The 2004 Indian Ocean earthquake was a megathrust earthquake that occurred underneath the ocean floor. The earthquake occurred sortly after christmas at 00:58:53 UTC on Sunday, 26 December 2004, with an epicenter off the west coast of Sumatra, Indonesia. The quake itself is known by the scientific community as the Sumatra–Andaman earthquake and the tsunami has various names, including the 2004 Indian Ocean tsunami, South Asian tsunami, Indonesian tsunami, and the Boxing Day tsunami. The earthquake was caused by subduction and triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing over 230,000 people in fourteen countries, and inundating coastal communities with waves up to 30 meters or 98 ft. high. It was one of the deadliest natural disasters in recorded history. Indonesia was the hardest-hit country, followed by Sri Lanka, India, and Thailand.

The megathrust earthquake was unusually large in geographical and geological extent. An estimated 1,600 kilometres of fault surface slipped (or ruptured) about 15 metres along the subduction zone where the India Plate slides under the overriding Burma Plate. The slip did not happen instantaneously but took place in two phases over a period of several minutes.

First the seismographic and acoustic data indicate that the first phase involved a rupture about 400 kilometres long and 100 kilometres wide, located 30 kilometers beneath the sea bed—the largest rupture ever known to have been caused by an earthquake. The rupture proceeded at a speed of about 2.8 kilometres per second beginning off the coast of Acehand proceeding north-westerly over a period of about 100 seconds.

Second a pause of about another 100 seconds took place before the rupture continued northwards towards the Andaman and Nicobar Islands. However, the northern rupture occurred more