基于DEM的岷江上游流域构造活动强度分析

目前,利用DEM衍生的地貌参数对大面积区域构造活动进行量化分析的研究相对较少。本文以岷江上游流域为例,利用ASTER GDEM数据和GIS技术,提取了该流域面积高程积分值(HI)、河长坡降指数(SL)、流域盆地不对称度(AF)、盆地形状指数(BS)、谷底宽度与谷肩高度比(VF)和水系分维数(FD)6种地貌参数,对其进行了等级划分,并量化了研究区相对构造活动强度(IAT)。结果显示:岷江上游流域有较高的SL、AF、BS值,较低的VF及FD值,中等HI值,其IAT值为1.33,分类等级为1级,表明该流域侵蚀程度强烈,流域形态狭长,河谷呈V型形态,受构造活动影响显著,地貌发育处于幼年期晚期,中年期早期。研究结果与区域地质背景较为吻合,该方法可为进一步探讨区域构造活动差异性提供新的手段。

Quantitative Analysis of the Tectonic Activity in Minjiang Drainage Basin Based on DEM

Geomorphic indices have been widely used in relative tectonic activity studies. Most studies provide semi-quantitative information to depict relative degree of tectonic activity in mountain fronts or small basins.Here we introduced an additional fractal dimension index（FD） which is found to improve the analysis of tectonic geomorphology. Based on ASTER-GDEM data and the technique of GIS, the other tectonic geomorphic indices are extracted in Minjiang River drainage basin including hypsometric integral, stream-gradient index, drainage basin asymmetry, drainage basin shape, ratio of valley floor width-to-height, and drainage elongation ratio.This drainage is located in the transitional region between Eastern Tibetan Plateau and Sichuan Basin with an area of 23 000 km2. The results obtained from these indices are combined to yield an index of relative active tectonics（IAT） that is obtained by the average of the different classes of geomorphic indices. Based on IAT value, four classes are defined： Class 1： very high relative tectonic activity with 1≤IAT1.5; Class 2： high with 1.5≤IAT2.0; Class 3： moderate with 2.0≤IAT2.5 and Class 4： low with 2.5≤IAT. Through the analysis of the geomorphic results in Minjiang River drainage basin, we conclude that the value of hypsometric index is moderate, the shape of hypsometric curve is convex-concave, Minjiang River basin tilt from right to left facing downstream,the shape of this basin is elongate, the stream length gradient index is high and the fractal dimension value is low, and this drainage have relatively higher tectonic activity（IAT=1.33）. The indicative value of IAT is consistent with the areas of known relative uplift rates, landforms and geology. This method provides a new insight for exploring diversities of relative tectonic activities on an areal basis.