Liberal paradox

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{{Earthquakes}}
'''Megathrust [[earthquakes]]''' occur at [[Subduction|subduction zone]]s at destructive [[plate boundaries]] ([[convergent boundary|convergent boundaries]]), where one [[tectonic plate]] is subducted (forced underneath) by another. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these type of [[earthquakes]] are the planet's most powerful, with [[moment magnitude]]s (<math>M_w</math>) that can exceed 9.0. Since 1900, all six earthquakes of magnitude 9.0 or greater have been megathrust earthquakes. No other type of known terrestrial source of tectonic activity has produced earthquakes of this scale.

==Terminology==
During the rupture, one side of the fault is pushed upwards relative to the other, and it is this type of movement that is known as [[Thrust fault|thrust]].<ref>[http://nthmp-history.pmel.noaa.gov/terms.html Tsunami Terms]</ref> They are one type of [[fault (geology)#Dip-slip faults|dip-slip faults]]. A thrust fault is a [[reverse fault]] with a dip of 45° or less.<ref>[http://earthquake.usgs.gov/learn/glossary/?termID=59 Earthquake Glossary - dip slip]</ref> [[fault (geology)#Oblique-slip faults|Oblique-slip faults]] have significant components of different slip styles. The term ''megathrust'' does not have a widely accepted rigorous definition, but is used to refer to an extremely large thrust fault, typically formed at the plate interface along a subduction zone such as the [[Sunda megathrust]].<ref>[http://cdsads.u-strasbg.fr/cgi-bin/nph-abs_connect?db_key=AST&db_key=PHY&db_key=PRE&qform=AST&arxiv_sel=astro-ph&arxiv_sel=cond-mat&arxiv_sel=cs&arxiv_sel=gr-qc&arxiv_sel=hep-ex&arxiv_sel=hep-lat&arxiv_sel=hep-ph&arxiv_sel=hep-th&arxiv_sel=math&arxiv_sel=math-ph&arxiv_sel=nlin&arxiv_sel=nucl-ex&arxiv_sel=nucl-th&arxiv_sel=physics&arxiv_sel=quant-ph&arxiv_sel=q-bio&sim_query=YES&ned_query=YES&adsobj_query=YES&aut_logic=OR&obj_logic=OR&author=&object=&start_mon=&start_year=&end_mon=&end_year=&ttl_logic=OR&title=megathrust&txt_logic=OR&text=&nr_to_return=200&start_nr=1&jou_pick=ALL&ref_stems=&data_and=ALL&group_and=ALL&start_entry_day=&start_entry_mon=&start_entry_year=&end_entry_day=&end_entry_mon=&end_entry_year=&min_score=&sort=SCORE&data_type=SHORT&aut_syn=YES&ttl_syn=YES&txt_syn=YES&aut_wt=1.0&obj_wt=1.0&ttl_wt=0.3&txt_wt=3.0&aut_wgt=YES&obj_wgt=YES&ttl_wgt=YES&txt_wgt=YES&ttl_sco=YES&txt_sco=YES&version=1 Geophysical literature search showing almost 200 papers with the word "megathrust" in the title] ''[[University of Strasbourg]]''</ref><ref>{{cite journal |last=Park |first= |last2=''et al.'' |year=2005 |title=Performance Review of the Global Seismographic Network for the Sumatra-Andaman Megathrust Earthquake |journal=Seismological Research Letters |volume=76 |issue=3 |pages=331–343 |doi=10.1785/gssrl.76.3.331 }}</ref>

==Areas==
The major subduction zone is associated with the [[Pacific Ocean|Pacific]] and [[Indian Ocean]]s and is responsible for the [[volcanic]] activity associated with the [[Pacific Ring of Fire]]. Since these earthquakes deform the [[ocean floor]], they almost always generate a significant series of [[tsunami]] waves. They are known to produce intense shaking for periods of time that can last for up to a few minutes.

==The Big One==
"The Big One" is a term often used in casual conversation by residents of [[California]], [[Oregon]], [[Washington (state)|Washington]], and [[British Columbia]] to describe the megathrust earthquake anticipated as inevitably striking the [[Cascadia Subduction Zone]]. Much of the United States infrastructure has been hardened specifically for the anticipation of "The Big One". The name has also been applied to a megathrust earthquake expected to happen in [[Tokyo]], [[Kantō region]], [[Japan]] with the epicenter in [[Sagami Bay]] where the [[Philippine Sea Plate]] and [[North American Plate]] movements cause big earthquakes regularly, with an interval of approximately 70 years.{{Citation needed|date=July 2012}}

==Examples==
Examples of megathrust earthquakes are listed in the following table.

{| class="wikitable sortable"
|-
!|Event
!|Estimated Magnitude <br/>([[Moment Magnitude|<math>M_W</math>]])
!|Tectonic Plates Involved
!|Other Details/Notes
|-
|<span style="display:none">0</span>[[365 Crete earthquake]]
|8.0+
|[[African Plate]] subducting beneath the [[Aegean Sea Plate]]
|
*The quake generated a large tsunami in the eastern [[Mediterranean Sea]] and caused significant vertical displacement in the island of [[Crete]].<ref>{{Dead link|date=January 2012}}<nowiki>http://ssn.dgf.uchile.cl/home/terrem.html</nowiki></ref>
|-
|[[869 Jogan Sanriku earthquake]]
|8.6–9.0
|[[Pacific Plate]] subducting beneath the [[Okhotsk Plate]]
|
*Slip length: 200 km over (125 mi over)
*Slip width: 85 km over (53 mi over)
|-
|[[1575 Valdivia earthquake]]
|8.5
|[[Nazca Plate]] subducting beneath the [[South American Plate]]
|
|-
|[[1700 Cascadia earthquake]]
|8.7–9.2
|[[Juan de Fuca Plate]] subducting beneath the [[North American Plate]]
|
*Slip length: 1000 km (625 mi)
*Slip motion: 20 m (60 ft)
|-
|[[1707 Hōei earthquake]]
|8.6
|[[Philippine Sea Plate]] subducting beneath the [[Eurasian Plate]]
|
*Duration: approximately 10 minutes
*Slip length: maybe 600 and 700 km (370 and 435 mi)
|-
|1737 [[Kamchatka earthquake]]
|8.3–9.0
|[[Pacific Plate]] subducting beneath the [[Okhotsk Plate]]
|
*Duration: 15 minutes
*Depth: 40 km
*Slip length: maybe 700 km over (435 mi over)
|-
|[[1755 Lisbon earthquake]]
|8.5–9.0 <ref name="Gutscher"/>
|Hypothesized to be part of a young subduction zone but origin still debated
|
*Destroyed Lisbon and was followed by a 20 metre high tsunami and many fires.
*It caused from ten to a hundred thousand deaths.
*The grave of [[Nuno Álvares Pereira]] was forever lost along with the Historical records of the voyages of [[Vasco da Gama]] and [[Christopher Columbus]]
|-
|[[1868 Arica earthquake]]
|8.5–9.0
|[[Nazca Plate]] subducting beneath the [[South American Plate]]
|
*Slip length: 600 km (370 mi)
|-
|[[1877 Iquique earthquake]]
|8.5–9.0?
|[[Nazca Plate]] subducting beneath the [[South American Plate]]
|
*Slip length: 420 and 450 km (230 and 245 mi)
|-
|[[1906 Ecuador-Colombia earthquake]]
|8.8
|[[Nazca Plate]] subducting beneath the [[South American Plate]]
|
|-
|[[1946 Nankaidō earthquake]]
|8.1
|[[Philippine Sea Plate]] subducting beneath the [[Eurasian Plate]]
|
*Slip length: maybe 300 km (190 mi)
|-
|1952 [[Kamchatka earthquake]]
|9.0
|[[Pacific Plate]] subducting beneath the [[Okhotsk Plate]]
|
*Depth: 30 km
*Slip length: maybe 600 km over (370 mi over)
|-
|[[1957 Andreanof Islands earthquake]]
|8.6
|[[Pacific Plate]] subducting beneath the [[North American Plate]]
|
*Depth: 33 km
*Slip length: maybe 700 km over (435 mi over)
|-
|1960 [[1960 Valdivia earthquake|Great Chilean Earthquake]]
|9.5
|[[Nazca Plate]] subducting beneath the [[South American Plate]]
|
*Duration: 5–6 minutes
*Depth: 33 km
*Slip length: 850 and 1000 km (530 and 625 mi)
*Slip width: 200 km (125 mi)
*Slip motion: 20 m (60 ft)
|-
|[[1964 Alaska earthquake]] ("Good Friday" earthquake)
|9.2
|[[Pacific Plate]] subducting beneath the [[North American Plate]]
|
*Duration: 4–5 minutes
*Depth: 25 km
*Slip length: 800 and 850 km (500 and 530 mi)
*Slip width: 250 km (155 mi)
*Slip motion: 23 m (70 ft)
|-
|[[2001 southern Peru earthquake]]
|8.4
|[[Nazca Plate]] subducting beneath the [[South American Plate]]
|
*Depth: 33 km
|-
|[[2004 Indian Ocean earthquake and tsunami|2004 Sumatra-Andaman earthquake]] ("Indian Ocean earthquake")
|9.1–9.3
|[[India Plate]] subducting beneath the [[Burma Plate]]
|
*The total vertical displacement measured by [[sonar]] survey is about 40 m in the vicinity of the epicenter and occurred as two separate movements which created two large, steep, almost vertical cliffs, one above the other.
*Duration: 8–10 minutes
*Depth: 30 km
*Slip length: 1000 and 1300 km (625 and 810 mi)
*Slip width: 180 km (110 mi)
*Slip motion: 33 m (110 ft)
|-
|[[2010 Chile earthquake|2010 Maule earthquake]] ("Chile earthquake")
|8.8
|[[Nazca Plate]] subducting beneath the [[South American Plate]]
|
*Depth: 35 km
*Slip length: 500 km (310 mi)
*Slip width: 200 km (125 mi)
|-
|[[2011 Tōhoku earthquake and tsunami]]
|9.0
|[[Pacific Plate]] subducting beneath the [[Okhotsk Plate]]<ref>{{cite web|url=http://earthquake.usgs.gov/earthquakes/recenteqsww/Quakes/usc0001xgp.php|title=Magnitude 8.9 – NEAR THE EAST COAST OF HONSHU, JAPAN 2011 March 11 05:46:23 UTC|date=11 March 2011|accessdate=11 March 2011|publisher=USGS}}</ref><ref>{{cite web|url=http://www.thestar.com/news/world/article/952957--how-mega-thrust-earthquake-caught-forecasters-by-surprise|title=How ‘mega-thrust" earthquake caught forecasters by surprise|date=12 March 2011|accessdate=12 March 2011|publisher=[[Toronto Star]]|author=Kenneth Kidd}}</ref><ref>{{cite journal |url = http://www.newscientist.com/blogs/shortsharpscience/2011/03/powerful-japan-quake-sparks-ts.html |title = Japan's quake updated to magnitude 9.0 |edition = Short Sharp Science |journal = [[New Scientist]] |date=11 March 2011<!- – 17:22 GMT -->|first = Michael |last = Reilly |accessdate=11 March 2011}}</ref>
|
*Duration: 6 minutes
*Depth: 30 km
*Slip length: 500 km (310 mi)
*Slip width: 200 km (125 mi)
*Slip motion: 20 m (60 ft)
|}

==References==
{{reflist|refs=
<ref name="Gutscher">{{cite journal|last=Gutscher|first=M.-A.|coauthors=Baptista M.A. & Miranda J.M.|year=2006|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|journal=Tectonophysics|volume=426|pages=153–166|doi=10.1016/j.tecto.2006.02.025|url=http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V72-4KBX4F6-1&_user=10&_coverDate=10%2F30%2F2006&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_searchStrId=1686129586&_rerunOrigin=scholar.google&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=03712ebb4ba96cc63271c6c93369c1e0&searchtype=a|bibcode = 2006Tectp.426..153G }}</ref>
}}

==External links==
*[http://earthquakescanada.nrcan.gc.ca/zones/cascadia/mega_e.php Natural Resources Canada: Giant Megathrust Earthquakes]

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

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