Slip partitioning of the Altyn Tagh fault based on geomorphic indices reveals uplift pattern

Active strike-slip fault systems in addition to oblique slip producing vertical displacement are often linked to contemporaneous thrust faults, which together contribute to regional uplift. However, how slip is partitionned along the different faults of the strike-slip fault system and the underlying mechanisms of slip-paretionning remain poorly understood. To address this issue, we investigated the northwestern margin of the Tibetan Plateau, focusing on the Altyn Tagh fault—a complex fault system that has undergone major Cenozoic tectonic deformation due to the ongoing convergence between the Indian and Asian plates. Using drainage networks and geomorphic indices, we developed a composite index of Relative Uplift Rate (RUR) to map spatial variations in uplift rates. Our analysis reveals significant along-strike variations in tectonic uplift and identifies four major tectonic anomalies from south to north: Qiemo, Subei, Changma, and the northern Qilian Shan. By integrating these results with geological constraints on horizontal slip rates, we explore the mechanism of slip partitioning along the fault. We find that although horizontal slip rates generally decrease northeastward, the vertical relative uplift rates do not follow the same pattern. Instead, within the Qilian Shan, vertical uplift rates are the highest compared to the southwestern fault junction areas. A key finding is that areas with high uplift rates correspond spatially to zones of geometrical fault complexity, such as fault bends or branching. These anomalies are further supported by patterns of seismic activity.