A GIS Approach to Analysis of Deep-Seated Slope Stability in Complex Geology.

We demonstrate the computer model r.rotstab.layers to explore the possibilities of GIS for catchment-scale deep-seated slope stability modelling in complex geology. This model makes use of a modification of the three-dimensional sliding surface model proposed by Hovland and revised and extended by Xie and co-workers. It evaluates the slope stability for a large number of ellipsoidal random slip surfaces which may be truncated at the interfaces between geological layers. This results in a spatial overview of potentially unstable regions. After demonstrating the functionality of the model with an artificial cone-shaped terrain, we test r.rotstab.layers for the 10 kmRipoli area in Umbria, central Italy. According to field observations in the Ripoli area, morpho-structural settings play a crucial role for deep-seated landslide distribution. We have prepared a model of the geological layers based on surface information on the strike and dip of each layer, and we use this model as input for r.rotstab.layers. We show that (1) considering the geological layers is essential for the outcome of deep-seated slope stability modelling, and (2) the seepage direction of the groundwater is a major source of uncertainty.