Abstract: The northeastern Qinghai-Xizang Plateau is the most distant area of the uplift and deformation of the Qinghai-Xizang Plateau, with intense crustal deformation. The study of the crustal tectonic movement and deformation of this area is of great significance to understand its characteristics of tectonics and dynamic mechanism. In this study, the GNSS velocity field from 1991 to 2016 is collected, the multi-scale spherical wavelet method is used to calculate the strain rate tensors, and the spatial distribution characteristics of principal strain rate, surface strain rate and maximum shear strain rate are analyzed. The strain rates show that most areas in the northeast edge of the Qinghai-Xizang Plateau are characterized by slight surface compression, less than 15 nstrain/a. The areas with high surface compression rate are concentrated in the northeast edge of the Qinghai-Xizang Plateau, among which the surface compression in the Qilian Mountain Fault Zone and Haiyuan fault zone is greater than 20 nstrain/a. There are high shear strain rates in the eastern Kunlun fault zone, Qilian Mountain Fault Zone, Haiyuan fault zone and the southern section of Liupanshan fault zone, with a maximum of about 40 nstrain/a. The focal mechanism solutions from 1904 to 2021 on the northeast edge of the Qinghai-Xizang Plateau are also collected. The stress field in the region is obtained by the method of regional damping stress inversion. The direction of the maximum principal stress is basically consistent with the direction of the principal strain rate, showing that the area at the south of 35°N is featured by EW compression, and the area at the north of 35°N is characterized by NE compression. The study also classifies the studied area as normal, thrust and strike slip zones according to the dip angles of the maximum and minimum principal stress. It shows that most zones within the Qinghai-Xizang Plateau and the northern section of Liupanshan fault are characterized by strike slip, while the Qilian Mountain Fault zone, Haiyuan fault zone and the south of West Qinling fault zone present compressive thrust movement, coinciding with the areas of high value in surface compression. Comparing the directions of principal stress axes and principal strain rate axes, we find that the deformation of the upper and middle crust in the northeast margin of the Qinghai-Xizang Plateau is vertically coherent, while the directions of principal stress and principal strain rates in the areas around the Tarim Basin, Alxa block and South China block are pretty different, likely related to the weak zones in the crust and local surface structures. The intense deformation and strong seismicity in these areas are possibly ascribed to the northeastward expansion of the Qinghai-Xizang Plateau impeded by the relatively rigid the Alxa block, Ordos block and South China block.

Key words: Northeastern Qinghai-Xizang Plateau, Strain rate field, Stress field, Multiscale spherical wavelet, Inversion of regional damping stress