It rarely appears as a great towering wave. Usually it appears as a rapidly rising or falling water level, a series of breaking waves, or a bore. The first wave in a series of waves is usually not the largest and can be either a rise or a fall in water level. Usually the timing of tsunami-generating events cannot be predicted in advance. With the aid of historical records of tsunamis and numerical models, it is possible to predict where tsunamis are most likely to be generated and the area where damage is most likely to be done.
Tsunamis can occur in any of the oceanic regions, but are most common in the Pacific Ocean.
The great size of the Pacific and the frequency of submarine earthquakes combine to produce many tsunamis. A tsunami is most frequently generated by a submarine earthquake, but not all submarine earthquakes cause tsunamis. Earthquakes generating a tsunami usually have a magnitude of at least 6 on the Richter scale and generally are of shallow depth. If a disastrous tsunami is to occur, the magnitude typically will be 7.6 or higher. Back to Page Index 2.