10 research outputs found
Méthodes géo-électriques appliquées à l'hydrogéologie - capacités et limites pour la caractérisation des aquifÚres de glissements de terrain et de bassins versants de montagne
This thesis aims at studying the contribution of geoelectric methods for constraining hydro-geological models of deep-seated landslides and mountainous watersheds. Such applications require slope-scale studies up to few hundreds of meters depth in heterogeneous and fractured media. 1D Controlled Source Audiomagnetotellurics (CSAMT) helped characterizing the deep structure of the Strengbach granitic catchment (weathering profile). 3D electrical resistivity tomography helped locating the damaged hard-rock and aquifers of the micashistic SĂ©chilienne landslide, validating hypothesis on its hydrogeological functioning. Time-lapse CSAMT and induced polarization experiments were conducted at the LodĂšve landslide where intense meteorological events cause loss of cohesion in clay and evaporite units. The sensitivity of measurements and the pertinence of 1D, 2D and 3D imagery are systematically discussed as the methodology was developed accordingly. The modeling of CSAMT data was explored as strong hypotheses limit the applicability of the method. Complementary information was systematically integrated to the geoelectrical interpretation.Cette thĂšse analyse la contribution de mĂ©thodes gĂ©oĂ©lectriques pour la caractĂ©risation hydrogĂ©ologique de glissements de terrain profonds et de bassins versants de montagne. Ces applications nĂ©cessitent des Ă©tudes Ă lâĂ©chelle du versant jusquâĂ plusieurs centaines de mĂštres de profondeur. Des sondages audiomagnĂ©totelluriques Ă source contrĂŽlĂ©e (CSAMT) ont permis de caractĂ©riser la structure profonde (profil dâaltĂ©ration) du bassin versant granitique du Strengbach. Une tomographie 3D de rĂ©sistivitĂ© Ă©lectrique du versant instable de SĂ©chilienne a amĂ©liorĂ© la localisation la roche endommagĂ©e et la comprĂ©hension de son fonctionnement hydrogĂ©ologique. Un suivi du signal CSAMT et de polarisation induite a Ă©tĂ© rĂ©alisĂ© sur le glissement de terrain de LodĂšve, oĂč les pluies cĂ©venoles dĂ©stabilisent des unitĂ©s argileuses et Ă©vaporitiques. La sensibilitĂ©, la rĂ©solution et la dimensionnalitĂ© des mesures sont systĂ©matiquement discutĂ©es. La modĂ©lisation de donnĂ©es CSAMT a Ă©tĂ© explorĂ©e car des hypothĂšses fortes limitent l'applicabilitĂ© de la mĂ©thode. Des informations complĂ©mentaires ont guidĂ© les interprĂ©tations gĂ©oĂ©lectriques
Méthodes géo-électriques appliquées à l'hydrogéologie - capacités et limites pour la caractérisation des aquifÚres de glissements de terrain et de bassins versants de montagne
This thesis aims at studying the contribution of geoelectric methods for constraining hydro-geological models of deep-seated landslides and mountainous watersheds. Such applications require slope-scale studies up to few hundreds of meters depth in heterogeneous and fractured media. 1D Controlled Source Audiomagnetotellurics (CSAMT) helped characterizing the deep structure of the Strengbach granitic catchment (weathering profile). 3D electrical resistivity tomography helped locating the damaged hard-rock and aquifers of the micashistic SĂ©chilienne landslide, validating hypothesis on its hydrogeological functioning. Time-lapse CSAMT and induced polarization experiments were conducted at the LodĂšve landslide where intense meteorological events cause loss of cohesion in clay and evaporite units. The sensitivity of measurements and the pertinence of 1D, 2D and 3D imagery are systematically discussed as the methodology was developed accordingly. The modeling of CSAMT data was explored as strong hypotheses limit the applicability of the method. Complementary information was systematically integrated to the geoelectrical interpretation.Cette thĂšse analyse la contribution de mĂ©thodes gĂ©oĂ©lectriques pour la caractĂ©risation hydrogĂ©ologique de glissements de terrain profonds et de bassins versants de montagne. Ces applications nĂ©cessitent des Ă©tudes Ă lâĂ©chelle du versant jusquâĂ plusieurs centaines de mĂštres de profondeur. Des sondages audiomagnĂ©totelluriques Ă source contrĂŽlĂ©e (CSAMT) ont permis de caractĂ©riser la structure profonde (profil dâaltĂ©ration) du bassin versant granitique du Strengbach. Une tomographie 3D de rĂ©sistivitĂ© Ă©lectrique du versant instable de SĂ©chilienne a amĂ©liorĂ© la localisation la roche endommagĂ©e et la comprĂ©hension de son fonctionnement hydrogĂ©ologique. Un suivi du signal CSAMT et de polarisation induite a Ă©tĂ© rĂ©alisĂ© sur le glissement de terrain de LodĂšve, oĂč les pluies cĂ©venoles dĂ©stabilisent des unitĂ©s argileuses et Ă©vaporitiques. La sensibilitĂ©, la rĂ©solution et la dimensionnalitĂ© des mesures sont systĂ©matiquement discutĂ©es. La modĂ©lisation de donnĂ©es CSAMT a Ă©tĂ© explorĂ©e car des hypothĂšses fortes limitent l'applicabilitĂ© de la mĂ©thode. Des informations complĂ©mentaires ont guidĂ© les interprĂ©tations gĂ©oĂ©lectriques
Méthodes géo-électriques appliquées à l'hydrogéologie - capacités et limites pour la caractérisation des aquifÚres de glissements de terrain et de bassins versants de montagne
Cette thĂšse analyse la contribution de mĂ©thodes gĂ©oĂ©lectriques pour la caractĂ©risation hydrogĂ©ologique de glissements de terrain profonds et de bassins versants de montagne. Ces applications nĂ©cessitent des Ă©tudes Ă lâĂ©chelle du versant jusquâĂ plusieurs centaines de mĂštres de profondeur. Des sondages audiomagnĂ©totelluriques Ă source contrĂŽlĂ©e (CSAMT) ont permis de caractĂ©riser la structure profonde (profil dâaltĂ©ration) du bassin versant granitique du Strengbach. Une tomographie 3D de rĂ©sistivitĂ© Ă©lectrique du versant instable de SĂ©chilienne a amĂ©liorĂ© la localisation la roche endommagĂ©e et la comprĂ©hension de son fonctionnement hydrogĂ©ologique. Un suivi du signal CSAMT et de polarisation induite a Ă©tĂ© rĂ©alisĂ© sur le glissement de terrain de LodĂšve, oĂč les pluies cĂ©venoles dĂ©stabilisent des unitĂ©s argileuses et Ă©vaporitiques. La sensibilitĂ©, la rĂ©solution et la dimensionnalitĂ© des mesures sont systĂ©matiquement discutĂ©es. La modĂ©lisation de donnĂ©es CSAMT a Ă©tĂ© explorĂ©e car des hypothĂšses fortes limitent l'applicabilitĂ© de la mĂ©thode. Des informations complĂ©mentaires ont guidĂ© les interprĂ©tations gĂ©oĂ©lectriques.This thesis aims at studying the contribution of geoelectric methods for constraining hydro-geological models of deep-seated landslides and mountainous watersheds. Such applications require slope-scale studies up to few hundreds of meters depth in heterogeneous and fractured media. 1D Controlled Source Audiomagnetotellurics (CSAMT) helped characterizing the deep structure of the Strengbach granitic catchment (weathering profile). 3D electrical resistivity tomography helped locating the damaged hard-rock and aquifers of the micashistic SĂ©chilienne landslide, validating hypothesis on its hydrogeological functioning. Time-lapse CSAMT and induced polarization experiments were conducted at the LodĂšve landslide where intense meteorological events cause loss of cohesion in clay and evaporite units. The sensitivity of measurements and the pertinence of 1D, 2D and 3D imagery are systematically discussed as the methodology was developed accordingly. The modeling of CSAMT data was explored as strong hypotheses limit the applicability of the method. Complementary information was systematically integrated to the geoelectrical interpretation
Analyse de scénarios de réduction de vitesse du trafic maritime pour la mitigation de la pollution sonore sous-marine en Mer Méditerranée occidentale
Le bruit gĂ©nĂ©rĂ© par le trafic maritime est un contributeur important du paysage sonore sous-marin. Il est identifiĂ© comme une pollution par la communautĂ© scientifique et pris en compte au sein des textes rĂ©glementaires et des politiques publiques. La Directive Cadre StratĂ©gie Milieu Marin (DCSMM 2008/56/CE) vise Ă garantir un Ă©quilibre entre protection de lâenvironnement marin et dĂ©veloppement socio-Ă©conomique par lâatteinte et le maintien du Bon Etat Ecologique (BEE). Le BEE est dĂ©fini par onze descripteurs, et notamment par le critĂšre D11C2 (bruit continu), Ă©valuĂ© sur des cartes du bruit gĂ©nĂ©rĂ© par le trafic maritime. <par> La mesure principale considĂ©rĂ©e afin de limiter le bruit de trafic est la rĂ©duction de la vitesse des navires. LâefficacitĂ© dâune telle mesure est cependant difficile Ă anticiper, dâune part parce quâun ralentissement des navires entrainerait une densification plus importante du trafic, et dâautre part, parce que la propagation acoustique est dĂ©pendante de lâenvironnement. <par> Ce cas dâĂ©tude vise Ă quantifier lâimpact de diffĂ©rents scĂ©narios de rĂ©duction de vitesse de navigation sur le bruit de trafic. Lâanalyse est menĂ©e en MĂ©diterranĂ©e Occidentale, dans une zone dâhabitat prĂ©fĂ©rentiel du rorqual commun, oĂč le trafic maritime est dense. <par> La plupart des navires sont Ă©quipĂ©s dâĂ©metteur AIS (SystĂšme dâIdentification Automatique), communiquant les informations relatives au navire (identifiant, activitĂ©, longueur, etc.) et Ă sa navigation (position, vitesse, cap, etc.). Ces informations sont utilisĂ©es pour modĂ©liser le bruit rayonnĂ©. Les zones de rĂ©duction de vitesse sont simulĂ©es en modifiant les dates d'Ă©mission des AIS. Les niveaux sont propagĂ©s dans lâenvironnement pour rĂ©aliser des cartes de bruit stratĂ©giques. <par> Les rĂ©sultats sont analysĂ©s en fonction des activitĂ©s principales du trafic maritime et des zones dâhabitats des rorquals communs. LâefficacitĂ© du ralentissement pour la rĂ©duction du bruit est discutĂ©e au regard de lâĂ©valuation du D11C2, avec une attention particuliĂšre sur la maĂźtrise des incertitudes
Large-Scale Simulation of a Shipping Speed Limitation Measure in the Western Mediterranean Sea: Effects on Underwater Noise
Underwater noise from shipping activity can impact marine ecosystems in the long term and at large scale. Speed limitation has been considered to reduce noise emission levels. In this article, the effects of speed limitation on shipping noise levels are investigated at high spatial resolution (5 arc-min) in the Western Mediterranean Sea. Scenarios of maximum speed limits of 10 kt and 15 kn are computed. The impact of a speed reduction is time-dependent and tends to redistribute sources of noise temporally, smoothing the contrasts existing in marine traffic at the daily scale. The effectiveness of the measure is evaluated over short successive time windows (6 h), allowing for capture of the dynamic of the effect of speed reduction. Several metrics are proposed to evaluate the effectiveness of speed reduction as a mitigation measure according to its temporal stability. This study illustrates complex phenomena related to (1) the increased vessel density in the speed limitation area due to longer navigation time and (2) deep-water and shallow-water propagations. The bathymetry and the local distribution of traffic are two elements of importance with respect to the effectiveness and the stability of the measure, whereas the traffic properties seem to impact the stability of the effect in particular, and deep waters seem to increase the effectiveness. This research shows the areas in which the proposed measure would be the most effective
Structure hydrogéologique d'un bassin versant montagneux granitique obtenue d'aprÚs des jeux de données de résistivité électrique issus de plusieurs méthodes
International audienceAbstract Altered crystalline catchments are complex to study and model, as they present multiâscale properties that control their hydrogeological behaviour and that are difficult to capture through a single geophysical imaging technique. Several volumes of interest must be sampled in order that both smallâscale (porosity, layering) and largeâscale (bedrock, weathering, faults) heterogeneities can be captured. We propose a geoelectrical model of the Strengbach catchment (Vosges Mountains, France), aiming at identifying the weathered structures and hydrogeological functioning of the aquifer. This is achieved through electrical resistivity tomography (ERT) and ControlledâSource AudioâMagnetotelluric (CSAMT) measurements and the use of appropriate measurement setâups. Metersâscale shallow contrasts in the top soil, catchmentâscale shallow contrasts (top 30Â m), and largeâscale vertical contrasts (up to 150Â m) were resolved through this methodology. A structural interpretation is proposed, based on information provided by borehole measurements (gamma ray, optical images), analysis of sampled waters, and geological mapping. The limits at depth of the weathered and fractured granite, not detected by ERT, are detected by CSAMT. The analysis showed that the weathering state of the granite controls, at first order, the electrical resistivity signal. Shallow geoelectrical signal (first 30Â m) is particularly driven by surface conductivity and hence by the clay content, whereas deep geoelectrical signal may arise from both the ionic content of pore waters and the clay content. A structural model is proposed and discussed. Geoelectrical contrasts revealed several qualities of weathered saprolite between the northern and the southern slopes. The inferred structural model and the distribution of weathered and unweathered crystalline units are considered for their respective effect on the hydrogeology, leading to the proposition of a new hydrogeological conceptual model of the catchment
Characterizing fractures and shear zones in crystalline rock using anisotropic seismic inversion and GPR imaging
ISSN:1029-7006ISSN:1607-796
Geophysical inversion and machine learning of dense 3D seismic and resistivity models for imaging deep landslide structures
International audienceGeophysical imaging methods are often applied for analysing landslides; they can help detecting and localizing the landslide structures, distinguishing between lithologies, layers and slip surfaces of variable mechanical responses, and identifying the fluid storage and circulation paths.We present a joined analysis of two 3D geophysical models acquired from a dense electrical resistivity tomography (Fullwaver nodes) and a dense seismic travel-time tomography (DENSAR nodes) acquired at the Viella landslide (Hautes-Pyrenees, France). Fusion of the two geophysical models and of ancillary geotechnical and hydrogeological information from boreholes is carried out using machine learning, in order to predict the location of the different slope structures