Abstract
Abstract. Approaches used to assess shallow slide susceptibility at the basin scale are conceptually different depending on the use of statistical or physically based methods. The former are based on the assumption that the same causes are more likely to produce the same effects, whereas the latter are based on the comparison between forces which tend to promote movement along the slope and the counteracting forces that are resistant to motion. Within this general framework, this work tests two hypotheses: (i) although conceptually and methodologically distinct, the statistical and deterministic methods generate similar shallow slide susceptibility results regarding the model's predictive capacity and spatial agreement; and (ii) the combination of shallow slide susceptibility maps obtained with statistical and physically based methods, for the same study area, generate a more reliable susceptibility model for shallow slide occurrence. These hypotheses were tested at a small test site (13.9 km2) located north of Lisbon (Portugal), using a statistical method (the information value method, IV) and a physically based method (the infinite slope method, IS). The landslide susceptibility maps produced with the statistical and deterministic methods were combined into a new landslide susceptibility map. The latter was based on a set of integration rules defined by the cross tabulation of the susceptibility classes of both maps and analysis of the corresponding contingency tables. The results demonstrate a higher predictive capacity of the new shallow slide susceptibility map, which combines the independent results obtained with statistical and physically based models. Moreover, the combination of the two models allowed the identification of areas where the results of the information value and the infinite slope methods are contradictory. Thus, these areas were classified as uncertain and deserve additional investigation at a more detailed scale.
Highlights
The evaluation of landslide susceptibility has been carried out worldwide based on three fundamental principles (Varnes and International Association of Engineering Geology, Commission on Landslides and Other Mass Movements on Slopes, 1984; Carrara et al, 1991; Hutchinson, 1995; Guzzetti, 2005): (i) the landslides can be recognized, classified, and mapped; (ii) the conditions that cause instability can be identified, registered, and used to build predictive models; and (iii) the occurrence of landslides can be spatially inferred
Statistical and physically based methods used to assess landslide susceptibility at the basin scale are conceptually distinct as the former are based on weighting environment predisposing factors, whereas the latter are supported by the computation of shearing and resistance forces along potential slip surfaces
The major constraints associated with statistical approaches have been summarized in previous works (Corominas et al, 2014; Fell et al, 2008a) and result from (i) the difficulty of establishing causal relationships between variables; (ii) problems arising from self-correlation between variables; (iii) the typically not normal statistical distribution of predictor variables; (iv) the limitations related to the quality of data, in particular the completion of the landslide inventory; and (v) the difficulty in transferring the results from the study area to other areas, even with similar characteristics
Summary
The evaluation of landslide susceptibility has been carried out worldwide based on three fundamental principles (Varnes and International Association of Engineering Geology, Commission on Landslides and Other Mass Movements on Slopes, 1984; Carrara et al, 1991; Hutchinson, 1995; Guzzetti, 2005): (i) the landslides can be recognized, classified, and mapped; (ii) the conditions that cause instability (predisposing factors) can be identified, registered, and used to build predictive models; and (iii) the occurrence of landslides can be spatially inferred Within this conceptual scheme, it is assumed that future landslides are more likely to occur in areas where geologic and geomorphologic conditions are similar to those that originated the slope instability in the past (Guzzetti et al, 1999).
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