The 2004 Indian Ocean earthquake was an undersea megathrust earthquake that occurred at 00:58:53 UTC on 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, 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 high. and triggered other earthquakes as far away as Alaska.The plight of the many affected people and countries prompted a widespread humanitarian response. In all, the worldwide community donated more than $7 billion (2004 U.S. dollars) in humanitarian aid. The hypocenter occurred between Simeulue and mainland Indonesia.
Earthquake characteristics
The earthquake was initially reported as moment magnitude 9.0. In February 2005 scientists revised the estimate of the magnitude to 9.3. Although the Pacific Tsunami Warning Center has accepted these new numbers, the United States Geological Survey has so far not changed its estimate of 9.1. The most recent studies in 2006 have obtained a magnitude of Mw 9.19.3. Dr. Hiroo Kanamori of the California Institute of Technology believes that Mw 9.2 is a good representative value for the size of this great earthquake.The hypocentre of the main earthquake was approximately 160 km (100 mi), in the Indian Ocean just north of Simeulue island, off the western coast of northern Sumatra, at a depth of 30 km (19 mi) below mean sea level (initially reported as 10 km). The northern section of the Sunda megathrust, which had been assumed dormant, ruptured; the rupture having a length of 1600 km. Splay faults or secondary "pop up faults" caused long narrow parts of the sea floor to pop up in seconds elevating the height and increased the speed of waves to cause the complete destruction of the nearby Indonesian town of Lhoknga.The ." United States Geological Survey. Each of these megathrust earthquakes also spawned tsunamis in the Pacific Ocean, but the death toll from these was significantly lower. The worst of these caused only a few thousand deaths, primarily because of the lower population density along the coasts near affected areas and the much greater distances to more populated coasts.Other very 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 (western North America, Juan de Fuca Plate and North American Plate). All of them are believed to be greater than magnitude 9, but no accurate measurements were available at the time.Tectonic plates
A The megathrust earthquake was unusually large in geographical and geological extent. An estimated 1,600 km (994 mi) of fault surface slipped (or ruptured) about 15 m (50 ft) along the subduction zone where the India Plate slides (or subducts) under the overriding 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 a rupture about 400 km (250 mi) long and 100 km (60 mi) wide, located 30 km (19 mi) beneath the sea bedthe largest rupture ever known to have been caused by an earthquake. The rupture proceeded at a speed of about 2.8 km/s (1.7 mi/s) or 10,000 km/h (6,300 mph), 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 mi/s) or 7,600 km/h (4,700 mph), continuing north for another five minutes to a plate boundary where the fault type changes from subduction to strike-slip (the two plates slide past one another in opposite directions). This reduced the speed of the water displacement and so reducing the size of the tsunami that hit the northern part of the Indian Ocean.
Aftershocks and other earthquakes
Locations of initial earthquake and all aftershocks measuring greater than 4.0 from December 26, 2004 to January 10, 2005. The site of the original quake is marked by the large star in the lower right square of the grid.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, which originated off the coast of the Sumatran island of Nias, registered a magnitude of 8.7, prompting debate among seismologists as to whether it should be classified as an aftershock of the December 2004 quake or as a "triggered earthquake" (which typically differs from an aftershock in that it is not located along the same fault line and may be as large or larger than the earthquake which triggered it). This earthquake was so large that it produced its own aftershocks (some registering a magnitude of as great as 6.1) and presently ranks as the 7th largest earthquake on record since 1900. Other aftershocks of up to magnitude 6.6 continued to shake the region daily for up to three or four months. 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.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. This is unusual, since earthquakes of magnitude 8 or more occur only about once per year on average. 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 earthquakes happened on opposite sides of the Indo-Australian Plate. However, the U.S. Geological Survey sees no evidence of a causal relationship in this incident. Coincidentally, the earthquake struck almost exactly one year (to the hour) after a 6.6 magnitude earthquake killed an estimated 30,000 people in the city of Bam in Iran on December 26, 2003.Some scientists confirm that the December earthquake had activated Leuser Mountain, a volcano in Aceh province along the same range of peaks as Mount Talang, while the 2005 Sumatran earthquake had sparked activity in Lake Toba, an ancient crater in Sumatra. Geologists say that the eruption of Mount Talang in April 2005 is connected to the December earthquake.Energy released
The energy released on the Earth's surface only (ME, which is the seismic potential for damage) by the 2004 Indian Ocean earthquake and tsunami was estimated at 1.1×1017 joules, or 26.3 megatons of TNT. This energy is equivalent to over 1502 times that of the Hiroshima atomic bomb, but less than that of Tsar Bomba, the largest nuclear weapon ever detonated. However, this is but a tiny fraction of the total work done MW (and thus energy) by this quake, 4.0×1022 joules (4.0×1029 ergs), the vast majority underground. This equates to 4.0×1022 J, over 363,000 times more than its ME. This is a truly enormous figure, equivalent to 9,560 gigatons of TNT equivalent (550 million times that of Hiroshima), or about 370 years of energy use in the United States at 2005 levels of 1.08×1020 J.The only recorded earthquakes with a larger MW were the 1960 Chilean and 1964 Alaskan quakes, with 2.5×1023 joules (250 ZJ) and 7.5×1022 joules (75 ZJ) respectively.The earthquake generated a seismic oscillation of the Earth's surface of up to 2030 cm (812 in), equivalent to the effect of the tidal forces caused by the Sun and Moon. The shock waves of the earthquake were felt across the planet; as far away as the U.S. state of Oklahoma, where vertical movements of 3 mm (0.12 in) were recorded. By February 2005, the earthquake's effects were still detectable as a 0.02 mm complex harmonic oscillation of the Earth's surface, which gradually diminished and merged with the incessant free oscillation of the Earth more than 4 months after the earthquake.Because of its enormous energy release and shallow rupture depth, the earthquake generated remarkable seismic ground motions around the globe, particularly due to huge Rayleigh elastic waves that exceeded 1 cm in vertical amplitude everywhere on Earth. The record section plot below displays vertical displacements of the Earth's surface recorded by seismometers from the IRIS/USGS Global Seismographic Network plotted with respect to time (since the earthquake initiation) on the horizontal axis, and vertical displacements of the Earth on the vertical axis (note the 1 cm scale bar at the bottom for scale). The seismograms are arranged vertically by distance from the epicenter in degrees. The earliest, lower amplitude, signal is that of the compressional (P) wave, which takes about 22 minutes to reach the other side of the planet (the antipode; in this case near Ecuador). The largest amplitude signals are seismic surface waves that reach the antipode after about 100 minutes. The surface waves can be clearly seen to reinforce near the antipode (with the closest seismic stations in Ecuador), and to subsequently encircle the planet to return to the epicentral region after about 200 minutes. A major aftershock (magnitude 7.1) can be seen at the closest stations starting just after the 200 minute mark. This aftershock would be considered a major earthquake under ordinary circumstances, but is dwarfed by the mainshock.Vertical-component ground motions recorded by the IRIS/USGS Global Seismographic Network.The shift of mass and the massive release of energy very slightly altered the Earth's rotation. The exact amount is not yet known, but theoretical models suggest the earthquake shortened the length of a day by 2.68 microseconds, due to a decrease in the oblate of the Earth. It also caused the Earth to minutely "wobble" on its axis by up to 2.5 cm (1 in) in the direction of 145° east longitude, or perhaps by up to 5 or 6 cm (2.0 to 2.4 in). However, because of 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, which in some cases can be up to 15 m (50 ft), will eventually offset the minor wobble produced by the earthquake.More spectacularly, there was 10 m (33 ft) movement laterally and 45 m (1316 ft) vertically along the fault line. Early speculation was that some of the smaller islands south-west of Sumatra, which is on the Burma Plate (the southern regions are on the Sunda Plate), might have moved south-west by up to 36 m (118 ft), but more accurate data released more than a month after the earthquake found the movement to be about 20 cm (7.9 in). Since movement was vertical as well as lateral, some coastal areas may have been moved to below sea level. The Andaman and Nicobar Islands appear to have shifted south-west by around 1.25 m (4.1 ft) and to have sunk by 1 m (3.28 ft).In February 2005, the Royal Navy vessel HMS Scott surveyed the seabed around the earthquake zone, which varies in depth between 1,000 m and 5,000 m (3,300 ft and 16,500 ft). The survey, conducted using a high-resolution, multi-beam sonar system, revealed that the earthquake had made a huge impact on the topography of the seabed. 1,500-meter (5,000 ft) high thrust ridges created by previous geologic activity along the fault had collapsed, generating landslides several kilometers wide. One such landslide consisted of a single block of rock some 100 m high and 2 km long (300 ft by 1.25 mi). The momentum of the water displaced by tectonic uplift had also dragged massive slabs of rock, each weighing millions of tons, as far as 10 km (7 mi) across the seabed. An oceanic trench several kilometres wide was exposed in the earthquake zone.The TOPEX/Poseidon and Jason 1 satellites happened to pass over the tsunami as it was crossing the ocean. These satellites carry radars that measure precisely the height of the water surface; anomalies of the order of 50 cm (20 in) were measured. Measurements from these satellites may prove invaluable for the understanding of the earthquake and tsunami. 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 the complex ways in which close proximity to the coast changes the size and shape of a wave.Tsunami characteristics
Animation of the tsunami caused by the earthquake showing how the tsunami radiated from the entire length of the rupture.Scale showing the size of the tsunami waves that hit Indonesia.The sudden vertical rise of the seabed by several metres during the earthquake displaced massive volumes of water, resulting in a tsunami that struck the coasts of the Indian Ocean. A tsunami which causes damage far away from its source is sometimes called a teletsunami and is much more likely to be produced by vertical motion of the seabed than by horizontal motion.The tsunami, like all others, behaved very differently in deep water than in shallow water. In deep ocean water, tsunami waves form only a small hump, barely noticeable and harmless, which generally travels at a very high speed of 500 to 1,000 km/h (310 to 620 mph); in shallow water near coastlines, a tsunami slows down to only tens of kilometres an hour, but in doing so forms large destructive waves. Scientists investigating the damage in Aceh found evidence that the wave reached a height of when coming ashore along large stretches of the coastline, rising to in some areas when travelling inland.Radar satellites recorded the heights of tsunami waves in deep water: at two hours after the earthquake, the maximum height was . These are the first such observations ever made. Unfortunately these observations could not be used to provide a warning, since the satellites were not built for that purpose and the data took hours to analyze.According to Tad Murty, vice-president of the Tsunami Society, the total energy of the tsunami waves was equivalent to about five megatons of TNT (20 peta). This is more than twice the total explosive energy used during all of World War II (including the two atomic bombs), but still a couple of orders of magnitude less than the energy released in the earthquake itself. In many places the waves reached as far as inland.Tsunami wave field in the . The northern regions of the Indonesian island of Sumatra were hit very quickly, while Sri Lanka and the east coast of India were hit roughly 90 minutes to two hours later. Thailand was also struck about two hours later despite being closer to the epicentre, because the tsunami travelled more slowly in the shallow Andaman Sea off its western coast.The tsunami was noticed as far as Struisbaai in South Africa, some away, where a high tide surged on shore about 16 hours after the earthquake. It took a relatively long time to reach this spot at the southernmost point of Africa, probably because of the broad continental shelf off South Africa and because the tsunami would have followed the South African coast from east to west. The tsunami also reached Antarctica, where tidal gauges at Japan's Showa Base recorded oscillations of up to a metre, with disturbances lasting a couple of days.Some of the tsunami's energy escaped into the Pacific Ocean, where it produced small but measurable tsunamis along the western coasts of North and South America, typically around 20 to 40 cm (7.9 to 15.7 in). At Manzanillo, Mexico, a 2.6 m (8.5 ft) crest-to-trough tsunami was measured. As well, the tsunami was large enough to be detected in Vancouver, British Columbia, Canada. This puzzled many scientists, as the tsunamis measured in some parts of South America were larger than those measured in some parts of the Indian Ocean. It has been theorized that the tsunamis were focused and directed at long ranges by the mid-ocean ridges which run along the margins of the continental plates.Signs and warnings
Maximum recession of tsunami waters at ." All Things Considered/NPR. December 27, 2004. However, not all tsunami causes this "disappearing sea" effect. In some cases, there are no warning signs at all: the sea will suddenly swell without retreating, surprising many people and giving them little time to flee.One of the few coastal areas to evacuate ahead of the tsunami was on the Indonesian island of Simeulue, very close to the epicentre. Island folklore recounted an earthquake and tsunami in 1907, and the islanders fled to inland hills after the initial shaking yet before the tsunami struck. On Maikhao beach in northern Phuket, Thailand, a 10-year-old British tourist named Tilly Smith had studied tsunami in geography class at school and recognised the warning signs of the receding ocean and frothing bubbles. She and her parents warned others on the beach, which was evacuated safely. John Chroston, a biology teacher from Scotland, also recognised the signs at Kamala Bay north of Phuket, taking a busload of vacationers and locals to safety on higher ground.Anthropologists had initially expected the aboriginal population of the Andaman Islands to be badly affected by the tsunami and even feared the endangered Onge tribe could have been wiped out. Of the six native tribes only the Nicobarese, who had converted to Christianity and taken up agriculture in place of their previous hunter-gatherer lifestyle, and mainland settlers suffered significant losses. Many of the aboriginal tribes evacuated and suffered fewer casualties.Phases and wave form
A tsunami can arrive at a coastline in one of two ways. First, there's the negative wave where the trough of the wave precedes the actual arrival of the crest or "wave" itself. Here, the common and better known warning sign of an impending tsunami strike is a rapidly receding sea followed by a sudden onrushing body of water traveling inland at high speed.The second form in which a tsunami arrives is the positive wave or crest first. In this case, the warning signs are much more vague if any. The sea will usually start rising immediately rather slowly at first without the receding phase, much more like an on-coming high tide but instead of stopping at tidal level it will keep on rising faster and faster until the crest of the tsunami passes and continues moving inland. Therefore, the second form of tsunami waves are usually more dangerous owing to the fact that it can arrive without much warning giving residents less time to prepare and outrun the tsunami. These two types of tsunamis are usually generated simultaneously (in opposing direction of travel) by a megathrust earthquake similar to the 2004 Indian Ocean earthquake.Retreat-rise cycle (negative wave)
The tsunami was a succession of several waves, occurring in retreat and rise cycles with a period of over 30 minutes between each peak. The third wave was the most powerful and reached highest, occurring about an hour and a half after the first wave. Smaller tsunami continued to occur for the rest of the day.Rise-retreat-rise cycle (positive wave)
If the crest of a tsunami arrives first, there won't be any recession. The sea level will increase rapidly to inundate everything in the path of the tsunami. This appears to be the case in countries such as Sri Lanka and India that lies to the west of the Andaman-Sumatra fault where the tsunami originates. After the first tsunami wave passed, water will then begin to flow back into the ocean receding at a quicker pace as the second wave arrives.Death toll and casualties
Measured in lives lost, this is one of the ten worst earthquakes in recorded history, as well as the single worst tsunami in history. Indonesia was the worst affected area, with most death toll estimates at around 170,000. However, another report by health minister Fadilah Supari has estimated the death total to be as high as 220,000 in Indonesia alone, giving a total of 280,000 casualties.The tsunami caused serious damage and deaths as far as the east coast of Africa, with the furthest recorded death due to the tsunami occurring at Rooi Els in South Africa, away from the epicentre. In total, eight people in South Africa died due to abnormally high sea levels and waves.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 because children were the least able to resist being overcome by the surging waters. Oxfam went on to report that as many as four times more women than men were killed in some regions because they were waiting on the beach for the fishermen to return and looking after their children in the houses.In addition to the large number of local residents, up to 9,000 foreign tourists (mostly Europeans) enjoying the peak holiday travel season were among the dead or missing, especially people from the Nordic countries. The European nation hardest hit may have been Sweden, whose death toll was 543.States of emergency were declared in Sri Lanka, Indonesia, and the Maldives. The United Nations estimated at the outset that the relief operation (which is presently still underway) would be the costliest in human history. UN Secretary-General Kofi Annan has stated that reconstruction would probably take between five and ten years. Governments and non-governmental organisations fear the final death toll may double as a result of diseases, prompting a massive humanitarian response.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, Sri Lanka); UTC+6: (Bangladesh); UTC+6:30: (Cocos Islands, Myanmar); UTC+7: (Indonesia (western), Thailand); UTC+7: (Malaysia, Singapore). Since the earthquake occurred at 00:58:53 UTC, add the above offsets to find the local time of the earthquake.Note: All figures are approximate and subject to change. The first column links to more details on specific countries.
1 Includes those reported under 'Confirmed'. If no separate estimates are available, the number in this column is the same as reported under 'Confirmed'.
2 Does not include approximately 19,000 missing people initially declared by Tamil Tiger authorities from regions under their control.
3 Data includes at least 2,464 foreigners.
4 Does not include South African citizens who died outside of South Africa (e.g., tourists in Thailand). For more information on those deaths, see this
1 Includes those reported under 'Confirmed'. If no separate estimates are available, the number in this column is the same as reported under 'Confirmed'.
2 Does not include approximately 19,000 missing people initially declared by Tamil Tiger authorities from regions under their control.
3 Data includes at least 2,464 foreigners.
4 Does not include South African citizens who died outside of South Africa (e.g., tourists in Thailand). For more information on those deaths, see this