Most often the changes in a relief of an oceanic bottom happening at earthquakes leading to formation of large dumpings, failures, etc. are an immediate cause of emergence of waves of a tsunami.
Catastrophic concussions generated on May 22 waves of a tsunami which extended across the Pacific Ocean and out of its limits with a speed of 650-700 km/h. On the Chilean coast fishing settlements and port constructions were destroyed; hundreds of people were carried away by waves. On the island of Chiloe of a wave destroyed four fifth all constructions.
On Japanese islands 36000 houses were flooded, overturned 900 vessels and fishing boats. On the island of Okinawa was lost and 180 people were missing, in the settlement of Momoisi 150 inhabitants were lost. It was never before noted that tsunami waves, having overcome such huge distance, kept the destructive force.
Still big violations of a relief of a bottom take place at earthquakes in the Pacific Ocean. So, at an underwater earthquake in the Sagami Sea (Japan) at a sudden raising of a site of an oceanic bottom about 22,5 cubic km of water which fell upon the coast in a tsunami wave mode were forced out.
It is known that the majority of earthquakes is dated for those belts of Earth within which formation of mountain systems proceeds, in particular young, belonging to a modern geological era. Earthquakes in areas of the close neighbourhood of large mountain systems with hollows of the seas and oceans are purest.