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| Some earthquakes are caused by the movement of magma in ]es, and such quakes can be an early warning of volcanic eruptions. A rare few earthquakes are caused by the build-up of large masses of water behind ]s. | Some earthquakes are caused by the movement of magma in ]es, and such quakes can be an early warning of volcanic eruptions. A rare few earthquakes are caused by the build-up of large masses of water behind ]s, such as the ]. | ||
Revision as of 16:02, 23 December 2001
An earthquake is a trembling or shaking movement of the earth's surface. Earthquakes occur every day, however the vast majority of them are minor and cause no damage. Large earthquakes can cause serious destruction and massive loss of life. Large earthquakes usually have a substantial initial tremour, followed by numerous aftershocks (smaller tremours). The underground point of origin of an earthquake is called its "focus" and the location on the surface directly above the focus is the epicentre.
The magnitude and intensity of an earthquake is measured using the Richter scale.
Earthquakes typically result from the movement of continental and oceanic plates, as described by plate tectonics. Pressures are built up along the boundaries of these plates in regions called faults until this pressure is released by a slippage of the plates some distance. The resulting release of energy creates a wave in the surrounding terrain, causing it to shake in an earthquake.
Some earthquakes are caused by the movement of magma in volcanoes, and such quakes can be an early warning of volcanic eruptions. A rare few earthquakes are caused by the build-up of large masses of water behind dams, such as the Kariba Dam.
Two types of waves are generated during an earthquake, known as "P" and "S" waves. "P" waves are longitudinal waves resulting from the compression of rock, while the "S" waves are tranverse waves caused by up-and-down motions. There is a difference in travel times between the two types of wave, depending on the material travelled through; and "P" waves are damped out in the earth's core. The combination of these factors has allowed scientists both to locate earthquake epicenters precisely, and to determine in general the structure of the earth's interior. This paragraph requires fact-checking and elaboration.
See also: San Andreas Fault, New Madrid Fault Zone