The Xianshuihe fault, located in the southeastern Tibetan Plateau, stands as one of the most active faults in China. As assessing earthquake hazard relies on access to long-term paleoseismological archives, this paper seeks to optimize the interpretation of paleoseismological records. We developed a code that evaluates the plausibility of rupture scenarios against sedimentary evidence from nine cores in three lakes over a 30 km fault segment. Earthquake-related deposits were identified through grain-size analysis, XRF core scanning, and SEM observations of thin sections. Age models based on short-lived radionuclides correlate these events with historical earthquakes, which are recorded with varying sensitivities to seismic intensity across the three lakes. Each site is then used as a binary paleoseismometer, indicating whether or not an earthquake reached a local intensity threshold. The combined evidence allows to evaluate rupture scenarios on the Xianshuihe fault, according to rupture length-magnitude scaling laws and intensity prediction equations. The most probable scenarios allow to discriminate the rupture area and magnitude range providing a good agreement with historical reconstructions. Our work demonstrates the potential of combining earthquake records to infer the magnitude and rupture zone of paleo-earthquakes, even with a limited dataset. Our approach, applicable across diverse geological settings and timescales, offers enhanced precision in understanding long-term paleoseismology covering multiple earthquake cycles. However, establishing the synchronicity of events in such an active area—where earthquake return times are typically < 100 years—demands highly accurate age models, which remains challenging.

The Xianshuihe (XSH) fault in eastern Tibet is one of the most active faults in China, with the next large earthquake most likely to occur along its SE part, where the fault splits into three parallel branches: Yalahe, Selaha and Zheduotang. Precisely quantifying their slip rates at various timescales is essential to evaluate regional earthquake hazard. Here, we expand our previous work on the Selaha fault, to the nearby Zheduotang and Moxi faults, and add observations on the Yalahe fault and on the newly discovered Mugecuo South fault zone. Using tectonic-geomorphology approaches with 10Be dating, we had determined average late Quaternary slip rates of 9.75±0.15 and 4.4±0.5 mm/yr along the NW and SE Selaha fault, respectively. Using the same methods here, we determine a slip rate of 3.7-5.4 mm/yr on the Zheduotang fault and of 10.4-14.8 mm/yr on the Moxi fault. This is consistent with the southeastward slip rate increase we had proposed along the XSH fault system from 6-8 mm/yr (Ganzi fault) to ~10 mm/yr (Selaha fault), and >10.4 mm/yr (Moxi fault). We eventually propose a new model for the SE Xianshuihe fault, where the large-scale Mugecuo pull-apart basin lies within an even larger scale compressive uplift zone in the XSH fault’s restraining bend, where the highest peak in eastern Tibet is located (Gongga Shan, 7556 m). Our slip rates determination allows to estimate a relatively high regional earthquake hazard of Mw~7 at present in the SE Xianshuihe fault.

The Xianshuihe fault in eastern Tibet is one of the most active faults in China, with the next large earthquake most likely to occur along its SE part near Kangding. Quantifying its slip rate along the three parallel branches (Yalahe, Selaha and Zheduotang) as well as along the Moxi fault is essential to evaluate regional earthquake hazard, necessary to the construction of the Chengdu-Lhasa railroad. Here, we expand our previous work on the Selaha fault to the Zheduotang and Moxi faults, with observations on the Yalahe fault and the newly discovered Mugecuo South fault zone. Using tectonic-geomorphology approaches (LiDAR, UAV and 10Be dating), we had determined late Quaternary slip rates of 9.75±0.15 and 4.4±0.5 mm/yr along the NW and SE Selaha fault, respectively, hence had inferred a ~5 mm/yr rate along the parallel Zheduotang fault. Here, using the same methods, we confirm such rate (4.5[+0.9/-0.8] mm/yr, ZDT moraine site) thus suggest a total slip rate of >8.9±1.4 mm/yr in the SE Xianshuihe fault. Our rate along the Moxi fault (12.5[+2.3/-2.1] mm/yr, MX moraine site) is higher than those along the Ganzi (6-8 mm/yr) and Xianshuihe (~10 mm/yr) faults farther NW, which reinforces our earlier finding of a southeastward slip rate increase, in agreement with the eastward decrease of GPS vector values (with respect to Eurasia) located north of the fault. Our study reveals a high regional earthquake hazard (Mw6.5 to 7.3) in the near future, which adds to the challenge of building the new railroad in such mountainous area.