On 26 December 2004, a magnitude 9.1 megathrust earthquake ruptured off the west coast of northern Sumatra, along the boundary between the India and Burma plates. The fault slipped over a length of roughly 1,300 kilometres, making it one of the longest ruptures ever documented and the shaking lasted for several minutes. It was among the three most powerful earthquakes recorded since modern instruments existed.
The sudden vertical displacement of the seafloor launched a series of tsunami waves across the entire Indian Ocean. The waves struck coastlines in Indonesia, Sri Lanka, India, Thailand and as far away as East Africa, catching millions of people with no warning system in place. Around 228,000 people were killed across fourteen countries, making it one of the deadliest natural disasters in recorded history.
The Indonesian province of Aceh, closest to the epicentre, suffered the greatest loss of life, with entire coastal communities obliterated. The catastrophe exposed the total absence of a tsunami warning network in the Indian Ocean and led directly to the creation of one. It also triggered one of the largest humanitarian relief efforts ever mounted.
The disaster led directly to the creation of the Indian Ocean Tsunami Warning System, launched in 2006 with dozens of seismic stations and deep-ocean buoys feeding data to national warning centres. The quake released so much energy that it measurably shortened the length of Earth's day by a few microseconds and slightly shifted the planet's mass distribution. Every 26 December, Indonesia, Thailand, Sri Lanka and other affected nations still hold memorial services for the estimated 228,000 victims.
NOAA's National Centers for Environmental Information (NCEI) lists the 2004 Indian Ocean tsunami as the deadliest event in its global historical tsunami database, with field surveys confirming runup heights exceeding 30 metres at points on Sumatra's western coast. Tide-gauge and DART deep-ocean buoy records from the event directly shaped the design of the Indian Ocean Tsunami Warning System launched in 2006, and NCEI's Significant Earthquake Database ranks the roughly 1,300 km rupture length among the longest ever recorded for a single earthquake anywhere on Earth.