Abstract:

The southern section of Longmenshan fault belt happened Dayi Ms 6.2 earthquake in 1970 and Lushan Ms 7.0 earthquake in 2013，indicating that this area has active neotectonics movement and is the ideal place to study the relation of structure, topography and river. This paper extracted the drainage basins of six rivers in the study area and their sub-drainage basins using GIS technology based on DEM data. These rivers are Xi River (R₁)，Chujiang River (R₂)，Xiejiang River (R₃)，Wenjing River (R₄)，Sanlang River (R₅)  and Tai’an River (R₆).The hypsometric integral values of these six rivers were calculated and their curves were drawn to analysis the tectonic activity and geomorphological evolution of the study area. The conclusion can be drawn as follows:(1) The hypsometric integral values descend from NW to SE,indicating that the regional activity descends from NW to SE and the contemporary strata exposed in the SE are younger than those in the NW.(2)The hypsometric integral value of SW segment on the hanging wall of Shuangshi-Dachuan fault is larger than that of SE segment, indicating that the tectonic activity of Shuangshi-Dachuan fault becomes waken from NW  to SE. (3)According to Ohmori’s model，with the pre-show style over thrust advancing forward to foreland, the evolutions of mountains, hills and plains can be speculated that ① in mountains, the uplift of mountain will continue until it reaches the highest point with hypsometric integral value equaling to 0.6，and hypsometric integral curves begin to change from S shape to convex shape, and the river will develop from mature stage to juvenile stage; ② in hills, the hypsometric integral curves begin to change from concave shape to S shape，and the river will develop from old stage to mature stage，then the hill will develop to be the mountain; ③ in plains, although the thrusting uplift increases,the local-rain belt will gradually close to the plain, causing the erosion intensity larger than uplift strength，thus the development mode will gradually become to be the hill development mode.

Key words: hypsometric integral, tectonic geomorphology, landform evolution, the southern section of Longmenshan