Megathrust earthquake

Megathrust earthquakes occur at subduction zones at destructive convergent plate boundaries, where one tectonic plate is forced underneath another. 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] It is mostly American terminology.

Areas

The major subduction zone is associated with the Pacific and Indian Oceans and is responsible for the volcanic activity associated with the Pacific Ring of Fire. Since these earthquakes deform the ocean floor, they often 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.

In Japan, the Nankai megathrust under the Nankai Trough is responsible for Nankai megathrust earthquakes and associated tsunamis.

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
  • The quake generated a large tsunami in the eastern Mediterranean Sea and caused significant vertical displacement in the island of Crete.
869 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 8.6–9.3[5] Philippine Sea Plate subducting beneath the Eurasian Plate
  • Duration: approximately 10 minutes
  • Slip length: maybe 600 and 700 km (370 and 435 mi)
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
  • Duration: 15 minutes
  • Depth: 40 km
  • Slip length: maybe 700 km over (435 mi over)
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
  • 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
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
  • 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 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)
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
  • 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)
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
  • Depth: 33 km
  • Slip length: 200 km (125 mi)
  • Slip width: 110 km (70 mi)
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
  • 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)
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
  • Depth: 35 km
  • Slip length: 500 km (310 mi)
  • Slip width: 200 km (125 mi)
2011 Tōhoku earthquake and tsunami 9.1[7] Pacific Plate subducting beneath the Okhotsk Plate[8][9]
  • Duration: 6 minutes
  • Depth: 29 km
  • Slip length: 500 km (310 mi)
  • Slip width: 200 km (125 mi)
  • Slip motion: 20 m (60 ft)
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
  • Depth: 20.1 km
  • Slip length: 170 km (105 mi)
  • Slip width: 70 km (45 mi)
2015 Illapel earthquake 8.3 Nazca Plate subducting beneath the South American Plate
  • Depth: 25 km
  • Slip length: 260 km (160 mi)
  • Slip width: 80 km (50 mi)

References

  1. "Tsunami Terminology". The National Tsunami Hazard Mitigation Program History, 1995–2005. Pacific Marine Environmental Laboratory.
  2. "Earthquake Glossary - dip slip". Earthquake Hazards Program. U.S. Geological Survey.
  3. 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. ISSN 0895-0695. doi:10.1785/gssrl.76.3.331.
  4. Fault curvature may control where big quakes occur, Eurekalert 24-NOV-2016
  5. 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.
  6. 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. ISSN 0040-1951. doi:10.1016/j.tecto.2006.02.025.
  7. "M 9.1 - near the east coast of Honshu, Japan". Earthquake Hazards Program. USGS. 2016. Retrieved 21 November 2016.
  8. Kidd, Kenneth (12 March 2011). "How "mega-thrust" earthquake caught forecasters by surprise". Toronto Star. Retrieved 12 March 2011.
  9. Reilly, Michael (11 March 2011). "1722 UTC, 11 March 2011: Japan's largest ever earthquake". Short Sharp Science. New Scientist. Retrieved 11 March 2011.
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