Abstract: Based on GNSS observation (from 1999 to 2007, and from 2009 to 2010) and continuous variation of deformation field, this study employed filtering and analysis of multi-kernel function and an unbiased algorithm of strain field to obtain movement and deformation field of the southeastern of Qinghai-Tibet Plateau before and after the M_S7.1 Yushu and M_S8.0 Wenchuan earthquakes. The observations showed: ① Tectonic activities of seismic source were significantly weakened at spatial and relative long time level before the Yushu and Wenchuan earthquake. The maximum positive strain and shear strain fell to the lowest level of regional tectonic activities. ② Spin shear deformation corresponding to the earthquake rupture was neither in nor far from the seismic source region, and there seemed an orderly coordinated action. The tectonic fault zone of Yushu earthquake was in the intermediate of regional right-lateral and left-lateral movements, while the largest stripe of left-lateral movement was 150 km away from the northeast of tectonic activity region, paralleling with the fault zone. Although structural fracture of Wenchuan earthquake was in the Longmen Mountain fault zone of right-lateral movement, the largest band of right-lateral movement was paralleled with this fault zone and in the northwestern activity zone with 200 km distance. ③ The range of large co-seismic horizontal deformation of the Yushu earthquake was actually small, while the post-seismic horizontal deformation of the Wenchuan earthquake remains significant. ④ The North and the surrounding of Litang-Dewu fault zone should be given more attentions because plane-strain was presented in the image of quadrant distribution, and both the maximum positive strain and maximum shear strain were showing sign of being locked.

Key words: Horizontal deformation field, GNSS, East margin of the Qinghai-Tibet Plateau, Yushu and Wenchuan earthquake