Mechanism of tsunami generation

�@Seabed rises due to the occurrence of a subduction zone earthquake.
�ASea level rises with the rise in the seabed.

�BA tsunami is generated in accordance with the rise in sea level.

・Mega swells, long wavelength

�CAfter the first wave, the second and third waves attack in succession.

・The tsunami piles up as this process is repeated.

�DArrival of a Tsunami

・The wave height increases when a tsunami approaches a coast (i.e., when the water depth reduces).

※Differences between a tsunami and a normal wave

A normal wave is generated by wind blowing over the sea surface.

Nomal wave

・A higher part of the wave goes beyond a sea wall.
・Sea level does not change.

Speed of tsunami

・A tsunami can in the open ocean can travel with speed of greater than that of a jet airplane.

A tsunami can move from one side of the Pacific Ocean to the other side.

When you feel the occurrence of earthquake, you must evacuate immediately:

・Please retreat from the seashore immediately and evacuate to the safety place after the earthquake occurs.
If Tsunami warning is broadcast after the earthquake occurs, you should follow the warning all the time.

You should leave the coast to keep out of danger.

You should evacuate to the nearest high land or evacuation area.

・In Japan, the municipality designates the evacuation areas and escape routes for the evacuees.

Evacuation continues for a while because the tsunami recurs.

If you cannot outrun the tsunami, you should evacuate to a substantial building.

・In Japan, the designation of “evacuation buildings” (reinforced concrete buildings of three or more stories) is being promoted.

You should evacuate to the third floor or above in the substantial building.

・If you can reach the third floor or above, your safety is almost ensured.
・When you have enough time to evacuate, go up to higher ground.

(Links)

TSUNAMI Digital Library
(Tsunami Digital Library Development Team)

Tsunami Warnings/Advisories, Tsunami Information
(Japan Meteorological Agency)