An earthquake is the release of energy that has slowly built up during the stress of increasing deformation of rocks. These energy releases take the form of seismic waves that radiate in all directions from the place of movement. Earthquakes can originate at or near the surface of the Earth, deep inside the crust, or even in the upper mantle. The place of origin is the focus (or the center), and the point directly above the focus on the surface is known as the epicenter. Earthquakes range from tremors so small that they are hardly noticeable, to great city destroying shocks This reflects their magnitude, the amount of shaking of the ground as the quake passes as measured by a seismograph.
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