We’ve all been hearing about the recent devastating earthquake and tsunami in Japan, and the resulting loss of life and property. Our thoughts are with the people of Japan as they work to find survivors and rebuild their lives. However, did you how it happened?
The Tohoku earthquake, as it is now named, was a submarine, megathrust earthquake. Submarine because it occured under the sea, and megathrust because it was caused by one tectonic plate bumping against another tectonic plate. The earth’s geography is marvelous. A molten center of magma with a cool crust that forms the land on which we live and also the ocean floors. The crust is not a single, uniform piece. It is actually composed of many pieces, called Tectonic plates, that are floating on the liquid magma underneath. As these pieces move about, they sometimes bump into each other, often with far-reaching consequences. The Himalayas were formed when the Indian plate bumped against the Eurasian plate! Due to the shallow dip of the plate boundary, which causes large sections to get stuck, megathrust earthquakes are among the world’s largest. In fact, all six earthquakes of magnitude 9.0 or greater that occured since 1900 have been megathrust earthquakes. In the case of the Tohoku earthquake, the Pacific tectonic plate, which moves at a rate of 8 to 9 cm (3.1 to 3.5 in) per year, dipped under the Okhotsk tectonic plate. The friction caused created the seismic waves and the resultant tsunami that wreaked such havoc on the coast of Japan.
Here is some further reading on tectonic plates, earthquakes and tsunami.
Megathrust earthquakes: http://en.wikipedia.org/wiki/Megathrust_earthquake