Integration of sedimentology and GPR for high-resolution imaging of a carbonate platform

Ground-Penetrating Radar (GPR) has not been widely applied to the recognition of ancient carbonate platform geometries. This paper reports the results of an integrated study performed on an Upper Jurassic outcrop from the southeast Paris basin, where coral bioherms laterally change into prograding depositional sequences. GPR profiles illustrate the different bedding planes and major erosional unconformities visible at outcrop. A GPR profile conducted at the base of the cliff displays a palaeotopographic surface on which the outcropping bioherms settled. The excellent penetration depths of the GPR (20 meters with a monostatic 200 MHz antenna) images the carbonate platform geometries, ranging between outcrop workscale (some few meters) and seismic scale (several hundreds of meters). This study supports recent evidence of icehouse conditions and induced sea-level fluctuations controlling the Upper Jurassic carbonate production

The influence of bedrock topography on the dynamics of two clayey landslides in the Trièves (French Alps)

International audienceThe two large adjacent landslides of Avignonet and Harmalière, affecting thick clayey quater- nary deposits, are located in the Trièves area (French Alps). Remote techniques (Lidar) and GPS measure- ments were used to characterize the two landslides. Results show major differences between the dynamics of the two landslides, both in morphology, displacement rate magnitudes and motion directions. Seismic noise measurements (H/V technique) were performed to map the clay layer thickness. Combined with Lidar derived DEM, these data yielded the paleo-topography of the seismic substratum made of compact alluvial layers and Mesozoic bedrock. The difference in dynamics between the two landslides is likely to result from the pres- ence of a ridge of compact formations at the Avignonet landslide toe, preventing an eastward deep active slid- ing to develop and explaining the observed shallow slip surfaces. To the South, this buttress disappears at the Harmalière toe, favoring a deep sliding in a Southeastern direction with a fast regression of the headscarp, which evolves into a mudslide at its base

Caractérisation de l'endommagement d'une argile par mesures de la vitesse des ondes de cisaillement

International audienceLes glissements de terrain dans les argiles génèrent un endommagement interne du versant. Des essais de laboratoire et in situ ont montré que la mesure du paramètre sismique Vs (vitesse de propagation des ondes de cisaillement) permet de caractériser l'endommagement du matériau argileux et d'imager la zone affectée par le glissement de terrain

Lithological control on the kinematic pattern and the location of slip surfaces in a large clayey landslide (Trièves, French Alps)

39 pages (espace double)Although it has been studied for more than 30 years, the large clayey Avignonet landslide (western French Alps) exhibits a heterogeneous kinematic pattern which is still poorly understood. Conducting electrical resistivity tomography profiles over the whole landslide has allowed the presence of a superficial coarser layer to be detected in its upper north-western part. The extension of this more permeable layer matches the zone exhibiting low slide velocities values (lower than 2 cm/yr),suggesting a lithological and hydrogeological control on the landslide activity. The presence of this coarser layer was not detected before, because investigation efforts concentrated on the southern inhabited areas where displacement rates are the highest (10 cm/yr to 50 cm/yr) and the slope is only composed of laminated clays. Combined interpretation of seismic reflected waves and geological data has also evidenced the presence of a 10m thick sandy alluvial layer interbedded in the clayey sequence. Comparison between reflectors and slip surfaces detected in boreholes suggests a significant role of this coarse layer on the location of the deepest slip surface at about 40m. This study highlights the control of both vertical and horizontal lithological variations on the Avignonet landslide process and the necessity of combining various investigation techniques for understanding the complexity of large landslide mechanism

Elaboration d'un modèle géologique de structure anticlinale complexe : contribution aux études géotechniques d'un tracé routier et de ses ouvrages d'art (voie des Mercureaux, Besançon, est de la France)

International audienceLa partie du contournement de Besançon nommée voie des Mercureaux traverse de part en part le faisceau bisontin, composé de formations triasiques et jurassiques plissées et fracturées. De nombreuses études géologiques et géotechniques soulignent la complexité du site. Une cartographie géologique détaillée entre deux ouvrages d'art, sur une distance d'environ 500 m au cœur de l'anticlinal des Mercureaux, est proposée, afi n de localiser précisément les failles et d'estimer l'infl uence de niveaux évaporitiques du Trias sur la stabilité du tracé e des ouvrages. Une étude de terrain de détail a permis, d'une part, d'établir un log stratigraphique précis afi n de pouvoir identifi er les différentes unités marneuses présentes et, d'autre part, de cartographier une surface importante afi n de comprendre l'organisation géologique au sein du vallon. La carte géologique établie est fondée sur la synthèse de données existantes (bibliographie, études géotechniques) ainsi que sur un travail de terrain et de laboratoire (analyse de faciès, mesures de pendages et de directions, paléontologie, analyse de forages et de diagraphies). La connaissance détaillée de l'organisation du secteur permet de disposer de données fi ables pour le dimensionnement des ouvrages et du tracé, et rend compte des pièges géologiques comme les failles, duplex et micro- duplex, pouvant générer des instabilités, ainsi que la présence de gypse à faible profondeur pouvant induire des montées de fontis

Monitoring sismique et électrique d'un glissement-coulée (Pont-Bourquin, Suisse)

International audienc

Monitoring sismique et électrique d'un glissement-coulée (Pont-Bourquin, Suisse)

International audienc