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An earthquake or earthquake is the result of the sudden release of energy accumulated by the constraints on the rocks. The result of the breakdown of rocks on the surface called a fault. The place of the breaking of rocks called strong focus. Less common is earthquakes caused by volcanic activity or of artificial origin (e.g. explosions). There is a large number of earthquakes every day, but most not felt by humans. About 100 000 earthquakes recorded each year on the planet. The most powerful of them are among the disasters the most devastating natural. The science that studies these phenomena is the Seismology (studied by seismologists) and the principal instrument of study is the seismograph (which produces seismograms) (Donald, 2009).

Main features

The origin of an earthquake called hypocenter or focus earthquakes. It can be found between the surface and up to seven hundred kilometers deep (limit of the upper mantle) for the deepest events. We talk about the epicenter of the earthquake, to describe the point on the surface of the earth which lies directly above the hypocenter.

Three types of earthquakes

An earthquake is a more or less violent shaking of the ground which may have three origins: rupture of a fault or fault segment (tectonic earthquake) intrusion and degassing of magma (volcanic earthquakes) explosion, collapse of a cavity (natural or earthquakes caused by physical activity). In practice, we classify the earthquakes into three categories according to the phenomena that produced them:

Tectonic Earthquakes

Earthquakes Tectonic is by far the most frequent and devastating. Much of the tectonic earthquakes took place to the boundaries of plates, where a shift occurs between two precarious environments. This shift, located on one or more vulnerabilities, blocked during inter-seismic periods (between earthquakes), and the energy accumulated by the elastic deformation of rocks. This energy shift and suddenly released in earthquakes. In areas of sub-duction, earthquakes represent half the number of those who are destroying the Earth, and dissipate 75% of seismic energy on the planet. This is the only place where there are deep earthquakes (300 to 645 km). At the level of mid-ocean ridges, earthquakes have shallow foci (0 to 10 km), corresponding to 5% of the total seismic energy (Schorlemmer, 2005).

Similarly, the level of large holes recess, place of earthquakes with foci of intermediate depth (0 to 20 km on average) corresponding to 15% of the energy. Releasing the stored energy does not generally in a single shock, and there may be several adjustments before returning to a stable configuration. Thus, there are aftershocks following the main shock of an earthquake of magnitude decreases, and over a period ranging from minutes to more than a year.

These aftershocks are sometimes more devastating than the main shock, because they can bring down the buildings that ripped into, so that help is at work. It can also be an answer even more strong than the main shock regardless of its magnitude. For example, an earthquake of 9.0 can be followed by a response of ...
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