Earthquake
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For other uses, see Earthquake (disambiguation).
"Seismic event" redirects here. For seismic migration, see Seismic migration.
Earthquake epicenters occur mostly along tectonic plate boundaries, and especially on the Pacific Ring of Fire.
Global plate tectonic movement
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Earthquakes
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An earthquake (also known as a quake, tremor or temblor) is the shaking of the
surface of the Earth resulting from a sudden release of energy in
the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from
those that are so weak that they cannot be felt to those violent enough to propel objects
and people into the air, and wreak destruction across entire cities. The seismicity,
or seismic activity, of an area is the frequency, type, and size of earthquakes
experienced over a period of time. The word tremor is also used for non-earthquake
seismic rumbling.
At the Earth's surface, earthquakes manifest themselves by shaking and displacing or
disrupting 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 hypocenter or focus. The epicenter is the point at ground level
directly above the hypocenter.
Contents
1Naturally occurring earthquakes
o 1.1Earthquake fault types
o 1.2Earthquakes away from plate boundaries
o 1.3Shallow-focus and deep-focus earthquakes
o 1.4Earthquakes and volcanic activity
o 1.5Rupture dynamics
o 1.6Tidal forces
o 1.7Earthquake clusters
1.7.1Aftershocks
1.7.2Earthquake swarms
2Intensity of earth quaking and magnitude of earthquakes
3Frequency of occurrence
4Induced seismicity
5Measuring and locating earthquakes
6Effects of earthquakes
o 6.1Shaking and ground rupture
o 6.2Soil liquefaction
o 6.3Human impacts
o 6.4Landslides
o 6.5Fires
o 6.6Tsunami
o 6.7Floods
7Major earthquakes
8Prediction
9Forecasting
10Preparedness
11Historical views
12Recent studies
13In culture
o 13.1Mythology and religion
o 13.2In popular culture
14See also
15References
16Sources
17External links
Naturally occurring earthquakes
Three types of faults:
A. Strike-slip
B. Normal
C. Reverse
Tectonic earthquakes occur anywhere in the earth where there is sufficient stored
elastic strain energy to drive fracture propagation along a fault plane. The sides of a
fault move past each other smoothly and aseismically only if there are no irregularities
or asperities along the fault surface that increase the frictional resistance. Most fault
surfaces do have such asperities, which leads to a form of stick-slip behavior. Once the
fault has locked, continued relative motion between the plates leads to increasing stress
and therefore, stored strain energy in the volume around the fault surface. This
continues until the stress has risen sufficiently to break through the asperity, suddenly
allowing sliding over the locked portion of the fault, releasing the stored energy.[1] This
energy is released as a combination of radiated elastic strain seismic waves,[2] frictional
heating of the fault surface, and cracking of the rock, thus causing an earthquake. This
process of gradual build-up of strain and stress punctuated by occasional sudden
earthquake failure is referred to as the elastic-rebound theory. It is estimated that only
10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of
the earthquake's energy is used to power the earthquake fracture growth or is
converted into heat generated by friction. Therefore, earthquakes lower the Earth's
available elastic potential energy and raise its temperature, though these changes are
negligible compared to the conductive and convective flow of heat out from the Earth's
deep interior.[3]
