Catastrophic “merging tsunami” doubled Japan devastation

The catastrophic tsunami, which hit the Japan shores in March 2011, was a long- hypothesized ‘merging tsunami’ that doubled its destructive power before reaching the shore, researchers say.

Satellites captured not just one wave front that day, but at least two, which merged to form a single double-high wave far out at sea – one capable of travelling long distances without losing its power.

Ocean ridges and undersea mountain chains pushed the waves together, but only along certain directions from the tsunami’s origin.

The discovery by researchers from NASA and the Ohio State University has helped explain how tsunamis can cross ocean basins to cause massive destruction at some locations while leaving others unscathed, and raises hope that scientists may be able to improve tsunami forecasts.

“It was a one-in-ten-million chance that we were able to observe this double wave with satellites,” said Y. Tony Song, a research scientist at NASA’s Jet Propulsion Laboratory (JPL) and the study’s principal investigator.

“Researchers have suspected for decades that such ‘merging tsunamis’ might have been responsible for the 1960 Chilean tsunami that killed many in Japan and Hawaii, but nobody had definitively observed a merging tsunami until now.”

According to C.K. Shum, Ohio State University, it is now possible to forecast tsunami danger more accurately, in specific coastal regions across the world.

“We were very lucky, not only in the timing of the satellite, but also to have access to such detailed GPS-observed ground motion data from Japan to initiate Tony’s tsunami model, and to validate the model results using the satellite data.”

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“Now 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.”

The researchers conjectured ridges and undersea mountain chains on the ocean floor deflected parts of the initial tsunami wave away from each other to form independent jets shooting off in different directions, each with its own wave front.

“Tools based on this research could help officials forecast the potential for tsunami jets to merge,” Song added.

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