A 25,000-yr-long integrated large earthquake record of the Xiaojiang Fault zone, southeastern Tibetan Plateau: New paleoseismic evidence from Yangzong Lake

The frequent occurrence of large earthquakes (surface wave magnitude, Ms≥7.0) along the Xiaojiang Fault zone (a key boundary fault system of the Tibetan Plateau) poses a serious threat to social security. However, the absence of long-term continuous records of such events increases the uncertainty surrounding the seismic behavior in this region. Paleoseismic investigations based on trenching are challenging due to subsurface rupturing during large earthquakes, destruction of on-fault deformation features, and the complex distribution of fault branches. Recent paleoseismic studies have suggested that event deposits in Yangzong Lake may preserve evidence of large historical earthquakes within the Xiaojiang Fault zone. Here, we present a 25,000-yr continuous record of large earthquakes in the fault zone, based on radiocarbon-dated event deposits identified by lithology, color, structure, mean grain size, sorting, Mn and Zr contents, and C/N ratio. These data are derived from two sediment cores from the depocenter of Yangzong Lake, supplemented by a reflection seismic image of the lake basin, and improve upon earlier trench-based paleoseismic records. The paleoseismic events recorded in Yangzong Lake (primarily originating from the middle segment of the fault) exhibit a weakly periodic recurrence pattern, with intervals ranging from 333±3 to 6320±651 yr and averaging 1765±460 yr. Integrated paleoseismic sequences from historical, trench-derived, and lacustrine records indicate an increase in seismicity along the Xiaojiang Fault zone during the Holocene, culminating in an unprecedented frequency of large earthquakes over the past millennium. This period of heightened seismic activity coincides with a notable intensification of human presence in the region. These findings highlight the urgent need for a comprehensive reassessment of paleoseismicity and seismic hazard in the area.