Late Quaternary Activity and Paleoseismicity of the Ritu Fault in the Western Bangong-Nujiang Suture Zone, Tibetan Plateau

The Bangong-Nujiang Suture Zone represents a critical tectonic unit within the Tibetan Plateau, and its tectonic activity is fundamental to understanding the plateau’s uplift and evolutionary processes. The western Tibetan Plateau contains many large-scale faults. These faults record geological information from the collision between the Indian and Eurasian plates. However, research on fault activity in this region is still limited. This study focuses on the Ritu Fault (RTF). It is an important part of the western Bangong-Nujiang Fault Zone in the western Tibetan Plateau. Through systematic field investigations, unmanned aerial vehicle (UAV) photogrammetry, trench excavations, and chronological dating, we investigate the Late Quaternary activity characteristics, slip rates, and paleoseismic history of the fault. The results indicate that: (1) the RTF strikes approximately E–W, dominated by dextral strike-slip motion with a component of extensional activity, and has been active since the Holocene; (2) the average slip rate of the RTF during the Late Quaternary (approximately 80 ka) is 1.74 ± 0.50 mm/a; (3) three paleoseismic events were identified in the trench, occurring at 19.5–15.4 ka BP (Event 3), 12.6–4.3 ka BP (Event 2), and <3.1 ka BP (Event 1), suggesting an earthquake recurrence interval of 7–8.2 ka. This study fills a critical gap in the research on active faults in the western Tibetan Plateau, providing new insights into the tectonic evolution of the region and offering significant implications for assessing regional seismic hazards.