1.Geophysical Exploration Center, China Earthquake Administration;2.College of Environmental Science & Engineering, Ocean University of China;3.Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences
地貌形态是构造和地表过程相互作用的复杂产物，主要通过构造活动和岩石的抗侵蚀能力等来调解。构造活动相对较弱的古老造山带往往可以忽略构造驱动的岩石抬升，使得研究岩石抗侵蚀能力对其地貌雕刻的贡献成为可能。但是目前大多数在活动造山带地貌研究的结果显示地貌主要受控于活动构造，关于岩性对地貌演化影响的报道较少。色尔滕山山前断裂为河套盆地北缘的一条重要控盆断裂，全新世以来该断裂的活动性较强，曾发生过两次较大震级地震（M 6.4和M 5.9）。前人活动构造研究表明该断裂的活动性具有空间差异，中部乌加河镇活动性最强，两端逐渐减弱。但相对河套盆地北缘其他大型断裂（如狼山山前断裂、乌拉山北缘断裂和大青山山前断裂），该断裂的地貌参数研究较少。同时其地貌演化特征及发育机理仍然不清楚，这些均制约了对该断裂的变形动力学理解。本文基于30 m分辨率的DEM数据对该断裂进行详细的河流地貌学参数研究，包括使用Arcgis和Matlab脚本提取色尔滕山山前33条河流的子流域盆地高程-面积积分（HI）和相应河道陡峭指数（Ksn）、河道纵剖面及其裂点等地貌学参数。结果表明研究区河流HI值大部分处于0.40~0.66之间，其中乌加河镇附近具有高值，流域盆地处于发育的壮年期。瞬态河道和稳态河道均沿着色尔滕山山前断裂走向有分布，可能表明色尔滕山山前大部分河道目前处于瞬时地貌向均衡地貌演化阶段，并且通过对比发现瞬态河道裂点成因存在岩性和构造共同控制的现象。河流陡峭指数空间分布差异性较大，乌加河镇附近（13~20号）陡峭指数较大，向两边陡峭指数逐渐减小，在S8河流以西又有增大的趋势。通过结合岩性和降雨情况分析发现，河道陡峭指数除了受岩性抗侵蚀能力影响外，同时其分布还基本与前人得到的色尔滕山山前断裂垂直滑移速率分布和垂直位错分布基本一致。综合来看，地貌参数的空间分布是岩性差异和色尔滕山山前断裂活动分段差异性共同控制的结果，表明该地区岩性和构造对地貌的协同塑造作用。
Topography is formed by the complex interactions between tectonics and erosional surface processes, which is primarily mediated by tectonic activity and bedrock erodibility. The rock uplift by tectonics can be negligible in the ancient orogens for its tiny tectonic activity, then it is possible to study the contribution of rock erodibility to the landscape evolution. However, most recent results show that topography is mainly controlled by tectonics in the active orogens, and the reports of lithological control on landscape evolution are not involved. As the controlling fault for the Hetao Basin, the Seerteng mountain-front fault had been active since the Holocene, which resulted the M 6.4 and M 5.9 history earthquake in the 1979 and 1934. Previous studies show that the center section (such as the Wujiahe site) has stronger activity than its west and east sections. However, the researches of geomorphic parameters are less than other faults in the northern margin of Hetao Basin (such as the Langshan fault, Wulashan fault and Daqingshan fault), which will hinder to understand its deformation dynamics. Using the 30 m DEM, we extracted the Hypsometric integral of 33 subbasins in the Seerteng Mountain and normalized channel steepness, longitudinal profile and the Knickpoint of the corresponding streams. The HI values are clustered between 0.44 and 0.66 with the highest value at the Wujiahe town, indicating that the evolution stage of the Seerteng Mountain is the “Middle” stage. The transient and steady rivers are all distributed along the fault, which reveal that the rivers in the Seerteng mountain-front are developed during the transient state and then evolved to the steady state. By comparing the knickpoint and lithology, we find that the knickpoints are under-controlled by tectonic uplift and/or lithology. The channel steepness (Ksn) has a character of spatial difference. The Ksn near the Wujiahe town is the highest, and it gradually decreases to the east and west part, then it increases to the west part at the River S8. By analyzing the rock lithology, precipitation and tectonic, the channel steepness (Ksn) is controlled by the lithology, and its spatial distribution is in accord with the fault activity (vertical slip rates and offsets). The landscape of the Seerteng Mountain is the results of the tectonic uplift and rock lithology.