All of them are believed to be greater than magnitude 9, but no accurate measurements were available at the time.
The undersea megathrust earthquake was caused when the Indian Plate was subducted by the Burma Plate and triggered a series of devastating tsunamis along the coasts of most landmasses bordering the Indian Ocean, killing 230,000–280,000 people in 14 countries, and inundating coastal communities with waves up to 30 metres (100 ft) high.
It was one of the deadliest natural disasters in recorded history.
These volatiles rise into the overlying plate causing partial melting and the formation of magma.
The rising magma intrudes into the crust above and exits the Earth's crust through volcanoes in the form of a volcanic arc.
Great earthquakes such as the Sumatra-Andaman event, which are invariably associated with megathrust events in subduction zones, have seismic moments that can account for a significant fraction of the global earthquake moment across century-scale time periods.
Of all the seismic moment released by earthquakes in the 100 years from 1906 through 2005, roughly one-eighth was due to the Sumatra-Andaman event.The 2004 Indian Ocean earthquake occurred at UTC on 26 December with the epicentre off the west coast of Sumatra, Indonesia.The shock had a moment magnitude of 9.1–9.3 and a maximum Mercalli intensity of IX (Violent).The raising of the sea floor significantly reduced the capacity of the Indian Ocean, producing a permanent rise in the global sea level by an estimated 0.1 millimetres (0.004 in).Locations of initial earthquake and all aftershocks measuring greater than 4.0 from 26 December 2004 to 10 January 2005.The megathrust earthquake was unusually large in geographical and geological extent.