How often does a tsuami happen each year?

Answer 1

Tsunamis are actually fairly rare; there have only been two big ones this century so far, and a half-dozen smaller ones. We have had very bad luck so far this century; first Indonesia, and now Japan, both monster quakes and enormous tsunamis.

Tsunamis aren't directly caused by earthquakes; they are caused by underwater landslides or upthrusts - which are often caused by earthquakes. So there is almost always an earthquake associated with any tsunami. If there isn't any underwater earth movement, there won't be a tsunami.