Multi criteria assessing approach of the slow-moving urban landslide hazard, the case of Moulay Yacoub town (Morocco)

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.