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Environment

#84: Yardstick for Killer Waves


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When a magnitude 8.8 earthquake ravaged Chile in February, the Pacific Tsunami Warning Center in Hawaii put most of the Pacific Rim on alert. With no way to know how big the resulting ocean wave might become, the center’s geophysicists had no choice but to prepare for the worst.

Aiming to do better, Tony Song of NASA devised a much more precise tsunami prediction system based on GPS readings; he tested it successfully for the first time this past year. Song’s technique predicts the exact scale of a tsunami by tracking ground motions to estimate how much water has been displaced on the ocean floor—and, by extension, how much energy is feeding the wave.

When the Chile earthquake struck, Song’s system showed that an underwater fault had slipped almost 10 feet, potentially enough to produce a tsunami several yards high. But then Song crunched the numbers and saw that the tsunami scored only a moderate 4.8 on his 10-point intensity scale, so he correctly predicted that it would not spread far beyond Chile.

Soon nations around the world, including India, Italy, Portugal, and Taiwan, began calling Song to inquire about his prediction system. He envisions eventually deploying one GPS receiver for every 12 miles of coastline to track the strength of developing tsunamis. “GPS adds a new dimension, a more complete picture that is very fast,” Song says. “We will tell not just what the tsunami is, but what it will be.”

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