A great earthquake occurred at 00:58:50 (UTC), at 6:58 a.m. local time, on Sunday, 26 December 2004. The magnitude 9.0 event was located off the West cosat of Northern Sumatra. This is the fourth largest earthquake in the world since 1900 and is the largest since the 1964 Prince William Sound, Alaska earthquake. The earthquake had a depth of 10 km.
The earthquake triggered massive tsunamis (soo-NAH-mee) that affected several countries throughout South and Southeast Asia. The tsunami crossed into the Pacific Ocean and was recorded along the west coast of South and North America. Tsunamis also occurred on the coasts of Cocos Island, Kenya, Mauritius, Reunion and Seychelles. The earthquake was felt (VIII) at Banda Aceh and (V) at Medan, Sumatra. It was also felt in Bangladesh, India, Malaysia, Maldives, Myanmar, Singapore, Sri Lanka and Thailand.
Relief agencies struggled to rush aid to more than 3 million people in Asia and Africa after Sunday's disastrous earthquake and tsunami waves. Casualty figures rose dramatically as rescue workers found the remains of entire villages in Indonesia, the nation worst hit, accounting for more than half of the casualties.
By 30 December 2004 the death toll from the Asian tsunami disaster had risen to over 100,000 people, and by 05 January 2005 the number approached 150,000.
In Sri Lanka, the southeastern coastline was the worst-hit. In this densely populated area many villages along the ocean were washed off the map. Galle was a scene of total catastrophe. Almost the entire seafront was obliterated, with no buildings within 100 meters of the waterfront escaping undamaged.
In India the Andaman Islands, Nicobar Islands, Kerala, Tamil Nadu, Chennai, Andhra Pradesh were all affected.
With half of the casualties being reported from Sumatra, Indonesia-the region nearest to the earthquake's epicenter-international relief organization officials warn that the overall casualty figures could rise to over 100,000. The death toll in Indonesia's Aceh province from a quake and tsunami that struck on Sunday might reach between 50,000 and 80,000. There were about 10,000 deaths in Meulaboh, the south-coast town nearest to the epicenter. Surveillance from flights over the town indicated it had been "wiped out", with up to 80 per cent of buildings destroyed, raising fears for the fate of the area's 100,000 residents.
In Thailand, this caused great loss of life and destruction to buildings and infrastructure in the popular resort areas of Phuket, Phi Phi Island, Krabi, and other smaller islands in that vicinity. Along the eastern coast of Phuket island, waves crashed over Rassada Pier as passengers were waiting to board ferries for Phi Phi Island. The Laguna Phuket was protected from a direct hit by the headland to its South and thus spared the serious damage reported from other areas of the island. Other areas affected included Bang Tao Beach, Kamala Beach, Patong Beach, Kata Beach, Karon Beach, Nai Harn Beach and Phuket Fantasea. There was total destruction of resort properties and infrastructure on the Phi Phi islands, and all operations had ceased. Phuket's Patong beach along the west of the island took the bulk of the damage, and two-thirds of Thailand's fatalities occurred there.
The Maldives's only international airport on the tiny island of Hululle reopened early on 27 December, after workers pumped out water that had inundated the runway. The entire island of Dhiffushi, a prime tourist destination, was submerged and would have to be rebuilt.
In Myanmar damage was reported only in the southern archipelago, with minimal to no impact reported at Ngapali, Chauntha, and Ngwe Saung beaches.
Praslin Island in Seychelles was also hit.
In April 2005 The number of people killed in the December 26 tsunami disaster which devastated 11 Indian Ocean countries has been revised down to 217,000 after Indonesia drastically reduced its number of missing. Indonesia remains the worst hit country, with 163,978 people dead or missing. According to the National Disaster Relief Coordination Agency, the number confirmed dead was 126,915 people while 37,063 were listed as missing. Officials said the figure had been reduced because many people listed as missing had now been identified among more than half a million homeless people living in temporary camps or other shelters. The toll in Sri Lanka, which was second hardest hit by the catastrophe, was 30,957, according to the Center for National Operations. The number of people listed as missing was 5,637, but many were expected to be among those never formally identified, hurriedly buried and included in the confirmed death toll.
Some energy from the tsunami in the Indian Ocean leaked into the Pacific basin, probably from south of the Australian continent. This energy produced minor sea level fluctuations at many places in the pacific. However, at Manzanillo, Mexico, sea level fluctuations were as much as 2.6 meters crest-to-trough probably due to focusing of energy by the East Pacific rise as well as local resonances.
The Indonesian region is one of the most seismically active zones of the earth; at the same time it has a leading position from the point of view of active and potentially active volcanoes. It is a typical island-arc structure with its characteristic physiographic features, such as a deep oceanic trench, a geanticline belt, a volcanic inner arc and a marginal basin.
The devastating megathrust earthquake of December 26, 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.
In the region of the earthquake, the India plate moves toward the northeast at a rate of about 6 cm/year relative to the Burma plate. This results in oblique convergence at the Sunda trench. The oblique motion is partitioned into thrust-faulting, which occurs on the plate-interface and which involves slip directed perpendicular to the trench, and strike-slip faulting, which occurs several hundred kilometers to the east of the trench and involves slip directed parallel to the trench. The December 26 earthquake occurred as the result of thrust-faulting.
The earthquake was followed by at least eight severe aftershocks. The aftershocks took place in three phases, starting in the south and moving north along a 750-mile line. Aftershocks were distributed along much of the shallow plate interface and primarily extended northwards of the epicenter to the Andaman Islands.
Preliminary locations of larger aftershocks following the megathrust earthquake show that approximately 1200 km of the plate boundary slipped as a result of the earthquake. By comparison with other large megathrust earthquakes, the width of the causative fault-rupture was likely over one-hundred km. From the size of the earthquake, it is likely that the average displacement on the fault plane was about fifteen meters. The sea floor overlying the thrust fault would have been uplifted by several meters as a result of the earthquake.
While affected countries rush to bury mass numbers of decomposing bodies amidst hot weather conditions, fears that disease outbreaks could unleash a second wave of tragedy increase as aid workers attempt to supply clean water/sanitation. With the focus turning from rescuing to caring for millions of homeless (mainly in hardest-hit Sri Lanka, Indonesia, and India), international aid agencies are faced with the obstacles of coordinating and assessing such a massive and unprecedented humanitarian relief effort. Furthermore, as relief operations continue, the possibility of anti-foreign resistance (i.e. Sri Lanka) especially in rebel occupied areas may prevent the delivery of aid and assistance. As the extent of damage and appeals are examined, expect increases in international donations.
Scientists knew in advance that southern Asia was going to be hit by a tsunami, but attempts to raise the alarm were hampered by the absence of early-warning systems in the region. Within 15 minutes of Sunday's earthquake, the Pacific Tsunami Warning Centre in Hawaii had sent an alert to 26 countries, including Thailand and Indonesia, but struggled to reach the right people. Television and radio alerts were not issued in Thailand until 9am local time - nearly an hour after the waves had hit.
A locally generated tsunami may reach a nearby shore in less than ten minutes. There is not sufficient time for the Pacific Tsunami Warning Center or for local authorities to issue a warning. For people living near the coast, the shaking of the ground is a warning that a tsunami may be imminent.