The Pacific Tsunami Warning Center (PTWC) was instituted in 1948 following the extensive damage and loss of life in Hawaii caused by the tsunami generated in the Aleutian Islands in 1946. The PTWC is comprised of member nations and states who seek to coordinate tsunami detection and warning efforts within the area. In this system, a "tsunami watch" is a message from the Honolulu Observatory that an earthquake which could cause a tsunami has occurred in the Pacific Basin. A "tsunami warning" consists of information from the Honolulu Observatory that an earthquake has occurred and that a tsunami is spreading across the Pacific Ocean, estimated time of arrival at various places is also given.
There are also regional warning systems for coasts in or close to areas capable of producing tsunamis. For these areas, "the rapid arrival of waves following an earthquake precludes the confirmation of wave generation prior to the issuance of effective warnings". Warnings must be issued on the basis of earthquake magnitude and location alone. The devastation associated with the 1964 Alaskan earthquake and tsunami, led to the institution of the Alaska Regional Tsunami Warning System in 1967. It serves as the regional warning center for Alaska, British Columbia, Washington, Oregon and California. This system was intended to detect, locate and calculate the magnitude of earthquakes in the region as quickly as possible and issue warnings to communities close to the epicenter.
Early warning, coupled with education of the affected populations, proper zoning, and suitable structural design can aid in reducing the disastrous effect of this natural hazard. If warning is received early enough (2 to 5 hours), which is possible for tsunamis generated at a distance, hasty preventive action can be taken: people can be evacuated, ships can clear harbors or seek safer anchorage, planes and rolling stock can be moved, buildings can be closed, shuttered, and sandbagged. For tsunamis generated by local events, however, the time from initiation of a tsunami to its arrival at shore can be as little as a couple of minutes. Residents in areas susceptible to tsunamis should be made aware of the need to seek high ground if they feel strong ground shaking. Coastal communities, should identify evacuation routes even if they do not have good information about potential inundation areas.