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.

Palaeogene Environmental evolution in East Asia remains ambiguous. Here we present integrative work including magnetostratigraphy, grain-size, geochemistry, and clay minerals from a 1609-m-thick fluviolacustrine sequence in eastern China. The results reveal two periods of tectonic control alternating with three periods of climatic control of the sedimentary evolution. Tectonic activity, as revealed by particle coarsening and reduced weathering, occurs during 65.6-59 Ma around the study area, and increases in Asia during 55-54 Ma in response to the India-Eurasia collision. Weathering enhances gradually in East Asia during 59-55 Ma, probably caused by global warming. Continuous global warming during 54-50.5 Ma is responsible for enhanced aridification in East Asia. From 50.5 to 37.6 Ma, global cooling weakens evapotranspiration and increases westerlies-derived moisture. Both aspects increase effective moisture and chemical weathering in East Asia. These results shed light on how alternating tectonism and climate change impact environmental evolution in Asia during the Palaeogene.

Key Points: • Three areas of tectonic activity are identified by analysis of the fluvial sediments from the Min River in eastern Tibet. • The dominance of fluvial silts, low relief and low slope-angles indicate weak activity of the Minjiang fault. • Stepwise increases in sands, relief, and slope-angle reveal increased tecton-ism in the Diexi-Wenchuan-Dujiangyan segments. Abstract The deposition of fluvial sediments in the tectonically active areas is mainly controlled by climate change and tectonic activity, meaning that fluvial sediments can provide a valuable record of regional climatic and tectonic signals. In this study, a detailed analysis was conducted on the grain-size of modern fluvial sediments from the upper Min River in eastern Tibet, and these data were combined with regional information about the vegetation, hydrology and geomorphology. The results indicate that modern regional tectonic activity in the study area can be divided into three segments. The fluvial sediments in Minjiangyuan-Diexi segment are dominated by fine silts (<63 ï¿¿m: 70.2%), showing low runoff and rainfall conditions and revealing a windblown origin influenced by climate change. This observation is consistent with the small hillslope angle and low relief in this segment, indicating weak activity of Minjiang fault. The coarse-grained fraction (>250 ï¿¿m) of fluvial sediments in Diexi-Wenchuan-Dujiangyan segments increases stepwise (A:6.2%, B:19.4%, C:33.8%) with a stable hydrological conditions, which corresponds well to the increasing trend in the regional relief and the steepness of hillslope angles. These observations indicate the phased enhancement of regional tectonic activity for Maoxian-Wenchuan fault. The fluvial sediments in Dujiangyan-Sichuan basin segment show good sorting and rounding, which is well correlated with significant increases in rainfall and runoff. There is also almost no evidence of tectonic activity in this segment. This study first develops an important research approach for revealing regional tectonic activity through fluvial sediment analysis in tectonically active regions. Plain Language Summary In tectonically active areas, intense tectonic activity tends to create steep ge-omorphology, and deeply affect erosion and sedimentation of river systems. Hence, whether fluvial sediments document changes of regional tectonic activity 1 deserve detailed investigation. In this study, the fluvial sediment of the Min River in the eastern Tibetan Plateau is taken as the research object. Based on grain size analysis of the Min River sediments, we reveal the close correlation between grain size variation and tectonic activity, under the comprehensive comparison of regional topography and geomorphology (slope, height difference) and hydrological conditions. We find that the fine-grained fluvial sediments from the Minjiangyuan to Diexi segment correspond to the weak fault activity of the Minjiang Fault, while the significant increase of coarse-grained composition from Diexi to Dujiangyan segment correspond to the enhancement of fault activity of the Maoxian-Wenchuan fault. This is supported by the greater slope angles and mountain relief from Diexi to Dujiangyan. Novelty of the research methods and reliability of results in this study provide a good reference for revealing regional tectonic activity through fluvial sediments in tectonically active areas.