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Waves of Destruction: Tsunami
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Catching a Tsunami in the Act

Catching a Tsunami in the Act

by Daniel Pendick

There is no way to stop a tsunami once set in motion, but there are ways to avoid getting killed by one. The Japanese government has invested billions in coastal defenses against tsunamis -- for example, building concrete sea walls to blunt the impact of the waves and gates that slam shut to protect harbors. But for large tsunamis, the rule is this: You can run, but you can't hide. So tsunami hazard experts are working on ways to make sure people know when a tsunami is coming and where they can run to get out of harm's way.

In Japan and the United States, the foundation of tsunami warnings systems is the seismometer. When officials detect a large, shallow earthquake under the ocean, they issue a warning. But this method is plagued by false alarms, since not every earthquake necessarily triggers a tsunami. For example, since Hawaii's Pacific Tsunami Warning Center was established in 1948, about 75 percent of warnings that resulted in costly evacuations turned out to be false alarms.

Design element
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 Tsunami damage.

Design element

After an earthquake off the coast of Peru, the Pacific Tsunami Warning Center in Hawaii created a computer model of the tsunami likely to result.

To get around this, tsunami watchdogs have turned to sensors that sit on the seafloor and detect the feathery touch of a tsunami passing overhead. Japan has laid a series of such bottom-pressure sensors along a cable stretching out from its coastline. Now the National Oceanic and Atmospheric Administration (NOAA) in the United States is adding bottom sensors to its warning system. When the sensors pick up a tsunami, a buoy anchored nearby relays the message to shore via satellite.

Depending on where the tsunami originates, the sensors could give hours of warning time. (See Tsunami spread animation, below.) They could even help people on the U.S. West Coast after an earthquake on the Cascadia fault, which lies minutes away in tsunami travel time. Though minutes of warning may not be enough in all cases, NOAA's Frank Gonzalez, the scientist heading the sensor project, still thinks the buoys are better than nothing. "A minute or two of warning will get you down the road another half mile and you'll be safe," he says. During the 1993 tsunami attack on Okushiri, Japan, Gonzalez says, "there were a number of incidences in which people were educated enough about tsunamis that they were out the door and up the hill in their pajamas within minutes of the warning, and it saved their lives."

Link to animation: Tsunami spread
Link to animation: Tsunami spread

Flash animation, 27K.
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So old-fashioned legwork still is the best defense against a tsunami. But where do you run? Because the height and inland reach of tsunamis can vary so much from one place to another along a coastline, it's not always so obvious. That's why tsunami-plagued regions are preparing for disaster with hazard-mapping programs. Scientists launch computer-simulated tsunamis at a digital representation of a coastline. This enables them to predict when the tsunami waves will hit the coast, how high they will be, and how far inland they will reach. Local officials use the maps to plan evacuation routes and guide zoning decisions. In Oregon, for instance, state law prohibits the construction of "critical facilities" such as hospitals and fire and police stations in mapped tsunami inundation zones.

Article: A Deadly Force | Sidebar One: Catching a Tsunami in the Act | Sidebar Two: Remembrance of Waves Past | ANIMATION
Hell's Crust: Our Everchanging Planet  |  The Restless Planet: Earthquakes
Out of the Inferno: Volcanoes  | Waves of Destruction: Tsunamis


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