Tsunami Warning Time

The amount of warning time a tsunami warning system can provide depends on the distance between your location and the location of the undersea event.  A tsunami can travel 500 to 600 mph in deep water, slowing as it approaches shore.  If the undersea earthquake that starts the tsunami is 500 miles offshore in deep water, for example, and the tsunami is headed your way, local authorities will be notified within minutes of the event and will have about one hour to issue the warnings to the public and announce directions for evacuation to a safe area.

In some cases, a local earthquake or undersea landslide close to shore can initiate a tsunami that strikes almost without warning.  In 1998, a 7.0 magnitude undersea earthquake near Papua, New Guinea, triggered a massive submarine landslide that started a 50-ft. tsunami close to shore.  The wave hit the shoreline within minutes and wiped out several villages along the New Guinea coast, stripping the land almost bare.  2200 people died.  In September, 2009 a 7.0 undersea quake and fault line rupture 125 miles from Samoa triggered a tsunami that hit Samoa and American Samoa without warning 15 minutes later.  Waves over 40 ft. high took more than 200 lives and caused extensive damage to property. 

Tsunami warning systems are effective when the undersea quake that starts the tsunami occurs in deep water several hundred miles from the nearest populated area.  In the Pacific Ocean, a quake will be picked up by seismometers, pressure sensors, and tidal gauges at the reporting stations of the Pacific Tsunami Warning System operated by 26 nations bordering the Pacific Basin.  The collected data registers on the instruments at the Pacific Tsunami Warning Center in Ewa Beach, Hawaii.  If readings indicate the disturbance may have started a tsunami, warnings are issued immediately to the areas in danger with approximate arrival time of the first wave.

As part of the international tsunami warning network, the United States has recently completed its own U.S. Tsunami Warning System that takes in the Pacific Tsunami Warning System, the West Coast & Alaska Tsunami Warning System, and the Atlantic Tsunami Warning System.  The U.S. system is composed of 39 DART (Deep Ocean Assessment and Reporting of Tsunami) and DART II stations.  Five stations are located in the Atlantic, Caribbean, and Gulf of Mexico, and the remaining 34 in the Pacific.  The DART system is made up of a pressure sensor resting on the ocean bottom that transmits continuous data by acoustic telemetry (sound waves) to a surface buoy anchored near the pressure sensor.  The buoy is equipped with a satellite link that relays the real time information to tsunami warning centers around the world.  Certain fluctuations in ocean bottom pressure can indicate the presence of a tsunami.