Seismic Waves (Tsunami)

A seismic wave or Tsunami is a devastating water wave generated by an undersea earthquake. They are commonly called "tidal waves", but are by no means created by the tides. The sudden slippage of the ocean floor near the source of an earthquake can send a train of seismic waves across the ocean. When the overriding plate along a subduction zone suddenly breaks free it moves upward raising the sea floor and the water above. The waves move outward in ever-expanding circles, nearly imperceptible in deep ocean water. As they approach land, water recedes from the shore. This dramatic action often entices the curious to investigate. But very shortly, a water rises rapidly and rushes landward.

tsunami formation

Figure OC.10 Formation of a tsunami
Courtesy USGS
Source: Surviving a Tsunami—Lessons from Chile, Hawaii, and Japan,
USGS Circular 1187 http://pubs.usgs.gov/circ/c1187/
Last accessed August 16, 2006

On December 26th, 2004 subduction between the Indian and Eurasian (more specifically the Burma) plates off the coast off the coast of Indonesia resulted in a magnitude 9 earthquake and large tsunami that devastated South Asia. [Watch "Violent Earth" from National Geographic.] The earthquake was a result of stresses being released when the Indian plate slid beneath the Burma plate. The resulting vertical movement of the ocean floor displaced hundreds of cubic meters of water and large waves propagated outward from the focus of the quake. The massive tsunami devastated coastal regions of South Asia as it crashed ashore.

View "Killer Tsunamis" from National Geographic

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For Citation: Ritter, Michael E. The Physical Environment: an Introduction to Physical Geography.
2006. Date visited. http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/title_page.html