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- All clear:
- Listen to radio or television for the "all clear" announcement. No sirens will be sounded.
- Amplitude:
- The rise above or drop below the ambient water level as read on a tide gauge.
- Arrival time:
- Time of arrival of the first wave ofa tsunami at a particular location.
- Bore:
- Traveling wave with an abrupt vertical front or wall of water. Under certain conditions, the leading edge of a tsunami wave may form a bore as it approaches and runs onshore. A bore may also be formed when a tsunami wave enters a river channel, and may travel upstream penetrating to a greater distance inland than the general inundation.
- CREST (Consolidated Reporting of Earthquakes and Tsunamis):
- A project funded through the Tsunami Hazard Mitigation Federal/State Working Group to upgrade regional seismic networks in AK, WA, OR, CA, and HI and provide real-time seismic information from these networks and the USNSN (United States National Seismograph Network) to the tsunami warning centers.
- ETA (Estimated Time of Arrival):
- Computed arrival time of the first tsunami wave at coastal communities after a specific earthquake has occurred.
- Evacuation zones:
- Areas likely to be impacted by a tsunamithat should be evacuated prior to wave arrival.
- First motion:
- Initial motion of the first wave, a rise in the water level is denoted by R, a fall by F.
- Free field offshore profile:
- A profile of the wave measured far enough offshore so that it is unaffected by interference from harbor and shoreline effects.
- Harbor resonance:
- The continued reflection and interference of waves from the edge of a harbor or narrow bay which can cause amplification of the wave heights, and extend the duration of wave activity from a tsunami.
- Horizontal inundation distance:
- The distance that a tsunami wave penetrates onto the shore, measured horizontally from the mean sea-level position of the water's edge. Usually measured as the maximum distance for a particular segment of the coast.
- ICG/ITSU (The International Coordination Group for the Tsunami Warning System in the Pacific):
- A United Nations organization under UNESCO (United Nations Educational, Scientific and Cultural Organization)responsible for international tsunami cooperation.
- Inundation:
- Refers to the distance flooded by a tsunami as it travels inland.
- ITIC:
- International Tsunami Information Center established in 1965. Monitors international activities of the Pacific Tsunami Warning Center and assists with many of the activities of ICG/ITSU.
- Leading-depression wave:
- Initial tsunami wave is a trough, causing a draw-down of water level.
- Leading-positive wave:
- Initial tsunami wave is a crest, causing a rise in water level. Also called a leading-elevation wave.
- Local/regional tsunami:
- Earthquake source within 1000 km of the area of interest. Local or near-field tsunami has a very short travel time (30 minutes or less), mid-field or regional tsunami waves have travel times on order of 30 minutes to 2 hours. Note: "Local" tsunami is sometimes used to refer to a tsunami of landslide origin.
- Marigram:
- Tide gauge recording showing wave height as a function of time.
- Marigraph:
- Aninstrumentthat records wave height.
- MLLW (Mean Lower Low Water):
- The average low tide water elevation, the lowest of the two daily cycles, often used as a reference to measure runup.
- Ms: Surface Wave Magnitude:
- Magnitude of an earthquake as measured from the amplitude of seismic surface waves. Often referred to by the media as "Richter" magnitude.
- Mw: Moment Magnitude:
- Magnitude based on the size and characteristics of the fault rupture, and determined from long-period seismic waves.A better measure of earthquake size than surface wave magnitude, especially for very large earthquakes. Calibrated to agree on average with surface wave magnitudes for earthquakes less than magnitude 7.5.
- NOAA (National Oceanic and Atmospheric Administration):
- Under the Department of Commerce, the federal agency responsible for tsunami warnings and monitoring.
- NWS (National Weather Service):
- The branch of NOAAthat operates the tsunami warning centers and disseminates warnings.
- PTWC (Pacific Tsunami Warning Center):
- Originally established in 1948 as the SSWWS (Seismic Sea Wave Warning System), located in Ewa Beach near Honolulu. Responsible for issuing warnings to Hawaii, to U.S. interests in the Pacific other than the west coast and Alaska, and to countries located throughout the Pacific.
- Period:
- The length of time between two successive peaks or troughs.
- Runup:
- Maximum height of the water onshore observed above a reference sea level. Usually measured at the horizontal inundation limit.
- Seiche:
- A standing wave oscillating in a partially or fully enclosed body of water. May be initiated by long period seismic waves, wind and water waves, or a tsunami.
- SSWWS (Seismic Sea Wave Warning System):
- The original tsunami warning center established in 1948 after the April 1, 1946 tsunami killed 159 in Hawaii.
- Teletsunami:
- Earthquake source more than 1000 km away from area of interest. Also called a distant-source or far-field tsunami.
- THRUST (The project for Tsunami Hazard Reduction Using System Technology:
- Sponsored by the Office for U.S. Foreign Disaster Assistance/Agency for International Development. A comprehensive program to mitigate tsunami hazards in developing countries.
- Tidal wave:
- Common term for tsunami used in older literature, historical descriptions, and popular accounts, but now considered incorrect. Tides, caused by the gravitational attractions of the sun and moon, may increase or decrease the impact of a tsunami, but have nothing to do with their generation or propagation.
- TIME (the Center for the Tsunami Inundation Mapping Effort):
- To assist the Pacific States in developing tsunami inundation maps.
- Tsunami:
- A Japanese term derived from the characters "tsu" meaning harbor and "nami" meaning wave. Now generally accepted by the international scientific community to describe waves in water produced by the displacement of the sea floor.
- Tsunami earthquake:
- A tsunamigenic earthquake which produces a much larger tsunami than expected for its magnitude.
- Tsunami evacuation maps:
- Listed in the front of many public telephone directories. These maps show areas historically inundated by tsunami wave. Using the maps, people and businesses located in evacuation zones can determine which areas are considered safe and which are not. Tsunami shelters are also shown on evacuation maps, but it is best to listen to the Emergency Alert System for announcement of local shelter locations.
- Tsunami evacuation zone:
- Refer to the Civil Defense maps in the front of your telephone book white pages or contact your County Civil Defense Agency.
- Tsunami magnitude:
- A number characterizing the strength of a tsunami based on the tsunami wave amplitudes. Several different tsunami magnitude determination methods have been proposed.
- Tsunami watch:
- Tsunami possible; prepare to evacuate, listen to a radio station in your county or official Civil Defense instructions and information.
- Tsunami watching:
- Tsunami confirmed; evacuate; listen to a radio station in your county for official Civil Defense instructions. Sirens will sound. Move inland to higher ground.
- Tsunamigenic earthquake:
- Any earthquake which produces a measurable tsunami.
- TWS (Tsunami Warning System):
- Organization of 26 Pacific member States which coordinates international monitoring and warning dissemination. Operates through ICG/ITSU.
- Urgent Tsunami Warning:
- A large earthquake has occurred; immediate evacuation of low-lying coastal areas. Move inland to higher ground.
- USNSN (United States National Seismic Network):
- Operated by the USGS (United States Geological Survey). Monitors real-time earthquake activity of magnitude greater than 5 worldwide, and magnitude greater than 3 in the continental United States.
- WC/ATWC (West Coast/Alaska Tsunami Warning Center):
- Originally established in 1967 to issue warnings to Alaska of local tsunami events. WC/ATWC is now responsible for issuing warnings for any event likely to impact either Alaska, the west coast of the US, or the Pacific coast of Canada.
- WCM (Warning Coordination Meteorologist):
- Regional weather service person responsible for providing information on the tsunami warning system to local agencies.
- Wrap Around Effect:
- Regardless of their direction of travel, tsunamis wrap around all coastlines. While wave heights vary, all coastal areas remain vulnerable, particularly harbors.
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