Abstract: In this paper, we analyze the crustal movements, strain field variations and large scale dynamic characteristics of horizontal movements before Wenchuan M_S8.0 earthquake, using GPS data obtained from the Crustal Movement Observation Network of China. In this process, some issues are discussed. First, the strain fields of Longmenshan fault zone which hosted the earthquake show slowly accumulating state, and the reason is the acting tectonic dynamics owing to the east movement of the Bayan Har block. Second, the differential movement between the Longmenshan fault and the South China block is within the errors of GPS observations. Third, the high value of compressive strain between 2004—2007 appeared at the epicenter area, which shows a stronger local squeezing action. Fourth, the data of GPS reference stations shows faster crustal shortening in the north-east direction, which is one of background of the increasing local tectonic dynamics in the Longmenshan fault zone.

Key words: Wenchuan M_S8.0 earthquake, GPS, Crustal movement, Strain field, Dynamic tectonic background