Seismic triggering of shallow landslides - linking threshold mechanics and hydrological considerations

The susceptibility of a landscape to earthquake-induced shallow landslides is a function of the seismic perturbation, the geologic and geomorphic settings, and soil-hydrological conditions. To systematically evaluate scenarios for potential coseismic triggering of landslides, we incorporated the inertial effects of real earthquake acceleration time histories into the STEP-TRAMM hydro-mechanic landslide triggering model to determine how seismicity may influence internal soil and root loading and load redistribution during shaking. At the core of the landscape scale hydro-mechanical model are bonds and mechanical strength thresholds that vary with soil type and land-cover (vegetation) and with soil wetness. The bonds are represented by a fiber-bundle model with strength thresholds defining whether a local failure progresses and triggers a landslide or if excess load is redistributed among neighboring soil elements. Seismic effects are represented as rapid, inertial loading that may locally modify stress conditions of bonds and may trigger landslides in the mechanically weakest locations on a given landscape. The new model will explicitly consider earthquake accelerations and directionality relative to slopes and translate the information to thresholds for different slopes, soils and hydration conditions. The influence of seismic acceleration will be assessed in consideration of antecedent rainfall conditions, the role of vegetation on the resilience of hillslopes, and the magnitude of failures observed.