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'Merging Tsunami' Amplified Destruction In Japan
Hugh Pickens writes "The magnitude-9.0 Tohoku-Oki temblor, the fifth-most powerful quake ever recorded, triggered a tsunami that doubled in intensity over rugged ocean ridges, amplifying its destructive power at landfall, as seen in data from NASA and European radar satellites that captured at least two wave fronts that day, which merged to form a single, double-high wave far out at sea. This wave was capable of traveling long distances without losing power. Ocean ridges and undersea mountain chains pushed the waves together along certain directions from the tsunami's origin. 'It was a one-in-10-million chance that we were able to observe this double wave with satellites,' says study team member Y. Tony Song. '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.' The study suggests scientists may be able to create maps that take into account all undersea topography, even sub-sea ridges and mountains far from shore to help scientists improve tsunami forecasts."
Better understanding and forecasting would be a fantastic thing. It would certainly save lives. However, after watching the footage of the tsunami in question, there's a little part of my brain that wonders whether it would do much more than tweak the odds for people in a few marginal cases.
I suppose where there's a much clearer use for this is in making infrastructure and resilience planning decisions. It will never be practical to say "people shouldn't live in areas that might be hit by tsunamis". As the "Boxing Day" tsunami demonstrated, the areas in question are absolutely vast - and as the Japanese tsunami demonstrated, they can stretch miles inland. I just don't see how countries could afford to give up such huge tracts of habitable land to mitigate against the risk of "once every couple of centuries" events. What might be practical, however, is to think about how to site critical pieces of infrastructure (such as... say... nuclear power plants, as well as hospitals, emergency response centres, transportation hubs) so as to minimise their exposure to these events - and understanding the paths that future tsunamis are likely to follow is going to be key to that.
And protecting your key infrastructure is vital to saving lives in the days and weeks after a catastrophe - particularly in nations less wealthy and less resilient than Japan (which understandably struggled even despite those advantages).
I though there was some commission to prevent mergers that cause harm to the general public?
What I find most interesting about tsunami is their ability to move energy so efficiently, with next to no loss. It's a wave traveling in a medium that has very little internal friction. This allows it to travel a tremendous distance without losing a lot of its energy.
The other thing is how it moves the energy when it's out in the ocean. Think of the tsunami when it's out in the middle of the ocean, and is generating a swell of say an inch. It's lifting a two mile column of water an inch up. That's a huge amount of energy.
When that wave approaches land, the distance from sea floor to sea level is much smaller, but the energy is mostly still there. So instead of raising it an inch, you get several meters. They refer to this as "coastal amplification" or something like that, but it's quite the nasty thing to pull when it hits landfall. If you were in a little skiff a few miles off the coast you may not even notice your boat rock, but if you were in that same boat a few hundred feet from the beach you'd be surfing in on a 25 meter high wave. What an amazing difference! It's no wonder Japan got yachts parked on streets a mile in from the coast.
Ocean floor topography plays a role in this too. And then you get effects like waves reflecting off entire continents and other large land masses, and opposite cases where little pockets here and there are sheltered from the effects due random luck involving coastal features. Tsunami are easily just as interesting a study as tornadoes or typhoons in their subtlety and power.
I work for the Department of Redundancy Department.