In addition, the Pacific Tsunami Warning Center in Hawaii, USA keeps track of all earthquakes to find their location and size. If they are likely to create tsunamis, all Pacific countries are notified. If tsunami waves are actually detected, the tsunami alerts become tsunami warnings, which allows all those at risk to start taking precautions.
Forces of Nature: ThinkQuest 2000 (Team #C003603)
http://library.thinkquest.org/C003603/english/tsunamis/prediction.shtml
The U.S. Coast and Geodetic Survey (USCGS) has a tidal-wave warning service in the Pacific area. Seismograph stations keep a lookout for earthquakes, and pinpoint their exact locations. The USCGS will then calculate the expected arrival time of predicted tsunamis, enabling warnings to be issued hours in advance. This gives people in at-risk areas enough time to evacuate to higher ground.