Landslide hazard Modelling
Predictive models of landslide movement are generally confined to single slopes where detailed geotechnical site investigations attempt to assess when and to what extent the slope-forming material, frequently an existing landslide deposit, will move.
Landslide hazard modelling methods for ranking slope instability factors and assigning the different hazard levels can be qualitative or quantitative and direct or indirect. Qualitative methods are subjective and portray the hazard zoning in descriptive (qualitative) terms. Quantitative methods produce numerical estimates (probabilities) of the occurrence of landslide phenomena in any hazard zone. Direct methods consist of the geomorphological mapping of landslide hazard. Indirect methods for landslide hazard assessment are essentially stepwise. They require first the recognition and mapping of landslides over a target region or a subset of it (training area). It follows the identification and mapping of a group of physical factors which are directly or indirectly correlated with slope instability (instability factors). They then involve an estimate of the relative contribution of the instability factors in generating slope-failures, and the classification of the land surface into domains of different hazard degree (hazard zoning).
The most important methods proposed in the literature can be grouped into few main categories (Guzzetti et al., 1999), namely: (i) heuristic or index-based methods; (iii) functional, statistically based models; (iii) geotechnical or physically based models.
The heuristic approach (i), based on the a priori knowledge of all causes and instability factors of landsliding in the area under investigation, is an indirect, mostly qualitative method, that depends on how well and how much the investigator understands the geomorphological processes acting upon the terrain. Instability factors are ranked and weighted according to their assumed or expected importance in causing mass movements (e.g. Mejı́a-Navarro et al., 1994).
The statistical models (ii) of slope instability are indirect and quantitative approaches and they are built on the assumption that the factors which caused slope-failure in a region are the same as those which will generate landslides in the future.
The process-based geotechnical models (iii) rely upon the understanding of few physical laws controlling slope instability (e.g. Montgomery and Dietrich, 1994; Terlien et al., 1995). These models couple shallow subsurface flow (i.e., the pore pressure spatial distribution), predicted soil thickness, and landsliding of the soil mantle (Dietrich et al., 1995). Stability conditions are generally evaluated by means of a static model, such as the “infinite slope model”, where the local equilibrium along a potential slip surface is considered.
Regarding the potential exploitation of EO data for landslide modelling, the main issues concern methodologies for combining (i) space measurement of past displacement derived from InSAR and/or PSI analyses, (ii) conventional in situ investigations and (iii) geotechnical modelling, to characterize and predict the hazard associated with slope instability under heavy rain, and to support the design of appropriate mitigation measures. These activities include development and testing of new data processing techniques (new PSI algorithms, data mining, etc.).