The ground underneath the seabed protrudes or subsides when an earthquake having a focus beneath the seabed occurs. This diastrophism makes the sea surface agitate vertically causing big waves which then turns into the propagating tsunami.
When the tsunami warning is announced, sailors undock their vessel and sail offshore as means of evacuation to avoid potential damages to their vessel. This is indeed a very rational maneuver because out in the ocean the tsunami behaves more or less like a big and deep tide that does not have the kind of wave energy capable of flipping over a ship, the kind predominant in places near the coast during the tsunami of the same scale.
The term “Tsunami” is a combination of two Japanese characters, both of which were derived from China: The character “Tsu” which means port, and “Nami” which means wave. The two characters combine to make one term which refers to a very destructive wave. The reason why these two characters were chosen is because this catastrophic wave does more damage to the ships docked at the port rather than these offshore. Presently the word “Tsunami” is used extensively throughout the world.
Tsunami velocity is the square root of the product of water depth and gravitational acceleration （v=√gd）. If the water depth is assumed to be 4,000m, the tsunami velocity reaches approximately 720km/h（200m/s）, which is the speed equivalent to that of a jet.

●Overview
The Imamura Laboratory adopts the difference method of the shallow water equation for the numerical calculation of tsunami. The tsunami analysis involves a number of simulations including the river backflow simulation to predict the inundation area and inundation height if future tsunamis were to occur. These calculations are used to evaluate the wave power imposed on houses and buildings and predict flotsam/ jetsam/ driftwood/debris transport, and wave height as well as velocity at each mesh point to illustrate a wave height distribution over a map. The information on the seabed terrain comes from the materials publicly released by the Japan Coast Guard.

● Conditions that can be input
The information describing the focus of the earthquake (the magnitude, distance between the focus and the epicenter, location), the seabed terrain data (seabed elevation and location), and terrain are all available to be input as conditions.

● Example of Analysis Result
An example of the result of calculation done on the Earthquake Off Fukushima Prefecture on July 19, 2008 is introduced here.
The scale of the earthquake is quite big (M =6.6), and the focus is approximately 10km underneath the earth’s surface.
The research findings showed that the earthquake arrival time was 20 minutes behind the arrival time predicted by the Japan Meteorological Agency, however the former almost coincided with the observed arrival time, which proved the accuracy of the system.

▲ Example of tsunami
height distribution