Journal of Earth Science, Vol. 29, No. 1, p. 193–209, February 2018 ISSN 1674-487X Printed in China https://doi.org/10.1007/s12583-017-0902-8 Dong, S. P., Zhang, P. Z., Zhang, H. P., et al., 2018. Drainage Responses to the Activity of the Langshan Range-Front Fault and Tec- tonic Implications. Journal of Earth Science, 29(1): 193–209. https://doi.org/10.1007/s12583-017-0902-8. http://en.earth-science.net Drainage Responses to the Activity of the Langshan Range-Front Fault and Tectonic Implications Shaopeng Dong * 1 , Peizhen Zhang 2, 3 , Huiping Zhang 2 , Wenjun Zheng 3 , Huixian Chen 4 1. Key Laboratory of Active Tectonics and Volcano, Institute of Geology, China Earthquake Administration, Beijing 100029, China 2. State Key Laboratory of Earthquake Dynamics, Institute of Geology, China Earthquake Administration, Beijing 100029, China 3. School of Earth Science and Geological Engineering, Sun Yan-Sen University, Guangzhou 510275, China 4. Map Supervision Center of SBSM, Beijing 100830, China Shaopeng Dong: https://orcid.org/0000-0001-8581-6006 ABSTRACT: Langshan, a monoclinic mountain, which started to uplift since Oligocene, bounds the northwest margin of the Hetao Basin. The continuous activity of the active normal Langshan range- front fault forms the typical basin-and-range landform in Langshan area and controls the landform evolution of Langshan. Langshan is an ideal place to study relationship between quantitative geomor- phological index and active deformation. According to study on knickpoints, fitting on longitudinal channel profiles and steepness index, we demonstrate that the main controlling factors on distribution of normalized steepness index of channels are not climate (precipitation), lithology, sediment flux, but tectonic factor, or the activity of Langshan range-front fault. The short channels in southeast flank, whose lengths are shorter than 16 km, may be still in the non-steady status. If not considering these short channels, the distribution of normalized steepness index along the Langshan range-front fault appears like M-shape pattern, while the normalized steepness index in the middle section is higher than those at both ends. This pattern is well consistent with geometrical segmentation model of the Langshan range-front fault. Combining previous active tectonic research on Langshan range-front fault, which demonstrates the Langshan range-front fault has been in the stage of linkup, we reasonably infer the Langshan range-front fault now is the result of linkup of both fault which continuously bilaterally ex- tended independently. Our tectonic geomorphological study also supports the conclusion that the Langshan range-front fault has been in the stage of linkup. The formation of several knickpoints due to tectonic factor may have been caused by slip-rate variation because of linkup of both independent faults. Based on cognition above, we also proposed the geological and geomorphological evolutionary model of the Langshan range-front fault since Oligocene. KEY WORDS: Langshan range-front fault, Hetao Basin, steepness index, Langshan, geomorphological evolutionary model. 0 INTRODUCTION Landform is always the competitive result between tectonic activity and surface erosion (Burbank and Anderson, 2011). So in many research areas, especially in the study of active tectonics, geomorphology has occupied the central position for a long time. In early stage, previous researchers have tried to reveal qualita- tive, or semi-quantitative amplitude and rate of different kinds of tectonic deformation on the base of geomorphological study, including the growth of fault-related folds (Rockwell et al., 1984), the reconstruction of paleoseismic events from fault scarps, de- terminations of displacement rates along fault systems (Wallace, 1977). These pioneering study results have proven that the *Corresponding author: spdong@ies.ac.cn © China University of Geosciences and Springer-Verlag GmbH Germany, Part of Springer Nature 2018 Manuscript received October 27, 2016. Manuscript accepted April 8, 2017. landscape contains an important archive of the rates and spatial distribution of deformation of active tectonics (Kirby and Whipple, 2012; Burbank and Anderson, 2011). Along with the development of digital elevation model (DEM) and geographic information system (GIS), the continual studies have finally promoted the proposal of classical physical model, bedrock stream-power incision model (Howard et al., 1994; Howard and Kerby, 1983), which provided the cornerstone and research ori- entation of abundant following quantitative geomorphological study (Summerfield, 2000). River channel formation and its dynamics over time have long been a major subject of study in geomorphology because of its important effect in shaping landform. Currently, several frequently-used quantitative indices, such as stream length- gradient index and Hack profile (Hack, 1973, 1957), concavity index and steepness index (Howard and Kerby, 1983), ratio of valley floor width to valley height (Bull, 1977), drainage basin asymmetry (Hare and Gardner, 1985), hypsometric integral (Strahler, 1952), and so on, have been developed to quantitatively