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Satellite Data Give New Insight into Japan’s 2011 Tsunami
December 8, 2011

Only a few buildings survived the tsunami’s wallop in Minamisanriku, seen here in November eight months later. Few towns inside the tsunami zone have begun rebuilding

07 December 2011

Data collected from U.S. and French satellites have led to confirmation of a “merging tsunami,” the monster wave that slammed the northeastern Japanese coastline last March.

Scientists made the discovery using radar satellite data that captured the motion of at least two wave fronts that day. The fronts merged to form a single, double-high wave far out at sea. Ocean ridges and undersea mountain chains pushed the waves together, making a wave capable of traveling long distances without losing power.

Scientist Y. Tony Song of NASA’s Jet Propulsion Laboratory in Pasadena, California, and Professor C.K. Shum of Ohio State University discussed their findings at the American Geophysical Union meeting in San Francisco December 5.

“It was a 1 in 10 million chance that we were able to observe this double wave with satellites,” Song said. He is the principal investigator in the NASA-funded study.

Researchers have suspected for decades that such “merging tsunamis” might be possible, and the superwaves were even thought to be involved in tsunami disasters of the past. But in the vastness of the world’s oceans, the phenomenon had never been spotted before.

“It was like looking for a ghost,” Song said. “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.”

Three satellites actually passed over the building wave in the Pacific Ocean on March 11. All three had radar altimeters on board, devices that measure sea-level changes within a few centimeters.

“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.

Up to now, hazard maps attempting to predict likely spots for a tsunami strike have used only topographical data near a particular shoreline. This study suggests that scientists might be able to make better predictions if they survey much broader undersea topography, even subsea ridges and mountains far from shore.

“Tools based on this research could help officials forecast the potential for tsunami jets to merge,” Song said. “This, in turn, could lead to more accurate coastal tsunami-hazard maps to protect communities and critical infrastructure.”