How do you measure almost imperceptible movements on a fault or detect magma swelling beneath the earth?
Until recently, scientists had to set up equipment at the place they wanted to study. That's fine if you're looking at a single, safe spot, but what if the focus is a 50-mile-long fault or the crater of an angry volcano?
A new technique known as interferometric synthetic aperture radar, or InSAR -- developed in part by Stanford geophysicist Howard Zebker -- is helping to solve that problem. The process involves combining radar measurements to come up with precise data. In an early test, after the magnitude 7.3 earthquake east of Los Angeles in 1992, researchers used the technique to measure the fault's readjustment.
"You can't call up earthquakes at will," says Paul Segall, a Stanford geophysics professor who uses the InSAR technology. "So anytime we have new data, we're excited."
One limitation has been that the satellites used for InSAR were built for other purposes. Zebker says that within five years he expects NASA to orbit a more sensitive system, specifically designed to help scientists understand how stresses build on faults before earthquakes.
