2004 Indian Ocean Earthquake

The 2004 Indian Ocean earthquake, known by the scientific community as the '''Sumatra-Andaman earthquake''', was an undersea in Modern History . The disaster is known in Asia and in the international media as the '''Asian Tsunami''', and also called the '''Boxing Day Tsunami''' in Australia , Canada , New Zealand , and the United Kingdom as it took place on Boxing Day .

The .'' Vol. 308, No. 5725, 1144-1146. May 20 , 2005 .

The earthquake originated in the Indian Ocean just north of Simeulue island, off the western coast of northern Sumatra , Indonesia . The resulting tsunami devastated the shores of Indonesia, Sri Lanka, South India , Thailand and other countries with waves up to 30 m (100 ft). It caused serious damage and deaths as far as the east coast of Africa , with the furthest recorded death due to the tsunami occurring at Port Elizabeth in South Africa , 8,000 km (5,000 mi) away from the Epicentre .

The plight of the many Affected People And Countries prompted a widespread Humanitarian Response . In all, the worldwide community donated more than US$7 billion in humanitarian aid to those affected by the earthquake.

EARTHQUAKE CHARACTERISTICS

of the earthquake, just north of Simeulue Island]]

The earthquake was initially reported as 9.0 on the .'' February 9 , 2005 . Although the Pacific Tsunami Warning Center has accepted these new numbers, the United States Geological Survey has so far not changed its original estimate of 9.0.

The Hypocentre of the main earthquake was at 3.316°N, 95.854°E (), approximately 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). The earthquake itself (apart from the tsunami) was felt 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 . The December 2004 earthquake just off the coast of Sumatra was actually a part of the Alpide belt.

Since 1900 the only earthquakes recorded with a greater magnitude were the 1960 .'' Each of these Megathrust Earthquake s 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 larger 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 ). These are all believed to have been of greater than magnitude 9, but no accurate measurements were available in those days.

Tectonic plates

caused by the earthquake.]]
The earthquake was unusually large in geographical extent. An estimated 1,200 km (750 mi) of , 2005 .

The India 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 cm/year (2 inches per year). The India Plate meets the Australasian 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 slips 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 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, the sea bed is estimated to have risen by several metres, displacing an estimated 30 km³ (7 cu mi) of water and triggering devastating .'' Vol. 308, No. 5725, 1126-1127. May 20 , 2005 .

Aftershocks and other earthquakes

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Numerous , 2005 . A debate arose among seismologists over whether the 2005 Sumatra Earthquake should be considered an aftershock of the December 2004 event or a "triggered earthquake" (an earthquake brought about by a previous earthquake),¹ as it was larger than typical aftershocks but on the same fault. 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 . 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 .²

An earthquake of magnitude 8.7 was reported shortly at 16:09:37 UTC (23:09:37 local time) on , 2005 .

Some scientists confirm that the December earthquake had activated .'' April 11 , 2005 .-->

Power of the earthquake

The total energy released by the 2004 Indian Ocean earthquake has been estimated as , 2004 . The entire Earth's surface is estimated to have moved vertically by up to 1 cm.

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 shortened the length of a day by 2.68 .'' December 29 , 2004 . 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 can be up to 15 M (50 ft).

More spectacularly, 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 souther regions are on the Sunda Plate , may have moved south-west by up to 20 m (66 ft), and some early estimates said up to 36 m (118 ft). However, more accurate data released, more than a month following the earthquake, present a more manageable figure of 20 cm (7.9 in).⁴ 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 sank by 1 m (3.28 ft).⁵

In February 2005 the .'' February 10 , 2005 .

By a beneficial and remarkable coincidence, the , 2004 tsunami in the Indian Ocean]. ''Aviso.'' Unlike data from Tide Gauge s 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 complex effects close to the coast. Inversion of this height data may help adjust the parameters for the source earthquake.

TSUNAMI CHARACTERISTICS

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.⁶

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 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.Paulson, Tom. " New findings super-size our tsunami threat ." ''Seattlepi.com.'' February 7 , 2005 .

.'' January 6 , 2005 .

According to .'' January 15 , 2005 .

Because the 1,200 km (745.6 mi) of faultline 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 epicentre. 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 Indian state of Kerala was hit by the tsunami 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.

Because of the distances involved, the tsunami took anywhere from fifteen minutes to seven hours (for 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 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.

Some of the tsunami's energy escaped into the , 2005 .

:See also: '' (3 MB ) to see exactly how and why some countries were more affected than others.''

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 System s in the Indian Ocean to detect tsunamis or to warn the general populace living around the ocean. 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, 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 this 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 March 28 , 2005 , a magnitude 8.7 earthquake hit roughly the same area of the Indian Ocean but did not result in a major tsunami.

In the aftermath of the disaster, there is now an awareness of the need for 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 .

Unfamiliarity with warning signs

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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 recognise 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 (1.6 mi) of exposed beach, with fatal results.Block, Melissa. " Sri Lankans Seek Lost Relatives After Tsunami ." '' All Things Considered / NPR .'' December 27 , 2004 .

One of the few coastal areas to evacuate ahead of the tsunami was on the Indonesian island of , 2005 . John Chroston , a biology teacher from Scotland, also recognised the signs at Kamala Bay north of Phuket, taking a busload of holidaymakers and locals to safety on higher ground.

Retreat and rise cycle

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 tsunamis continued to occur for the rest of the day.

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2004 Indian Ocean Earthquake