Predicting Tsunamis

Great progress has been made in predicting tsunamis, both in the long term and in the short term, following tsunami earthquakes. Much of the long-term progress reflects recognition of the association of tsunamis with plate tectonic boundaries, particularly convergent margins. Certain areas along these convergent margins are susceptible to tsunami-generating earthquakes, either because of the types of earthquakes that characterize that region, or because thick deposits of loose unconsolidated sediments characteristically slide into trenches in other areas. Progress in short-term prediction of tsunamis stems from the recognition of the specific types of seismic wave signatures that are associated with tsunamigenerating earthquakes. Seismologists are in many cases able to immediately recognize certain earthquakes as potentially tsunami-generating and issue an immediate warning for possibly affected areas.

Tsunamis are generated mainly along convergent tectonic zones, mostly in subduction zones. The motion of the tsunami-generating faults in these areas is typically at right angles to the trench axis. After many years of study, geologists have documented a relationship between the direction of the motion of the fault block and the direction toward which most of the tsunami energy (expressed as wave height) is directed. Most earthquakes along subduction zones move at right angles to the trench, and the tsunamis are also preferentially directed at right angles away from the trench. This relationship causes certain areas around the Pacific to be hit by more tsunamis than others, because there is a preferential orientation of trenches around the Pacific. Most tsunamis are generated in southern Alaska (the tsunami capital of the world), are directed toward Hawaii, and glance the west coast of the lower 48 states, whereas earthquakes in South America direct most of their energy at Hawaii and Japan.

Continue reading here: Tsunami Hazard zones and Risk Mapping

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