Analysis And Research Of Sichuan Regional Crustal Deformation Based On GPS

The intersections of eastern Qinghai-Tibet plateau and western Yangzi block are Xianshuihe fault,Anninghe-Zemuhe fault and Longmenshan fault which nvolve part of Chuan-Dian,Chuan-Qing and Yangzi blocks. Nowadays these faults are active tectonic zones in Sichuan district with the most intense seismic activity in China. So monitoring the trend of these active faults' movement and research on modern tectonic activity of blocks by using high precise GPS observation technology will provide great help to the monitoring and relief of disaster.GPS measurements acquired from 1999～2005 have been processed using GAMIT/GLOBK software, and the station velocity field respect to Eurasia reference frame is obtained. On the basis of velocity field, characteristics of the block and faults' tectonic activity as well as the mechanism of dynamics are analyzed and discussed by means of least square fitting under the hypotheses of rigid mass. It shows that modern velocities of Chuan-Dian,Chuan-Qing and Yangzi block movement are 17.6±1.0mm/a,11.4±0.7mm/a,9.6±1.1mm/a respectively; the directions are 50.1°S E,79.9°S E,66.5°S E respectively. All block move towards SE direction and rotate clockwise to some extent. Among the main faults Xianshuihe fault is the most active one with the velocity of 7.2mm/a, and followed by Anninghe-Zemuhe faults about 4～6mm/a. The last comes to Longmenshan fault and Daliangshan fault. All faults are left-lateral strike-slip faults except Longmenshan fault which is right-lateral strike-slip fault. These special characters possibly result from the jostle of the India plate. The blocks are pushed to move towards southeast by the India plate, but obstructed from the Yangzi block because it is stable. So jostle and collision are caused to make the slip velocity different on both sides of the fault, and results in rotation clockwise.To analyze the stability of Sichuan GPS network, time series of coordinates of each fiducial station are calculated. The result shows that the coordinates have good repeatability which indicates the high precision of coordinates. The result also reveals the fact that the precision in horizontal direction is higher than that in the vertical direction. On the other hand some systematic impacts still existed in the time series of coordinates, which may be caused by some un-modeling factors.