You had to have felt this: That 7.2 magnitude quake that resonated across the Southwest April 4? The earth moved alright -- a whopping two-and-a-half feet. New airborne-radar images of the epicenter of the Sierra El Mayor quake released by the NASA's Jet Propulsion Laboratory in Pasadena tell some of the story.
The rocking and rolling 32 miles south-southeast of Calexico took part of the earth's crust 31 inches downward and to the south, according to NASA. The images are the first-ever airborne-radar depictions of what a major shaker can do to the planet. Actually , the scientists found the earth moved even more -- much more -- south of the border:
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The quake's maximum ground displacements of up to 3 meters (10 feet) actually occurred well south of where the UAVSAR measurements stop at the Mexican border. However, these displacements were measured by JPL geophysicist Eric Fielding using synthetic aperture radar interferometry from European and Japanese satellites and other satellite imagery, and by mapping teams on the ground.
NASA scientists got the shots by using flying a Gulfstream-III aircraft 41,000 feet in the air. The plane took off from its Dryden Flight Research Center, Edwards, Calif.
Since last year NASA has been using airborne-radar to measure the distance between the plane and the earth along parts of the San Andreas fault, thus providing a baseline for quakes such as the Sierra El Mayor shaker.
"The data are giving scientists a baseline set of imagery in the event of future quakes," states NASA. "These images can then be combined with post-quake imagery to measure ground deformation, determine how slip on faults is distributed, and learn more about fault zone properties."