Abstract:
Located at the northern edge of the Qinghai-Tibet Plateau and the western end of the Qilian Mountains, the Shibaocheng-Changma Basin and its surrounding areas are characterized by numerous active tectonic features and intense tectonic activity. Among these, the Shibaocheng-Yingzishan Fault Zone, as the largest reverse fault-fold belt in the basin, exhibits complex tectonic deformation patterns and distinct fault dislocation landforms. This region is an ideal area for studying basin-mountain tectonic deformation and its deep-shallow tectonic relationships, as well as for understanding the tectonic conversion relationships between different faults and crustal shortening patterns. This study employs high-precision unmanned aerial vehicle (UAV) Structure-from-Motion (SfM) photogrammetry techniques, combined with field survey results, to conduct a detailed interpretation of faulted landforms. It analyzes the latest activity characteristics and tectonic deformation patterns of the Daxueshan Beishan Fault within the eastern segment of the Yingzuishan Fault. It also employs cosmogenic nuclide dating methods to age-date key faulted landforms, and further calculates the Late Quaternary deformation rates through analyses of the deformation patterns and deformation amounts of multi-level terraces and their corresponding landform surfaces.The research results indicate that the Daxueshan Beishan Fault consists of two rows of faults. The thrusting action of the front-edge fault has formed multiple reverse fault-fold belts within the basin, while the rear-edge fault has developed bend-moment normal faults associated with fold, forming a typical reverse fault-normal fold combination. Fault activity caused the front-edge fault (Lujiaai segment) terraces T3 and T4 to experience vertical displacements of 6.56±0.34 m and 16.09±1.13 m, respectively. Based on terrace age calculations, the vertical slip rate of this fault segment is approximately 0.15±0.01 mm/a,with a horizontal shortening rate of approximately 0.12±0.02 mm/a and the overall thrust rate is approximately 0.19±0.03 mm/a. The deep slip surface extends southward to DaxueShan Fault at a depth of approximately 2.7±0.5 km, forming a typical thin-skinned reverse fault-fold deformation zone, which is the result of the fault system's forward-extending compression and expansion into the basin interior.