On 26 December 2004, at 07:58:53 local time (UTC+7), a major earthquake with a magnitude of 9.1–9.3 M_w struck with an epicentre off the west coast of northern Sumatra, Indonesia. The undersea megathrust earthquake, known by the scientific community as the Sumatra–Andaman earthquake, was caused by a rupture along the fault between the Burma Plate and the Indian Plate, and reached a Mercalli intensity up to IX in some areas.

A massive tsunami with waves up to 30 m (100 ft) high, known in some countries as the Boxing Day Tsunami after the Boxing Day holiday, devastated communities along the surrounding coasts of the Indian Ocean, killing an estimated 227,898 people in 14 countries in one of the deadliest natural disasters in recorded history. The direct results caused major disruptions to living conditions and commerce in coastal provinces of surrounded countries, including Aceh (Indonesia), Sri Lanka, Tamil Nadu (India) and Khao Lak (Thailand). Banda Aceh reported the largest number of deaths.

The earthquake was the third-largest ever recorded based upon seismographic measurements, the largest in the 21st century and had the longest duration of faulting ever observed, between eight and ten minutes. It caused the planet to vibrate as much as 10 mm (0.4 in), and also remotely triggered earthquakes as far away as Alaska. Its epicentre was between Simeulue and mainland Sumatra. The plight of the affected people and countries prompted a worldwide humanitarian response, with donations totalling more than US$14 billion.