Destructiveness of Japan's Tsunami Explained

NASA and Ohio State University researchers found it was a "merging tsunami," where two wave fronts merged to create a double-high wave front far out to sea that could travel long distances without losing power.

Researchers from NASA and Ohio State University gave a briefing Dec. 5 during the American Geophysical Union meeting in San Francisco in which they explained why the March 2011 tsunami that devastated parts of northeastern Japan was so powerful. It was "a long-hypothesized 'merging tsunami'" produced when two wave fronts merged.

They based this on data from three NASA and European radar satellites that showed at least two wave fronts that day. These merged to form a double-high wave far out at sea that could travel long distances without losing power; ocean ridges and undersea mountain chains pushed the waves together along certain directions from the tsunami's point of origin. The discovery helps to explain how tsunamis cause major damage at some locations while leaving others unharmed, and it may help in tsunami forecasting.

Research scientist Y. Tony Song of NASA's Jet Propulsion Laboratory in Pasadena, Calif., and Professor C.K. Shum of Ohio State gave the briefing, according to NASA's news release. "It was a one in 10 million chance that we were able to observe this double wave with satellites," said Song, the principal investigator in the NASA-funded study. "Researchers have suspected for decades that such 'merging tsunamis' might have been responsible for the 1960 Chilean tsunami that killed about 200 people in Japan and Hawaii, but nobody had definitively observed a merging tsunami until now. It was like looking for a ghost. A NASA-French Space Agency satellite altimeter happened to be in the right place at the right time to capture the double wave and verify its existence."

"We can use what we learned to make better forecasts of tsunami danger in specific coastal regions anywhere in the world, depending on the location and the mechanism of an undersea quake," Shum said.

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