Unveiling the Activity of a Young Fault: Insights from the 2021 Maduo Earthquake

Faults grow through fault lengthening and slip accumulation, which are episodic processes related to the repetition of earthquakes. It is most often recorded in geomorphology. Meanwhile, the activity and seismic hazard of the ‘slow-moving’ faults are often overlooked due to their weak imprints in landforms, especially at their initial formation stage. The 2021 Mw 7.4 Maduo earthquake triggered a ~158-km long surface rupture along the poorly-known and geomorphically subtle Jiangcuo fault, which is one of the distributed faults in the Bayan Har block and splays that merge with the Kunlun Pass fault. The slip rate of the Jiangcuo fault is thus crucial for comprehending how the strain is distributed between the major and subsidy faults in the complete fault system of the Bayan Har block, as well as the broader deformation process at a large scale. In this study, we present three sites where the Jiangcuo fault left-laterally displaces Holocene geomorphic features (e.g., terraces, fans, and channels). Through the detailed interpretations of high-resolution Digital Elevation Models (DEMs), field investigations, and credible Optically Stimulated Luminescence (OSL) dating of displaced geomorphic features, we document an average left-lateral slip rate of 2.1 ± 0.2 mm/yr since ~12 ka of the Jiangcuo fault. Furthermore, we conservatively updated existing slip rates of the large strike-slip faults (East Kunlun fault, Ganzi-Yushu-Xianshuihe fault) bounding the Bayan Har block. Synthesizing the slip rate of the Jiangcuo fault with the updated rates of the bounding faults, our findings suggest that the Jiangcuo fault accommodates ∼10% of the total deformation in the Bayan Har block. This study provides valuable insights into the impact of younger faults on regional deformation processes.