A ~50 ka seismic record along the Litang fault system, eastern Tibet

Understanding the rhythm of the seismicity along the active faults needs long-term record of the seismicity. In eastern Tibet， the Litang fault system constitutes a sinistral strike-slip Holocene active fault system mainly comprising three secondary faults (Maoyaba， Litang and Kanga-Dewu)， which offests the entire western Sichuan Plateau and nearly parallel to the Xianshuihe fault zones. The Litang fault system is one of most prominent active structures with high seismic risk， with 3 historical earthquakes of 7.5 > M > 7.0 since 1700. Despite many Holocene earthquakes revealed by trenches along the fault， a longer-term record of seismic history since the late Quaternary along the Litang fault system remains scare. Here， we investigated eight well-preserved fluvial-lacustrine sections in the Litang Basin along the Litang fault system， with sedimentary ages spanning from 50 ka to the present dated by optically stimulated luminescence. In these sections， abundant deformation features (including convolute structures， load structures， flame structures， ball-and-pillow structures， pseudonodules， liquefied diapirs， thixotropic diapirs， clastic dykes， liquefied breccias and micro-faults) are presented， which are characterized by soft-sediment deformation structures. We interpreted these soft sedimentary deformation structures as expressions of seismic shocks， indicative of 22 seismic events of Ms ≥ 6.0， which show non-characteristic earthquake recurrence pattern since 50 ka. At least 6， 8， and 5 paleo-earthquake events recorded by trenches have been identified along the Maoyaba fault， Litang fault and Kanga-Dewu fault since the Holocene， respectively. The Maoyaba fault and the Litang fault， as well as the Litang fault and Kangga-Dewu fault may belong to the same seismogenic structure， potentially experiencing co-seismic ruptures simultaneously， highlighting the presence of cascading fractures within the Litang fault system. Since 5000 a， the interval between strong earthquake recurrence times gradually decreases， suggesting an increasing risk of strong earthquake along the Litang fault. This study provides a lengthy record of paleo-earthquake along the Litang fault system， eastern Tibet， which may improve our understanding of regional seismic activity.