<p>The earthquake-induced failure behavior of jointed rock slopes is closely linked to the dynamic degradation of the joint shear strength. The rock joint surface may undergo reciprocal shear motion under earthquakes, which involves changes in shear mechanical properties. To better capture the dynamic and cyclic behavior of rock joints under seismic loading, a displacement-dependent joint peak shear strength degradation model was developed based on cyclic shear tests on artificial joint samples. The proposed model characterizes the frictional weakening of rock joints subjected to repeated shearing, with all the parameters derivable from standard laboratory tests. The model was then implemented in the Universal Distinct Element Code (UDEC) computational platform through a user-defined joint constitutive model interface and subsequently applied to simulate earthquake-induced landslide processes. The numerical results reveal that frictional weakening has a more significant effect on deeper basal rock blocks than on near-surface layers in high-speed, long-runout landslides. By incorporating joint strength degradation, the model successfully captures essential dynamic features of seismic landslides, including enhanced mobility and realistic deposition morphology. The comparative analysis demonstrates that the slip-weakening model significantly outperforms the traditional Mohr‒Coulomb criterion in predicting landslide runout distances and final deposit patterns. These findings highlight the critical role of joint degradation mechanisms in accurately simulating large-scale seismic landslides.</p>