Tsunami

In 1965, the Intergovernmental Oceanographic Commission of the United Nations Educational, Scientific, and Cultural Organization agreed to expand the United States' existing tsunami warning center at Ewa Beach, Hawaii. This marked the formation of the Pacific Tsunami Warning Center (PTWC) which is now operated under the U.S. Weather Service. The objectives of the PTWC are to "detect and locate major earthquakes in the Pacific basin; determine whether or not tsunami have been generated; and to provide timely and effective information and warnings to minimize tsunami effects."

The PTWC is the administrative center for all the associated centers, committees, and commissions of the International Tsunami Warning System (ITWS). Japan, the Russian Federation, and Canada also have tsunami warning systems and centers and they coordinate with the PTWC. In total, 27 countries now belong to the ITWS.

The ITWS is based on a world-wide network of seismic and tidal data and information dissemination stations, and specially trained people. Seismic stations measure movement of the earth's crust and are the foundation of the system. These stations indicate that some disturbance has occurred that may be powerful enough to generate tsunami. To confirm the tsunami following a seismic event, there are specially trained people, called tide observers, with monitoring equipment that enables them to detect differences in the wave patterns of the ocean. Pressure gauges deployed on the ocean can detect changes of less than 0.4 in (1 cm) in the height of the ocean, which indicates wave height. Also, there are accelerometers set inside moored buoys that measure the rise and fall of the ocean, which will indicate the wave speed. These data are used together to help researchers confirm that a tsunami has been generated. Tsunami can also be detected by satellite monitoring methods such as radar and photographic images.