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An earthquake also is called earthquake or tremor of earth is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with aseismometer, also known as a seismograph. The moment magnitude of an earthquake is conventionally reported, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causingserious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale.
At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacing the ground.When a large earthquake epicenter is located offshore, the seabed sometimes suffers sufficient displacement to cause a tsunami. The shaking in earthquakes can also trigger landslides and occasionallyvolcanic activity.
In its most generic sense, the word earthquake is used to describe any seismic event — whether a natural phenomenon or an event caused by humans — that generates seismic waves.Earthquakes are caused mostly by rupture of geological faults, but also by volcanic activity, landslides, mine blasts, and nuclear experiments. An earthquake's point of initial rupture is called its focusor hypocenter. The term epicenter refers to the point at ground level directly above the hypocenter.

Naturally occurring earthquakes

Tectonic earthquakes will occur anywhere within the earthwhere there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. In the case of transform or convergent type plate boundaries, which form the largest faultsurfaces on earth, they will move past each other smoothly and aseismically only if there are no irregularities or asperities along the boundary that increase the frictional resistance. Most boundaries dohave such asperities and this leads to a form of stick-slip behaviour.

Once the boundary has locked, continued relative motion between the plates leads to increasing stress and therefore, stored...
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