Asian Tsunami Case Study 2004 Chevrolet

The 2004 Indian Ocean earthquake occurred at 00:58:53 UTC on 26 December with the epicentre off the west coast of Sumatra, Indonesia. The shock had a moment magnitude of 9.1–9.3 and a maximum Mercalli intensity of IX (Violent). The underseamegathrust earthquake was caused when the Indian Plate was subducted by the Burma Plate and triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing 230,000–280,000 people in 14 countries, and inundating coastal communities with waves up to 30 metres (100 ft) high. It was one of the deadliest natural disasters in recorded history. Indonesia was the hardest-hit country, followed by Sri Lanka, India, and Thailand.

It is the third-largest earthquake ever recorded on a seismograph and had the longest duration of faulting ever observed, between 8.3 and 10 minutes.[10] It caused the entire planet to vibrate as much as 1 centimetre (0.4 inches)[11] and triggered other earthquakes as far away as Alaska.[12] Its epicentre was between Simeulue and mainland Indonesia.[13] The plight of the affected people and countries prompted a worldwide humanitarian response. In all, the worldwide community donated more than US$14 billion (2004) in humanitarian aid.[14] The event is known by the scientific community as the Sumatra–Andaman earthquake.[15][16] The resulting tsunami was given various names, including the 2004 Indian Ocean tsunami, South Asian tsunami, Indonesian tsunami, Christmas tsunami and the Boxing Day tsunami.

Earthquake characteristics

The earthquake was initially documented as moment magnitude 8.8. In February 2005 scientists revised the estimate of the magnitude to 9.0.[17] 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 9.1–9.3. 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.[18]

The hypocentre of the main earthquake was approximately 160 km (100 mi) off the western coast of northern Sumatra, in the Indian Ocean just north of Simeulue island at a depth of 30 km (19 mi) below mean sea level (initially reported as 10 km (6.2 mi)). The northern section of the Sunda megathrust ruptured over a length of 1,300 km (810 mi).[13] The earthquake (followed by the tsunami) was felt in Bangladesh, India, Malaysia, Myanmar, Thailand, Singapore, Sri Lanka and the Maldives.[19] Splay faults, or secondary "pop up faults", caused long, narrow parts of the sea floor to pop up in seconds. This quickly elevated the height and increased the speed of waves, completely destroying the nearby Indonesian town of Lhoknga.[20]

Indonesia lies between the Pacific Ring of Fire along the north-eastern islands adjacent to New Guinea, and the Alpide belt that runs along the south and west from Sumatra, Java, Bali, Flores to Timor.

Great earthquakes such as the Sumatra-Andaman event, which are 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. Of all the seismic moment released by earthquakes in the 100 years from 1906 through 2005, roughly one-eighth was due to the Sumatra-Andaman event. This quake, together with the Good Friday earthquake (Alaska, 1964) and the Great Chilean earthquake (1960), account for almost half of the total moment.

Since 1900 the only earthquakes recorded with a greater magnitude were the 1960 Great Chilean earthquake (magnitude 9.5) and the 1964 Good Friday earthquake in Prince William Sound (9.2). The only other recorded earthquakes of magnitude 9.0 or greater were off Kamchatka, Russia, on 4 November 1952 (magnitude 9.0)[21] and Tōhoku, Japan (magnitude 9.1) in March 2011. Each of these megathrust earthquakes also spawned tsunamis in the Pacific Ocean. However, the death toll from these was significantly lower, primarily because of the lower population density along the coasts near affected areas and the much greater distances to more populated coasts and also due to the superior infrastructure and warning systems in MEDCs (More Economically Developed Countries) such as Japan.

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.

Foreshock

The 2002 Sumatra earthquake is believed to have been a foreshock, predating the main event by over two years.[22]

Tectonic plates

Main article: Plate tectonics

The megathrust earthquake was unusually large in geographical and geological extent. An estimated 1,600 kilometres (1,000 mi) of fault surface slipped (or ruptured) about 15 metres (50 ft) along the subduction zone where the Indian 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 kilometres (250 mi) long and 100 kilometres (60 mi) wide, located 30 kilometres (19 mi) beneath the sea bed—the largest rupture ever known to have been caused by an earthquake. The rupture proceeded at a speed of about 2.8 kilometres per second (1.7 miles per second) (10,000 km/h or 6,200 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) (7,500 km/h or 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).

The Indian Plate is part of the great Indo-Australian Plate, which underlies the Indian Ocean and Bay of Bengal, and is drifting north-east at an average of 6 centimetres per year (2.4 inches per year). 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 beneath the Burma Plate, which carries the Nicobar Islands, the Andaman Islands, and northern Sumatra. The India Plate sinks 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 overlying plate causing partial melting and the formation of magma. The rising magma intrudes into the crust above and 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, the sea floor is estimated to have risen by several metres, displacing an estimated 30 cubic kilometres (7.2 cu mi) of water and triggering devastating tsunami waves. The waves did not originate from a point source, as was inaccurately depicted in some illustrations of their paths of travel, but rather radiated outwards along the entire 1,600-kilometre (1,000 mi) length of the rupture (acting as a line source). 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 floor significantly reduced the capacity of the Indian Ocean, producing a permanent rise in the global sea level by an estimated 0.1 millimetres (0.004 in).[23]

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 magnitude 8.7 2005 Nias–Simeulue earthquake, which originated off the coast of the Sumatran island of Nias, is not considered an aftershock, despite its proximity to the epicenter, and was most likely triggered by stress changes associated with the 2004 event.[24] The earthquake produced its own aftershocks (some registering a magnitude of as great as 6.1) and presently ranks as the third largest earthquake ever recorded on the moment magnitude or Richter magnitude scale.

Other aftershocks of up to magnitude 6.6 continued to shake the region daily for three or four months.[25] 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 subantarcticAuckland 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.[26] However, the U.S. Geological Survey sees no evidence of a causal relationship between these events.[27]

The December earthquake is thought to have triggered activity in both Leuser Mountain[28] and Mount Talang,[29] volcanoes in Aceh province along the same range of peaks, while the 2005 Nias–Simeulue earthquake had sparked activity in Lake Toba, an ancient crater in Sumatra.[30]

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 1.1×1017joules,[31] or 26 megatons of TNT. This energy is equivalent to over 1,500 times that of the Hiroshima atomic bomb, but less than that of Tsar Bomba, the largest nuclear weapon ever detonated; however, the total work done MW (and thus energy) by the quake was 4.0×1022joules (4.0×1029ergs),[32] the vast majority underground, which is over 360,000 times more than its ME, equivalent to 9,600 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.[33]

The earthquake generated a 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. The seismic 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 20 μm (0.02 mm; 0.0008 in) 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.[34]

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 (0.4 in) in vertical amplitude everywhere on Earth. The record section plot 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. The aftershock would be considered a major earthquake under ordinary circumstances, but is dwarfed by the mainshock.

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 oblateness of the Earth.[35] 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,[36] or perhaps by up to 5 or 6 cm (2.0 or 2.4 in).[37] 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.

There was 10 m (33 ft) movement laterally and 4–5 m (13–16 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 (120 ft), but more accurate data released more than a month after the earthquake found the movement to be about 20 cm (8 in).[38] 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 ft 1 in) and to have sunk by 1 m (3 ft 3 in).[39]

In February 2005, the Royal Navy vessel HMS Scott surveyed the seabed around the earthquake zone, which varies in depth between 1,000 and 5,000 m (550 and 2,730 fathoms; 3,300 and 16,400 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-metre-high (5,000 ft) thrust ridges created by previous geologic activity along the fault had collapsed, generating landslides several kilometres 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 (6 mi) across the seabed. An oceanic trench several kilometres wide was exposed in the earthquake zone.[40]

The TOPEX/Poseidon and Jason-1 satellites happened to pass over the tsunami as it was crossing the ocean.[41] 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.[42] 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

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 that 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.[43]

The tsunami, like all others, behaved very differently in deep water than in shallow water. In deep ocean water, tsunami waves form only a low, very broad 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 per 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 metres (80 ft) when coming ashore along large stretches of the coastline, rising to 30 metres (100 ft) in some areas when traveling inland.[5]

Radar satellites recorded the heights of tsunami waves in deep water: at two hours after the earthquake, the maximum height was 60 centimetres (2 ft). These are the first such observations ever made. 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.[44][45]

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 petajoules), which 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 2 km (1.2 mi) inland.[46]

Because the 1,600 km (1,000 mi) fault affected by the earthquake 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 relatively near the epicenter. It also benefited from the fact that the earthquake proceeded more slowly in the northern rupture zone, greatly reducing the energy of the water displacements in that region.

Coasts that have a landmass between them and the tsunami's location of origin are usually safe; however, tsunami waves can sometimes diffract around such landmasses. Thus, the state of Kerala was hit by the tsunami despite being on the western coast of India, and the western coast of Sri Lanka suffered substantial impacts. Distance alone was no guarantee of safety, as Somalia was hit harder than Bangladesh despite being much farther away.

Because of the distances involved, the tsunami took anywhere from fifteen minutes to seven hours to reach the coastlines.[47][48] 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 struck about two hours later despite being closer to the epicentre, because the tsunami traveled more slowly in the shallow Andaman Sea off its western coast.

The tsunami was noticed 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 Struisbaai 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 (3 ft 3 in), with disturbances lasting a couple of days.[49]

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).[50] At Manzanillo, Mexico, a 2.6 m (8 ft 6 in) crest-to-trough tsunami was measured. As well, the tsunami was large enough to be detected in Vancouver, British Columbia, Canada, which 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.[51]

Signs and warnings

Despite a lag of up to several hours between the earthquake and the impact of the tsunami, nearly all of the victims were taken completely by surprise. There were no tsunami warning systems in the Indian Ocean to detect tsunamis or to warn the general population living around the ocean.[52] Tsunami detection is not easy because while a tsunami is in deep water it has little height and a network of sensors is needed to detect it. Setting up the communications infrastructure to issue timely warnings is an even bigger problem, particularly in a relatively poor part of the world.

Tsunamis are much more frequent 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 the earthquake struck), no warning system exists in that ocean. Tsunamis there are relatively rare despite earthquakes being relatively frequent in Indonesia. The last major tsunami was caused by the Krakatoa eruption of 1883. It should be noted that not every earthquake produces large tsunamis; on 28 March 2005, a magnitude 8.7 earthquake hit roughly the same area of the Indian Ocean but did not result in a major tsunami.

The first warning sign of a possible tsunami is the earthquake itself. However, tsunamis can strike thousands of kilometres away where the earthquake is only felt weakly or not at all. Also, in the minutes preceding a tsunami strike, the sea often recedes temporarily from the coast, which was observed on the eastern side of the rupture zone of the earthquake such as around the coastlines of Aceh province, Phuket island and Khao Lak area in Thailand, Penang island of Malaysia and the Andaman and Nicobar islands. Around the Indian Ocean, this 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.[53] However, not all tsunamis cause 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.

Reportedly, scuba divers near the abundant coral reefs in Thailand and the Maldives were caught off guard by violent, swirling underwater currents. The divers described the experience like being in a 'washing machine'. Coral reef animals such as fish were also absent as the tsunami passed by.[54]

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 and before the tsunami struck. These tales and oral folklore from previous generations may have helped the survival of the inhabitants.[55] On Maikhao beach in northern Phuket, Thailand, a 10-year-old British tourist named Tilly Smith had studied tsunami in geography 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.[56]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 already depopulated Onge tribe could have been wiped out.[57] Many of the aboriginal tribes evacuated and suffered fewer casualties.[58][59] Oral traditions developed from previous earthquakes helped the aboriginal tribes escape the tsunami. For example, the folklore of the Onges talks of "huge shaking of ground followed by high wall of water". Almost all of the Onge people seemed to have survived the tsunami.[60]

Aceh province, Sumatra, Indonesia

The tsunami struck the west and north coasts of northern Sumatra, particularly in Aceh province, Indonesia, during the early morning. At Ulee Lheue in Banda Aceh, a survivor described three waves, with the first wave rising only to the foundation of the buildings. This was followed by a large withdrawal of the sea before the second and third waves hit.[61] The tsunami reached shore 15–20 minutes after the earthquake, and the second was bigger than the first. A local resident living at Banda Aceh stated that the wave was 'higher than my house'.[62] Another resident living 2 km (1.2 mi) near the coast on the outskirt of the city informed that the tsunami was 'like a wall, very black' in colour and had a 'distinct sound' getting louder as it nears the coast.[63]

The maximum runup height of the tsunami was measured at a hill between Lhoknga and Leupung, located on the west coast of the northern tip of Sumatra, near Banda Aceh, and reached more than 30 m (100 ft).[6]

The tsunami heights in Sumatra:[64]

  • 15–30 m (49 ft–98 ft) on the west coast of Aceh.
  • 6–12 m (19.7 ft–39.4 ft) on the Banda Aceh coast.
  • 6 m (19.7 ft) on the Krueng Raya coast (3 oil tanks floated out)
  • 5 m (16.4 ft) on the Sigli coast.
  • 3–6 m (9.8 ft–19.7 ft) on the north coast of Weh Island directly facing the tsunami source.
  • 3 m (9.8 ft) on the opposite side of the coast of Weh Island facing the tsunami.

The tsunami height on the Banda Aceh coast were lower than half of that on the west coast. The tsunami height was reduced by half from 12 m (39.4 ft) at Ulee Lheue to 6 m (19.7 ft) a further 8 km (4.97 miles) to the northeast. The inundation was observed to lie 3–4 km (1.86–2.49 miles) inland throughout the city. Flow depths over the ground were observed to be over 9 m (29.5 ft) in the seaside section of Ulee Lheue and tapered landward. The level of destruction was more extreme on the northwestern flank of the city in the areas immediately inland of the aquaculture ponds. The area toward the sea was wiped clean of nearly every structure, while closer to the river—dense construction in a commercial district showed the effects of severe flooding. The flow depth was just at the level of the second floor, and there were large amounts of debris piled along the streets and in the ground-floor storefronts. One of the reasons seems to be that there is an archipelago between Lhoknga and Banda Aceh. Within 2–3 km (1.24–1.86 miles) from the shoreline, houses, except for strongly-built reinforced concrete ones with brick walls, which seemed to have been partially damaged by the earthquake before the tsunami attack, were completely swept away or destroyed by the tsunami.[64][65]

Three small islands: Weh, Breueh, and Nasi, lie just north of the capital city. The tsunami effects on two of the islands, Breueh and Nasi were extreme, with a runup of 10–20 m (33–66 ft) on the west-facing shores. Coastal villages were completely destroyed by the tsunami waves. On Pulau Weh, however, the island experienced strong surges in the port of Sabang, yet there was little damage with a reported runup values of 3–5 m (9.8–16.4 ft), which was most likely shadowed from the direct tsunami attack by the islands to the southwest.[65]

In Lhoknga, a town in Aceh Besar Regency, Aceh Special Region, Indonesia, located on the western side of the island of Sumatra, 13 km (8.08 miles) southwest of Banda Aceh was completely flattened and destroyed by the 2004 Boxing Day tsunami, where its population dwindled from 7,500 to 400. The tsunami waves were almost 30 m (98.4 ft) high. Eyewitnesses reported 10 to 12 waves, the second and third ones being the highest. The sea receded (drawback) 10 minutes after the earthquake and the first wave came rapidly landward as a turbulent flow (flood) with depths ranging from 0.5 to 2.5 m (1.64 ft–8.20 ft) high. The second and third waves was 15–30 m (49.2 ft–98.4 ft) high at the coast, described having an appearance to a surf wave (cobra-shaped) but 'taller than the coconut trees' and was 'like a mountain'.[66] Consequently, the tsunami also stranded cargo ships and barges and destroyed a cement factory near the Lampuuk coast.[6][67][68] Moreover, surveyed areas by scientists show runup heights over 20 m (65.6 ft) on the northwest coast of Sumatra in the Aceh province with a maximum runup of 51 m (167.3 ft).[69]

In Meulaboh based on survivor testimonies, tsunami arrived after the sea receded about 500 m (0.31 miles), followed by an advancing small tsunami. The second and third destructive waves arrived later, which exceeded the height of the coconut trees. The inundation distance is about 5 km (3.1 miles).[70]

Such high and fast waves arising from the epicentre by a megathrust earthquake were later found to be due to splay faults, secondary faults arising due to cracking of the sea floor to jut upwards in seconds, causing waves' speed and height to increase. A large slip of 30 m (98.4 ft) was estimated on the subfault located off the west coast of Aceh province. Another factor is subsidence at Banda Aceh (20–60 cm), Peukan Bada (>20 cm), Lhok Nga and Leupung (>1.5 m).[64]

Other towns on Aceh's west coast hit by the disaster included Leupung, Lhokruet, Lamno, Patek, Calang, Teunom, and the island of Simeulue. Affected or destroyed towns on the region's north and east coast were Pidie Regency, Samalanga, Panteraja and Lhokseumawe.

The very high fatality in the area is mainly due to the unpreparedness of the population from such an event. Helicopter survey showed entire settlements virtually destroyed with destruction miles inland with only some mosques left standing, which provided refuge for the people from the tsunami.

Andaman and Nicobar Islands, India

The tsunami arrived in the Andaman and Nicobar Islands minutes after the earthquake, and it caused extensive devastation to the islands' environment. Specifically, the Andaman Islands were moderately affected while the island of Little Andaman and the Nicobar Islands were severely affected by the tsunami. The tsunami survey were carried out in Little Andaman (mainly at Hut Bay), South Andaman (mainly in and around Port Blair), Car Nicobar (along Kankana-Mus sector), Great Nicobar (mainly at Campbell Bay and Joginder Nagar area).[71]

In the South Andaman, based on local eyewitnesses, tsunami waves attacked three times. Of the three, the third one was the most devastating. Flooding occurred at the coastlines of the islands and low-lying areas inland, which are connected to open sea through creeks. Inundation has been observed, along east coast of South Andaman Island and is found to be restricted at Chidiyatapu, Burmanallah, Kodiaghat, Beadnabad, Corbyn’s cove and Marina Park/Aberdeen Jetty areas. Along the west coast, the inundation has been observed around Guptapara, Manjeri, Wandoor, Collinpur and Tirur regions. Several near shore establishments and numerous infrastructures such as seawalls and a 20 MW diesel generated power plant at Bamboo Flat were extensively damaged.[71]

Results of the tsunami survey in South Andaman along Chiriyatapu, Corbyn’s Cove and Wandoor beaches:

  • 5.0 m (16.4 ft) in maximum tsunami height with a run-up of 4.24 m (13.9 ft) at Chiriyatapu Beach.
  • 5.48 m (18 ft) in maximum tsunami height and run-up at Corbyn's Cove Beach.
  • 6.64 m (21.8 ft) in maximum tsunami height and run-up of 4.63 m (15.2 ft) at Wandoor Beach.

Meanwhile, in the Little Andaman, tsunami waves impinged on the eastern shore of this island 25 to 30 minutes after the earthquake. It was a four-wave cycle; out of which the fourth one was most devastating with a tsunami wave height of about 10 m (33 ft). The tsunami water had converted the settlements at Hut Bay into rubbles within a range of 1 km inland from the seashore. Everything was destroyed including the jetty and the breakwater. Run up level up to 3.3 m (10.8 ft) have been measured.[71]

Moreover, in Malacca located on the island of Car Nicobar, According to local people, three pulses of tsunami waves attacked the area three times. The first wave that came 5 minutes after the earthquake was preceded by recession of the seawater up to 600–700 m (1969–2297 ft), exposing the seabed. The second and third waves came with a 10 minutes interval after the first and second waves respectively. The third wave was the strongest, with a maximum tsunami wave height of 11 m (36 ft) and was accompanied by a loud noise. The landward flow direction measured from bent rods was towards S800 W and the back flow was towards east direction. The inundation limit is 1.125 m (0.41 ft) from the sea water/land contact (on the date of measurement) towards west and restricted up to 10 m.[71] Furthermore, waves nearly 3 stories high devastated the Indian Air Force base, located just south of Malacca. The tsunami waves attacked the area three times with a maximum tsunami wave height of 11 m (36 ft). Inundation limit was found to be up to 1.25 km (4101 ft) inland. The impact of the waves was so severe that four Oil tankers of IOC were thrown almost 800 m (2624 ft) from the seashore near Malacca to Air force colony main gate.[71] In Chuckchucha and Lapati, the tsunami arrived in a three wave cycle with a maximum tsunami wave height of 12 m (39 ft).

In Campbell Bay of Great Nicobar island, the tsunami waves hit the area three times with an inundation limit of 250–550 m (820–1804 ft). The first wave came within 5 minutes of the earthquake. The second and third waves came 10 minutes after first and second waves respectively. The second wave was the strongest with a loud noise. Deadly tsunami waves wreaked havoc in this densely populated Jogindar Nagar area, situated 13 km south of Campbell Bay. According to local information, tsunami waves attacked the area thrice. The first wave came 5 minutes after the main shock (0629 hrs.) with a marginal drop in sea level. Second wave came 10 minutes after the first one with a maximum height of 4.84 m (15.9 ft) and caused the major destruction. The third wave came within 15 minutes after the second one with a lower wave height. The maximum inundation limit due to tsunami water intrusion has been found to be about 500 m (0.5 km).[71]

The worst affected island in the Andaman & Nicobar chain is Katchall Island with 303 people confirmed dead and 4,354 missing out of a total population of 5,312.[72][73][74]

Eyewitnesses at Port Blair recall that the water receded before the first wave, and the third wave was the tallest and caused the most damage. However, at Hut Bay, Malacca and Campbell Bay — locations far south of Port Blair — it was reported that the water level rose by about 1–2 m (3.3 ft–6.6 ft) from the normal sea level and remained there before the first wave crashed ashore.

Reports of tsunami wave height:[75][76]

  • 1.5 m (4.9 ft) at Diglipur and Rangat at North Andaman Island.
  • 8 m (26.2 ft) high at Campbell Bay (in Great Nicobar Island),
  • 10–12 m (32.8 ft–39.4 ft) high at Malacca (in Car Nicobar Island) and at Hut Bay (in Little Andaman Island).
  • 3 m (9.8 ft) high at Port Blair (in South Andaman Island).

The significant shielding of Port Blair and Campbell Bay by steep mountainous outcrops may have contributed to the relatively low wave heights at these locations, whereas the open terrain along the eastern coast at Malacca and Hut Bay likely contributed to the great height of the tsunami waves [73][77]

Indeed, many infrastructures near the coasts and buildings were harshly damaged by the waves.[74]

Sri Lanka

The tsunami first arrived on the eastern coast and subsequently refracted around the southern point of Sri Lanka (Dondra Head). The refracted tsunami waves inundated the southwestern part of Sri Lanka after some of its energy had been reflected from impact with the Maldives.[78] Sri Lanka is located 1,700 km (1056.33 miles) far from the epicenter and the tsunami source, so no one felt the ground shake and the tsunami hit the entire coastline of Sri Lanka around 2 hours after the earthquake.[79] It seems that the tsunami flooding consisted of three main waves, with the second being the largest and most destructive.[80] The first tsunami waves had initially caused a small flood (positive wave) as it struck the Sri Lankan coastline. Moments later, the ocean floor was exposed to as much as 1 km (0.62 miles) in places due to drawback (negative wave), which was followed by a massive second tsunami wave in the form of a flood. Certain locations managed to reduce the power of the waves through construction of seawalls and breakwaters.

The largest run-up measured was at 12.5 m (41 ft) with inundation distance of 390 m to 1.5 km (0.242 miles-0.932 miles) in Yala.[81] In Hambantota, tsunami run-ups are measured at 11 m (36.1 ft) with the greatest inundation distance of 2 km (1.24 miles), and tsunami run-up measurements along the Sri Lankan coasts are at 2.4–11 m (7.87 ft–36.1 ft).[78][81] Tsunami waves measured on the east coast ranged from 4.5 m-9 m (14.8 ft–29.5 ft) at Pottuvill to around Batticaloa, 2.6 m- 5 m (8.53 ft–16.4 ft) in the northeast around Trincomalee and 4 m-5 m (13.1 ft–16.4 ft) in the west coast from Moratuwa to Ambalangoda.

Sri Lanka tsunami height survey:[79][80]

  • 9 m (29.5 Ft) at Koggala.
  • 6 m (19.7 ft) at Galle port.
  • 4.8 m (15.7 ft) around the Galle coast.
  • 8.71 m (28.6 ft) at Nonagama.
  • 4.9 m (16.1 ft) at Weligama.
  • 4 m (13.1 ft) at Dodundawa.
  • 4.7 m (15.4 ft) at Ambalangoda.
  • 4.7 m (15.4 ft) at Hikkaduwa Fishery Harbour.
  • 10 m (33 ft) at Kahawa.
  • 4.8 m (15.7 ft) at North Beach of Beruwala.
  • 6 m (19.7 ft) at Paiyagala.

The Sumudra Devi, a passenger train out of Colombo, was derailed and overturned by the tsunami.[82] The tsunami caused the 2004 Sri Lanka tsunami-rail disaster which took at least 1,700 lives, making it the largest single rail disaster in world history by death toll. Estimates based on the state of the shoreline and a high-water mark on a nearby building place the tsunami 7.5–9 m (24.6 ft to 29.5 ft) above sea level and 2–3 m (6.6 ft to 9.8 ft) higher than the top of the train.[79]

In Sri Lanka, the civilian casualties were second only to those in Indonesia. Reports vary on the number of deaths since many people are still missing and the country lacks adequate communications. The eastern shores of Sri Lanka faced the hardest impact since they were facing the epicenter of the earthquake. The southwestern shores were hit later, but the death toll was just as severe. The southwestern shores are a hotspot for tourists as well as the fishing economy. Tourism and fishing industries created high population densities along the coast.[83]

The coastal lifestyle of people and degradation of the natural environment in Sri Lanka contributed to the high death tolls. In addition to the high number of fatalities, approximately 90,000 buildings were destroyed. Houses were easily destroyed since they were built mostly from wood.[83]

Thailand

The tsunami hit the southwest coast of southern Thailand, which was about 500 km (310.69 miles) from the epicenter. The region is prominent with tourists internationally. Since the tsunami hit during high tide, its damage was severe. Approximately 5,400 people were killed and 3,100 people were reported missing in Thailand. The places where the tsunami struck were Khao Lak, Phuket Island, the Phi Phi Islands, Koh Racha Yai, Koh Lanta Yai and Ao Nang of Krabi province, offshore archipelagos like the Surin Islands, the Similan Islands, and coastal areas of Satun, Ranong, Phang Nga, Trang and Krabi provinces.

The country experienced the largest tsunami runup height of any location outside of Sumatra, which occurred at Khao Lak

The epicenter of the 2004 Indian Ocean earthquake and associated aftershocks in French.
A pie chart comparing the seismic moment release for the largest earthquakes from 1906 to 2005 compared to all other earthquakes for the same period
Locations of initial earthquake and all aftershocks measuring greater than 4.0 from 26 December 2004 to 10 January 2005. The site of the original quake is marked by the large star in the lower right square of the grid.
The tsunami strikes Ao Nang, Thailand.
NOAA's tsunami travel time (TTT) map for the 2004 Indian Ocean tsunami. The TTT map calculates the first-arrival travel times of the tsunami, following their generation at the earthquake epicenter. Note that the maps do not provide the height or the strength of the wave, only the arrival times. The number tags represent hours after the initial event. Map contours represent 1-hour intervals. Red indicates 1- to 4-hour arrival times, Yellow indicates 5- to 6-hour arrival times, Green indicates 7- to 14-hour arrival times, and Blue indicates 15- to 21-hour arrival times. Maps were generated from earthquake epicenters in the NGDC Global Historical Tsunami Database using NGDC 2-Minute Gridded Global Relief Data bathymetry. The map was created through models based on quality-controlled source data, and an integration of many data sets together.
Scale showing the size of the tsunami waves that hit Indonesia
Tsunami wave field in the Bay of Bengal one hour after the M=9.2 earthquake. View to the northwest.
Maximum recession of tsunami waters at Kata Noi Beach, Thailand, prior the third—and strongest—tsunami wave (sea visible in the right corner, the beach is at the extreme left), 10:25 am local time.
A two-story house damaged by the tsunami showing the tsunami inundation height in downtown Banda Aceh.
An overturned cement carrier, the Sinar Andalas caused by the tsunami in Lhoknga.
Fishermen's boat stranded in Kallady, Batticaloa, Sri Lanka.

Case study: Boxing Day Tsunami, 2004

On 26 December 2004 a tsunami occurred in the Indian Ocean. It was the result of the Indio-Australian Plate subducting below the Eurasian Plate. It was caused by an earthquake measuring more than magnitude 9. The earthquake caused the seafloor to uplift, displacing the seawater above.

  • In open ocean the tsunami measured less than 1 metre high.
  • The tsunami travelled at speeds up to 800km per hour.
  • When the Tsunami reached the shores, the height of the wave increased to 15 metres in some areas.

Main impacts

  • A quarter of a million people died.
  • Two million people were made homeless.
  • People were swept away in the waters, which arrived rapidly and with little warning.
  • Thirteen countries were affected, the worst being Indonesia.
  • Indonesia was hit by the tsunami first. Fourty-five minutes later the tsunami reached Thailand.
  • Mangrove swamps helped to act as a barrier to reduce the energy of the water in some areas.
  • Short-term aid, such as water purification tablets, temporary housing and medical supplies were given from international countries.
  • Islands reliant on tourism and fishing, such as the Maldives, had to rebuild their industries.
  • An early warning system between countries surrounding the Indian Ocean has been set up.

Now try a Test Bite.

Map of Indian Ocean tsunami 2004

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