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

       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. - more - 2

       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 1,860mile-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.