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>> Tsunami Vocabulary and Terminology

Tsunami - Tsunamis are ocean waves produced by earthquakes or underwater landslides. The word is Japanese and means "harbor wave," because of the devastating effects these waves have had on low-lying Japanese coastal communities. Tsunamis are often incorrectly referred to as tidal waves, but a tsunami is actually a series of waves that can travel at speeds averaging 450 (and up to 600) miles per hour in the open ocean.

In the open ocean, tsunamis would not be felt by ships because the wavelength would be hundreds of miles long, with an amplitude of only a few feet. This would also make them unnoticeable from the air. As the waves approach the coast, their speed decreases and their amplitude increases. Unusual wave heights have been known to be over 100 feet high. However, waves that are 10 to 20 feet high can be very destructive and cause many deaths or injuries.

From an initial tsunami generating source area, waves travel outward in all directions much like the ripples caused by throwing a rock into a pond. As these waves approach coastal areas, the time between successive wave crests varies from 5 to 90 minutes. The first wave is usually not the largest in the series of waves, nor is it the most significant. Furthermore, one coastal community may experience no damaging waves while another, not that far away, may experience destructive deadly waves. Depending on a number of factors, some low-lying areas could experience severe inland inundation of water and debris of more than 1,000 feet.

Tsunami Watch - An alert issued to areas outside the warned area. The area included in the watch is based on the magnitude of the earthquake. For earthquakes over magnitude 7.0, the watch area is 1 hour tsunami travel time outside the warning zone. For all earthquakes over magnitude 7.5, the watch area is 3 hours tsunami travel time outside the warning zone. The watch will either be upgraded to a warning in subsequent bulletins or will be cancelled depending on the severity of the tsunami.

Tsunami Warning - Indicates that a tsunami is imminent and that coastal locations in the warned area should prepare for flooding. The initial warning is typically based on seismic information alone. Earthquakes over magnitude 7.0 trigger a warning covering the coastal regions within 2 hours tsunami travel time from the epicenter. When the magnitude is over 7.5, the warned area is increased to 3 hours tsunami travel time. As water level data showing the tsunami is recorded, the warning will either be cancelled, restricted, expanded incrementally, or expanded in the event of a major tsunami.

Emergency Alert System - http://www.fcc.gov/eb/eas/

Emergency Alert System in Washington - http://www.wsab.org/eas/eas.html

All-Hazards NOAA Weather Radio - http://www.nws.noaa.gov/nwr/

All-Hazards NOAA Weather Radio in Washington state

All-Hazard Alert Broadcast (AHAB) - A self-sufficient wind or solar powered warning system located in remote locations. It activates a brilliant blue US Coast Guard light and siren heard for at least a mile upon receipt of an emergency message, such as a tsunami watch or warning. It also records and repeats the verbal emergency message for those near the AHAB. http://www.earthquakeconference.org/response.html

Tide Gauge - An instrument that measures the alternate rising and falling of the waters of the ocean, and of bays, rivers, etc., connected therewith. The tide ebbs and flows twice in each lunar day, or the space of a little more than twenty-four hours.

Seismometer - http://vulcan.wr.usgs.gov/Glossary/Seismicity/description_seismic_monitoring.html

Pacific Northwest Seismic Network (PNSN) - http://www.pnsn.org/

Cascadia Region Earthquake Workgroup (CREW) - http://www.crew.org/

NOAA Center for Tsunami Research (located at the Pacific Marine Environmental Laboratory) - http://nctr.pmel.noaa.gov/ (includes tsunami and tsunami monitoring links)

Tsunami Detection Buoys - http://www.ndbc.noaa.gov/dart.shtml (located in the north Pacific Ocean)

West Coast/Alaska Tsunami Warning Center - http://wcatwc.arh.noaa.gov/ (responsible for coastal waters from Alaska to California, including Washington)

Pacific Tsunami Warning Center - http://www.prh.noaa.gov/ptwc/ (responsible for all American interests in the Pacific, including Hawaii)

International Tsunami Warning Center - http://itic.ioc-unesco.org (responsible for the other 25 member nations in the Pacific Ocean Basin)

NOAA - National Oceanic and Atmospheric Administration - http://www.noaa.gov

NOAA/National Weather Service - http://www.weather.gov

NOAA/National Weather Service Seattle - http://www.wrh.noaa.gov/sew/

NOAA/National Weather Service Portland - http://www.wrh.noaa.gov/pqr/

TsunamiReady - http://www.tsunamiready.noaa.gov/

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