A new space-based technique for mapping earthquakes views Earth's surface from an angle, instead of from directly above, to map horizontal movement as little as a few millimeters. The resulting data are critical to understanding what the ground under your feet might do in the future.

When an earthquake strikes, seismologists use myriad tools and techniques to map the displaced fault and glean clues about whether the temblor might have added or removed  stress to adjacent faults -- all hints of possible future seismic activity.

The new method overcomes limitations of the Global Positioning System, which requires ground sensors coupled with satellites to measure movement in selected spots. With  GPS subtle but important changes can go unnoticed.

The emerging satellite technique is   fast improving how researchers review an earthquake.  The novel approach is all in the angle of view. Satellite-based radar can already accurately  measure altitude differences from above -- a vertical component seen from directly  overhead. By changing the angle of view to 23 degrees off vertical, adding the element of time, and then applying a little math, researchers can see how far the ground moved horizontally during an earthquake.

 
When a magnitude 7.1 earthquake moved the ground in Southern California on Oct. 16 this year, two plates of Earth's crust slid past each other in what researchers call a strike-slip fault. Like cars on a road moving in the opposite direction, the two plates  moved a total of 17 feet in relation to each other -- each plate moving roughly half that distance.

 
Traditional methods can measure the overall movement, but undetectably small variations at critical points can reveal important information about what the fault might do next, or what adjacent faults might do, Peltzer said. Stress and strain builds and recedes in neighboring faults each time a surrounding batch of rock snaps under the pressure of Earth's continuously moving plates.

informatin adapted from Satellites Get a New Angle on EarthQuakes