From: baalke@kelvin.jpl.nasa.gov (Ron Baalke)
Subject: Viking Photos Shows Evidence of Marsquakes
Followup-To: sci.space
News-Software: VAX/VMS VNEWS 1.3-4   
Keywords:  Viking, Mars, JPL, USGS, MESUR
Reply-To: baalke@kelvin.jpl.nasa.gov
Organization: Jet Propulsion Laboratory
Date: Sat, 7 Nov 1992 07:39:44 GMT

Paula Cleggett-Haleim
Headquarters, Washington, D.C.         November 6, 1992
(Phone:  202/358-1547)

Jim Doyle
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone:  818/354-5011)

RELEASE:  92-198

VIKING PHOTOS SHOW MARS MAY EXPERIENCE FREQUENT QUAKES

     Mars was once very active tectonically and may still be
shaken by quakes daily, according to scientists using NASA's
Viking Orbiter photos of the red planet's surface.

     In a science paper published today, Drs. Matthew
Golombek, W. Bruce Banerdt and David M. Tralli of the Jet
Propulsion Laboratory and Dr. Kenneth L. Tanaka of the U.S.
Geological Survey said Mars is more seismically active than
the moon, but less so than Earth.

     "Because Mars is smaller than Earth, little more than
half the size, a magnitude 6 quake on Mars would have 10
times the effect it would on Earth," Golombek said.

     Marsquakes of that magnitude may occur about once every
4 and a half years, he said.  A marsquake of about magnitude
4, however, might happen somewhere on the planet once a month
on an average.  Yet, a quake of magnitude 4 would be
detectable throughout the planet, again because of its size
and presumed  structure.

     Tectonic features on Mars are found mostly around the
Tharsis region, a large volcanic plateau with associated
features that cover the entire western hemisphere of the
planet.

     Tectonism in that region occurred mainly during two
periods in the planet's history -- the earliest possibly as
long ago as 4-billion years and the most recent ending
possibly less than one-billion years ago.

     Features that formed during the first seismic period
include many narrow graben or long ditch-like or trough
features with faults along their sides.  Also formed at that
time was a system of concentric wrinkle ridges, larger graben
and rifts, and the deep rift valleys of Mars' great 1,860-
mile-long (3,000-kilometer) canyon, the Valles Marineris.

     During the second period, tectonism caused an enormous
set of radial grabens that extend up to thousands of
kilometers from the center of the plateau and rift zones of
Valles Marineris, along with other prominent features.

     Tectonism and seismic activity have decreased from the
earlier period to the present, Golombek said, as would be
expected if the seismic activity is governed by simple
cooling of the lithosphere -- the rigid outer crust and upper
part of the mantle -- of the planet.

     The scientists said that while Mars is less seismically
active than Earth, their studies predict that about two
marsquakes of magnitude 5 or greater occur per year, about a
hundred quakes of magnitude 3 or greater occur per year.

     "That is a promising prospect for seismological
investigations on future missions to Mars," Golombek said.

     Golombek is the Project Scientist for the Mars
Environmental Survey (MESUR) project which would place a
network of landers, each with a seismometer, in different
locations on the Martian surface.  Recordings of marsquakes
by seismometers at different locations will help determine
the internal structure of the red planet.

     The network of instrumented landers is planned to be
deployed over three Mars launch opportunities.  Four would be
sent in 1999, four more in 2001 and the final eight launched
with four each on two launch vehicles in 2003.

     A precursor mission called MESUR Pathfinder is under
study as part of NASA's proposed Discovery Program of small,
low-cost planetary missions.  MESUR Pathfinder would place a
single lander on Mars with a robotic rover deploying, among
other instruments, a seismometer as early as 1996.

     The paper, published today in Science magazine, is
entitled "A Prediction of Mars Seismicity from Surface
Faulting."

     The Discovery Program and the Viking mission are managed
by NASA's Office of Space Science and Applications, NASA
Headquarters, Washington, D.C.

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    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
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