Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. 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.
The 1946 Aleutian Islands earthquake occurred near the Aleutian Islands, Alaska on April 1, 1946. The shock measured 8.6, 9.3 or 7.4. It had a maximum Mercalli intensity of VI (Strong). It resulted in 165–173 casualties and over US $26 million in damage. The seafloor along the fault was elevated, triggering a Pacific-wide tsunami with multiple destructive waves at heights ranging from 45–138 ft (14–42 m). The tsunami obliterated the Scotch Cap Lighthouse on Unimak Island, Alaska among others, and killed all five lighthouse keepers. Despite the destruction to the Aleutian Island Unimak, the tsunami had almost an imperceptible effect on the Alaskan mainland.
The Okhotsk microplate is a proposed minor tectonic plate covering the Kamchatka Peninsula, Magadan Oblast, and Sakhalin Island of Russia; Hokkaido, Kantō and Tōhoku regions of Japan; the Sea of Okhotsk, as well as the disputed Kuril Islands.
Many major earthquakes have occurred in the region of the Kamchatka Peninsula in far eastern Russia. Events in 1737, 1923 and 1952, were megathrust earthquakes and caused tsunamis. There are many more earthquakes and tsunamis originating from the region.
The Aleutian Trench is an oceanic trench along a convergent plate boundary which runs along the southern coastline of Alaska and the Aleutian islands. The trench extends for 3,400 kilometres (2,100 mi) from a triple junction in the west with the Ulakhan Fault and the northern end of the Kuril–Kamchatka Trench, to a junction with the northern end of the Queen Charlotte Fault system in the east. It is classified as a "marginal trench" in the east as it runs along the margin of the continent. The subduction along the trench gives rise to the Aleutian Arc, a volcanic island arc, where it runs through the open sea west of the Alaska Peninsula. As a convergent plate boundary, the trench forms part of the boundary between two tectonic plates. Here, the Pacific Plate is being subducted under the North American Plate at a dip angle of nearly 45°. The rate of closure is 7.5 centimetres (3 in) per year.
The 1957 Andreanof Islands earthquake occurred at 04:22 local time on March 9 with a moment magnitude estimated between 8.6 and 9.1 and a maximum Modified Mercalli intensity of VIII (Severe). It occurred south of the Andreanof Islands group, which is part of the Aleutian Islands arc. The event occurred along the Aleutian Trench, the convergent plate boundary that separates the Pacific Plate and the North American plates near Alaska. A basin-wide tsunami followed, with effects felt in Alaska and Hawaii, and strong waves recorded across the Pacific rim. Total losses were around $5 million.
The 1995 Antofagasta earthquake occurred on July 30 at 05:11 UTC with a moment magnitude of 8.0 and a maximum Mercalli intensity of VII. The Antofagasta Region in Chile was affected by a moderate tsunami, with three people killed, 58 or 59 injured, and around 600 homeless. Total damage from the earthquake and tsunami amounted to $1.791 million.
The 1994 Kuril Islands earthquake – also known as the Hokkaido Toho-oki earthquake – occurred on . The magnitude of this earthquake was put at 8.3, or 8.1. The epicenter was located at about 70 km east of Shikotan Island. The shaking and tsunami caused road and building damage. At least 10 people were reported dead.
The 1959 Kamchatka earthquake occurred on May 4 at with a moment magnitude of 8.0–8.3, and a surface wave magnitude of 8.25. The epicenter was near the Kamchatka Peninsula, Russian SFSR, USSR. Building damage was reported in Petropavlovsk-Kamchatsky. The maximum intensity was VIII (Damaging) on the Medvedev–Sponheuer–Karnik scale. The intensity in Petropavlovsk-Kamchatsky was about VIII MSK.
On January 1, 1996, at 4:05 p.m. Central Indonesia Time, an earthquake with an epicenter in the Makassar Strait struck north of Minahasa on the island of Sulawesi, Indonesia. The earthquake measured 7.9 on the moment magnitude scale and was centered off Tolitoli Regency in Central Sulawesi, or 25 km from the Tonggolobibi village. A tsunami of 2–4 m (6.6–13.1 ft) was triggered by this earthquake as a result. At least 350 buildings were badly damaged, nine people died and 63 people were injured.
The Nemuro-Oki earthquake in scientific literature, occurred on June 17 at 12:55 local time. It struck with an epicenter just off the Nemuro Peninsula in northern Hokkaidō, Japan. It measured 7.8–7.9 on the moment magnitude scale (Mw ), 8.1 on the tsunami magnitude scale (Mt ) and 7.4 on the Japan Meteorological Agency magnitude scale (MJMA ).
On April 13, 1923 at 15:31 UTC, an earthquake occurred off the northern coast of the Kamchatka Peninsula in the USSR, present-day Russia. The earthquake had a surface-wave magnitude (Ms ) of 6.8–7.3 and an estimated moment magnitude (Mw ) of 7.0–8.2. This event came just two months after a slightly larger earthquake with an epicenter struck south of the April event. Both earthquakes were tsunamigenic although the latter generated wave heights far exceeding that of the one in February. After two foreshocks of "moderate force", the main event caused considerable damage. Most of the 36 casualties were the result of the tsunami inundation rather than the earthquake.
The 1737 Kamchatka earthquake occurred on October 17 or 16 near the southern tip of present-day Russia's Kamchatka Peninsula. The shock was felt at approximately 03:00 local time or 16:00 UTC by residents on the peninsula and Kuril Islands. The earthquake struck at a shallow depth of roughly 40 km beneath the peninsula. The earthquake had an estimated magnitude of 9.0–9.3 on the moment magnitude scale.
The 1982 Urakawa earthquake was a 6.9 earthquake that struck off the coast of Urakawa, Japan, on 11:32 (JST), March 21, 1982. The epicenter was 42.1°N 142.6°E. The earthquake was the largest earthquake in the history of the region. The earthquake caused 167 injuries and damage in Tomakomai and Sapporo.
An earthquake occurred off the coast of the Alaska Peninsula on July 28, 2021, at 10:15 p.m. local time. The large megathrust earthquake had a moment magnitude of 8.2 according to the United States Geological Survey (USGS). A tsunami warning was issued by the National Oceanic and Atmospheric Administration (NOAA) but later cancelled. The mainshock was followed by a number of aftershocks, including three that were of magnitude 5.9, 6.1 and 6.9 respectively.
The 2021 South Sandwich Islands earthquakes were a pair of powerful earthquakes, followed by many strong aftershocks which struck along the South Sandwich Trench in August 2021. The quakes measured 7.5 and 8.1 on the moment magnitude scale, according to the United States Geological Survey. The mainshock is tied with another event in 1929 as the largest earthquake ever recorded in the South Atlantic region, and is tied with the 2021 Kermadec Islands earthquake as the second largest earthquake of 2021.
The 1841 Kamchatka earthquake occurred in the Pacific Ocean on May 17 at 08:00 local time. The earthquake had an epicenter off the Russian Far East's Kamchatka Peninsula. With an estimated moment magnitude of 9.0 or higher, it is one of the largest to strike the region. A large tsunami with up to 15 meters in run-up along the coast.
The 1940 Shakotan earthquake occurred on August 2 at 00:08:22 JST with a moment magnitude (Mw ) of 7.5 and maximum JMA seismic intensity of Shindo 4. The shock had an epicenter off the coast of Hokkaido, Japan. Damage from the shock was comparatively light, but the accomanying tsunami was destructive. The tsunami caused 10 deaths and 24 injuries on Hokkaido, and destroyed homes and boats across the Sea of Japan. The highest tsunami waves were recorded at the coast of Russia while along the coast of Hokkaido, waves were about 2 m.
The 1958 Kuril Islands earthquake or Etorofu earthquake was a Mw 8.3–8.4 earthquake that struck near the Kuril island of Iturup on November 6, 1958, at 22:58 UTC, or 09:58 on the 7th local time. The earthquake occurred as the result of shallow reverse faulting along the Kuril-Kamchatka Trench, and caused Modified Mercalli Intensity (MMI) X (Extreme) shaking, as well as a tsunami 5 m (16 ft) high. Iturup sustained significant damage as a result of the shaking and tsunami, with other locations along the Kuril Islands also reporting strong damage.
