Apport de l'imagerie radar SAR-ERS à l'analyse de la géométrie de la déformation récente dans les monts des Béni Snassen (Maroc nord-oriental). Contribution of the imagery radar SAR-ERS to the analysis of the geometry of the recent deformation in the Beni Snassen mounts (North-eastern Morocco).

International audienceLes techniques de traitement permettent, dès à présent, une exploitation opérationnelle des images satellitaires radar SAR-ERS dans un contexte cartographique. L'utilisation de cette imagerie au Maroc nord-oriental a permis d'extraire la géométrie de la déformation. Trois réseaux de failles de direction NW-SE, NE-SW et ENE-WSW apparaissent au travers des principales unités morphologiques. La disposition et le caractère récent des jeux de ces failles sont confirmés sur le terrain. Ceci a permis d'établir un modèle d'évolution structurale des monts des Béni Snassen dans le cadre de l'évolution des chaînes maghrébines en contexte de collision entre les plaques lithosphériques Afrique - Europe. Image processing techniques already allow the operational use of radar satellite SAR-ERS imagery for cartography. Its use in North-eastern Morocco made it possible to extract the geometry of the deformation. Three directions of major faults oriented NW-SE, NE-SW and ENE-WSW appear to the breadth of the main morphological units. The arrangement and the recent character of the sets of these faults are confirmed on the field. This was used to establish a model of structural evolution of the Beni Snassen mounts within the framework of the evolution of the maghrebin chains in context of collision between the African - European lithospheric plates

Trente Ans de l'Evolution Spatiotemporelle du Glissement De "Bou Halla" à l'Aide de la Photogrammétrie Numérique et du MNT

International audienceLa caractérisation géométrique et cinématique, à différentes échelles d'un glissement de terrain, est une étape indispensable à la compréhension de la dynamique d'un tel phénomène. La télédétection spatiale est un outil particulièrement bien adapté pour cette caractérisation puisqu'elle permet d'obtenir une vision synoptique de l'édifice, à différentes échelles spatiales (du centimètre à la dizaine de mètres) et temporelles (quelques heures à plusieurs années), en s'affranchissant des problèmes d'accès. Jusqu'à ce jour peu de travaux ont mis à profit les avantages de la photogrammétrie numérique dans le domaine des risques géomorphologiques et des mouvements de terrains en particulier. La tâche principale restant pour l'instant est le développement des techniques et des matériels. Plusieurs géologues ont défini selon cette méthode les vecteurs de déplacements d'un certain nombre de repères naturels identifiés sur deux clichés aériens. Ceci a permis aussi d'établir des cartes de déformations superficielles et de mesurer le déplacement d'éléments remarquables de la surface topographique sur des sites instables (Casson et al., 2005 ; Van Ash et al., 2006 ; et Méric et al., 2007 ...). L'originalité de notre travail est basée sur la construction automatique des MNTs à partir des couples stéréoscopique, et l'orthorectification des photoaériennes permettant de projeter chaque image dans un même référentiel, afin de poursuivre l'activité spatiotemporelle d'un mouvement de terrain

Probabilistic Landslide risk assessment - Application to Eastern Rif (Morocco)

The present study is consecrated to the probabilistic mapping of the landslide risk at the local scale of an area that belongs to Al Hoceima city in the western Rif of Morocco. The study focuses mainly on the spatial analysis of multi sources data by using an environment GIS (Geographic Information Systems), and the application of the bivariate probabilistic model to qualify the risk susceptibility. The employed methodology is based on three stages. First, the evaluation of landslide susceptibility (S) by the analysis model cited before. Second, the identification and the estimation of the potential consequences (C) for the existing issues. Finally, the landslide risk (R) is evaluated by combining the susceptibility and the potential consequences map. This study requires the use of spatial analysis techniques. It also refers to the risk maps scale, generally reduced and being inappropriate at the urban project area. The obtained risk map defines four risk intensities with a spatial resolution of two meters

Probabilistic Landslide risk assessment - Application to Eastern Rif (Morocco)

The present study is consecrated to the probabilistic mapping of the landslide risk at the local scale of an area that belongs to Al Hoceima city in the western Rif of Morocco. The study focuses mainly on the spatial analysis of multi sources data by using an environment GIS (Geographic Information Systems), and the application of the bivariate probabilistic model to qualify the risk susceptibility. The employed methodology is based on three stages. First, the evaluation of landslide susceptibility (S) by the analysis model cited before. Second, the identification and the estimation of the potential consequences (C) for the existing issues. Finally, the landslide risk (R) is evaluated by combining the susceptibility and the potential consequences map. This study requires the use of spatial analysis techniques. It also refers to the risk maps scale, generally reduced and being inappropriate at the urban project area. The obtained risk map defines four risk intensities with a spatial resolution of two meters

Weights of evidence method for landslide susceptibility mapping in Tangier, Morocco

Tangier region is known by a high density of mass movements which cause several human and economic losses. The goal of this paper is to assess the landslide susceptibility of Tangier using the Weight of Evidence method (WofE). The method is founded on the principle that an event (landslide) is more likely to occur based on the relationship between the presence or absence of a predictive variable (predisposing factors) and the occurrence of this event. The inventory, description and analysis of mass movements were prepared. Then the main factors governing their occurrence (lithology, fault, slope, elevation, exposure, drainage and land use) were mapped before applying WofE. Finally, the ROC curves were established and the areas under curves (AUC) were calculated to evaluate the degree of fit of the model and to choose the best landslide susceptibility zonation. The prediction accuracy was found to be 70%. Obtained susceptibility map shows that 60% of inventoried landslides are in the high to very high susceptibility zones, which is very satisfactory for the validation of the adopted model and the obtained results. These zones are mainly located in the N-E and E part of the Tangier region in the soft and fragile facies of the marls and clays of the Tangier unit, where landuse is characterized by dominance of arable and agricultural land (lack of forest cover). From a purely spatial point of view, the localization of these two classes of susceptibility is completely corresponding to the ground truth data, that is to say that all the environmental and anthropogenic conditions are in place for making this area prone to landslide hazards. The obtained map is a decision-making tool for presenting, comparing and discussing development and urban scenarios in Tangier. These results fall within the context of sustainable development and will help to mitigate the socio-economic impacts usually observed when landslides are triggered

Qualitative and quantitative evaluation of the ground movement risk on an urban cartographic scale Example of QUEMADO (Eastern Rif, Morocco)

The morphostructural examination of QUEMADO slope, contributes to distinguish the vulnerability indications that refer to the ground movements. They are supported by the combination of geological, geo morphological, hydro geological parameters. In addition, the seismic activity that is known in this area increases the vulnerability of the coastal areas. Thus, many cracks and locatable indices in the studied area constitute a witnesses of movement risk that threat directly the projects, the installations and the urban constructions of Al Hoceima city, in proximity of the studied cliff. The present study is consecrated to achieve a comparative study of the evaluated risk “ground movement” by two methodological approaches. The qualitative approach which is most usually employed, and the quantitative approach that requires a scientific effort of adaptation and reproducibility. The risk evaluation is based on using four data components; mainly the topographical slope, the lithology, the geomorphology and the ground occupation. The results were interpreted by a discrete analysis of the unstable areas through the land reconnaissanc