A tsunami only results from a vertical displacement of water, meaning an earthquake in which two plates simply grind against one another won't generate a giant wave. If you put your hand directly in the water, and lift your hand up in a vertical direction, that water will go up and down and generate a wave. The ATWC issues tsunami watches and warnings to local, state, national and international users as well as the media. They, as well as the National Oceanic and Atmospheric Administration's Weather Radio System, disseminate the information to the public. The U.S. Coast Guard also broadcasts urgent marine warnings to coastal users.
Local authorities are then responsible for evacuating residents.