基于DEM的青藏高原东北缘宛川河流域地貌的定量表达与新构造活动分析 英文标题:Quantitative Analysis of Morphology and Its Neotectonic Implication in the Wanchuan Catchment Based on Digital Elevation Models

现代地表形态为地球内部构造活动与地表外动力过程的共同产物，定量获取地表形态特征可以为反演近地表的构造活动过程提供重要信息。地貌形态指数是对地表形态的定量化表达，可以揭示区域构造活动痕迹、评估新构造活动状况。青藏高原东北缘为青藏高原最新扩展前缘部位。兰州-中卫段黄河流域地貌特征记录了相关的构造活动信息与地表演化过程。宛川河主体位于青藏高原东北部的榆中盆地，是黄河在兰州-中卫段一级小支流，构造活动活跃。流域内发育两组断裂带，分别为马衔山-兴隆山断裂系与宛川河断裂。前人在此开展过多次地震与新构造活动的研究，但对宛川河断裂是否存在以及断裂性质等方面的认识仍然不够全面，存有很多争议。本文采用多个地貌形态指数如河长坡降指数(SL)与Hack剖面、山前曲折度(SMF)、河谷宽高比(VF)、流域不对称性(AF)及盆地测高等，定量获取了宛川河流域的地貌形态特征，同时结合相关地质资料与野外勘测数据综合评估流域构造活动状态，得到以下认识:1)SL/K异常高值识别出的宛川河流域裂点主要分布于南北两侧的断层之上，其中北部的裂点比南部多，表征流域构造活动非常活跃。宛川河北部穿过宛川断裂的多条南北向沟谷存在多个裂点，并且不同沟谷的裂点分布在大致相同的几个海拔高程，可能表明宛川河断裂存有多期活动。北部裂点的位置主要沿断层分布，而南部除了有沿断裂分布的裂点以外，还有沿岩性分界线分布的裂点，表明北部裂点主要受断裂活动控制，而南部的裂点除了构造成因外，部分受到岩性差异的影响。野外断层崖、断层三角面、裂隙等构造地貌的特征和分布以及裂点的调查佐证了结果的可靠性，同时也证实宛川河断裂活动性强。2)宛川河南部的山前曲折度(SMF)指数为1.83～2.88，北部的SMF指数为1.03～1.18;北部的SMF值显示了顺直的山前缘，与野外观察到的断层崖(面)的分布一致，表明宛川河北部近期新构造活跃;宛川河北部支流的河谷宽高比(VF)指数在0.36～2.34之间，其中79%的VF值小于1，南部支流的河谷宽高比(VF)指数为0.55～13。VF值指示宛川河北部山体存在构造抬升活动，且新构造活动比南部活跃;北部测高积分(HI)均值为0.48，南部测高积分均值为0.40，表明研究区地形发展处于幼年与壮年期，且HI指示北部山体的构造抬升速率大于河流侵蚀速率。3)流域盆地不对称性(AF)指数的指向与研究区域构造应力的方向一致，表明宛川河局部迁移改向与构造活动相关;而局部AF指数的相反指向则与宛川河流域的褶皱隆起及掀斜断块运动相关。宛川河断裂东部穿过断层南北向河流的平移位错，表明宛川河断裂东端可能存在走滑运动特征。

Modern surface landforms are the combined product of tectonic activities within the Earth’s interior and exogenic processes on the surface. Quantitatively acquiring surface landform characteristics can provide critical information for inversing near-surface tectonic activity processes. Geomorphic indices, which are quantitative expressions of surface landforms, can reveal regional tectonic activity traces and evaluate neotectonic activity status. The northeastern margin of the Tibetan Plateau is the latest expanding front of the plateau. The geomorphic characteristics of the Yellow River basin in the Lanzhou-Zhongwei section record relevant tectonic activity information and landscape evolution processes. The main body of the Wanchuan River is located in the Yuzhong Basin in the northeastern Tibetan Plateau, and it is a first-order small tributary of the Yellow River in the Lanzhou-Zhongwei section, with active tectonic activity. Two fault zones are developed in the basin, namely the Maxian Mountain-Xinglong Mountain fault system and the Wanchuan River fault. Previous studies have conducted multiple researches on earthquakes and neotectonic activities here, but the understanding of the existence of the Wanchuan River fault and its nature is still incomplete and controversial. In this study, multiple geomorphic indices including stream-length gradient index (SL), Hack profiles, mountain front sinuosity index (SMF), valley floor width-to-height ratio (VF), drainage basin asymmetry (AF), and hypsometric integral (HI) were used to quantitatively obtain the geomorphic characteristics of the Wanchuan River basin. Meanwhile, combined with relevant geological data and field survey data, the tectonic activity status of the basin was comprehensively evaluated, leading to the following understandings: 1) The knickpoints in the Wanchuan River basin identified by abnormally high SL/K values are mainly distributed on the faults on the north and south sides, with more knickpoints in the north than in the south, indicating that the tectonic activity of the basin is very active. Multiple north-south valleys in the northern part of the Wanchuan River that cross the Wanchuan Fault have multiple knickpoints, and the knickpoints of different valleys are distributed at roughly the same several elevation levels, which may indicate that the Wanchuan River fault has multiple phases of activity. The locations of the northern knickpoints are mainly distributed along the fault, while in the south, in addition to the knickpoints distributed along the fault, there are also knickpoints distributed along the lithologic boundary, indicating that the northern knickpoints are mainly controlled by fault activity, while the southern knickpoints are partially affected by lithological differences in addition to tectonic origins. The characteristics and distribution of tectonic landforms such as field fault scarps, fault triangular facets, and fractures, as well as the survey of knickpoints, corroborate the reliability of the results, and also confirm that the Wanchuan River fault has strong activity. 2) The mountain front sinuosity index (SMF) of the southern part of the Wanchuan River ranges from 1.83 to 2.88, while that of the northern part ranges from 1.03 to 1.18; the SMF values in the north show a straight mountain front, which is consistent with the distribution of fault scarps observed in the field, indicating that the northern part of the Wanchuan River has recently active neotectonics. The valley floor width-to-height ratio (VF) of the northern tributaries of the Wanchuan River ranges from 0.36 to 2.34, with 79% of the VF values being less than 1, while that of the southern tributaries ranges from 0.55 to 13. The VF values indicate that there is tectonic uplift activity in the northern mountains of the Wanchuan River, and the neotectonic activity is more active than that in the south. The average hypsometric integral (HI) of the north is 0.48, and that of the south is 0.40, indicating that the topography of the study area is in the juvenile and mature stages of development, and the HI indicates that the tectonic uplift rate of the northern mountains is greater than the river erosion rate. 3) The direction of the drainage basin asymmetry (AF) index is consistent with the direction of the tectonic stress in the study area, indicating that the local migration and diversion of the Wanchuan River is related to tectonic activity; while the opposite direction of the local AF index is related to the fold uplift and tilted fault block movement of the Wanchuan River basin. The translational dislocation of the north-south river crossing the fault in the eastern part of the Wanchuan River fault indicates that there may be strike-slip movement characteristics at the eastern end of the Wanchuan River fault.

搜集汇总

背景与挑战

背景概述

该数据集基于数字高程模型（DEM），采用多种地貌形态指数对青藏高原东北缘宛川河流域的地貌特征进行了定量分析。研究揭示了该流域构造活动活跃，特别是宛川河断裂存在多期活动迹象，并评估了南北部构造抬升与侵蚀速率的差异。