2004 Indian Ocean earthquake

The 2004 Indian Ocean earthquake, known by the scientific community as the Sumatra-Andaman earthquake, was an undersea earthquake that occurred at 00:58:53 UTC (07:58:53 local time) on December 26 2004. The tsunami generated by the earthquake killed approximately 275,000 people, making it one of the deadliest disasters in modern history. The disaster is also known as the Boxing Day Tsunami.

Quake characteristics

The earthquake was initially reported as 8.6 on the Richter scale. The Pacific Tsunami Warning Center (PTWC) also estimated it at 8.5 shortly after the earthquake. On the moment magnitude scale, which is more accurate for quakes of this size, the earthquake's magnitude was first reported as 8.1 by the U.S. Geological Survey. After further analysis, this was increased to 8.5, 8.9, and 9.0 (USGS, 2004, http://earthquake.usgs.gov/recenteqsww/Quakes/usslav.htm). In February 2005, some scientists revised the estimate of magnitude to 9.3. Although the Pacific Tsunami Warning Center has accepted this, the USGS has so far not changed its estimate of 9.0 (McKee, 9 Feb 2005, http://www.newscientist.com/article.ns?id=dn6991). The most definitive estimate so far has put the magnitude at 9.15 http://www.sciencemag.org/cgi/content/summary/308/5725/1125.

Related Topics:
Richter scale - Pacific Tsunami Warning Center - Moment magnitude scale - U.S. Geological Survey - February 2005

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The hypocentre of the main earthquake was at 3.316°N, 95.854°E (3° 19′ N, 95° 51.24′ E), some 160 km (100 miles) west of Sumatra, at a depth of 30 km (18.6 miles) below mean sea level (initially reported as 10 km). This is at the extreme western end of the Ring of Fire, an earthquake belt that accounts for 81 percent of the world's largest earthquakes (USGS FAQ, http://earthquake.usgs.gov/faq/hist.html#1). The earthquake itself (apart from the tsunami) was felt as far away as Bangladesh, India, Malaysia, Myanmar, Thailand, Singapore and the Maldives.

Related Topics:
Hypocentre - 160 km - 30 km - Mean sea level - Ring of Fire - Bangladesh - India - Malaysia - Myanmar - Thailand - Singapore - Maldives

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Since 1900 the only earthquakes recorded with a greater magnitude were the 1960 Great Chilean Earthquake (magnitude 9.5), the 1964 Good Friday Earthquake in Prince William Sound (9.2), and the March 9 1957 earthquake http://neic.usgs.gov/neis/eq_depot/usa/1957_03_09.html in the Andreanof Islands (9.1). The only other recorded earthquake of magnitude 9.0 was in 1952 off the southeast coast of Kamchatka http://neic.usgs.gov/neis/eq_depot/world/1952_11_04.html (see Top 10 earthquakes). Each of these megathrust earthquakes also spawned tsunamis (in the Pacific Ocean), but the death toll from these was significantly lower; a few thousand for the worst one, probably because of the lower population density along the coasts near affected areas and the much greater distances to more populated coasts.

Related Topics:
1900 - 1960 - Great Chilean Earthquake - 1964 - Good Friday Earthquake - Prince William Sound - March 9 - 1957 - Andreanof Islands - 1952 - Kamchatka - Megathrust earthquake - Population density

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Other large megathrust earthquakes occurred in 1868 (Peru, Nazca Plate and South American Plate); 1827 (Colombia, Nazca Plate and South American Plate); 1812 (Venezuela, Caribbean Plate and South American Plate) and 1700 (Cascadia Earthquake, western US and Canada, Juan de Fuca Plate and North American Plate). These are all believed to have been of greater than magnitude 9, but no accurate measurements were available in those days.

Related Topics:
1868 - Peru - Nazca Plate - South American Plate - 1827 - Colombia - 1812 - Venezuela - Caribbean Plate - 1700 - Cascadia Earthquake - Canada - Juan de Fuca Plate - North American Plate

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Tectonic plates

The earthquake was unusually large in geographical extent. An estimated 1200 km (750 miles) of faultline slipped about 15 m (50 ft) along the subduction zone where the India Plate dives under the Burma Plate. The slip did not happen instantaneously but took place in two phases over a period of several minutes. Seismographic and acoustic data indicate that the first phase involved the formation of a rupture about 400 km (250 miles) long and 100 km (60 miles) wide, located 30 km (19 miles) beneath the sea bed - the longest known rupture ever known to have been caused by an earthquake. The rupture proceeded at a speed of about 2.8 km/s (1.7 miles/s) or 10,000 km/h (6,300 miles/h), beginning off the coast of Aceh and proceeding north-westerly over a period of about 100 seconds. A pause of about another 100 seconds took place before the rupture continued northwards towards the Andaman and Nicobar Islands. However, the northern rupture occurred more slowly than in the south, at about 2.1 km/s (1.3 miles/s), continuing north for another five minutes to a plate boundary where the fault changes from subduction to strike-slip (the two plates push past one another in opposite directions) thus reducing the speed of the water displacement and so reducing the size of the tsunami that hit the northern part of the Indian Ocean http://www.ldeo.columbia.edu/news/2005/07_20_05.htm.

Related Topics:
1200 km - Faultline - 15 m - Subduction zone - India Plate - Burma Plate - Aceh

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The India Plate is part of the great Indo-Australian Plate, which underlies the Indian Ocean and Bay of Bengal, and is drifting northeast at an average of 6 cm/year (2 inches/year). The India Plate meets the Australasian Plate (which is considered a portion of the great Eurasian Plate) at the Sunda Trench. At this point the India Plate subducts the Burma Plate, which carries the Nicobar Islands, the Andaman Islands and northern Sumatra. The India Plate slips deeper and deeper beneath the Burma Plate until the increasing temperature and pressure drive volatiles out of the subducting plate. These volatiles rise into the mantle above and trigger melt which exits the earth's mantle through volcanoes (see Volcanic arc). The volcanic activity that results as the Indo-Australian plate subducts the Eurasian plate has created the Sunda Arc.

Related Topics:
Indo-Australian Plate - Indian Ocean - Bay of Bengal - Eurasian Plate - Sunda Trench - Nicobar Islands - Andaman Islands - Sumatra - Volcanic arc - Sunda Arc

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As well as the sideways movement between the plates, the sea bed is estimated to have risen by several metres, displacing an estimated 30 km³ of water and triggering devastating tsunami waves. The waves did not originate from a point source, as mistakenly depicted in some illustrations of their spread, but radiated outwards along the entire 1200 km (750 miles) length of the rupture. This greatly increased the geographical area over which the waves were observed, reaching as far as Mexico, Chile and the Arctic. The raising of the sea bed significantly reduced the capacity of the Indian Ocean, producing a permanent rise in the global sea level by an estimated 0.1 mm. http://www.sciencemag.org/cgi/content/full/sci;308/5725/1126

Related Topics:
Tsunami - Mexico - Chile - Arctic

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Aftershocks and other earthquakes

Numerous aftershocks were reported off the Andaman Islands, the Nicobar Islands and the region of the original epicentre in the hours and days that followed. The largest aftershock was 8.7 epicentred off the Sumatran island of Nias http://www.investors.com/breakingnews.asp?journalid=26681113&brk=1. Other aftershocks of up to magnitude 6.6 continue to shake the region on a daily basis http://wwwneic.cr.usgs.gov/neis/bulletin/ http://earthquake.usgs.gov/recenteqsww/Maps/10/95_5.html.

Related Topics:
Aftershock - Andaman Islands - Nicobar Islands - Nias

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The 2004 Indian Ocean earthquake came just three days after a magnitude 8.1 earthquake in an uninhabited region west of New Zealand's sub-Antarctic Auckland Islands, and north of Australia's Macquarie Island http://earthquake.usgs.gov/recenteqsww/Quakes/ussjal.htm. This is unusual, since earthquakes of magnitude 8 or more occur only about once per year on average http://earthquake.usgs.gov/faq/hist.html#8. Some seismologists have speculated about a connection between these two earthquakes, saying that the former one might have been a catalyst to the Indian Ocean earthquake, as the two quakes happened on opposite sides of the Indo-Australian Plate http://www.news.com.au/common/story_page/0,4057,11787870%255E28477,00.html (a 6.5 earthquake occurred on 19 February 2005 off Sulawesi at the other end of the Indonesian island chain). However the US Geological Survey sees no evidence of a causal relationship http://earthquake.usgs.gov/eqinthenews/2004/usslav/neic_slav_faq.html.

Related Topics:
Sub-Antarctic - Auckland Islands - Macquarie Island - Indo-Australian Plate - 19 February - Sulawesi - US Geological Survey

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Coincidentally the earthquake struck almost exactly one year (to the hour) after a magnitude 6.6 earthquake killed an estimated 30,000 people in the city of Bam in Iran http://earthquake.usgs.gov/recenteqsww/Quakes/uscvad.htm.

Related Topics:
Bam - Iran

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As well as continuing aftershocks, the energy released by the original earthquake continued to make its presence felt well after the event. A week after the earthquake, its reverberations could still be measured, providing valuable scientific data about the Earth's interior http://www.reuters.co.uk/newsArticle.jhtml?type=topNews&storyID=650823.

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An earthquake of magnitude 8.7 was reported shortly at 16:09:37 UTC (23:09:37 local time) on March 28 2005 approximately at the same location (see 2005 Sumatran earthquake). It is likely a very large aftershock of the original earthquake. This earthquake had strong aftershocks of its own, including magnitude 6.0 and 6.1 quakes. At 8.7, it ranks as the 7th largest earthquake since 1900.

Related Topics:
UTC - March 28 - 2005 - 2005 Sumatran earthquake

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An earthquake magnitude 6.7 struck on 10 April at 1729 local time (1029 GMT) about 120km (75 miles) south-west of the city of Padang. See BBC News: Sumatra shaken by new earthquake - also see Wikinews

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Some scientists warn that geological stresses caused by the recent quakes may even have increased the possibility that the Lake Toba supervolcano could erupt. http://www.news.com.au/story/0,10117,12716344-2,00.html According to the Toba catastrophe theory, this could threaten human life on Earth.

Related Topics:
Lake Toba - Supervolcano - Toba catastrophe theory

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Some scientists confirm that the December quake had activated Leuser Mountain, a volcano in Aceh province along the same range of peaks as Talang, while the 2005 Sumatran earthquake) had sparked activity in lake Toba, an ancient crater in Sumatra. http://www.hindustantimes.com/news/181_1317370,00050004.htm

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Coincidentally, Mount Talang has since eruptedhttp://abcnews.go.com/Technology/wireStory?id=661767 and is now on top alert.

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Power of the earthquake

The total energy released by the earthquake in the Indian Ocean has been estimated as 4.3 exajoules (4.3×1018 joules) http://www.sciencemag.org/cgi/content/full/sci;308/5725/1126. This is equivalent to 100 gigatons of TNT, or about as much energy as is used in the United States in 6 months. It is estimated to have resulted in an oscillation of the Earth's surface of about 20-30 cm (8 to 12 inches), equivalent to the effect of the tidal forces caused by the Sun and Moon http://www.reuters.co.uk/newsArticle.jhtml?type=topNews&storyID=650823. The shock waves of the earthquake were felt across the planet; as far away as Oklahoma, vertical movements of 3 mm (0.12 inches) were recorded http://www.muskogeephoenix.com/news/stories/20041228/localnews/1795857.html. The entire Earth's surface is estimated to have moved vertically by up to 1 cm.

Related Topics:
4.3 exajoules - Joules - Gigatons of TNT - Tidal forces - Sun - Moon - Oklahoma

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The shift of mass and the massive release of energy very slightly altered the Earth's rotation. The exact amount is yet undetermined, but theoretical models suggest the earthquake shortened the length of a day by 2.68 microseconds (2.68 µs) (or about one billionth of the length of a day) http://www.nasa.gov/home/hqnews/2005/jan/HQ_05011_earthquake.html due to a decrease in the oblateness of the Earth. It also caused the Earth to minutely "wobble" on its axis by up to 2.5 cm (1 inch) in the direction of 145° east longitude http://slate.msn.com/id/2111443/, http://www.cnn.com/2004/TECH/science/12/29/quake.wobble.reut/index.html or perhaps by up to 5 or 6 cm (2.0 to 2.4 inches) http://news.xinhuanet.com/english/2004-12/29/content_2389519.htm. However, due to tidal effects of the Moon, the length of a day increases at an average of 15 µs per year, so any rotational change due to the earthquake will be lost quickly. Similarly, the natural Chandler wobble of the Earth can be up to 15 m (50 ft).

Related Topics:
Microsecond - Oblate - Longitude - Moon - Chandler wobble - M

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More spectacularly, there was 10 m (33 feet) movement laterally and 4 to 5 m (13 to 16 feet) vertically along the fault line. Early speculation was that some of the smaller islands southwest of Sumatra may have moved southwest by up to 20 m (66 feet). There were also calculations that the northern tip of Sumatra, which is on the Burma Plate (the southern regions are on the Sunda Plate), may have moved up to 36 m (118 ft) southwest. Since movement was vertical as well as lateral, some coastal areas may now be below sea level. Measurements using GPS and satellite imagery are being used to determine the extent and nature of actual geophysical change http://www.timesleader.com/mld/timesleader/10574872.htm. The Andaman and Nicobar Islands appear to have shifted southwest http://www.seires.net/content/view/122/52/ by around 4 m, according to GPS data.

Related Topics:
Sumatra - Burma Plate - Sunda Plate - GPS - Satellite imagery

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In February 2005, the Royal Navy vessel HMS Scott surveyed the sea bed around the earthquake zone, which varies in depth between 1,000 m (3,300 feet) and 5,000 m (16,500 feet) west of Sumatra. The survey, conducted using a high-resolution multi-beam sonar system, revealed that the earthquake had had a huge impact on the topography of the sea bed. It had created large thrust ridges, about 1,500 m high, which have collapsed in places to produce large landslides several kilometres across. One landslide consisted of a single block of material some 100 m (300 feet) high and 2 km (1.25 miles) long. The force of the displaced water was such that individual blocks of rock, massing millions of tons apiece, were dragged as much as 10 km (7 miles) across the sea bed. An newly-formed oceanic trench several kilometres wide was also found in the earthquake zone http://www.newscientist.com/article.ns?id=dn6994.

Related Topics:
Royal Navy - HMS ''Scott'' - Sonar - Landslides - Oceanic trench

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By a beneficial and remarkable coincidence, satellites TOPEX/Poseidon and Jason 1 happened to pass over the tsunami as it was crossing the ocean http://topex-www.jpl.nasa.gov/newsroom/press-releases/20050111.html. These satellites carry radars that measure precisely the height of the water surface; anomalies of the order of 50 cm (20 inches) were measured. Measurements from these satellites may prove invaluable for the understanding of the earthquake and tsunami http://www.aviso.oceanobs.com/html/applications/geophysique/tsunami_uk.html. Unlike data from tide gauges installed on shores, measurements obtained in the middle of the ocean can be used for computing the parameters of the source earthquake without having to compensate for complex effects close to the coast. Inversion of this height data may help adjust the parameters for the source earthquake.

Related Topics:
TOPEX/Poseidon - Jason 1 - Radar - Tide gauge

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