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2004 Indian Ocean earthquake and tsunami

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The 2004 Indian Ocean earthquake was a magnitude 9.0 undersea earthquake on December 26, 2004 which generated tsunamis that caused one of the deadliest natural disasters in modern history.

File:2004 Indonesia Tsunami (192px).gif
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.

This rare type of earthquake known as a megathrust earthquake struck at 00:58:53 UTC (07:58:53 local time) in the Indian Ocean off the western coast of northern Sumatra, Indonesia. It was the largest earthquake on Earth since the 9.2-magnitude Good Friday Earthquake off Alaska in 1964, and tied for fourth largest since the establishment of accurate global seismographic record keeping by 1900.

The tsunamis were the deadliest by far in all of recorded history. They devastated the shores of Indonesia, Sri Lanka, India, Thailand and other countries with waves of up to 15 m (50 feet) in height. Even the east coast of Africa (especially Somalia) was hit, despite being located 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.

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], the earthquake's magnitude was first reported as 8.1 by the U.S. Geological Survey, but after further analysis they increased this first to 8.5 and 8.9 and finally 9.0 [2].

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] 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]. (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.

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]. 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 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)

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 the Nicobar Islands were also reported, including ones of magnitude 7.1 [6], and 6.6 [7]. 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]. This would normally be unusual, since earthquakes of magnitude 8 or more typically occur only about once per year on average [9]. 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].

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].

Power of the earthquake

The total energy released by a magnitude 9.0 earthquake is equivalent to 32,000 megatons of TNT [12] 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]. 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], [15]. 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.

Tsunami characteristics

See larger version

The 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]

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] ). 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.

Failure to detect the tsunamis

Malé, the capital island of Maldives was severely hit by the tsunamis – here you can see onlookers not realising the intensity of the tsunamis

Despite the time lapse measured in hours, nearly all of the victims were taken completely by surprise.

This is partly because of the fact that a tsunami is not easy to detect while it is still travelling over deep ocean. In deep water, a tsunami has a very low height and is undetectable by the ordinary observer; aerial surveillance, satellite photos and ocean-going vessels will not notice it. It is only when the tsunami reaches shallow water (typically near a coastline) that its waves reach large heights. The very word "tsunami" means "harbour wave" in Japanese: fishermen would return from fishing in deep water to find harbours devastated by a wave that they themselves had not even noticed.

Only a warning system that monitors data from a network of automated sensors can detect a tsunami in deep water. No such warning system existed in the Indian Ocean due to the rarity of tsunamis in that ocean; the last major tsunami in the Indian Ocean was caused by the Krakatoa eruption of 1883.

Tsunamis usually occur along the Pacific Ocean coasts of the "Ring of Fire", and a warning system has been in place there since 1965. However, only the extreme western edge of the "Ring of Fire" lies within the Indian Ocean; nearly all of it is in the Pacific. Therefore tsunamis are rare in the Indian Ocean and a warning system there had not been a priority.

Even though scientists were well aware of the potential danger of a tsunami following any undersea earthquake, the lack of a tsunami monitoring system in the Indian Ocean meant that they had no way to know for sure that it had actually occurred or how strong it would be. They could only detect a lack of any danger to Pacific Ocean coasts, which were fully shielded behind large land masses and experienced only minor fluctuations in sea level as part of a global ripple effect. Scientists were also hampered by the fact that the initial estimate for the magnitude of the earthquake was 8.1 (this was a factor in the failure of Thai meteorologists to issue a warning [18]). The determination that the earthquake had actually been much stronger was not made until after the tsunamis had already struck.

Unfamiliarity with warning signs

In the minutes preceding a tsunami strike, the sea often recedes temporarily from the coast. People in Pacific regions are more familiar with tsunamis and often recognize this phenomenon as a sign to head for higher ground; however in the Indian Ocean region, this rare sight reportedly induced people, especially children, to visit the coast to investigate and collect fish stranded in as much as 2.5 km of exposed beachland, with fatal results.

However, on Maikhao beach in Thailand, a 10 year old British girl, Tilly Smith, recognised the signs when the tide rushed out and boats on the horizon began bobbing violently. She told her mother she had just been studying tsunami in geography at school and that they should leave the beach. Her parents warned others on the beach and so this was one of the few areas where no-one was reported killed or seriously injured [19]. One of the few populations that evacuated before the tsunami was that of the small Indonesian island of Simeulue, very close to the epicentre. Initial reports state that the residents were warned by island folklore recounting a devastating earthquake and tsunami in 1907 and fled en masse to inland hills after the initial shaking and before the tsunami struck. [20]

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.

Relief agencies report that one-third of the dead appear to be children. This is a result of the high proportion of children in the populations of many of the affected regions and the fact that children were the least able to resist being dragged by the surging waters. Coastal fishing communities and their fisherfolk, some of the poorest people in the region, have been the most devastated with high loss of life as well as boats and fishing gear.

In addition to the large number of local residents, up to 5,000 foreign tourists (mostly Europeans) enjoying the peak travel season were among the dead, especially Scandinavians [21]. The European nation hardest hit may have been Sweden [22].

States of emergency were declared in Sri Lanka, Indonesia and Maldives. The United Nations has declared that the current relief operation will be the costliest one ever. UN Secretary-General Kofi Annan has stated that reconstruction would probably take between five and ten years. Governments and NGOs fear the final death toll may double as a result of diseases, prompting a massive humanitarian response.

This is the most deadly and destructive tsunami in recorded history, the previous record being the 1703 tsunami at Awa, Japan that killed over 100,000 people ([23]) and one of the ten worst earthquakes ([24]).

For purposes of establishing timelines of local events, the time zones of affected areas are: UTC+3: (Kenya, Madagascar, Somalia, Tanzania); UTC+4: (Mauritius, Réunion, Seychelles); UTC+5: (Maldives); UTC+5:30: (India); UTC+6: (Bangladesh, Sri Lanka); UTC+6:30: (Cocos Islands, Myanmar); UTC+7: (Indonesia (western), Thailand); UTC+8: (Malaysia, Singapore). Since the quake occurred at 00:58:53 UTC, add the above offsets to find the local time of the quake. A list of times can be found at a USGS site.

Template:2004 Indian Ocean earthquake casualties

Countries affected

File:Sumatra devastation1.jpg
A village near the coast of Sumatra lies in ruin.

A description of the countries most affected by the earthquake and resulting tsunamis is below – for detailed information about each country see their individual articles. To make the article easier to read, the description of nations with a smaller number of casualties, as well as the account of nations that have lost citizens who were travelling abroad, are listed as other countries affected by the 2004 Indian Ocean earthquake.

Impact on Indonesia
Indonesia's Ministry of Health confirmed about 94,000 dead[25], mainly in the northern province Aceh of the island Sumatra, and have not finished counting. In addition, the Indonesian ambassador to Malaysia said that up to 400,000 may be dead in villages that "show no signs of life", though the accuracy of this claim is unknown ([26], [[27]).
Impact on India
The tsunami toll has risen to 14,872 dead or feared dead, the Home Ministry website said. The majority of them being in the state of Tamil Nadu. There are still about 7,000 people missing in the Andaman and Nicobar Islands. The estimated number of casualties in India is 16,000, split roughly equally between the Andaman and Nicobar Islands and the Indian mainland.
Impact on Malaysia
Despite its proximity to the incident, Malaysia escaped the kind of damage that struck countries thousands of miles further away. The number of deaths currently stands at 68 with 52 in Penang, 12 in Kedah, 3 in Perak and 1 in Selangor.
Impact on the Maldives
In the Maldives, 76 were killed and 32 reported missing, with both figures expected to rise as communication links are restored.
Impact on Myanmar
Independent media reports 90 people killed in Myanmar due to the tsunami.
Impact on Somalia
Villages and coastal communities in Somalia, as far as 4,500 km (2,800 mi) from the epicentre of the earthquake, were swept away and destroyed by the huge waves. One hundred seventy-six people were confirmed dead and more than 50,000 have been displaced.
Impact on Sri Lanka
Sri Lankan authorities report 46,229 confirmed deaths, mostly children and the elderly. The south and east coasts were worst hit. One and a half million people have been displaced from their homes.
Impact on Thailand
The Thai government reports 4,800 [28] confirmed deaths, 8,953 injuries [29] and 6,475 [30] missing.
Impact on other countries
A number of other countries were also affected either directly or indirectly by the earthquake. Countries such as Tanzania lost citizens as the tsunami struck its shores and other countries suffered significant property damage. Meanwhile, nations like Oman and Australia reported only non-deadly ocean swells. Citizens from countries from around the world have been killed, or remain missing, in the aftermath of the natural disaster. Many foreign tourists were visiting the famed beaches of Thailand and Sri Lanka during the Christmas vacation.
See also Impact on Norway.

Casualties in historical context

File:2004 indian ocean earthquake tectonic.jpg
Regional map showing physiographic features, tectonic plate movements, and locations of volcanoes, earthquakes, and impact craters (Credit: USGS)

The earthquake was the fourth most powerful recorded since 1900, and the estimates of the final death toll now range from 130,000 to over 150,000 due to the ensuing tsunami. The deadliest earthquakes since 1900 were the Tangshan, China earthquake of 1976, in which at least 255,000 were killed, the Tsinghai, China earthquake of 1927 (200,000), the Great Kanto earthquake which struck Tokyo in 1923 (143,000), and the Gansu, China earthquake of 1920 (200,000). The deadliest known earthquake in history occurred in 1556 in Shaanxi, China, with an estimated death toll of 830,000, though figures from this time period may not be reliable [31].

This 2004 tsunami appears to be the most deadly tsunami in recorded history. The most deadly tsunami in history prior to 2004 was the result of an earthquake near Awa, Japan in 1703 that killed 100,000. Forty-thousand people were killed in 1782 by a tsunami in the South China Sea, and the tsunami created by the 1883 eruption of Krakatoa is thought to have resulted in 36,000 deaths. The most deadly tsunami between 1900 and 2004 occurred in Messina, Italy on the Mediterranean Sea where the earthquake and tsunami killed 70,000 in 1908. The most deadly tsunami in the Atlantic Ocean resulted from the 1755 Lisbon earthquake that, combined with the toll from the actual earthquake and resulting fires, killed over 100,000.

This 2004 tsunami seems to be the worst natural disaster since the Bhola cyclone (Bangladesh), which is estimated to have killed 500,000.


Early warning systems

Relative size of a 10 m (33 ft) wave

See also: Tsunami - Warning systems

The death toll of the 2004 Indian Ocean earthquake was particularly high due to the lack of an early warning system for tsunamis comparable to the one that has existed for the Pacific Ocean since 1965. The latter [32] was put into place in the aftermath of tsunamis resulting from the magnitude 9.2 Good Friday Earthquake of 1964.

The first reaction of many to the disaster has been to question governmental priorities in not having constructed such a system, but as the region had not seen a large tsunami since the Krakatoa eruption of 1883, it was not previously felt justified.

The US Geological Survey has stated that if a monitoring and warning system had been in place, the loss of life could have been reduced, especially in areas that were struck by tsunamis a couple of hours after the initial tremor, such as Sri Lanka and India and Thailand.

In the aftermath of the earthquake, there has been a flurry of proposals to extend the tsunami warning system to the Indian Ocean, and it seems likely that this will happen. India has already announced that it will do so [33], and Malaysia has proposed the same [34]. Thailand is also expected to join; it is already a member of the Pacific tsunami warning system, but all of its ocean buoys, which relay information from wave sensors on the ocean floor, are on the east (Pacific) coast of the country.

Some have even proposed creating a global tsunami warning system that would cover the Atlantic Ocean and Caribbean as well.

Post-tsunami humanitarian situation

Indonesian refugees gather under an approaching helicopter to receive food and supplies.

Main article: Humanitarian response to the 2004 Indian Ocean earthquake

A great deal of humanitarian aid is needed due to widespread damage to infrastructure, food and water shortages, and economic damage. World Health Organization crisis chief David Nabarro stated that the baseline for past crises suggests that a a further 50,000 deaths from diseases and other causes would not be exceptional ([35]). Epidemics are of special concern, as they are highly likely due to the high population density and tropical climate of the affected areas. The United Nations has stated that the largest relief operation in history is underway. The overwhelming concern of humanitarian and government agencies is to provide fresh drinking water to contain the spread of diseases such as cholera, diphtheria, dysentery and typhoid. Nations all over the world have so far provided over 2 billion U.S. dollars in aid for damaged regions, with the Japan government offering the most at $500 million, the Australian federal government pledging $US 450 million, the United States government offering $350 million, the World Bank offering $250 million, UK government and public offering $140 million, Swedish government and public offering $125 million and Norwegian government and public offering $60 million (the Norwegian government is expected to offer an additional amount of at least $160 million). Officials estimate that billions of dollars will be needed.

Some economists advanced the view that damage to the affected countries' economies will be minor because tourism and fishing make up only a small part of their overall economies. However, other economists state that damage to infrastructure is more of a factor than the percentage of GDP of those industries directly affected. (New York Times January 3 2005)

Significant effort is being spent in burying bodies hurriedly, explicitly to prevent the spread of disease. However, the public health threat of unburied trauma victims is not as great as that of those who die of infectious disease; the World Health Organization (WHO) characterises it as "negligible" in comparison. Furthermore, improperly buried corpses may contaminate underground water supplies. Many argue that the limited resources available should be focused on the survival and health needs of the living. On the other hand, religious and cultural practices, the aesthetic distaste of unburied bodies, and the negative impact on morale of leaving the dead unattended to, continue to motivate for prompt burial.

See also

Wikinews

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- Database by SEA-EAT bloggers giving details about persons missing/found, aid efforts and ways to donate

Ongoing news collections

Scientific reports

Tsunami Videos

Photos

Forums and discussion

Sites to help family and friends locate missing loved ones are listed on the "Links to search for missing people" section of the "Other countries affected by the 2004 Indian Ocean earthquake" page.

Blogs

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