Environment: Interview

Lost in Japan: How to defend against tsunamis

Dr. Jörn Lauterjung, who develops tsunami early warning systems at the German Research Centre for Geosciences, tells us more about these monster waves.
The wave from a tsunami crashes over a street in Miyako City, Iwate Prefecture in northeastern .../ Credits: Reuters
Allianz Knowledge: It wasn’t the earthquake but the following tsunami that caused most devastation in Japan. How did this massive wave develop?
Jörn Lauterjung: This tsunami was triggered by an 8.9-magnitude earthquake around 250 miles (400 kilometers) from Tokyo, off the coastal city of Sendai.

The tremor itself was a result of the Pacific tectonic plate submerging beneath the North American and Eurasian tectonic plates.

I always compare this with a flat spring as they are used for utility vehicles. What basically happened was that the submerging plate, our flat spring, couldn’t stand the stress anymore.

When it cracked, the upper part of the Pacific plate rebounded, thereby rising the sea level by up to 4 meters along a 100 to 150 kilometer-long fracture zone. This resulted in a wave that travelled at high speed through the ocean towards the shore.

How big was this tsunami compared to the Indian Ocean tsunami in 2004?

Even if we talk of the Japan earthquake as one of the four or five strongest quakes ever recorded, the energy set free by the Sumatra tremor was even higher in terms of sea level displacement. The Japan tsunami reached a wave height of about 10 meters. The one which hit Indonesia surged by up to 25 meters.

But it’s not only the height of the wave that is so dangerous. It’s the wave length of 200 meters and more that unfolds the deadly impact as this huge volume of water enriched with debris, cars, ships and even parts of houses crashes into shore. The chances of surviving in this water are close to zero.

Dr. Jörn Lauterjung develops tsunami early warning systems at the German Research Centre for Geosciences. Dr. Jörn Lauterjung develops tsunami early warning systems at the German Research Centre for Geosciences. What lessons were learned from the Indian Ocean tsunami?
What the 2004 tsunami exposed was that there was no warning system in place. Unlike in the Pacific Ocean, there was no real precedent for a tsunami like this in the Indian Ocean.

Of course that changed immediately afterwards. Structures were developed to deal with this kind of natural force. National Tsunami Warning Focal Points (TWFPs) were established, local authorities were trained in disaster management, which led to a higher awareness on the part of the people.

Escape routes from beaches now point out where to evacuate in case of emergency: parking garages, hotels and other public houses can be used as shelter.

In some areas with no natural hills and higher buildings even Tsunami Evacuation Raised Earth Parks (TEREPs) have been established. I would say that if another tsunami similar to the one of 2004 happened far less people would perish.

Speaking of tsunami warning systems, did the Japanese one fail?
Not at all. The Japanese warning system is known as one of the best in the world. They have a very dense net of seismometers. They know that they face one of the highest tsunami risks in the world.
Three minutes after the first shock a major tsunami warning was issued. The only problem was that the wave hit the coastline just 15 minutes later. It was just not enough time for evacuation.
That sounds terrifying because if Japan can’t stand such a tsunami, who else can?
There is very little you can do against a 10 or 20-meter tsunami. The best protection is nature itself. This was the lesson to be learned from the Indian Ocean tsunami. Coral reefs provide a good defence. They weaken the tsunami on their way ashore. If the coral reefs off the coast of Sri Lanka had not been removed by humans, the impact would have been less disastrous.

Of course you can think of artificial control structures, like breakwaters made out of concrete. But these would be enormous building works raising the question of cost and benefit.

Statistically speaking, a tsunami of this size happens once every 100 to 150 years. For the Indian Ocean this natural disaster only occurs once every 400 to 600 years.

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Comments (12)

Gagan deep from earth a planat: 15.02.2014, 19:13

yes i do undeerstand it very harmfull for us at last earth is our plant we are living at we need to understand differance between eartt and human .hunman has feeling .at second end earth does not have any feeling .in this cramstance human is prior to earth . human is most power full animal of this earth so being human

Team toxic 3313: 07.09.2013, 03:02

those are some good defences but truly there is no defence that can stop a tsunami completely.

janica smith: 23.09.2011, 07:15

the only thing i can say about natural disaster specially tsunami is that,,,,,it is not man made,whether we like it or not, it will happen anytime, in my part , all i can say is just pray , and pray and pray to the almighty,,,,i am sure evry good thing will happen to good people,,,,,thats all,,,,,janica of phiils

dev dongol: 29.08.2011, 01:40

Just stay away from the coast so that settlement is out of the reach by the tsunami. Connect the sea side by roads only for visits. You may like to visit my blog (devbahadurdongol.blogspot.com) for the solutions to climate change and power crisis (no coal, no thermal, no nuclear ) only hydro.
My email address is dev.dangol@yahoo.co.uk

nasangsil: 17.05.2011, 04:27

great information-thank you.

Michael Grimm (editor): 11.04.2011, 10:40

@Wimpy3: Thank you very much for your comment. You are absolutely right, the interaction of tectonic plates is a very complex event. The following animation is about the Sumatra tremor and tsunami. However, it shows the same principle according to which the Japanese tsunami had been triggered.
http://www.youtube.com/watch?v=4Xebwzb3dDE
For the impact on Japan see following link provided by the USGS: http://walrus.wr.usgs.gov/tsunami/sendai11/sendai11b_Nsmall.mov
I hope this will help.

Wimpy3: 09.04.2011, 22:45

I read approx. 72 words in two paragraphs trying to understand the physical action of the tectonic plates and still do not understand what happened as described by "rebounded". Because a picture or graphic is worth a thousand words and I have not came across one yet, hopefully the author or science can make a graphic showing the forces and rupture action, and make it available to all news agencies, so people may better understand their earth. Allianz please coordinate this with the author.

Armand Vervaeck: 09.04.2011, 19:51

We agree however with Dr. Jörn Lauterjung Tsunami Evacuation Raised Earth Parks (TEREPs). It would be a great solution in river valleys, flat beach areas etc. An additional conclusion is to NOT to build again in destructed areas.

Armand Vervaeck: 09.04.2011, 19:42

We agree with Dr. Jörn Lauterjung in a lot of what he said, but we disagree in what could be done to cope with it. Those people who felt safe behind a tsunami wall of 10 meters when a wave of 15 meter strikes the coast will not tell it to their children anymore. Those locations who have been destroyed by this tsunami were also destroyed with waves of 20 meters or more in a number of historic earthquakes.

We agree however that thousands of people had NO chance of escaping due to the short time that was left in between the mainshock and the arrival of the waves.

However - a lot could be done to use modern telecommunications in combination with ie smartphones. If the elevators in Tokyo can stop securely at the next level and if the Shinkansen bullet trains can lose their power by measuring the P waves, an immediate alert can easily be send to smartphones in many prefectures at risk (as you said 3 minutes after the mainshock). The only what has to be done is a few of simple applications combined with the JMA alert system. The Japanese government could make the app mandatory installed on for every smartphone sold in Japan. Is this science-fiction. NO, certainly not.
It will not save all of them, but every chance to make less victims has to be taken.
Japan would be a great place to try it out.

Armand Vervaeck
SOS Earthquakes non-profit organization
+32478299395
quakesos@hotmail.com
http://earthquake-report.com
http://www.QuakeSOS.com
QuakeSOS & QuakeSOS+ iPhone applications

euroatlantic: 09.04.2011, 18:40

"Hopefully," said tsunami expert Jörn Lauterjung from GFZ, "it must come not only to disaster, before a proper warning system is installed."
http://www.spiegel.de/wissenschaft/natur/0,1518,755801,00.html



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