How Earthquakes Cause Tsunamis
The illustration below shows a subduction earthquake (one where a denser plates shifts below its neighboring plate, at left). Energy is transferred and the displaced water forms a wave. As the wave travels and enters shallower water in the coastal area, it begins to increase in amplitude (National Geographic).
If you wish to help out by donating to the Japanese Tsunami Relief Fund, American Red Cross has already setup a donation process. Click here for the Red Cross Donation Form of their Site.