Large deep-seated landslides in the northern Rif Mountains (Northern Morocco) : inventory and analysis

Abstract

This work aims to contribute to the knowledge of large-scale slope instability phenomena in the northern Rif Mountain, whose setting is presented in the first chapter. On a second chapter we analyse the topography of the Rif belt resorting to morphometric parameters extracted from digital terrain data. Our results indicate a concentration of surface uplift and tectonically induced drainage network incision along the Internai Domain and southern sector of the Ketama Unit, defining two zones of distinct deformation that are consistent with the transpression models for northern Africa. In the chapter 3 we study the frequency-size and spatial distribution of 3610 bedrock landslides (La> 0.01km2). lhe results show that while the precipitation related to humid climatic condition throughout the Quaternary has certainly favoured the triggering of very large landslides (>1km2 ) along the south-western sector of the mountain chain, the importance of deep-seated bedrock fracturing in close proximity to active tectonic structures and high relief sites clearly outlines the role of seismic ground acceleration in producing large-scale slope instability events. lhe fourth chapter constitutes a preliminary approach to study slope instability based on PSlnSAR technique. lhe velocity and density of persistent PSs was analyzed to refine the classification of the activity status of the inventoried landslides using the PSI-based matrix approach. Furthermore, we used Hotspot and Cluster analysis (PSI-HCA) in order to detect PSs clusters associated with slow gravitational movement. lhe comparison between the results that were obtained through the PSIHCA and PSI-based matrix approach confirm the capability of both methods to detect landslide activity. lhe final chapter focuses on a detailed study of a complex deep-seated landslide. Field data collection enabled the identification of paleoseismic activity in landslide triggering. Furthermore, according to Holocene climatic reconstructions, the age constrains for the landslide reactivations are placed during one of the driest and hottest phases of the Holocene, which suggests that slope deformation is decoupled from the Holocene climatic trends.