Study On The 3D Surface Deformation Of The Longmenshan Fault Zone

The Longmenshan is located in the eastern margin of the Qinghai-Tibet Plateau, which has complex geological structures and high seismic activities. It has been attracted much attention of scholars in china and elsewhere in the world for its special geological structure background. In this paper, the research object is the Wenchuan earthquake in 2008. Firstly,3D surface deformation has been calculated based on GPS-InSAR integrated deformation model with additional systematic parameters, and the characteristics of displacement change be analyzed. Secondly, using Okada dislocation model (1985), dislocation-disclination model(2013),spherical dislocation model (1992) to calculate the coseismic displacement field respectively, then the relationship between the fault movement and surface displacements was discussesed, to verify the effectiveness of the dislocation-disclination model. The main research contents and achievements are as follows:1) We used the GPS-InSAR integrated deformation model to calculate the 3D coseismic deformation field of the Wenchuan earthquake. 31 GPS points of the study area be selected as the calibration point, to calculate the residual of the displacement of each GPS point and statistic its distribution. The results show that: the 3D surface deformation mainly occured in Yingxiu, Beichuan and Qingchuan area, the displacement of east-west direction is maximum,reached 2m, it prove the Wenchuan earthquake mainly appear thrust movement in east-west direction. In the north-south direction, the maximal displacement reached ± 0.6 m,the vertical direction in both sides of the fault shows a downward movement, the maximum displacement is -0.6m, which is consistent with the field survey results. From the 31 GPS points displacement residuals obtained that the 3D deformation field calculated by this theory is consistant with 31 GPS observed value, and the calculation precision of the north-south direction is highest, the vertical direction is minimum, the root mean square error of E?N?U is 3.16 cm, 1.89cm and 4.23 cm respectively, it has high precision for the coseismic deformation.2) We used Okada dislocation model (1985), dislocation-disclination model (2013),spherical dislocation model (1992) respectively and combined with four different slip distribution models to calculated the GPS coseismic 3D deformation field (2008), and compared with the measured 3D deformation field, it shows that dislocation-disclination model combine with Shen Zhengkang slip distribution model obtains the residual mean is (?)=0.00012, the trace is tr? 0.00543. So, this combined model is better than the other models according the residual analysis of unbiasedness and effectiveness.3) Finally, based on the dislocation-disclination and Shen Zhengkang slip distribution combined model, we calculated the 3D deformation filed and the residual distribution of 3361 points obtained by GPS-InSAR data fusion. It shows that residual mean relationship of each component is ?(?)n? <? (?)e?<?(?)u? ,he variance is ?n2 <?e2< ?n2, From the unbiasedness and effectiveness of residual to analysis, the simulation effect of north-south direction is optimal and vertical is worst. For the overall simulation results, the trace of residual is tr?= 0.00543,it shows that the movement trend is consistent with the measured results, which also verify the validity of the dislocation-disclination model.