
http://www.colorado.edu/news/releases/2007/285.html
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