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.