滇中河网特征及其对断层活动的响应

Characteristics of River Networks in the Central Yunnan Province and Their Responses to Tectonic Activities

滇中地区作为青藏高原东南缘构造活动最强烈的地区之一,发育了许多活动走滑断裂,并且在该区域上密布着不同级别的河网,为利用河网分析断裂活动提供了有利条件。为揭示滇中河网发育与断裂活动内在联系,本文基于30 m分辨率的SRTM-3数字高程模型(DEM)在ArcGIS环境下提取了滇中地区金沙江、珠江、红河内的20条支流的河流网络,分析其典型的河网参数(分支比和长度比),通过这些比值与Horton定律描述的一般性河流网络进行对比。同时,基于ArcGIS空间分析技术及Matlab程序脚本系统,对这20条河流流域纵剖面进行定量化研究,分析其河道基岩侵蚀力模型,得到S-A拟合图解。结果表明:滇中地区金沙江、珠江、红河中大多数与断裂带重合的高级别河流的支流,河网发育明显地受到了断裂活动的影响;在河道基岩侵蚀力模型S-A拟合图中呈现为上凸和下凹相间排列,这一现象在金沙江流域的各支流最为显著,造成这一现象的原因可能是研究区内的河道主要受走滑断裂控制,当断裂以压扭性为主时,河道的隆升量大于剥蚀量,S-A拟合曲线表现为上凸;当断裂以张扭性为主时,河道的隆升量小于剥蚀量,S-A拟合曲线表现为下凹。通过对河网构造地貌特征的研究可以使我们更好地理解该地区的构造活动特征。

The central Yunnan province is located in the Southeast of the Tibetan Plateau.Being one of the most tectonically active regions,it is cut by several active strike-slip faults.It is an ideal place to investigate the relationship between the active tectonics and river systems.Here,the SRTM-DEM with spatial resolution of 30 m was used as the basic dataset,and the ArcGIS and MATLAB software were used to the extract profile characteristics of 20 tributaries from the Jinsha River,the Pearl River,and the Red River in the central Yunnan province.First,the networks of the 20 tributaries were mapped and analyzed.Secondly,the relationship between tectonic uplift and fluvial incision was analyzed by steep index(Ks).The results show that(1)the networks are represented by the Horton Laws for the streams of the lower orders but deviate dramatically at the highest order.(2)S-A plots all exhibit alternate convex and concave forms.It can be inferred that the developments of high-order rivers were significantly affected by the strike-slips faults.The analysis of fluvial geomorphology can help us to further investigate the tectonic activities and characteristics of the central Yunnan province.