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Shake, Rattle, and Radar

September 30, 2009
by Adam Mann

Constantly subjected to pressure from inside the Earth, the ground we live on creeps and stretches in ways we don’t normally notice. But scientists at Berkeley’s Active Tectonics Research Group are paying attention. Using data from satellites and a technique called Interferometric Synthetic Aperture Radar (InSAR), they hope to discover key information that could reliably predict earthquakes.

InSAR uses satellites flying 500 miles above Earth’s surface to obtain a detailed two-dimensional map of a particular region over the course of a few weeks. The radar sensors aboard these satellites can scan the ground in excruciating detail; they have a resolution of one-half inch or smaller. Scientists compare two images taken at separate times using a method called interferometry. Essentially, they subtract one picture from the other; wherever the ground has shifted, a pattern somewhat resembling an oil slick appears on the image. These telltale markings provide important clues to the behavior of the earth before and after a quake.

Professor Roland Burgmann, who works at Berkeley’s Seismological Lab, is thrilled with the technique. “There is a huge amount of detail about the nature of an earthquake that we can obtain more and more rapidly. I think it’s fair to say that for most recent continental earthquakes, InSAR-based studies have made significant contributions.”

The reason for its success lies in the method’s unique advantages over ground-based observation. InSAR can be used to detect strain building up in a particular region, allowing scientists to target areas for intense geological research and deploy their resources more effectively. It is also able to see “blind thrust” faults, where fault lines lie just below the surface. Such faults have given rise to extremely damaging earthquakes, including the 1994 Northridge quake that shook Los Angeles and caused an estimated $40 billion in property damage and lost business. Measuring and modeling of changes such as buckling and warping of the ground can help scientists determine where to expect earthquakes.

Many researchers, including Burgmann, remain skeptical as to whether scientists will ever go beyond mere probability based forecasting for a particular fault line. Nevertheless, NASA has proposed launching a satellite named DESDynI that would be dedicated to InSAR studies of the Earth. With this satellite in orbit, scientists would be able to more quickly obtain a huge amount of detail about the nature of earthquakes. Perhaps this information will uncover new possibilities and steer us in the best direction for more research.

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