The 2004 Indian Ocean earthquake was an undersea earthquake that occurred at 00:58:53 UTC on December 26, 2004, with an epicentre off the west coast of Sumatra, Indonesia. It is known by the scientific community as the Great Sumatra-Andaman earthquake, and the following tsunami is known as the Asian Tsunami or the Boxing Day Tsunami.
(Animation of the tsunami caused by the earthquake showing how the tsunami radiated from the entire length of the 1,600 km (994 mi) rupture.)
The earthquake was caused by subduction and triggered a series of devastating tsunami along the coasts of most landmasses bordering the Indian Ocean, killing more than 225,000 people in eleven countries, and inundating coastal communities with waves up to 30 meters (100 feet) high. It was one of the deadliest natural disasters in history. Indonesia, Sri Lanka, India, and Thailand were hardest hit.
With a magnitude of between 9.1 and 9.3, it is the second largest earthquake ever recorded on a seismograph. This earthquake had the longest duration of faulting ever observed, between 8.3 and 10 minutes. It caused the entire planet to vibrate as much as 1 cm (0.5 inches)and triggered other earthquakes as far away as Alaska.
The earthquake was initially reported as moment magnitude 9.0. In February 2005 scientists revised the estimate of the magnitude to 9.3. Although the Pacific Tsunami Warning Center has accepted these new numbers, the United States Geological Survey has so far not changed its estimate of 9.1. The most recent studies in 2006 have obtained a magnitude of Mw 9.1 to 9.3. Dr. Hiroo Kanamori of the California Institute of Technology believes that Mw = 9.2 is a good representative value for the size of this great earthquake.
The hypocenter of the main earthquake was at 3°18′58″N 95°51′14″E / 3.316, 95.854, approximately 160 km (100 mi), in the Indian Ocean just north of Simeulue Island, off the western coast of northern Sumatra, at a depth of 30 km (19 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.