The 2004 Sumatra quake ruptured a record 1,300 km of fault for ten minutes
On 26 December 2004 a magnitude 9.2–9.3 megathrust earthquake struck off Aceh in northern Sumatra. Its fault tore for at least ten minutes along more than a thousand kilometres, and the tsunami it launched, up to 30 metres high, killed an estimated 227,898 people in 14 countries around the Indian Ocean.
Scientists call it the Sumatra–Andaman earthquake. It began at 07:58 local time about 160 km off Sumatra’s west coast, just north of Simeulue island, some 30 km below the sea, where the Indian plate dives beneath the Burma plate at the Sunda Trench. The Indian plate creeps north-east at about 60 millimetres a year, and in the quake roughly 1,600 km of fault slipped about 15 metres in two phases over several minutes. The 2002 Sumatra earthquake is thought to have been a foreshock.
Its size was first put at 8.8. The US Geological Survey officially lists 9.1, while most later studies, including Hiroo Kanamori’s estimate of 9.2, place it at 9.2 to 9.3. That makes it the strongest quake recorded in Asia and in the 21st century, and the second or third strongest since 1900, behind Chile in 1960 at 9.5 and possibly Alaska in 1964 at 9.2. The rupture, 1,200 to 1,300 km long, and the duration of faulting are both the longest ever observed. It alone released about an eighth of all seismic moment from 1906 to 2005.
The seafloor rose by several metres, shoving aside about 30 cubic kilometres of water. Because the whole rupture acted as a line source, waves were detected as far as Mexico, Chile and the Arctic, and the worst damage fell on Aceh, Sri Lanka, Tamil Nadu and Khao Lak in Thailand.
The planet itself rang. The ground surface swayed by up to 200–300 millimetres, Oklahoma recorded vertical movement of 3 millimetres, and faint oscillations were still measurable in February 2005. Aftershocks up to magnitude 7.2 continued for months, and the separate magnitude 8.6 Nias–Simeulue quake of 2005 was probably triggered by the stress changes.
Source: 2004 Indian Ocean earthquake and tsunami
