Directionality of earthquake-induced slope displacements from numerical analysis and sliding block approaches

Abstract

Earthquake ground shaking intensity differs at different azimuthal orientations (ground motion directionality), which could also result in orientational variations in earthquake-induced slope displacements. Therefore, the range of seismic displacements (e.g., the median and maximum values over all orientations) that may occur by considering the directions of downslope movement and strong shaking is important to evaluate seismic landslide hazard of site-specific slopes. This study performs comprehensive directionality analyses of seismic slope displacement based on two-dimensional numerical and sliding-block approaches. Four slope models with clay and sand soil layers and slope angle of 30° and 40° are analyzed using 75 ground motion records rotated over all orientations. Different sliding-block models are considered, including rigid-block analysis and two coupled flexible-block representations of one-dimensional soil columns with only sliding mass and full site respectively. The results indicate that the orientation variation of slope displacements is much larger than the ground motion parameters. The directionality characteristics of seismic slope displacement from numerical calculation can be well captured by the sliding-block analyses, although significant differences in the computed displacement values are observed. A procedure is proposed to obtain the maximum and median values of seismic slope displacement over all orientations from advanced numerical analysis at low computational cost.