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The undersea 2004 Indian Ocean earthquake that occurred on December 26, 2004 produced tsunamis that were among the deadliest natural disasters in modern history. The tsunamis devastated the shores of Indonesia, Sri Lanka, India, Thailand, and other countries with waves of up to 15 m (50 feet) in height, even hitting as far as the east coast of Africa, especially Somalia, 4,500 km (2,800 miles) or more west of the epicenter. The plight of the many affected people and countries prompted a widespread humanitarian response.
This rare megathrust earthquake took place at 00:58:53 UTC (07:58:53 local time) in the Indian Ocean off the western coast of northern Sumatra, Indonesia. At a magnitude of 9.0, it was the largest since the 9.2-magnitude Good Friday Earthquake off Alaska in 1964, and it tied for fourth largest since 1900, when accurate global seismographic record-keeping began.
Animation of the tsunami caused by the earthquake. (See also the full-length version)
Note: tsunamis have very low height while travelling over deep ocean, and ocean-going vessels in their path will usually not even notice them; high waves only occur when shallow water is reached, typically near coastlines.
Contents [showhide]
1 Quake characteristics
1.1 Aftershocks and other earthquakes
1.2 Power of the earthquake
2 Tsunami characteristics
3 Damage and casualties
3.1 Countries affected
3.2 Casualties in historical context
4 Signs and warnings
4.1 Failure to detect the tsunamis
4.2 Unfamiliarity with warning signs
5 Post-tsunami humanitarian situation
6 See also
7 External links
7.1 Wikinews
7.2 Ongoing news collections
7.3 Scientific reports
7.4 Tsunami Videos
7.5 Photos
7.6 Forums and discussion
7.7 Further reading
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Quake characteristics
Locations of the initial earthquake and aftershocks.The earthquake was initially reported as 6.8 on the Richter scale. On the moment magnitude scale, which is more accurate for quakes of this size [1] (http://earthquake.usgs.gov/faq/meas.html), the earthquake's magnitude was first reported as 8.1 by the U.S. Geological Survey, but after further analysis the USGS increased this first to 8.5, 8.9, and finally to 9.0 [2] (http://earthquake.usgs.gov/recenteqsww/Quakes/usslav.htm).
Since 1900, the only earthquakes recorded with a greater magnitude were the 1960 Great Chilean Earthquake (magnitude 9.5) and two Alaskan quakes: the 1964 Good Friday Earthquake in Prince William Sound (9.2) and a March 9, 1957 quake [3] (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 [4] (http://neic.usgs.gov/neis/eq_depot/world/1952_11_04.html). (See Top 10 earthquakes (http://neic.usgs.gov/neis/eqlists/10maps_world.html)). 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.
The hypocentre was at 3.316°N, 95.855°E, some 160 km (100 mi) west of Sumatra, at a depth of 30 km (18.6 mi) 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% of the world's largest earthquakes [5] (http://earthquake.usgs.gov/faq/hist.html#1). The quake itself (apart from the tsunamis) was felt as far away as Bangladesh, India, Malaysia, Myanmar, Singapore, Thailand and the Maldives.
The earthquake was unusually large in geographical extent. An estimated 1,200 km (750 mi) of faultline slipped 20 m (60 ft) along the subduction zone where the India Plate dives under the Burma Plate. The seabed of the Burma plate is estimated to have risen several metres vertically up over the India plate, creating shock waves in the Indian Ocean that traveled at up to 800 km/h (500 mi/h), forming tsunamis which, while less than a metre high in deep water, resulted in huge waves when they reached land.
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/yr (2 in/yr) (or 20 m (60 ft) per 330 years; i.e. this earthquake moved this fault 330 years worth). The India Plate meets the Burma 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 includes 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 turns the subducting edge of the India Plate into magma which eventually pushes the magma above it out through the volcanoes (see Volcanic arc). This process is interrupted by the locking of the plates for several centuries until the build up of stress causes their release resulting in a massive earthquake and tsunami. The volcanic activity that results as the Indo-Australian plate subducts the Eurasian plate has created the Sunda Arc.
Tectonic plates at epicentre (Credit: USGS)[edit]
Aftershocks and other earthquakes
Numerous aftershocks of magnitude between 5.7 and 6.3 were reported off the Andaman Islands in the hours and days that followed. Aftershocks off Nicobar Islands were also reported, including ones of magnitude 7.1 [6] (http://earthquake.usgs.gov/recenteqsww/Quakes/ussmax.htm), and 6.6 [7] (http://earthquake.usgs.gov/recenteqsww/Quakes/ussmbj.htm). Other aftershocks between magnitude 5.0 and 6.5 occurred near the location of the original quake.
The earthquake came just three days after a magnitude 8.1 earthquake in a completely uninhabited region west of New Zealand's sub-Antarctic Auckland Islands, and north of Australia's Macquarie Island [8] (http://earthquake.usgs.gov/recenteqsww/Quakes/ussjal.htm). This would normally be unusual, since earthquakes of magnitude 8 or more typically occur only about once per year on average [9] (http://earthquake.usgs.gov/faq/hist.html#8). Seismologists have speculated about a possible 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 tectonic plate [10] (http://www.news.com.au/common/story_page/0,4057,11787870%255E28477,00.html).
Coincidentally, the earthquake struck almost exactly one year (within an hour) after a magnitude 6.6 earthquake killed an estimated 30,000 people in the city of Bam in Iran [11] (http://earthquake.usgs.gov/recenteqsww/Quakes/uscvad.htm).
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Power of the earthquake
The total energy released by a magnitude 9.0 earthquake is equivalent to 32,000 megatons of TNT [12] (http://earthquake.usgs.gov/faq/meas.html#19) or 133 exajoules (1.33×1020 joules). This exceeds the total amount of energy consumed in the United States in one year by 30%, or the energy released by the wind of a hurricane like Hurricane Isabel over a period of 70 days [13] (http://www.sciencedaily.com/releases/2003/10/031031062553.htm). Using the mass-energy equivalence formula E = mc2, this amount of energy is equivalent to a mass of about 1500 kg (3300 lb). Equivalently, this amount of energy is enough to boil 10,000 litres (2,600 US gallons) of water for every person on Earth. Note that each unit of the magnitude scale represents a 31.6-fold increase in energy; every two units signifies 1,000 times more energy.
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 may have shortened the length of a day by as much as three microseconds (3 µs) and caused the Earth to minutely "wobble" on its axis by up to 2.5 cm (1 inch) [14] (http://slate.msn.com/id/2111443/), [15] (http://www.cnn.com/2004/TECH/science/12/29/quake.wobble.reut/index.html). However, due to tidal effects of the Moon, the length of a day increases by 15 µs every year, so any rotational speedup due to the earthquake will be quickly lost. Similarly, the natural Chandler wobble of the Earth can be up to 15 m (50 ft).
Based on one seismic model, some of the smaller islands southwest of Sumatra may have moved southwest up to 20 m (66 ft). The northern tip of Sumatra, which is on the Burma Plate (the southern regions are on the Sunda Plate), may also have moved southwest up to 36 m (118 ft). However, other models suggest that most of the movement would have been vertical rather than lateral. Onsite measurements using GPS will be used to determine the extent and nature of actual geophysical movement.
[edit]
Tsunami characteristics
See larger versionThe earthquake triggered massive tsunamis that struck the coasts of the Indian Ocean, the deadliest tsunamis by far in all of recorded history.
According to Tad Murty, vice-president of the Tsunami Society, the total energy of the tsunami waves was about five megatons of TNT. This is more than twice the total explosive energy used during all of World War II (including the two atomic bombs), but still almost four orders of magnitude less than the energy released in the earthquake itself [16] (http://www.canada.com/montreal/montrealgazette/news/story.html?id=2257b78c-3897-4594-ad86-18c0eb661bea).
See a full-length animation of how the waves travelled — large file (about 1 MB) — to see exactly how and why some countries were more affected than others
Because the 1,200 km of faultline affected by the quake was in a nearly north-south orientation, the greatest strength of the tsunami waves was in an east-west direction. Bangladesh, which lies at the northern end of the Bay of Bengal, had very few casualties despite being a low-lying country regularly devastated by cyclones.
Coasts that have a land mass between them and the tsunami's location of origin are usually safe; however, tsunami waves can sometimes diffract around such land masses. Thus, the Indian state of Kerala was hit by tsunamis despite being on the western coast of India. Also, distance alone is no guarantee of safety: Somalia was hit harder than Bangladesh despite being much farther away.
Due to the distances involved, the tsunamis took anywhere from fifteen minutes to seven hours (for Somalia) to reach the various coastlines (see travel time maps: [17] (http://tsun.sscc.ru/tsulab/20041226trt.htm) ). The hardest hit areas of Indonesia were hit very quickly; on the other hand Sri Lanka and the east coast of India were hit roughly two hours later. Thailand also took about two hours to be hit, despite its closer distance, because the tsunami travelled more slowly in the shallow seas off its western coast.
[edit]
Damage and casualties
Countries most directly affected by the 2004 Indian Ocean earthquake.The death toll from the earthquake, the tsunamis and the resultant floods was reported to be more than 150,000, with tens of thousands of people reported missing, and over a million left homeless. Early news reports about eight hours after the earthquake spoke of a toll only in the "hundreds", but the numbers rose steadily over the following week.