High seismic activity off the coast of Japan are the cause for this threat of tsunamis, when the earthquake causes the seafloor along the fault suddenly shifts vertically, this motion shifts the water column above and is what creates the tsunami. Anytime there is a high magnitude earthquake there is a risk it could be followed by a tsunami. The Tsunami Warning Network determines the risk after each quake by determining whether a vertical shift occurred at the fault and by looking at measurement ofs water height recorded around the Pacific Ocean by the TWN (Tsunami Warning Network).
Japan does everything it can to protect themselves from the threat of tsunamis. They have implemented an earthquake warning system that sends out texts to phones and emergency broadcasts to TVs. Also a ocean-based tsunami warning system, where a network of buoys sitting on the seafloor detect changes in water pressure and can detect tsunamis forming, this emits a signal to the warning center where they put out an alert.
Model of early warning buoys.
Of course you only have so much warning with these types of hazards, In the devastating 9.0 earthquake that struck Japan in 2011 there was only a 80 second warning for the quake and the warning for the following tsunami was a huge under estimation. To further help protect from tsunamis 40% of Japan's coastline is protected by concrete seawalls ranging from 10-35 feet tall, and the country is currently planning on the construction of vertical evacuation structures for areas most at risk.
Seawalls being breached in 2011 tsunami in Japan.
Parry,Wynne. "What's the Science Behinf Japan's Quake and Tsunami". Live Science. Mar 11, 2011. http://www.livescience.com/
Demetriou,Danielle. "Tsunami two years on: Japan finally gets warning system that would have saved hundreds of lives." The Telegraph. Mar 9, 2013. http://www.telegraph.co.uk/
Knight,Will. "How Japan's Earthquake and Tsunami Warning Systems Work" MIT Technology Review. Mar 11,2011. http://www.technologyreview.com/
something a bit controversial is that if we know tsunami waves can reach more than 130 ft, at least in certain places, shouldnt there be a 100 ft high seawall, instead of 20 ft??? what is your opinion?
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