Updated 3/20/2005 At 9.0 Magnitude, this was the largest earthquake in the world since the 1964 Alaskan quake. It struck on December 26 at 6:58 AM local time (00:58 GMT). The epicenter was 255 km (160 miles) SSE of Banda Aceh, Sumatra, Indonesia 315 km (195 miles) W of Medan, Sumatra, Indonesia 1260 km (790 miles) SSW of BANGKOK, Thailand 1590 km (990 miles) NW of JAKARTA, Java, Indonesia.
Casualties have been very high, with over 283,000 dead, especially from the tsunami generated by the earthquake. The tsunami, reported as 15 - 20 feet high, fanned out over the Indian Ocean causing severe and sudden flooding in Sri Lanka, India, Thailand, Indonesia and other areas. Over a million people have been reported as homeless in Sri Lanka alone, at least 5 million were left without the basic necessities of life. Over 100,000 are reported dead in Indonesia. This tsunami was one of the largest ever in terms of casualties because it hit in heavily populated low lying coastal areas that were not well prepared. The lack of a warning system meant that most people were caught by surprise. It has been a long time since there has been a tsunami in this region. Unlike the Pacific Ocean, which has a well developed warning system, the Indian Ocean has no way to warn of an impending tsunami. Scientists knew as soon as the quake happened that it posed a danger of tsunami, but there was no way to get the word to the coastal areas in time. There were only a few minutes to a couple of hours between the quake and the tsunami. Communications were not up to the task.
The scope of this disaster is well beyond what is normal for even a strong earthquake. The tsunami hit 14 different countries, with severe damage in four (Indonesia, Thailand, India and Sri Lanka), spread out over thousands of miles. India reported that they had sufficient resources to provide needed aid in their own country and send some to Sri Lanka as well. Sri Lanka has a long coastline that suffered badly needs assistance, but with the interior undamaged can mobilize fairly well to receive and distribute aid. Indonesia is much worse off. They have to cope with quake damage and tsunami damage, as well as a less well developed infrastructure that make communications and travel difficult. There are shortages of petrol and machinery, such as forklifts that would make the relief effort easier.
People reported seeing the ocean pull back, exposing the sea floor and then return as a swift rise in the sea level, like an extremely high tide, inundating villages near the coast. The wave then pulled back, sucking houses, trees, people...everything in its path out to sea. These waves have a long period, so there are many minutes until the next wave hits. The process is similar to the ripples formed when a stone is thrown into water. Each successive wave carries more debris, causing more damage. The zone of damage extends up to 2 miles inland along the entire coast. Most buildings in this zone are severly damaged or destroyed, with a thick layer of mud covering everything. Food, water, electricity, and housing are all non existant or in short supply.
The area of the quake itself in Aceh province has seen severe damage from the earthquake and from the tsunami in coastal areas. Reports suggest that there may be over 100,000 dead in Sumatra alone. There have been reports of many buildings destroyed. Large amounts of international aid were desparately needed and relief supplies were sent from throughout the world. Some of the most severely affected areas did not receive any aid for a week after the disaster due to the huge need and difficulty of reaching remote areas. Observers repeatedly reported that the scope of the disaster was unbelievable, with almost complete destruction along hundreds of miles of coastal areas.
There have been many powerful aftershocks along the whole 745 mile fault that was affected, notably in the Andaman and Nicobar islands. Three months after the initial quake, aftershocks over magnitude 5 occur every few days along the fault line.
Both Aceh province and parts of Sri Lanka have been embroiled in civil wars that have slowed the flow of information and may hinder the distribution of government aid in contested or rebel held areas. Aceh has been under military control with very little access for foreigners. An independece movement has been fighting the Indonesian government for several years. Portions of Sri Lanka that were hard hit are under the control of Tamil rebels, in a war that has lasted for many years.
The scope of the disaster made it difficult to even bury the dead. Most have been buried in mass graves, although efforts were made to photograph the dead with photos and in places take DNA samples. It is hoped that these will help relatives identify victims. The World Health Organization has warned of danger of disease outbreaks that could kill thousands more. They say that dead bodies do not pose a threat, although they are unpleasant, but contaminated water supplies do. There have already been reports of outbreaks of diarhea, but the main danger is in the next few weeks. Water supplies within the affected areas have all been contaminated. Sanitation was already precarious in some of these areas. Now they have nothing. Clean water is high on the priority list for aid. Hundreds of millions of dollars of aid have been pledged from many countries around the world. Naval vessels are on the way to help but took several days to arrive. Because of the huge area involved and the limited communications available, it took days to even get reports from many areas, especially in Indonesia.
This explanation of the quake from the BBC:
How the Quake unfolded (BBC 12/27/04)
According to the USGS "The devastating megathrust earthquake of December 26th, 2004 occurred on the interface of the India and Burma plates and was caused by the release of stresses that develop as the India plate subducts beneath the overriding Burma plate. The India plate begins its descent into the mantle at the Sunda trench which lies to the west of the earthquake's epicenter. The trench is the surface expression of the plate interface between the Australia and India plates, situated to the southwest of the trench, and the Burma and Sunda plates, situated to the northeast." The interactions of these plates, along with the Indian Plate, the Pacific Plate and the Phillipines Plate, make this one of the most seismiscally and volcanically active regions of the world. Subduction earthquakes are the largest known. The 1964 Alaskan quake and the 9.5 Magnitude Chilean quake of 1960 were both subduction quakes.
In this case the subducting plate is being forced down into the earth under an overriding plate. Heat rising as the plate hits the earth's mantle and melts rises to form a volcanic island chain - Indonesia. Since the descending plate is fairly rigid and flat, when the magma rises, it creates an arc of volcanic islands on the curved surface of the Earth, which shows the direction of the plate movement nicely. The Aleutian Islands are another nice example of this process.
(See the Plate Tectonics page for more information on these processes.)
A tsumani, or tidal wave, occurs when an earthquake displaces a portion of the seafloor. In this case, according to USA Today, a section of seafloor 745 miles long was raised 100 feet by the quake. This sudden movement displaced a massive amount of water, which fanned out from the epicenter. This wave moved at 500 miles an hour across the Bay of Bengal, the Indian Ocean and the Pacific Ocean. If you look at a map of the region you will see that the areas hardest hit were across the Bay of Bengal from the epicenter at the Western edge of Indonesia.
See also the following news stories:
Also destroyed was the Citadel,Arg-e-Bam, mostly dating from the Safavid period in the 16th and 17th C. This was a major historic structure, parts of which date back 2,000 years. As the largest mud brick structure in the world, and a major historic site, it was on the Unesco's list of World Heritage Sites. Bam is on major trade routes to India and the far east, as well as being an oasis in the desert has given it a special importance. The Citadel was a major tourist attraction, the loss of which will be devastating to the nation's cultural heritage and the local economy. Authorities say that it will be reconstructed, but that, of course, is far from the same as having the original.