A megathrust earthquake is an interplate earthquake
where one tectonic plate slips beneath (subducts) another. Due to the size
of the tectonic plates and the shallow dip of the plate boundary, these earthquakes
are among the world's largest, with moment magnitudes that can exceed 9.0.
For the most part they occur in the Pacific and Indian
Oceans and are connected to the Ring of Fire. Since these earthquakes deform
the ocean floor, they almost always generate a significant tsunami.
All five earthquakes since 1900 of magnitude 9 or greater
have been megathrust earthquakes.
Some examples of megathrust earthquakes are:
- 1700 Cascadia Earthquake (magnitude 9.0) — Juan de
Fuca Plate subducting the North American Plate, slip length 1000 km
- 1737 Kamchatka earthquake (magnitude 9.3) — Pacific
Plate subducting the Okhotsk Plate, duration 15 minutes, depth 40 km.
- 1755 Lisbon earthquake (magnitude ~9) — believed
to be part of a young subduction zone.
- 1952 Kamchatka earthquake (magnitude 9.0) — Pacific
Plate subducting the Okhotsk Plate, depth 30 km.
- 1957 Andreanof Islands earthquake (magnitude 8.6)
— Pacific Plate subducting the North American Plate.
- 1960 Great Chilean Earthquake (magnitude 9.5) — Nazca
Plate subducting the South American Plate, depth 33 km, slip length
1000 km (625 mi), slip width 200 km (125 mi), slip motion
20 m (60 ft).
- 1964 Good Friday Earthquake (magnitude 9.2) — Pacific
Plate subducting the North American Plate, duration 4–5 minutes, depth
25 km, slip length 800 km (500 mi), slip motion 9 m (30 ft).
- 2004 Indian Ocean earthquake (magnitude 9.3) — India
Plate subducting the Burma Plate, duration 8 - 10 minutes, slip length 1200 km
(750 mi), slip motion 15 m (45 ft)