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Earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The moment magnitude of an earthquake is conventionally reported, or the related and mostly obsolete Richter magnitude, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale.

At the Earth's surface, earthquakes manifest themselves by a shaking and sometimes displacement of 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 occasionally volcanic 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, huge amounts of gas migration, mainly methane deep within the earth, but also by volcanic activity, landslides, mine blasts, and nuclear experiments.

An earthquake's point of initial rupture is called its focus or hypocenter. The term epicenter means the point at ground level directly above this.

Landslides and avalanches

Earthquakes can cause landslides and avalanches, which may cause damage in hilly and mountainous areas.

Fires

Following an earthquake, fires can be generated by break of the electrical power or gas lines. In the event of water mains rupturing and a loss of pressure, it may also become difficult to stop the spread of a fire once it has started.

Soil liquefaction

Soil liquefaction occurs when, because of the shaking, water-saturated granular material temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, as buildings or bridges, to tilt or sink into the liquefied deposits.

Tsunami

Undersea earthquakes and earthquake-triggered landslides into the sea, can cause Tsunami. See, for example, the 2004 Indian Ocean earthquake.

Human impacts

Earthquakes may result in disease, lack of basic necessities, loss of life, higher insurance premiums, general property damage, road and bridge damage, and collapse of buildings or destabilization of the base of buildings which may lead to collapse in future earthquakes.

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article Earthquake.