Quantitative Analysis Of Tectonic Landform Of The Middle-up Stream Region Of Weihe River And Its Significance Based On ASTER-GDEM

The Middle-up stream region of Weihe River which is located in the northeast margin of Qinghai-Tibetan plateau, which is the intersection of tectonic syntaxis, between near E-W to north margin of Western Qinlin structure zone and near N-S to Helanshan structure zone. Also, the study area is front site where is the propagation and accretion of intra-continental deformation in the periphery of Qinghai-Tibetan Plateau. It has significantly relative tectonic activity since late Pleistocene, accompany uplift of the plateau.Based on DEM, slope, relief, swath profile methods and so on, we studied the geomorphic characteristics and main types, which included basin landform of Weihe, loess plateau landform of Ningnan-Longxi-Shanbei and mountain landform of Liupanshan-Qinling.Geomorphic indices are useful tools for studying relative active tectonics, and they are obtained directly or secondhand based on GIS and RS softwares. It is useful to distinguish and analyze the abnormal phenomena relative to active tectonics, particularly in the area of relatively higher tectonic activity. The geomorphic indexes including hypsometric integral, drainage basin asymmetry, the stream-gradient index, mountain-front sinuosity, valley floor width-valley height ratio, drainage basin shape, and so on. Combining geological background and mathematical statistics, we used the experience of other countries for reference, presented a new method for evaluating relative active tectonics (Iat). It is obtained by the average of the different classes of geomorphic indices, and we divide into four classes from relatively low to highest tectonic activity:1.0≤Iat<1.5, very high;1.5≤Iat<2.0, high;2.0≤Iat<2.5, moderate;2.5<Iat<3.0, low.The Middle-up stream region of Weihe River divided26second drainage basins and72third drainage basins, based on DEM data and ArcGIS software. Then we exacted separately the geomorphic indices of the sub-drainage basins. The main conclusions are listed as below.Firstly, the area relatively higher tectonic activity is located in the upstream region of Weihe River, e.g. Bangsha drainage, Shandan drainage, Danan drainage, Maohe drainage and Jihe drainage. The area is6050.92km2, about14.42%of the whole drainage basin area, in which Maohe drainage is the highest tectonic activity (Iat=1.33).Secondly, the area relatively middle tectonic activity is located in the middle stream region and north bank of upstream region of Weihe River, e.g. Xianhe drainage, Sandu drainage, Qianhe drainage, Niutou drainage, Hengshui drainage, Qishui drainage, Jinling drainage,Qinjiang drainage, Shitou drainage and so on. The area is24388.50km2, about58.13%of the whole drainage basin area.Thirdly, the area relatively lower tectonic activity is located in the north bank of upstream region of Weihe River, e.g. Hulu and Qinqi drainage. The area is11518.61km2, about27.45%of the whole drainage basin area.Form the geological background, historical earthquake and filed observations on landform, we tested and verified the conclusions. They are consistent with filed observations on landform and geology. We think the method which has prominently effects and significance to explore their diversities of relative tectonic activity.Comparing relative tectonic activity of the drainage basin and development characteristics and ages of those terraces form previous research, the results show that the rapidly uplift and E-trending extrusion of Qinghai-Tibetan Plateau is the main control factor of geomorphic development and evolution since late Pleistocene. Under the background, the development and evolution of geomorphology the Middle-up stream region of Weihe River are dominated by north margin of Western Qinlin fault zone and near N-W to Nanhuashan-Liupanshan fault zone.