Abstract
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.
Highlights
Landslides belong to natural hazards facing Morocco, especially in the Rif regions [1,2,3,4,5,6,7]
The theory is based on three hypotheses [14]: (a) potential landslides will occur under the same conditions as in the past; (b) the predisposing factors are priori known and introduced into the analysis; (c) all landslides are inventoried on the study area
We noted that land use, elevation and fracturing play a major role and that the density of the drainage and the exposure are relatively less influential whereas the slope and the lithology occupy an intermediate place in the triggering of the landslides
Summary
Landslides belong to natural hazards facing Morocco, especially in the Rif regions [1,2,3,4,5,6,7]. Winds are humid from the west, linked to the Azores High which is centered on the Canary Islands, but when the anticyclone is displaced on the Iberian side, the often violent winds are NE direction. In summer it is a warm, dry east wind (Chergui) which blows in gusts (speed over 50kms / h) 2 to 3 days in a row, several times a month.Tangier is located in the external domain of the Rif’s chain, where the Rif is the western end of the Maghrebian Alpine chain outcropping along the Mediterranean coast of North Africa from Calabria to the Gibraltar Arc [18,19]. Such a morphology is the result of the combination of highly contrasted lithology, climatic system, active tectonic regime, and the erosive dynamics giving rise to several mass movements
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