New data shows power of Japan tsunami

ATLANTA, March 8 (UPI) -- U.S. researchers say their mapping of the March 2011 tsunami that devastated Japan could help the country prepare for possible similar future events.

Using eyewitness video and terrestrial laser scanners from atop the highest buildings that survived the tsunami, researchers at Georgia Tech have mapped the tsunami's height and flood zone to learn more about the flow of the devastating currents.

The mapping could produce flooding forecasts that influence future evacuation plans and building designs, preventing loss of life and property damage in Japan and in other areas of the world susceptible to tsunamis, a Georgia Tech release said Thursday.

"The ultimate goal is to save lives," researcher Hermann Fritz said. "In order to do so, we have to have a better understanding of what worked and didn't work."

The researchers surveyed the impact of the tsunami on a fishing town in Kesennuma Bay, where 1,500 people died.

The bay has been hit by historic tsunamis in 1896, 1933, 1960 and 2010, making it the most vulnerable in Japan, and its coastal structures and other mitigation measures were designed based on conservative, historic high-water marks rather than probable maximum tsunamis, they said.

Fritz and his team used lasers to scan the port and bay entrance, creating a three-dimensional, topographic model of the flood zone.

They determined the tsunami reached a maximum height of 30 feet, followed by outflow currents of 36 feet per second less than 10 minutes later, a speed impossible to survive or navigate by vessels, Fritz said.

"What we can learn from the hydrograph is confirmation that the water goes out first, drawing down to more than negative 3 meters (30 feet) on the landward side of the trench, which can make vessels hit ground inside harbors," Fritz said.

"During the subsequent arrival of the main tsunami wave, the water rushing back in changed the water level by 40 feet, engulfing the entire city in 12 minutes," he said.