The 2004 Indian Ocean earthquake, known by the scientific community as the great Sumatra-Andaman earthquake,1 an undersea earthquake, occurred at 00:58:53 UTC (07:58:53 local time) December 26, 2004, with an epicentre off the west coast of Sumatra, Indonesia. The earthquake triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing large numbers of people and inundating coastal communities across South and Southeast Asia, including parts of Indonesia, Sri Lanka, India, and Thailand. The disaster has been variously named the Boxing Day Tsunami in Australia, Canada, New Zealand, and the United Kingdom, because it took place on Boxing Day. The tsunami occurred exactly one year after the 2003 earthquake that devastated the southern Iranian city of Bam and exactly two years before the 2006 Hengchun earthquake.
The 2004 Indian Ocean earthquake, and series of catastrophic tsunamis that followed in its wake, had a lesson to teach. The world community needs to put in place early detection systems, possibly sponsored by the United Nations, that would undoubtedly save lives. Although this earthquake happened close to large population centers that had little time to act even with warnings, nations farther away would have had time to issue life-saving warnings. Poorer nations are usually in the greatest need of early warning technology but the least able to pay for it. A United Nations sponsored initiative to put in place early warning systems for earthquakes, cyclones, typhoons, tornadoes, and tsunamis would take the world a great distance closer to creating a safe planet for all people, rich and poor.
Initially, reports identified the earthquake as moment magnitude, Mw 9.0 (note that this is not the Richter scale or local magnitude scale, Ml, which is known to saturate at higher magnitudes). In February 2005 scientists revised the estimate of the magnitude to Mw9.3.2Tetsuo Tobita et al., 3
The hypocentre of the main earthquake sits at 3.316° N 95.854° ECoordinates: 3.316° N 95.854° E, approximately 160 km (100 mi) west of Sumatra, at a depth of 30 km (19 mi) below mean sea level (initially reported as 10 km). People felt the earthquake itself (apart from the tsunami) as far away as Bangladesh, India, Malaysia, Myanmar, Thailand, Singapore, and the Maldives.
Indonesia lies between the Pacific Ring of Fire along the north-eastern islands adjacent to and including New Guinea and the Alpide belt along the south and west from Sumatra, Java, Bali, Flores, and Timor.
Great earthquakes such as the Sumatra-Andaman event, invariably associated with megathrust events in subduction zones, have seismic moments that can account for a significant fraction of the global earthquake moment across century-scale time periods. The Sumatra-Andaman earthquake measured the largest earthquake since 1964, and the second largest since the Kamchatka earthquake of October 16, 1737.
Of all the seismic moment released by earthquakes in the 100 years from 1906 through 2005, roughly one-eighth arose as a result of the Sumatra-Andaman event. That quake, together with the Good Friday Earthquake (Alaska, 1964) and the Great Chilean Earthquake (1960), account for almost half of the total moment. The much smaller but still catastrophic 1906 San Francisco earthquake has been included in the diagram at right for perspective. Mw denotes the magnitude of an earthquake on the moment magnitude scale.
Since 1900, the 1960 Great Chilean Earthquake (magnitude 9.5) and the 1964 Good Friday Earthquake in Prince William Sound (9.2) constitute the only earthquakes recorded with a greater magnitude. An earthquake off Kamchatka, Russia, on November 4, 1952, (magnitude 9.0 represents the only other recorded earthquake of magnitude 9.0 or greater). Each of those megathrust earthquakes also spawned tsunamis in the Pacific Ocean, but the death toll from those measured significantly lower. The worst of those 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 (Cascadia Earthquake, western U.S. and Canada, Juan de Fuca Plate and North American Plate). Geologists calculate that those all had a magnitude 9, but no accurate measurements exist.
Tectonic platesEpicentre of the earthquake, just north of Simeulue Island
The earthquake covered an unusually large area in geographical extent. An estimated 1,600 km (994 mi) of faultline slipped about 15 m (50 ft) along the subduction zone where the India Plate slides under the Burma Plate. The slip 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 bed-the longest 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. 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 changes from subduction to strike-slip (the two plates push past one another in opposite directions). That reduced the speed of the water displacement and so reducing the size of the tsunami that hit the northern part of the Indian Ocean.4
The India Plate constitutes a part of the great Indo-Australian Plate, which underlies the Indian Ocean and Bay of Bengal, drifting north-east at an average of 6 cm/year (2 inches per year). The India Plate meets the Burma Plate (considered a portion of the great Eurasian Plate) at the Sunda Trench. At that point the India Plate subducts beneath 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. Those volatiles rise into the crust above and trigger melt which exits the earth's crust through volcanoes in the form of a volcanic arc. The volcanic activity that results as the Indo-Australian plate subducts the Eurasian plate has created the Sunda Arc.
As well as the sideways movement between the plates, estimates put the rise of the sea bed at several metres, displacing an estimated 30 km³ (7 cu mi) of water and triggering devastating tsunami waves. Rather than originating from a point source, as inaccurately depicted in some illustrations of their paths of travel, the waves radiated outwards along the entire 1,600 km (994 mi) length of the rupture (acting as a line source). That greatly increased the geographical area waves covered, 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.5
Aftershocks and other earthquakesLocations of initial earthquake and all aftershocks measuring greater than 4.0 from December 26, 2004-January 10, 2005. The large star in the lower right square of the grid marks the site of the original quake. (Credit: USGS)
Reports of numerous aftershocks off the Andaman Islands, the Nicobar Islands and the region of the original epicentre had been received in the hours and days that followed. The largest aftershock, originating off the coast of the Sumatran island of Nias, registered a magnitude of 8.7, prompting debate among seismologists as to whether to classify the event as an aftershock of the December 2004 quake or as a "triggered earthquake" (which typically differs from an aftershock in laying along a different fault line, often as large or larger than the earthquake which triggered it).6 That earthquake produced its own aftershocks (some registering a magnitude of as great as 6.1) and presently ranks as the seventh 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.7 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, scientists still measured reverberations, 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. Geologists note that as unusual, since earthquakes of magnitude 8 or more occur only about once per year on average.8 Some seismologists have speculated about a connection between those 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. 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.
Energy of the earthquake
Early estimated placed the total energy released by the 2004 Indian Ocean earthquake as high as 3.35 exajoules (3.35×1018 joules). That equals over 930 terawatt hours, 0.8 gigatons of TNT, or about as much energy used in the United States in 11 days. A new seismic energy release estimate, generated on September 30, 2005, using new data, placed the amount of energy released by the earthquake at the somewhat smaller figure of 1.1×1018 joules, equivalent to about 250 megatons of TNT. The earthquake generated seismic oscillation of the Earth's surface of up to 20-30 cm (8-12 in), equivalent to the effect of the tidal forces caused by the Sun and Moon. People felt the shock waves of the earthquake across the planet; as far away as the U.S. state of Oklahoma, where scientists recorded vertical movements of 3 mm (0.12 in).
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 (surface) 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 have been arranged vertically by distance from the epicenter in degrees. The earliest, lower amplitude, signal represents 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 represent 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. That aftershock would be considered a major earthquake under ordinary circumstances, but the mainshock dwarfed it.Vertical-component ground motions recorded by the IRIS/USGS Global Seismographic Network
In February 2005, the British 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 kilometers wide appeared in the earthquake zone.9
The TOPEX/Poseidon and Jason 1 satellites happened to pass over the tsunami as it crossed the ocean. Those satellites carry radars that measure precisely the height of the water surface; anomalies of the order of 50 cm (20 in) had been measured. Measurements from those satellites may prove invaluable for the understanding of the earthquake and tsunami.10 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 characteristicsAnimation of the tsunami caused by the earthquake showing how the tsunami radiated from the entire length of the 1,600 kilometre (994 mi) rupture.
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. Scientists sometimes call a tsunami which causes damage far away from its source a "teletsunami,," usually produced by vertical motion of the seabed rather than by horizontal motion.11
The tsunami, like all others, behaves 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 24 m (80 ft) when coming ashore along large stretches of the coastline, rising to 30 m (100 ft) 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 reached 60 cm (2 ft). Those represent the first such observations ever made although they lacked the capacity to provide a warning since the satellite data took hours to analyze.1213
According to Tad Murty, vice-president of the Tsunami Society, the total energy of the tsunami waves equaled about five megatons of TNT (20 petajoules). That amounts to 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 2 km (1.24 mi) inland.
The 1,600 km (994 mi) of faultline affected by the earthquake lay in a nearly north-south orientation, the greatest strength of the tsunami waves moved 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 relatively near the epicentre, benefiting from the earthquake proceeded more slowly in the northern rupture zone. That greatly reducing the energy of the water displacements in the region.
Coasts that have a landmass between them and the tsunami's location of origin usually escaped damage, although on occasion tsunami waves sometimes diffract around such landmasses. Thus, the tsunami hit the Indian state of Kerala despite sitting on the western coast of India, and the western coast of Sri Lanka also suffered substantial impacts. Also distance alone lacks a guarantee of safety; Somalia got hit harder than Bangladesh despite being much farther away.
Because of the distances involved, the tsunami took anywhere from fifteen minutes to seven hours (for Somalia) to reach the various coastlines.1415 The northern regions of the Indonesian island of Sumatra received waves very quickly, while Sri Lanka and the east coast of India suffered hits roughly 90 minutes to two hours later. Waves also Thailand 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.
Observers noticed the tsunami as far as Struisbaai in South Africa, some 8,500 km (5,300 mi) away, where a 1.5 m (5 ft) high tide surged on shore about 16 hours after the earthquake. It took a relatively long time to reach that 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 meter, with disturbances lasting a couple of days.16
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 tsunami measured 2.6 m (8.5 ft) crest-to-trough, large enough for detection in Vancouver, British Columbia, Canada. That puzzled many scientists, as the tsunamis in some parts of South America measured larger than those in some parts of the Indian Ocean. Some scientists theorized that the tsunamis focused, directed at long ranges by the mid-ocean ridges running along the margins of the continental plates.
Signs and warnings
Despite a lag of up to several hours between the earthquake and the impact of the tsunami, the killer waves took nearly all of the victims completely by surprise. No tsunami warning systems in the Indian Ocean exist to detect tsunamis or to warn the general populace living around the ocean. Tsunami physics complicate detection; while a tsunami runs in deep water it has little height. Secondly, detection requires a network of sensors to detect it. Setting up the communications infrastructure to issue timely warnings constitutes an even bigger problem, particularly in a relatively poor part of the world.
Tsunamis occur much more frequently in the Pacific Ocean because of earthquakes in the "Ring of Fire," and an effective tsunami warning system has long been in place there. Although the extreme western edge of the Ring of Fire extends into the Indian Ocean (the point where this earthquake struck), no warning system exists in that ocean. Tsunamis have been relatively rare despite earthquakes frequently hitting Indonesia. The Krakatoa eruption of 1883 caused the last major tsunami. Large earthquakes only occasionally produce large tsunamis; on March 28, 2005, a magnitude 8.7 earthquake hit roughly the same area of the Indian Ocean without resulting in a major tsunami.
In the aftermath of the disaster, awareness has increased for the need of a tsunami warning system for the Indian Ocean. The United Nations started working on an Indian Ocean Tsunami Warning System and by 2005 had the initial steps in place. Some have even proposed creating a unified global tsunami warning system, to include the Atlantic Ocean and Caribbean.Maximum recession of tsunami waters at Kata Noi Beach, Thailand, before the third, and strongest, tsunami wave (sea visible in the right corner, the beach is at the extreme left), 10:25 A.M. local time.
The earthquake itself serves as the first warning sign of a possible tsunami, although a tsunami can strike thousands of kilometres away from the epicenter of the earthquake with slight or negligible movement felt. In the minutes preceding a tsunami strike, the sea often recedes temporarily from the coast, proving another warning sign. Around the Indian Ocean, that rare sight reportedly induced people, especially children, to visit the coast to investigate and collect stranded fish on as much as 2.5 km (1.6 mi) of exposed beach, with fatal results.17
People on the Indonesian island of Simeulue, very close to the epicentre, number among the few coastal areas to evacuate ahead of the tsunami. 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 ten-year-old British tourist named Tilly Smith who had studied tsunami in geography class at school, recognized the warning signs of the receding ocean and frothing bubbles. She and her parents warned others on the beach, leading to everyone evacuating safely.18 John Chroston, a biology teacher from Scotland, also recognized the signs at Kamala Bay north of Phuket, taking a busload of vacationers and locals to safety on higher ground.
Retreat and rise cycle
The tsunami constituted a succession of several waves, occurring in retreat and rise cycles with a period of over thirty minutes between each peak. The third wave proved the most powerful and reached highest, occurring about an hour and a half after the first wave. Smaller tsunamis continued to occur for the rest of the day.
Receding waters after the second tsunami, 10:20 A.M.
3rd tsunami wave, 11:00 A.M.
4th tsunami wave, 11:22 A.M.
Damage and casualties
The U.S. Geological Survey initially recorded the toll as 283,100 killed, 14,100 missing, and 1,126,900 people displaced. Early news reports after the earthquake spoke of a toll in the hundreds, but the numbers rose steadily over the following week. More recent figures indicate that the actual casualties numbered 186,983 dead and 42,883 missing, for a total of 229,866, as more and more displaced survivors have been found and name duplications eliminated from the lists of victims. Measured in lives lost, the disaster makes the list of the top ten worst earthquakes in recorded history, as well as the single worst tsunami in history.
Relief agencies report that children appeared to total one-third of the dead, a result of the high proportion of children in the populations of many of the affected regions. Also children had the least ablity to resist being overcome by the surging waters. Oxfam went on to report that as many as four times more women than men died in some regions because they waited on the beach for the fishermen to return and they looked after their children in the houses.19
In addition to the large number of local residents, up to 9,000 foreign tourists (mostly Europeans) enjoying the peak holiday travel season numbered among the dead or missing, especially people from the Nordic countries. The European nation hardest hit may have been Sweden, whose death toll hit 428 dead, with 116 missing.20
Sri Lanka, Indonesia, and the Maldives declared states of emergency. The United Nations estimated at the outset that the relief operation (presently still underway) would become 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 organizations 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 affected areas time zones follow: 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 earthquake occurred at 00:58:53 UTC, add the above offsets to find the local time of the earthquake.
|Indonesia||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".130,736||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".167,799||n/a||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".37,063||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".500,000+21|
|Sri Lanka2||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".35,32222||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".35,322||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".21,41122||n/a||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".516,15022|
|India||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".12,405||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".18,045||n/a||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".5,640||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".647,599|
|Thailand||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".5,395323||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".8,212||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".8,45724||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".2,81723||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".7,000|
|Somalia||&&&&&&&&&&&&&078.&&&&&078||&&&&&&&&&&&&0289.&&&&&028925||n/a||n/a||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".5,00026|
|Myanmar (Burma)||&&&&&&&&&&&&&061.&&&&&061||&&&&&&&&&&&&0400.&&&&&0400-60027||&&&&&&&&&&&&&045.&&&&&045||&&&&&&&&&&&&0200.&&&&&020028||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".3,200|
|Maldives||&&&&&&&&&&&&&082.&&&&&08229||&&&&&&&&&&&&0108.&&&&&010830||n/a||&&&&&&&&&&&&&026.&&&&&026||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".15,000+|
|Madagascar||n/a||n/a||n/a||n/a||0Expression error: Unrecognised punctuation character ","..Expression error: Unrecognised punctuation character ",".1,000+38|