The Crustal Deformation Pattern In China Inferred From Global Positionging System Measuremants

China continent is characterized by considerable intraplate deformation that is witnessed by widespread earthquakes, arisen from the continental collision between Eurasia and Indian plates and interactions among sub-plates. A quantitative description, with suitable resolution and precision, of tectonic kinematics is a prerequisite for qualitative understanding of physical properties of continental lithosphere and its dynamic aspects which control the continent deformation, which are of critical to reveal earthquake mechanism and forecast earthquake. In the last decade, kinematic demonstration of continent deformation at a large scale of 2-3 thousands of kilometers in Asia was mainly rooted in the observations of Quaternary active faulting and a summation of one-century long seismic moment tensors. Because of the limited amount geologic works in critical areas such as Tibet and rather shorter catalog of historic earthquakes available for inversion, the derived velocity field depicting the ongoing crustal movement was poorly constrained.And any attempt to improve its precision and resolution in relative short period is hampered by many limiting factors that remains nowadays. To the contrary, Global Positioning System (GPS) measurement, with its outstanding merits such as high precision, low expense, dense distribution and flexible survey mode revolutionizes monitoring of the crustal movement at all scales ranging from global plate motion for several thousands of kilometers to local fault slip within several kilometers. From 1990s, the GPS data have been accumulating progressively in China. As yet, a unified measurement of crustal deformation velocity field for the Chinese mainland has been available, based on the sophisticated analysis of these data. With that, tectonic deformation velocity field and its gradient field are inferred through fitting to the GPS-derived velocity data. This work advances the former studies by matching directly over 1000 GPS velocities with a continuous horizontal velocity field for the entire China using the method assumed that continental deformation is distributed continuously.The instantaneous active deformation in Asia was approximated numerically by various methods such as f crustal flow and rigid blocks. The tenet of these methods is attributed to assumptions describing the kinematic behavior of crust deformation as continuum flow or block-like motion. Although active faults which delineate generally boundaries of rigid blocks in Asia are distributed over the Tibet and its adjacent regions with moderate and major faulting, A school of thoughts suggested that the kinematics of crust deformation is analogous to response of a thin viscous sheet drived by gravitational potentional difference, therefore it can be treated as continuous viscous medium. Base on this, this study applies Bi-cubic Spline interpolation function on the earth sphere to best matching GPS site velocities in order to recovery a unified crustal deformation field.This paper summarizes the tectonic movement and dynamics background in China, and firstly simulates the contemporary horizontal velocity and strain rate fields (~1200 velocity vectors) in China, assuming that the crust can be treated as a continuum, the velocity field inferred from the GPS rates has an overall precision better than 2 mm/yr. Secondly, on the basis of block-like model on framework of active tectonics in China continent, two kinds of block-like kinematic model to fit the GPS velocity field are investigated . The GPS vectors are inverted simultaneously for the rotation and fault locking . the slip rates of the major faults are inferred. and motion velocity and Euler rotation poles are calculated for each block of which the internal strain rate are assessed too.Our modeling demonstrates that:(1) The collision between India and Eurasia plate is the main driving force which controls horizontal component of crustal deformation in most of China continent;(2) The velocity field and direction of principal stress axis have a clockwise rotation of about 180°around the Eastern Himalaya Syntaxis. The rotation shows that the stress field in southeast China is mainly influenced by the combined forces transferred from plate boundaries to east and southwest;(3) The Pacific and Philippine Sea plates are important factors modulating the stress field of the eastern China;(4) The extrusion rate toward N13.5°E direction increases from south to north, and reaches to the maximum along the Mani-Yushu-Ganzi-Litang, which suggests there exists an eastward crust flow, bounded to the north, by the Mani-Yushu-Ganzi-Litang zone. The eastward extrusion doesn't extend beyond the east boundary of the Tibetan Plateau. The eastward extrusion is translated into a clockwise rotation around the Eastern Himalaya Syntaxis;(5) In the velocity field, a large fraction, ~90 %, of India's convergence with Eurasia is absorbed by crust thickening, especially the north-south shortening across the Himalaya. The Tibetan plateau is subject to widespread E-W extension at a rate up to 16mm/yr;(6) localized deformation is concentrated on the Altyn Tagh faul associated with 5.8±1.5mm/yr of left-lateral strike-slip, and N-S compression of 6.5±2.0mm/yr is founded to occur within a zone between Qilian Shan and Alashan. The convergent rate is estimated to 19.0 +/-2.0mm/yr across Himalaya and south Tibet, 14.0±1.1 mm/yr in the western Tien Shan, and 7.9±1.2 mm/yr on central segment of Tien Shan;(7) India rotates relative to Eurasia about a pole at (27.9°N 19.6°E 0.395°/Ma), south of China moves at 8.0±1.5 mm/yr in the direction of N120°±7.4°E, corresponding to a pole at 63.38°N,159.87°W,0.088°/Ma. Tarim Basin rotates clockwise relative to Eurasia about a pole (37.39°N,96.4°E,-0.533°/Ma), Erdos block rotates counterclockwisely relative to Eurasia about a pole at 49.06°N,118.51°E with a rate of 0.213°/Ma.The studies indicate that the GPS velocity field can matched equally well with plate-like model and continuous deformation model at a uncertainty of 1-2 mm/yr attained by existing measurements, though overall misfit of the GPS inversion is in slightly favor of the continuous deformation model. In fact the consistency between GPS velocity and the block model also preclude the conclusion that the continuous deformation model is superior to the block model in kinematic description of continental deformation. To the contrary, this studies argue for a widely accepted opinion that the continent tectonic deformation may be described best by block-like motion and interaction among them along the edges but the present-day motion rates of blocks are in generally not so fast as we thought before.