Saturday, June 20, 2009

NASA-JPL to use new technology to map change in California's surface

Saturday, June 20, 2009
Years of worry create a permanently wrinkled forehead. Laughter and a lifetime of smiles lead to deep creases near the nose and mouth. Decades of squinting create crows feet next to the eyes.

Like a face, the Earth's surface is changing constantly. And, like a face, most of the changes are too subtle to notice as they happen. It's only with a glance through the photo album that the changes become apparent.

Using an airborne radar system and, eventually, a new satellite, NASA plans to create its own photo album of California's faults. It's a tool that should allow earthquake scientists to get a better idea of what faults are doing and which faults might cause earthquakes in the future.

"We can see which faults are active and how active they are," said Andrea Donnellan, one of the NASA Jet Propulsion Laboratory researchers who will study radar images of the Earth's surface in Southern California.

"We can determine if a fault broke recently or not and, if not, we can make an assessment of when the next earthquake might be."

In February, a small NASA jet outfitted with a radar array flew over California, making what amounts to a three-dimensional map of the Earth's surface. In the next few months, the jet, flown out of NASA's Dryden Flight Research Center at Edwards Air Force Base, will repeat its flight.

NASA will map the state four times a year, Donnellan said. Eventually - anywhere from four to 10 years from now - a NASA

satellite will survey the Earth's surface every eighth day, she said.

A computer model will record even the most minuscule changes between the two maps. Those changes, Donnellan said, amount to some shift in the Earth's surface.

"We're interested in measuring the deformation of the Earth's surface," she said. "We can measure all over California how the ground is moving."

Faults are the boundaries between massive rock plates that cover the Earth's surface. As those plates move, they can either slide slowly past each other - a phenomenon that results in small, quiet earthquakes - or get stuck and allow pressure to build up, eventually moving past each other in larger quakes, Donnellan said.

Whether a fault is slow-moving or stuck, NASA's radar should be able to see some tell-tale signs over time, she said.

San Bernardino County is home to sections of two major faults, the San Andreas and the San Jacinto. Sally McGill, a professor of geology at Cal State San Bernardino, said both faults are active and both are, as Donnellan described, stuck.

Over time, as it surveys and resurveys the area, McGill said, NASA's radar array might be able to see strain building along local faults.

"What they might be able to see is elastic strain accumulation," McGill said. "That means the (rock) plates are still trying to move, but they're stuck so they're bending."

Imagine a road crossing the San Andreas Fault, McGill said. If the fault were "creeping," that is, if the rock plates were moving past each other without building up strain, the road would simply break at the point where it crossed the fault, with each side moving away from the other.

But if the fault is building up strain, things would look normal at the point where the road crosses. Go down the road in either direction, and it's a different story.

If the road extended for a few miles on either side of the fault, McGill said, an overhead view of the road might show that after a few years, the road is no longer a perfectly straight line.

"There would be bending on each end of the line," she said.

When faults are stuck, Donnellan said, the built up strain doesn't show at the fault itself.

"If you see some (movement) that's not right at the fault, then the fault is locked," Donnellan said. "So it can produce larger earthquakes."

That's the kind of movement - minuscule changes in a road, for instance - the NASA radar will look for.

Using that information over time will let NASA get a sense of how much strain is building up along a fault. It can use that information, Donnellan said, to determine where, statistically, an earthquake is likely to hit.

"Based on a fault's earthquake history and what the strain (on a fault) looks like now, we can estimate the probability of an earthquake within the next five or 10 years," she said.

That kind of prediction won't help evacuate an area before an earthquake strikes, but it could be helpful in other ways.

"You can target when you're going to retrofit buildings," she said. "You can mitigate a lot more than if you just know the earthquake is going to happen tomorrow."

But that's still years in the future, Donnellan said. NASA won't have enough data for any kind of serious prediction for several years.


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