remote sensing Article Active Strike-Slip Faulting and Systematic Deflection of Drainage Systems along the Altyn Tagh Fault, Northern Tibetan Plateau Peng Chen 1,2,3,*, Bing Yan 4 and Yuan Liu 5 1 Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China 2 Key Laboratory of Active Tectonics and Geological Safety, Ministry of Natural Resources, Beijing 100081, China 3 Key Laboratory of Deep-Earth Dynamics of Ministry of Natural Resources, Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China 4 College of Oceanography, Hohai University, Nanjing 210098, China; [email protected] 5 School of Earth Science and Resources, Chang’an University, Xi’an 710054, China; [email protected] * Correspondence: [email protected] Abstract: Systematic deflection of drainage systems along strike-slip faults is the combination of re- peated faulting slipping and continuous headward erosion accumulated on the stream channels. The measurement and analysis of systematically deflected stream channels will enhance our understand- ing on the deformational behaviors of strike-slip faults and the relationship between topographic response and active strike-slip faulting. In this study, detailed interpretation and analysis of remote sensing images and DEM data were carried out along the Altyn Tagh Fault, one typical large-scale strike-slip fault in the northern Tibetan Plateau, and together with the statistical results of offset amounts of 153 stream channels, revealed that (i) the drainage systems have been systematically de- flected and/or offset in sinistral along the active Altyn Tagh Fault; (ii) The offset amounts recorded by Citation: Chen, P.; Yan, B.; Liu, Y. Active Strike-Slip Faulting and stream channels vary in the range of 7 m to 72 km, and indicate a positively related linear relationship Systematic Deflection of Drainage between the upstream length L and the offset amount D, the channel with bedrock upstream generally Systems along the Altyn Tagh Fault, has a better correlation between L and D than that of non-bedrock upstream; (iii) River capture and Northern Tibetan Plateau. Remote abandonment are commonly developed along the Altyn Tagh Fault, which probably disturbed the Sens. 2021, 13, 3109. https:// continuous accumulation of offset recorded on individual stream channel, suggesting that the real doi.org/10.3390/rs13163109 maximum cumulative displacement recorded by stream channels might be larger than 72 km (lower bound) along the Altyn Tagh Fault. Along with the cumulative displacements recorded by other Academic Editor: Tomaž Podobnikar regional-scale strike-slip faults in the Tibetan Plateau, these results demonstrate that the magnitude of tectonic extrusion along these first-order strike-slip faults after the collision of India–Asia plates Received: 28 June 2021 might be limited. Accepted: 4 August 2021 Published: 6 August 2021 Keywords: strike-slip faulting; systematic deflection; drainage systems; Altyn Tagh Fault; eastward extrusion; Tibetan Plateau Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. 1. Introduction Topographic evolution is a joint result of the tectonic deformation that tends to build topography and the surface processes that tend to tear them down [1]. Therefore, the topo- graphic feedback associated with tectonism is an important tool to study the deformational Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. characteristics and behaviors of faulting and folding, especially for somewhere that is This article is an open access article actively deforming [2–4]. Among all these geomorphic indicators, drainage systems exhibit distributed under the terms and excellent quality for quantitatively assess the tectonic process and present-day crustal defor- conditions of the Creative Commons mation [5–8]. The geometry and morphology of drainage systems usually make a change Attribution (CC BY) license (https:// when across active faults or folds [2,7–10], of which the most commonly used topographic creativecommons.org/licenses/by/ marker is the systematic deflection and/or offset of stream channels produced by strike-slip 4.0/). faulting [4,11–13]. For example, based on the restoration of three main tributaries of the Remote Sens. 2021, 13, 3109. https://doi.org/10.3390/rs13163109 https://www.mdpi.com/journal/remotesensing Remote Sens. 2021, 13, x FOR PEER REVIEW 2 of 19 Remote Sens. 2021, 13, 3109 topographic marker is the systematic deflection and/or offset of stream channels produced2 of 19 by strike-slip faulting [4,11–13]. For example, based on the restoration of three main trib- utaries of the Yangtze River, the total displacement along the strike-slip Ganzi-Yushu- Yangtze River, the total displacement along the strike-slip Ganzi-Yushu-Xianshuihe Fault Xianshuihe Fault in the southeastern Tibetan Plateau was suggested to be ~60 km [4]. in the southeastern Tibetan Plateau was suggested to be ~60 km [4]. Along the Fuyun Along the Fuyun Fault in northwestern China, the characteristic slip of 6.3 m was obtained Fault in northwestern China, the characteristic slip of 6.3 m was obtained by analyzing by analyzing the offset distribution of 290 deflected stream channels and terraces [14]. The the offset distribution of 290 deflected stream channels and terraces [14]. The single-event single-event offset of the 1920 Haiyuan Ms 8.5 earthquake on the Haiyuan Fault in the offset of the 1920 Haiyuan Ms 8.5 earthquake on the Haiyuan Fault in the northeastern Tibetannortheastern Plateau Tibetan was reevaluated Plateau was to reevaluated be ~5 m based to be on ~5 them based offset on measurement the offset measurement of stream channelsof stream by channels the high-resolution by the high-resolution light detection light and detection ranging and (LiDAR) ranging data (LiDAR) [15]. Similarly, data [15]. theSimilarly, characteristic the characteristic slip of ~6 m atslip the of eastern ~6 m at Altyn the eastern Tagh Fault Altyn was Tagh revealed Fault accordingwas revealed to the ac- resultscording of to 321 the offset results measurements of 321 offset belowmeasurem 30 ments [16 ].below Thus, 30 the m measurement[16]. Thus, the and measurement analyses ofand offset analyses stream of channels offset stream represent channels an effective represent method an effective to study method the recurrence to study behaviors the recur- andrence displacement behaviors and accumulation displacement of strike-slip accumulation faults. of strike-slip faults. However,However, previous previous publications publications are are mainly mainly focused focused on on the the maximum maximum cumulative cumulative displacementdisplacement or or local local expressions expressions of of drainage drainage systems systems produced produced by by certain certain strike-slip strike-slip fault.fault. A A complete complete and and systematic systematic measurement measurement and and analysis analysis of of offset offset amounts amounts of of stream stream channelschannels along along the the entire entire strike-slip strike-slip fault fault is is still still lacking, lacking, which which hinders hinders our our understanding understanding onon how how the the stream stream channels channels with with different different orders orders of of magnitude magnitude response response and and accumulate accumulate thethe strike-slip strike-slip displacement displacement at at different different timescales. timescales. TheThe accumulation accumulation of of offset offset amount amount on on stream stream channel channel is is achieved achieved through through repeated repeated faultfault slipping slipping events events during during long-term long-term geologic geol history.ogic history. Meanwhile, Meanwhile, the upstream the upstream of stream of channelsstream channels lengthens lengthens with the continuous with the continuous headward erosionheadward process. erosion Based process. on the Based interaction on the betweeninteraction strike-slip between faulting strike-slip and faulting offset accumulation, and offset accumulation, a hypothesis a hypothesis concerning concerning with the upstreamwith the lengthupstream of stream length channelof stream and channel offset amountand offset was amount reached was [13 reached,17]. [13,17]. InIn this this study, study, we we chose chose the the Altyn Altyn Tagh Tagh Fault, Faul thet, the northern northern border border of the of Tibetanthe Tibetan Plateau Plat- (Figureeau (Figure1), as 1), a carrier as a carrier to study to study the relationshipthe relationship between between strike-slip strike-slip faulting faulting and and offset offset cumulationcumulation of of drainage drainage systems. systems. With With the the availability availability of of high-resolution high-resolution remote remote sensing sensing image,image, and and three-dimensional three-dimensional stereoscopic stereoscopic inspected inspected technology, technology, the the seismic seismic recurrence recurrence characteristicscharacteristics of of active active faults faults could could be be revealed revealed by by precise precise measurement measurement and and analyses analyses of of offsetoffset amounts amounts of of rivers rivers or or gullies gullies [ 14[14–16].–16]. In In order order to to get ge at a better better understanding understanding of of the the geomorphicgeomorphic feedback feedback to to strike-slip strike-slip faultingfaulting andand improveimprove knowledge of fault