The great tsunami earthquake occurred on Sunday, 26 December 2004, at 00:58:50 UTC (6:58:50 a.m. local time). The epicenter was at 3.298°N, 95.779°E and its focal depth was very shallow (much less than 33 km - possibly about 10km) Land Topography and Relief Map of the Ocean Floor showing major fracture zones from tectonic plate interaction in relation to the epicenter of the 26 December 2004 earthquake The moment magnitude of the earthquake - which is larger than the Richter magnitude - was 9 (USGS NEIC (WDCS-D)).

This makes it the fourth largest earthquake in the world since 1900 and the largest since the 1964 Alaska earthquake. The quake was widely felt in Sumatra, the Nicobar and Andaman Islands, Malaysia, Myanmar, Singapore, Thailand, Bangladesh and India. As of 1 January, 2005, there were about 84 aftershocks with magnitudes ranging from 5.0 to 7.0 in the region of Northern Sumatra and the Nicobar and Andaman Islands. Twenty six (26) of these - including the largest- occurred on 26 December 2004, the same day as the main earthquake. Since 1 January 2005, many more aftershocks have occurred. The aftershocks are expected to continue for several weeks and months. Some of the major aftershocks have occurred near the epicenter of a past earthquake, which had occurred on 26 June 1941, and some in the area near the Nicobar Islands where the 1881 earthquake had occurred.