La cartographie d’inventaire, première étape de l’évaluation de l’aléa et du risque mouvements de terrain dans le Rif, Maroc

e-ISSN : 2458-7184International audienceThe last two decades have witnessed an important growth in population numbers, and consequently in infrastructures. This has called a better understanding of geomorphological hazards and risks in the Rifean mountains. While the human activities have a direct influence on mass wasting formations via changes of original slopes, heavy-traffic transit, mining, urban development and planning. Geological complexity, steep geomorphology and abundant rainfall also increase landslides hazard. Therefore, the first step of any study on landslide hazard and risk is inevitably the compilation of a landslide inventory using GIS tools. Then a 1/300 000-scale landslides inventory map has been established for the Rifean region (North of Morocco) using extensive geomorphological analysis based on remote sensing imagery and aerial photo-interpretations consolidated with field surveys. 4177landslides were identified, which covered an area of 1065 km², accounting for 3 % of the study area (about 37000 km²). The minimum, the average and the maximum mass wasting areas are respectively 0.0004, 0.1 and 1.47km². This inventory enabled us to recognize three major families of slope failures morphologies: (i) landslides represented by two subtypes: superficial landslides and landslides - undercutting initiated by the erosive action of rivers (64.4%), (ii) rock-falls (25.2%) and (iii) debris flows (10.4%).Les deux dernières décennies ont connu une croissance importante de la population, et donc en infrastructures. Ce qui implique la nécessité d’une meilleure compréhension des aléas et des risques géomorphologiques dans les montagnes du Rif. L’action anthropique exerce une influence directe sur la formation de mouvements de terrain par la modification des pentes naturelles, un trafic intense, l’exploitation des carrières, l’aménagement et l’urbanisme. La complexité géologique, une géomorphologie abrupte et des précipitations intenses et irrégulières ont aussi un grand effet sur la genèse de ce type de phénomènes. Par conséquent, la première étape de toute étude sur l’aléa et risque mouvements de terrain (MT) consiste inévitablement en la constitution d’un inventaire de MT à l’aide des outils SIG. Un inventaire à l’échelle 1/300 000 de MT a été établi pour la région rifaine (nord du Maroc) à l’aide d’analyses géomorphologiques approfondies basées sur le traitement des images satellitales et des interprétations des photographiques aériennes avec des missions ponctuelles de terrain. 4177 MT ont été identifiés, couvrant une superficie de 1065 km² et représentant 3% de la zone d’étude (environ 37 000 km²). Les superficies minimale, moyenne et maximale sont respectivement de 0,0004, 0,1 et 1,47 km². Cet inventaire a permis de reconnaître trois grandes familles de morphologies de mouvements de versants: (i) les glissements de terrain représentés par des glissements superficiels et des glissements par sapement provoqués par l’action érosive des rivières (64,4%), (ii) des éboulements (25,2%) et ( iii) coulées de débris (10,4%)

A comparative modeling of landslides susceptibility at a meso-scale using frequency ratio and analytic hierarchy process models in geographic information system: the case of African Alpine Mountains (Rif, Morocco)

International audienceLandslides represent a major natural hazard for all countries in the world. The Rif mountains in Morocco suffer from different types of landslides. Some of them are very active and present a significant risk to urban areas and transport systems. Consequently, in terms of sustainable development, landslide susceptibility mapping is essential to assess the levels of danger posed by these phenomena. This study aims at evaluating landslide susceptibility using two different approaches based on a statistical method (Frequency Ratio, FR) and on a heuristic method (Analytic Hierarchy Process, AHP). The second purpose is to compare them to select the most relevant and reproducible one with a view to applying it to areas having a similar geomorphological context. This study includes a precise inventory map representing the spatial distribution of three landslide categories within 892 sites. Rock falls, flows and landslides were studied using field survey and satellite imagery. Nine thematic layers of predisposing factors controlling landslides occurrence were prepared. The final result is presented in the form of six susceptibility maps of rockfalls, flows and landslides for FR and AHP models. The result of the success rates (AUC) indicates that the FR method is better with an AUC of 88% for rock fall, 89% for flows and 87% for landslides, while the AUC is 83%, 84% and 76%, respectively for the AHP method. Moreover, the results indicate which method to use for similar regions to produce indicative mapping and help users select priority areas prone to landslides