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CRUSTAL MOTION ON SHANXI RIFT ZONE BEFORE AND AFTER WENCHUAN EARTHQUAKE

Based on the newly obtained GPS data and the “block loading” FEA method, the crustal movement of Shanxi rift zone within two time span (1999-2007, 2007-2009) , which before and after the Wenchuan earthquake are simulated, respectively. The results show that the stress and strain fields assume opproximately unifrom NW??SE extension before the earthquake. However, after the earthquake they are featured with remarkable compression accompanied with notable extension in the south region. Compared with 1999-2007, in 2007-2009 the maximum principal compressive and tensile stress increases 5-6 times and about 2 times,respectively, and from the north region to the south region of Shanxi rift zone, the direcion of the principal compressive stress changes from NW to NEE. Such stress and strain variation is verified by time??series of across??fault short level survey, long distance level survey and baseline of GPS continuous site. It indicates that the compressive and strike??slip displacement between Erdos block and North China Plain block increased after the Wenchuan earthquake. As a result, the crustal deformation and tectonic stress field of the Shanxi rift zone,which located in the boundary of the two blocks, change distinctly.