Figure 2. A) An earthquake results from plate shifting at a subduction zone (oceanic plate being subducted under continental plate). Displaced water forms a tsunami. B) Tsunami separates into two distinct waves - local (to right) and distant (to deep water). C) As local wave encounters continental slope, it gains amplitude (height) and slows down. The trough of the wave, if it encounters the coast first, will cause a drop in water level (drawdown). Note the distant wave traveled much farther from the point of origin since it is moving faster in deep water (adapted from USGS). Note: Wave heights and slopes are exaggerated in comparison to water depths.
Last updated on October 6, 2005