## 4 Discussion on Failure Mechanism
It can be observed that during Stage III, the slope's structure undergoes significant changes, with the overall sliding surface intensifying further and the free face  
Figure 14: Failure mode diagram of slope cross-bedrock fault (**(a–c)**: soil body rupture at the slope crest, (**d–f**): soil body rupture at the slope toe). fully forming. This allows for the prediction of the potential hazards and scale of cross-fault slope instability. At the same time, the sliding surface and free face of the slope form the existing slope structure, providing a geological conceptual model for subsequent numerical simulations and model tests under loads such as rainfall and earthquakes, which can be used for comparative analysis and validation. In summary, at different stages, mitigation measures such as early warning, stability safety calculations, and subsequent disaster experiments and simulation analyses can be applied. By implementing these scientific mitigation strategies, a monitoring system for cross-fault slopes can be established to promptly detect and provide early warning of safety hazards. In slope design, the impact of the sliding surface and its geometric characteristics on slope stability should be thoroughly considered. In the analysis of slope-induced disasters, real geological conceptual models provide essential data for subsequent experiments and numerical simulations. These effective prevention and control measures can significantly enhance slope stability and reduce the risk of instability. This study investigated and analyzed real cases of seismic damage caused by landslides across normal bedrock faults, with typical examples including the Dongmiaojia landslide and the Lianhuasi ancient landslide. The Dongmiaojia landslide was influenced by the displacement of the main fault bedrock. The fault traversed the top of the landslide, forming the rear cutting and separation surface. This caused the appearance of a fault rupture zone and steeply inclined cracks at the slope crest, which extended into the mountain, resulting in tensile cracking damage. With significant fault displacement, the rupture zone and cracks continued to develop and penetrate toward the slope body, deepening and enlarging the rear tensile crack surface. Over time, the combined effects of the weight of the slope and other loads caused the local weak zones to become fully penetrated, leading to the formation of the Dongmiaojia landslide [61; 62; 63], as shown in Figure 15.  
The Lianhuasi ancient landslide is the oldest reported high-speed long-runout landslide in China. The Huashan Mountain front fault displacement directly cut through the toe of the landslide, resulting in a significant height difference and the formation of the main rupture zone (potential slip surface). Due to the weight of the mountain, continuous sliding occurred along the main rupture zone (shear rupture zone), eventually causing  
Figure 15: Geological profile of Dongmiaojia landslide. the rupture surface to penetrate and shear out. Under inertia, the landslide continued to slide. According to [PERSON] et al., the large cracks caused by bedrock dislocation lead to the accumulation of a substantial amount of rock blocks due to the weight of the slope and the collapse of the overlying rock and soil mass. Subsequent secondary landslides occur under the influence of the weight of the slope and heavy rainfall, compounded by additional geological disasters, such as collapses [64; 65; 66; 67], as shown in Figure 16.  
An analysis of these typical seismic damage cases indicates that the causative mechanisms and failure processes of cross-bedrock fault slope models are generally consistent with actual seismic damage scenarios. Both can be characterized by the formation of a main rupture zone or a penetrative sliding surface in the slope due to fault displacement in the bedrock, leading to instability. This initial instability is then exacerbated by secondary landslides triggered by earthquakes, rainfall, and the weight of the slope itself.