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Earthquakes

DEFINITION:
Earthquake, trembling or shaking movement of the earth's surface. Most earthquakes are minor tremors. Larger earthquakes usually begin with slight tremors but rapidly takethe form of one or more violent shocks, and end in vibrations of gradually diminishing force called aftershocks. The subterranean point of origin of an earthquake is called its focus; the point onthe surface directly above the focus is the epicenter. The magnitude and intensity of an earthquake is determined by the use of scales, e.g., the Richter scale[->0]. Richter scale , measure of themagnitude of seismic waves from an earthquake, devised in 1935 by the American seismologist Charles F. Richter.


Causes of Earthquakes:
The short answer is that earthquakes are caused by faulting, asudden lateral or vertical movement of rock along a rupture (break) surface.
Here's the longer answer: The surface of the Earth is in continuous slow motion. This is plate tectonics--the motionof immense rigid plates at the surface of the Earth in response to flow of rock within the Earth. The plates cover the entire surface of the globe. Since they are all moving they rub against each otherin some places (like the San Andreas Fault in California), sink beneath each other in others (like the Peru-Chile Trench along the western border of South America), or spread apart from each other(like the Mid-Atlantic Ridge). At such places the motion isn't smooth--the plates are stuck together at the edges but the rest of each plate is continuing to move, so the rocks along the edges aredistorted (what we call "strain"). As the motion continues, the strain builds up to the point where the rock cannot withstand any more bending. With a lurch, the rock breaks and the two sides move. Anearthquake is the shaking that radiates out from the breaking rock. http://www.slideshare.net/ajp/gcse-earthquakes-ap

Effects:

Earthquakes produce various damaging effects to the areas they...