Résumé : Le Rif Marocain en général et la ville d’Al Hoceima et sa périphérie urbaine plus particulièrement, connaissent fréquemment des aléas géomorphologiques, notamment les glissements de terrain qui entravent la gestion urbaine. Ce type d’aléa naturel est de grande actualité, aussi bien sur le plan scientifique que sur le plan médiatique, à cause de l’augmentation de la vulnérabilité, due aux circonstances des changements globaux (réchauffements climatiques) et à la forte urbanisation, souvent irrationnelle. L’objectif de cet article est la mise en place d’une approche objective visant l’évaluation de la susceptibilité aux glissements de terrain dans la ville d’Al Hoceima et sa périphérie. La théorie de l’évidence, qui est une méthode probabiliste bivariée, est fondée sur les règles de Bayes qui consistent à calculer la probabilité d’occurrence spatiale de glissements de terrain, en se basant sur la notion de probabilité à priori et de probabilité à posteriori, tout en considérant les glissements de terrain comme variable à modéliser et chaque facteur causatif comme variable prédictive. Le but de ce travail est de procéder à un zonage d’aléa glissement de terrain tout en assurant une bonne prédiction de ce phénomène avec une bonne résolution spatiale. Les résultats de la courbe de ROC (Receiver Operating Characteristic) montre que la confrontation de la carte de susceptibilité, des glissements de terrain à la carte d’inventaire, permet une capacité de prédiction considérable (AUC=0,889). Ceci pousse au constat selon lequel, plus de 2/3 des glissements de terrain inventoriés s’inscrivent dans des classes de susceptibilité élevée et très élevée. Ce produit cartographique peut constituer un puissant outil d’aide permettant la formulation des suggestions, dans le but d’optimiser l’évaluation du risque de glissements de terrain dans les zones exposées à ce phénomène. Mots clés : SIG, Théorie de l’évidence, Susceptibilité aux glissements de terrain, Al Hoceima (Maroc)

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Since many decades, the town of Moulay Yacoub (MY) has undergone an intensification of its urbanization to meet the demands of rental housing for the visitors of the hydrothermal springs, which is considered as the only attraction of the town. Unfortunately, the majority of the buildings, both private and public, suffer from varying levels of damages where the lithological and geomorphic field features are to blame, without omitting the anthropogenic effects. In fact, the town is built on a marly hill conducive to slope movements, ranging from shallow solifluctions to large landslides, besides the swelling/shrinkage behaviour of these marls. The paper presents a multi-source approach to investigate the activity and the interactions of slow urbanized landslides and expansive soils within the urban perimeter of Moulay Yacoub. Indeed, the desiccation cracks of marly soils reveal their expansive behaviour, also attested by the swelling values. The other geotechnical parameters obtained from laboratory tests show that the shallow marls samples are severely weathered compared to those of the compacted deep ones. The Borehole data and seismic noise survey allows the detection of several impedance contrasts corresponding to the shallow weathered-deep marls interfaces which in some cases represent the rupture surfaces of gravitational processes. The very slow but perennial activities of the later are attested by the inclinometers, the PS-InSAR monitoring and building damages. The case study provides a good opportunity to highlight the complementarity of the multi-source tasks which stand as a further contribution to fostering this kind of integrated approaches at the slope scale.

The Mediterranean coasts are known for their tourist attractiveness due to its richness in fishing resources and beach resorts as well as landscapes at the level of different ecosystems (forests, rocky and sandy beaches). The construction of the Mediterranean coastal road (RN16), which aims to enhance the tourist value of these resources and to improve access to this coastal region, has triggered an almost radical modification in the development process of this area, where the risks are increasing because of the multiplication of the challenges and the hazards due to the instability of its slopes. These events are mainly the result of marine erosion, the involvement of geological, geomorphological, climatic factors and also anthropic parameters with a strong littoralisation. The study area is characterized by active tectonics translated by the presence of faulting sets affecting the rock mass. The aim of this study is to assess the characteristics of the rock mass and its stability, and to anticipate landslide occurrence frequency with a particular size in a specified region with a certain rock mass quality as well. The methodology followed in this work consists of the elaboration of a complete inventory of landslides, the fracturation analysis and the rock mass engineering conducted to evaluate the stability of the slopes and the statistical analysis of the landslide size distribution. The combination of these two approaches has allowed us to assess qualitatively and quantitatively the landslide hazard on coastal rocky fractured areas.