WATER SAFETYWhat if a Tsunami hits?

Learn about Tsunami

Let's understand how a Tsunami is generated and how to escape from it. Evacuate to higher ground to protect your life.

How fast a Tsunami travels and how high it can reach

Earthquake=Tsunami→Evacuation “Go to higher ground immediately!”

The deeper the ocean, the faster a Tsunami travels. A Tsunami can travel as fast as a jet plane in offshore waters. On the other hand, the shallower the ocean is, the slower the Tsunami becomes. The waves catch up with the preceding waves and merges into a larger wave. Even though the speed is slower in shallow water it does not mean that you can escape by running. If you want to survive from a Tsunami, evacuate as soon as possible. If you start evacuating after you see a Tsunami on your site, it is too late. If you feel an earthquake near the coast, or if a Tsunami warning is issued, evacuate immediately even if you do not actually see a Tsunami. (Cited from the website of the Japan Meteorological Agency)

Tsunami signs, etc.

Pictograms of Wide-area Evacuation sites(top-left) Tsunami Evacuation sites(top-right), Evacuation sites (buildings)(bottom-left), and Tsunami Evacuation Buildings(bottom-right)

Tsunami warning (Tsunami Danger Zone)

Let's check the Height above sea level regularly.

Tsunami hazard maps and Tsunami signs indicate areas that are expected to be flooded in the event of a Tsunami and Evacuation sites. It is important to check evacuation routes and locations regularly, considering various situations. Also, Tsunami warnings and advisories are categorized into Major Tsunami Warnings (5m, 10m, and over 10m), Tsunami Warnings (3m), and Tsunami Advisories (1m) depending on its height.

What you should do in case of a Tsunami

  1. Obtain a Tsunami hazard map or check the Tsunami signs.
  2. Check the actual evacuation route based on the Tsunami hazard map.
  3. Obtain accurate information on Tsunami warnings and advisories from J-alert, disaster preparedness radio, disaster preparedness e-mail, local radio stations, TV, and lifesavers’ call.

Tsunami Flags

U Flag of International Maritime Signal Flags

Tsunami flags may be used as a means of Tsunami alert communication to beach users. Flags guiding people to evacuate from the waterfront were specified by the international standard ISO20712-2 in 2008, using the international standard safety color red. The International Lifesaving Federation (ILS), an international organization of which the Japan Lifesaving Association is a member, also recommends this regulation. The U flag, an International Maritime Signal Flag, is used to guide evacuations near water. Japan Lifesaving Association promotes awareness of Tsunami Evacuation Guide Flags as a flag to advise people that a Tsunami is expected and that they should evacuate immediately. It is easily recognized by foreigners and is not easily affected by the angle of light.

Preparing for Tsunami Damage

The Power of Tsunami

Japan is an earthquake-prone country

“If you are caught in a 1-meter Tsunami, you will almost certainly die.” A shocking analysis has been released by the Cabinet Office. Japan is an island nation and an earthquake-prone country. You never know when a Tsunami will hit. A 1 meter high Tsunami may not sound like a big deal. If you imagine an ordinary wave (surface of seawater created by wind), it probably is not a big deal. However, the same ocean has completely different characteristics when it becomes a Tsunami. If we say that a normal wave is just made by the power of the surface, a Tsunami is made of a mass of seawater, which can float a car with a height of only 30cm and damage a wooden house with a height of only 1m. A Tsunami is much more powerful than you might think, even if it is a knee-high wave.

Tsunami height
  • 0 - 30cm A healthy adult can just stand but cannot walk.
  • 30 - 50 cm Cars and containers start to float. Can stand by clinging on to something.
  • 50 - 70 cm Over knee high and the power of water becomes strong. Even a healthy adult can be swept away.
  • 70 - 100 cm It is impossible to stand still. The probability of death hit by large drifting objects is close to 100%.

It is easy to understand that a large wave, tens of meters high is impossible to fight, but a Tsunami is a completely different type of wave. For this reason a warning is issued even for a small Tsunami of only tens of centimeters.

Be careful of the second and subsequent waves

What is even more frightening about Tsunami is that they do not stop but continue. It can become higher after the second wave. In the event of a huge earthquake, Tsunami generated at different locations along the long Tsunami fault zone will overlap each other and reflect off the coast, hitting the coast of each region multiple times. In addition to the first wave, large Tsunami will repeatedly hit the coast for five to six hours to half a day. (Cabinet Office press release.) The first wave is a "push wave" that pushes in and the second wave is a "pull wave" that pulls in drifting objects such as destroyed houses and cars into the sea with enormous force. Depending on the direction and topography, such as bays and cliffs, there may be nowhere for the water to go, and the wave height may be up to four times higher than the expected wave height. In the Great East Japan Earthquake, a 40.1-meter run-up was observed in Ayari Bay, Ofunato City, Iwate Prefecture.

Lessons from the disaster area

Tsunami Tendenko

U Flag of International Maritime Signal Flags

The story of how 99.8% of the children and students in Kamaishi City, Iwate Prefecture, who followed this lesson survived became widely known as the "Miracle of Kamaishi. Tendenko is a dialect word meaning "by yourself" or "each". It means, "When the Tsunami comes, run away by yourselves”. To put it more precisely, when you feel an earthquake near the coast, the first thing you should do is to think about protecting yourself from the Tsunami. Make your own decisions without waiting for anyone else's instructions, and protect yourself by running to the highest ground as soon as possible, even without worrying about your family.

  • Sense the danger and act on your own.
  • Go to higher ground as soon as possible.
  • Don't worry about your family.

It may seem strange not to wait for instructions and not caring about families. However, in the recent Great Earthquake and Tsunami, many people lost their lives because they were worried about their families and went back to the shorefront, because they gave priority to instructions from their schools or companies, who are not experts on Tsunami. On the other hand, many lives were saved by the "Tsunami Tendenko”. In an emergency, we must do our best to protect ourselves in each situation. Talk to your loved ones in advance to promise to protect yourself first in case of an emergency, and where to meet each other if the phone is disconnected.

Things to be aware of when a Tsunami hits

Where is the evacuation site?

Tsunami Evacuation Site sign

If you are by the sea, check the Tsunami evacuation sites in advance. When a Tsunami hits, there is nothing to do other than to flee to higher ground.

Go to the nearest high ground as soon as possible

If you feel a tremor by the coast, even if it seems slight, do not think that it is not a big deal, but go to the nearest high ground as soon as possible. If there is no high ground, evacuate as far as possible from the shore. If that is difficult, go to a building made of reinforced concrete or steel and go to a higher floor.

Do not get into a car

Walking is the principle. If you are in a car and think you are going to get stuck in a traffic jam, park it on the side of the road with the keys in the ignition, and get out of the car and evacuate. It's not only traffic jams that you need to worry about, but also the fact that it is difficult to open the windows if they are swamped by a Tsunami. The water pressure will prevent the doors from opening. Can you break the window glass and get out? Usually, it will be quite difficult to do so.

When evacuating, stay away from the ocean and rivers

Get away from the ocean and rivers as soon as possible. On November 22, 2016, the day of the Tsunami, there is a video of the Sunaoi River flowing backwards through Tagajo City, Miyagi Prefecture, possibly due to the earthquake. When evacuating, it is extremely dangerous to approach water that is flowing upstream vigorously.


The most frightening thing about Japan's frequent earthquakes is that many people have become accustomed to them. They do not pay attention to them, thinking, "It won't be a big deal this time“. Don't stop doubting, and don't rely on past experiences that have worked so far. In addition, Tsunami can be caused not only by earthquakes in Japan but also by major earthquakes from overseas. It is important to pay attention to warnings and advisories. Don't forget the power of nature. Even a small Tsunami of a few centimeters can easily wash away an adult. If anything happens, protect yourself and evacuate, do not give up until the very end.