Simplified analysis of coseismic slope displacement and hillslope weakening

Abstract

This paper introduces a simplified physics-based numerical slope stability model that accurately models progressive failure, the impact of changing landslide geometry, and the legacy of weakening caused by coseismic shaking. The model incorporates the wave equation and employs finite difference to preserve mass and momentum during landslide movements. The model agrees well with physical modeling of a shake table test and a reactivation of a coseismic landslide in the Port Hills of New Zealand. The model is explored through a sensitivity analysis to compare the influence of softening and several strength parameters on the overall progressive or catastrophic failure mechanism of a given slope. The study found that earthquakes can result in no weakening, partial weakening, and full rupture of the slope, leading to negligible, modest, or significant coseismic displacement, respectively. Further, seismic events might leave a legacy of weakened hillslopes with lowered disturbance thresholds for catastrophic failure during subsequent seismic or hydrological events. However, if some strength regain is considered, an equilibrated state of non-catastrophic movements from continued disturbances can be sustained. The results suggest that past seismic events can potentially influence the timing and nature of slope failure in certain instances. The proposed method's ability to capture evolving, large-deformation changes in landslide geometry over time make it a valuable tool for simple site-specific studies and hazard analyses.