Landslide Hazard in the Marly Context of Moulay Yacoub Territory, Northern Morocco

In the Rif Mountain belt, landslides affecting the slopes constitute a major obstacle for the development of urban and sub-urban extensions and hinder infrastructure implementation and even food production projects in the region. Moreover, the interaction of the socioeconomic development and these instability phenomena significantly increases, which urges identifying the influencing parameters and prioritizing areas of risk to maximize harm reduction and to avoid costly outcomes. In the present study, we will address the risk of landslides at a broad scale as well as at detailed scale in the territory of Moulay Yacoub province. The latter is dominated by marly hills where the predisposition factors are mainly the slope gradient, lithology, and rainfall without omitting the anthropogenic factors. At a broad scale, the evaluation of the parameter-control level showed that anthropogenic factors are strongly involved, especially the land use, where the conversion of brushwood areas to cereal farming lands, which dominate the territory, highly increases the predisposition of slopes to shallow landslides as earthflows and soil creep phenomena. On a detailed scale, the characterization of the landslide hazard in the urban perimeter of Moulay Yacoub town showed that most buildings of the latter suffer from varying levels of damage related to the lithological, climate, and geomorphic settings of the site. In fact, the slopes of the town are affected by deep slides (exceeding 15 m in certain cases), whose rupture surfaces exploit the lithological contrast between the weathered layer and the compacted marls bedrock. The monitoring campaign using inclinometers data and PS-INSAR results show that these slides evolve with rotational components and are very slow. The analysis of the rainfall data and the displacement velocities show that the acceleration events follow the relatively long rainfall periods. Furthermore, the analysis of the damage confirms that the highly damaged constructions are located on the main scarps of the slides. Indeed, this present study highlights the complementarity of techniques used in this multi-disciplinary approach and the interest of the use of heuristic and statistical methods at a broad scale in the evaluation of predisposing factors and consequently the identification of high-risk areas, which presents an anticipatory move before any urban project planning or other.