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{{Short description|Sudden movement of the Earth's crust}}
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{{Use American English|date=August 2021}}
[[File:Quake epicenters 1963-98.png|thumb|upright=1.35|Earthquake [[epicenter]]s occur mostly along [[Plate tectonics|tectonic plate]] boundaries, especially on the Pacific [[Ring of Fire]].]]
{{Earthquakes}}

An '''earthquake''', also called a '''quake''', '''tremor''', or '''temblor''', is the shaking of the [[Earth]]'s surface resulting from a sudden release of energy in the [[lithosphere]] that creates [[seismic wave]]s. Earthquakes can range in [[Seismic intensity scales|intensity]], from those so weak they cannot be felt, to those violent<!-- Note: the essential point is /abruptness/, not "strength". --> enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The [[seismicity]] at a particular location in the Earth is the average rate of seismic energy release per unit volume.

In its most general sense, the word ''earthquake'' is used to describe any seismic event that generates seismic waves. Earthquakes can occur naturally or be induced by human activities, such as [[mining]], [[fracking]], and [[nuclear weapons testing]]. The initial point of rupture is called the [[hypocenter]] or focus, while the ground level directly above it is the [[epicenter]]. Earthquakes are primarily caused by geological [[Fault (geology)|faults]], but also by [[volcanism]], landslides, and other seismic events.

Significant historical earthquakes include the [[1556 Shaanxi earthquake]] in China, with over 830,000 fatalities, and the [[1960 Valdivia earthquake]] in Chile, the largest ever recorded at 9.5 [[Seismic magnitude scales|magnitude]]. Earthquakes result in various effects, such as ground shaking and [[soil liquefaction]], leading to significant damage and loss of life. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a [[tsunami]]. Earthquakes can trigger [[landslide]]s. Earthquakes' occurrence is influenced by [[tectonic]] movements along faults, including normal, reverse (thrust), and strike-slip faults, with energy release and rupture dynamics governed by the [[elastic-rebound theory]].

Efforts to manage earthquake risks involve prediction, forecasting, and preparedness, including [[seismic retrofit]]ting and [[earthquake engineering]] to design structures that withstand shaking. The cultural impact of earthquakes spans myths, religious beliefs, and modern media, reflecting their profound influence on human societies. Similar seismic phenomena, known as [[marsquake]]s and [[moonquakes]], have been observed on other celestial bodies, indicating the universality of such events beyond Earth.

== Terminology ==
An earthquake is the shaking of the surface of [[Earth]] resulting from a sudden release of energy in the [[lithosphere]] that creates [[seismic wave]]s. Earthquakes may also be referred to as ''quakes'', ''tremors'', or ''temblors''. The word ''tremor'' is also used for [[Episodic tremor and slip|non-earthquake seismic rumbling]].

In its most general sense, an ''earthquake'' is any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused mostly by the rupture of geological [[Fault (geology)|faults]] but also by other events such as volcanic activity, landslides, mine blasts, [[fracking]] and [[Underground nuclear testing|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.

The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The [[seismicity]] at a particular location in the Earth is the average rate of seismic energy release per unit volume.

==Major examples==
{{Main|Lists of earthquakes}}

[[File:Map of earthquakes 1900-.svg|thumb|upright=1.8|Earthquakes (M6.0+) since 1900 through 2017]]
[[File:USGS magnitude 8 earthquakes since 1900.svg|thumb|upright=1.8|Earthquakes of magnitude 8.0 and greater from 1900 to 2018. The apparent 3D volumes of the bubbles are linearly proportional to their respective fatalities.<ref>{{Cite web|url=https://earthquake.usgs.gov/earthquakes/eqarchives/year/mag8/magnitude8_1900_date.php|archiveurl=https://web.archive.org/web/20160414014457/http://earthquake.usgs.gov/earthquakes/eqarchives/year/mag8/magnitude8_1900_date.php|url-status=dead|title=USGS: Magnitude 8 and Greater Earthquakes Since 1900|archivedate=April 14, 2016}}</ref>]]

One of the most devastating earthquakes in recorded history was the [[1556 Shaanxi earthquake]], which occurred on 23 January 1556 in [[Shaanxi]], China. More than 100,000 people died, with the region losing up to 830,000 people afterwards due to emigration, plague, and famine.<ref>{{cite web |url=https://earthquake.usgs.gov/earthquakes/world/most_destructive.php |title=Earthquakes with 50,000 or More Deaths |archive-url=https://web.archive.org/web/20091101175733/http://earthquake.usgs.gov/earthquakes/world/most_destructive.php |archive-date=November 1, 2009 |url-status=dead |publisher=United States Geological Survey}}</ref> Most houses in the area were [[yaodong]]s—dwellings carved out of [[loess]] hillsides—and many victims were killed when these structures collapsed. The [[1976 Tangshan earthquake]], which killed between 240,000 and 655,000 people, was the deadliest of the 20th century.<ref>Spignesi, Stephen J. (2005). ''Catastrophe!: The 100 Greatest Disasters of All Time''. {{ISBN|0-8065-2558-4}}</ref>

The [[1960 Valdivia earthquake|1960 Chilean earthquake]] is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitude on 22 May 1960.<ref name="usgsfacts"/><ref name="wp100414"/><!----url does not contain box statistics that print edition does and is included for info only----> Its epicenter was near Cañete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the [[Good Friday earthquake]] (27 March 1964), which was centered in [[Prince William Sound]], Alaska.<ref>{{cite web|url=http://www.gps.caltech.edu/uploads/File/People/kanamori/HKjgr77.pdf |title=The Energy Release in Great Earthquakes |author=Kanamori Hiroo |publisher=Journal of Geophysical Research |access-date=2010-10-10 |url-status=dead |archive-url=https://web.archive.org/web/20100723182215/http://www.gps.caltech.edu/uploads/File/People/kanamori/HKjgr77.pdf |archive-date=2010-07-23 }}</ref><ref>{{cite web |url=https://earthquake.usgs.gov/learn/topics/how_much_bigger.php |title=How Much Bigger? |publisher=United States Geological Survey |access-date=2010-10-10 |archive-date=2011-06-07 |archive-url=https://web.archive.org/web/20110607144219/http://earthquake.usgs.gov/learn/topics/how_much_bigger.php |url-status=live }}</ref> The ten largest recorded earthquakes have all been [[megathrust earthquake]]s; however, of these ten, only the [[2004 Indian Ocean earthquake]] is simultaneously one of the deadliest earthquakes in history.

Earthquakes that caused the greatest loss of life, while powerful, were deadly because of their proximity to either heavily populated areas or the ocean, where earthquakes often create [[tsunamis]] that can devastate communities thousands of kilometers away. Regions most at risk for great loss of life include those where earthquakes are relatively rare but powerful, and poor regions with lax, unenforced, or nonexistent seismic building codes.

==Occurrence==
[[File:Fault types.svg|thumb|Three types of faults:<br />
A. [[strike-slip fault|Strike-slip]]<br />
B. [[Normal fault|Normal]]<br />
C. [[Reverse fault|Reverse]]
]]

[[Tectonics|Tectonic]] earthquakes occur anywhere on the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a [[Fault (geology)|fault plane]]. The sides of a fault move past each other smoothly and [[Aseismic creep|aseismically]] only if there are no irregularities or [[Asperity (faults)|asperities]] along the fault surface that increases the frictional resistance. Most fault surfaces do have such asperities, which leads to a form of [[Stick-slip phenomenon|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 [[Potential energy|stored energy]].<ref name="Ohnaka">{{cite book | url=https://books.google.com/books?id=Bp0gAwAAQBAJ&pg=PA234 | title=The Physics of Rock Failure and Earthquakes | publisher=Cambridge University Press | author=Ohnaka, M. | year=2013 | page=148 | isbn=978-1-107-35533-0}}</ref> This energy is released as a combination of radiated elastic [[Strain (materials science)|strain]] [[seismic waves]],<ref>{{cite journal | last1 = Vassiliou | first1 = Marius | last2 = Kanamori | first2 = Hiroo | year = 1982 | title = The Energy Release in Earthquakes | journal = Bull. Seismol. Soc. Am. | volume = 72 | pages = 371–387 }}</ref> 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 (geology)|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 [[Structure of the Earth|Earth's deep interior.]]<ref name="USGS1">{{cite web|last=Spence |first=William |author2=S.A. Sipkin |author3=G.L. Choy |title=Measuring the Size of an Earthquake |publisher=United States Geological Survey|year=1989 |url=https://earthquake.usgs.gov/learning/topics/measure.php |access-date=2006-11-03 |url-status=dead |archive-url=https://web.archive.org/web/20090901233601/http://earthquake.usgs.gov/learning/topics/measure.php |archive-date=2009-09-01 }}</ref>

===Fault types===
{{Further|Fault (geology)|Strike and dip}}
There are three main types of fault, all of which may cause an [[interplate earthquake]]: normal, reverse (thrust), and strike-slip. Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and where movement on them involves a vertical component. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip.

The topmost, brittle part of the Earth's crust, and the cool slabs of the tectonic plates that are descending into the hot mantle, are the only parts of our planet that can store elastic energy and release it in fault ruptures. Rocks hotter than about {{cvt|300|C||}} flow in response to stress; they do not rupture in earthquakes.<ref>{{cite journal |last1=Sibson |first1=R.H. |year=1982 |title=Fault Zone Models, Heat Flow, and the Depth Distribution of Earthquakes in the Continental Crust of the United States |journal=Bulletin of the Seismological Society of America |volume=72 |issue=1 |pages=151–163}}</ref><ref>Sibson, R.H. (2002) "Geology of the crustal earthquake source" International handbook of earthquake and engineering seismology, Volume 1, Part 1, p. 455, eds. W H K Lee, H Kanamori, P C Jennings, and C. Kisslinger, Academic Press, {{ISBN|978-0-12-440652-0}}</ref> The maximum observed lengths of ruptures and mapped faults (which may break in a single rupture) are approximately {{cvt|1000|km|||}}. Examples are the earthquakes in [[1957 Andreanof Islands earthquake|Alaska (1957)]], [[1960 Valdivia earthquake|Chile (1960)]], and [[2004 Indian Ocean earthquake and tsunami|Sumatra (2004)]], all in subduction zones. The longest earthquake ruptures on strike-slip faults, like the [[San Andreas Fault]] ([[1857 Fort Tejon earthquake|1857]], [[1906 San Francisco earthquake|1906]]), the [[North Anatolian Fault]] in Turkey ([[1939 Erzincan earthquake|1939]]), and the [[Denali Fault]] in Alaska ([[2002 Denali earthquake|2002]]), are about half to one third as long as the lengths along subducting plate margins, and those along normal faults are even shorter.

==== Normal faults ====
Normal faults occur mainly in areas where the crust is being [[Extensional tectonics|extended]] such as a [[divergent boundary]]. Earthquakes associated with normal faults are generally less than magnitude 7. Maximum magnitudes along many normal faults are even more limited because many of them are located along spreading centers, as in Iceland, where the thickness of the brittle layer is only about {{convert|6|km|spell=in||}}.<ref>Hjaltadóttir S., 2010, "Use of relatively located microearthquakes to map fault patterns and estimate the thickness of the brittle crust in Southwest Iceland"</ref><ref>{{cite web |title=Reports and publications &#124; Seismicity &#124; Icelandic Meteorological office |url=http://en.vedur.is/earthquakes-and-volcanism/reports-and-publications/ |access-date=2011-07-24 |publisher=En.vedur.is |archive-date=2008-04-14 |archive-url=https://web.archive.org/web/20080414235419/http://en.vedur.is/earthquakes-and-volcanism/reports-and-publications/ |url-status=live }}</ref>

==== Reverse faults ====
Reverse faults occur in areas where the crust is being [[Thrust tectonics|shortened]] such as at a [[convergent boundary]]. Reverse faults, particularly those along convergent boundaries, are associated with the most powerful earthquakes (called [[megathrust earthquake]]s) including almost all of those of magnitude 8 or more. Megathrust earthquakes are responsible for about 90% of the total seismic moment released worldwide.<ref>{{citation |last1=Stern |first1=Robert J. |title=Subduction zones |journal=Reviews of Geophysics |volume=40 |issue=4 |page=17 |year=2002 |bibcode=2002RvGeo..40.1012S |doi=10.1029/2001RG000108 |s2cid=247695067|doi-access=free }}</ref>

==== Strike-slip faults ====
[[Strike-slip fault]]s are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Strike-slip faults, particularly continental [[Transform fault|transforms]], can produce major earthquakes up to about magnitude 8. Strike-slip faults tend to be oriented near vertically, resulting in an approximate width of {{cvt|10|km|||}} within the brittle crust.<ref>{{cite web |title=Instrumental California Earthquake Catalog |url=http://wgcep.org/data-inst_eq_cat |url-status=dead |archive-url=https://web.archive.org/web/20110725021215/http://wgcep.org/data-inst_eq_cat |archive-date=2011-07-25 |access-date=2011-07-24 |publisher=WGCEP}}</ref> Thus, earthquakes with magnitudes much larger than 8 are not possible.

[[File:Kluft-photo-Carrizo-Plain-Nov-2007-Img 0327.jpg|thumb|left|Aerial photo of the San Andreas Fault in the [[Carrizo Plain]], northwest of Los Angeles]]

In addition, there exists a hierarchy of stress levels in the three fault types. Thrust faults are generated by the highest, strike-slip by intermediate, and normal faults by the lowest stress levels.<ref>{{cite journal | last1 = Schorlemmer | first1 = D. | last2 = Wiemer | first2 = S. | last3 = Wyss | first3 = M. | year = 2005 | title = Variations in earthquake-size distribution across different stress regimes | journal = Nature | volume = 437 | issue = 7058| pages = 539–542 |bibcode = 2005Natur.437..539S |doi = 10.1038/nature04094 | pmid = 16177788 | s2cid = 4327471 }}</ref> This can easily be understood by considering the direction of the greatest principal stress, the direction of the force that "pushes" the rock mass during the faulting. In the case of normal faults, the rock mass is pushed down in a vertical direction, thus the pushing force (''greatest'' principal stress) equals the weight of the rock mass itself. In the case of thrusting, the rock mass "escapes" in the direction of the least principal stress, namely upward, lifting the rock mass, and thus, the overburden equals the ''least'' principal stress. Strike-slip faulting is intermediate between the other two types described above. This difference in stress regime in the three faulting environments can contribute to differences in stress drop during faulting, which contributes to differences in the radiated energy, regardless of fault dimensions.

=== Energy released ===
For every unit increase in seismic magnitude, there is a roughly thirty-fold increase in the energy released. For instance, an earthquake of magnitude 6.0 releases approximately 32 times as much energy as an earthquake of magnitude 5.0, and a 7.0 magnitude earthquake releases about 1,000 times as much energy as a 5.0 magnitude earthquake. An 8.6-magnitude earthquake releases the same amount of energy as 10,000 atomic bombs of the size used in [[World War II]].<ref>Geoscience Australia.{{full citation needed|date=December 2022}}</ref>

This is so because the energy released in an earthquake, and thus its magnitude, is proportional to the area of the fault that ruptures<ref>{{cite journal |last1=Wyss |first1=M. |year=1979 |title=Estimating expectable maximum magnitude of earthquakes from fault dimensions |journal=Geology |volume=7 |issue=7| pages=336–340 |bibcode=1979Geo.....7..336W |doi=10.1130/0091-7613(1979)7<336:EMEMOE>2.0.CO;2}}</ref> and the stress drop. Therefore, the greater the length and width of the faulted area, the greater the resulting magnitude. The most important parameter controlling the maximum earthquake magnitude on a fault, however, is not the maximum available length, but the available width because the latter varies by a factor of 20. Along converging plate margins, the dip angle of the rupture plane is very shallow, typically about 10 degrees.<ref>{{cite web |url=http://www.globalcmt.org/CMTsearch.html |title=Global Centroid Moment Tensor Catalog |publisher=Globalcmt.org |access-date=2011-07-24 |archive-date=2011-07-19 |archive-url=https://web.archive.org/web/20110719183137/http://www.globalcmt.org/CMTsearch.html |url-status=live }}</ref> Thus, the width of the plane within the top brittle crust of the Earth can reach {{cvt|50–100|km|||}} (such as in [[2011 Tōhoku earthquake and tsunami|Japan, 2011]], or in [[1964 Alaska earthquake|Alaska, 1964]]), making the most powerful earthquakes possible.

===Focus===
{{Main|Depth of focus (tectonics)}}
[[File:HotelSanSalvador.jpg|thumb|Collapsed Gran Hotel building in the [[San Salvador]] metropolis, after the shallow [[1986 San Salvador earthquake]]]]

The majority of tectonic earthquakes originate in the Ring of Fire at depths not exceeding tens of kilometers. Earthquakes occurring at depths less than {{cvt|70|km|||}} are classified as "shallow-focus" earthquakes, while those with focal depths between {{cvt|70|and|300|km|}} are commonly termed "mid-focus" or "intermediate-depth" earthquakes.

In [[subduction]] zones, where older and colder [[oceanic crust]] descends beneath another tectonic plate, [[deep-focus earthquake]]s may occur at much greater depths (ranging from {{cvt|300|to|700|km|}}).<ref>{{cite web| publisher = [[National Earthquake Information Center]]| title = M7.5 Northern Peru Earthquake of 26 September 2005| date = 17 October 2005| url = ftp://hazards.cr.usgs.gov/maps/sigeqs/20050926/20050926.pdf| archive-url = https://web.archive.org/web/20170525100314/ftp://hazards.cr.usgs.gov/maps/sigeqs/20050926/20050926.pdf| archive-date = 2017-05-25| url-status = dead| access-date = 2008-08-01}}</ref> These seismically active areas of subduction are known as [[Wadati–Benioff zone]]s. Deep-focus earthquakes occur at depths where the subducted [[lithosphere]] should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by [[olivine]] undergoing a [[phase transition]] into a [[spinel]] structure.<ref name="olivine">{{cite journal| last1 = Greene II | first1 = H.W.| last2 = Burnley | first2 = P.C.| title = A new self-organizing mechanism for deep-focus earthquakes| journal = Nature| volume = 341| issue = 6244| pages = 733–737| date = October 26, 1989| doi = 10.1038/341733a0| bibcode=1989Natur.341..733G| s2cid = 4287597}}</ref>

===Volcanic activity===
{{main|Volcano tectonic earthquake}}

Earthquakes often occur in volcanic regions and are caused there, both by [[tectonic plates|tectonic]] faults and the movement of [[magma]] in [[volcano]]es. Such earthquakes can serve as an early warning of volcanic eruptions, as during the [[1980 eruption of Mount St. Helens]].<ref>{{Cite book|last=Foxworthy and Hill|year=1982|title=Volcanic Eruptions of 1980 at Mount St. Helens, The First 100&nbsp;Days: USGS Professional Paper 1249}}</ref> Earthquake swarms can serve as markers for the location of the flowing magma throughout the volcanoes. These swarms can be recorded by [[seismometers]] and [[tiltmeter]]s (a device that measures ground slope) and used as sensors to predict imminent or upcoming eruptions.<ref>{{cite web|url=https://pubs.usgs.gov/gip/earthq1/volcano.html|title=Volcanoes and Earthquakes|publisher=United States Geological Survey|date=January 7, 1998|author=Watson, John|author2=Watson, Kathie|access-date=May 9, 2009|archive-date=March 26, 2009|archive-url=https://web.archive.org/web/20090326093352/http://pubs.usgs.gov/gip/earthq1/volcano.html|url-status=live}}</ref>

===Rupture dynamics===
A tectonic earthquake begins as an area of initial slip on the fault surface that forms the focus. Once the rupture has been initiated, it begins to propagate away from the focus, spreading out along the fault surface. Lateral propagation will continue until either the rupture reaches a barrier, such as the end of a fault segment, or a region on the fault where there is insufficient stress to allow continued rupture. For larger earthquakes, the depth extent of rupture will be constrained downwards by the [[brittle-ductile transition zone]] and upwards by the ground surface. The mechanics of this process are poorly understood because it is difficult either to recreate such rapid movements in a laboratory or to record seismic waves close to a nucleation zone due to strong ground motion.<ref name="NRS"/>

In most cases, the rupture speed approaches, but does not exceed, the [[S wave|shear wave]] (S wave) velocity of the surrounding rock. There are a few exceptions to this:

==== Supershear earthquakes ====
[[File:Kahramanmaraş after 7.8 magnitude earthquake in Türkiye 5.jpg|250px|thumb|right|The [[2023 Turkey–Syria earthquakes]] ruptured along segments of the [[East Anatolian Fault]] at supershear speeds; more than 50,000 people died in both countries.<ref name="MelgarEtAl23">{{cite journal |last1=Melgar |first1=Diego |last2=Taymaz |first2=Tuncay |last3=Ganas |first3=Athanassios |last4=Crowell |first4=Brendan |last5=Öcalan |first5=Taylan |last6=Kahraman |first6=Metin |last7=Tsironi |first7=Varvara |last8=Yolsal-Çevikbilen |first8=Seda |last9=Valkaniotis |first9=Sotiris |last10=Irmak |first10=Tahir Serkan |last11=Eken |first11=Tuna |last12=Erman |first12=Ceyhun |last13=Özkan |first13=Berkan |last14=Dogan |first14=Ali Hasan |last15=Altuntaş |first15=Cemali |title=Sub- and super-shear ruptures during the 2023 Mw 7.8 and Mw 7.6 earthquake doublet in SE Türkiye |journal=Seismica |year=2023 |volume=2 |issue=3 |page=387 |doi=10.26443/seismica.v2i3.387|s2cid=257520761 |doi-access=free |bibcode=2023Seism...2..387M }}</ref>]]
[[Supershear earthquake]] ruptures are known to have propagated at speeds greater than the S wave velocity. These have so far all been observed during large strike-slip events. The unusually wide zone of damage caused by the [[2001 Kunlun earthquake]] has been attributed to the effects of the [[sonic boom]] developed in such earthquakes.

==== Slow earthquakes ====
[[Slow earthquake]] ruptures travel at unusually low velocities. A particularly dangerous form of slow earthquake is the [[tsunami earthquake]], observed where the relatively low felt intensities, caused by the slow propagation speed of some great earthquakes, fail to alert the population of the neighboring coast, as in the [[1896 Sanriku earthquake]].<ref name="NRS">{{cite book|last=National Research Council (U.S.). Committee on the Science of Earthquakes|title=Living on an Active Earth: Perspectives on Earthquake Science|chapter-url=http://www.nap.edu/openbook.php?record_id=10493&page=282|access-date=8 July 2010|year=2003|publisher=National Academies Press|location=Washington, D.C.|isbn=978-0-309-06562-7|page=[https://archive.org/details/livingonactiveea0000unse/page/418 418]|chapter=5. Earthquake Physics and Fault-System Science|url=https://archive.org/details/livingonactiveea0000unse/page/418}}</ref>

====Co-seismic overpressuring and effect of pore pressure====
During an earthquake, high temperatures can develop at the fault plane, increasing pore pressure and consequently vaporization of the groundwater already contained within the rock.<ref name=Sibson>{{cite journal|last1=Sibson |first1= R.H.|year=1973|title=Interactions between Temperature and Pore-Fluid Pressure during Earthquake Faulting and a Mechanism for Partial or Total Stress Relief|journal= Nat. Phys. Sci. |volume=243|issue= 126|pages=66–68|doi= 10.1038/physci243066a0|bibcode= 1973NPhS..243...66S}}</ref><ref name=Rudnicki>{{cite journal|last1=Rudnicki |first1= J.W.|last2=Rice |first2= J.R.|year=2006|title=Effective normal stress alteration due to pore pressure changes induced by dynamic slip propagation on a plane between dissimilar materials|journal= J. Geophys. Res. |volume= 111, B10308|issue= B10|doi=10.1029/2006JB004396|bibcode= 2006JGRB..11110308R|s2cid= 1333820|url=https://dash.harvard.edu/bitstream/1/2668811/1/Rice_PorePressDynSlip.pdf|url-status=live|archive-url=https://web.archive.org/web/20190502041503/https://dash.harvard.edu/bitstream/handle/1/2668811/Rice_PorePressDynSlip.pdf;jsessionid=071046244FA1B0E26418CE95B726BA0E?sequence=1|archive-date=2019-05-02|archive-format=PDF}}</ref><ref name=Guerriero>{{cite journal|last1=Guerriero |first1= V |last2=Mazzoli |first2= S.|year=2021|title=Theory of Effective Stress in Soil and Rock and Implications for Fracturing Processes: A Review|journal=Geosciences  |volume=11|issue= 3 |pages=119|doi=10.3390/geosciences11030119|bibcode= 2021Geosc..11..119G |doi-access=free}}</ref> In the coseismic phase, such an increase can significantly affect slip evolution and speed, in the post-seismic phase it can control the [[Aftershock]] sequence because, after the main event, pore pressure increase slowly propagates into the surrounding fracture network.<ref name=Nur>{{cite journal|last1=Nur |first1= A |last2=Booker |first2= J.R.|year=1972|title=Aftershocks Caused by Pore Fluid Flow?|journal=Science |volume=175|issue= 4024 |pages=885–887|doi= 10.1126/science.175.4024.885 |pmid= 17781062 |bibcode= 1972Sci...175..885N |s2cid= 19354081 }}</ref><ref name=Guerriero /> From the point of view of the [[Mohr-Coulomb theory|Mohr-Coulomb strength theory]], an increase in fluid pressure reduces the normal stress acting on the fault plane that holds it in place, and fluids can exert a lubricating effect. As thermal overpressurization may provide positive feedback between slip and strength fall at the fault plane, a common opinion is that it may enhance the faulting process instability. After the mainshock, the pressure gradient between the fault plane and the neighboring rock causes a fluid flow that increases pore pressure in the surrounding fracture networks; such an increase may trigger new faulting processes by reactivating adjacent faults, giving rise to aftershocks.<ref name=Nur /><ref name=Guerriero /> Analogously, artificial pore pressure increase, by fluid injection in Earth's crust, may [[Induced seismicity|induce seismicity]].

===Tidal forces===
{{main|Tidal triggering of earthquakes}}
[[Tides]] may trigger some [[seismicity]].<ref>{{cite journal | last1=Hartzell | first1=Stephen | last2=Heaton | first2=Thomas | title=The fortnightly tide and the tidal triggering of earthquakes | journal=Bulletin of the Seismological Society of America | volume=80 | issue=2 | date=1990-04-01 | issn=1943-3573 | doi=10.1785/BSSA0800020504 | doi-access=free | pages=504–505 | bibcode=1990BuSSA..80..504H | url=https://authors.library.caltech.edu/records/39ffh-nrm98/files/1282.full.pdf?download=1}}</ref>

===Clusters===
Most earthquakes form part of a sequence, related to each other in terms of location and time.<ref name=WAAFEC>{{cite web|url=https://earthquake.usgs.gov/eqcenter/step/explain.php|title=What are Aftershocks, Foreshocks, and Earthquake Clusters?|url-status=dead|archive-url=https://web.archive.org/web/20090511175245/http://earthquake.usgs.gov/eqcenter/step/explain.php|archive-date=2009-05-11}}</ref> Most earthquake clusters consist of small tremors that cause little to no damage, but there is a theory that earthquakes can recur in a regular pattern.<ref>{{cite web|url=https://earthquake.usgs.gov/research/parkfield/repeat.php|title=Repeating Earthquakes|publisher=United States Geological Survey|date=January 29, 2009|access-date=May 11, 2009|archive-date=April 3, 2009|archive-url=https://web.archive.org/web/20090403074132/http://earthquake.usgs.gov/research/parkfield/repeat.php|url-status=live}}</ref> Earthquake clustering has been observed, for example, in Parkfield, California where a long-term research study is being conducted around the [[Parkfield earthquake]] cluster.<ref>{{Cite web |title=The Parkfield, California, Earthquake Experiment |url=https://earthquake.usgs.gov/learn/parkfield/ |access-date=2022-10-24 |publisher=United States Geological Survey |archive-date=2022-10-24 |archive-url=https://web.archive.org/web/20221024200153/https://earthquake.usgs.gov/learn/parkfield/ |url-status=live }}</ref>

====Aftershocks====
{{Main|Aftershock}}
[[File:2016 Central Italy earthquake wide.svg|thumb|upright=1.25|Magnitude of the [[August 2016 Central Italy earthquake|Central Italy earthquakes of August]] and [[October 2016 Central Italy earthquakes|October 2016]] and [[January 2017 Central Italy earthquakes|January 2017]] and the aftershocks (which continued to occur after the period shown here)]]
An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. Rapid changes of stress between rocks, and the stress from the original earthquake are the main causes of these aftershocks,<ref name=Britannica>{{Cite web|title=Aftershock {{!}} geology|url=https://www.britannica.com/science/aftershock-geology|access-date=2021-10-13|website=Encyclopædia Britannica|archive-date=2015-08-23|archive-url=https://web.archive.org/web/20150823124854/https://www.britannica.com/science/aftershock-geology|url-status=live}}</ref> along with the crust around the ruptured [[Fault (geology)|fault plane]] as it adjusts to the effects of the mainshock.<ref name="WAAFEC" /> An aftershock is in the same region as the main shock but always of a smaller magnitude, however, they can still be powerful enough to cause even more damage to buildings that were already previously damaged from the mainshock.<ref name=Britannica/> If an aftershock is larger than the mainshock, the aftershock is redesignated as the mainshock and the original main shock is redesignated as a [[foreshock]]. Aftershocks are formed as the crust around the displaced [[Fault (geology)|fault plane]] adjusts to the effects of the mainshock.<ref name=WAAFEC/>

====Swarms====
{{Main|Earthquake swarm}}
Earthquake swarms are sequences of earthquakes striking in a specific area within a short period. They are different from earthquakes followed by a series of [[aftershock]]s by the fact that no single earthquake in the sequence is the main shock, so none has a notably higher magnitude than another. An example of an earthquake swarm is the 2004 activity at [[Yellowstone National Park]].<ref>{{cite web|url=https://volcanoes.usgs.gov/yvo/2004/Apr04Swarm.html|title=Earthquake Swarms at Yellowstone|publisher=United States Geological Survey|access-date=2008-09-15|archive-date=2008-05-13|archive-url=https://web.archive.org/web/20080513060550/http://volcanoes.usgs.gov/yvo/2004/Apr04Swarm.html|url-status=live}}</ref> In August 2012, a swarm of earthquakes shook [[Southern California]]'s [[Imperial Valley]], showing the most recorded activity in the area since the 1970s.<ref>{{cite news|last=Duke|first=Alan|title=Quake 'swarm' shakes Southern California|url=http://www.cnn.com/2012/08/26/us/california-quake-swarm/index.html|publisher=CNN|access-date=27 August 2012|archive-date=27 August 2012|archive-url=https://web.archive.org/web/20120827120248/http://www.cnn.com/2012/08/26/us/california-quake-swarm/index.html|url-status=live}}</ref>

Sometimes a series of earthquakes occur in what has been called an ''earthquake storm'', where the earthquakes strike a fault in clusters, each triggered by the shaking or [[coulomb stress transfer|stress redistribution]] of the previous earthquakes. Similar to [[aftershock]]s but on adjacent segments of fault, these storms occur over the course of years, with some of the later earthquakes as damaging as the early ones. Such a pattern was observed in the sequence of about a dozen earthquakes that struck the [[North Anatolian Fault]] in Turkey in the 20th century and has been inferred for older anomalous clusters of large earthquakes in the Middle East.<ref>{{cite journal |title=Poseidon's Horses: Plate Tectonics and Earthquake Storms in the Late Bronze Age Aegean and Eastern Mediterranean |journal=Journal of Archaeological Science |year=2000 |author=Amos Nur |issn=0305-4403 |volume=27 |issue=1 |pages=43–63 |url=http://water.stanford.edu/nur/EndBronzeage.pdf |doi=10.1006/jasc.1999.0431 |last2=Cline |first2=Eric H. |bibcode=2000JArSc..27...43N |url-status=dead |archive-date=2009-03-25 |archive-url=https://web.archive.org/web/20090325050459/http://water.stanford.edu/nur/EndBronzeage.pdf}}</ref><ref>{{cite web |url=https://www.bbc.co.uk/science/horizon/2003/earthquakestorms.shtml |title=Earthquake Storms |work=[[Horizon (BBC TV series)|Horizon]] |date=1 April 2003 |access-date=2007-05-02 |archive-date=2019-10-16 |archive-url=https://web.archive.org/web/20191016045550/http://www.bbc.co.uk/science/horizon/2003/earthquakestorms.shtml |url-status=live }}</ref>

===Frequency===
[[File:Comerio, Luca (1878-1940) - Vittime del terremoto di Messina (dicembre 1908).jpg|thumb|The [[1908 Messina earthquake|Messina earthquake]] and tsunami took about 80,000 lives on December 28, 1908, in [[Sicily]] and [[Calabria]].<ref name="CFTI5">{{Cite web |url=https://storing.ingv.it/cfti/cfti5/quake.php?21318IT |title=1908 12 28, 04:20:27 Calabria meridionale-Messina (Italy)  |last1=Guidoboni E. |last2= Ferrari G. |website=CFTI5 Catalogue of Strong Earthquakes in Italy (461 BC – 1997) and Mediterranean Area (760 B.C. – 1500) |last3=Mariotti D. |last4=Comastri A. |last5=Tarabusi G. |last6=Sgattoni G. |last7=Valensise G}}</ref>]]

It is estimated that around 500,000 earthquakes occur each year, detectable with current instrumentation. About 100,000 of these can be felt.<ref name="usgsfacts">{{cite web|url=https://www.usgs.gov/natural-hazards/earthquake-hazards/science/cool-earthquake-facts|title=Cool Earthquake Facts|publisher=United States Geological Survey|access-date=2021-04-21|archive-date=2021-04-20|archive-url=https://web.archive.org/web/20210420165152/https://www.usgs.gov/natural-hazards/earthquake-hazards/science/cool-earthquake-facts|url-status=live}}</ref><ref name="wp100414">{{Cite news | first=Margaret Webb | last=Pressler | title=More earthquakes than usual? Not really. | department=KidsPost | newspaper= The Washington Post| pages= C10 | date=14 April 2010 }}</ref><!----url does not contain box statistics that print edition does and is included for info only----> Minor earthquakes occur very frequently around the world in places like California and Alaska in the U.S., as well as in El Salvador, Mexico, Guatemala, Chile, Peru, Indonesia, the Philippines, Iran, Pakistan, the [[Azores]] in Portugal, Turkey, New Zealand, Greece, Italy, India, Nepal, and Japan.<ref>{{cite web |url=https://earthquake.usgs.gov/ |title=Earthquake Hazards Program |publisher=United States Geological Survey |access-date=2006-08-14 |archive-date=2011-05-13 |archive-url=https://web.archive.org/web/20110513032733/https://earthquake.usgs.gov/ |url-status=live }}</ref> Larger earthquakes occur less frequently, the relationship being [[Gutenberg–Richter law|exponential]]; for example, roughly ten times as many earthquakes larger than magnitude 4 occur than earthquakes larger than magnitude 5.<ref>{{Cite web|url=https://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php|archiveurl=https://web.archive.org/web/20100524161817/http://earthquake.usgs.gov/earthquakes/eqarchives/year/eqstats.php|url-status=dead|title=USGS Earthquake statistics table based on data since 1900|archivedate=May 24, 2010}}</ref> In the (low seismicity) United Kingdom, for example, it has been calculated that the average recurrences are:
an earthquake of 3.7–4.6 every year, an earthquake of 4.7–5.5 every 10&nbsp;years, and an earthquake of 5.6 or larger every 100&nbsp;years.<ref>{{cite web |url=http://www.quakes.bgs.ac.uk/hazard/Hazard_UK.htm |title=Seismicity and earthquake hazard in the UK |publisher=Quakes.bgs.ac.uk |access-date=2010-08-23 |archive-date=2010-11-06 |archive-url=https://web.archive.org/web/20101106121058/http://quakes.bgs.ac.uk/hazard/Hazard_UK.htm |url-status=live }}</ref> This is an example of the [[Gutenberg–Richter law]].

The number of seismic stations has increased from about 350 in 1931 to many thousands today. As a result, many more earthquakes are reported than in the past, but this is because of the vast improvement in instrumentation, rather than an increase in the number of earthquakes. The [[United States Geological Survey]] (USGS) estimates that, since 1900, there have been an average of 18 major earthquakes (magnitude 7.0–7.9) and one great earthquake (magnitude 8.0 or greater) per year, and that this average has been relatively stable.<ref>
{{cite web
 |title       = Common Myths about Earthquakes
 |url         = https://earthquake.usgs.gov/learning/faq.php?categoryID=6&faqID=110
 |publisher   = United States Geological Survey
 |access-date  = 2006-08-14
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20060925135349/http://earthquake.usgs.gov/learning/faq.php?categoryID=6&faqID=110
 |archive-date = 2006-09-25
}}</ref> In recent years, the number of major earthquakes per year has decreased, though this is probably a statistical fluctuation rather than a systematic trend.<ref>[https://earthquake.usgs.gov/learn/topics/increase_in_earthquakes.php Are Earthquakes Really on the Increase?] {{webarchive|url=https://web.archive.org/web/20140630233346/http://earthquake.usgs.gov/learn/topics/increase_in_earthquakes.php |date=2014-06-30 }}, USGS Science of Changing World. Retrieved 30 May 2014.</ref> More detailed statistics on the size and frequency of earthquakes is available from the United States Geological Survey.<ref>
{{cite web
 |title=Earthquake Facts and Statistics: Are earthquakes increasing?
 |url=https://neic.usgs.gov/neis/eqlists/eqstats.html
 |publisher=United States Geological Survey
 |access-date=2006-08-14
 |url-status=dead
 |archive-url=https://web.archive.org/web/20060812060818/http://neic.usgs.gov/neis/eqlists/eqstats.html
 |archive-date=2006-08-12
}}</ref> A recent increase in the number of major earthquakes has been noted, which could be explained by a cyclical pattern of periods of intense tectonic activity, interspersed with longer periods of low intensity. However, accurate recordings of earthquakes only began in the early 1900s, so it is too early to categorically state that this is the case.<ref>[http://www.australiangeographic.com.au/journal/the-10-biggest-earthquakes-in-recorded-history.htm/ The 10 biggest earthquakes in history] {{Webarchive|url=https://web.archive.org/web/20130930084024/http://www.australiangeographic.com.au/journal/the-10-biggest-earthquakes-in-recorded-history.htm/ |date=2013-09-30 }}, Australian Geographic, March 14, 2011.</ref>

Most of the world's earthquakes (90%, and 81% of the largest) take place in the {{convert|40000|km|mi|adj=mid|-long}}, horseshoe-shaped zone called the circum-Pacific seismic belt, known as the Pacific [[Ring of Fire]], which for the most part bounds the [[Pacific plate]].<ref>
{{cite web
 |title       = Historic Earthquakes and Earthquake Statistics: Where do earthquakes occur?
 |url         = https://earthquake.usgs.gov/learning/faq.php?categoryID=11&faqID=95
 |publisher   = United States Geological Survey
 |access-date  = 2006-08-14
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20060925142008/http://earthquake.usgs.gov/learning/faq.php?categoryID=11&faqID=95
 |archive-date = 2006-09-25
}}</ref><ref>
{{cite web
 |url         = https://earthquake.usgs.gov/learning/glossary.php?termID=150
 |publisher   = United States Geological Survey
 |title       = Visual Glossary – Ring of Fire
 |access-date  = 2006-08-14
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20060828152638/http://earthquake.usgs.gov/learning/glossary.php?termID=150
 |archive-date = 2006-08-28
}}</ref> Massive earthquakes tend to occur along other plate boundaries too, such as along the [[Himalayan Mountains]].<ref>{{cite journal | last1 = Jackson | first1 = James | year = 2006 | title = Fatal attraction: living with earthquakes, the growth of villages into megacities, and earthquake vulnerability in the modern world | url = http://rsta.royalsocietypublishing.org/content/364/1845/1911.full | journal = [[Philosophical Transactions of the Royal Society]] | volume = 364 | issue = 1845 | pages = 1911–1925 | doi = 10.1098/rsta.2006.1805 | pmid = 16844641 | bibcode = 2006RSPTA.364.1911J | s2cid = 40712253 | access-date = 2011-03-09 | archive-date = 2013-09-03 | archive-url = https://web.archive.org/web/20130903085953/http://rsta.royalsocietypublishing.org/content/364/1845/1911.full | url-status = live | url-access = subscription }}</ref>

With the rapid growth of [[Megacity|mega-cities]] such as Mexico City, Tokyo, and Tehran in areas of high [[seismic risk]], some seismologists are warning that a single earthquake may claim the lives of up to three million people.<ref>"[http://cires.colorado.edu/~bilham/UrbanEarthquakesGlobal.html Global urban seismic risk] {{Webarchive|url=https://web.archive.org/web/20110920015358/http://cires.colorado.edu/~bilham/UrbanEarthquakesGlobal.html |date=2011-09-20 }}." Cooperative Institute for Research in Environmental Science.</ref>

===Induced seismicity===
{{main|Induced seismicity}}
While most earthquakes are caused by the movement of the Earth's [[tectonic plate]]s, human activity can also produce earthquakes. Activities both above ground and below may change the stresses and strains on the crust, including building reservoirs, extracting resources such as coal or oil, and injecting fluids underground for waste disposal or [[fracking]].<ref>{{cite journal |author1=Fougler, Gillian R. |author2=Wilson, Miles |author3=Gluyas, Jon G. |author4=Julian, Bruce R. |author5=Davies, Richard J. |author-link1=Gillian Foulger |title=Global review of human-induced earthquakes |journal=[[Earth-Science Reviews]] |date=2018 |volume=178 |pages=438–514 |doi=10.1016/j.earscirev.2017.07.008 |bibcode=2018ESRv..178..438F |doi-access=free }}</ref> Most of these earthquakes have small magnitudes. The 5.7 magnitude [[2011 Oklahoma earthquake]] is thought to have been caused by disposing wastewater from oil production into [[injection wells]],<ref>{{cite news |last1=Fountain |first1=Henry |title=Study Links 2011 Quake to Technique at Oil Wells |newspaper=The New York Times |url=https://www.nytimes.com/2013/03/29/science/earth/2011-oklahoma-quake-tied-to-wastewater-disposal-at-oil-wells.html |access-date=July 23, 2020 |date=March 28, 2013 |archive-date=July 23, 2020 |archive-url=https://web.archive.org/web/20200723135240/https://www.nytimes.com/2013/03/29/science/earth/2011-oklahoma-quake-tied-to-wastewater-disposal-at-oil-wells.html |url-status=live }}</ref> and studies point to the state's oil industry as the cause of other earthquakes in the past century.<ref>{{cite journal |author1=Hough, Susan E. |author-link1=Susan Hough |author2=Page, Morgan |title=A Century of Induced Earthquakes in Oklahoma? |journal=[[Bulletin of the Seismological Society of America]] |date=2015 |volume=105 |issue=6 |pages=2863–2870 |doi=10.1785/0120150109 |bibcode=2015BuSSA.105.2863H |url=https://pubs.geoscienceworld.org/ssa/bssa/article-abstract/105/6/2863/331910/A-Century-of-Induced-Earthquakes-in-Oklahoma-A?redirectedFrom=fulltext |access-date=July 23, 2020 |archive-date=July 23, 2020 |archive-url=https://web.archive.org/web/20200723210546/https://pubs.geoscienceworld.org/ssa/bssa/article-abstract/105/6/2863/331910/A-Century-of-Induced-Earthquakes-in-Oklahoma-A?redirectedFrom=fulltext |url-status=live |url-access=subscription }}</ref> A [[Columbia University]] paper suggested that the 8.0 magnitude [[2008 Sichuan earthquake]] was induced by loading from the [[Zipingpu Dam]],<ref>{{cite journal |last1=Klose |first1=Christian D. |title=Evidence for anthropogenic surface loading as trigger mechanism of the 2008 Wenchuan earthquake |journal=Environmental Earth Sciences |date=July 2012 |volume=66 |issue=5 |pages=1439–1447 |doi=10.1007/s12665-011-1355-7|arxiv=1007.2155 |bibcode=2012EES....66.1439K |s2cid=118367859 }}</ref> though the link has not been conclusively proved.<ref>{{cite news |last1=LaFraniere |first1=Sharon |title=Possible Link Between Dam and China Quake |newspaper=The New York Times |url=https://www.nytimes.com/2009/02/06/world/asia/06quake.html |access-date=July 23, 2020 |date=February 5, 2009 |archive-date=January 27, 2018 |archive-url=https://web.archive.org/web/20180127101432/http://www.nytimes.com/2009/02/06/world/asia/06quake.html |url-status=live }}</ref>

==Measurement and location==
{{Main|Seismic magnitude scales|Seismology}}

The instrumental scales used to describe the size of an earthquake began with the [[Richter scale]] in the 1930s. It is a relatively simple measurement of an event's amplitude, and its use has become minimal in the 21st century. [[Seismic waves]] travel through the [[Earth's interior]] and can be recorded by [[seismometer]]s at great distances. The [[surface-wave magnitude]] was developed in the 1950s as a means to measure remote earthquakes and to improve the accuracy for larger events. The [[moment magnitude scale]] not only measures the amplitude of the shock but also takes into account the [[seismic moment]] (total rupture area, average slip of the fault, and rigidity of the rock). The [[Japan Meteorological Agency seismic intensity scale]], the [[Medvedev–Sponheuer–Karnik scale]], and the [[Mercalli intensity scale]] are based on the observed effects and are related to the intensity of shaking.

=== {{anchor|Magnitude}}Intensity and magnitude ===
The shaking of the earth is a common phenomenon that has been experienced by humans from the earliest of times. Before the development of strong-motion accelerometers, the intensity of a seismic event was estimated based on the observed effects. Magnitude and intensity are not directly related and calculated using different methods. The magnitude of an earthquake is a single value that describes the size of the earthquake at its source. Intensity is the measure of shaking at different locations around the earthquake. Intensity values vary from place to place, depending on the distance from the earthquake and the underlying rock or soil makeup.<ref>{{Cite book |last1=Earle |first1=Steven |date=September 2015 |title=Physical Geology |edition=2nd |chapter=11.3 Measuring Earthquakes |chapter-url=https://opentextbc.ca/geology/chapter/11-3-measuring-earthquakes/|access-date=2022-10-22 |archive-date=2022-10-21 |archive-url=https://web.archive.org/web/20221021040843/https://opentextbc.ca/geology/chapter/11-3-measuring-earthquakes/ |url-status=live }}</ref>

The [[Seismic magnitude scales#Richter|first scale for measuring earthquake magnitudes]] was developed by [[Charles Francis Richter]] in 1935. Subsequent scales ([[seismic magnitude scales]]) have retained a key feature, where each unit represents a ten-fold difference in the amplitude of the ground shaking and a 32-fold difference in energy. Subsequent scales are also adjusted to have approximately the same numeric value within the limits of the scale.<ref>{{Harvnb|Chung|Bernreuter|1980|p=1}}.</ref>

Although the mass media commonly reports earthquake magnitudes as "Richter magnitude" or "Richter scale", standard practice by most seismological authorities is to express an earthquake's strength on the [[seismic scale#Mw|moment magnitude]] scale, which is based on the actual energy released by an earthquake, the static seismic moment.<ref>{{cite web |title=USGS Earthquake Magnitude Policy (implemented on January 18, 2002) |url=https://earthquake.usgs.gov/aboutus/docs/020204mag_policy.php |publisher=United States Geological Survey |url-status=dead |archive-url=https://web.archive.org/web/20160504144754/http://earthquake.usgs.gov/aboutus/docs/020204mag_policy.php |archive-date=2016-05-04 }} A copy can be found at {{cite web |title=USGS Earthquake Magnitude Policy |url=http://dapgeol.tripod.com/usgsearthquakemagnitudepolicy.htm |access-date=2017-07-25 |archive-date=2017-07-31 |archive-url=https://web.archive.org/web/20170731230704/http://dapgeol.tripod.com/usgsearthquakemagnitudepolicy.htm |url-status=live }}</ref><ref>{{Cite journal |last1=Bormann |first1=P |last2=Di Giacomo |first2=D |date=2011 |title=The moment magnitude Mw and the energy magnitude Me: common roots and differences |url=https://doi.org/10.1007/s10950-010-9219-2 |journal=Journal of Seismology |volume=15 |issue=2 |pages=411–427 |doi=10.1007/s10950-010-9219-2 |via=Springer Link}}</ref>

=== Seismic waves ===
Every earthquake produces different types of seismic waves, which travel through rock with different velocities:
* Longitudinal [[P waves]] (shock- or pressure waves)
* Transverse [[S waves]] (both body waves)
* [[Surface wave]]s – ([[Rayleigh wave|Rayleigh]] and [[Love wave]]s)

==== Speed of seismic waves ====
[[Propagation velocity]] of the seismic waves through solid rock ranges from approx. {{Convert|3|km/s|mi/s|abbr=on}} up to {{Convert|13|km/s|mi/s|abbr=on}}, depending on the [[density]] and [[Elasticity (physics)|elasticity]] of the medium. In the Earth's interior, the shock- or P waves travel much faster than the S waves (approx. relation 1.7:1). The differences in travel time from the [[epicentre|epicenter]] to the observatory are a measure of the distance and can be used to image both sources of earthquakes and structures within the Earth. Also, the depth of the [[hypocenter]] can be computed roughly.

'''P wave speed'''
* Upper crust soils and unconsolidated sediments: {{Convert|2-3|km|mi|abbr=on}} per second
* Upper crust solid rock: {{Convert|3-6|km|mi|abbr=on}} per second
* Lower crust: {{Convert|6-7|km|mi|abbr=on}} per second
* Deep mantle: {{Convert|13|km|mi|abbr=on}} per second.

'''S waves speed'''
* Light sediments: {{Convert|2-3|km|mi|abbr=on}} per second
* Earths crust: {{Convert|4-5|km|mi|abbr=on}} per second
* Deep mantle: {{Convert|7|km|mi|abbr=on}} per second

==== Seismic wave arrival ====
As a consequence, the first waves of a distant earthquake arrive at an observatory via the Earth's mantle.

On average, the kilometer distance to the earthquake is the number of seconds between the P- and S wave arrival times, multiplied by 8.<ref>{{cite web |url=http://hypertextbook.com/facts/2001/PamelaSpiegel.shtml |title=Speed of Sound through the Earth |publisher=Hypertextbook.com |access-date=2010-08-23 |archive-date=2010-11-25 |archive-url=https://web.archive.org/web/20101125091130/http://hypertextbook.com/facts/2001/PamelaSpiegel.shtml |url-status=live }}</ref> Slight deviations are caused by inhomogeneities of subsurface structure. By such analysis of seismograms, the Earth's core was located in 1913 by [[Beno Gutenberg]].

S waves and later arriving surface waves do most of the damage compared to P waves. P waves squeeze and expand the material in the same direction they are traveling, whereas S waves shake the ground up and down and back and forth.<ref>{{cite web|url=https://newsela.com/articles/govt-science-earthquakes/id/26756/|title=Newsela {{!}} The science of earthquakes|website=newsela.com|access-date=2017-02-28|archive-date=2017-03-01|archive-url=https://web.archive.org/web/20170301005337/https://newsela.com/articles/govt-science-earthquakes/id/26756/|url-status=live}}</ref>

=== Location and reporting ===
{{main|Epicenter}}

Earthquakes are not only categorized by their magnitude but also by the place where they occur. The world is divided into 754 [[Flinn–Engdahl regions]] (F-E regions), which are based on political and geographical boundaries as well as seismic activity. More active zones are divided into smaller F-E regions whereas less active zones belong to larger F-E regions.

Standard reporting of earthquakes includes its [[Richter magnitude scale|magnitude]], date and time of occurrence, [[geographic coordinates]] of its [[epicenter]], depth of the epicenter, geographical region, distances to population centers, location uncertainty, several parameters that are included in USGS earthquake reports (number of stations reporting, number of observations, etc.), and a unique event ID.<ref>{{cite web |url=http://geographic.org/earthquakes/real_time_details.php?id=recenteqsww/Quakes/usc000f1s0.php&lat=-10.7377&lon=165.1378 |title=Magnitude 8.0 – SANTA CRUZ ISLANDS Earthquake Details |work=Global Earthquake Epicenters with Maps |author=Geographic.org |access-date=2013-03-13 |archive-date=2013-05-14 |archive-url=https://web.archive.org/web/20130514143205/http://geographic.org/earthquakes/real_time_details.php?id=recenteqsww/Quakes/usc000f1s0.php&lat=-10.7377&lon=165.1378 |url-status=live }}</ref>

Although relatively slow seismic waves have traditionally been used to detect earthquakes, scientists realized in 2016 that gravitational measurement could provide instantaneous detection of earthquakes, and confirmed this by analyzing gravitational records associated with the [[2011 Tōhoku earthquake and tsunami|2011 Tohoku-Oki]] ("Fukushima") earthquake.<ref>{{cite web|url=https://www.researchgate.net/blog/post/changes-to-earths-gravity-offer-early-earthquake-warning|title=Earth's gravity offers earlier earthquake warnings|access-date=2016-11-22|archive-date=2016-11-23|archive-url=https://web.archive.org/web/20161123201125/https://www.researchgate.net/blog/post/changes-to-earths-gravity-offer-early-earthquake-warning|url-status=live}}</ref><ref>{{cite web|url=https://cosmosmagazine.com/geoscience/gravity-shifts-could-sound-early-earthquake-alarm|title=Gravity shifts could sound early earthquake alarm|access-date=2016-11-23|archive-date=2016-11-24|archive-url=https://web.archive.org/web/20161124100006/https://cosmosmagazine.com/geoscience/gravity-shifts-could-sound-early-earthquake-alarm|url-status=dead}}</ref>

==Effects==
[[File:1755 Lisbon earthquake.jpg|thumb|1755 copper engraving depicting [[Lisbon]] in ruins and in flames after the [[1755 Lisbon earthquake]], which killed an estimated 60,000 people. A [[tsunami]] overwhelms the ships in the harbor.]]

The effects of earthquakes include, but are not limited to, the following:

===Shaking and ground rupture===
[[File:Haiti earthquake damage.jpg|thumb|Damaged buildings in [[Port-au-Prince]], [[2010 Haiti earthquake|Haiti]], January 2010]]

Shaking and [[surface rupture|ground rupture]] are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures. The severity of the local effects depends on the complex combination of the earthquake [[Richter magnitude scale|magnitude]], the distance from the [[epicenter]], and the local geological and geomorphological conditions, which may amplify or reduce [[wave propagation]].<ref>{{cite web |url=http://www.abag.ca.gov/bayarea/eqmaps/doc/contents.html |title=On Shaky Ground, Association of Bay Area Governments, San Francisco, reports 1995, 1998 (updated 2003) |publisher=Abag.ca.gov |access-date=2010-08-23 |url-status=dead |archive-url=https://web.archive.org/web/20090921082202/http://www.abag.ca.gov/bayarea/eqmaps/doc/contents.html |archive-date=2009-09-21 }}</ref> The ground-shaking is measured by [[ground acceleration]].

Specific local geological, geomorphological, and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes. This effect is called site or local amplification. It is principally due to the transfer of the [[seismic]] motion from hard deep soils to soft superficial soils and the effects of seismic energy focalization owing to the typical geometrical setting of such deposits.

Ground rupture is a visible breaking and displacement of the Earth's surface along the trace of the fault, which may be of the order of several meters in the case of major earthquakes. Ground rupture is a major risk for large engineering structures such as [[dams]], bridges, and [[nuclear power stations]] and requires careful mapping of existing faults to identify any that are likely to break the ground surface within the life of the structure.<ref>{{cite web|url=http://www.consrv.ca.gov/cgs/information/publications/cgs_notes/note_49/Documents/note_49.pdf|title=Guidelines for evaluating the hazard of surface fault rupture, California Geological Survey|publisher=California Department of Conservation|year=2002|url-status=dead|archive-url=https://web.archive.org/web/20091009065422/http://www.consrv.ca.gov/cgs/information/publications/cgs_notes/note_49/Documents/note_49.pdf|archive-date=2009-10-09}}</ref>

===Soil liquefaction===
{{Main|Soil liquefaction}}
Soil liquefaction occurs when, because of the shaking, water-saturated [[granular]] material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits. For example, in the [[1964 Alaska earthquake]], soil liquefaction caused many buildings to sink into the ground, eventually collapsing upon themselves.<ref>{{cite web|url=https://earthquake.usgs.gov/regional/states/events/1964_03_28.php |title=Historic Earthquakes – 1964 Anchorage Earthquake |publisher=United States Geological Survey |access-date=2008-09-15 |url-status=dead |archive-url=https://web.archive.org/web/20110623111831/http://earthquake.usgs.gov/regional/states/events/1964_03_28.php |archive-date=2011-06-23 }}</ref>

===Human impacts===
[[File:Ghajn Hadid Tower closer view.JPG|thumb|Ruins of the [[Għajn Ħadid Tower]], which collapsed during the [[1856 Heraklion earthquake]]]]

Physical damage from an earthquake will vary depending on the intensity of shaking in a given area and the type of population.  Underserved and developing communities frequently experience more severe impacts (and longer lasting) from a seismic event compared to well-developed communities.<ref>{{Cite web |title=The wicked problem of earthquake hazard in developing countries |url=https://www.preventionweb.net/news/wicked-problem-earthquake-hazard-developing-countries |access-date=2022-11-03 |website=preventionweb.net |date=7 March 2018|archive-date=2022-11-03 |archive-url=https://web.archive.org/web/20221103025507/https://www.preventionweb.net/news/wicked-problem-earthquake-hazard-developing-countries |url-status=live }}</ref> Impacts may include:
* Injuries and loss of life
* Damage to critical infrastructure (short and long-term)
** Roads, bridges, and public transportation networks
** Water, power, sewer and gas interruption
** Communication systems
* Loss of critical community services including hospitals, police, and fire
* General [[property damage]]
* Collapse or destabilization (potentially leading to future collapse) of buildings

With these impacts and others, the aftermath may bring disease, a lack of basic necessities, mental consequences such as panic attacks and depression to survivors,<ref>{{cite web |url=http://www.nctsn.org/trauma-types/natural-disasters/earthquakes |title=Earthquake Resources |date=30 January 2018 |publisher=Nctsn.org |access-date=2018-06-05 |archive-date=2018-03-21 |archive-url=https://web.archive.org/web/20180321183320/http://www.nctsn.org/trauma-types/natural-disasters/earthquakes |url-status=live }}</ref> and higher insurance premiums. Recovery times will vary based on the level of damage and the socioeconomic status of the impacted community.

===Landslides===
{{further|Landslide}}

China stood out in several categories in a study group of 162 earthquakes (from 1772 to 2021) that included landslide fatalities. Due to the [[2008 Sichuan earthquake]], it had 42% of all landslide fatalities within the study (total event deaths were higher). They were followed by Peru (22%) from the [[1970 Ancash earthquake]], and Pakistan (21%) from the [[2005 Kashmir earthquake]]. China was also on top with the highest area affected by landslides with more than 80,000&nbsp;km<sup>2</sup>, followed by Canada with 66,000&nbsp;km<sup>2</sup> ([[1988 Saguenay earthquake|1988 Saguenay]] and [[1946 Vancouver Island earthquake|1946 Vancouver Island]]). Strike-slip (61 events) was the dominant fault type listed, followed closely by thrust/reverse (57), and normal (33).<ref>{{citation | last1=Seal | first1=Dylan M | last2=Jessee | first2=Anna Nowicki | last3=Hamburger | first3=Michael | last4=Dills | first4=Carter | last5=Allstadt | first5=Kate E | title=Comprehensive Global Database of Earthquake-Induced Landslide Events and Their Impacts (ver. 2.0, February 2022) | date=2022 | publisher=U.S. Geological Survey | doi=10.5066/P9RG3MBE}}</ref>

===Fires===
[[File:Sfearthquake3b.jpg|thumb|Fires of the [[1906 San Francisco earthquake]]]]
{{Further|Conflagration}}

Earthquakes can cause fires by damaging [[electric power|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. For example, more deaths in the [[1906 San Francisco earthquake]] were caused by fire than by the earthquake itself.<ref>{{cite web|url=https://earthquake.usgs.gov/regional/nca/1906/18april/index.php|title=The Great 1906 San Francisco earthquake of 1906|publisher=United States Geological Survey|access-date=2008-09-15|archive-date=2017-02-11|archive-url=https://web.archive.org/web/20170211170826/https://earthquake.usgs.gov/regional/nca/1906/18april/index.php|url-status=dead}}</ref>

===Tsunami===
[[File:2004-tsunami.jpg|thumb|The tsunami of the [[2004 Indian Ocean earthquake]]]]
{{main|Tsunami}}

Tsunamis are long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water—including when an earthquake [[Submarine earthquake|occurs at sea]]. In the open ocean, the distance between wave crests can surpass {{convert|100|km|mi}}, and the wave periods can vary from five minutes to one hour. Such tsunamis travel 600–800&nbsp;kilometers per hour (373–497 miles per hour), depending on water depth. Large waves produced by an earthquake or a submarine landslide can overrun nearby coastal areas in a matter of minutes. Tsunamis can also travel thousands of kilometers across open ocean and wreak destruction on far shores hours after the earthquake that generated them.<ref name=Noson>{{Cite book|last1=Noson|first1=L.L.|last2=Qamar|first2=A.|last3=Thorsen|first3=G.W.|publisher=Washington State Earthquake Hazards|year=1988|title=Washington Division of Geology and Earth Resources Information Circular 85|url=http://file.dnr.wa.gov/publications/ger_ic85_earthquake_hazards_wa.pdf|access-date=2019-12-01|archive-date=2020-02-04|archive-url=https://web.archive.org/web/20200204162651/https://file.dnr.wa.gov/publications/ger_ic85_earthquake_hazards_wa.pdf|url-status=live}}</ref>

Ordinarily, subduction earthquakes under magnitude 7.5 do not cause tsunamis, although some instances of this have been recorded. Most destructive tsunamis are caused by earthquakes of magnitude 7.5 or more.<ref name=Noson/>

===Floods===
{{further|Flood}}

Floods may be secondary effects of earthquakes if dams are damaged. Earthquakes may cause landslips to dam rivers, which collapse and cause floods.<ref>{{cite web|url=http://www.quakes.bgs.ac.uk/earthquakes/historical/historical_listing.htm |title=Notes on Historical Earthquakes |publisher=[[British Geological Survey]] |access-date=2008-09-15 |url-status=dead |archive-url=https://web.archive.org/web/20110516173115/http://www.quakes.bgs.ac.uk/earthquakes/historical/historical_listing.htm |archive-date=2011-05-16 }}</ref>

The terrain below the [[Sarez Lake]] in Tajikistan is in danger of catastrophic flooding if the [[landslide dam]] formed by the earthquake, known as the [[Usoi Dam]], were to fail during a future earthquake. Impact projections suggest the flood could affect roughly five million people.<ref>{{cite news|url=https://news.bbc.co.uk/2/hi/asia-pacific/3120693.stm|title=Fresh alert over Tajik flood threat|date=2003-08-03|publisher=BBC News|access-date=2008-09-15|archive-date=2008-11-22|archive-url=https://web.archive.org/web/20081122134305/http://news.bbc.co.uk/2/hi/asia-pacific/3120693.stm|url-status=live}}</ref>

==Management==

===Prediction===
{{Main|Earthquake prediction}}

[[Earthquake prediction]] is a branch of the science of [[seismology]] concerned with the specification of the time, location, and [[seismic scale|magnitude]] of future earthquakes within stated limits.<ref>{{Harvnb|Geller|Jackson|Kagan|Mulargia|1997|p=1616}}, following {{Harvtxt|Allen|1976|p=2070}}, who in turn followed {{Harvtxt|Wood|Gutenberg|1935}}</ref> Many methods have been developed for predicting the time and place in which earthquakes will occur. Despite considerable research efforts by [[seismologist]]s, scientifically reproducible predictions cannot yet be made to a specific day or month.<ref name="ludwin">[http://www.geophys.washington.edu/SEIS/PNSN/INFO_GENERAL/eq_prediction.html Earthquake Prediction] {{Webarchive|url=https://web.archive.org/web/20091007165545/http://www.geophys.washington.edu/SEIS/PNSN/INFO_GENERAL/eq_prediction.html |date=2009-10-07 }}. Ruth Ludwin, U.S. Geological Survey.</ref> Popular belief holds earthquakes are preceded by [[earthquake weather]], in the early morning.<ref>{{Cite news |last=Lafee |first=Scott |date=April 9, 2010 |title=Quake myths rely on cloudy facts |url=https://www.sandiegouniontribune.com/2010/04/09/quake-myths-rely-on-cloudy-facts/ |access-date=July 3, 2024 |work=[[The San Diego Union-Tribune]]}}</ref><ref>{{Cite web |title=Is there earthquake weather? |url=https://www.usgs.gov/faqs/there-earthquake-weather |url-status=live |archive-url=https://web.archive.org/web/20240303155939/https://www.usgs.gov/faqs/there-earthquake-weather |archive-date=March 3, 2024 |access-date=July 3, 2024 |publisher=United States Geological Survey}}</ref>

===Forecasting===
{{Main|Earthquake forecasting}}

While [[forecasting]] is usually considered to be a type of [[prediction]], [[earthquake forecasting]] is often differentiated from [[earthquake prediction]]. Earthquake forecasting is concerned with the probabilistic assessment of general earthquake hazards, including the frequency and magnitude of damaging earthquakes in a given area over years or decades.<ref>{{Harvnb|Kanamori|2003}}, p. 1205.  See also {{Harvnb|International Commission on Earthquake Forecasting for Civil Protection|2011}}, p. 327.</ref> For well-understood faults the probability that a segment may rupture during the next few decades can be estimated.<ref>Working Group on California Earthquake Probabilities in the San Francisco Bay Region, 2003 to 2032, 2003, {{cite web |title=Bay Area Earthquake Probabilities|url=https://earthquake.usgs.gov/regional/nca/wg02/index.php |access-date=2017-08-28 |url-status=dead |archive-url=https://web.archive.org/web/20170218174649/http://earthquake.usgs.gov/regional/nca/wg02/index.php |archive-date=2017-02-18 }}</ref><ref>{{Cite journal|last=Pailoplee|first=Santi|date=2017-03-13|title=Probabilities of Earthquake Occurrences along the Sumatra-Andaman Subduction Zone|journal=Open Geosciences|volume=9|issue=1|pages=4|doi=10.1515/geo-2017-0004|issn=2391-5447|bibcode=2017OGeo....9....4P|s2cid=132545870|doi-access=free}}</ref>

[[Earthquake warning system]]s have been developed that can provide regional notification of an earthquake in progress, but before the ground surface has begun to move, potentially allowing people within the system's range to seek shelter before the earthquake's impact is felt.

===Preparedness===
{{main|Earthquake preparedness}}

The objective of [[earthquake engineering]] is to foresee the impact of earthquakes on buildings, bridges, tunnels, roadways, and other structures, and to design such structures to minimize the risk of damage. Existing structures can be modified by [[seismic retrofitting]] to improve their resistance to earthquakes. [[Earthquake insurance]] can provide building owners with financial protection against losses resulting from earthquakes. [[Emergency management]] strategies can be employed by a government or organization to mitigate risks and prepare for consequences.

[[Artificial intelligence]] may help to assess buildings and plan precautionary operations. The Igor [[expert system]] is part of a mobile laboratory that supports the procedures leading to the seismic assessment of masonry buildings and the planning of retrofitting operations on them. It has been applied to assess buildings in [[Lisbon]], [[Rhodes]], and [[Naples]].<ref>{{Cite journal|last1=Salvaneschi|first1=P.|last2=Cadei|first2=M.|last3=Lazzari|first3=M.|date=1996|title=Applying AI to Structural Safety Monitoring and Evaluation|journal=IEEE Expert|volume=11|issue=4|pages=24–34|doi= 10.1109/64.511774}}</ref>

Individuals can also take preparedness steps like securing [[water heating|water heaters]] and heavy items that could injure someone, locating shutoffs for utilities, and being educated about what to do when the shaking starts. For areas near large bodies of water, earthquake preparedness encompasses the possibility of a tsunami caused by a large earthquake.

==In culture==

[[File:Lycosthène.jpg|thumb|An image from a 1557 book depicting an earthquake in Italy in the 4th century BCE]]

From the lifetime of the Greek philosopher [[Anaxagoras]] in the 5th century BCE to the 14th century CE, earthquakes were usually attributed to "air (vapors) in the cavities of the Earth."<ref name=World>{{cite encyclopedia
|title=Earthquakes
|encyclopedia=Encyclopedia of World Environmental History
|volume=1: A–G
|pages=358–364
|publisher=Routledge
|year=2003 }}</ref> [[Pliny the Elder]] called earthquakes "underground thunderstorms".<ref name=World/>  [[Thales]] of Miletus (625–547 BCE) was the only documented person who believed that earthquakes were caused by tension between the earth and water.<ref name=World/>

In [[Norse mythology]], earthquakes were explained as the violent struggle of the god [[Loki]] being punished for the murder of [[Baldr]], god of beauty and light.<ref>{{cite book|last=[[Snorri Sturluson|Sturluson, Snorri]]|title=Prose Edda|year=1220|isbn=978-1-156-78621-5|title-link=Prose Edda|publisher=General Books }}</ref> In [[Greek mythology]], [[Poseidon]] was the cause and god of earthquakes.<ref name="Dimock1990">{{cite book|author=George E. Dimock|title=The Unity of the Odyssey|url=https://books.google.com/books?id=hS1acr-lOeEC&pg=PA179|year=1990|publisher=Univ of Massachusetts Press|isbn=978-0-87023-721-8|page=179}}</ref> In [[Japanese mythology]], [[Namazu]] (鯰) is a giant [[catfish]] who causes earthquakes.<ref>{{Cite encyclopedia|url=http://www.worldhistory.org/Namazu/|title=Namazu|encyclopedia=World History Encyclopedia|access-date=2017-07-23}}</ref> In [[Taiwan]]ese folklore, the [[Tē-gû]] (地牛)  is a giant earth [[True buffalo|buffalo]] who causes earthquakes.<ref>{{cite web |url=https://artouch.com/gumeishu/content-144675.html |title=Earthquake Island, Taiwan: The Ground Buffalo Myth, Deities and Earthquakes |work=ARTouch |date=14 June 2024 |access-date=2025-05-05 }}</ref>

In the [[New Testament]], [[Gospel of Matthew|Matthew's Gospel]] refers to earthquakes occurring both after the [[death of Jesus]] ([[Matthew 27:51]], 54) and at his [[Resurrection of Jesus|resurrection]] ([[Matthew 28:2]]).<ref>Allison, D., ''56. Matthew'', in Barton, J. and Muddiman, J. (2001), [https://b-ok.org/dl/946961/8f5f43 The Oxford Bible Commentary] {{Webarchive|url=https://web.archive.org/web/20171122193211/http://b-ok.org/dl/946961/8f5f43 |date=2017-11-22 }}, p. 884</ref>

In modern popular culture, the portrayal of earthquakes is shaped by the memory of great cities laid waste, such as [[Great Hanshin earthquake|Kobe in 1995]] or [[1906 San Francisco earthquake|San Francisco in 1906]].<ref name="Van Riper 60">{{cite book|last=Van Riper|first=A. Bowdoin|title=Science in popular culture: a reference guide|url=https://archive.org/details/sciencepopularcu00ripe|url-access=limited|publisher=[[Greenwood Press]]|location=Westport|year=2002|page=[https://archive.org/details/sciencepopularcu00ripe/page/n77 60]|isbn=978-0-313-31822-1}}</ref> Fictional earthquakes tend to strike suddenly and without warning.<ref name="Van Riper 60" /> For this reason, stories about earthquakes generally begin with the disaster and focus on its immediate aftermath, as in ''Short Walk to Daylight'' (1972), ''[[A Wrinkle in the Skin|The Ragged Edge]]'' (1968) or ''[[Aftershock: Earthquake in New York]]'' (1999).<ref name="Van Riper 60" /> A notable example is Heinrich von Kleist's classic novella, ''[[The Earthquake in Chile]]'', which describes the destruction of Santiago in 1647. [[Haruki Murakami]]'s short fiction collection ''[[After the Quake]]'' depicts the consequences of the Kobe earthquake of 1995.

{{anchor|big one}}The most popular single earthquake in fiction is the hypothetical "Big One" expected of California's [[San Andreas Fault]] someday, as depicted in the novels ''[[Richter 10]]'' (1996), ''[[Goodbye California (novel)|Goodbye California]]'' (1977), ''[[2012 (film)|2012]]'' (2009), and ''[[San Andreas (film)|San Andreas]]'' (2015), among other works.<ref name="Van Riper 60" />

==Outside of Earth==
{{main|Quake (natural phenomenon)}}
Phenomena similar to earthquakes have been observed on other planets (e.g., ''[[marsquake]]s'' on Mars) and on the Moon (e.g., ''[[moonquake]]s'').

==See also==
{{div col}}
* {{annotated link|Alpide belt}}
* {{annotated link|European-Mediterranean Seismological Centre|abbr=EMSC|aka=Centre Sismologique Euro-Méditerranéen|aka_lang=fr|only=explicit}}
* {{annotated link|Helioseismology|space_cat=no}}
* {{annotated link|Injection well}}
* {{annotated link|IRIS Consortium}}
* [[Lists of earthquakes]]
* {{annotated link|Seismological Society of America|abbr=SSA}}
* {{annotated link|Seismotectonics}}
* {{annotated link|Vertical displacement}}
{{div col end}}

==References==
{{Reflist}}

==Sources==
{{Div col|colwidth=30em}}
{{refbegin}}
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|doi= 10.1785/BSSA0660062069
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* {{Citation
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* {{Citation
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 |last1= Chung
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 |publisher= Office of Scientific and Technical Information (OSTI)
 |doi= 10.2172/5073993
 |osti= 5073993
 |url= https://www.osti.gov/scitech/servlets/purl/5073993/
 |access-date= 2017-07-21
 |archive-date= 2020-01-22
 |archive-url= https://web.archive.org/web/20200122134130/https://www.osti.gov/biblio/5073993/
 |url-status= live
 |doi-access= free
 }}, NUREG/CR-1457.
* Deborah R. Coen. ''The Earthquake Observers: Disaster Science From Lisbon to Richter'' ([[University of Chicago Press]]; 2012) 348 pages; explores both scientific and popular coverage
* {{citation
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 |date= 14 March 1997
 |title= Earthquakes Cannot Be Predicted
 |journal= Science
 |volume= 275
 |issue= 5306
 |page= 1616
 |doi= 10.1126/science.275.5306.1616
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 |url= http://moho.ess.ucla.edu/~kagan/Geller_et_al_1997.pdf
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* {{citation
 |author= International Commission on Earthquake Forecasting for Civil Protection
 |date= 30 May 2011
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 |volume= 54
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* {{citation
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{{refend}}
{{div col end}}

==Further reading==
{{Library resources box
|by=no
|onlinebooksabout=yes
|about=yes
|label=Earthquakes
|viaf= |lccn= |lcheading=earthquakes |wikititle=
}}
* {{cite book |title=Natural Hazards and Disasters |first1=Donald |last1=Hyndman |first2=David |last2=Hyndman |isbn=978-0-495-31667-1 |publisher=Brooks/Cole: [[Cengage Learning]] |year=2009 |edition=2nd |chapter-url=https://books.google.com/books?id=8jg5oRWHXmcC&pg=PT54 |chapter=Chapter 3: Earthquakes and their causes }}
* {{cite journal | last1=Liu | first1=ChiChing | last2=Linde | first2=Alan T. | last3=Sacks | first3=I. Selwyn | title=Slow earthquakes triggered by typhoons | journal=Nature | volume=459 | issue=7248 | date=2009 | issn=0028-0836 | doi=10.1038/nature08042 | pages=833–836| pmid=19516339 | bibcode=2009Natur.459..833L | s2cid=4424312 }}

==External links==
{{Wikiquote}}
{{commons}}
{{Wikivoyage|Earthquake safety}}
{{wiktionary}}
* [https://earthquake.usgs.gov/ Earthquake Hazards Program] of the U.S. Geological Survey
* [http://www.iris.edu/dms/seismon.htm IRIS Seismic Monitor] – IRIS Consortium

{{Geotechnical engineering|state=collapsed}}
{{Natural disasters}}
{{Authority control}}

[[Category:Earthquakes| ]]
[[Category:Geological hazards]]
[[Category:Lithosphere]]
[[Category:Natural disasters]]
[[Category:Seismology]]