View source for Intraplate earthquake

{{short description|Earthquake that occurs within the interior of a tectonic plate}}
{{Globalize|1=article|2=Anglosphere|date=April 2024}}
{{Earthquakes}}
[[File:New Madrid Seismic Zone activity 1974-2011.svg|thumb|Distribution of seismicity associated with the [[New Madrid seismic zone]] (since 1974). This zone of intense earthquake activity is located deep within the interior of the North American plate.]]

An '''intraplate earthquake''' occurs in the ''interior'' of a [[Plate tectonics|tectonic plate]], in contrast to an [[interplate earthquake]] on the ''boundary'' of a tectonic plate.<ref>{{Cite journal|last1=Iwata |first1=Tomotaka |last2=Asano |first2=Kimiyuki |year=2011 |title=Characterization of the Heterogeneous Source Model of Intraslab Earthquakes Toward Strong Ground Motion Prediction |journal=Pure and Applied Geophysics |volume=168 |issue=1–2 |pages=117–124 |doi=10.1007/s00024-010-0128-7 |bibcode=2011PApGe.168..117I |s2cid=140602323 }}</ref><ref>{{Cite journal|last1=Senoa |first1=Tetsuzo |last2=Yoshida |first2=Masaki |year=2004 |title=Where and why do large shallow intraslab earthquakes occur? |journal=Physics of the Earth and Planetary Interiors |volume=141 |issue=3 |pages=183–206 |doi=10.1016/j.pepi.2003.11.002 |bibcode=2004PEPI..141..183S }}</ref> They are relatively rare compared to the more familiar interplate earthquakes. Buildings far from plate boundaries are rarely protected with [[seismic retrofit]]ting, so large intraplate earthquakes can inflict heavy damage. Examples of damaging intraplate earthquakes are the devastating [[2001 Gujarat earthquake]], the [[2011 Christchurch earthquake]], the [[2012 Indian Ocean earthquakes]], the [[2017 Puebla earthquake]], the [[1811–1812 New Madrid earthquakes]], and the [[1886 Charleston earthquake]].<ref>{{cite journal|title=Intraplate Triggered Earthquakes: Observations and Interpretation|first1=Susan E.|last1=Hough|author-link=Susan Hough|first2=Leonardo|last2=Seeber|first3=John G.|last3=Armbruster|url=http://bssa.geoscienceworld.org/content/93/5/2212.short|journal=Bulletin of the Seismological Society of America|publisher=[[Seismological Society of America]]|volume=101|number=3|date=October 2003|pages=2212–2221|doi=10.1785/0120020055|bibcode=2003BuSSA..93.2212H|citeseerx=10.1.1.189.5055}}</ref> An earthquake that occurs within a subducting plate is known as an '''intraslab earthquake'''.

==Description==
The Earth's [[Crust (geology)|crust]] is made up of seven primary and eight secondary [[Plate tectonics|tectonic plate]]s, plus dozens of tertiary microplates. The large plates move very slowly on top of [[convection]] currents in the underlying [[Mantle (geology)|mantle]]. Because they do not all move in the same direction, plates often directly [[Convergent boundary|collide]] or slide [[Fault (geology)|laterally along each other]], a tectonic environment that makes interplate earthquakes frequent.

By contrast, relatively few earthquakes occur in intraplate environments away from plate junctures.<ref>{{cite journal |last1=Yang |first1=Xiaotao |title=Seismicity of the Ste. Genevieve Seismic Zone based on Observations from the EarthScope OIINK Flexible Array |journal=Seismological Research Letters |volume=85 |issue=6 |pages=1285–1294 |doi=10.1785/0220140079 |url=https://pubs.geoscienceworld.org/ssa/srl/article/85/6/1285/315533/seismicity-of-the-ste-genevieve-seismic-zone-based|year=2014 |bibcode=2014SeiRL..85.1285Y |url-access=subscription }}</ref> These earthquakes often occur at the location of ancient failed [[rift]]s, partial fractures of existing plates, because they may leave a weakness in the crust vulnerable to regional tectonic strain.

Intraslab earthquakes radiate more seismic energy than interplate earthquakes ([[megathrust earthquake]]s) of a similar magnitude. This variation makes ''seismic energy'' a better measure for the potential macroseismic effects of an earthquake than the more common ''[[seismic moment]]'' used to calculate the magnitude {{M|w}}.<ref>{{Cite journal|last1=Leyton |first1=Felipe |last2=Ruiz |first2=Javier A. |last3=Camposa |first3=Jaime |last4=Kausel |first4=Edgar |year=2009 |title=Intraplate and interplate earthquakes in Chilean subduction zone: A theoretical and observational comparison |journal=Physics of the Earth and Planetary Interiors |volume=175 |issue=1 |pages=37–46 |doi=10.1016/j.pepi.2008.03.017 |bibcode=2009PEPI..175...37L |hdl=10533/130959 |hdl-access=free }} ''citing'' Choy, G.L.; Boatwright, J.; Kirby, S., 2002. The radiated seismic energy and apparent stress of interplate and intraslab earthquakes at subduction-zone environments: Implications for seismic hazard estimation, in The Cascadia subduction zone and related subduction systems–Seismic structure, intraslab earthquakes and processes, and earthquake hazards, Open-File Report 02–328, pp. 107–114, eds Kirby, S.H.; Wang, K.; Dunlop, S., US Geological Survey, Menlo Park, CA.</ref>

==Examples==
Examples of intraplate earthquakes include those in [[Mineral, Virginia]], in [[2011 Virginia earthquake|2011]] (estimated magnitude 5.8), [[Newcastle, New South Wales]] in [[1989 Newcastle earthquake|1989]], [[New Madrid seismic zone|New Madrid]] in [[1811–1812 New Madrid earthquakes|1811 and 1812]] (estimated magnitude as high as 8.6),<ref>Penick, James L. ''The New Madrid Earthquakes''. Columbia, MO: University of Missouri Press, 1981. {{ISBN|0-8262-0344-2}}</ref> the [[1755 Cape Ann earthquake|Boston (Cape Ann) earthquake of 1755]] (estimated magnitude 6.0 to 6.3), earthquakes felt in [[New York City]] in 1737 and 1884 (both quakes estimated at 5.5 magnitude), and the [[1886 Charleston earthquake|Charleston earthquake]] in South Carolina in 1886 (estimated magnitude 6.5 to 7.3). The Charleston quake was particularly surprising because, unlike Boston and New York, the area had almost no history of even minor earthquakes.

In 2001, [[2001 Gujarat earthquake|a large intraplate earthquake]] devastated the region of [[Gujarat]], India. The earthquake occurred far from any plate boundaries, which meant the region above the [[epicenter]] was unprepared for earthquakes. In particular, the [[Kutch district]] suffered tremendous damage, where the death toll was over 12,000 and the total death toll was higher than 20,000.

In 2017, the 24–29&nbsp;km deep magnitude 6.5 [[2017 Botswana earthquake|Botswana earthquake]] that shook eastern Botswana occurred at over 300&nbsp;km from the nearest active plate boundary.<ref name=":0">{{Cite journal|last1=Kolawole|first1=F.|last2=Atekwana|first2=E. A.|last3=Malloy|first3=S.|last4=Stamps|first4=D. S.|last5=Grandin|first5=R.|last6=Abdelsalam|first6=M. G.|last7=Leseane|first7=K.|last8=Shemang|first8=E. M.|date=2017-09-09|title=Aeromagnetic, gravity, and Differential Interferometric Synthetic Aperture Radar analyses reveal the causative fault of the 3 April 2017 Mw6.5 Moiyabana, Botswana, earthquake|journal=Geophysical Research Letters|volume=44|issue=17|pages=8837–8846|doi=10.1002/2017gl074620|issn=0094-8276|bibcode=2017GeoRL..44.8837K|s2cid=134584787 }}</ref> The event occurred in an underpopulated area of Botswana.

The [[1888 Río de la Plata earthquake|1888 earthquake]] in [[Río de la Plata]] was an intraplate quake,<ref>{{cite journal |last= Benavídes Sosa |first= Alberto |date= 1998 |title= Seismicidad y seismotectónica en Uruguay |journal= Física de la Tierra |url= https://revistas.ucm.es/index.php/FITE/article/viewFile/FITE9898110167A/12147  |pages= 167–186 |issue= 10 |language= es}}</ref> from reactivated faults in the Quilmes Trough, far from the boundaries of the [[South American plate]]. With a magnitude greater than 5.0 it was felt "in the cities of Buenos Aires, La Plata and other small towns and villages along the Rio de Plata coastal regions."<ref name="Rossello-2020">{{Cite journal |last1=Rossello |first1=Eduardo Antonio |last2=Heit |first2=Benjamín |last3=Bianchi |first3=Marcelo |year=2020 |title=Shallow intraplate seismicity in the Buenos Aires province (Argentina) and surrounding areas: is it related to the Quilmes Trough? |journal=Boletín de Geología |volume=42 |issue=2 |pages=31–48 |doi=10.18273/revbol.v42n2-2020002 |s2cid=219934403 |url=https://www.redalyc.org/journal/3496/349665545003/html/ |archive-url=https://web.archive.org/web/20220804031500/https://www.redalyc.org/journal/3496/349665545003/html/ |archive-date=4 August 2022 |url-status=live |doi-access=free }}</ref> The towns of [[Punta del Este]] and [[Maldonado, Uruguay|Maldonado]] in Uruguay were hit by a tsunami generated by the quake.<ref name="Rossello-2020" />

==Causes==
Many cities live with the [[seismic risk]] of a rare, large intraplate earthquake. The cause of these earthquakes is often uncertain. In many cases, the causative fault is deeply buried<ref name=":0" /> and sometimes cannot even be found. Some studies have shown that quakes can be caused by fluids moving up the crust along ancient fault zones.<ref name=":0" /><ref>{{Cite journal|last1=Gardonio|first1=B.|last2=Jolivet|first2=R.|last3=Calais|first3=E.|last4=Leclère|first4=H.|date=2018-07-13|title=The April 2017 Mw6.5 Botswana Earthquake: An Intraplate Event Triggered by Deep Fluids|journal=Geophysical Research Letters|volume=45|issue=17|pages=8886–8896|doi=10.1029/2018gl078297|issn=0094-8276|url=https://hal.archives-ouvertes.fr/hal-02185463/file/2018_Gardonio_GRL.pdf|bibcode=2018GeoRL..45.8886G|s2cid=134667492}}</ref> In such circumstances, it is difficult to estimate the [[seismic hazard]] for a given city, especially if there was only one earthquake in historical times. Some progress is being made in understanding the [[fault mechanics]] driving these earthquakes.

Intraplate earthquakes may be unrelated to ancient fault zones and instead caused by deglaciation or erosion.<ref>{{cite news |last1=Shobe |first1=Charlie |title=Can Rivers Cause Earthquakes? |url=https://blogs.scientificamerican.com/observations/can-rivers-cause-earthquakes/ |access-date=26 December 2018 |work=[[Scientific American]] |date=18 December 2018}}</ref>

==Prediction==
Scientists continue to search for the causes of these earthquakes, and especially for some indication of how often they recur. The best success has come with detailed micro-seismic monitoring, involving dense arrays of [[seismometer]]s.  In this manner, very small earthquakes associated with a causative fault can be located with great accuracy, and in most cases these line up in patterns consistent with faulting. [[Cryoseism]]s can sometimes be mistaken for intraplate earthquakes.

==Intraslab earthquake==
In seismology, an intraslab earthquake occurs within a subducting plate, known as [[Slab (geology)|slab]]s. They are most frequent in older slabs which are colder, whereas younger slabs that are warmer rarely produce earthquakes. They can be detected within these slabs at depths exceeding {{cvt|500|km}}; they are also the source of intermediate and deep-focus earthquakes.<ref name="Nakajima19">{{cite journal |last1=Nakajima |first1=Junichi |title=Revisiting Intraslab Earthquakes Beneath Kyushu, Japan: Effect of Ridge Subduction on Seismogenesis |journal=Journal of Geophysical Research: Solid Earth |date=2019 |volume=124 |issue=8 |pages=8660–8678 |doi=10.1029/2019JB017869}}</ref> Intraslab earthquakes at depths {{cvt|20–60|km}} are considered shallow earthquakes and can be destructive to cities. One of the deadliest earthquakes of the 20th century was the [[1970 Ancash earthquake]], measuring {{M|w}} 7.9 and occurring off the coast of Peru. The [[2001 Nisqually earthquake|2001 Nisqually]] and [[1949 Olympia earthquake]]s were also intraslab events.<ref name="Seno04">{{cite journal |last1=Seno |first1=Tetsuzo |last2=Yoshida |first2=Masaki |title=Where and why do large shallow intraslab earthquakes occur? |journal=Physics of the Earth and Planetary Interiors |date=2004 |volume=141 |issue=3 |pages=183–206 |doi=10.1016/j.pepi.2003.11.002|bibcode=2004PEPI..141..183S }}</ref>

==See also==
* {{annotated link|New Madrid seismic zone}}
* {{annotated link|Wabash Valley seismic zone}}
* {{annotated link|Saint Lawrence rift system}}

== References ==
{{Reflist}}

== Further reading ==
* Stein, S., and S. Mazzotti (2007). "Continental Intraplate Earthquakes: Science and Policy Issues", Geological Society of America, Special Paper 425.

==External links==
* [http://sprg.ssl.berkeley.edu/matt/seismo.html Intraplate Earthquakes: Possible Mechanisms for the New Madrid and Charleston Earthquakes]
* [http://www.seis.sc.edu/projects/SCSN/history/Publications/G&T_SRL_2003.pdf ''Symptomatic Features of Intraplate Earthquakes'' – PDF]
* [https://web.archive.org/web/20060508201837/http://www.rcep.dpri.kyoto-u.ac.jp/members/iio/ronbun_list/eps2002_1001.pdf ''A physical understanding of large intraplate earthquakes'' – PDF]
* [https://earthquake.usgs.gov/eqcenter/eqinthenews/2006/usslav/ Earthquake Hazards Program, USGS]
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[[Category:Types of earthquake]]

[[ja:地震#内陸地殻内地震]]