Step 2: Designating a theoretical Tsunami.
A theoretical tsunami can be designed using two main sources of information:
a. Data from the largest past tsunami (as identified by relatively precise high water marks or geological evidence). Estimating highest water levels is necessary, but insufficient without an accompanying estimated arrival time of the tsunami (determined by the distance between the wave source and the coastline in question), and an evacuation time for people, ships and boats;
b. Recent seismic (or earthquake) data relating to the possible generation of tsunamis along specific coasts. It is worth noting that the largest earthquake does not necessarily generate the largest tsunami; even a relatively small magnitude earthquake can provoke a tsunami. Therefore, evaluations of an earthquake’s epicentre, scale, depth and location, energy direction and displacement of fault motion are used in designing a theoretical tsunami.
A special note on distant tsunamis
Distant tsunamis, caused by undersea earthquakes far off the coast, can take four hours or more to arrive onshore. Those registering high waves are infrequent. This lack of data means making a projection for a theoretical tsunami based on the statistical analysis of a distant tsunami is very difficult. However, among those that have been observed, the Lisbon earthquake and tsunami of 1755 in the northeast Atlantic, the Great Chile Earthquake of 1960 in the Pacific Ocean and the Great Sumatra Tsunami of 2004 in the Indian Ocean are considered valid to use as the basis for a theoretical tsunami..
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