TSUNAMI FROM EARTHQUAKE

The undersea 2004 Indian Ocean earthquake occurred at 00:58:53 UTC (07:58:53 local time) on December 26, 2004, generating tsunamis that were among the deadliest disasters in modern history. At a magnitude of 9.0, it was the largest earthquake since the 9.2 magnitude Good Friday Earthquake off Alaska in 1964, and it tied for fourth largest since 1900. Originating in the Indian Ocean off the western coast of northern Sumatra, Indonesia, the tsunamis devastated the shores of Indonesia, Sri Lanka, India, Thailand, and other countries with waves of up to 15 m (50 feet) high, even reaching Somalia on the east coast of Africa, 4,500 km (2,800 miles) west of the epicenter.

At least 150,000 people are known to have died as a result of the tsunamis and the count is still taking place. The true final toll may never be known due to bodies swept out to sea, but it is likely to be higher than the current estimate. Relief agencies warn of the possibility of more deaths to come as a result of epidemics and starvation. The plight of the many affected people and countries prompted a widespread humanitarian response.

Quake characteristics

Locations of the initial earthquake and aftershocks.

The earthquake was initially reported as 6.8 on the Richter scale. On the moment magnitude scale, which is more accurate for quakes of this size, the earthquake's magnitude was first reported as 8.1 by the U.S. Geological Survey, but after further analysis the USGS increased this first to 8.5, 8.9, and finally to 9.0.

Since 1900, the only earthquakes recorded with a greater magnitude were the 1960 Great Chilean Earthquake (magnitude 9.5) and two Alaskan quakes: the 1964 Good Friday Earthquake in Prince William Sound (9.2) and a March 9, 1957 quake in the Andreanof Islands (9.1). The only other recorded earthquake of magnitude 9.0 was in 1952 off the southeast coast of Kamchatka. Each of these megathrust earthquakes also spawned tsunamis (in the Pacific Ocean), but the death toll from these was significantly lower — a few thousand for the worst one — probably because of the lower population density along the coasts near affected areas and the much greater distances to more populated coasts.

The hypocentre was at 3.316°N, 95.854°E, some 160 km (100 mi) west of Sumatra, at a depth of 30 km (18.6 mi) below mean sea level (initially reported as 10 km). This is at the extreme western end of the "Ring of Fire", an earthquake belt that accounts for 81% of the world's largest earthquakes. The quake itself (apart from the tsunamis) was felt as far away as Bangladesh, India, Malaysia, Myanmar, Singapore, Thailand and the Maldives.

The earthquake was unusually large in geographical extent. An estimated 1,200 km (750 mi) of faultline slipped 20 m (60 ft) along the subduction zone where the India Plate dives under the Burma Plate. The seabed of the Burma plate is estimated to have risen several metres vertically up over the India plate, creating shock waves in the Indian Ocean that traveled at up to 800 km/h (500 mi/h), forming tsunamis which, while less than a metre high in deep water, resulted in huge waves when they reached land.

The India Plate is part of the great Indo-Australian Plate, which underlies the Indian Ocean and Bay of Bengal, and is drifting northeast at an average of 6 cm/yr (2 in/yr) (or 20 m (60 ft) per 330 years; i.e. this earthquake moved this fault 330 years worth). The India Plate meets the Burma Plate (which is considered a portion of the great Eurasian Plate) at the Sunda Trench. At this point the India Plate subducts the Burma Plate which includes the Nicobar Islands, the Andaman Islands and northern Sumatra. The India Plate slips deeper and deeper beneath the Burma Plate until the increasing temperature and pressure turns the subducting edge of the India Plate into magma which eventually pushes the magma above it out through the volcanoes. This process is interrupted by the locking of the plates for several centuries until the build up of stress causes their release resulting in a massive earthquake and tsunami. The volcanic activity that results as the Indo-Australian plate subducts the Eurasian plate has created the Sunda Arc.

Aftershocks and other earthquakes

Numerous aftershocks were reported off the Andaman Islands, the Nicobar Islands, and the region of the original epicenter in the hours and days that followed. The largest aftershock was 7.1 off the Nicobar Islands. Other aftershocks of up to magnitude 6.6 continue to shake the region on a daily basis.

The 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 quakes happened on opposite sides of the Indo-Australian tectonic plate. However the USGS sees no evidence of a causal relationship.

Coincidentally, the earthquake struck almost exactly one year (to the hour) after a magnitude 6.6 earthquake killed an estimated 30,000 people in the city of Bam in Iran.

Power of the earthquake

The total energy released by the earthquake in the Indian Ocean has been estimated as 2.0 exajoules (2.0×10¹⁸ joules). Using the mass-energy equivalence formula E = mc², this amount of energy is equivalent to a mass of about 22 kg (49 lb). Note that each unit of the magnitude scale represents a 31.6-fold increase in energy; every two units signifies 1,000 times more energy.

The shift of mass and the massive release of energy very slightly altered the Earth's rotation. The exact amount is yet undetermined, but theoretical models suggest the earthquake may have shortened the length of a day by as much as three microseconds (3 µs) and caused the Earth to minutely "wobble" on its axis by up to 2.5 cm (1 inch). However, due to tidal effects of the Moon, the length of a day increases by 15 µs every year, so any rotational speedup due to the earthquake will be quickly lost. Similarly, the natural Chandler wobble of the Earth can be up to 15 m (50 ft).

Based on one seismic model, some of the smaller islands southwest of Sumatra may have moved southwest up to 20 m (66 ft). The northern tip of Sumatra, which is on the Burma Plate (the southern regions are on the Sunda Plate), may also have moved southwest up to 36 m (118 ft). Movement was likely both vertical as well as lateral. Measurements using GPS and satellite imagery are being used to determine the extent and nature of actual geophysical change.

Tsunami characteristics

The earthquake triggered massive tsunamis that struck the coasts of the Indian Ocean, the deadliest tsunamis by far in all of recorded history.

According to Tad Murty, vice-president of the Tsunami Society, the total energy of the tsunami waves was about five megatons of TNT (20 petajoules). 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.

Two radar satellites that happened to be overhead at the right moment recorded two wavefronts 500–850 km apart with a height of 50 cm. These are the first such observations ever made.

Because the 1,200 km of faultline affected by the quake was in a nearly north-south orientation, the greatest strength of the tsunami waves was in an east-west direction. Bangladesh, which lies at the northern end of the Bay of Bengal, had very few casualties despite being a low-lying country.

Coasts that have a land mass between them and the tsunamis' location of origin are usually safe; however, tsunami waves can sometimes diffract around such land masses. Thus, the Indian state of Kerala was hit by tsunamis despite being on the western coast of India, and the western coast of Sri Lanka also suffered substantial impacts. Also, distance alone is no guarantee of safety: Somalia was hit harder than Bangladesh despite being much farther away.

Due to the distances involved, the tsunamis took anywhere from fifteen minutes to seven hours (for Somalia) to reach the various coastlines. 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 two hours later. Thailand was also struck about two hours later, despite being closer to the epicenter, because the tsunami travelled more slowly in the shallow Andaman Sea off its western coast.

 Damage and casualties

 The death toll from the earthquake, the tsunamis and the resultant floods totals to over 175,000 people with tens of thousands reported missing, and over a million left homeless. Early news reports after the earthquake spoke of a toll only in the "hundreds", but the numbers rose steadily over the following week.

Relief agencies report that one-third of the dead appear to be children. This is a result of the high proportion of children in the populations of many of the affected regions and the fact that children were the least able to resist being overcome by the surging waters.

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, especially Scandinavians. The European nation hardest hit may have been Sweden.

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

Measured in lives lost, this is one of the ten worst earthquakes in history. It is also the single worst tsunami in history; the previous record was the 1703 tsunami at Awa, Japan that killed over 100,000 people.

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

Countries affected

The earthquakes and resulting tsunamis affected a large number of countries in Southeast Asia and beyond including Indonesia, Sri Lanka, India, Thailand, Myanmar, Malaysia, the Maldives and Somalia, including citizens of many other countries travelling in the region.

Casualties in historical context

The earthquake was the fourth most powerful recorded since 1900, and the confirmed death toll so far is 175,000, in large part due to the ensuing tsunami. The deadliest earthquakes since 1900 were the Tangshan, China earthquake of 1976, in which at least 255,000 were killed, the earthquake of 1927 in Xining, Qinghai, China (200,000), the Great Kanto earthquake which struck Tokyo in 1923 (143,000), and the Gansu, China earthquake of 1920 (200,000). The deadliest known earthquake in history occurred in 1556 in Shaanxi, China, with an estimated death toll of 830,000, though figures from this time period may not be reliable.

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

The 2004 earthquake and tsunamis seems to be the worst natural disaster since the 1970 Bhola cyclone (Bangladesh), which is estimated to have killed 500,000.

 Signs and warnings

Despite a lag of up to several hours between the earthquake and the impact of the tsunamis, nearly all of the victims were taken completely by surprise. This is because there is no tsunami warning system in the Indian Ocean to detect tsunamis, and equally importantly, warn the general populace living around the ocean quickly. Tsunami detection is not easy because while a tsunami is in deep water it has a very low 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.

Scientists were also hampered by the fact that the initial estimate for the magnitude of the earthquake was 8.1. The determination that the earthquake had actually been much stronger (and the chance of a significant resulting tsunami much larger) was not made until after the tsunamis had already struck.

Tsunamis usually occur in the Pacific Ocean due to 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 due to the rarity of tsunamis there — the last major one was caused by the Krakatoa eruption of 1883.

In the aftermath of the disaster there is a new awareness of the need for a tsunami warning system for the Indian Ocean. The UN aims to have a working East Asia and Southeast Asia early warning system within a year [26] (http://www.un.org/apps/news/story.asp?NewsID=12932&Cr=tsunami&Cr1=). Some have even proposed creating a unified global tsunami warning system, to include the Atlantic Ocean and Caribbean.

Unfamiliarity with warning signs

The first warning sign of a possible tsunami is the earthquake itself; however tsunamis can strike thousands of miles 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. People in Pacific regions are more familiar with tsunamis and often recognize this phenomenon as a sign to head for higher ground. However, 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 of exposed beach, with fatal results. 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 — before the tsunami struck. On Maikhao beach in northern Phuket, Thailand, a 10 year old British girl named Tilly Smith had studied tsunamis in geography class at school and recognised the warning sign of the receding ocean. She and her parents warned others on the beach, which was evacuated safely.

Human component in magnitude of damage

An article in The Wall Street Journal by Andrew Browne (December 31, 2004) commented that human destruction of coral reefs that had formerly protected coastal areas was a significant factor in the loss of life and damage in the area. The article pointed to The Surin Island chain off Thailand's coast as an example of protection afforded by the still intact reefs of the area. Only a small handful of people perished in the protected areas. Many other reef areas around the Indian Ocean had been dynamited because they were considered impediments to shipping. Other factors have been the removal of coastal dunes and coastal mangrove forests.

Post-tsunami humanitarian situation

A great deal of humanitarian aid is needed due to widespread damage of the infrastructure, shortages of food and water, and economic damage. The United Nations suggests that a further 150,000 at extreme risk of disease. Epidemics are of special concern, as they are likely due to the high population density and tropical climate of the affected areas. The overwhelming concern of humanitarian and government agencies is to provide sanitation facilities and fresh drinking water to contain the spread of diseases such as cholera, diphtheria, dysentery and typhoid.

Nations all over the world have so far provided over 3 billion U.S. dollars in aid for damaged regions, with the Australian federal government pledging $US 810 million, the German government offering $660 million, the Japanese government offering $500 million, the United States government offering $350 million, and the World Bank offering $250 million. Officials estimate that billions of dollars will be needed.

Coastal fishing communities and their fisherfolk, some of the poorest people in the region, have been the most devastated with high loss of life as well as boats and fishing gear.

Some economists believe that damage to the affected countries' economies will be minor because losses in the tourism and fishing industries are a relatively small percentage of the GDP. However, others caution that damage to infrastructure is an overriding factor. In some areas, drinking water supplies and farm fields may have been contaminated for years by salt water from the ocean. Significant effort is being spent in burying bodies hurriedly to prevent the spread of disease and acquiesce to tradition and religious concerns. Some, including the World Health Organization, would argue that the public health risk of these unburied bodies is in fact minimal and this tremendous effort would be better spent attending to the urgent needs of the living. There is also a concern that hasty mass burials may contaminate water supplies.