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PUBLIC INFORMATION OFFICE
JET PROPULSION LABORATORY
CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIF. 91109 TELEPHONE: (818) 354-5011
Contact: Joan Zyda
FOR IMMEDIATE RELEASE Oct. 23, 1991
Strike-slip earthquake faults, which are prevalent on Earth
in several varieties, have been found on Mars and on two of
Jupiter's Galilean satellites, Europa and Ganymede, according to
a planetary geologist at the Jet Propulsion Laboratory in
Pasadena, Calif.
Dr. Matthew P. Golombek of JPL's Earth and Space Sciences
Division is a co-convener of a symposium on the discoveries at
the Geological Society of America's 1991 annual meeting on
Wednesday, Oct. 23 at the San Diego Convention Center. The title
of the symposium will be "Strike-Slip Faulting: Geological and
Geophysical Perspectives."
A strike-slip fault refers to a geological process whereby
motion occurs parallel to the surface expression of the fault.
"Strike-slip faults are relatively uncommon tectonic
features in our solar system. No other planet or satellite has
nearly the number or variety of strike-slip faults found on
Earth," said Golombek, a structural geologist who specializes in
Earth and planetary tectonics.
However, studies of planetary images from spacecraft reveal
that strike-slip faults exist on Mars, Europa and Ganymede. The
faults on Europa and Ganymede suggest that a thin mechanical
lithosphere existed on those bodies in the past, Golombek said.
The lithosphere is the strong outer layer of the planets and
satellites that includes the crust and the outer part of the
mantle.
The faults are not active on Mars, Europa or Ganymede at
present. But on Europa, the faults indicate that quake activity
probably took place there "about a hundred million years ago,"
Golombek said.
Meanwhile, on Mars and Ganymede, the faults show that
strike-slip faulting occurred on those bodies "a few billion
years ago," he added. In contrast, the strike-slip faults on
Earth remain active today.
On Mars, about 10 strike-slip faults have been sighted. The
faults are about 10 to 20 kilometers (6.2 to 12.4 miles) long and
show a slippage (or displacement) of less than 1 kilometer (0.62
mile).
But the faults on Europa, the second Galilean satellite
around Jupiter, and Ganymede, the third Galilean satellite and
the largest satellite in the solar system, are significantly
larger and more numerous.
On Europa, about 100 strike-slip faults have been spotted.
The faults are about 50 to 100 kilometers (31 to 62 miles) long
and show a slippage of 5 to 10 kilometers (3.1 to 6.2 miles).
On Ganymede, about 100 such faults have been found. They areabout 100 kilometers (62 miles) in length, showing a slippage of
10 kilometers (6.2 miles).
"By studying these features," Golombek said, "planetary
geologists can get a better understanding of the physical
processes involved in the strike-slip faulting of Earth."
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# 1392 JPL-PIO