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What is a tsunami?

A tsunami is a high tidal wave generated by a shift in the ocean floor, which is in most cases caused by earthquakes.
Most parts of the Japanese seacoast have experienced a tsunami.
The Sanriku coast in the Tohoku region has been especially hard hit.
The reason, scientists assume, is the formation of a ria coastline, consisting of a multitude of narrow and complicated bays, which may make the tsunami wave exceptionally high.
Immediately after an earthquake off the southwestern coast of Hokkaido 1n 1993, a major tsunami with a peak height of 20 meters hit the coast of Okushiri island.The number of dead and missing totaled 230.