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.