<P> The 2002 Sumatra earthquake is believed to have been a foreshock, predating the main event by over two years . </P> <P> The megathrust earthquake was unusually large in geographical and geological extent . An estimated 1,600 kilometres (1,000 mi) of fault surface slipped (or ruptured) about 15 metres (50 ft) along the subduction zone where the Indian Plate slides (or subducts) under the overriding Burma Plate . The slip did not happen instantaneously but took place in two phases over a period of several minutes: Seismographic and acoustic data indicate that the first phase involved a rupture about 400 kilometres (250 mi) long and 100 kilometres (60 mi) wide, located 30 kilometres (19 mi) beneath the sea bed--the largest rupture ever known to have been caused by an earthquake . The rupture proceeded at a speed of about 2.8 kilometres per second (1.7 miles per second) (10,000 km / h or 6,200 mph), beginning off the coast of Aceh and proceeding north - westerly over a period of about 100 seconds . A pause of about another 100 seconds took place before the rupture continued northwards towards the Andaman and Nicobar Islands . However, the northern rupture occurred more slowly than in the south, at about 2.1 km / s (1.3 mi / s) (7,500 km / h or 4,700 mph), continuing north for another five minutes to a plate boundary where the fault type changes from subduction to strike - slip (the two plates slide past one another in opposite directions). </P> <P> The Indian Plate is part of the great Indo - Australian Plate, which underlies the Indian Ocean and Bay of Bengal, and is drifting north - east at an average of 6 centimetres per year (2.4 inches per year). The India Plate meets the Burma Plate (which is considered a portion of the great Eurasian Plate) at the Sunda Trench . At this point the India Plate subducts beneath the Burma Plate, which carries the Nicobar Islands, the Andaman Islands, and northern Sumatra . The India Plate sinks deeper and deeper beneath the Burma Plate until the increasing temperature and pressure drive volatiles out of the subducting plate . 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 . The volcanic activity that results as the Indo - Australian Plate subducts the Eurasian Plate has created the Sunda Arc . </P> <P> As well as the sideways movement between the plates, the sea floor is estimated to have risen by several metres, displacing an estimated 30 cubic kilometres (7.2 cu mi) of water and triggering devastating tsunami waves . The waves did not originate from a point source, as was inaccurately depicted in some illustrations of their paths of travel, but rather radiated outwards along the entire 1,600 - kilometre (1,000 mi) length of the rupture (acting as a line source). This greatly increased the geographical area over which the waves were observed, reaching as far as Mexico, Chile, and the Arctic . 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). </P>

When did tsunami hit south and southeast asia in the recent past