Editing Megathrust earthquake

{{short description|Type of earthquake at convergent plate boundaries}}
{{Earthquakes}}

'''Megathrust earthquakes''' occur at [[convergent boundary|convergent plate boundaries]], where one [[tectonic plate]] is forced underneath another. The earthquakes are caused by slip along the [[thrust fault]] that forms the contact between the two plates. These [[interplate earthquake]]s are the planet's most powerful, with [[Moment magnitude scale|moment magnitudes]] (''M<sub>w</sub>'') that can exceed 9.0.<ref name="meier-etal-2017">{{cite journal |last1=Meier |first1=M.-A. |last2=Ampuero |first2=J. P. |last3=Heaton |first3=T. H. |title=The hidden simplicity of subduction megathrust earthquakes |journal=Science |date=22 September 2017 |volume=357 |issue=6357 |pages=1277–1281 |doi=10.1126/science.aan5643|pmid=28935803 |bibcode=2017Sci...357.1277M |s2cid=206660652 |url=https://resolver.caltech.edu/CaltechAUTHORS:20170925-075055125 }}</ref><ref name="nrc-canada">{{cite web |title=Questions and Answers on Megathrust Earthquakes |url=https://earthquakescanada.nrcan.gc.ca/zones/cascadia/qa-en.php |publisher=Natural Resources Canada |access-date=23 September 2020 |date=19 October 2018}}</ref> Since 1900, all [[earthquake]]s of magnitude 9.0 or greater have been megathrust earthquakes.<ref>{{Citation |first1= Arch C. |last1= Johnston |first2= Stephen |last2= Halchuk |date= June–July 1993 |title= The seismicity data base for the Global Seismic Hazard Assessment Program |journal= Annali di Geofisica |volume= 36 |issue= 3–4 |pages= 133–151 |url= http://www.annalsofgeophysics.eu/index.php/annals/article/download/4260/4329}}, pp. 140, 142 ''et seq''.</ref>

The thrust faults responsible for megathrust earthquakes often lie at the bottom of [[oceanic trench]]es; in such cases, the earthquakes can abruptly displace the sea floor over a large area. As a result, megathrust earthquakes often generate [[tsunami]]s that are considerably more destructive than the earthquakes themselves. [[Teletsunami]]s can cross ocean basins to devastate areas far from the original earthquake.

==Terminology and mechanism==
[[Image:Subduction-en.svg|right|thumb|400px|Diagram of a [[subduction]] zone. The megathrust fault lies on the top of the subducting slab where it is in contact with the overriding plate.]]

The term ''megathrust'' refers to an extremely large [[thrust fault]], typically formed at the plate interface along a subduction zone, such as the [[Sunda megathrust]].<ref name="ParkButler2005">{{cite journal | first1=J. | first10=G. | first11=K. | first12=R. | last1=Park | last10=Ekstrom | last11=Anderson | last12=Aster | title=Performance Review of the Global Seismographic Network for the Sumatra-Andaman Megathrust Earthquake | last2=Butler | first2=R. | last3=Anderson | first3=K. | last4=Berger | first4=J. | last5=Davis | first5=P. | last6=Benz | first6=H. | last7=Hutt | first7=C. R. | last8=McCreery | first8=C. S. | last9=Ahern | first9=T. | journal=Seismological Research Letters | year=2005 | volume=76 | issue=3 | pages=331–343 | issn=0895-0695 | doi=10.1785/gssrl.76.3.331 | bibcode=2005SeiRL..76..331P | display-authors=3}}</ref><ref name=BilekLay2018>{{cite journal |last1=Bilek |first1=Susan L. |last2=Lay |first2=Thorne |title=Subduction zone megathrust earthquakes |journal=Geosphere |date=1 August 2018 |volume=14 |issue=4 |pages=1468–1500 |doi=10.1130/GES01608.1|bibcode=2018Geosp..14.1468B |s2cid=133629102 |doi-access=free }}</ref> However, the term is also occasionally applied to large thrust faults in continental collision zones, such as the [[Himalayas|Himalayan]] megathrust.<ref>{{cite journal |last1=Elliott |first1=J.R.|last2=Jolivet |first2=R. |last3=González |first3=P. J. |last4=Avouac |first4=J.-P. |last5=Hollingsworth |first5=J. |last6=Searle |first6=M. P. |last7=Stevens |first7=V.L.|title=Himalayan megathrust geometry and relation to topography revealed by the Gorkha earthquake |journal=Nature Geoscience |date=February 2016 |volume=9 |issue=2 |pages=174–180 |doi=10.1038/ngeo2623|bibcode=2016NatGe...9..174E|url=http://eprints.whiterose.ac.uk/95920/8/GonzalezHimalayan%20Megathrust%20Geometry.pdf}}</ref> A megathrust fault can be {{convert|1000|km|sigfig=1|sp=us}} long.<ref name="PNSN"/>

[[File:Nor rev.png|thumb|upright=1.25|right|Cross-sectional illustration of normal and reverse faults]]
A thrust fault is a type of [[reverse fault]], in which the rock above the fault is displaced upwards relative to the rock below the fault. This distinguishes reverse faults from [[normal fault]]s, where the rock above the fault is displaced downwards, or [[strike-slip fault]]s, where the rock on one side of the fault is displaced horizontally with respect to the other side. Thrust faults are distinguished from other reverse faults because they dip at a relatively shallow angle, typically less than 45°,<ref name="DipSlipDefinition">{{cite web | url=https://earthquake.usgs.gov/learn/glossary/?termID=59 | title=Earthquake Glossary – dip slip | department=Earthquake Hazards Program| publisher=United States Geological Survey }}</ref> and show large displacements.<ref>{{cite book |last1=Fossen |first1=Haakon |title=Structural geology |date=2016 |publisher=Cambridge University Press |location=Cambridge, United Kingdom |isbn=9781107057647 |pages=485, 488, 491 |edition=Second}}</ref><ref name="ThrustDefinition">{{cite web | url=http://nthmp-history.pmel.noaa.gov/terms.html | title=Tsunami Terminology | work=The National Tsunami Hazard Mitigation Program History, 1995–2005 | publisher=Pacific Marine Environmental Laboratory | url-status=dead | archive-url=https://web.archive.org/web/20110225143835/http://nthmp-history.pmel.noaa.gov/terms.html | archive-date=2011-02-25 }}</ref> In effect, the rocks above the fault have been thrust over the rocks below the fault. Thrust faults are characteristic of areas where the [[Earth's crust]] is being compressed by tectonic forces.{{sfn|Fossen|2016|p=356}}

Megathrust faults occur where two [[tectonic plates]] collide. When one of the plates is composed of [[oceanic lithosphere]], it dives beneath the other plate (called the ''overriding plate'') and sinks into the [[Earth's mantle]] as a ''[[slab (geology)|slab]]''. The contact between the colliding plates is the megathrust fault, where the rock of the overriding plate is displaced upwards relative to the rock of the descending slab.<ref name=BilekLay2018/> Friction along the megathrust fault can lock the plates together, and the subduction forces then build up strain in the two plates. A megathrust earthquake takes place when the fault ruptures, allowing the plates to abruptly move past each other to release the accumulated strain energy.<ref name="PNSN">{{cite web |title=Cascadia Subduction Zone |url=https://www.pnsn.org/outreach/earthquakesources/csz |publisher=Pacific Northwest Seismic Network |access-date=7 October 2021}}</ref>

==Occurrence and characteristics==
{{See also|List of megathrust earthquakes}}
Megathrust earthquakes are almost exclusive to tectonic subduction zones and are often associated with the [[Pacific Ocean|Pacific]] and [[Indian Ocean]]s.<ref name=BilekLay2018/> These subduction zones are also largely responsible for the [[volcanic]] activity associated with the Pacific [[Ring of Fire]].<ref name="NOAO">{{cite web |title=What is the Ring of Fire? |url=https://oceanexplorer.noaa.gov/facts/rof.html |website=Ocean exploration |publisher=National Ocean and Atmospheric Administration |access-date=7 October 2021}}</ref>

Since these earthquakes deform the [[ocean floor]], they often generate strong [[tsunami]] waves.<ref>{{cite journal |last1=Maksymowicz |first1=A. |last2=Chadwell |first2=C. D. |last3=Ruiz |first3=J. |last4=Tréhu |first4=A. M. |last5=Contreras-Reyes |first5=E. |last6=Weinrebe |first6=W. |last7=Díaz-Naveas |first7=J. |last8=Gibson |first8=J. C. |last9=Lonsdale |first9=P. |last10=Tryon |first10=M. D. |title=Coseismic seafloor deformation in the trench region during the Mw8.8 Maule megathrust earthquake |journal=Scientific Reports |date=April 2017 |volume=7 |issue=1 |pages=45918 |doi=10.1038/srep45918|pmid=28378757 |pmc=5381107 |bibcode=2017NatSR...745918M }}</ref> Subduction zone earthquakes are also known to produce intense shaking and ground movements that can last for up to 3–5 minutes.<ref>{{cite journal |last1=Megawati |first1=K. |last2=Pan |first2=T.-C. |title=Regional Seismic Hazard Posed by the Mentawai Segment of the Sumatran Megathrust |journal=Bulletin of the Seismological Society of America |date=1 April 2009 |volume=99 |issue=2A |pages=566–584 |doi=10.1785/0120080109|bibcode=2009BuSSA..99..566M }}</ref>

In the [[Indian Ocean]] region, the [[Sunda megathrust]] is located where the [[Indo-Australian plate]] subducts under the [[Eurasian plate]] along a {{convert|5500|km|}} fault off the coasts of [[Myanmar]], [[Sumatra]], [[Java]] and [[Bali]], terminating off the northwestern coast of [[Australia]]. This subduction zone was responsible for the [[2004 Indian Ocean earthquake and tsunami]].<ref name="Sieh">{{cite journal |last1=Sieh |first1=Kerry |journal=Journal of Earthquake and Tsunami |date=March 2007 |volume=01 |issue=1 |pages=1–19 |doi=10.1142/S179343110700002X | title = The Sunda megathrust: past, present and future}}</ref> In parts of the megathrust south of [[Java]], referred to as the [[Sunda Trench|Java Trench]], for the western part, {{M|w}} 8.9 is possible, while in the eastern Java segment, {{M|w}} 8.8 is possible, while if both were to rupture at the same time, the magnitude would be {{M|w}} 9.1.<ref>{{Cite journal |last1=Widiyantoro |first1=S. |last2=Gunawan |first2=E. |last3=Muhari |first3=A. |last4=Rawlinson |first4=N. |last5=Mori |first5=J. |last6=Hanifa |first6=N. R. |last7=Susilo |first7=S. |last8=Supendi |first8=P. |last9=Shiddiqi |first9=H. A. |last10=Nugraha |first10=A. D. |last11=Putra |first11=H. E. |date=2020-09-17 |title=Implications for megathrust earthquakes and tsunamis from seismic gaps south of Java Indonesia |journal=Scientific Reports |language=en |volume=10 |issue=1 |pages=15274 |doi=10.1038/s41598-020-72142-z |pmid=32943680 |pmc=7499206 |bibcode=2020NatSR..1015274W |issn=2045-2322}}</ref>

In the [[South China Sea]] lies the [[Manila Trench]], which is capable of producing {{M|w}} 9.0 or larger earthquakes,<ref>{{Cite journal |last1=Megawati |first1=Kusnowidjaja |last2=Shaw |first2=Felicia |last3=Sieh |first3=Kerry |last4=Huang |first4=Zhenhua |last5=Wu |first5=Tso-Ren |last6=Lin |first6=Yunung |last7=Tan |first7=Soon Keat |last8=Pan |first8=Tso-Chien |date=2009-09-04 |title=Tsunami hazard from the subduction megathrust of the South China Sea: Part I. Source characterization and the resulting tsunami |url=https://www.sciencedirect.com/science/article/pii/S1367912008001922 |journal=Journal of Asian Earth Sciences |series=Tsunamis in Asia |volume=36 |issue=1 |pages=13–20 |doi=10.1016/j.jseaes.2008.11.012 |bibcode=2009JAESc..36...13M |hdl=10220/8672 |issn=1367-9120|hdl-access=free }}</ref> with the maximum magnitude at Mw 9.2 or higher.<ref>{{Cite journal |last1=Zhao |first1=Guangsheng |last2=Niu |first2=Xiaojing |date=2024-01-26 |title=Tsunami Hazard Assessment in the South China Sea Based on Geodetic Locking of the Manila Subduction Zone |url=https://nhess.copernicus.org/preprints/nhess-2023-227/ |journal=Natural Hazards and Earth System Sciences Discussions |volume=24 |issue=7 |language=English |pages=2303–2313 |doi=10.5194/nhess-2023-227|doi-access=free }}</ref>

In Japan, the Nankai megathrust under the [[Nankai Trough]] is responsible for [[Nankai megathrust earthquakes]] and associated tsunamis.<ref name="Hirahara">{{cite web |url=http://www.jamstec.go.jp/esc/publication/annual/annual2004/pdf/3project/chapter2/6hirahara.pdf |title=Simulation of Earthquake Generation Process in a Complex System of Faults |last=Hirahara |first=K. |author2=Kato N. |author3=Miyatake T. |author4=Hori T. |author5=Hyodo M. |author6=Inn J. |author7=Mitsui N. |author8=Sasaki T. |author9=Miyamura T. |author10=Nakama Y. |author11=Kanai T. |year=2004 |work=Annual Report of the Earth Simulator Center April 2004 – March 2005 |pages=121–126 |access-date=2009-11-14 |archive-date=2011-09-27 |archive-url=https://web.archive.org/web/20110927124357/http://www.jamstec.go.jp/esc/publication/annual/annual2004/pdf/3project/chapter2/6hirahara.pdf |url-status=dead }}</ref> The largest megathrust event within the last 20 years was the magnitude 9.0–9.1 [[2011 Tōhoku earthquake and tsunami|Tōhoku earthquake]] along the [[Japan Trench]] megathrust.<ref>{{cite web |date=7 November 2016 |title=M 9.1 – 2011 Great Tohoku Earthquake, Japan |url=https://earthquake.usgs.gov/earthquakes/eventpage/official20110311054624120_30/executive#executive |access-date=3 June 2022 |department=Earthquake Hazards Program |publisher=United States Geological Survey}}</ref>

In North America, the [[Juan de Fuca plate]] subducts under the [[North American plate]], creating the [[Cascadia subduction zone]] from mid Vancouver Island, British Columbia down to Northern California. This subduction zone was responsible for the [[1700 Cascadia earthquake]].<ref>{{cite news |title=A Major Earthquake in the Pacific Northwest Looks Even Likelier |url=https://www.theatlantic.com/science/archive/2016/08/a-major-earthquake-in-the-pacific-northwest-just-got-more-likely/495407/ |work=The Atlantic |date=August 16, 2016}}</ref> The [[Aleutian Trench]], of the southern coast of [[Alaska]] and the [[Aleutian Islands]], where the North American plate overrides the [[Pacific plate]], has generated many major earthquakes throughout history, several of which generated Pacific-wide tsunamis,<ref>{{cite journal |last1=Witter |first1=Rob |last2=Briggs |first2=Rich |last3=Engelhart |first3=Simon E. |last4=Gelfenbaum |first4=Guy |last5=Koehler |first5=Rich D. |last6=Nelson |first6=Alan |last7=Selle |first7=SeanPaul La |last8=Corbett |first8=Reide |last9=Wallace |first9=Kristi |title=Evidence for frequent, large tsunamis spanning locked and creeping parts of the Aleutian megathrust |journal=GSA Bulletin |date=1 May 2019 |volume=131 |issue=5–6 |pages=707–729 |doi=10.1130/B32031.1|bibcode=2019GSAB..131..707W |s2cid=134362013 }}</ref> including the [[1964 Alaska earthquake]]; at magnitude 9.1–9.2, it remains the largest recorded earthquake in North America, and the third-largest earthquake instrumentally recorded in the world.<ref>{{Cite journal |last1=Ichinose |first1=Gene |last2=Somerville |first2=Paul |last3=Thio |first3=Hong Kie |last4=Graves |first4=Robert |last5=O'Connell |first5=Dan |date=2007 |title=Rupture process of the 1964 Prince William Sound, Alaska, earthquake from the combined inversion of seismic, tsunami, and geodetic data |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2006JB004728 |journal=Journal of Geophysical Research: Solid Earth |language=en |volume=112 |issue=B7 |doi=10.1029/2006JB004728 |bibcode=2007JGRB..112.7306I |issn=0148-0227}}</ref>

In the [[Himalayan region]], where the [[Indian plate]] subducts under the [[Eurasian plate]], the largest recorded earthquake was the [[1950 Assam–Tibet earthquake]], at magnitude 8.7. It is estimated that earthquakes with magnitude 9.0 or larger are expected to occur at an interval of every 800 years, with the highest boundary being a magnitude 10, though this is not considered physically possible. Therefore, the largest possible earthquake in the region is a magnitude 9.7, assuming a single rupture of the whole Himalayan arc and assuming standard scaling law, which implies an average slip of 50 m.<ref>{{Cite journal |last1=Stevens |first1=V. L. |last2=Avouac |first2=J.-P. |date=2016-02-16 |title=Millenary M w > 9.0 earthquakes required by geodetic strain in the Himalaya |url=https://agupubs.onlinelibrary.wiley.com/doi/10.1002/2015GL067336 |journal=Geophysical Research Letters |language=en |volume=43 |issue=3 |pages=1118–1123 |doi=10.1002/2015GL067336 |issn=0094-8276}}</ref>

A megathrust earthquake could occur in the [[Lesser Antilles subduction zone]], with a maximum magnitude of 9.3, or potentially even 10.3 through recent evaluations, a value not considered impossible.<ref name=":0">{{Cite journal |last1=Roger |first1=J. |last2=Frère |first2=A. |last3=Hébert |first3=H. |date=2014-07-25 |title=Impact of a tsunami generated at the Lesser Antilles subduction zone on the Northern Atlantic Ocean coastlines |url=https://adgeo.copernicus.org/articles/38/43/2014/ |journal=Advances in Geosciences |language=English |volume=38 |pages=43–53 |doi=10.5194/adgeo-38-43-2014 |doi-access=free |bibcode=2014AdG....38...43R |issn=1680-7340}}</ref>

The largest recorded megathrust earthquake was the [[1960 Valdivia earthquake]], estimated between magnitudes 9.4–9.6, centered off the coast of Chile along the [[Peru-Chile Trench]], where the [[Nazca plate]] subducts under the [[South American plate]].<ref>{{cite journal |last1=Ojeda |first1=Javier |last2=Ruiz |first2=Sergio |last3=del Campo |first3=Francisco |last4=Carvajal |first4=Matías |title=The 21 May 1960 Mw 8.1 Concepción Earthquake: A Deep Megathrust Foreshock That Started the 1960 Central-South Chilean Seismic Sequence |journal=Seismological Research Letters |date=1 May 2020 |volume=91 |issue=3 |pages=1617–1627 |doi=10.1785/0220190143|bibcode=2020SeiRL..91.1617O |s2cid=216347638 }}</ref> This megathrust region has regularly generated extremely large earthquakes.

The largest possible earthquakes are estimated at magnitudes of 10 to 11, most likely caused by a combined rupture of the [[Japan Trench]] and [[Kuril–Kamchatka Trench]], or individually the [[Aleutian Trench]] or Peru–Chile Trench.<ref>{{Cite web |last=Kyodo |date=2012-12-15 |title=Magnitude 10 temblor could happen: study |url=https://www.japantimes.co.jp/news/2012/12/15/national/magnitude-10-temblor-could-happen-study/ |access-date=2023-10-20 |website=The Japan Times |language=en}}</ref><ref>{{Cite journal |last=Matsuzawa |first=Toru |date=2014-06-01 |title=The Largest Earthquakes We Should Prepare for |url=https://www.fujipress.jp/jdr/dr/dsstr000900030248/ |journal=Journal of Disaster Research |volume=9 |issue=3 |pages=248–251 |doi=10.20965/jdr.2014.p0248|doi-access=free }}</ref><ref>{{Cite journal |last1=Hirose |first1=Fuyuki |last2=Maeda |first2=Kenji |last3=Yoshida |first3=Yasuhiro |date=2019-12-01 |title=Maximum magnitude of subduction earthquakes along the Japan-Kuril-Kamchatka trench estimated from seismic moment conservation |url=https://academic.oup.com/gji/article/219/3/1590/5553983 |journal=Geophysical Journal International |language=en |volume=219 |issue=3 |pages=1590–1612 |doi=10.1093/gji/ggz381 |doi-access=free |issn=0956-540X|url-access=subscription }}</ref><ref>{{Cite journal |last1=Yoshida |first1=Masaki |last2=Santosh |first2=M. |date=2020-07-01 |title=Energetics of the Solid Earth: An integrated perspective |journal=Energy Geoscience |volume=1 |issue=1–2 |pages=28–35 |doi=10.1016/j.engeos.2020.04.001 |bibcode=2020EneG....1...28Y |issn=2666-7592|doi-access=free }}</ref> Another possible area could be the Lesser Antilles subduction zone.<ref name=":0" />

A study reported in 2016 found that the largest megathrust quakes are associated with downgoing slabs with the shallowest dip, so-called [[flat slab subduction]].<ref>{{cite journal|url=https://www.eurekalert.org/pub_releases/2016-11/uoo-fcm112216.php |title=Fault curvature may control where big quakes occur, Eurekalert 24-NOV-2016 |journal=Science |volume=354 |issue=6315 |pages=1027–1031 |doi=10.1126/science.aag0482 |pmid=27885027 |date=2016-11-24 |access-date=2018-06-05|last1=Bletery |first1=Quentin |last2=Thomas |first2=Amanda M. |last3=Rempel |first3=Alan W. |last4=Karlstrom |first4=Leif |last5=Sladen |first5=Anthony |last6=De Barros |first6=Louis |doi-access=free |bibcode=2016Sci...354.1027B }}</ref>

Compared with other earthquakes of similar magnitude, megathrust earthquakes have a longer duration and slower rupture velocities. The largest megathrust earthquakes occur in subduction zones with thick sediments, which may allow a fault rupture to propagate for great distances unimpeded.<ref name=BilekLay2018/>

==See also==
* [[Lists of earthquakes]]

==References==
{{reflist}}

==Further reading==
*{{cite journal | url=https://www.researchgate.net/publication/223469777 | first1=M.-A. | last1=Gutscher | title=The Gibraltar Arc seismogenic zone (part 2): Constraints on a shallow east dipping fault plane source for the 1755 Lisbon earthquake provided by tsunami modeling and seismic intensity | last2=Baptista | first2=M.A. | last3=Miranda | first3=J.M. | journal=Tectonophysics | year=2006 | volume=426 | issue=1–2 | pages=153–166 | issn=0040-1951 | doi=10.1016/j.tecto.2006.02.025| bibcode=2006Tectp.426..153G }}

==External links==
*[https://web.archive.org/web/20090502013322/http://earthquakescanada.nrcan.gc.ca/zones/cascadia/mega-eng.php Giant Megathrust Earthquakes] – [[Natural Resources Canada]]

[[Category:Megathrust earthquakes| ]]
[[Category:Plate tectonics]]
[[Category:Types of earthquake]]
[[Category:Tsunami]]