Japan tsunami a rare ‘double wave’

By AAP with Emily Verdouw December 8, 2011
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The Japan tsunami generated from one of the most destructive earthquakes was a rare double wave, says NASA.

THE MASSIVE EARTHQUAKE OFF the coast of Japan in March 2011 caused a rare ‘merging tsunami’ in which two waves combined to amplify the destruction after landfall, according to NASA.

For the first time ever, US and European radar satellites captured images of the two wave fronts of the tsunami, confirming the existence of the long-hypothesised process, which forms a “single, double-high wave far out at sea.”

“This wave was capable of travelling long distances without losing power. Ocean ridges and undersea mountain chains pushed the waves together along certain directions from the tsunami’s origin,” NASA said in a statement. “The discovery helps explain how tsunamis can cross ocean basins to cause massive destruction at some locations while leaving others unscathed,” it said, adding that the research could help to improve forecasts.

‘One-in-10 million chance’ of double tsunami wave sighting

“It was a one-in-10-million chance that we were able to observe this double wave with satellites,” said Tony Song, of NASA’s Jet Propulsion Laboratory, which partnered with Ohio State University for the 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,” he said.

But DR Gary Huftile, geologist and lecturer at Queensland University of Technology, says it sounds like they’re throwing a new term at the tsunami when the real issue is that Japan’s earthquake mapping led to a tragic mistake – one they failed to prepare for.

“They thought they had sufficiently built up their protection of those nuclear power plants to a certain level, and that level off the coast line dropped – and so they got flooded.”

Japan tsunami hard to predict

Gary explains that as this tsunami formed, the coast line dropped to the extent that it appeared nothing like it was before, a dramatic occurrence that couldn’t have been predicted and that was exacerbated by the location of the nuclear plant.

“I think the only thing that would have worked would be if they didn’t trust their own maps and essentially exaggerated their levels of flooding. They essentially had mapped every tsunami that ever occurred and had it very well mapped; Japan are very good at this – no one in the world are better than Japan at this – but because they didn’t build everything a couple of metres higher than what maps showed, they got it wrong. I think it’s a thoroughly understandable mistake, but it’s still a mistake,” he says.

The 9.0-magnitude underwater earthquake and tsunami on March 11 left 20,000 people dead or missing, devastated large areas of north-eastern Japan and sparked a nuclear crisis at the Fukushima nuclear plant.

VIDEO: NASA simulation of the double tsunami