Tsunamis are nothing new to the people of Japan, in fact the word tsunami originates there, with the word for harbor (tsu) and wave (nami).

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/

10% of the world's active volcanoes reside in Japan, more than any other country, 100 of which are currently active.  These volcanoes are part of the Pacific Ring of Fire and are caused by subduction zones of the Pacific plate beneath continental and other oceanic plates along its margins.

The Japan Meteorological Agency (JMA) provides the nation with early warning information for earthquakes, tsunamis and volcanic eruptions.  Usually the general population will get a decent warning before any threatening volcanic activity since magma flow is easier to predict than an earthquake but of course volcanoes are not 100% predictable and can erupt without warning.  
Which is what happened on September 27, 2014 at the second largest volcano in Japan, Mount Ontake, when volcano classified as a level 1 at the time(normal/nonthreatening) erupted without magma.  At least 56 hikers were killed and many more injured and missing.  In rare cases like this when no prior warning is given there is little that can be down to take precautionary measures.  

Mount Ontake during it's eruption on September 27, 2014

Some of active volcanoes in Japan have now be equipped with reinforced concrete shelters near the crater and along trails for hikers to take shelter in during a sudden eruption.  After the devastation at Mount Ontake which many believe could have been lessened with an adequate amount of shelters the nation want's to increase the amount provided at each volcano but budgeting is currently an issue.  Currently Mount Fuji one of Japan's most popular hiking spots has no shelters in place.  

Concrete shelters

V.Grasso and A.Singh, UNEP (Dec 2011, forthcoming): Early Warning Systems: www.jma.go.jp/jm/en/Activities/earthquake.html,.com

"Volcanoes of Japan" Volcano Discovery.  http://www.volcanodiscovery.com/

A country better prepared than anyone

Japan has a huge amount of seismic activity due to it's close proximity to tectonic plate boundaries.  They have on average 1,500 earthquakes each year, of course many of these are very small but they do experience a few very catastrophic quakes happening each century, The most recent of which occurred in 2011, which was a record breaking 9.0 followed by a horrific tsunami.  


The people of Japan have learned from these past disasters and invest heavily in earthquake and tsunami preparation.  At an early age children in Japan are taught what to do during an earthquake; from diving under desks to staying away from falling debris.  Every office and most houses have an earthquake emergency kits, with food, water, and medical supplies. Offices and school also keep hard-hats and gloves for use in the event of a quake.

Japan has some of the strictest building codes to protect against the larger earthquakes.  With limits of how much a building is allowed to even sway during a quake and most high-rise towers contain extra steel bracing. giant rubber pads and hydraulic shock absorbers, this makes all of Japan's newer buildings some of the safest in the world.  Yet many of Japan's quakes are followed by tsunamis which are a disaster in themselves.  Which is why they've invested in sea walls to protect their most vulnerable areas.  

Glanz, James. Onishi, Norimitsu "Japan’s Strict Building Codes Saved Lives." http://www.nytimes.com/ March 11, 2011Foster, Peter "Japan earthquake: country better prepared than anyone for quakes and tsunamis" http://www.telegraph.co.uk/ 11 mar 2011