what are the causes of earthquake
An earthquake is a vibration or tremor produced in the Earth’s crust. It is caused by the disturbances originating deep inside the Earth’s crust.
Meteors falling on the Earth’s surface
Underground explosions. For example, underground nuclear tests.
Collapsing structures such as mines etc.
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Anearthquake(also known as aquake,tremorortemblor) is the result of a sudden release of energy in theEarth'scrustthat createsseismic waves. Theseismicity,seismismorseismic activityof an area refers to the frequency, type and size of earthquakes experienced over a period of time.
Earthquakes are measured using observations fromseismometers. Themoment magnitudeis the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe. The more numerous earthquakes smaller than magnitude 5 reported by national seismological observatories are measured mostly on the local magnitude scale, also referred to as theRichterscale. These two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly almost imperceptible or weak and magnitude 7 and over potentially cause serious damage over larger areas, depending on their depth. The largest earthquakes in historic times have been of magnitude slightly over 9, although there is no limit to the possible magnitude. The most recent large earthquake of magnitude 9.0 or larger was a9.0 magnitude earthquake in Japan in 2011(as of October 2012), and it was the largest Japanese earthquake since records began. Intensity of shaking is measured on the modifiedMercalli scale. The shallower an earthquake, the more damage to structures it causes, all else being equal.
At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. When theepicenterof a large earthquake is located offshore, the seabed may be displaced sufficiently to cause atsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.
In its most general sense, the wordearthquakeis used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of geologicalfaults, but also by other events such as volcanic activity, landslides, mine blasts, andnuclear tests. An earthquake's point of initial rupture is called itsfocusorhypocenter. Theepicenteris the point at ground level directly above the hypocenter.
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