An earthquake is the vibration, sometimes violent, of the Earth's surface that follows a release of energy in the Earth's crust. This energy can be generated by a sudden dislocation of segments of the crust, by a volcanic eruption, or even by man made explosions.
Most destructive earthquakes--the kind which people generally have in mind when they think about earthquakes, and those of the greatest human and scientific significance--are caused by the sudden dislocation of large rock masses along geological faults within the earth's crust. These are known as tectonic earthquakes.
