Tsunamis

Tsunami is the Japanese term for large waves that hit the power mahadasyat coast. Radius can reach tens or even hundreds of kilometers of coastline. Tsunami waves can occur when a large earthquake on the seabed. Did the earthquake that occurred on the mainland can not cause the tsunami? I guess it can happen but the potential of small and great potential is the earthquake is located in the seabed that is due to shifting tectonic plates of the earth by earthquake and volcanic sea mountains such as Mount Krakatoa in Indonesia in the 19th century that the dust vulkaniknya almost covers the whole world.