Megathrust earthquake
Encyclopedia
Megathrust earthquakes occur at subduction zone
s at destructive plate boundaries (convergent boundaries
), where one tectonic plate is forced under (subducts) another. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these earthquakes are among the world's largest, with moment magnitudes (
) 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 tectonic activity can produce earthquakes of this scale.
. They are one type of dip-slip faults. A thrust fault is a reverse fault with a dip of 45° or less. 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
.
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 long periods, such as several minutes.
Subduction
In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. These 3D regions of mantle downwellings are known as "Subduction Zones"...
s at destructive plate boundaries (convergent boundaries
Convergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
), where one tectonic plate is forced under (subducts) another. Due to the shallow dip of the plate boundary, which causes large sections to get stuck, these earthquakes are among the world's largest, with moment magnitudes (
) 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 tectonic activity can produce 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 thrustThrust fault
A thrust fault is a type of fault, or break in the Earth's crust across which there has been relative movement, in which rocks of lower stratigraphic position are pushed up and over higher strata. They are often recognized because they place older rocks above younger...
. They are one type of dip-slip faults. A thrust fault is a reverse fault with a dip of 45° or less. 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
Sunda megathrust
The Sunda megathrust is a fault that extends approximately 5,500 km from Myanmar in the north, running along the southwestern side of Sumatra, to the south of Java and Bali before terminating near Australia...
.
Areas
The major subduction zone is associated with the PacificPacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
and Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
s and is responsible for the volcanic activity associated with the Pacific Ring of Fire
Pacific Ring of Fire
The Pacific Ring of Fire is an area where large numbers of earthquakes and volcanic eruptions occur in the basin of the Pacific Ocean. In a horseshoe shape, it is associated with a nearly continuous series of oceanic trenches, volcanic arcs, and volcanic belts and/or plate movements...
. Since these earthquakes deform the ocean floor, they almost always generate a significant series of tsunami
Tsunami
A tsunami is a series of water waves caused by the displacement of a large volume of a body of water, typically an ocean or a large lake...
waves. They are known to produce intense shaking for long periods, such as several minutes.
Examples
Examples of megathrust earthquakes are listed in the following table.| Event | Estimated Moment Magnitude ( ) |
Tectonic Plates Involved | Other Details/Notes |
|---|---|---|---|
| 365 Crete earthquake 365 Crete earthquake The AD 365 Crete earthquake was an undersea earthquake that occurred at about sunrise on 21 July 365 in the Eastern Mediterranean, with an assumed epicentre near Crete. Geologists today estimate the quake to have been 8 on the Richter Scale or higher, causing widespread destruction in central and... |
8.0+ | African Plate African Plate The African Plate is a tectonic plate which includes the continent of Africa, as well as oceanic crust which lies between the continent and various surrounding ocean ridges.-Boundaries:... subducting beneath the Aegean Sea Plate Aegean Sea Plate The Aegean Sea Plate is a small tectonic plate located in the eastern Mediterranean Sea under southern Greece and far western Turkey. Its southern edge is a subduction zone south of Crete, where the African Plate is being swept under the Aegean Sea Plate... |
|
| 1575 Valdivia earthquake 1575 Valdivia earthquake The 1575 Valdivia earthquake was an earthquake in Chile that caused the subsequent flood of Valdivia much like the 1960 Valdivia earthquake caused the ensuing Riñihuazo flooding. It occurred at 14:30 local time on December 16, 1575. It had an estimated magnitude of 8.5 on the surface wave... |
8.5 | Nazca Plate Nazca Plate ]The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction along the Peru-Chile Trench of the Nazca Plate under the South American Plate is largely responsible for the... subducting beneath the South American Plate South American Plate The South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge.... |
|
| 1700 Cascadia earthquake | 8.7–9.2 | Juan de Fuca Plate Juan de Fuca Plate The Juan de Fuca Plate, named after the explorer of the same name, is a tectonic plate, generated from the Juan de Fuca Ridge, and subducting under the northerly portion of the western side of the North American Plate at the Cascadia subduction zone... subducting beneath the North American Plate North American Plate The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust... |
|
| 1737 Kamchatka earthquake | 9.0–9.3 | Pacific Plate Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate.... subducting beneath the Okhotsk Plate Okhotsk Plate The Okhotsk Plate is a tectonic plate covering the Sea of Okhotsk, the Kamchatka Peninsula, Sakhalin Island and Tōhoku and Hokkaidō in Japan. It was formerly considered a part of the North American Plate, but recent studies indicate that it is an independent plate, bounded on the north by the... |
|
| 1755 Lisbon earthquake 1755 Lisbon earthquake The 1755 Lisbon earthquake, also known as the Great Lisbon Earthquake, was a megathrust earthquake that took place on Saturday 1 November 1755, at around 9:40 in the morning. The earthquake was followed by fires and a tsunami, which almost totally destroyed Lisbon in the Kingdom of Portugal, and... |
9.0 | Hypothesized to be part of a young subduction zone but origin still debated | |
| 1868 Arica earthquake 1868 Arica earthquake The 1868 Arica earthquake was an earthquake that occurred on August 13, 1868, near Arica, then part of Peru, now part of Chile, at 21:30 UTC. It had an estimated magnitude between 8.5 and 9.0... |
9.0 | Nazca Plate Nazca Plate ]The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction along the Peru-Chile Trench of the Nazca Plate under the South American Plate is largely responsible for the... subducting beneath the South American Plate South American Plate The South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge.... |
|
| 1877 Iquique earthquake 1877 Iquique earthquake The 1877 Iquique earthquake occurred at 21:16 local time on 9 May . It had a magnitude of 8.8 on the moment magnitude scale and a maximum felt intensity of XI on the Mercalli intensity scale and triggered a devastating tsunami... |
8.8 | Nazca Plate Nazca Plate ]The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction along the Peru-Chile Trench of the Nazca Plate under the South American Plate is largely responsible for the... subducting beneath the South American Plate South American Plate The South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge.... |
|
| 1946 Nankaidō earthquake 1946 Nankaido earthquake The 1946 Nankaidō earthquake was a great earthquake in Nankaidō, Japan. It occurred on December 20, 1946 at 19:19 UTC. The earthquake measured between 8.1 and 8.4 on the moment magnitude scale, and was felt from Northern Honshū to Kyūshū... |
8.1 | Philippine Sea Plate subducting beneath the Eurasian Plate Eurasian Plate The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia... |
|
| 1952 Kamchatka earthquake | 9.0 | Pacific Plate Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate.... subducting beneath the Okhotsk Plate Okhotsk Plate The Okhotsk Plate is a tectonic plate covering the Sea of Okhotsk, the Kamchatka Peninsula, Sakhalin Island and Tōhoku and Hokkaidō in Japan. It was formerly considered a part of the North American Plate, but recent studies indicate that it is an independent plate, bounded on the north by the... |
|
| 1957 Andreanof Islands earthquake 1957 Andreanof Islands earthquake The 1957 Andreanof Islands earthquake was a magnitude 8.6 MW megathrust earthquake that took place on March 9, 1957. It was centered at in the Alaska-Aleutian megathrust, south of the Andreanof Islands group of the Aleutian Islands in the U.S... |
8.6–9.1 | Pacific Plate Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate.... subducting beneath the North American Plate North American Plate The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust... |
|
| 1960 Great Chilean Earthquake | 9.5 | Nazca Plate Nazca Plate ]The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction along the Peru-Chile Trench of the Nazca Plate under the South American Plate is largely responsible for the... subducting beneath the South American Plate South American Plate The South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge.... |
|
| 1964 Alaska earthquake ("Good Friday" earthquake) | 9.2 | Pacific Plate Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate.... subducting beneath the North American Plate North American Plate The North American Plate is a tectonic plate covering most of North America, Greenland, Cuba, Bahamas, and parts of Siberia, Japan and Iceland. It extends eastward to the Mid-Atlantic Ridge and westward to the Chersky Range in eastern Siberia. The plate includes both continental and oceanic crust... |
|
| 2004 Sumatra-Andaman earthquake ("Indian Ocean earthquake") | 9.1–9.3 | India Plate India Plate The India Plate or Indian Plate is a tectonic plate that was originally a part of the ancient continent of Gondwanaland from which it split off, eventually becoming a major plate. About 50 to 55 million years ago , it fused with the adjacent Australian Plate... subducting beneath the Burma Plate Burma Plate The Burma Plate is a small tectonic plate or microplate located in Southeast Asia, often considered a part of the larger Eurasian Plate. The Andaman Islands, Nicobar Islands, and northwestern Sumatra are located on the plate... |
Sonar Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels... 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. |
| 2010 Maule earthquake 2010 Chile earthquake The 2010 Chile earthquake occurred off the coast of central Chile on Saturday, 27 February 2010, at 03:34 local time , having a magnitude of 8.8 on the moment magnitude scale, with intense shaking lasting for about three minutes. It ranks as the sixth largest earthquake ever to be recorded by a... ("Chile earthquake") |
8.8 | Nazca Plate Nazca Plate ]The Nazca Plate, named after the Nazca region of southern Peru, is an oceanic tectonic plate in the eastern Pacific Ocean basin off the west coast of South America. The ongoing subduction along the Peru-Chile Trench of the Nazca Plate under the South American Plate is largely responsible for the... subducting beneath the South American Plate South American Plate The South American Plate is a continental tectonic plate which includes the continent of South America and also a sizeable region of the Atlantic Ocean seabed extending eastward to the Mid-Atlantic Ridge.... |
|
| 2011 Tōhoku earthquake and tsunami 2011 Tōhoku earthquake and tsunami The 2011 earthquake off the Pacific coast of Tohoku, also known as the 2011 Tohoku earthquake, or the Great East Japan Earthquake, was a magnitude 9.0 undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST on Friday, 11 March 2011, with the epicenter approximately east... |
9.0 | Pacific Plate Pacific Plate The Pacific Plate is an oceanic tectonic plate that lies beneath the Pacific Ocean. At 103 million square kilometres, it is the largest tectonic plate.... subducting beneath the Okhotsk Plate Okhotsk Plate The Okhotsk Plate is a tectonic plate covering the Sea of Okhotsk, the Kamchatka Peninsula, Sakhalin Island and Tōhoku and Hokkaidō in Japan. It was formerly considered a part of the North American Plate, but recent studies indicate that it is an independent plate, bounded on the north by the... |
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