NASA: Two Waves Formed Japan's Destructive Tsunami

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A tsunami that devastated coastal areas of Japan in March was actually the result of two waves coming together to form a "merging tsunami," according to researchers from NASA and Ohio State University.

NASA and European radar satellites captured images of at least two wave fronts forming in the ocean after a 9.0 earthquake struck the region in March. They came together in a single wave that, because of its joined strength, was able to travel long distances without losing steam over ocean ridges and mountain chains that continuously pushed the waves together, according to NASA.

This observation--powered by satellite data and images and computer simulations--was a rare glimpse of how tsunamis can cross miles of ocean to cause massive destruction in some places, while leaving others unharmed, researchers said.

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They hope to use the information to better predict tsunami activity and develop better forecasting and warning systems. The combined earthquake/tsunami disaster killed nearly 16,000 people and created a nuclear crisis at Japan's Fukushima Daiichi power plant.

"It was a one in 10 million chance that we were able to observe this double wave with satellites," said Y. Tony Song, a research scientist with NASA's Jet Propulsion Laboratory (JPL). Song is the principal investigator for the study, which paired NASA and Ohio State University researchers and was funded by the space agency.

He said researchers had believed for years in the phenomenon of two waves forming to cause a tsunami of this kind, but it had never before been proven.

"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," Song said.

That altimeter--a device that measures sea-level changes--was aboard the NASA-Centre National d'Etudes Spaciales Jason-1 satellite, which passed over the tsunami March 11. Two other satellites--the NASA-European Jason-2 and the European Space Agency's EnviSAT--also crossed over the wave at different locations and measured it as it was forming.

Current predictions for where a tsunami will hit are based on topography maps of the sea floor, which has ridges and mountains that push tsunamis in various directions, according to NASA. For this reason, its destruction once it hits land can appear random.

However, by verifying the wave formation observed by the satellites through computer simulations and using other data, scientists may be able to create maps that take into account a vaster region of the seafloor to make better predictions in the future, according to NASA.

One of JPL's aims is to better predict tsunami activity. Last year the facility successfully tested a GPS-based prediction system for assessing the risk and size of tsunamis that may result from large earthquakes.

A JPL team used realtime data from its Global Differential GPS network to successfully predict the size of the tsunami that resulted from a magnitude 8.8 quake on Feb. 27, 2010 in Chile.

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