2004 Indian Ocean earthquake

The 2004 Indian Ocean earthquake, known by the scientific community as the Sumatra-Andaman earthquake, was an undersea earthquake that occurred at 00:58:53 UTC (07:58:53 local time) on December 26 2004. The tsunami generated by the earthquake killed approximately 275,000 people, making it one of the deadliest disasters in modern history. The disaster is also known as the Boxing Day Tsunami.

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 (Earthquakes and tsunamis, Lorca et al.).

Related Topics:
Tsunami - Indian Ocean

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

(large file, about 1 MiB) to see exactly how and why some countries were more affected than others

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 miles/h); in shallow water near coastlines, a tsunami slows down to only tens of kilometres an hour but in doing so forms large destructive waves http://www.prh.noaa.gov/itic/library/about_tsu/faqs.html#8. Scientists investigating the damage in Aceh found evidence that the wave reached a height of 80 feet (24 m) when coming ashore along large stretches of the coastline, rising to 100 feet (30 m) in some areas when travelling inland http://seattlepi.nwsource.com/local/211012_tsunamiscience07.html.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Radar satellites recorded the heights of tsunami waves in deep water: at two hours after the earthquake, the maximum height was 60 cm (2 ft). These are the first such observations ever made. However, these observations could not have been used to provide a warning, because the satellites were not intended for that purpose and the data took hours to analyze http://www.noaanews.noaa.gov/stories2005/s2365.htm http://www.newscientist.com/article.ns?id=dn6854.

Related Topics:
Radar - Cm - Ft

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 http://www.canada.com/montreal/montrealgazette/news/story.html?id=2257b78c-3897-4594-ad86-18c0eb661bea. In many places the waves reached as far as 2 km (1.24 mi) inland http://www.newscientist.com/channel/being-human/mg18524825.100.

Related Topics:
Tad Murty - Tsunami Society - Megaton - TNT - Peta - World War II - Atomic bomb - Orders of magnitude - Km - Mi

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 relatively near the epicenter. It also benefitted from the fact that the earthquake proceded more slowly in the northern rupture zone, greatly reducing the energy of the water displacements in that region. http://www.sciencemag.org/cgi/content/full/sci;308/5725/1126

Related Topics:
Bangladesh - Bay of Bengal

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Coasts that have a land mass between them and the tsunami's 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 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.

Related Topics:
Diffract - Kerala - India - Somalia - Bangladesh

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Because of the distances involved, the tsunami took anywhere from fifteen minutes to seven hours (for Somalia) to reach the various coastlines (see travel time maps: http://tsun.sscc.ru/tsulab/20041226trt.htm, http://staff.aist.go.jp/kenji.satake/Sumatra-E.html). The northern regions of the Indonesian island of Sumatra were hit very quickly, while Sri Lanka and the east coast of India were hit roughly 90 minutes to two hours later. Thailand was also struck about two hours later, despite being closer to the epicentre, because the tsunami travelled more slowly in the shallow Andaman Sea off its western coast.

Related Topics:
Somalia - Indonesia - Sumatra - Thailand - Andaman Sea

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The tsunami was noticed as far as Struisbaai in South Africa, some 8,500 km (5,300 miles) away, where a 1.5 m (5 feet) high ‘tide’ surged onshore about 16 hours after the quake. 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 http://www.iol.co.za/index.php?set_id=1&click_id=13&art_id=vn20041228044643745C770443.

Related Topics:
Struisbaai - South Africa

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 inches) http://wcatwc.arh.noaa.gov/IndianOSite/IndianO12-26-04.htm. At Manzanillo, Mexico, a 2.6 m (8.5 feet) crest-to-trough tsunami was measured. This puzzled many scientists, as the tsunamis measured in some parts of South America were larger than those measured in some parts of the Indian Ocean. It has been theorized that the tsunamis were focused and directed at long ranges by the mid-ocean ridges which run along the margins of the continental plates. http://www.livescience.com/forcesofnature/050825_tsunami_waves.html

Related Topics:
Pacific Ocean - Manzanillo - Mexico - Mid-ocean ridges

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 equally importantly, 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 http://www.newscientist.com/article.ns?id=dn6839, particularly in a relatively poor part of the world.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Scientists were also hampered by the incorrect initial estimates for the magnitude of the earthquake, which was originally put at 8.1. The determination that the earthquake had actually been much stronger (and the resulting tsunami much larger) was not made until after the tsunami had already struck.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Tsunamis are much more frequent 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. 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 quake hit roughly the same area of the Indian Ocean but did not result in a major tsunami.

Related Topics:
"Ring of Fire" - Krakatoa - 1883 - March 28

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

In the aftermath of the disaster there is now an awareness of the need for a tsunami warning system for the Indian Ocean. The UN has started working on an Indian Ocean Tsunami Warning System and aims to have initial steps in place by end 2005 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. See International Early Warning Programme.

Related Topics:
UN - Indian Ocean Tsunami Warning System - Atlantic Ocean - Caribbean - International Early Warning Programme

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

See also the 2004 Indian Ocean tsunami timeline, a minute to minute account by the National Oceanic and Atmospheric Administration (NOAA).

Related Topics:
2004 Indian Ocean tsunami timeline - National Oceanic and Atmospheric Administration - NOAA

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 (1.6 miles) of exposed beach, with fatal results http://www.npr.org/templates/story/story.php?storyId=4246573.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

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 http://www.timesonline.co.uk/article/0,,18690-1422835,00.html. 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 signs of the receding ocean and frothing bubbles. She and her parents warned others on the beach, which was evacuated safely http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2005/01/01/ugeog.xml&sSheet=/portal/2005/01/01/ixportaltop.html.

Related Topics:
Simeulue - 1907 - Phuket - Tilly Smith

~ ~ ~ ~ ~ ~ ~ ~ ~ ~