Study On The Fault Activity Of Northern Segment Longmenshan And Its Control Effect On The River System Process

The northern segment of Longmenshan orogen refers to the extension of the northeast part, bouned to Beichuan,An'xian, which across Sichuan and Gansu provinces and located in the northern margin of Yangtze plate and southern margin of Qinling orogenic belt which is China's backbone. This article relying on National Natural Science Foundation Emergency Project"Study on Surface Ruptures and Deformation of Wenchuan Earthquake", comprehensive field surveys on surface rupture characteristics and the actual information from trenches, study on the quaternary fault activity of northern segment Longmenshan and its control effect on the earth surface process.The northern segment of Longmenshan has three main fault from NW to SE: Qingchuan-Pingwu fault, north segment of Beichuan-Yingxiu fault, north segment of Pengxian-Guanxian fault. It separated by a few thrust which is NE strike and SW orientation and show a clear segmentation. The three major fault general show the thrust which is from NW to SE and obvious right-lateral strike-slip. It is still has a strong activity today which show as the seismic activity, steep terrain, break of river terraces and line topography.The Quaternary activities of Longmenshan belt could be seen at the three main fault. The three fault at middle and south segment of Longmenshan all has a significant linear image and good interconnectivity. On the contrary, the linear image is not obvious and the interconnectivity is poor at the northern segment of Longmenshan. The activity of Beichuan-yingxiu fault is the most strong in the three main fault of Longmenshan fault zone.There is exist one main surface rupture zone in the northern segment of Longmenshan fault after Wenchuan earthquake. This rupture has a single structure and the change trend of vertical and horizontal dislocation are different. The vertical dislocation is gradually decreased from SW to NE which the horizontal dislocation is increased slowly. The horizontal dislocation come to the maximum at Pingtong, and then show the decreasing trend as the vertical dislocation Seismic moment can change the topography of the earthquake zone, and accordingly the river system has undergone the appropriate adjustments. Wenchuan Earthquake led to a complete record of river style changes throughout the earthquake and the quantitative relationship between the evolution of water.