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Despite advances, science of forecasting a tsunami is inexact

Weeks after the Feb. 27 earthquake hit Chile, a blackout affected millions of residents Sunday. The country is trying to recover from the 8.8-magnitude earthquake that rocked the country last month and caused a tsunami that damaged the country's coastal region and put other countries throughout the Pacific on alert. Strong aftershocks hit the country March 5 and again March 11.

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By Joel Achenbach and Rob Stein
Washington Post Staff Writer
Sunday, February 28, 2010

Saturday was a tense day in and around the Pacific Ocean. There was a wave on the loose. It was reputed to travel at the speed of a jet airplane. Beyond that, this tsunami was a mystery. No one knew precisely how big it would be when it came ashore. So went a very long day, full of anxious waiting and much staring at a sea that did little to signal its intentions.

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The sirens sounded at dawn in Hawaii, where more than 144,000 were told to head to higher ground. Tsunami warnings were posted from Panama to Japan, from Ecuador to New Zealand. Australia made the tsunami-warning list. So did Antarctica.

Authorities told Californians to get out of the water to avoid being swept away by strong currents. The forecasts showed the waves reaching Nome, Alaska, more than 24 hours after the huge earthquake off the coast of Chile.

By Saturday evening, the calamity had not materialized. Although reports were still coming in, it did not appear to have been a killer tsunami like some in the past.

Jenifer Rhoades, tsunami program coordinator for the National Weather Service, said officials would rather err on the side of warning people about the worst-case scenario than play down the risk.

"Forecasting tsunamis is a relatively new science. We learn a lot every time we have an event like this," she said. "We dodged a bullet this time, but since tsunami science is not exact, we erred on the side of caution."

The tsunami when it reached Easter Island on Saturday measured only about a foot above sea level. Ditto on Tahiti. On the Marquesas Islands, it reached six feet. Talcahuano, a coastal town in Chile, reported a 7.7-foot wave. There were reports of three people drowned and more missing on the islands of Juan Fernandez, off the Chilean coast.

By the time the tsunami reached Hawaii, the waves topped out at three feet, and warnings soon were lifted for most of the Pacific. Even though Hawaii was spared, other areas might remain in danger, Nathan Becker, an oceanographer at the Pacific Tsunami Warning Center in Honolulu, said Saturday night.

"It's still moving across the Pacific, and could go all the way to Japan," Becker said. "Hawaii may not be having big waves, but there might be somebody further downstream who does. Japan might, or perhaps Guam."

Indeed, early Sunday, Japan was evacuating coastal areas, still fearing waves of more than 9 feet.

If nothing else, this was a dramatic test of the Pacific tsunami warning system, which uses buoys sprinkled across the ocean to detect tsunamis in real time. The Indian Ocean lacks such a system, which might have minimized the casualties from the catastrophic tsunami of 2004.

Even with scientific measurements, forecasts, alarms and civil defense measures, Saturday's events showed that tsunamis are unpredictable. And even if a wave is measured precisely in the open sea, its effect can be greatly magnified by shallow bays and harbors.


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