The Altyn Tagh fault zone is a sizeable sinistral strike-slip fault on the northern margin of the Qinghai-Tibet Plateau, and its eastern section is obliquely connected with the northwest Qilian Mountain thrust fault zone. The left-lateral strike-slip action of the Altyn Tagh fault zone and the Qilian Mountain thrust belt constitute a structural transformation relationship. The activity behavior of this fault, especially the amount of sinistral dislocations, segmentation, and slip rate, has always been a hot topic of discussion among scholars. At present, based on geological methods and geodetic research, the slip rates of different sections of the Altyn Tagh Fault have been obtained, with a time scale ranging from tens of thousands of years to decades. The research results generally support the gradual attenuation of the slip rate of the Altyn Tagh fault zone from about 93° E to the east, indicating that its left-lateral attenuation is absorbed by a series of NW-trending thrust faults on its eastern side, and this trend has changed little for decades. The above work provides a framework for us to study the structural transformation relationship between the Altyn Tagh fault zone and the Qilian Mountains thrust belt in time and space. However, due to the limitations of previous observation points, especially the different methods of fault geomorphology measurement and dating used by various authors, there are significant differences in the obtained fault slip rates. Currently, it is not possible to analyze the segmented characteristics of the slip rate in the east section of the Altyn Tagh fault zone further and its spatial relationship with the Qilian Mountain thrust structural zone based on this. In recent years, the application of UAV aerial survey technology has allowed image data to be obtained at the centimeter to millimeter level, making the study of tectonic geomorphology more refined. Researchers can obtain the cumulative displacement or co-seismic displacement of several seismic cycles through micro-faulted landforms and reconstruct the dislocation accumulation process of active faults.The transfixion terraces developed across the Altyn Tagh fault are mainly controlled by regional tectonic uplift and climate change, showing regional synchronization in time, which provides convenience for the comparison of regional landforms. Although there are differences in the grading standards of terraces at different sites and the dating methods are not completely consistent, the chronological sequence of the late Quaternary river terraces in the study area generally shows good consistency. From new to old, it is about 3-4kaBP, 6-8kaBP, 10-13kaBP, 20-21kaBP and 40-50ka BP, which provides a research basis for our subsequent comparison of the displacement amount of river terraces. Based on the high-resolution image data obtained by unmanned aerial vehicle photogrammetry (SfM), this paper carried out a detailed interpretation of the 127km section of the eastern section of the Altyn fault zone and measured and counted the dislocations of different levels of risers at 9 typical river terrace dislocation points. Based on the distribution of cumulative displacement of the same terrace, the kinematic segmentation characteristics and tectonic mechanism of the eastern section of the Altyn Tagh fault zone are discussed. To define the displacement more accurately, we considered the following factors; 1) Usually, the riser is not a straight line but a curve formed by the free swing of the river bed; 2) Strictly speaking, a riser is a slope with a certain width, consisting of an upper edge, a lower edge, and a middle slope zone. When measuring displacement, we cannot only measure the upper edge or lower edge of the scarp but must consider it comprehensively. Based on the above prerequisites, this paper uses two envelope lines to surround the upper and lower edges of the riser and measures the distance between the corresponding envelope lines on both sides of the fault to obtain the displacement of different levels of scarp in the river terrace. Based on the above measurement methods, four dislocation values, A1-A4 and B1-B4, were obtained from the curve envelope of the upper and lower edge of the terrace scarp on both sides of the fault, respectively. After calculating the corresponding mean value, the standard deviation of the four measured values was estimated to reflect the dispersion degree of different measured values relative to the mean value, which was used as the error range of the measurement results.The results show that the late Quaternary left-lateral cumulative displacement tends to decline along the Altyn fault zone eastward. The cumulative dislocations are roughly the same in the same fault segment, which may indicate the consistency of seismic ruptures within the segment. In addition, the dislocation amount of the same-level terrace scarp between adjacent fault segments shows a stepwise decrease, indicating the tectonic transformation relationship of the miter fault and the possible seismic rupture segmentation, which provides a basis for the active segmental research and potential earthquake-generating capacity evaluation of the Altyn fault zone. A horizontal dislocation of 2-3m occurred on the front scarp of the Tl terrace in the Gaoyangou area, indicating that the latest earthquake surface dislocation event may have occurred in the Hongliugou-Shaping section at the easternmost end of the Altyn Tagh fault zone. © 2024 State Seismology Administration. All rights reserved.
