Japan tsunami footage to help predict future waves

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Scientists will study footage like this to learn more about tsunami behaviour

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When the powerful earthquake of 11 March triggered a tsunami that struck swathes of Japan's north-east coast, residents, TV crews and fixed cameras captured images of the devastating wave.

Footage of the debris-filled water sweeping across fields and through houses has since been broadcast all over the world.
But as well as providing an idea of how it felt to experience the tragedy first-hand, experts say the images can now be used to better understand the characteristics of tsunamis and help save lives in the future.
"Without exaggeration, it will lead to a quantum leap in the way that we calculate and we estimate how fast the tsunami propagates on land," says Dr Costas Synolakis from the University of California and the Hellenic Centre for Marine Research in Greece.
He has studied more than 20 tsunamis over the past two decades.
He says that while there are multiple methods for predicting the path of a tsunami across the ocean, much less is known about what happens when the giant wave reaches land.

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In the business we call them the fingers of God, it's almost like the tsunami energy is channelled in certain specific directions.”

End Quote Dr Costas Synolakis University of California

Dr Synolakis told BBC World Service's Science in Action programme that the footage emerging from Japan would help address this lack of knowledge.

"We really did not understand as well how the tsunami floods and inundates inland," he said. "It really depends on what kind of structures you have, whether it's farm land, whether it's an airport, whether it's roads.
"All of this is going to be incredibly useful data to develop even better models to forecast inundation. It'll be wonderful if we were able to do that five, 10, 15 minutes before it actually happens."
As an earthquake strikes, early models of tsunamis are produced by millions of calculations and vast amounts of data-gathering which attempt to accurately predict the size and path of the wave.
Much of this data is collected by tsunamographs, instruments that lie up to 5,000 metres below the water's surface, measuring changes in water pressure and transmitting information to nearby buoys.
The buoys then send this data, via satellite, back to warning centres.
"As the wave keeps on propagating across the Pacific, more and more tsunamograph recordings become available, so the forecast improves," said Dr Synolakis.

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A Japanese news team run for cover as the tsunami hits Sendai

However, even with these increasingly sophisticated techniques, there are still surprises.
Often, due to inconsistencies in the sea bed and other natural variations, a tsunami can take a dramatically different course.
"In the business we call them the fingers of God, it's almost like the tsunami energy is channelled in certain specific directions," he said.
Another limitation of this system, known as the Method of Splitting Tsunami (MOST), is that it deals almost exclusively with what tsunamis do in the ocean and to the immediate coastline, whereas the Japan disaster has shown the need for a better understanding of what occurs when a wave heads far inland.
"The application of MOST has been primarily to try to predict inundation and save people along open beaches," said Dr Synolakis. "It hasn't really been used to predict tsunami water heights and depths on powerplants and structures because that had been considered a secondary priority by civil defence.

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"The first thing that civil defence around the world wants to know is how many people are at risk along coast lines. They never paid attention to industrial facilities. I think this event is going to change all that."

Dr Synolakis believes lessons learned from Japan will undoubtedly lead to safer, more flood resilient buildings - particularly power plants.
"Back 40 years ago, when [the Fukushima Daiichi nuclear plant] was designed, we didn't understand tsunamis at all. We were basically in the very early stages of estimating tsunami floods."
Yet, even with better equipped building defences, some natural disasters will always cause devastation.
"I've been in the field in over 20 tsunamis since 1992. This was the worst that I've ever seen - it was unimaginable, even though I consider myself a fairly seasoned tsunamista."