Magazine article National Defense

Scientists Say They Are Closer Than Ever to Predicting Earthquakes

Magazine article National Defense

Scientists Say They Are Closer Than Ever to Predicting Earthquakes

Article excerpt

* Every time a major earthquake strikes, governments are criticized for not responding faster. The U.S. military, often called upon to assist in relief operations, usually arrives on the scene within hours or days. One way to speed up response efforts is by predicting exactly when and where a quake will occur so that authorities can mobilize in advance. But nailing down a specific time and place has remained an elusive endeavor despite considerable research by seismologists who for decades have had mixed results attempting to forecast quakes. Now new findings are offering hope.

Researchers have discovered that there are warning signs that can be detected in the weeks and hours prior to temblors. If monitored with proper sensors, the signals could help military officials better position troops for relief efforts.

Quakes result when the Earth's tectonic plates slip suddenly on a geological fault, or break in the crust. That slip releases pent up kinetic energy that travels to the surface in waves. Several million quakes rock the planet annually, the U.S. Geological Survey reports. But only a handful of those tremors reach the destructive magnitudes that cause widespread damage and claim lives.

A number of countries are investing resources to develop systems to detect the small mechanical waves that often precede earthquakes by a few seconds. But there are other signs of an imminent tremor. Casual observers have noted seeing lights in the sky for hours or days prior to quakes. Some have noticed animals behaving oddly while others have measured changes in telecommunications signals and anomalies of infrared light on the ground. These phenomena long have been dismissed as hallucinations or coincidences, but researchers have correlated them to subsequent Earth-shaking episodes.

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The cause of these seemingly unrelated occurrences has been traced to a single culprit: the rocks lying deep within the Earth's crust. As tectonic plates move, they place enormous pressure on rocks at the faults. Rocks are normally thought to be insulators. But when stressed they release particles called positive-hole charge carriers that travel tens of miles through the crust to the surface.

Friedemann Freund, a San Jose State University physics professor who is conducting rock-stressing experiments at NASA's Ames Research Center, has measured electrical currents flowing out of pressurized stones ranging in size from millimeter fragments to boulders weighing several tons. "The idea that rocks are insulators is no longer valid," he says. "If you have square kilometers of area, you can pump thousands of amperes through the Earth's crust. …

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