Numerical models of translational landslide rupture surface growth

We analyze the initiation and enlargement of the rupture surface of transla tional landslides as a fracture phenomenon using a two-dimensional boundary -element method. Both processes are governed largely by the stress field an d the pre-existing planes of weakness in a slope. Near the ground surface, the most compressive stress becomes either parallel or perpendicular to the slope, depending on the topography and regional stresses. The shear stress available to drive slope-parallel sliding in a uniform slope thus is small , and therefore pre-existing weaknesses are required in many cases for slid ing. Stresses in a uniform slope favor the initiation of sliding near the s lope base. Sliding can progress upslope from there in retrogressive fashion . Most slopes are not uniform and notches in a slope will concentrate stres ses and generally promote sliding there. As the region of sliding at depth enlarges, the stress concentration near the edge of the area of slip will t end to rise. Stress concentrations can become sufficient to open fractures above and below a basal slide plane, in keeping with observations. If one t ip of a slide plane intersects the ground surface, then stresses near the o ther tip can increase markedly, as can slip. Our analyses show that slope-p arallel sliding along a plane at depth will cause downslope extension in th e upslope half of a slide mass and shortening in the downslope half, consis tent with observations. Displacement profiles that could be interpreted as rotational can result from sliding along such a plane, however careful anal ysis of surface deformation can be used to understand sliding at depth.