Field investigations on large-scale instability triggered by the Chenghai-Binchuan fault zone, northwestern Yunnan, China

Abstract Background The Chenghai-Binchuan fault zone in northwestern Yunnan Province, China, is a tectonically active structure with frequent paleo-landslides, largely controlled by normal faulting and left-lateral strike-slip motion. Methods To systematically investigate their formation mechanisms, and chronological evolution, To examine their formation and chronology, 284 landslides across representative zones were analyzed, with selected cases field-investigated to characterize morphology and classify failure mechanisms. Field investigations combined with OSL and ESR dating were used to estimate the timing of the major landslide events. Results Field observations show that paleo-landslides are strongly concentrated along active fault traces, and that some of them exhibit large, coherent accumulations with well-preserved stratigraphy, long horizontal runouts with limited vertical displacement, whereas others display pronounced creep deformation characteristics, together with steep rear scarps and well-developed tensile fractures. Their kinematic features include bedding-controlled creep, tensile-fracture sliding, ejection, and widely distributed shallow instability or collapse. Chronological analyses reveal that large paleo-landslides occurred between 485 ± 32 ka and 13.0 ± 0.7 ka, accompanied by long-lived landslide-dammed lakes. The integrated evidence indicates that strong fault–slope coupling, expressed through long-term creep weakening and abrupt seismic acceleration, exerts the primary control on the initiation, evolution, and spatial clustering of major paleo-landslides. Conclusion These findings provide new insights into the mechanisms and temporal evolution of fault-controlled paleo-landslides and their implications for landscape development in seismically active regions.