By Kristina Bartlett Brody, Science News
Jeff McGuire says he does not want to be known as the guy who predicts earthquakes. But in September 2008, a magnitude 6.0 quake shook the bottom of the ocean at a fault along the East Pacific Rise—within 10 kilometers from where and within the year-and-a-half window that McGuire and his colleagues had predicted.
It is in fact possible to predict a large quake on a short timescale, says McGuire, of the Woods Hole Oceanographic Institution—when the geology is relatively simple, as on a transform fault along the East Pacific Rise. And his year-and-a-half time frame is short compared with the typically decades-long forecasts for large earthquakes on other types of faults.
On the continents, however, the geology is not so simple. Most big quakes happen at the boundaries between oceanic and continental plates, on faults known to have experienced big quakes in the past. Yet some of the largest quakes in the United States happened nowhere near a plate boundary, and some big quakes have occurred where no fault had previously been known to exist. Decades of false starts and failures have led many experts to conclude that making accurate short-term predictions of those rare but big earthquakes is a hopeless quest.
“We understand the complexity of earthquakes,” says David Jackson, a seismologist at the University of California, Los Angeles. “Big ones start as little ones and find enough energy to keep going.” Figuring out when big ones are going to happen requires knowing much more about how quakes begin, and also about how big they will grow once they start.
“It may be that the amount of information that we need to have about the fault to predict how big an earthquake will grow is, for all practical purposes, unknowable,” says geophysicist Greg Beroza of Stanford University. “Still, until we have a deeper understanding of fault behavior, I think it’s important to keep an open mind.”
More and more researchers’ minds have been opening. While scientists aren’t exactly optimistic, some of their pessimism about prediction is fading, says Susan Hough, a seismologist in the U.S. Geological Survey’s Pasadena, Calif., office. “There’s a lot more talk in serious seismology circles about prediction.”
Fueling the new attitude are tools, knowledge, technologies and data that researchers didn’t have before, says Mike Blanpied of the USGS Earthquake Hazards Program and the National Earthquake Prediction Evaluation Council. Some 4,000 stations, for example, now monitor Earth’s known faults. Global Positioning Systems constantly watch the ground move. Instruments that measure tiny changes in strain and motion deep underground are embedded in some of the world’s most dangerous faults. And computers store and process huge data sets on it all.
These ingredients add up to a perfect recipe for a mathematical approach to understanding earthquakes—and offer the intriguing possibility that a quantitative picture of the ways quakes change how rocks share and trade stress underground could help in determining when a small quake will become a big one.
“There’s a lot of data now to work with that didn’t exist earlier,” Blanpied says.
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