96 lines
4.2 KiB
Plaintext
96 lines
4.2 KiB
Plaintext
SUBJECT: MORE ON QUAKES ON MARS FILE: UFO3347
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11/6/92: VIKING PHOTOS SHOW MARS MAY EXPERIENCE FREQUENT QUAKES
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Paula Cleggett-Haleim
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Headquarters, Washington, D.C. November 6, 1992
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Jim Doyle
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Jet Propulsion Laboratory, Pasadena, Calif.
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RELEASE: 92-198
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Mars was once very active tectonically and may still be shaken by quakes
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daily, according to scientists using NASA's Viking Orbiter photos of the red
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planet's surface.
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In a science paper published today, Drs. Matthew Golombek, W. Bruce
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Banerdt and David M. Tralli of the Jet Propulsion Laboratory and Dr. Kenneth
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L. Tanaka of the U.S. Geological Survey said Mars is more seismically active
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than the moon, but less so than Earth.
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"Because Mars is smaller than Earth, little more than half the size, a
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magnitude 6 quake on Mars would have 10 times the effect it would on Earth,"
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Golombek said.
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Marsquakes of that magnitude may occur about once every 4 and a half
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years, he said. A marsquake of about magnitude 4, however, might happen
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somewhere on the planet once a month on an average. Yet, a quake of magnitude
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4 would be detectable throughout the planet, again because of its size and
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presumed structure.
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Tectonic features on Mars are found mostly around the Tharsis region, a
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large volcanic plateau with associated features that cover the entire western
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hemisphere of the planet.
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Tectonism in that region occurred mainly during two periods in the
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planet's history -- the earliest possibly as long ago as 4-billion years and
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the most recent ending possibly less than one-billion years ago.
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Features that formed during the first seismic period include many narrow
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graben or long ditch-like or trough features with faults along their sides.
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Also formed at that time was a system of concentric wrinkle ridges, larger
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graben and rifts, and the deep rift valleys of Mars' great 1,860-mile-long
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(3,000-kilometer) canyon, the Valles Marineris.
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During the second period, tectonism caused an enormous set of radial
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grabens that extend up to thousands of kilometers from the center of the
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plateau and rift zones of Valles Marineris, along with other prominent
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features.
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Tectonism and seismic activity have decreased from the earlier period to
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the present, Golombek said, as would be expected if the seismic activity is
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governed by simple cooling of the lithosphere -- the rigid outer crust and
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upper part of the mantle -- of the planet.
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The scientists said that while Mars is less seismically active than Earth,
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their studies predict that about two marsquakes of magnitude 5 or greater
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occur per year, about a hundred quakes of magnitude 3 or greater occur per
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year.
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"That is a promising prospect for seismological investigations on future
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missions to Mars," Golombek said.
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Golombek is the Project Scientist for the Mars Environmental Survey
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(MESUR) project which would place a network of landers, each with a
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seismometer, in different locations on the Martian surface. Recordings of
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marsquakes by seismometers at different locations will help determine the
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internal structure of the red planet.
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The network of instrumented landers is planned to be deployed over three
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Mars launch opportunities. Four would be sent in 1999, four more in 2001 and
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the final eight launched with four each on two launch vehicles in 2003.
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A precursor mission called MESUR Pathfinder is under study as part of
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NASA's proposed Discovery Program of small, low-cost planetary missions.
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MESUR Pathfinder would place a single lander on Mars with a robotic rover
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deploying, among other instruments, a seismometer as early as 1996.
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The paper, published today in Science magazine, is entitled "A Prediction
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of Mars Seismicity from Surface Faulting."
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The Discovery Program and the Viking mission are managed by NASA's Office
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of Space Science and Applications, NASA Headquarters, Washington, D.C.
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- END OF FILE -
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