Thesis (M.Sc.)--Chulalongkorn University, 2008

The objective of this research is to study how Sudaland block, especially Thailand, deforms before and after the Sumatra-Andaman 2004 mega-earthquake by using GPS measurement and strain analysis. The studies used data, colleted between 1994 and 2006, from 6 regional GPS sites consisting of Phuket, Chumporn, Chonburi, Uthaithanee, Srisaket and Lampang in Thailand, and one GPS site from the northern part of Malaysia. During 1994-2004 before the mega-earthquake on the December 26, 2004, it was found that Thailand as the whole area had moved horizontally nearly at the same rate to the east with the average rate of approximately 33.2 ± 1.1 millimeters per year. The horizontal strain rate was found to be less than 30 nanostrain per year, which was not significant. However, this horizontal strain rate showed the similarity in pattern as the movement of Sagaing fault. After the mega-earthquake, it caused the change of horizontal movement in the direction to southwest at the different rates. It was also found that Thailand has the principal strain rate tensors as the extension type in the direction of northeast – southwest. The strain rate tensors were agreed with the movement of Sumatran trench. In addition, the results revealed that the Nias earthquake produced the same velocities and strain rates pattern as the mega-earthquake. This implies that the Nias earthquake is an aftershock of the mega-earthquake.