Space technology that lets scientists use satellites to measure deformations in the surface after major earthquakes can yield important clues to future slippage along fault lines if it's moved in close for better resolution.
This interferogram of the Calexico, Calif., area was collected from a NASA Gulfstream III equipped with a synthetic aperture radar (SAR). In the 110-by-20-kilometer swath, the different-colored bands overlaid on a Google Earth satellite image represent surface displacements of 11.9 centimeters, or about 4.7 inches.
The bands reveal changes in the distance from the aircraft - flying at an altitude of 41,000 feet - and the ground in GPS-guided passes on Oct. 21, 2009, and April 13, 2010. A week before the second flight, on April 4, a magnitude 7.2 earthquake struck nearby Baja California, in Mexico, killing two people, injuring hundreds more and causing severe damage to buildings. Aftershocks are marked with red, orange and yellow dots, and major faults are shown as red lines.
Experts at the Jet Propulsion Laboratory study maps like this to learn more about the San Andreas fault in California, which is part of a fault system that stretches deep into Mexico. The airborne radar, known as UAVSAR for Uninhabited Aerial Vehicle SAR, flies most of the length of California every six months to measure strain along the fault lines that could lead to more earthquakes.
"UAVSAR's unprecedented resolution is allowing scientists to see fine details of the Baja earthquake's fault system activated by the main quake and its aftershocks," said Scott Hensley of JPS, principal investigator on the project. "Such details aren't visible with other sensors."
Some of those sensors -- SARs on Japanese and European satellites -- allowed JPL's Eric Fielding to measure ground displacements of as much as 3 meters -- about 10 feet -- deeper into Mexico. But this enlargement of one of the California airborne passes shows changes in ground level as small as a centimeter.
"Geologists are finding the exquisite details of the many small fault ruptures extremely interesting and valuable for understanding the faults that ruptured in the April 4 quake," stated Fielding in a JPL press release on the subject.