Building a Multilake Paleoseismometer for the Xianshuihe Fault (Tibetan Plateau, China)

Abstract

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 retrieved nine sediment cores from 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. We developed a code that evaluates the plausibility of rupture scenarios against sedimentary evidence: Each site is used as a binary paleoseismometer, indicating whether or not an earthquake reached a local intensity threshold. The combined evidence from the three sites 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 data set. 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.