Studying the development and evolution characteristics of typical geological hazards along trunk highways in strong earthquake mountainous areas and their disaster-forming dynamic processes holds significant theoretical and practical importance for early hazard identification, risk assessment, and disaster prevention and mitigation in transportation corridors. This paper takes the southern segment of the Longmenshan Fault Zone as the study area, integrating field investigations, remote sensing interpretation, and GIS spatial analysis techniques to reveal the superimposed influence patterns of the 2013 and 2022 Lushan multi-phase seismic events on co-seismic geological hazards along the Baoxing section of National Highway 351. Furthermore, the three-dimensional two-phase Material Point Method (MPM) is employed to quantitatively simulate the entire process of initiation–movement–river blockage of the Xinhua Village high-position accumulation landslide, and key techniques for scenario deduction of high-position collapse-landslide hazards in seismically active areas are discussed.

The results indicate:

(1) A total of 215 co-seismic geological hazards triggered by the 2022 earthquake were identified in the study area, primarily distributed on slopes within 1500 m elevation on both sides of the Donghe River valley, with slope angles between 30° and 50°. A shared distribution characteristic with the 2013 co-seismic hazards is that steep slopes in hard rock areas are high-incidence zones for hazards.

(2) The development and distribution of the 2022 co-seismic geological hazards are mainly controlled by topographic, fluvial, and fault factors, showing weak spatial coupling with the epicenter location. Hazard points posing greater impacts on the highway primarily developed at prominent mountain sections with multiple free faces and near the fault zone, and were significantly influenced by the superposition of multi-phase seismic events and historical rainfall.

(3) The Xinhua Village high-position landslide, affected by the superimposed effects of multi-phase earthquakes, rainfall, and freeze-thaw cycles, exhibited a progressively retrogressive deformation pattern expanding upwards over the past decade, ultimately leading to large-scale instability and river blockage under the strong 2022 earthquake. The 3D two-phase MPM simulation reproduced the entire process of landslide movement → water entry and surge → accumulation and dam formation. The results show a landslide volume of approximately 760,000 m³, a maximum runout distance of about 609 m, and a maximum surge height of 8 m. The simulated post-failure deposit morphology is largely consistent with field observations.

The research findings provide theoretical and technical support for pre-disaster risk assessment and post-disaster reconstruction of trunk highways in strong earthquake mountainous areas.