The Anti-Atlas is reviewed and examined in the light of its geodynamic significance as a Palaeozoic basin and fold belt. Shortening is accommodated by polyharmonic buckle folding of the cover in a thick-skinned fashion without the development of any significant thrust/duplex systems. The Anti-Atlas is heavily inverted deep intracratonic basin, rather than a former passive margin of the Palaeo-Tethys Ocean. Inversion took place in Late Carboniferous to Early Permian times. Main shortening directions changed from NW-SE to north-south and maybe NE-SW through time, leading to the development of dome and basin patterns on scales from 100 m to 10 km.

The late Variscan Anti‐Atlas of Morocco shows some conspicuous deviations from the standard anatomy of foreland fold‐and‐thrust belts. Large basement inliers crop out at a very short distance of less than 50 km behind the southeastern front of the fold belt, reminiscent of Windriver‐style basement uplifts. In contrast to the Rocky Mountain foreland, however, the Anti‐Atlas basement uplifts punctuate tightly folded Paleozoic cover series similar in tectonic style to the Appalachian Valley and Ridge province. Cover shortening is exclusively accommodated by buckle folding, and the Anti‐Atlas fold belt lacks any evidence for duplexing or thrust faults other than the occasional steep reverse fault found near basement inliers. Basement domes have classically been considered as the result of vertical tectonics in a horst and graben fashion, or, alternatively, as large “plis de fond” [Argand, 1924], basement folds. Unfolding of a large portion of an Ordovician quartzite marker bed reveals a minimum shortening of 17% (30 km). Balancing this section at the crustal scale indicates a lower crustal detachment level at 18 to 25 km depth. Basement shortening is inferred to be accommodated through massive inversion of former extensional faults, inherited from a Late Proterozoic‐Lower Cambrian rifting phase.

We document two phases of folding within the central part of the Late Palaeozoic Anti‐Atlas chain of Morocco. A first generation of SW–NE folds involve a horizontal shortening of 10–20%, accommodated by polyharmonic buckle folding of contrasting wavelengths in Ordovician Jbel Bani quartzites and Devonian Jbel Rich carbonates. A second generation of folds with similar style and wavelengths in an E–W direction lead to complex interference patterns. Dome and basins are developed within the Jbel Rich and within Lower Cambrian dolomites. Both folding phases are related to thick‐skinned uplift of Precambrian basement in a Laramide style. In contrast to the typical Rocky Mountain foreland style, however, cover deformation in the Anti‐Atlas is mostly decoupled from the undying basement along thick incompetent horizons such as the Lower Cambrian Lie‐de‐Vin and Silurian shales.

<p>Since two centuries the European Alps are a natural laboratory to study continental lithosphere deformation during mountain building. Since the early studies, a constant question has been to evaluate the importance of vertical versus horizontal displacements in the building of reliefs. Whilst the occurrence of large thrust sheets, as initially proposed from field observations, are now well explained in the frame of plate tectonics, controversies still arise on the precise geometry, amount, and timing of major thrusting during the orogeny.</p><p>We present a new detailed 3D structural study of the cover/basement relationships in the Chamonix synclinorium in between the Mont-Blanc (MB) and Aiguilles Rouges (AR) ranges. These massifs are two of the main external basement ranges of the western Alps.  The study allows deciphering the area structural history: the Mesozoic sedimentary cover has been thrust at least 10km NW above the Helvetic Basal Décollement (HBD) before to be offset by late steep thrusts during exhumation in the Miocene.</p><p>Such interpretation fundamentally diverges from the classical view of the sedimentary cover of the Chamonix synclinorium being expulsed from a former graben during a single deformation phase and implies that a major thrust phase lasting ~10 Ma has been overlooked. Our observations show that the HBD was a major thrust system active between ~30 and ~20 Ma, possibly until 15 Ma, with a shortening of more than 10km in the south to 20km in the north. It extends below most of the subalpine ranges and emerges in front of the Bauges and within the Chartreuse and Vercors massifs, and was rooted east of the External Cristalline Massifs (Mont-Blanc and Belledonne). During the Miocene, the HBD was cut by steep reverse faults and uplifted above the basement culmination of the External Cristalline Massifs obscuring its continuity and precluding its recognition as a major structure even if it was previously described at several localities.</p>

<p>A 3D litho-structural model synthetizes a geological setting by defining 3D geometries of lithological layers considering stratigraphic relationships, weathering and tectonics. It combines quantitative and qualitative data from different dimensions and acquisition types (field measures and observations, geophysics, boreholes, DEM) into a single structured database. This aesthetic 3D representation enables to work on the same object, despite different sources of datasets, making it a highly useful integrative tool for various ways to monitor and analyze landslides prone areas.</p><p>This type of model is used on site scale for large phenomena, for a better understanding of their internal structure and to extract information to be included for failure numerical modelling. However, there are a very few examples of 3D geological models used for large areas subject to spatially limited events. Indeed, the transition from 2D to 3D information remains difficult, especially in case of sparse input data, reinforcing 3D interpretation uncertainties and decreasing the robustness of the model. Thus, most of regional scale geological 3D models used for landslides analyses are simplified and the different lithological layers used for susceptibility and hazard assessments suffer from uncertainties difficult to quantify.</p><p>The aim of this contribution is to show how two local scale 3D geological models can contribute and improve the robustness of a regional 3D geological model for the purpose of landslide susceptibility and hazard assessment. The local and regional 3D geological models integrate different data types of uneven quality by successive iterations, to interpret structural and lithological layers geometries with GeoModeller. This software is based on cokriging calculation method of orientation and location of geological interfaces and faults. The regional model will be compared to the local 3D models results, as references to assess regional model uncertainties. This iterative process enables to improve each 3D model with different data sets from one scale to another. Still, models results must be confirmed by field validation to reduce uncertainties as much as possible.</p><p>This study focuses on the 40 km long French Basque coast in the southwest of France, which presents complex faulting and geological heterogeneities inherited from the Pyrenean orogeny – these are relatively well mapped along the shore. Both of the local sites are different and characteristic of regional coastal geomorphological types and of specific lithological formations. These are made of flyschs, limestones and marls, the top of which are more or less weathered and capped by Quaternary detritic formations of variable thickness. This coast is subject to various types of shallow and moderately deep instabilities (slides, rockfalls and flows). By defining the geometry of lithology and faults, the 3D models results will enable to:</p><ul><li>Characterize how lithology and structures, as predisposition factors, influence landslides susceptibility to specific landslide types,</li> <li>Integrate lithological layers and structural discontinuities to physical-based models to assess landslide susceptibility and hazard on regional (1 : 25,000) and on local (1 : 2,500) scales,</li> <li>Improve the geological knowledge of the French Basque coast.</li> </ul>