Megathrust earthquake: Difference between revisions
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==Terminology== |
==Terminology== |
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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 | 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}}</ref> However, the term is also occasionally applied to large thrust faults in continental collision zones, such as the [[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}}</ref> A megathrust fault can be {{convert|1000|km|sigfig=1|sp=us}} long.<ref name="PNSN"/> |
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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 | work=Earthquake Hazards Program| publisher=U.S. 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> Thrust faults are characteristic of areas where the [[Earth's crust]] is being compressed by tectonic forces.{{sfn|Fossen|2016|p=356}} |
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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 |website=Pacific Northwest Seismic Network |access-date=7 October 2021}}</ref> |
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==Areas== |
==Areas== |
Revision as of 01:07, 7 October 2021
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Earthquakes |
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Megathrust earthquakes occur at 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 earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0.[1][2] Since 1900, all earthquakes of magnitude 9.0 or greater have been megathrust earthquakes.[3]
The thrust faults responsible for megathrust earthquakes lie at the bottom of oceanic trenches, and the earthquakes can abruptly displace the sea floor over a large area. As a result, megathrust earthquakes often generate tsunamis that are considerably more destructive than the earthquakes themselves. Teletsunamis can cross ocean basins to devastate areas far from the original earthquake.
Terminology
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.[4][5] However, the term is also occasionally applied to large thrust faults in continental collision zones, such as the Himalayan megathrust.[6] A megathrust fault can be 1,000 kilometers (600 mi) long.[7]
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 faults, where the rock above the fault is displaced downwards, or strike-slip faults, 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°,[8] and show large displacements.[9][10] Thrust faults are characteristic of areas where the Earth's crust is being compressed by tectonic forces.[11]
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. 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.[5] 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.[7]
Areas
Megathrust earthquakes are almost exclusive to tectonic subduction zones and are often associated with the Pacific and Indian Oceans. These subduction zones are not only responsible for megathrust earthquakes but are also largely responsible for the volcanic activity associated with the Pacific Ring of Fire.
Since the earthquakes associated with these subduction zones deform the ocean floor, they often generate a significant series of tsunami waves. Subduction zone earthquakes are also known to produce intense shaking and ground movements for significant periods of time that can last for up to 5–6 minutes.
In the Indian Ocean region, the Sunda megathrust is located where the Indo-Australian Plate is subducting under the Eurasian Plate and extends 5,500 kilometres (3,400 mi) off the coasts of Myanmar, Sumatra, Java and Bali before terminating off the northwestern coast of Australia. This subduction zone was responsible for the 2004 Indian Ocean earthquake and tsunami.
In Japan, the Nankai megathrust under the Nankai Trough is responsible for Nankai megathrust earthquakes and associated tsunamis.
In North America, the Juan de Fuca Plate is subducting under the North American Plate creating the Cascadia subduction zone which stretches from mid Vancouver Island, British Columbia to Northern California. This subduction zone was responsible for the 1700 Cascadia earthquake.[12] 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, including the 1964 Alaska earthquake; at magnitude 9.2, it remains the largest recorded earthquake in North America, and the second-largest earthquake instrumentally recorded in the world.
The largest recorded megathrust earthquake was the 1960 Valdivia earthquake, estimated magnitude 9.4–9.6, centered off the coast of Chile along the Peru-Chile trench, where the Nazca Plate is subducting under the South American Plate. This megathrust region has regularly generated extremely large earthquakes historically, the largest megathrust event within the last 20 years being the magnitude 8.8 2010 Chile earthquake.
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.[13]
Notable examples
Notable examples of megathrust earthquakes, which have caused many deaths and extensive damage, are listed in the following table.
Event | Estimated Magnitude (Mw) |
Tectonic Plates Involved | Other Details/Notes |
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365 Crete earthquake | 8.0+ | African Plate subducting beneath the Aegean Sea Plate |
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869 Sanriku earthquake | 8.6–9.0 | Pacific Plate subducting beneath the Okhotsk Plate |
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1575 Valdivia earthquake | 8.5 | Nazca Plate subducting beneath the South American Plate |
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1700 Cascadia earthquake | 8.7–9.2 | Juan de Fuca Plate subducting beneath the North American Plate |
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1707 Hōei earthquake | 8.7–9.3[14] | Philippine Sea Plate subducting beneath the Eurasian Plate |
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1730 Valparaíso earthquake | 9.1–9.3 | Nazca Plate subducting beneath the South American Plate |
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1746 Lima-Callao earthquake | 8.6–8.8 | Pacific Plate subducting beneath the Nazca Plate |
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1755 Lisbon earthquake | 8.5–9.0 [15] | Hypothesized to be part of a young subduction zone but origin still debated; related to the Azores–Gibraltar Transform Fault |
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1868 Arica earthquake | 8.5–9.0 | Nazca Plate subducting beneath the South American Plate |
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1877 Iquique earthquake | 8.5–9.0? |
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1906 Ecuador–Colombia earthquake | 8.8 | ||
1923 Great Kantō earthquake | 7.9–8.2 | Philippine Sea Plate subducting beneath the Okhotsk Plate |
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1932 Jalisco earthquakes | 8.2 | Rivera Plate and Cocos Plate subducting beneath the North American Plate |
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1940 Lima earthquake | 8.2 | Nazca Plate subducting beneath the South American Plate along the Peru-Chile trench. | |
1946 Nankaidō earthquake | 8.1 | Philippine Sea Plate subducting beneath the Eurasian Plate |
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1952 Kamchatka earthquake | 9.0 | Pacific Plate subducting beneath the Okhotsk Plate |
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1957 Andreanof Islands earthquake | 8.6 | Pacific Plate subducting beneath the North American Plate |
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1960 Great Chilean earthquake | 9.5 | Nazca Plate subducting beneath the South American Plate |
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1964 Alaska earthquake ("Good Friday" earthquake) | 9.2 | Pacific Plate subducting beneath the North American Plate |
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1985 Mexico City earthquake | 8.0 | Cocos Plate subducting beneath the North American Plate | |
2004 Sumatra-Andaman earthquake ("Indian Ocean earthquake") | 9.1–9.3 | India Plate subducting beneath the Burma Plate |
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2005 Nias–Simeulue earthquake | 8.6 | Indo-Australian Plate subducting beneath the Eurasian Plate | |
2010 Chile earthquake | 8.8 | Nazca Plate subducting beneath the South American Plate |
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2011 Tōhoku earthquake and tsunami | 9.1[16] | Pacific Plate subducting beneath the Okhotsk Plate[17][18] |
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See also
References
- ^ Meier, M.-A.; Ampuero, J. P.; Heaton, T. H. (22 September 2017). "The hidden simplicity of subduction megathrust earthquakes". Science. 357 (6357): 1277–1281. Bibcode:2017Sci...357.1277M. doi:10.1126/science.aan5643. PMID 28935803. S2CID 206660652.
- ^ "Questions and Answers on Megathrust Earthquakes". Natural Resources Canada. Government of Canada. 19 October 2018. Retrieved 23 September 2020.
- ^ Johnston, Arch C.; Halchuk, Stephen (June–July 1993), "The seismicity data base for the Global Seismic Hazard Assessment Program", Annali di Geofisica, 36 (3–4): 133–151, pp. 140, 142 et seq.
- ^ Park, J.; Butler, R.; Anderson, K.; et al. (2005). "Performance Review of the Global Seismographic Network for the Sumatra-Andaman Megathrust Earthquake". Seismological Research Letters. 76 (3): 331–343. doi:10.1785/gssrl.76.3.331. ISSN 0895-0695.
- ^ a b Bilek, Susan L.; Lay, Thorne (1 August 2018). "Subduction zone megathrust earthquakes". Geosphere. 14 (4): 1468–1500. doi:10.1130/GES01608.1.
- ^ Elliott, J.R.; Jolivet, R.; González, P. J.; Avouac, J.-P.; Hollingsworth, J.; Searle, M. P.; Stevens, V.L. (February 2016). "Himalayan megathrust geometry and relation to topography revealed by the Gorkha earthquake". Nature Geoscience. 9 (2): 174–180. doi:10.1038/ngeo2623.
- ^ a b "Cascadia Subduction Zone". Pacific Northwest Seismic Network. Retrieved 7 October 2021.
- ^ "Earthquake Glossary – dip slip". Earthquake Hazards Program. U.S. Geological Survey.
- ^ Fossen, Haakon (2016). Structural geology (Second ed.). Cambridge, United Kingdom: Cambridge University Press. pp. 485, 488, 491. ISBN 9781107057647.
- ^ "Tsunami Terminology". The National Tsunami Hazard Mitigation Program History, 1995–2005. Pacific Marine Environmental Laboratory. Archived from the original on 2011-02-25.
- ^ Fossen 2016, p. 356.
- ^ "A Major Earthquake in the Pacific Northwest Looks Even Likelier". The Atlantic. August 16, 2016.
- ^ Bletery, Quentin; Thomas, Amanda M.; Rempel, Alan W.; Karlstrom, Leif; Sladen, Anthony; De Barros, Louis (2016-11-24). "Fault curvature may control where big quakes occur, Eurekalert 24-NOV-2016". Science. 354 (6315): 1027–1031. Bibcode:2016Sci...354.1027B. doi:10.1126/science.aag0482. PMID 27885027. Retrieved 2018-06-05.
- ^ Ishikawa, Yuzo (February 2012). Re-evaluation of Mw of the 1707 Hoei earthquake (PDF). G-EVER1 Workshop. Tsukuba, Japan: Asia-Pacific Region Global Earthquake and Volcanic Eruption Risk Management (G-EVER1) Consortium.
- ^ Gutscher, M.-A.; Baptista, M.A.; Miranda, J.M. (2006). "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". Tectonophysics. 426 (1–2): 153–166. Bibcode:2006Tectp.426..153G. doi:10.1016/j.tecto.2006.02.025. ISSN 0040-1951.
- ^ "M 9.1 – near the east coast of Honshu, Japan". Earthquake Hazards Program. USGS. 2016. Retrieved 21 November 2016.
- ^ Kidd, Kenneth (12 March 2011). "How "mega-thrust" earthquake caught forecasters by surprise". Toronto Star. Retrieved 12 March 2011.
- ^ Reilly, Michael (11 March 2011). "1722 UTC, 11 March 2011: Japan's largest ever earthquake". New Scientist. Retrieved 11 March 2011.