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NSF PR 01-55 - June 29, 2001
Media contacts:
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Cheryl Dybas, NSF
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(703) 292-8070
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cdybas@nsf.gov
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Harvey Leifert, AGU
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(202) 777-7507
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hleifert@agu.org
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Andrea Elyse Messer, Penn State
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(814) 865-9481
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aem1@psu.edu
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Program contact:
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David Fountain, NSF
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(703) 292-8552
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dfountai@nsf.gov
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This material is available primarily
for archival purposes. Telephone numbers
or other contact information may be out
of date; please see current contact information
at media
contacts.
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All Earthquake Fault Lines not Equal
Temperature Tied To Movement
While most scientists assume that both sides of a geologic
fault move equal distances during an earthquake, National
Science Foundation (NSF)-funded researchers at Pennsylvania
State University and the University of Miami have
discovered that not all strike slip faults act that
way.
"In the past, no one looked at the contrast between
the two sides of a strike slip fault," says geologist
Kevin Furlong at Penn State. "These faults have always
been modeled as if both sides were equal by definition."
Furlong, doctoral student Rocco Malservisi, and geologist
Timothy Dixon of the University of Miami investigated
the Eastern California Shear Zone, a strike-slip fault
system running parallel to the San Andreas fault about
240 kilometers [150 miles] east of San Francisco.
This area, on the Nevada/California border, is the
eastern edge of the interface of the Pacific and North
American plate boundaries and is linked to the San
Andreas fault.
"By considering variations in mechanical properties
of the crust, these scientists have put a new twist
on how we look at ground motion associated with large
earthquakes along strike-slip faults," says David
Fountain, program director in NSF's division of earth
sciences, which supported the research. "The results
suggest that ground motion could be much larger on
one side of a fault than the other. These differences
in motion persist long after an earthquake occurs
and, using modern instrumentation, such as GPS and
satellite interferometry, should be detectable for
decades."
In a strike-slip fault, the ground on each side of
the fault moves along the fault line, but in opposite
directions. The western side of this fault (consisting
of the Sierra Nevada Mountains) and the eastern side
of the fault (known as the Basin and Range) have very
different heat flow properties. Researchers believe
this difference causes the contrast between the two
sides.
"The Sierra Nevada to Basin and Range is an abrupt
transition, thermally and mechanically," says Furlong.
The heat flow on the Sierra Nevada side is much lower
than on the Basin and Range side, making the Sierra
Nevada side colder as well. These temperature differences
can be dramatic.
Malservisi, Furlong, and Dixon report on their on-site
study of this fault in the July 15 issue of the journal
Geophysical Research Letters, published by
the American Geophysical Union. Using permanent location
markers and Geographic Positioning System (GPS) equipment,
they were able to record the difference in movement
on each side to about one millimeter [0.04 inches].
"Before the accuracy of GPS became so good, it was
impossible to do this kind of research," says Furlong.
"We could not have seen the difference before."
NSF is an independent federal agency which supports
fundamental research and education across all fields
of science and engineering, with an annual budget
of about $4.5 billion. NSF funds reach all 50 states,
through grants to about 1,800 universities and institutions
nationwide. Each year, NSF receives about 30,000 competitive
requests for funding, and makes about 10,000 new funding
awards.
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