: Earthquakes

What is the Definition of an Earthquake?


An earthquake is the sudden, sometimes violent movement of the earth's surface from the release of energy in the earth's crust.



What Causes Most Earthquakes?


The crust of the earth when it is subject to tectonic forces, bends slightly. But, because the crust is rigid, when the stress or pressure exceeds the strength of the rocks, the crust breaks and snaps into a new position. Vibrations called seismic waves are generated and travel both through the earth and along its surface. These seismic waves cause the movement we call earthquakes.




Where Are Earthquakes Likely to Occur?



Within areas of the crust are fractures, known as faults, along which two crustal blocks have slipped or moved against each other. One block may move up while the other moves down, or one may move horizontally in one direction and the other in the opposite direction. Geologists and seismologists (scientists who study earthquakes and the processes that create them) have found that earthquakes occur repeatedly at faults, which are zones of weakness in the earth's crust.




How Many Earthquakes Happen Each Year?



There are over a million quakes annually, including those too small to be felt.


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