As described earlier, a tsunami is originated by an earthquake, underwater landslides, underwater volcanoes. The most common cause of a tsunami are earthquakes, called tsunamigenic earthquakes. The continents and sea floor that cover the earth's surface are part of a worldwide system of plates that are in motion. These motions are very slow, only an inch or two per year.
Earthquakes occur where the edges of plates run into one another.
Such edges are called fault lines or faults. Sometimes the forces along faults can build up over long periods of tome so that when the rocks finally break an earthquake occurs. To generate tsunamis earthquakes must occur underneath or near the ocean, be large and create movements in the ocean floor. All oceanic regions of the world can experience tsunamis, but the Pacific Ocean there is a much more frequent occurrence of large, destructive tsunamis because of the many large earthquakes along the margins of the Pacific Ocean. The deep ocean trenches off the coasts of Alaska, the Kuril Islands, Russia and South America are well known for their violent underwater earthquakes and a the source area for destructive Pacific-wide tsunamis.