Earthquakes

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  • Earthquakes
definition
  • Sudden, violent movement of the Earth's crust.
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broader
Abstract from DBPedia
    An earthquake (also known as a quake, tremor or temblor) is the perceptible shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes can be violent enough to toss people around and destroy whole cities. The seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. Earthquakes are measured using observations from seismometers. The moment magnitude is 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 the Richter magnitude scale. These two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly 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. Intensity of shaking is measured on the modified Mercalli 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 the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity. In its most general sense, the word earthquake is used to describe any seismic event — whether natural or caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter.

    地震(じしん、英: Earthquake)という語句は、以下の2つの意味で用いられる。 1. * 地震学における定義: 地球表面を構成している岩盤(地殻)の内部で、固く密着している岩石同士が、断層と呼ばれる破壊面を境目にして、急激にずれ動くこと。これによって大きな地面の振動が生じこれを地震動(じしんどう)という。 2. * 大地のゆれ: 地震動のことで一般的にはこちらも「地震」と呼ばれる。「地震」(なゐふる)という語句は『日本書紀』にも見え、その他古文書の記録にも登場するが、これらは今日の地震学における地震動のことであり、また「大地震」、「小地震」などと共に震度の程度を表すものでもあった。 地震を対象とした学問を地震学という。地震学は地球物理学の一分野であり、構造地質学と密接に関わっている。

    (Source: http://dbpedia.org/resource/Earthquake)

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