The Sumatra-Andaman earthquake completely changed the crustal motion pattern in Thailand, in both the horizontal and vertical directions. GPS data from campaigns and fixed (continuous) sites in Indonesia, Malaysia and Thailand show that the Sundaland block, on which all tidal stations in Thailand are situated, was considerably deformed (Vigny et al., 2005). Horizontally, the direction of motion changed abruptly from mainly eastward (~30 mm/yr) towards the earthquake epicentre in the southwest. Small,
but significant, coseismic jumps between 5 and 10 mm were detected even at stations
more than 3000 km away from the earthquake epicentre. In the vertical direction, ground displacements in the near field (close to the earthquake epicentre), determined from various techniques, show a characteristic pattern: a region of (co-seismic) uplift near the Sumatra trench and a region of subsidence away from it (Subarya et al., 2006).
Evidence of 1500 mm uplift near the epicentre of the earthquake was shown in Sieh (2005) in the form of emerged coral reefs. In the far field the elastic dislocation slip model (Meltzner et al., 2006) predicts co-seismic subsidence that decreases when moving further away from the Sumatra trench, where the earthquake epicentre is located.