Scientific Method / Science & Exploration

Tsunami wrestling

Although we can?t predict when they occur, a good understanding of how tsunami …

Tsunamis are among the most unpredictable natural disasters known to mankind.  As the December 2004 tsunami proved, they can decimate wide areas of coast land with little or no warning whatsoever.  The problems associated with tsunami prediction, warning, and risk assessment are difficult, however progress is being made on the later two.  Risk assessment requires that one predict how a tsunami wave propagates and accurately model the details of the wave breaking on a particular stretch of coast line.

Traditionally, tsunamis have been modeled as solitons.  Normally a pulse will naturally spread as it travels.  Solitons prevent this spreading by modifying the medium in such a way as to exactly compensate for the spread induced by the medium.  If solitons were the correct description for tsunamis then they would always arrive in a single wave.  The December Tsunami shows that this model doesn’t reflect a tsunami’s real world behavior.  For example; more than a single wave was recorded at most beaches and the first wave was not the biggest, which is not in agreement with soliton predictions.  In response to this mathematicians have been thinking about alternatives.   They show that the wave has no time to spread so a soliton description is unnecessary, however the compensating mechanism (which is a nonlinear hydrostatic pressure, which is governed by the size and speed of the earth movement that generated the wave) is important.  Other important factors necessary to the model are; oceanic currents, and change in sea depth with distance.  The various solutions to the tsunami propagation equation produce a different number of waves with varying intensity depending on those parameters.  These solutions agree qualitatively with observed tsunami records, which is much better than those produced by a pure soliton approach.

This doesn’t help anyone predict tsunamis but it can help governments decide on the risk level associated with various costal regions in their respective communities, which is never a bad thing.

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