Steep fault-controlled slopes are widely distributed in the high mountain valley region along the eastern margin of the Tibetan Plateau. Under climate change and increasingly frequent extreme events, the risk of rainfall–seismic cascading failures has increased markedly. In such cascades, rainfall infiltration preconditions the slope by modifying seepage and pore pressure, and subsequent seismic loading acts as an immediate trigger. For fault-controlled slopes, strong heterogeneity and preferential flow paths promote localized weakening within the fault damage zone. Seismic shaking is then more likely to generate amplified response and concentrated deformation around these weakened zones. This coupling links hydrological deterioration to dynamic failure and can lower the instability threshold, thereby accelerating the transition from progressive weakening to sudden collapse. Motivated by the Mogangling landslide, this study develops a numerical model of a fault-controlled slope. Finite element analyses are conducted to simulate transient seepage and seismic dynamic response under rainfall-conditioned states, and limit equilibrium evaluation is used to quantify stability degradation and potential sliding characteristics. Rainfall characteristics, including intensity and duration and their combinations, are treated as key input variables to generate time-dependent pore-pressure fields for subsequent seismic loading. Seismic inputs with different peak ground accelerations are applied to assess acceleration amplification, cyclic stress ratio, deformation concentration, and safety factor reduction. The study aims to identify key stages and controlling factors along the cascade, including how rainfall-driven weakening governs the formation of vulnerable zones and how seismic loading activates instability along these zones. The outcomes improve understanding of rainfall–seismic cascading failures in fault-controlled slopes and provide a basis for resilient risk control in high mountain valleys by supporting robustness-oriented prevention before failure and preparedness and recovery-oriented decision making after earthquake-triggered slope instability.

Cascading failure; Rainfall-seismic coupling; Fault-controlled slope; Rainfall characteristics; Dynamic response; Stability degradation