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A scientific description of the definitions and things you need to know about earthquakes

British Dictionary definitions for earthquake earthquake noun a sudden release of energy in the earth's crust or upper mantle, usually caused by movement along a fault plane or by volcanic activity and resulting in the generation of seismic waves which can be destructiveRelated adjective: Earthquakes are caused by the release of built-up stress within rocks along geologic faults or by the movement of magma in volcanic areas.

They are usually followed by aftershocks. See Note at fault. Show More A Closer Look: Fractures in Earth's crust, or lithosphere, where sections of rock have slipped past each other are called faults. Earthquakes are caused by the sudden release of accumulated strain along these faults, releasing energy in the form of low-frequency sound waves called seismic waves.

Although thousands of earthquakes occur each year, most are too weak to be detected except by seismographs, instruments that detect and record vibrations and movements in the Earth. Three kinds of waves accompany earthquakes.

The nature of earthquakes

Primary P waves have a push-pull type of vibration. Secondary S waves have a side-to-side type of vibration. Both P and S waves travel deep into Earth, reflecting off the surfaces of its various layers. S waves cannot travel through the liquid outer core.

Locating and measuring earthquakes

Surface L waves-named after the nineteenth-century British mathematician A. Love-travel along Earth's surface, causing most of the damage of an earthquake. The total amount of energy released by an earthquake is measured on the Richter scale. Each increase by 1 corresponds to a tenfold increase in strength.

Earthquakes above 7 on the Richter scale are considered severe. The famous earthquake that flattened San Francisco in 1906 had a magnitude of 7.

Earthquake

See faultRichter scaleand seismology. Show More Note Earthquakes are particularly likely where such plates are sliding past each other, as in the San Andreas Fault. Note Earthquakes cannot be accurately predicted, although the likelihood of a region's suffering an earthquake can be estimated.

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