Megathrust Earthquakes

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"The 1964 Alaska earthquake, also known as the Great Alaskan Earthquake, the Portage Earthquake and the Good Friday Earthquake, was a megathrust earthquake that began at 5:36 P.M. AST on Good Friday, March 27, 1964. Across south-central Alaska, ground fissures, collapsing buildings, and tsunamis resulting from the earthquake caused about 143 deaths.

Lasting nearly four minutes, it was the most powerful recorded earthquake in U.S. and North American history, and the second most powerful ever measured by seismograph. It had a magnitude of 9.2, at the time making it the second largest earthquake in recorded history.

The powerful earthquake produced earthquake liquefaction in the region. Ground fissures and failures caused major structural damage in several communities, much damage to property and several landslides. Anchorage sustained great destruction or damage to many inadequately engineered houses, buildings, and infrastructure (paved streets, sidewalks, water and sewer mains, electrical systems, and other man-made equipment), particularly in the several landslide zones along Knik Arm. Two hundred miles southwest, some areas near Kodiak were permanently raised by 30 feet (9.1 m). Southeast of Anchorage, areas around the head of Turnagain Arm near Girdwood and Portage dropped as much as 8 feet (2.4 m), requiring reconstruction and fill to raise the Seward Highway above the new high tide mark.

In Prince William Sound, Port Valdez suffered a massive underwater landslide, resulting in the deaths of 30 people between the collapse of the Valdez city harbor and docks, and inside the ship that was docked there at the time. Nearby, a 27-foot (8.2 m) tsunami destroyed the village of Chenega, killing 23 of the 68 people who lived there; survivors out-ran the wave, climbing to high ground. Post-quake tsunamis severely affected Whittier, Seward, Kodiak, and other Alaskan communities, as well as people and property in British Columbia, Oregon, and California. Tsunamis also caused damage in Hawaii and Japan. Evidence of motion directly related to the earthquake was reported from all over the earth."

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"The 1960 Valdivia earthquake or Great Chilean Earthquake (Spanish: Terremoto de Valdivia/Gran terremoto de Chile) of Sunday, 22 May 1960 is to date the most powerful earthquake ever recorded on Earth, rating 9.5 on the moment magnitude scale. It occurred in the afternoon (19:11 GMT, 15:11 local time) and its resulting tsunami affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, southeast Australia, and the Aleutian Islands in Alaska.

The epicenter was near Lumaco (see map) some 570 km (350 mi) south of Santiago, with Temuco being the closest large city, while Valdivia was the most affected city. It caused localised tsunamis that severely battered the Chilean coast, with waves up to 25 metres (82 ft). The main tsunami raced across the Pacific Ocean and devastated Hilo, Hawaii. Waves as high as 10.7 metres (35 ft) were recorded 10,000 kilometres (6,200 mi) from the epicenter, and as far away as Japan and the Philippines.

The death toll and monetary losses arising from such a widespread disaster are not certain. Various estimates of the total number of fatalities from the earthquake and tsunamis have been published, with the USGS citing studies with figures of 2,231; 3,000; or 5,700 killed,[4] and another source uses an estimate of 6,000 dead.[3] Different sources have estimated the monetary cost ranged from 400 million to 800 million US dollars[4] (or 2.9 to 5.8 billion in 2011 dollars, adjusted for inflation)."

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"The 2004 Indian Ocean earthquake was an undersea megathrust earthquake that occurred at 00:58:53 UTC on Sunday, December 26, 2004, with an epicentre off the west coast of Sumatra, Indonesia. The quake itself is known by the scientific community as the Sumatra-Andaman earthquake. The resulting tsunami is given various names, including the 2004 Indian Ocean tsunami, South Asian tsunami, Indonesian tsunami, and Boxing Day tsunami.

The earthquake was caused by subduction and triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing over 230,000 people in fourteen countries, and inundating coastal communities with waves up to 30 meters (98 ft) high. It was one of the deadliest natural disasters in recorded history. Indonesia was the hardest-hit country, followed by Sri Lanka, India, and Thailand.

With a magnitude of Mw 9.1–9.3, it is the third largest earthquake ever recorded on a seismograph. The earthquake had the longest duration of faulting ever observed, between 8.3 and 10 minutes. It caused the entire planet to vibrate as much as 1 centimetre (0.4 inches) and triggered other earthquakes as far away as Alaska. Its epicentre was between Simeulue and mainland Indonesia. The plight of the affected people and countries prompted a worldwide humanitarian response. In all, the worldwide community donated more than $14 billion (2004 U.S. dollars) in humanitarian aid."

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"The 2011 earthquake off the Pacific coast of Tōhoku (东北地方太平洋冲地震 Tōhoku-chihō Taiheiyō Oki Jishin?), also known as the 2011 Tohoku earthquake, or the Great East Japan Earthquake, was a magnitude 9.0 (Mw) undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST (05:46 UTC) on Friday, 11 March 2011, with the epicenter approximately 70 kilometres (43 mi) east of the Oshika Peninsula of Tōhoku and the hypocenter at an underwater depth of approximately 32 km (20 mi). It was the most powerful known earthquake ever to have hit Japan, and one of the five most powerful earthquakes in the world since modern record-keeping began in 1900. The earthquake triggered powerful tsunami waves that reached heights of up to 40.5 metres (133 ft) in Miyako in Tōhoku's Iwate Prefecture, and which, in the Sendai area, travelled up to 10 km (6 mi) inland. The earthquake moved Honshu 2.4 m (8 ft) east and shifted the Earth on its axis by estimates of between 10 cm (4 in) and 25 cm (10 in).

The tsunami caused a number of nuclear accidents, primarily the ongoing level 7 meltdowns at three reactors in the Fukushima I Nuclear Power Plant complex, and the associated evacuation zones affecting hundreds of thousands of residents. Many electrical generators were taken down, and at least three nuclear reactors suffered explosions due to hydrogen gas that had built up within their outer containment buildings after cooling system failure. Residents within a 20 km (12 mi) radius of the Fukushima I Nuclear Power Plant and a 10 km (6.2 mi) radius of the Fukushima II Nuclear Power Plant were evacuated. In addition, the U.S. recommended that its citizens evacuate up to 80 km (50 mi) of the plant.

The Japanese National Police Agency confirmed 15,845 deaths, 5,893 injured, and 3,380 people missing across eighteen prefectures, as well as over 125,000 buildings damaged or destroyed. The earthquake and tsunami caused extensive and severe structural damage in Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse. Japanese Prime Minister Naoto Kan said, "In the 65 years after the end of World War II, this is the toughest and the most difficult crisis for Japan." Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water.

Early estimates placed insured losses from the earthquake alone at US$14.5 to $34.6 billion. The Bank of Japan offered ¥15 trillion (US$183 billion) to the banking system on 14 March in an effort to normalize market conditions. The World Bank's estimated economic cost was US$235 billion, making it the most expensive natural disaster in world history."

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"The main earthquake struck at 16:58 GMT (04:58 local time) on November 4, 1952. Initially assigned a magnitude of 8.2, the quake was revised to 9.0 Mw in later years. A large tsunami resulted, causing destruction and loss of life around the Kamchatka peninsula and the Kuril Islands. Hawaii was also struck, with estimated damages of up to US$1 million and livestock losses, but no human casualties were recorded. Japan reported no casualties or damage. The tsunami reached as far as Alaska, Chile, and New Zealand.

The hypocentre was located at 52.75°N 159.5°E, at a depth of 30 km. The length of the subduction zone fracture was 600 km. Aftershocks were recorded in an area of approximately 247,000 km2, at depths of between 40 and 60 km. A recent analysis of the tsunami runup distribution based on historical and geological records give some indication as to the slip distribution of the rupture."

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