Plate Tectonics

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How does the movement of plates cause earthquakes?

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The processes of the earth that cause earthquakes are fairly simple to understand and might be compared to a puzzle.  The earth is made up of four layers, beginning at the utmost interior with the inner core, followed by the outer core.  The action, however, occurs in the protective layers of the mantle and crust, which cover the earth's core and allow life to flourish above. The mantle is actually comprised of what are called tectonic plates, massive slabs of solid rock that slowly drift, cluster and separate, covering the earth like puzzle pieces. 

The phenomenon known as the earthquake is a "sudden slip on a fault, and the resulting ground shaking and radiated seismic energy caused by the slip" (USGS Earthequake Glossary). The edges of the tectonic plate boundaries create what are called faults. You may already be familiar with some of the more famous and active faults, like the San Andreas Fault that runs along the West coast of the United States. The plate boundaries are jagged, "sliding, shearing, or grinding past each other" ( and easily become stuck along these fault lines. "Since the edges of the plates are rough, they get stuck while the rest of the plate keeps moving" (USGS). This causes a build-up of frictional energy, as the rest of the plate continues to move, putting stress on the plate boundary. When the plates suddenly become unstuck and slip past each other, that stored potential energy is released, causing a huge jolt that manifests itself in varying degrees of destruction to the man-made infrastructure above the crust.

[USGS Earthquake Glossary: ]

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