Space-View Video of Big Quake

THE National Aeronautics and Space Administration (NASA) used satellite photos to make a video showing how the ground moved along fault lines during California's strongest earthquake in decades last June.

It's the first time fault motion has been observed by using images from space, says Robert Crippen, a geologist at the space agency's Jet Propulsion Laboratory in Pasadena, Calif.

Mr. Crippen, not related to the astronaut with the same name, brought the video to San Francisco for the American Geophysical Union's fall meeting.

The five-day convention, which opened last Monday, drew about 6,000 scientists studying Earth, space, the atmosphere, and the oceans.

The video provides a bird's-eye-view of how faults in California's Mojave Desert moved June 28 during the magnitude-7.5 Landers earthquake, California's strongest in 40 years and the third strongest quake this century.

The quake and its magnitude-6.6 Big Bear aftershock killed a child and injured more than 400 people. Movement occurred along several faults in the sparsely populated area roughly 100 miles east-northeast of Los Angeles.

Crippen and Ronald Blom made the video using enlargements of still pictures taken by a French Earth-observing satellite named SPOT. For each of several different sites near the Landers epicenter, Crippen matched pictures taken when SPOT passed directly overhead 11 months before the quake and 27 days afterward.

The technique used to create the fault-motion video is similar to the way weather satellite images are used to show cloud motion on television weather reports, NASA said.

For each site, the video rapidly alternates between the "before" and "after" images. The flickering images show the location of fault lines and in some cases reveal newly formed cracks.

The scientists are using the video to create computerized maps of ground motion. With the help of a supercomputer, they hope such maps will let them measure quake-related ground movements in unprecedented detail.