GPS analyses of the Sumatra-Andaman earthquake



The Sumatra, Indonesia, earthquake on 26 December 2004 was one of the most devastating earthquakes in history. With a magnitude of Mw = 9.3 (revised based on normal-mode amplitudes by Stein and Okal,, it is the second largest earthquake recorded since 1900. It occurred about 100 km off the west coast of northern Sumatra, where the relatively dense Indo-Australian plate moves beneath the lighter Burma plate, resulting in stress accumulation.

The average relative velocity of the two plates is about 6 cm/yr. On 26 December 2004, however, the two plates moved by a distance of several meters, releasing the stress accumulated over hundreds of years. The result was a devastating tsunami that hit coastlines across the Indian Ocean, killing about 300,000 people in Indonesia, Sri Lanka, India, Thailand, Burma, Malaysia, Somalia, and other countries (Guardian, 29 January 2005,,15671,1380895,00.html).