Coseismic and postseismic creep in the Andaman Islands associated with the 2004 Sumatra‐Andaman earthquake

Two field campaigns (March 2005 and March 2006) for measurements of biological indicators and eyewitness accounts confirm that large coseismic and postseismic surface deformation occurred over the Andaman Islands in association with the 2004 Sumatra‐Andaman earthquake. Amount of uplift was as large as 1.3 m in the islands off NW coast, and decreased to ESE with a zone of subsidence in the SE Andaman. The coseismic deformation did not generate large seismic waves or tsunamis, indicating that slip was much slower than that off Sumatra. The coseismic uplift was followed by postseismic subsidence, which was evidenced by local residents to have occurred within two months after the earthquake. A simple dislocation model explains the deformation pattern by a coseismic rupture (50 km wide with its down‐dip limit 130 km east of the trench axis) followed by an up‐dip propagation of the rupture front for about 10 km.