"A tsunami or seismic sea wave is a series of waves of extremely long wavelength and period caused by an underwater disturbance. Although most tsunamis are associated with large earthquakes in which the epicenters underlie or border the ocean floor, the generating mechanism is not positively known. Vertical displacement of the ocean floor during an earthquake may be responsible, or possible submarine avalanches on the slope of oceanic trenches, or generation of resonant oscillations of trench water by long-period earthquake waves. Submarine volcanic eruptions also have been known to generate tsunamis. All submarine earthquakes do not produce tsunamis, and all tsunamis are not large enough to cause damage; however, occasional large waves have caused great destruction and loss of life in coastal areas. At present, there is no way. to determine if an earthquake has generated a tsunami, except to note the occurrence and epicenter of the earthquake and then detect the arrival of the characteristic waves at a network of tide stations. The waves, although often called tidal waves, have nothing to do with the tides."
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