Megathrust earthquake
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Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another, caused by slip along the thrust fault that forms the contact between them. These interplate earthquakes are the planet's most powerful, with moment magnitudes (Mw) that can exceed 9.0. Since 1900, all 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.[1] They are a type of dip-slip fault. A thrust fault is a reverse fault with a dip of 45° or less.[2] 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.[3]
Areas
Subduction zones are mostly associated with the Pacific and Indian Oceans and are 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 nearly 3,000 miles 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 the United States and Canada, the Juan De Fuca Plate is subducting under the North American Plate creating the Cascadia subduction zone which stretches from Middle Vancouver, British Columbia to Northern California. This subduction zone was responsible for the 1700 Cascadia 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.[4]
Examples
Examples of megathrust earthquakes are listed in the following table.
| Event | Estimated Magnitude (Mw) |
Tectonic Plates Involved | Other Details/Notes |
|---|---|---|---|
| 365 Crete earthquake | 8.0+ | African Plate subducting beneath the Aegean Sea Plate |
|
| 869 Sanriku earthquake | 8.6–9.0 | Pacific Plate subducting beneath the Okhotsk Plate |
|
| 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 |
|
| 1707 Hōei earthquake | 8.6–9.3[5] | Philippine Sea Plate subducting beneath the Eurasian Plate |
|
| 1730 Valparaíso earthquake | 8.7–9.0 | Nazca Plate subducting beneath the South American Plate |
|
| 1737 Kamchatka earthquake | 8.3–9.0 | Pacific Plate subducting beneath the Okhotsk Plate |
|
| 1746 Lima-Callao earthquake | 8.6–8.8 | Pacific Plate subducting beneath the Nazca Plate |
|
| 1755 Lisbon earthquake | 8.5–9.0 [6] | Hypothesized to be part of a young subduction zone but origin still debated; related to the Azores–Gibraltar Transform Fault |
|
| 1868 Arica earthquake | 8.5–9.0 | Nazca Plate subducting beneath the South American Plate |
|
| 1877 Iquique earthquake | 8.5–9.0? |
| |
| 1906 Ecuador–Colombia earthquake | 8.8 |
| |
| 1923 Great Kantō earthquake | 8.2 | Philippine Sea Plate subducting beneath the Okhotsk Plate |
|
| 1942 Peru earthquake | 8.2 | Nazca Plate subducting beneath the South American Plate | |
| 1946 Nankaidō earthquake | 8.1 | Philippine Sea Plate subducting beneath the Eurasian Plate |
|
| 1952 Kamchatka earthquake | 9.0 | Pacific Plate subducting beneath the Okhotsk Plate |
|
| 1960 Great Chilean earthquake | 9.5 | Nazca Plate subducting beneath the South American Plate |
|
| 1963 Kuril Islands earthquake | 8.5 | Pacific Plate subducting beneath the Eurasian Plate | |
| 1964 Alaska earthquake ("Good Friday" earthquake) | 9.2 | Pacific Plate subducting beneath the North American Plate |
|
| 1965 Rat Islands earthquake | 8.7 | Pacific Plate subducting beneath the North American Plate | |
| 1985 Mexico City earthquake | 8.0 | Cocos Plate subducting beneath the North American Plate | |
| 2001 southern Peru earthquake | 8.4 | Nazca Plate subducting beneath the South American Plate |
|
| 2003 Hokkaido earthquake | 8.3 | Pacific Plate subducting beneath the Okhotsk Plate | |
| 2004 Sumatra-Andaman earthquake ("Indian Ocean earthquake") | 9.1–9.3 | India Plate subducting beneath the Burma Plate |
|
| 2005 Nias–Simeulue earthquake | 8.6 | Indo-Australian Plate subducting beneath the Eurasian Plate | |
| 2006 Kuril Islands earthquake | 8.3 | Pacific Plate subducting beneath the Okhotsk Plate | |
| 2010 Chile earthquake | 8.8 | Nazca Plate subducting beneath the South American Plate |
|
| 2011 Tōhoku earthquake and tsunami | 9.1[7] | Pacific Plate subducting beneath the Okhotsk Plate[8][9] |
|
| 2013 Okhotsk Sea earthquake | 8.3 | Pacific Plate subducting beneath the Okhotsk Plate | |
| 2014 Iquique earthquake | 8.2 | Nazca Plate subducting beneath the South American Plate |
|
| 2015 Illapel earthquake | 8.3 |
|
References
- ^ "Tsunami Terminology". The National Tsunami Hazard Mitigation Program History, 1995–2005. Pacific Marine Environmental Laboratory. Archived from the original on 2011-02-25.
{{cite web}}: Unknown parameter|deadurl=ignored (|url-status=suggested) (help) - ^ "Earthquake Glossary - dip slip". Earthquake Hazards Program. U.S. Geological Survey.
- ^ 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.
- ^ 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. 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.
{{cite conference}}: External link in|conferenceurl=|conferenceurl=ignored (|conference-url=suggested) (help) - ^ 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". Short Sharp Science. New Scientist. Retrieved 11 March 2011.