Tectonic Geomorphology Analysis Of Piedmont Rivers In The Southern Segmentof The Longmen Shanat The Eastern Margin Of The Tibetan Plateau

In April 20, 2013, Lushan earthquake occurred in the southern segment of Longmen Shan, indicating the strong activity of this area. Based on the DEM data and ArcGIS10.2 software, we extract the microscopic topography parameters(slope, exposure) and macro topography parameters(topography degrees) of piedmont basin in southern segment of Longmen Shan. And combining with the area-elevation points(three-dimensional), asymmetric catchment basin(two-dimensional), mathematical fitting function analysis in river longitudinal profile(one-dimensional), water-plane distribution form, we do quantitative research of the topography in this region. Combining with active tectonic materials andprevious research results, we obtain tectonic activity differences and stress characteristics of the study area:(1)The landforms differences of study area are generally controlled by the tectonic activity, showing the distribution of geomorphic parameters are in accordance with the distribution of fault. The tectonic activity in study area gradually weak from NW to SE, the specific performance are: the slope, relief and area-elevation points decrease from NW to SE; the directionality of exposure and asymmetric catchment basin decrease from NW to SE; drainage basin in the mountain area is mostly trellis drainage, and in the hills and plain in SE is mostly dendritic drainage; the scarps are exist in the intersection between river longitudinal profile and fault, and become small from upstream to downstream.(2) The Shuangshi-Dachuan's fault is divided into SW and NE segments from Lanniba, the fault activity decrease from SW to NE, the specific performance are: the directionality of exposure in SW segment is better and the area-elevation points in SW segment is higher; the directionality of asymmetric catchment basin in SW segment is better; the scarps in the intersection between river longitudinal profile and Shuangshi-Dachuan's fault become small from SW to NE; the displacements of right lateral fault in the intersection of Shuangshi-Dachuan's fault and Chujiang river, Wenjing river, Sanlang river, Taian river drainage basins are decreased.(3) We select the the regional of mountains strongest tectonic activity to reflect the state of stress in this study area, as far as possible eliminate the interference of other factors. Through the regional of the mountain's slope and the advantage of the tendency in the catchment basin, it is concluded that this area of the principal stress direction may be NW. Shuangshi-Dachuan's NE fault slope segment and sub-catchment basin tends to become confused, probably due to the region near the boundary between the Longmen Shan or partly within the southern and central segments, while changing the direction of stress.(4) The piedmont basin in southern segment of Longmen Shan generated intense erosion and the basin is in old age. It is follows: In the area elevation curve shape integral study, two river basins integral curves forms are the s-shaped(prime period), four river basins are concave-shaped(old age). The best form of the mathematical fitting in Longitudinal segment of the river is that four rivers are logarithmic function fitting, a river is exponential functionfitting, a river is power function fitting.