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Tsunami Glossary
bore phenomena
A steep, turbulent, rapidly moving wave front that typically occurs in river mouths or estuaries; bottom friction slows the advancing wave front, and water piles up behind to produce a nearly vertical bore face.
epicenter
The point on the earth's surface directly above the location in the earth (focus) where an earthquake originates.
false warning
A warning for a potential tsunami, which proved to be an insignificant tsunami.
insignificant tsunami
A tsunami having no measured run-up of a meter or more anywhere in the Hawaiian Islands.
inundation
The maximum horizontal distance inland that a tsunami penetrates.
locally generated tsunami
A tsunami striking some coastal areas of the Hawaiian Islands and generated by a displacement of the ocean floor adjacent to the Hawaiian Islands.
Lower low water
Refers to the lowest point reached by the lowest low tide in areas having mixed tides.
mean sea level
The average height of the sea-surface.
no warning
A significant tsunami occurred but no warning was given.
Pacific-wide tsunami
A tsunami striking some coastal areas of the Hawaiian Islands, generated by displacement of the ocean floor along the margins of the Pacific (e.g., Japan, Kamchatka, Aleutians, Chile).
plate tectonics
The theory that the earth's surface is divided into a number of rigid plates that are either converging, diverging, or slipping past one another; these motions generate volcanism and earthquakes along the plate boundaries.
Richter scale
A logarithmic scale used for measuring earthquake magnitude; each unit represents a 10-fold increase in ground movement and a 32-fold increase in energy.
rogue waves
Unexpectedly high waves which in some instances come from a direction different from the predominant waves in the local area; many theorize that a rogue wave is the coincidence of several wave trains, the crest of one train superimposed and amplifying others.
run-up
The maximum vertical height of the sea surface reached during a tsunami with reference to mean sea-level; run-up is also referred to as the amplitude or height of the tsunami.
seiche
The back and forth oscillation of a standing wave; typically occurring in enclosed or partially enclosed bodies of water, the oscillations continue pendulum fashion after the generating force ceases.
seismographs
Instruments used for measuring earthquake size and the position on the earth's surface over which they occur.
shallow water wave
A wave occurring in water with a depth less than one-twentieth of the average wavelength.
significant tsunami:
A tsunami having a measured runup of one meter or more anywhere in the Hawaiian Islands.
subduction zone
An area of convergence between a sinking plate and an overriding plate.
tidal wave
Often the name incorrectly identifying a tsunami; tidal waves are the extremely long period waves driven by the forces producing the tides.
tide
The regular, periodic rise and fall of the sea surface resulting from the gravitational forces of the Moon and Sun (and other celestial bodies to a small extent) acting on the Earth's surface.
travel time
The time it takes the tsunami to travel from the source to an area where it has an effect.
tsunami (seismic sea wave)
A series of ocean waves characterized by having long periods and wavelengths and can travel with speeds greater than 500 miles per hour. Tsunami waves can be generated by sudden displacements in the sea floor, landslides, or volcanic activity; in the deep ocean their height may only be a few inches, as they encounter shallow water their heights increase drastically, resulting in a sudden increase in sea level, thereby flooding low-lying coastal areas.
tsunami incident
Differing tsunami incidents consist of differing possible combinations of the types of tsunamis (significant or insignificant), source areas (local or pacific-wide), and warnings (valid, false, or no warning).
valid warning
A warning for a potential tsunami, which proved to be a significant tsunami.
wave crest
The highest part of a wave.
wave period
The time required for two successive wave crests or troughs to pass a point in space.
wave trough
The lowest part of a wave.
wavelength
The horizontal distance between two successive wave crests or troughs.



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130 Kamehameha Ave Hilo, HI 96720 tel: 808-935-0926 FAX: 808-935-0842 email:
Last Revised November 2007