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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 are about 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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