Relations Between Landslides Induced By Wenchuan Earthquake And InSAR Deformation Field And Coulomb Stress Change

On May 12,2008, the Ms 8.0 Wenchuan earthquake occurred in the Longmenshan fault zone in the southwest region of China. And the earthquake triggered tens of thousands of coseismic landslides in the mountainous area, which caused serious casualties and loss of properties. So the study on the impact factors, movement mechanisms, hazard range of earthquake-induced landslides is of great significance for landslides risk assessment and prediction. The earthquake is the key impact factor of coseismic landslide occurrence. The quantitative analysis on the effect of terrain and seismic parameters on earthquake-induced landslides can provide important technical support for the mechanism interpretation of landslides and hazard mitigation.The coseismic surface deformation field measured by InSAR can provide observation data for interpretation of surface deformation characteristics, analysis of surface damages, and inference of focal mechanism, and provides important source data for relation research between coseismic deformation field and earthquake-induced landslides. This thesis proposes a fusion method through combining range deformation obtained by offset-tracking and radar light of sight deformation obtained by InSAR for extracting the complete deformation along slant-range direction to analyze its effect on coseismic landslides.The fault movement of Wenchuan earthquake produces the obvious surface rupture traces. Using the filtering method in the frequency domain, this study removes ionosphere effect in the azimuthal deformation field extracted by offset-tracking method. Based on corrected azimuthal deformation field, the surface rupture traces of Beichuan-Yingxiu and Guanxian-Jiangyou are automatically recognized using Sobel operator, which are used to analyze the spatial relation between earthquake-induced landslides and distance to surface rupture traces.The Coulomb stress changes caused by the giant earthquake have major influence on other surface process or underground rupture events following the main quake. The coulomb stress changes of surface slope can provide significant data for analyzing the occurrence of coseismic landslides. According to the static Coulomb stress calculation method and surface slope geometry determined from the topographic data, this thesis calculates the static Coulomb stresses of surface slope caused by the faulting motion of Beichuan-Yingxiu and Guanxian-Jiangyou faults, which are used to analyze the effects on the earthquake-induced landslides.Using remotely sensed optical images,935 small or medium and 123 large coseismic landslides are interpreted in the study, and this thesis studies the impact of terrain factors, coseismic surface deformation field, distance to rupture traces and static Coulomb stress change on the cosiesmic landslides by the spatial statistic method. The analysis results and conclusions can be summarized as the following. (1) Coseismic landslides were more likely triggered on the terrain with the slope gradients from 20° to 40°, with the aspects of east and southeast directions, and with the elevations from 1000 to 2000 meters, and especially most of large landslides occurred at the elevation from 1000 to 1500 meters. (2) Coseismic landslides were more likely triggered in a region less than 20 km away from the surface rupture traces, and especially most of large landslides occurred in a region less than 5 km away from the surface ruptures. (3) Compared with the strike-slip motion of fault, the thrust motion more likely triggered landslides, and coseismic landslides most occurred in the region with surface deformation more than 0.6 m along the slant-range direction. (4) Coseismic landslides were more likely triggered in the positive Coulomb stress field caused by Beichuan-Yingxiu and Guanxian-Jiangyou faults, and most of large landslides were triggered in the positive static Coulomb stress field caused by the Beichuan-Yingxiu fault.