High above Earth where seismic waves never reach, satellites may be able to detect earthquakes–before they strike.

Although earthquakes seem to strike out of the blue, the furious energy that a quake releases builds up for months and years beforehand in the form of stresses within Earth’s crust. At the moment, forecasters have no direct way of seeing these stresses or detecting when they reach critically high levels.

That may be changing, however. Satellite technologies being developed at NASA and elsewhere might be able to spot the signs of an impending quake days or weeks before it strikes, giving the public and emergency planners time to prepare.

“There are several satellite-based methods that show promise as precursors to earthquake activity,” says Jacob Yates, a researcher at NASA’s Goddard Space Flight Center. “One method is Interferometric-Synthetic Aperture Radar (InSAR). Basically, InSAR is when two radar images of a given tectonic area are combined in a process called data fusion, and any changes in ground motion at the surface may be detected.”

This technique is sensitive enough to detect slow ground motions as tiny as 1 mm per year. That kind of sensitivity, combined with the landscape-wide view that satellites can offer, lets scientists see the tiny motions and contortions of land around a fault line in more detail than ever before. By watching these motions, they can figure out where points of high strain are building up.

A group of NASA and university scientists led by Carol Raymond of JPL recently studied the feasibility of forecasting earthquakes from space. Their report, which was released in April, outlines a 20-year plan to deploy a network of satellites–the Global Earthquake Satellite System (GESS)–using InSAR to monitor fault zones around the world.

With some practice, says Raymond, scientists eventually should be able to use the InSAR data to infer when stresses in the Earth’s crust have reached a dangerous level, issuing a monthly “hazard assessment” for a given fault. Forecasters might report that the likelihood of having a major quake on, say, the San Andreas fault during the coming month is 2%, or 10%, or 50%.

Current methods are less certain. For example, the US Geological Survey recently released an updated assessment of the earthquake risk in the San Francisco Bay Area based on the seismic history of the area, its geology, and computer models. The study reported a 62% chance of a major quake (magnitude 6.7 or greater) hitting the area sometime within the next 30 years–not exactly something to plan your day around.

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