arrival time: Time of arrival, usually of the first wave, of the first wave of the 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.
ETA: Estimated Time of Arrival.
first motion: Initial motion of the first wave
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.
inundation: The depth to which a particular location is covered by water.
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.
marigram: Tide gage recording showing wave height as a function of time.
marigraph: The instrument which records wave height.
Mw: Moment Magnitude. Magnitude based on the size and characteristics of the fault rupture, and determined from long-period seismic waves. It is 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.
normal earthquake: An earthquake caused by slip along a sloping fault where the rock above the fault moves downwards relative to the rock below.
Pacific Disaster Center (PDC): An information processing center to support emergency managersin the Pacific region. Funded by the U.S. Department of Defense.
period: The length of time between two successive peaks or troughs. May vary due to complex interference of waves. Tsunami periods generally range from 5 to 60 minutes.
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.
strike-slip earthquake: An earthquake caused by horizontal slip along a fault.
thrust earthquake: An earthquake caused by slip along a gently sloping fault where the rock above the fault is pushed upwards relative to the rock below. The most common type of earthquake source of damaging tsunamis.
tidal wave: Common term for tsunami used in older literature, historical descriptions and popular accounts. 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. However, most tsunamis give the appearance of a fast-rising tide or fast-ebbing as they approach shore and only rarely as a near-vertical wall of water.
travel time: Time that it took the tsunami to travel from the source to a particular location.
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 a series of travelling waves in water produced by the displacement of the sea floor associated with submarine earthquakes, volcanic eruptions, or landslides.
tsunami earthquake: A tsunamigenic earthquake which produces a much larger tsunami than expected for its magnitude.
tsunamigenic earthquake: Any earthquake which produces a tsunami.
tsunami magnitude: A number which characterizes the strength of a tsunami based on the tsunami wave amplitudes. Several different tsunami magnitude determination methods have been proposed.
TWS: Tsunami Warning System, organization of 26 Pacific Member States which coordinates
international monitoring and warning dissemination.