Some 80 percent of all the planet's earthquakes occur along the rim of the Pacific Ocean, called the "Ring of Fire" because of the preponderance of volcanic activity there. Most earthquakes occur at fault zones, where tectonic plates – giant rock slabs that make up the Earth's upper layer – collide or slide against each other. These impacts are usually gradual and unnoticeable on the surface; however, immense stress can build up between plates. When this stress is released quickly, it sends massive vibrations, called seismic waves, often hundreds of miles through the rock and up to the surface.
(Adaptado de http://environment.nationalgeographic.com/envir onment/natural-disasters/earthquake-profile/. Acessado em 22/06/2014.)
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