An earthquake is an unpredictable event in which masses of rock shift below the Earth's surface, releasing enormous amounts of energy and sending out shock waves which sometimes cause the ground to shake dramatically. Not all earthquakes cause calamity, but they are known to be one of the Earth's most destructive forces. Entire structures, including houses and dams, have been known to collapse in an earthquake.

Earthquakes occur along fault lines, which are boundaries of different layers, or plates, of rock masses on the crust and within the Earth. The movement of one immense plate can shift great masses of weight and pressure onto other weaker layers. When this pressure gives way, an earthquake can take place.

An earthquake's power can be measured in two ways: by intensity and magnitude. While intensity of a quake is usually described through people's perceptions and the severity of building destruction, magnitude...