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Despite advances, science of forecasting a tsunami is inexact

A crowd gathers above Oahu’s southern shore in anticipation of a possible tsunami in Honolulu. Quake waves were measured at only 3 feet or less in Hawaii. Officials praised the Pacific tsunami warning system.

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A crowd gathers above Oahu’s southern shore in anticipation of a possible tsunami in Honolulu. Quake waves were measured at only 3 feet or less in Hawaii. Officials praised the Pacific tsunami warning system.

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.

Evacuation alarms first sounded in Hawaii's vulnerable coastal areas at 6 a.m. Saturday. The Navy moved more than a half dozen vessels to try to avoid damage from a tsunami. A frigate, three destroyers and two smaller vessels were sent out of Pearl Harbor and a cruiser out of Naval Base San Diego.

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 occurred off the coast of Chile.

By Saturday evening, the calamity had not materialized. Japan, however, was still bracing for a direct hit and waves up to 10 feet. Scientists worried the giant wave could gain strength as it rounded the planet and consolidated — as happened in 1960 when a tsunami killed dozens in Hilo, Hawaii, then went on to claim some 200 lives in Japan — though the first wave to hit Japan's outlying islands today was just 4 inches high.

Jenifer Rhoades, tsunami program coordinator of the National Weather Service, said officials would rather err on the side of warning people about the worst-case scenario. "Forecasting tsunamis is a relatively new science. We learn a lot every time we have an event like this," she said. "In some ways you want to ensure people respond to the event based on the information we have available to us."

The wave when it reached Easter Island Saturday measured only about a foot above sea level. Ditto on Tahiti. On the Marquesas Islands, it reached 6 feet. Talcahuano, a coastal town in Chile, reported a 7.7-foot wave.

But by the time the tsunami reached Hawaii, the waves measured only about 3 feet or less.

"I think we've dodged a bullet," Gerard Fryer of the National Tsunami Warning Center told reporters in Honolulu. "We've been watching the gauges, and the wave heights are below danger levels everywhere."

Fryer said the waves were only about half the size of what scientists had predicted would hit the islands, calling their relatively small size "our biggest surprise."

"We'll be looking into that — it's been a long day," he said.

In retrospect, he said, "this is almost the best sort of tsunami you could possibly have. One that's big enough that everyone can see that something happened, but not big enough to cause any damage."

Witnesses on the Big Island, where the first of the waves hit, reported an apparent shallowing of the water at Hilo Bay, followed by fast-moving currents filled with sediment as water rushed in.

Other islands had similar reports, according to Los Angeles Times. In Oahu, surfers were wading through shin-high water in areas that normally would be waist-deep before the current flowed back.

At Kahului Harbor in Maui, residents said, sediment-laden waters flowed about 100 yards onshore.

Authorities said there were isolated reports of looting in low-lying areas that had been evacuated for hours.

"We've checked with each county. There was no assessment of any damage in any county, which was quite remarkable," Hawaii Gov. Linda Lingle said. "It's just wonderful that nothing happened and no one was hurt or injured."

Half an hour before the tsunami was forecast to hit, Waikiki Beach was an eerie, nearly deserted scene. Cars lined the roads on higher ground, with onlookers, many in an apparently festive mood, gathering in good viewing spots. But tourists and beachgoers began flooding back from high ground once the warning was canceled shortly before 2 p.m.

Los Angeles County fire officials did not warn people to stay off beaches. But National Weather Service meteorologists said harbors could see a little bit more turbulence. Minor damage to a dock was reported in Ventura. A surfing contest outside San Diego went on as planned.

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 precisely measured in the open sea, its effect can be can be greatly magnified by shallow bays and harbors.

"Harbors are like musical instruments. They have specific pitches, if you wish, specific frequencies," said Emile Okal, a professor of earth and planetary sciences at Northwestern University who has spent his career studying tsunamis. "The structure of a harbor is such that for some of these periods it can amplify the wave."

Okal was in Tahiti, in a laboratory, when his instruments sounded an alarm signaling a major earthquake. The initial reading showed an 8.5-magnitude quake in Chile, Okal said. It was in the early evening, Tahiti time. He would not get more than 40 minutes sleep during the night.

He knew what tsunamis could do. He knew that the 2004 tsunami not only killed over 100,000 in Indonesia, and some 30,000 in Sri Lanka, but it crossed the breadth of the Indian Ocean and killed 300 on the African coast in Somalia.

Over short distances, tsunamis can create waves of stunning dimensions. A tsunami in 1946 created a wave 138 feet high that obliterated a lighthouse in the Aleutian Islands where five people were stationed. "They found some human remains a few days later, but not much to speak of," Okal said.

Information from the Associated Press, Los Angeles Times and New York Times was used in the report.

Despite advances, science of forecasting a tsunami is inexact 02/27/10 [Last modified: Sunday, February 28, 2010 12:01am]
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