青藏高原周边地区河流分形特征与地貌、构造活动耦合关系

青藏高原周边地区的地貌特征与形成演化机制一直是科学界研究的热点。选择青藏高原周边典型地区河流分形特征、地貌特征及构造活动性进行研究,发现喜马拉雅断裂带、龙门山断裂带和阿尔金断裂带控制的区域构造活动性强烈,历史地震记录频繁,大震较多,河流形态与地貌演化特征也非常相似,河流纵剖面变化很快,长波长下凹型,河流坡降比大,地形起伏度大,河流形态变化简单,河流分维值低;青藏高原东北缘构造活动性不强烈,历史地震记录偏低,大震极少,河流纵剖面变化缓慢,近似长波长微振幅上凸型,河流坡降比小,地形起伏度较小,河流形态错综复杂、分维值高;青藏高原东南缘,构造活动性较强烈,历史地震记录频繁,大震较多,但由于该区域平均多年侵蚀速率比较低,同时河流下切深度大,河流纵剖面变化缓慢,也是近似长波长微振幅上凸型,河流坡降比小,河网发育较成熟,河网分维值较高。通过对比发现,降水量的变化对该区域侵蚀速率的影响远小于构造活动性的作用,在分析河网形态特征时可以不考虑降水量空间变化的影响。

A study of the coupling relationship be-tween fractal characteristics of river, geomorphology and tectonic activity in areas around the Tibetan Plateau

The research on the geomorphological characteristics and the mechanism of the formation and evolution in areas around the Tibetan Plateau has been a hot issue in recent years. In this paper, the authors studied the fractal characteristics of the river net-work, geomorphic features and tectonic activity in areas around the Tibetan Plateau. There are strong tectonic activities, frequently strong historical earthquakes, many large earthquakes in the Himalaya fault zone, Longmenshan Mountain fault zone and Altun fault zone, and there are many similarities in river pattern characteristics and geomorphic evolution, such as quick changes of the longitudi-nal profile and concave shape with long wavelength, steep stream gradient ratio, high relief, simple river pattern and low fractal dimen-sion of river. Tectonic activities are not strong on the northeastern margin of the Tibetan Plateau as compared with features of the Hi-malaya fault zone in this aspect, as shown by rare strong historical earthquakes, slow changes of the longitudinal profile and convex shape with long wavelength and micro-amplitude, slow stream gradient ratio, small relief, complex river pattern and high fractal di-mension of river. There are strong tectonic activities, frequent strong historical earthquakes, many large earthquakes on the southeast-ern margin of the Tibetan Plateau, but because the regional average annual erosion rate is very low, and stream trenching is very deep, the change of the longitudinal profile is slow, its shape is convex with long wavelength and micro-amplitude, the stream gradi-ent ratio is slow, the river pattern is complex, and the fractal dimension of the river is high. The authors hold that the regional erosion rate is much more controlled by the tectonic activity than by the precipitation, and therefore the influence of the spatial variation of precipitation can be largely ignored in the analysis of river pattern characteristics.