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International audience; For the interpretation of archaeological geophysical data as archaeological features, it is essential that the recorded anomalies can be clearly delineated and analyzed, and therefore, care has been taken to obtain the best possible data. However, as with all measurements, data are degraded by unwanted components, or noise. This review clarifies the terminology, discusses the four major sources of noise (instrument, use of instrument, external, soil), and demonstrates how it can be characterized using geostatistical and wavenumber methods. It is important to recognize that even with improved instruments, some noise sources, like soil noise, may persist and that degraded data may be the result of unexpected sources, for example, global positioning system synchronization problems. Suggestions for the evaluation and recording of noise levels are provided to allow estimation of the limit of detection for archaeological geophysical anomalies.; Pour l'interprétation des données géophysiques archéologiques en tant que caractéristiques archéologiques, il est essentiel que les anomalies enregistrées puissent être clairement délimitées et analysées, et par conséquent, en prenant soin d'obtenir les meilleures données possibles. Cependant, comme pour toutes les mesures, les données sont dégradées par des composantes indésirables ou du bruit. Cet article de synthèse clarifie la terminologie, discute des quatre principales sources de bruit (instrument, utilisation d'un instrument, externe, sol) et montre comment il peut être caractérisé à l'aide de méthodes géostatistiques et de nombres d'onde. Il est important de reconnaître que même avec des instruments très performants, certaines sources de bruit, comme le bruit du sol, peuvent persister et que des données dégradées peuvent être le résultat de sources inattendues, par exemple des problèmes de synchronisation du système de positionnement global. Des suggestions pour l'évaluation et l'enregistrement des niveaux de bruit sont fournies pour permettre l'estimation de la limite de détection des anomalies géophysiques archéologiques.

This contribution reviews the challenges of imaging collisional orogens, focusing on the example of the Pyrenean domain. Indeed, important progresses have been accomplished regarding our understanding of the architecture of this mountain range over the last decades, thanks to the development of innovative passive imaging techniques, relying on a more thorough exploitation of the information in seismic signals, as well as new seismic acquisitions. New tomographic images provide evidence for continental subduction of Iberian crust beneath the western and central Pyrénées, but not beneath the eastern Pyrénées. Relics of a Cretaceous hyper-extended and segmented rift are found within the North Pyrenean Zone, where the imaged crust is thinner (10–25 km). This zone of thinned crust coincides with a band of positive Bouguer anomalies that is absent in the Eastern Pyrénées. Overall, the new tomographic images provide further support to the idea that the Pyrénées result from the inversion of hyperextended segmented rift systems., Cette contribution passe en revue les enjeux de l’imagerie des orogènes collisionnels, en se focalisant sur l’exemple du domaine pyrénéen. Au cours des dernières décennies, notre compréhension de l’architecture de cette chaîne de montagnes a connu des avancées importantes grâce au développement de techniques innovantes d’imagerie passive, s’appuyant sur une exploitation plus poussée de l’information dans les signaux sismiques, ainsi que de nouvelles acquisitions sismiques. Les nouvelles images tomographiques mettent en évidence la subduction continentale de la croûte ibérique sous les Pyrénées occidentales et centrales, mais pas sous les Pyrénées orientales. Les reliques d’un rift Crétacé hyper-étendu et segmenté se trouvent dans la zone nord-pyrénéenne, où la croûte imagée est plus mince (10–25 km). Cette zone de croûte amincie coïncide avec une bande d’anomalies de Bouguer positives qui est absente dans les Pyrénées orientales. Les nouvelles images tomographiques viennent globalement renforcer l’idée que les Pyrénées résultent de l’inversion de systèmes de rifts segmentés et hyper-étirés., This work is part of the OROGEN research project, a tripartite partnership between the CNRS, TOTAL and BRGM., With the institutional support of the ‘Severo Ochoa Centre of Excellence’ accreditation (CEX2019-000928-S).

The Yadana carbonate buildup is a mature gas field, located in the Andaman Sea, offshore Myanmar and producing since 1998. The reservoir is an isolated carbonate platform, Oligocene to Miocene in age, sealed below 1200 m of siliciclastic sediments. Predicting hydrocarbon resources and water flows during the production has become a major challenge for such mature carbonate gas fields. The present PhD work involves the implementation of a methodology that allows the construction of a detailed reservoir architecture that accounts for significant heterogeneity. The work is multiscale and multidisciplinary, covering discipline such as sedimentology, diagenesis, geochemistry, rock physics, geophysics and based on a large and comprehensive dataset including, cores, well logs, petrophysical measurements, production data and seismic data. First, three types of carbonate factory produced sediment on top of the platform under prevailing oligophotic to mesophotic conditions and periods of varying particulate organic matter supplies. The limited lateral changes in facies and the layer-cake depositional architecture inferred from well correlations, and the seismic expression suggest a deposition on a flat shelf. Carbonate production and accumulation were mainly controlled by light penetration, nutrient content and hydrodynamic conditions which are related to changes in monsoonal intensity, terrestrial runoff during the early Miocene in the Andaman Sea. Secondly, with an average porosity of 28%, the diagenesis is an important controlling factor of the reservoir properties. Mud-supported, coral-rich sediments record significant early marine dissolution of aragonite and early lithification of the matrix and a major decrease in porosity (up to10%) below the gas-water contact suggests a major phase of porosity evolution during and/or after the hydrocarbon emplacement. By modifying drastically porosity and pore networks, the diagenesis largely controls the acoustic architecture and seismic expression of the reservoir. The well-to-seismic tie allowed to precisely evidencing the origin of the main seismic reflectors. They may form, within the gas zone, at the boundary between two diagenetic/acoustic units or result from the interference between reflection at the base and top of such intervals. Early marine lithification of coral-rich intervals generates high amplitude and continuous reflectors and a stratigraphy-cross-cutting reflector forming at a major and laterally continuous shift in porosity relates differential diagenetic evolution between the gas and the water zones. Finally, because the scattering of the elastic properties at a given porosity in carbonate is mainly relative to pore type variations, a rock physics inversion scheme based on DEM approaches (Differential Effective Medium modeling; Xu and Payne 2009) has been developed to quantify the pore type effect from the well log and the seismic elastic properties. After the calibration of the method to the real pore type geometry from rock data, the inversion is performed (upscaling) on the 3D seismic data to map the geobodies relative to pore type variations. This approach allows a relevant prediction of geological seismic scale heterogeneity impacting for example the fluid flows and the water rises in the reservoir during the production.Providing a robust framework for the characterization of the Yadana gas reservoir, the thesis gives further insights into the understanding of geological and environmental factors controlling Cenozoic isolated carbonate systems in South East Asia. This work highlights the interdependence existing between geology and seismic imaging and demonstrates that an integrated geological/geophysical characterization of carbonate reservoirs are essential for both the exploration and the production of hydrocarbon resources., La plateforme carbonatée de Yadana est le réservoir principal d’un champ de gaz en Mer d’Andaman, au large des côtes Birmanes produisant depuis 1998. Le réservoir est d’âge Oligocène-Miocène et est scellé par 1200 m de sédiments silicoclastiques. Prédire les ressources en hydrocarbure et les mouvements des fluides durant la production est un challenge majeur pour ce champ devenu mature. Le présent travail de thèse met en place une méthodologie aboutissant à la construction détaillée de l’architecture du réservoir. Ce travail est multi-échelle, intégratif, multidisciplinaire couvrant des domaines tels que la sédimentologie, la diagenèse, la géochimie, la physique des roches, la géophysique et se base sur un large et complet jeu de données incluant des carottes, des diagraphies, des mesures petrophysiques, des données de production ainsi que des données de sismique 3D. D’un point de vue sédimentologique, trois types d’usines à carbonates ont été identifiés, produisant les sédiments au sommet de la plateforme dans des conditions oligophotiques à mésophotiques. Les faibles modifications latérales de facies et l’architecture de dépôt en couches stratifiées déduite des corrélations de puits et de l’imagerie sismique suggèrent un dépôt sur un haut-fond à faible relief. La production et l’accumulation des carbonates étaient, au début du Miocène principalement contrôlé par la pénétration de la lumière, la teneur en éléments nutritifs et les conditions hydrodynamiques elles-mêmes liées aux variations d’intensité de la mousson, aux apports terrigènes et à l’activité des courants d’upwelling en mer d’Andaman.Avec une porosité moyenne de 28%, la diagenèse est un facteur de contrôle important des propriétés réservoir. Les sédiments riches en coraux enregistrent une dissolution marine de l’aragonite ainsi qu’une lithification précoce de la matrice. L’analyse géochimique suggère que le hiatus de dépôt au sommet de la plateforme est lié à un ennoiement de la plate-forme. La diminution importante de la porosité (jusqu’à 10%) en dessous du contact gaz-eau suggère une phase majeure d’évolution de la porosité pendant et/ou après la mise en place des hydrocarbures. En modifiant considérablement la porosité et le réseau poreux, la diagenèse contrôle en grande partie l’architecture acoustique et sismique du réservoir. La calibration puits sismique a permis de mettre en évidence l’origine des réflecteurs sismiques. Ils se forment ainsi, dans la zone à gaz, à la limite entre deux unités diagénétiques ou résultent d’interférences entre les réflexions de la base et du sommet de ces intervalles. La lithification marine précoce des intervalles à coraux génère des réflecteurs de fortes amplitudes, continus, et assimilables à des lignes-temps chronostratigraphiques. En revanche, un réflecteur diachrone, recoupant la stratigraphie, est généré au niveau d’un contraste de porosité au voisinage du contact eau-hydrocarbure. Enfin, une méthode d’inversion pétrophysique basée sur une approche DEM (Differential Effective Medium theory) a été développée et appliquée sur les données de sismique 3D. Cette approche a permis de prédire de manière pertinente les hétérogénéités géologiques ayant une incidence sur les écoulements de fluide et la montée du niveau d’eau dans le réservoir. Fournissant un cadre géologique robuste à la caractérisation du réservoir de Yadana, la présente thèse apporte également des informations supplémentaires sur la compréhension des facteurs géologiques et environnementaux contrôlant les systèmes de carbonates isolés cénozoïques en Asie du Sud-Est. Ce travail met en évidence l’interdépendance existante entre la géologie et l’imagerie sismique et démontre que les caractérisations paléoenvironnementale et diagénétique sont essentielles à la fois en phase d’exploration, mais aussi en phase d’évaluation et de production d’hydrocarbures.

Near Surface Geoscience Conference and Exhibition 2019, La Haye, PAYS-BAS, 08-/09/2019 - 12/09/2019; To prevent catastrophic consequences imputed to levee breakage, the identification of the subsoil constitutive materials, as well as the detection of interfaces and anomalies are crucial. During investigation campaigns, complementary geophysical and geotechnical methods are usually used. These two sets of methods provide data with very different spatial scales, levels of incompleteness, uncertainty and inaccuracy. The effective combination of these two different types of data is challenging. In this work, we propose the fusion of geophysical and geotechnical data by means of Belief Functions, implementing Smets and Dempster-Shafer rules. We demonstrate our approach on a real case study, at Saint-Clément-des-Levées (France) including one geophysical method (electrical resistivity tomography) and two geotechnical ones (cone penetrometer and grain size analysis after drilling). This work also aims at supplying a better visual representation of a levee section with related degrees of belief. Our results highlight the ability of our fusion methodology to properly characterize the considered materials as well as to indicate the positions of the interfaces and the associated levels of confidence.

Fluvial levees are assets of major importance for protecting human lives and activities. To prevent the risk of failures and to assess their stability, survey campaigns involving geophysical and geotechnical methods are needed. These two types of methods play highly complementary roles and provide information of different natures, uncertainties and spatial distributions. In this work, we first present the function of fluvial levees and describe the associated physical properties that may become pathological and lead to failure mechanisms. Then for each presented investigation method, we introduce : its basic principles, its ability to characterize specific physical properties (or characteristics) of fluvial levees, and then its advantages and drawbacks under specific environmental conditions. It should be emphasized that geophysical and geotechnical methods are placed on an equal footing in order to assist agencies and levee managers in selecting the most relevant ones to assess the condition of their levees and characterize potential weak zones, according to a specific type of pathology and to the environmental constraints. Throughout this review, we introduce a certain amount of literature that is believed to be of potential interest to the research community as well. We also draw attention to some lack of information on the application of specific methods to levee investigation. Finally, we discuss some complementarities of the presented methods and we propose a dedicated comparative table, leading us to suggest new method combinations for levee investigation.

A ~1000 m3 rockslide occurred close to Lorca (SE Spain) during the main shock (Mw = 5.1) of the May 2011 seismic sequence. The location of the rockslide, within 10 km of the earthquake epicenter and along the southern slope of a valley in which similar geological conditions occur on both slopes of the valley, suggests a significant near-field effect due to local seismic response. This could be related to the specific interaction between the topography and the obliquely propagating seismic waves. A dynamic stress strain numerical model was constructed using the FLAC 7.0 finite difference code to back analyze the Lorca rockslide event and relate its occurrence to both the local seismic amplification and the interaction between seismic waves and local topography. The results indicate that only for seismic waves with incidence angles in the range 0°–50° are the occurred slope instabilities expected. These results do not significantly change when varying the values for either stiffness or strength parameters within the range of the experimental data., This work was partially funded by research groups VIGROB-53 and VIGROB-184 (Universidad de Alicante) and by the projects tec2008–06764–c02–02 and CGL2011–30153–c02–02.

24th European Meeting of Environmental and Engineering Geophysics, PORTO, PORTUGAL, 09-/09/2018 - 13/09/2018; To prevent disastrous consequences imputed to levee breakage, assessment methodologies have to be improved. Geophysical and geotechnical investigation methods are usually used to make such assessments. However, the effective combination of these two specific types of data remains a challenge. We propose the fusion of geophysical and geotechnical data by means of Belief Functions. Here we demonstrate our approach on a synthetic case study including geophysical (electrical resistivity) and geotechnical (cone-bearing) data and by implementing Smets and PCR5 normalization rules. This new data combination approach allows the characterization of horizontal interfaces and of a geological structure initially hidden by the effects of a highly conductive body.

A groundwater exploration work in the Tamanrasset region in southern Algeria was started in August 2016 to assess the water reserves in the hydrogeological system related to the Oued Tamanrasset underflow water table which overcomes a volcanic basement. Five (05) electrical resistivity tomography (ERT) surveys were conducted in Tamanrasset area by using ABEM Terrameter LS system. the low electrical contrast between wet alluvium and water saturated alterites makes difficult the electrical response interpretation. to overcome the difficulties of interpretation of ERT profiles, field investigations, laboratory tests and software simulations, were carried out in order to clearly identify the structure of the hydrogeological system. The experimental investigation of the electrical characteristics of the alluvium as a function of water saturation was carried by the use of two devices (Wenner α and Schlumberger). Samples true resistivity values varies between 50 Ω.m for a 100% saturated sample and 1250 Ω.m for a 25% saturation sample. The interpretation of the measurements by the RES2DINV software made it possible to give 2D images of the subsoil up to a depth of 50 m. the electrical contrast between the bedrock and the overlying formations made it possible to identify it, however, it was difficult to distinguish alterites from alluvium. A methodology combining piezometric survey, geo-electrical measurements and field observations improves the interpretation of electrical tomography profiles and the application of the ERT method for accurate characterization of water resources in the Tamanrasset region.

When water cannot be discharged to superficial water body or the discharge volume needs to be limited, treated wastewater downstream a treatment plant can be infiltrated. Operational and environmental challenges emerge from this practice: how to size infiltration facilities and what will be the impact of the treated wastewater on groundwater quality? Preliminary studies are recommended for soil-based constructed wetlands and compulsory when permanent infiltration is needed. Unfortunately there is no guideline on how to deal with spatial heterogeneity of soil properties. They can greatly influence water pathway in the soil and the quantities of treated wastewater that can infiltrate. The aim of this article is to introduce a methodology that associates geophysical measurements and more localized ones in order to better described the near-surface with a particular focus on field saturated hydraulic conductivity. Starting from the fastest and coarsest method, the suggested hierarchical process allows optimizing the sampling strategies for longer and more accurate measurements. Therefore, such a methodology, while increasing the quality of results, may also reduce the time and cost of preliminary studies. Two applications are presented demonstrating the advantages of associating several methods. They also underline the input of using geophysical methods on soil that have been largely modified by human activity. Lorsqu'il n'existe pas d'autre exutoire possible ou que l'on souhaite réduire les volumes déversés vers le milieu récepteur superficiel, l'eau usée traitée à la sortie des stations d'épuration est infiltrée à proximité. Cette pratique fait émerger des questionnements d'ordre opérationnel et environnemental : comment dimensionner un ouvrage d'infiltration et quels sont les impacts éventuels sur le milieu récepteur souterrain ? Des études préalables sont recommandées pour les zones de rejet végétalisées et obligatoires dans le cas des zones d'infiltration mais aucun document ne précise comment prendre en compte l'hétérogénéité spatiale des propriétés du sol. Ces dernières pouvant fortement influencer le cheminement de l'eau vers la nappe ainsi que les quantités susceptibles d'être infiltrées. Le présent article introduit une méthodologie couplant des mesures géophysiques spatialisées et des mesures ponctuelles afin de décrire au mieux la configuration de la proche surface, notamment sa conductivité hydraulique au champ. Le processus hiérarchique proposé permet, en allant de la mesure la plus rapide et la moins précise, à la mesure la plus longue et la plus précise, d'optimiser les plans d'échantillonnage et ainsi réduire le temps et le coût de l'étude. Deux exemples d'application de la méthodologie sont présentés mettant particulièrement en évidence la complémentarité des outils et l'apport de la géophysique notamment sur des milieux fortement remaniés par l'homme.

This paper investigates the combined use of extensive geotechnical, hydrogeological and geophysical techniques to assess a small earth dyke with a permanent hydraulic head, namely a canal embankment. The experimental site was chosen because of known issues regarding internal erosion and piping phenomena. Two leakages were visually located following the emptying of the canal prior to remediation works. The results showed a good agreement between the geophysical imaging techniques (Electrical Resistivity Tomography, P- and SH-waves Tomography) and the geotechnical data to detect the depth to the bedrock and its lateral variations. It appeared that surface waves might not be fully adapted for dyke investigation because of the particular geometry of the studied dyke, non-respectful of the 1D assumption, and which induced depth and velocity discrepancies retrieved from Rayleigh and Love waves inversion. The use of these classical prospecting techniques however did not allow to directly locate the two leakages within the studied earth dyke. The analysis of ambient vibration time series with a modified beam-forming algorithm allowed to localize the most energetic water flow prior to remediation works. It was not possible to detect the leakage after remediation works, suggesting that they efficiently contributed to significantly reduce the water flow. The second leakage was not detected probably because of a non-turbulent water flow, generating few energetic vibrations.

About a decade ago, a large field of pockmarks, covering an overall area of 36 km(2) was discovered in water depths of < 30m in the central part of the Bay of Concarneau (Southern Brittany, France). This field, composed of features from 5 m to 35 m in diameter and < 1 m in depth, is characterized by unusual high densities of pockmarks, up to 5840 per square kilometre. Geophysical data correlated with sedimentary samples acquired in 2005 and 2009 show that pockmarks and their immediate surroundings are associated with dense tubes benches cover, built by a filter-feeding amphipod: Haploops nirae, forming original benthic communities. Two complementary surveys were carried out in April 2011 (Pock and Ploops) and April 2014 (Pock and Tide), on the Oceanographic Vedette (O/V) Haliotis (Ifremer/Genavir), to map the limit of the pockmarks and Haploops fields with the maximum accuracy. The link between the presence of the Haploops nirae communities and the occurrence of pockmarks / gas was then established and the proposed hypothesis was that tidal cycles may provide a good candidate for a short-term (monthly) triggering mechanism of fluid expulsion (Baltzer A, Ehrhold A, Rigolet C, Souron A, Cordier C, Clouet H. 2014. Geophysical exploration of an active pockmark field in the Bay of Concarneau, southern Brittany, and implications for resident suspension feeders. Geo-Marine Letters, 34, 215-230). Due to the high-level precision (50 cm) of the positioning system (Magellan Aquarius Ixsea Hydrins) coupled with the RTK attitude system, these new bathymetric and imagery maps together with the sub-bottom Chirp profiles, allow us to compare the data sets from April 2011 and April 2014. The superimposition of the two data sets shows that the distribution of the pockmarks remains similar between these 2 dates (i.e. for 3 years), for the group of large, widely scattered pockmarks, which are deeply rooted in the Holocene palaeo-valley infills and for the group of pockmarks identified as the trawl-scour pockmarks, initiated by trawling action. Most of the pockmarks present very recent shapes without any infilling but sonar imagery reveals that some of them have been covered by a thin muddy layer, thereby reflecting, at least, a temporary cessation of expulsion or a different activity. Chirp profiles indicate some acoustic flares above the pockmarks, revealing gas/fluid expulsion. Different gas clues within the sedimentary column, such as acoustic turbidity, enhanced gas reflectors (EGR), chimneys pipes, occur at exactly the same places on the chirp seismic profiles from 2011 and 2014. Therefore, contrary to most examples described in the literature, this pockmarks field is still active., Un large champs de pockmarks, couvrant une surface de 36 km2, a été découvert il y a une dizaine d'années, dans la partie centrale de la Baie de Concarneau (Bretagne sud, France), par moins de 30 m de fond. Ce champs de pockmarks, composé de cratères mesurant de 10 à 30 m de diamètre pour des profondeurs de 1 m maximum est caractérisé par une densité exceptionnelle, atteignant jusqu'à 5840 structures par km2. Des données géophysiques, corrélées et complétées par des prélèvements sédimentaires entre 2005 et 2009, ont montré que ce champs de pockmarks est associé à la présence de colonies de Haploops nirae, petit amphipode filtreur benthique, habitant dans des tubes fixés sur le fond et formant de larges banquettes. Deux campagnes complémentaires ont été réalisées en Avril 2011 (Pock and Ploops) et Avril 2014 (Pock and Tide), sur la vedette océnographique Haliotis (Ifremer/Génavir), afin de cartographier très précisément la limite des champs de Haploops et des pockmarks. Le lien constaté (mais non élucidé) de la présence des colonies de Haploops et de ces pockmarks implique une activité répétée des pockmarks, et la marée comme facteur déclenchant à court terme constitue l'hypothèse la plus robuste (Baltzer A, Ehrhold A, Rigolet C, Souron A, Cordier C, Clouet H. 2014. Geophysical exploration of an active pockmark field in the Bay of Concarneau, southern Brittany, and implications for resident suspension feeders. Geo-Marine Letters, 34, 215–230). Grâce au système de positionnement RTK, les données d'imagerie, de bathymétrie et de l'échosondeur à sédiments (chirp) ont pu être parfaitement superposées et donc comparées entre 2011 et 2014. Les premiers résultats montrent que la répartition des pockmarks reste similaire entre ces 2 dates pour le groupe de grands pockmarks dispersés, enracinés plus profondément dans le remplissage sédimentaire holocène des paléo-vallées et le groupe de pockmarks plus petits, plus denses, alignés le long des traces de chaluts de pêcheurs. La plupart des pockmarks présente des cratères sans remplissage sédimentaire, bien qu'il existe dans certains, un fin drappage de vase révélé par l'imagerie sonar, reflétant des arrêts temporaires de l'activité d'expulsion des fluides ou bien un fonctionnement différent. Les profils chirp montrent également des panaches dans la colonne d'eau, indiquant de probables expulsions de fluides/gaz. Plusieurs indices de la présence de gaz sont systématiquement visibles dans la colonne sédimentaire, tels que “la turbidité acoutisque”, les “réflecteurs acoustiques marqués”, les “chimneys pipes”. Ainsi, contrairement à beaucoup d'exemples cités dans la littérature, ce champs de pockmarks est encore actif.

In anticipation of the upcoming InSight mission, which is expected to deploy a single seismic station on the Martian surface in November 2018, we describe a methodology that enables locating marsquakes and obtaining information on the interior structure of Mars. The method works sequentially and is illustrated using single representative 3-component seismograms from two separate events: a relatively large teleseismic event (Mw5.1) and a small-to-moderate-sized regional event (Mw3.8). Location and origin time of the event is determined probabilistically from observations of Rayleigh waves and body-wave arrivals. From the recording of surface waves, averaged fundamental-mode group velocity dispersion data can be extracted and, in combination with body-wave arrival picks, inverted for crust and mantle structure. In the absence of Martian seismic data, we performed full waveform computations using a spectral element method (AxiSEM) to compute seismograms down to a period of 1 s. The model (radial profiles of density, P- and S-wave-speed, and attenuation) used for this purpose is constructed on the basis of an average Martian mantle composition and model areotherm using thermodynamic principles, mineral physics data, and viscoelastic modeling. Noise was added to the synthetic seismic data using an up-to-date noise model that considers a whole series of possible noise sources generated in instrument and lander, including wind-, thermal-, and pressure-induced effects and electromagnetic noise. The examples studied here, which are based on the assumption of spherical symmetry, show that we are able to determine epicentral distance and origin time to accuracies of ∼ 0.5–1° and ± 3–6 s, respectively. For the events and the particular noise level chosen, information on Rayleigh-wave group velocity dispersion in the period range ∼ 14–48 s (Mw5.1) and ∼ 14–34 s (Mw3.8) could be determined. Stochastic inversion of dispersion data in combination with body-wave travel time information for interior structure, allows us to constrain mantle velocity structure to an uncertainty of ∼ 5%. Employing the travel times obtained with the initially inverted models, we are able to locate additional body-wave arrivals including depth phases, surface and Moho (multiple) reflections that may otherwise elude visual identification. This expanded data set is reinverted to refine interior structure models and source parameters (epicentral distance and origin time).

The seismic imaging methods currently in the development stage need to be tested for experimental validation under controlled conditions. Yet natural media are very complex, and moreover, the parameters along the measurement profile prove difficult to evaluate independently of the seismic method itself. To satisfy this need, the ultrasonic measurement laboratory (MUSC) presented in this research has been devised to experimentally model seismic field measurements by using reduced-scale models. This facility is composed of small-scale models of the underground, an optical table with two moving arms, a laser interferometer, and adapted piezoelectric transducers used as the seismic sources. The source system has been adapted to simulate the behavior of a point-surface seismic source. This is essential to reproduce the spatial energy distribution of a surface seismic source and supersedes the sources used in the past for other reduced-scale seismic experimental models. The comparisons of experimental data collected with MUSC and numerical data simulated by means of finite-element viscoelastic modeling indicate very good agreement of time arrivals and amplitudes for a range of propagation distances until the amplitude has decreased to the system noise level. These results demonstrate that the MUSC laboratory is a system with plenty of promise for validating seismic imaging methods through testing on a perfectly known propagation model prior to field application.

International audience; Wave flume experiments have been performed to investigate a sandy cliff recession under monochromatic wave forcing. We varied the wave climate through the wave energy flux F and the surf similarity parameter j. The various processes of the cliff erosion cycle are depicted. The sea bed evolution mostly depends on the surf similarity parameter j. Steep planar (j > 0.7), gentle planar (0.5 < j < 0.7) and bared (j < 0.5) profiles are observed. We observed different bar dynamics, including steady and unsteady self-sustained oscillating states. Then we analyze the role of the eroded material on the cliff recession rate. We show that the cliff recession rate increases with the wave energy flux. Moreover, for a given wave energy flux, it is larger for a gentle planar profile than for a bared profile. However it is similar for both a bared profile and a steep planar profile. The cliff recession rate is not a monotonic function of the cliff height as the type of bottom profile influences the wave energy at the cliff.

International audience; The coastal area of Jableh, in the vicinity of the Saladin and Al-Marquab castles, is a fertile alluvial plain located on the northwestern part of Syria, in what was once the crusader Principality of Antioch. In order to detail the coastal environment during the crusader period in the Middle East, palynological analyses have been conducted on the underlying coastal-alluvial deposits. The recovered sediments represent a continuous record of the environmental history of the area spanning a c. AD 850—1850 cal. yr period, from the Muslim Era up to and including the late Ottoman times. During the local crusader period (AD 1100—1270), the area was dominated by an arborescent mattoral mixed with a xerophytic shrub-steppe. The alluvial plain was slightly waterlogged and colonized by a wetland meadow with an open vegetation of steppe-like character on bare surfaces and fresh arable soils. The riparian and open deciduous riverine forests were weakly developed. Signs of agricultural activities are mainly recorded for the High Medieval period (AD 1000—1300), with an increase of vineyards in the coastal area. Since c. AD 1250 cal. yr until the end of the crusader period, agricultural activities never reached the same intensity as during the Mameluke Sultanate and the Ottoman Empire.

Tectonic, environmental and human evolution in the Afar triangle ; This review describes the evolution of the Afar Region, documented through abundant geological and palaeontological literature. The region constitutes the heart of the Arabo-African rift system. Its history has been characterized by intense tectonic and volcanic activities. These favoured the fossilization of abundant biological and cultural evidence from the Miocene (ca. 11 Ma) up to now. The main prehuman species that lived in the Afar are described in their environmental context, and their evolution is commented. The Afar, as a centre of evolution, as a dead-end or as a dispersal pathway, provides unique archives of our deep history., Cet article propose une synthèse de l’évolution de la région Afar documentée par de nombreux travaux géologiques et paléontologiques. La région est le cœur du système de rift arabo-africain. Son histoire est marquée par une activité tectonique et volcanique intense. Cette activité a permis la fossilisation de nombreux témoins biologiques et culturels depuis le Miocène (vers 11 Ma) jusqu’à l’actuel. Les principales espèces de préhumains ayant vécu dans l’Afar sont décrites dans leur contexte environnemental et leur évolution est commentée. L’Afar, qu’il s’agisse d’un centre d’évolution, d’un cul-de-sac ou d’une zone de passage, nous offre des archives uniques au monde sur notre histoire profonde., Boisserie Jean-Renaud. Évolutions tectonique, environnementale et humaine dans le triangle afar. In: Annales d'Ethiopie. Volume 25, année 2010. pp. 115-138.

The area described in this article was ‘detected’ by the Laboratory for Landscape Archeology and Remote Sensing, University of Siena research team during aerial prospection in spring 2005. Analysis of the aerial photographs allowed interpretation of the site as a triple-ditched enclosure. During subsequent field-walking survey a number of archaeological artefacts were collected and mapped. Differential global positioning system (DGPS) survey confirmed the morphological pattern of the site, which seems to represent a survival of the Early Medieval Age settlement pattern on the coastal plain. The field-walking and DGPS surveys were followed by a programme of geophysical survey combining three different methods: differential magnetics (Overhauser probe), ground-penetrating radar (GPR) and Automatic Resistivity Profiler (ARP©, Geocarta). Finally, three sample areas were excavated, mainly to test the evidence collected previously. The excavation data – ditches, post-holes, domestic pottery, animal bones, and wall remains – support the interpretation of the site as the first earth-and-timber castle mound, or motte, to be identified in Tuscany. Copyright © 2009 John Wiley & Sons, Ltd.

In this study, near-surface geophysical techniques are used to investigate the physical characteristics of the Buyukcekmece landslide (Istanbul, Turkey). The Buyukcekmece landslide has continuous activity at a low velocity and is classified as a complex mechanism. It includes rototranslational parts, several secondary scarps, several landslide terraces, and evidence of two earth flows. It mainly develops in the clayey layers of the Danismen Formation. According to our findings, P-wave velocities ranging from 300 m/s to 2400 m/s do not provide notable discrimination between sliding mass and stable soil. They show variations in blocks reflecting a complex structure. We obtained the S-wave velocity structure of the landslide up to 80 m by combining the analysis of MASW and ReMi. It is clear that S-wave velocities are lower in the landslide compared to those of the stable area. Identical S-wave velocities for the entire area at depths higher than 60 m may point out the maximum thickness of the landslide mass. Resonance frequencies obtained from the H/V analysis of the landslide area are generally higher than those of the stable area. The depths computed by using an empirical relationship between the resonance frequency and the soil thickness point out the failure surfaces from 10 to 50 m moving downslope from the landslide crown area. The resistivity values within the landslide are generally lower than 30 Ω m, i.e., a typical value for remolded clayey debris. The geophysical results reflect an overview of the geological model, but the complexity of the landslide makes it difficult to map the landslide structure in detail.

The mysterious loss of five calvaria of Homo erectus and three skulls of Homo sapiens sapiens, unearthed from Zhoukoudian, a world cultural heritage site, during World War II is a great loss for paleoanthro- pological research. Although frontal and occipital bones of Homo erectus were unearthed in 1966, additional important human fossils cannot be found due to the fact that most of the fossil-bearing deposits were removed in early diggings at ZKD Locality 1, the so-called Peking Man Site. From 1995 to 2004, a series of in situ geological and geophysical investigations using electromagnetic, electric panel, magnetic, microgravity, electric tomograms, surface seismic waves, ground penetrating radar, and test drilling methods, were conducted on Dragon Bone Hill, where the Peking Man Site is located. Here, we report that some geophysical anomalies have been clearly detected and there are still significant deposits suitable for archaeological excavations in hidden cavities in the hill, which demonstrate how some civil engineering methods can be employed for archaeological purposes.

In order to investigate aquifers, several geophysical surveys have been carried out in the Baril area of the southern flank of Piton de la Fournaise volcano on Reunion in the Indian Ocean using audiomagnetotelluric (AMT), very-low-frequency (VLF) and self-potential (SP) methods. We present the results with emphasis on a comparison between SP data and the findings of geoelectric surveys. AMT soundings have indicated, from the surface downward, three layers : (i) resistive volcanic rocks, (ii) an intermediate resistivity layer, and (iii) a conductive basement attributed to a seawater-bearing aquifer. VLF measurements allow the mapping of the first layer apparent resistivity, and therefore its bottom, when the true resistivity is supposed to be isotropic and homogenous. When this assumption does not hold, only the SP method permits the mapping of this bottom. Because of the good agreement between the SP and electromagnetic results, we propose the SP method as the first tool that should be used in studying shallow hydrogeological structures in volcanic areas. (Résumé d'auteur)

A geophysical survey was carried out on the eastern flank of Piton de la Fournaise volcano in the Grand Brule area using combined audiomagnetotelluric (AMT) and time domain electromagnetic (TDEM) techniques. The aims of the present study were firstly to define the shallow geoelectrical structure, and subsequently to locate large bodies of ground water with anomalous electrical properties. Most of the AMT sites are isotropic across the entire observational bandwidth (7500-10 Hz), except for a few sites where static-shift effects are present. Joint one-dimensional interpretation of the TDEM and AMT data indicates basically three-layered structures with the following resistivity zones, progressing from the surface downward: (1) a resistive unsaturated surface layer of subaerial basaltic flows with a 2000 to 10,000 ohin-m resistivity, its base being approximately at mean sea level, (2) an intermediate-resistivity layer (100-250 ohm-m) 50–300 m thick, interpreted as being fresh-water-saturated basaltic formations, and (3) a low-resistivity layer of less than 15 ohm-m probably due to more saline water at depth and/or higher clay content in crushed materials. In the center of the study area, the results have also shown the presence of a prominent boundary dividing the area into a southern zone where the aquifer sequence is thin (60-100 m) and a northern zone corresponding to a relatively thick aquifer (>150 m). Geoelectrical models are compared with the available geological information given by two geothermiic exploration drillings. The coastal drill hole gives a crucial information, i.e. the thick intermediate-resistivity layer in the northern part of Grand Brule can be related to water-saturated alluvium deposits down to 200 m below sea level. AMT and TDEM soundings have revealed a major paleoalluvial drainage system buried under recent lava flows. A delimitation of sectors with different hydrogeological characteristics can be proposed.

Surface geophysics has been used for a number of years to solve a variety of major groundwater exploration problems in coastal and island regions. The electrical properties of near‐surface rocks are highly dependent on porosity, degree of saturation, and pore fluid resistivity (Keller and Frischknecht, 1966). Because the resistivity of the formations decreases with increasing salinity of the water content, electrical methods, such as vertical electrical soundings, time‐domain electromagnetic soundings, and audiomagnetotellurics (AMT), are well‐suited for mapping changes in groundwater salinity and, in particular, for detecting a fresh water‐salt water interface.

The velocity structure in the crest beneath the central Andes of northern Bolivia is obtained by the simultaneous inversion of local earthquake arrival-time data for velocity and hypocentral parameters. The data were recorded between October 1990 and February 1991 by the French "Lithoscope" network; the 34 vertical, short-period seismic stations were installed along a 320-km-long profile crossing two main morphological units of the Andean chain; the Altiplano and the Eastern Cordillera. The arrival times of seismic waves generated by earthquakes located in the subduction zone of the Nazca plate underneath the South American plate were inverted using a modified version of Thurber's 3-D iterative simultaneous inversion code. The results are consistent with the inversion of teleseismic travel-time residuals from the same network and closely correlate with the mapped surface geological features. The Altiplano Basin is characterized by a low-velocity zone down to 20 km, enclosed by the San Andres and Laurani faults. At the surface, the Cordillera Real fault zone (CRFZ) bounds to the west the high P-wave velocity anomaly lying under the axial zone of the Eastern Cordillera. The velocity discontinuity dips steeply to the southwest, to the bottom of the crust. From the velocity model, the depth of the Moho is estimated to be 66 km under the Altiplano. Moreover, the different behaviour of P- and S-waves found below the Western Cordillera and above the slab is consistent with the presence of partially melted asthenosphere that may be responsible for the magmatic activity. Finally, the seismicity defines, between 90 and 225 kin, a part of the slab dipping to the north-northeast with a low angle of about 30 ° .

Resistivity investigations were carried out on an elementary watershed in SW Cameroon, firstly to assess the applicability of direct-current (DC) resistivity methods to solve various pedological problems in intertropical regions, and subsequently to determine the relationships between electrical resistivities and pedological properties of lateritic soil systems. The survey included measurements in pits with a small Wenner fixed-spacing array (SWA), vertical electrical soundings (VES) and vertical electrical “quick soundings” (VEQS) both using the Schlumberger configuration. The VES data were interpreted using a conventional multilayer inversion program to obtain best-fit models. Constraints to the interpretation of these data were provided by SWA and pedological information from existing observation pits. The results of the interpretation reveal five distinct geoelectrical layers overlying a resistive bedrock. The first is a thin organo-mineral upper layer with low resistivities in the range 250–450 Ωm. The second layer corresponds to micro-aggregated clayey materials and is more resistive (1300–1800 Ωm). The third represents the main part of ferruginous materials and is even more resistive (2000–4500 Ωm). The fourth corresponds to unsaturated saprolite and the last to saturated saprolite (ground water) with resistivities ranging from 800 to 1500 Ωm and from 150 to 250 Ωm, respectively. Estimates of soil volumes for the entire study area were obtained from VEQS interpretations. Most of the soil cover corresponds to saprolite (74%, 1 4 being saturated by ground water), while topsoil and ferruginous materials represent 14 and 12%, respectively. Finally, geophysical results based upon 1-D inversion provide a satisfactory approximation of the various lateritic components' 3-D geometry over the watershed. The study provides original quantitative results concerning the behaviour of intertropical soil systems as well as some geomorphological keys for soil mapping at a regional scale.

ISI Document Delivery No.: 129XZ Times Cited: 1 Cited Reference Count: 36 Cited References: Altamimi Z., 2007, J GEOPHYS RES, V112 Arnault S, 2011, MAR GEOD, V34, P319, DOI 10.1080/01490419.2011.584833 BAMBER JL, 1994, INT J REMOTE SENS, V15, P925 Berry PAM, 2005, GEOPHYS RES LETT, V32, DOI 10.1029/2005GL022814 Bertiger W, 2010, J GEODESY, V84, P327, DOI 10.1007/s00190-010-0371-9 BERTIGER WI, 1994, J GEOPHYS RES-OCEANS, V99, P24449, DOI 10.1029/94JC01171 BIRKETT C, 1995, INT GEOSCI REMOTE SE, P1979 Birkett CM, 2002, J GEOPHYS RES-ATMOS, V107, DOI 10.1029/2001JD000609 Birkett CM, 1998, WATER RESOUR RES, V34, P1223, DOI 10.1029/98WR00124 Birkett CM, 2010, MAR GEOD, V33, P204, DOI 10.1080/01490419.2010.488983 Birkett CM, 1995, J GEOPHYS RES-OCEANS, V100, P25179, DOI 10.1029/95JC02125 Bonnefond P, 2010, MAR GEOD, V33, P80, DOI 10.1080/01490419.2010.487790 Cheng KC, 2010, MAR GEOD, V33, P186, DOI 10.1080/01490419.2010.487802 Cretaux JF, 2011, MAR GEOD, V34, P291, DOI 10.1080/01490419.2011.585110 Cretaux JF, 2009, J GEODESY, V83, P723, DOI 10.1007/s00190-008-0289-7 Dettmering D, 2010, MAR GEOD, V33, P150, DOI 10.1080/01490419.2010.487779 Dumont J.P., 2008, OSTM JASON 2 PRODUCT Frappart F, 2006, REMOTE SENS ENVIRON, V100, P252, DOI 10.1016/j.rse.2005.10.027 Frappart F, 2005, REMOTE SENS ENVIRON, V99, P387, DOI 10.1016/j.rse.2005.08.016 Fu L., 1991, EOS T AM GEOPHYS UNI, V72 Haines BJ, 2010, MAR GEOD, V33, P91, DOI 10.1080/01490419.2010.491028 Leon JG, 2006, J HYDROL, V328, P481, DOI 10.1016/j.hydrol/2005.12.006 Loyer S, 2012, J GEODESY, V86, P991, DOI 10.1007/s00190-012-0559-2 Marty J.C., 2009, DOCUMENTATION ALGORI, P564 Mercier F., 2007, EOS T AGU S, V89 Mercier F., 2003, JOINT EGS AGU M NIC Mertikas SP, 2010, MAR GEOD, V33, P114, DOI 10.1080/01490419.2010.488973 Mertikas SP, 2011, MAR GEOD, V34, P261, DOI 10.1080/01490419.2011.584837 MORRIS CS, 1994, J GEOPHYS RES-OCEANS, V99, P24527, DOI 10.1029/94JC01642 Pavlis NK, 2012, J GEOPHYS RES-SOL EA, V117, DOI 10.1029/2011JB008916 Ponchaut F, 1998, CR ACAD SCI II A, V326, P13, DOI 10.1016/S1251-8050(97)83198-9 Quartly G.D., 2010, MARINE GEODESY S1, V33 Roux E., 2008, HYDROL SCI J, V53 Silva J.S., 2010, REMOTE SENS ENVIRON, V114, P2160 Washburn SA, 2011, MAR GEOD, V34, P277, DOI 10.1080/01490419.2011.590114 Watson C, 2011, MAR GEOD, V34, P242, DOI 10.1080/01490419.2011.584834 Seyler, Frederique Calmant, Stephane da Silva, Joecila Santos Moreira, Daniel Medeiros Mercier, Franck Shum, C. K. SEYLER, Frederique/D-5518-2011; SILVA, Joecila/B-1478-2014 CASAM Project; IHESA Project; CPRM; IRD (Dinamica Fluvial do Sistema Amazonas-Solimoes); CNES (TOSCA project FOAM); NASA; OSU Climate, Water, and Carbon (CWC) Program CASAM and IHESA Projects supported this research. GPS field work was funded by CPRM and IRD (Dinamica Fluvial do Sistema Amazonas-Solimoes) and by CNES (TOSCA project FOAM). The authors thank the students involved in the Research Initiation Program of RHASA, Research Team at Amazonas State University, Brazil, who produced the Jason 2 time series. The Ohio State University (OSU) component of the research is partially supported by NASA, and by the OSU Climate, Water, and Carbon (CWC) Program. 1 ELSEVIER SCI LTD OXFORD ADV SPACE RES; A major interest of radar altimetry over rivers is to monitor water resources and associated risk in basins where there is little or no conventional in situ data. The objective of the present study is to calibrate altimetry data in a place where conventional data are available, and use the results to estimate the potential error committed in the estimation of water levels in an ungauged or poorly gauged basin. The virtual stations extracted with Jason-2 in this study concern a very broad sample of river channel width and complexity. Minimum channel width has been estimated at 400 m. Unlike TOPEX/Poseidon (TIP), Jason-2 seems to have the capability to distinguish the river bed from its floodplain. The quality of the results obtained with Jason-2 is incomparably better than that obtained with TIP. Despite the fact that no absolute calibration has been assessed for river in this study, the bias calculated converge around 0, 35 m, which could be then the error estimated on the water stage derived from Jason-2 ranges, when no other validation is available. ICE3 algorithm seems to be performing as well as ICE1, and further research is needed to design retracking algorithm specifically for continental water. (C) 2012 COSPAR. Published by Elsevier Ltd. All rights reserved.

SUMMARY Altimetric measurements of sea-surface heights have long been used to locate uncharted marine features. Newly available data sets (Geosat-GM, ERS-1 and Topex/Poseidon), now allow the topography of submarine volcanoes to be accurately restored and a method based upon inverse modelling is presented in this paper. This method allows a joint assimilation of altimetric data and shipborne profiles of bathymetry and/or gravity anomalies when available. Furthermore, uncertainties can be computed together with the topography, which constitutes a noticeable improvement since these parameters are still missing in the usual bathymetric data bases. Tests are performed using simulated data, in order to characterize the errors which may or must occur with the modelled topography of a previously unknown volcano, in particular the errors due to data uncertainties and the lack of precise knowledge of sensitive parameters that are used in the modelling. These errors can be maintained under the 100 m level (rms) for altimetric data with a measurement noise of 5 cm (rms) or less, which is achieved for Geosat, ERS-1 and Topex/Poseidon altimeters. An example of inversion of Seasat data is presented in the case of a seamount in French Polynesia.

Controlling factors (predisposition, triggering) of landslides as well as their mechanism and kinematic behaviour can be extremely heterogeneous and interact on very versatile time constants. Numerous gaps exist in the evaluation of the hazard associated with this process, in particular for slow landslides which can evolve into faster slides. Indeed, landslides show some behaviour which is very variable in time and space which is characterized by a large range of displacement rates (from less than 1 centimetre per year to a few meters per day) and the presence of irregularities and large heterogeneities in the distribution of their petrophysical properties. Classical techniques of observation and investigation allow us to get only localized information which is not enough to quantify the time and spatial variability. As a result of which landslide numerical models are calibrated and validated over a limited amount of data. Recent developments in multiparameter geophysical imaging allowed some improvements in the direct and indirect acquisition of data on the deformation (photogrammetry, images correlation, laser scanner) and petrophysical parameters (electric tomography and seismic refraction). Although not as precise as the classical techniques, they have the advantage of providing multi-scaled and spatially distributed information. A major difficulty is to combine this spatial information to the ones obtained with classical technologies (GPS, extensometry, piezometry, geotechnology) and integrate them into a conceptual model coherent for the modelisation. Some scientific works have begun to combine different approaches obtained from field observations (geomorphology, geology) and instrumental data (hydrogeophysics, photogrammetry, laser scan). The objective is to develop methodologies which allow one to spatially determine the diverse major characteristics of landslides (intern structuration, hydrologic behaviour, kinematic behaviour, deformation mechanism). A conceptual model of the functioning and modelling of the hydro-mechanical behaviour of landslides with Z-soil and Slow-Mov codes is proposed. The sites selected for our analysis are the marly landslides of Super-Sauze and La Valette in the basin of Barcelonnette (Alpes-de-Haute-Provence). The research is presented in four parts and the objectives are as follows: 1. To characterize the internal structure and 3D geometry of landslides with the help of geophysical, geotechnical and geomorphologic data ; 2. To propose a hydrological conceptual model of the non saturated zone followed by temporal and spatial monitoring of electric resistivity and piezometric data analysis ; 3. To characterize the kinematics of landslides from terrestrial remote sensing platforms (photogrammetry and laser scan) combined with aerial platforms and differential GPS monitoring. 4. To identify the thresholds of hydrological and kinematics regime changes with numerical modelling. The results highlight the vast scope of application of the main imaging technologies for the investigation of landslides and allow us to define their limitations of use. Some future research will develop these various methodologies for surveillance purposes and to improve the predictive capabilities of the hazard., Les facteurs de contrôle (prédisposition, déclenchement) des glissements de terrain, leurs mécanismes et leurs comportements cinématiques peuvent être extrêmement hétérogènes et interagir sur des constantes de temps très variées. De nombreuses lacunes existent dans l'évaluation de l'aléa associé à ces processus, en particulier pour les glissements lents qui peuvent évoluer en coulées rapides. Les glissements-coulées présentent en effet des comportements très variables dans le temps et dans l'espace caractérisés par un large spectre de vitesses de déplacement (de moins de un centimètre par jour à plusieurs mètres par jour) et la présence de discontinuités et de grandes hétérogénéités dans la répartition de leurs propriétés pétro-physiques. Les techniques d'observation et d'investigation classiques permettent d'obtenir des informations ponctuelles qui ne sont pas suffisantes pour quantifier ces variabilités spatiales et temporelles. Une des conséquences est que, bien souvent, les modèles numériques de glissement ne sont calés et validés que sur un nombre limité d'observations in-situ. Les développements récents en imagerie géophysique multi-paramètres ont permis de progresser dans l'acquisition directe et indirecte de données sur la déformation (photogrammétrie, corrélation d'images, scanner laser) et les paramètres pétro-physiques (tomographie électrique et sismique réfraction). Malgré une précision souvent inférieure à celles des techniques classiques, elles ont l'avantage de fournir des informations multi-échelles et distribuées spatialement. Combiner ces informations spatiales à celles obtenues par les techniques classiques (GPS, extensométrie, piézométrie, géotechnique) et les intégrer dans un modèle conceptuel cohérent pour la modélisation numérique constitue une difficulté majeure. Des travaux scientifiques ont été engagés en combinant différentes approches issues d'observations de terrain (géomorphologie, géologie) et de données instrumentales (hydrogéophysique, photogrammétrie, scanner laser). L'objectif est de développer des méthodologies permettant de déterminer spatialement les différentes caractéristiques majeures des glissement-coulées (structuration interne, comportement hydrologique, comportement cinématique, mécanisme de déformation). Un modèle conceptuel de fonctionnement et des modélisations du comportement hydro-mécanique des glissements-coulées avec les codes Z-Soil et Slow-Mov sont proposés. Les sites d'étude retenus pour notre analyse sont les glissements-coulées marneux de Super-Sauze et de La Valette dans le Bassin de Barcelonnette (Alpes-de-Haute-Provence). Les travaux de recherche sont présentés en quatre parties dont les objectifs sont : 1. De caractériser la structuration interne et la géométrie 3D des glissement-coulées à l'aide de données géophysiques, géotechniques et géomorphologiques ; 2. De proposer un modèle conceptuel hydrologique de la zone non saturée par suivi temporel et spatial de résistivités électriques et par l'analyse de données piézométriques ; 3. De caractériser la cinématique des glissements-coulées à partir de plateformes terrestres de télédétection (photogrammétrie et scanner laser) combinées à des plateformes aériennes et à des suivis par GPS différentiel ; 4. D'identifier des seuils de modifications de régimes hydrologiques et cinématiques par la modélisation numérique. Les résultats soulignent le vaste champ d'application des principales techniques d'imagerie pour l'investigation des glissement-coulées et permettent de définir leurs limites d'utilisation. Des études futures devraient permettre de développer ces différentes méthodologies à des fins opérationnelles de surveillance et pour améliorer les capacités de prédiction de l'aléa.

La Belgique et les régions voisines sont situées loin des limites des plaques tectoniques, pourtant, l'activité sismique y démontre l'existence de phénomènes géodynamiques récents. Le séisme historique le plus important (magnitude 6 ¼) au nord des Alpes s'est produit le 18 septembre 1692 dans le nord de l'Ardenne et a été fortement destructeur dans la région de Verviers, provoquant des dégâts légers jusqu'à Londres. L'étude de l'activité sismique en Ardenne et l'identification de failles actives en lien avec la tectonique active régionale est donc primordiale pour la caractérisation du cadre séismotectonique et donc de l'évaluation de l'aléa sismique de la région.L'activité sismique depuis 1985, date de l'installation du réseau sismique moderne en Belgique, a été étudiée en matière de localisation relative des séismes et de caractérisation de leur distribution spatiale en relation avec les mécanismes au foyer. Cette étude a été effectuée après adaptation, comparaison et évaluation de la qualité des différents algorithmes de relocalisation disponibles. Une structuration de l'Ardenne a été mise en évidence en étudiant la relation entre la distribution géographique et la profondeur d'occurrence des séismes. Différents alignements des foyers sismiques et le lien avec une structure plane ont été déterminés, par exemple dans la région de Charleroi, sous les Hautes-Fagnes ou dans la région de Manderfeld. La corrélation entre les structures de la croûte sous l'Ardenne mises en évidence par les grandes études géophysiques dans les années 70-80 et la distribution géographique des séismes illustrent le rôle important joué par la Zone Faillée de Hockai, qui limite l'Ardenne en terme de propriétés rhéologiques déduites de la profondeur des foyers sismiques. Nous montrons aussi la faiblesse de l'hypothèse affirmant que la Faille du Midi accommode la déformation actuelle dans nos régions. De même, la corrélation entre les anomalies magnétiques et gravimétriques de la croûte sous l'Ardenne a été étudiée qualitativement. Les causes et conséquences du soulèvement Cénozoïque ont été critiquées objectivement. Cette première partie permet de dessiner un cadre séismotectonique bien défini en Ardenne.L'identification de failles actives sur le terrain en Ardenne est compliquée par le faible taux de déformation qu'elle subi. Les grands tremblements de terre sont peu fréquents et leur trace éventuelle à la surface est rapidement effacée par l'érosion et l'altération. La Zone Faillée de Hockai (ZFH), siège supposé du séisme de 1692, a été étudiée par des méthodes de prospections géophysiques le long d'un profil de 6 km sur la Crête de la Vecquée. Différentes structures ont pu être mises en évidence, certaines en lien avec la stratigraphie et d'autres avec des structures faillées orientées dans une direction similaire à celles connues pour la ZFH. Ce premier profil d'envergure donne des arguments importants pour la recherche de failles actives en lien avec la ZFH au niveau de la Crête de la Vecquée et leur lien potentiel avec la séquence de séismes de 1989-1990., Doctorat en Sciences, info:eu-repo/semantics/nonPublished

La Belgique et les régions voisines sont situées loin des limites des plaques tectoniques, pourtant, l'activité sismique y démontre l'existence de phénomènes géodynamiques récents. Le séisme historique le plus important (magnitude 6 ¼) au nord des Alpes s'est produit le 18 septembre 1692 dans le nord de l'Ardenne et a été fortement destructeur dans la région de Verviers, provoquant des dégâts légers jusqu'à Londres. L'étude de l'activité sismique en Ardenne et l'identification de failles actives en lien avec la tectonique active régionale est donc primordiale pour la caractérisation du cadre séismotectonique et donc de l'évaluation de l'aléa sismique de la région. L'activité sismique depuis 1985, date de l'installation du réseau sismique moderne en Belgique, a été étudiée en matière de localisation relative des séismes et de caractérisation de leur distribution spatiale en relation avec les mécanismes au foyer. Cette étude a été effectuée après adaptation, comparaison et évaluation de la qualité des différents algorithmes de relocalisation disponibles. Une structuration de l'Ardenne a été mise en évidence en étudiant la relation entre la distribution géographique et la profondeur d'occurrence des séismes. Différents alignements des foyers sismiques et le lien avec une structure plane ont été déterminés, par exemple dans la région de Charleroi, sous les Hautes-Fagnes ou dans la région de Manderfeld. La corrélation entre les structures de la croûte sous l'Ardenne mises en évidence par les grandes études géophysiques dans les années 70-80 et la distribution géographique des séismes illustrent le rôle important joué par la Zone Faillée de Hockai, qui limite l'Ardenne en terme de propriétés rhéologiques déduites de la profondeur des foyers sismiques. Nous montrons aussi la faiblesse de l'hypothèse affirmant que la Faille du Midi accommode la déformation actuelle dans nos régions. De même, la corrélation entre les anomalies magnétiques et gravimétriques de la croûte sous l'Ardenne a été étudiée qualitativement. Les causes et conséquences du soulèvement Cénozoïque ont été critiquées objectivement. Cette première partie permet de dessiner un cadre séismotectonique bien défini en Ardenne. L'identification de failles actives sur le terrain en Ardenne est compliquée par le faible taux de déformation qu'elle subi. Les grands tremblements de terre sont peu fréquents et leur trace éventuelle à la surface est rapidement effacée par l'érosion et l'altération. La Zone Faillée de Hockai (ZFH), siège supposé du séisme de 1692, a été étudiée par des méthodes de prospections géophysiques le long d'un profil de 6 km sur la Crête de la Vecquée. Différentes structures ont pu être mises en évidence, certaines en lien avec la stratigraphie et d'autres avec des structures faillées orientées dans une direction similaire à celles connues pour la ZFH. Ce premier profil d'envergure donne des arguments importants pour la recherche de failles actives en lien avec la ZFH au niveau de la Crête de la Vecquée et leur lien potentiel avec la séquence de séismes de 1989-1990., Doctorat en Sciences, info:eu-repo/semantics/published

La prospection géophysique multi-méthodes du pergélisol alpin dans la Valle di Sceru (sud des Alpes suisses, Canton du Tessin) à l’aide de méthodes thermiques (température des sources et de la surface du sol), à l’aide de méthodes thermiques (température des sources et de la surface du sol), de résistivité (sondage géoélectrique) et électromagnétiques (VLF-R et conductivimètre EM31) a permis de déterminer la répartition et les caractéristiques du pergélisol dans les glaciers rocheux et les éboulis étudiés. La répartition du pergélisol dans les glaciers rocheux est assez homogène et généralement contrôlée par les conditions topoclimatiques du site. Pour les éboulis, au contraire, l’extension spatiale du pergélisol est le plus souvent hétérogène et la probabilité d’occurrence du pergélisol diminue en direction du haut du versant. Les processus qui semblent contrôler la répartition du pergélisol dans les éboulis sont les échanges d’air advectifs, la redistribution de la neige (par le vent et les avalanches) et le granoclassement longitudinal. L’étude a également permis de tester les méthodes électromagnétiques utilisées et de les valider pour la prospection du pergélisol alpin. The multi-method geophysical prospecting of alpine permafrost in the Sceru Valley (southern Swiss Alps, Ticino Canton) with thermal methods (spring temperature and ground surface temperature monitoring), DC-resistivity method (Vertical Electrical Sounding) and electromagnetic methods (VLF-R and conductivity-meter EM 31), allowed determining the permafrost distribution and characteristics in the investigated rockglaciers and talus slopes. The permafrost distribution is quite homogeneous in the rockglaciers, where it is generally controlled by the topoclimatic conditions of the site. In the talus slopes, the permafrost distribution is quite heterogeneous and the probability of permafrost occurrence decreases upslope. The main processes controlling this particular permafrost distribution are the chimney effect, the redistribution of snow by wind and avalanches and, finally, the increase of grain size downslope. The study also allowed testing electromagnetic methods and to validating their application in the prospecting of alpine permafrost.

Audiomagnetotelluric (AMT) soundings have been made at 14 sites along a 7 km profile in the Tonkouto-Leoba area across Early Proterozoic formations of the Kedougou Inlier in Eastern Senegal. The purpose of the study was to gain information about the electrical properties of the Mako Supergroup. The results, shown in the form of apparent resistivity pseudosections, indicate marked anisotropies for orthogonal components recorded at all sites. Consequently, two-dimensional (2-D) modelling is required to establish the electrical characteristics of the major geological units. The modelling results indicate resistivities in the range 20 000– 100 000 Ωm for the Early Proterozoic units which extend to depths of 18 km. A major discontinuity characterized by a resistivity of 1000 Ωm may arise from a structural change associated with the southeastern boundary of the Kakadian batholith. Beneath the highly resistive formations, a sharp fall of resistivity has been detected, which may be due in part to the presence of trapped fluids.

International audience; Results from geophysical investigations (electrical resistivity, electromagnetic mapping and seismic refraction) on an excavated cell of the Ouled Fayet (Algiers, Algeria) pilot landfill indicated the presence of an underground runoff and permeable soil underneath the cell. These results contradict those obtained by a feasibility study, based, however, only on the analysis of seventy-six 10-m drilling cores. The 1D boreholes information has been proven to be insufficient and to give biased results. The presence of water at depth is evidenced by lower resistivity, high conductivity anomalies and increase of P-wave velocity. Thus, to the contrary of what is claimed in the feasibility study, a threat of leachate pollution is real. This study shows that landfill construction studies cannot give trustful results without geophysical investigations. More specifically, in Algeria, it is imperative to elaborate a landfill construction code, which should include mandatory geophysical prospecting and deeper drilling cores.

To progress in the monitoring and understanding of soil water processes, geophysical methods can be helpful because they are noninvasive and as such do not disturb either the structure or the water dynamics of the soil. In this study we attempt to image water infiltration dynamics under a tension infiltrometer in a vertical two-dimensional (2D) plane using electrical resistivity tomography (ERT). Two-dimensional images of soil electrical resistivity at different times were obtained using a Wenner array with 32 electrodes and a 10-cm spacing during the infiltration of a Cl– or Br– solution at 0.36 and 0.34 M, respectively. This procedure allowed monitoring the development of the infiltration bulb through time. Both unipotential and multipotential infiltrations were performed and used to derive soil hydraulic conductivity and sorptivity values. Anion concentrations in soil samples taken after infiltration were compared with resistivity values obtained with ERT measurements. The axisymetrical pattern of the multipotential infiltration exhibited large distortions, well detected and imaged by the ERT and consistent with the anion concentration data. In general, images derived from 2D inversions of ERT measurements underestimated the depth of the infiltration bulb. Axisymetrical inversion software would be helpful for the interpretation of ERT data taken below tension disc infiltrometers. The ERT on a small scale seems a helpful and promising tool for deriving in situ soil hydraulic parameters and for monitoring infiltration processes without the need for placing sensors into the soil.

The Aghajari field is located in the Dezful Embayment, one of major structural zone in Zagros fold-thrust belt containing most of Iranian oil fields. The late Oligocene-early Miocene Asmari formation is one of the main reservoir rocks of SW Iran with several decades of production history from different oil fields in the region. The objective of the present Ph-D thesis is to improve the structural understanding of the Aghajari field using 3D seismic imaging for the first time, and well seismic. the lack of seismic response of the dipping horizons in the reservoir oil zone constitutes a major identified difficulty. Given the dip values of 30° to 45° of the reflectors in the pay zone, the P-P reflections are expected to appear mainly on the horizontal components of the VSP data, justifying the processing of the 3 components (3C). An innovative method of 3C VSP orientation was developed. The 3C VSP results confirm the presence of dipping reflectors, with dip values in agreement with surface seismic, on the eastern flank of the structure. Several new approaches of seismic imaging have been applied in order to investigate and improve the reservoir illumination. The “Beyond Dix” workflow of CGGVERITAS was applied to land seismic data for the first time; this process enables to build a depth/velocity model from the dips read on the PSTM image (pre-stack time migration), and the residual move out corrections. The depth migrated image is improved in the overburden, unfortunately not at reservoir level, due to low signal to noise, interference with multiples, thus poor dip and velocity determination in the reservoir interval. A new Kirchhoff PSTM prototype technique was developed in IFP, allowing a selection of azimuth sector, offset range and geological dip, with automatic optimization of the local dip. The results from this new technique show clear improvements in dip determination and signal to noise ratio of the migrated image. The additional study of another exploration anticline in Zagros, using surface seismic, well data, VSP and geological information illustrates how an integrated data analysis can improve the understanding of deep structures, and therefore help making more reliable drilling decisions, if achieved timely. In Zagros, Surface seismic is definitely a good tool for the structural exploration, but its application to fine reservoir studies has not been demonstrated, in spite of the efforts achieved in the present study., Le Champ d'Aghajari est situé dans le Dezful, une des zones du Zagros structurée par d'importantes failles de charriage, et contenant la majeure partie des champs d'huile iraniens. La formation calcaire de l'Asmari, datant de la fin Oligocène à début Miocène, constitue l'une des principales couches réservoir du Sud-Ouest de l'Iran, avec un historique de production de plus d'un demi siècle pour plusieurs champs de cette région. L'objectif de cette thèse est de mieux comprendre la structure de ce champ, connu principalement par les puits de production,grâce à la première sismique 3D récemment acquise et en intégrant les informations fournies par la sismique de puits. Le problème principal est que le toit et la base du réservoir n'apparaît pas dans la zone à huile du réservoir, où les interfaces sont très pentés. Étant donné l'importance des pendages (environ 40°), les réflexions en sismique de puits zéro offset sont attendues principalement sur les composantes horizontales, ce qui rend impératif le traitement des 3 composantes. Une méthode originale d'orientation des 3 composantes est employée et les résultats confirment laprésence de réflecteurs pentés, en accord avec la sismique de surface sur le côté Est de la structure.Plusieurs nouvelles approches d'imagerie ont été appliquées afin de comprendre et résoudre les problèmes d'illumination de la zone réservoir. Nous avons appliqué pour la première fois en terrestre l'approche « Beyond Dix » de CGGVERITAS qui permet de construire un modèle profondeur à partir de pendages et courbure résiduelles move-out mesurée sur les images PSTM (pré-stack time migration). Les résultats migrés en profondeur sont plus précis dans le recouvrement mais la zone réservoir n'est pas améliorée. La raison en est queles images temps ne permettent pas de mesurer les pendages et courbures résiduelles dans la zone d'intérêt en raison d'une part de fort multiples et d'autre part d'u niveau de bruit important.Une nouvelle technique prototype de migration PSTM a été développée à l' IFP, permettant une sélection de l'azimut, du pendage géologique et la recherche automatique du meilleur pendage locale. L'application de ces techniques est très encourageante et montre qu'il est possible d'extraire les réflexions pentées en améliorant le rapport signal sur bruit de la migration elle-même.L'étude additionnelle d'exploration d'une autre structure anticlinale du Zagros, par utilisation combinée de sismique de surface, des données de puits, du PSV et de l'information géologique, illustre comment l'analyse intégrée des données permet d'améliorer la compréhension des structures profondes, et de contribuer à prendre de meilleures décisions de forage, dans la mesure où cette intégration est suffisamment rapide.Au final, dans le Zagros, la sismique de surface est définitivement une bonne méthode d'exploration structurale, mais son application aux études fines de réservoir n'a pas été démontrée, malgré les efforts effectués.

International audience; This paper presents the results of a geophysical survey which was performed in the Sarliève marsh, located in the north of the Massif Central (France). The studied area corresponds to an ancient lake filled with 6 m of Lategla-cial to historic sediments. The numerous cores and excavations previously performed in basin areas show the presence of thick fine grained and carbonated lake deposits. The mineralogical study of these deposits allows us to distinguish two main types of formations, which differ in their composition and origin. In the lower part of the sedimentary filling, the SDLF formation is generally characterized by abundant chalky and dolomitic layers, probably formed by chemical precipitation in an endoreic environment. It was found only in the distal (or depocenter) parts of the ancient lake. The upper part of the filling corresponds to calcitic clayey silty sediments (CF), mainly of detrital origin. They can be found both in the distal and proximal parts of the ancient lake. In order to precise the geometry of the marsh sedimentary filling and to discriminate between these two fine grained sediment types (SDLF and CF), an electromagnetic survey was carried out using an EM31 conductivity meter. It was completed by 16 electrical soundings performed within the marsh. The electromagnetic survey enables us to draw a large-scale conductivity map, which highlights the presence of a highly conductive zone (HCZ) in the central part of the marsh, more pronounced in the south. The HCZ is bordered by more resistive and heterogeneous fields, where conductive structures are visible. We show that there is no clear correlation between the measured conductivity and the total lacustrine sediment thickness. However, the HCZ is related to the distal parts of the ancient lake, locally identified from borehole data. In the corresponding sedimentary filling, the SDLF formation appears as a very low resistive layer (about 1.2 ⍀.m) on the electrical soundings. It explains the high conductivity of the distal lacustrine sediments. We finally combine the cores and the geophysical data to estimate the spatial extent and the volume of the SDLF formation of the whole marsh. This study shows that geophysics can contribute to distinguish, in a globally homogeneous fine grained sedimentary filling (carbonated clayey silts), lacustrine sediments formed in very different contexts, one as chemical precipitation, the other of detrital origin; Dans cette note, nous présentons les résultats d'une prospection géophysique réalisée dans le marais de Sar-liève, situé au sud de Clermont-Ferrand, dans le Massif central. La zone étudiée correspond à un ancien lac d'une super-ficie d'environ 5 km 2 , qui a été drainé et asséché au cours du XVII e siècle. Les nombreux forages carottés réalisés dans le marais ont montré la présence d'un remplissage sédimentaire épais (maximum 6 m) allant du Tardiglaciaire à l'époque historique. Des zones de deltas et de bassins lacustres ont été identifiées. Dans les zones de bassins lacustres, les sédiments sont argilo-silteux et carbonatés, et d'apparence assez homogène. Deux grands types de formations sédi-mentaires y ont été distingués d'après leur composition minéralogique et leur origine. Dans la partie inférieure du rem-plissage, la formation SDLF est caractérisée par des sédiments dolomitiques surmontés d'une épaisse couche constituée de séquences de lamines carbonatées. Ces dépôts se seraient formés par précipitation chimique en milieu lacustre peu profond et confiné (milieu endoréique). Cette formation n'a été repérée que dans la partie centrale du marais, correspon-dant aux zones de bassins les plus profondes de l'ancien lac (faciès distaux). Les dépôts plus superficiels (formation CF) sont principalement de nature détritique argilo-silteuse et sont riches en calcite. Ils traduisent un milieu exoréique. Ils se retrouvent dans presque toute l'ancienne zone lacustre, aussi bien en position distale que proximale (deltas et bassins). Afin de connaître la géométrie des dépôts dans le marais et de distinguer SDLF de CF dans les zones de bassin, une prospection géophysique électromagnétique a été effectuée au moyen d'un conductivimètre EM31 (méthode slingram). Seize sondages électriques ont aussi été réalisés sur différents secteurs du marais. Les mesures électromagnétiques permettent d'établir une carte de conductivité apparente du site dans ses parties nord et sud. Nous mettons ainsi en évidence la présence d'une zone fortement conductrice dans l'axe central N-S du ma-rais, plus prononcée au sud. Cette zone est entourée de terrains plus résistants et hétérogènes, où des poches conductri-ces sont repérées. Aucun paléochenal surcreusé dans le substrat n'est mis en évidence. Nous montrons qu'il n'existe pas de corrélation nette entre la conductivité apparente et l'épaisseur totale de sédiments lacustres. Par contre, l'axe central o 6 1. UPRES EA 2100, Lab. GéEAC, Univ. François Rabelais, Parc de Grandmont, 37200 Tours, France. Florent.hinschberger@univ-tours.fr 2. UMR 7619 Sisyphe, Univ. Pierre et Marie Curie (Paris 6), case 105, 4 place Jussieu, 75252 Paris cedex 05, France. Guerin@ccr.jussieu.fr Manuscrit déposé le 19 décembre 2005 ; accepté après révision le 29 mai 2006. très conducteur du marais correspond aux zones distales de l'ancien lac, reconnues ponctuellement grâce aux carottages. Dans le remplissage des zones distales, la formation SDLF se signale sur les sondages électriques par une très faible ré-sistivité (environ 1,2 ⍀.m), expliquant la forte conductivité apparente des faciès distaux. Nous utilisons enfin les don-nées géophysiques, en complément des informations fournies par les carottages, pour évaluer l'étendue et le volume de la formation SDLF sur l'ensemble du marais. Cette étude montre finalement qu'il est possible d'utiliser la géophysique pour différencier entre eux, au sein d'un remplissage sédimentaire à faciès peu différenciés (silts argileux carbonatés), des dépôts lacustres formés dans des conditions très différentes, par précipitation chimique dominante d'une part, et par sédimentation détritique dominante d'autre part.

Une étude stratigraphique à forte résolution spatiale a été menée sur un des derniers méandres de la Marne à Neuilly-sur-Marne à l'Est de Paris (France). Ce travail met en lumière des discontinuités et des variabilités spatiales importantes dans l'enregistrement sédimentaire holocène. L'ensemble des dépôts a été modélisé sous forme de séquences et une première chrono-typologie a été mise en place. Elle montre une incision préboréale (antérieure à 9600 BP) localisée, suivie d'un remplissage essentiellement tourbeux et calcaire. L'abaissement du plan d'eau au début de l'Holocène provoque l'abandon d'anciens chenaux tardiglaciaires partiellement réutilisés durant l'Atlantique. Cette dernière période est associée à une discontinuité importante due à une incision, initiant plusieurs générations de chenaux de moindre importance qui érodent partiellement les dépôts holocènes antérieurs. Une séquence associée au remplissage d'une noue héritée du tardiglaciaire a été protégée de ces chenaux par la présence d'une île centrale. Ces dépôts organiques et carbonatés correspondent à la première moitié de l'Holocène et constituent ainsi une séquence ''relique'' très localisée. Des apports limoneux importants apparaissent dès le Subboréal (postérieurement à 3300 BP) et s'intensifient durant le Subatlantique. Les chenaux secondaires finissent par s'engorger puis devenir temporaires, tandis que la quasi totalité du méandre est recouverte par des limons de débordement. Les premiers résultats stratigraphiques sont ici présentés ainsi que des résultats géophysiques. Ils illustrent la variabilité de l'enregistrement holocène et s'intègrent dans une étude plus large visant à spatialiser précisément l'ensemble des observations effectuées sur le site. Ces résultats posent les bases d'une macro-séquence holocène à l'échelle du méandre. The first stratigraphic results, depicting the variability of the Holocene record of the Marne river at Neuilly-sur-Marne in the East of Paris (France) are presented in this study. They take part in a broader survey that will spatialize the whole observations carried out on the site. Stratigraphic study highlights major discontinuities and spacial variabilities in the Holocene sedimentary record. The alluvial deposits were divided into sequences and a chrono-typology was build. It shows a localised Preboreal incision (former to 9600 BP), subsequently filled by a peaty and calcareous deposit. At the beginning of the Holocene, the lowering of the base level causes the abandonment of Late Glacial channels partially re-used later during the Atlantic. During that last period, an incision episode initiates the development of 2nd order channels which partially cut into the older Holocene deposits. Early Holocene organic and carbonated deposits associated with the fillings of an oxbow inherited from the Late Glacial period are preserved from these channels incision by the presence of an island. Important silty clay deposition occurs during the Subboreal (after 3300 BP) and increases during the Subatlantique. The secondary channels become almost dammed by these deposits and diverge temporary, while the entire meander is covered and sealed by silty overbank deposits. These results lead to the foundation of an Holocene macrosequence at meander's scale for the Marne valley.

RESUME . Geologiquement le site etudie appartient au Tangerois et plus precisement a la nappe numidienne. Cette nappe est caracterisee par une formation greseuse presentant des intercalations marno-shisteuses. Les gres numidiens, d'âge oligocene, peuvent atteindre et presenter selon certains endroits des puissances de l'ordre de 1000m d'epaisseur. Dans la region de Mediouna, cette formation presente par contre une puissance de quelques centaines de metres (100 a 300m). Du point de vue hydrogeologique, les flyschs a dominante greseuse dont fait partie la nappe numidienne ne contiennent pas de nappes d'eau generalisees : l'eau pouvant s'y trouver est localisee dans des drains principaux qui, generalement, sont des fractures ou des failles. Dans ce contexte particulier, l'etude geophysique consiste en une prospection electrique par courant continu. Deux sondages et quatre traines electriques Schlumberger furent realises. L'appareil de mesure de la resistivite est le RESISTIVIMETRE GTR-2 a sommation de signaux et a compensation automatique de la polarisation spontanee de GEOTRADE INSTRUMENTS. Le traitement des donnees de resistivites apparentes mesurees, realise a l'aide du logiciel WinSev 3.3 de GEOSOFT, a permis de circonscrire l'epaisseur des gres numidiens qui constituent le reservoir potentiel. Ce traitement a egalement permis de mettre en evidence l'identification d'un couloir de failles large de 20 m et se poursuivant sur une profondeur atteignant au moins les 30 m. Les tres faibles valeurs de resistivites mesurees au niveau de ce couloir, elles-meme tres contrastees avec les resistivites de l'encaissant, soulignent la possibilite de l'existence d'un aquifere. La prospection geophysique appliquee a la recherche des eaux souterraines est ainsi un outil determinant dans la prise de decision dans la realisation des sondages de reconnaissance. ABSTRACT. Geophysical methods have been used to study aquifer features at Mediouna (Tangier, Morocco). Electrical soundings allow to determine the vertical structure of weathered layer. And electrical profiling allows to define the horizontal structure. Thank to this additional information, the geometry of the aquifer is better known and will be used to better exploit the aquifer resources. MOTS CLES: geophysique, resistivite, nappe, faille, aquifere, Maroc. KEYWORDS: geophysics, resistivity, water table, fault, aquifer, Morocco. Journal des Sciences Pour l'Ingenieur No.4 2004 : 13-22

Geophysical methods have already shown their interest for the continuous characterisation of soils over landscapes, rapidly and, non-intrusively. But in bottomland areas, difficulties are encountered in relating geophysical properties to soil spatial distribution due to large variations in the depth, texture and/or water content of soils. Indeed, respective variations of these parameters can result in ambiguous geophysical responses. For example, a decrease in soil water content, which causes an increase in electrical resistivity, may be offset by an increase in soil clay content, inducing a decrease in resistivity. The objective of this study was to improve the continuous characterisation of soils affected by an excess of water by using a combination of geophysical techniques. Three techniques, the radio-magnetotelluric (RMT), the ground penetrating radar (GPR) and the electrostatic quadrupole (ESQP) were implemented along eight representative transects where soils were extensively described. The soil cover shows a succession from downslope to upslope consisting in fibric Fluvisols, gleyic Fluvisols, and Albefluvisols. None of the geophysical methods allows us to distinguish all soil limits and to estimate the geometry of soil horizons. The ESQP discriminates Fluvisols from Albefluvisols, whereas the RMT above all reveals differences in soil material thickness, which do not permit to discriminate between these soils. In complement, the GPR allows the estimation of the geometry of organic horizons and anthropic structures, such as ditches. Finally, the combination of these three techniques allows us to assess the main features of soil spatial distribution in bottomlands. To cite this article: V. Chaplot et al., C. R. Geoscience 336 (2004).

The detailed time-space distribution of acoustic emission (AE) events during the catastrophic fracture of rock samples containing a pre-existing joint or potential fracture plane is obtained under triaxial compression using a high-speed 32-channel waveform recording system, and the results are discussed with respect to the prediction and characterization of catastrophic fault failure. AE activity is modeled quantitatively in terms of the seismic b -value of the magnitude–frequency relation, the self-excitation strength of the AE time series, and the fractal dimension of AE hypocenters. Consistent with previous studies on rock samples containing a fracture plane with several asperities, the present analyses reveal three long-term phases of AE activity associated with damage creation on heterogeneous faults, each clearly identifiable based on the above parameters. A long-term decreasing trend and short-term fluctuation of the b -value in the phase immediately preceding dynamic fracture are identified as characteristic features of the failure of heterogeneous faults. Based on the experimental results it is suggested that precursory anomalies related to earthquakes and other events associated with rock failure are strongly dependent on the heterogeneity of the fault or rock mass. A homogeneous fault or rock mass appears to fracture unpredictably without a consistent trend in precursory statistics, while inhomogeneous faults fracture with clear precursors related to the nature of the heterogeneity.

Pedological soil surveys usually based on auger sampling encounter methodological and economic difficulties. Electrical resistivity (ER) techniques could be used as a simple and practical method to determine their spatial variability. However, attempts to map soils using ER techniques have very often limited success, especially in bottomland areas, due to large variations inherent in ground data. The aim of this study is to seek the interest of a geophysical method, the radio magnetotelluric-resistivity (Radio-MT), to map field-scale hydromorphic horizons for loamy pedological systems in bottomlands characterized by large variations of soil water content and depth to upper boundary of saprolite. The sampling survey was carried in the Armorican massif (western France). The electrical measurements were taken along transects on an agricultural field (80×150 m). The soil sampling was performed on a regular grid with a mesh of 10 m. On each point, some soil properties were measured (type and thickness of the loamy horizons, depth to the upper boundary of saprolite, soil water content at 10, 20, 40 and 60 cm depths). A direct relationship between apparent resistivity and horizon type distribution was not established. The best correlations were between the electrical conductivity and depth to the upper boundary of saprolite and topsoil water content. The correlation coefficients, r, are 0.51 and 0.34, respectively. To identify the soil types, we modeled the influence of these two soil properties by multiple regression technique. Deviations from the regression model were then interpreted by taking into account the succession of soil horizons. These results seem to indicate that the electrical method used in this study could not be directly used to evaluate spatial prediction of the hydromorphic soil distribution, but indirectly by taking into account soil properties such as the soil water content and the upper boundary of saprolite.

A. Cazenave : Ingénieur de Recherche CNES – Toulouse (Examinateur); A. Arnéodo : Directeur de Recherches CNRS – Bordeaux (Examinateur); J-L.. Bouchez : Professeur à l'Université de Toulouse III (Président); D. Gibert : Professeur à l'Université de Rennes I (Rapporteur); M. de Saint-Blanquat : Chargé de Recherches à l'Université de - Toulouse III (Directeur de thèse); D. Sornette : Directeur de Recherches CNRS – Nice-Sophia Antipolis (Rapporteur); G. Ouillon : Ingénieur CEA à l'Université de Nice-Sophia Antipolis (Invité). Transparents de soutenance disponibles (ond*.pdf) Defense transparencies available (wave*.pdf); This work is devoted to the development of processing methods of Earth and Planetary Sciences data. Because geophysical and geological signals are, by nature, characterised by complex dynamics, non-stationarity and/or multi-scale behaviour, their analysis could be considerably improved by the use of non-stationary methods. So, we propose to use methods based on the mathematical formalism of the wavelet transform. Presented and illustrated on various synthetic and natural examples, local and multi-scale wavelets properties offer many advantages in respect to classical signal analysis methods (Fourier Transform, Windowed Fourier Transform ...). In particular, the one- or two- dimensional developed techniques transform the information into a “space-scale” representation revealing the complex dynamics, the multi-scale behaviour and/or the interactions within the investigated system. Requiring any hypothesis on the nature of the analysed signal, these techniques are general-purpose and allow the recognition of the processes acting on various systems. - Applied to the study of relative geomagnetic paleointensity, the re-inspection of magnetic records from Ocean Drilling Program (ODP) Site 983, characterised by significant components close to the Earth orbital parameters (eccentricity, obliquity, precession), suggested that the orbital frequencies embedded in the paleointensity record are the expression of lithologic variations, and probably not a characteristic of the geodynamo itself, and confirmed the representativity of the paleointensity record and its usefulness to be correlated to other records. - In the frame of seismic monitoring, we have developed an automatic seismic phase picking algorithm. Used as band-pass filters intrinsically well localised in time and frequency, wavelets allow quasi real time picking of local and teleseismic events, rejecting uncertain picks and noise. - Based on methodological developments related with the investigation of two-dimensional galaxies fields and fractures fields, we have developed a new method which applied to the study of mineral organisation of magmatic rock sections enabled us to detect and quantify in terms of size, shape, orientation and spatial distribution the different levels of mineral organisation, and consequently to better define the dynamical history of the plutons. - Applied to the the spatial distribution of seismic events the 1980 Arudy earthquake sequence (M=5.1, Western Pyrennes), 2D anisotropic wavelets allowed identification of the possible active rupture planes which combined with available focal mechanisms and geological and geomorphological markers leaded to propose and validate a local tectonic model which takes the form of a horse tail termination of an E-W sub-vertical dextral strike-slip fault.; Ce mémoire concerne le développement de méthodes de traitement, de mise en relation et d'interprétation de données des Sciences de la Terre. Partant du constat que, de par leur nature complexe (non-stationnarité, multi-échelles), les signaux géophysiques-géologiques gagneraient beaucoup à être étudiés à l'aide de méthodes non-stationnaires, nous proposons d'utiliser des méthodes d'analyse basées sur le formalisme mathématique de la transformation en ondelettes continues. Présentées et illustrées sur des exemples synthétiques et naturels, les propriétés d'analyse locale et multi-échelles des ondelettes ouvrent de nombreuses perspectives, inaccessibles avec les méthodes classiques du traitement du signal. En particulier, les techniques développées à une ou deux dimensions visent à éclater toute l'information dans une représentation « espace-échelle », propice à dévoiler la dynamique complexe, la nature multi-échelles et/ou les interactions au sein du système étudié. Ne nécessitant aucune hypothèse sur la nature des signaux, ces techniques sont polyvalentes et permettent de reconnaître les processus agissant sur divers systèmes. L'analyse en ondelette a été appliquée à l'étude de la paléointensité relative du champ magnétique terrestre. La ré-inspection des enregistrements magnétiques du site Ocean Drilling Program 983, caractérisés par des composantes significatives à des fréquences correspondant aux paramètre orbitaux de la Terre, a permis d'opter pour une origine lithologique (climatique) plutôt que pour l'expression de la géodynamo elle-même. On confirme ainsi la représentativité de l'enregistrement de la paléointensité et sa possibilité à être corrélé avec d'autres enregistrements mondiaux. Dans le cadre de la surveillance sismique, nous avons développé un algorithme de pointé automatique de phases sismiques. Utilisées comme des filtres passe-bande naturellement bien localisés en temps et en fréquence, nous avons montré que les ondelettes permettent de détecter, de distinguer et de pointer les séismes proches et lointains, en rejetant les pointés incertains et le bruit. Sur les bases de développements méthodologiques liés à l'étude bi-dimensionnelle des champs de galaxies et des champs de fractures, nous avons développé une nouvelle méthode qui, appliquée aux organisations minérales de sections de granite, a permis de détecter et de quantifier en termes de taille, de forme, d'orientation et de distribution spatiale, les différents niveaux d'organisation minérale. A partir de cette approche, on peut étudier le comportement complexe d'un magma –milieu biphasé solide liquide- qui cristallise tout en se déformant, et ainsi, mieux cerner l'histoire dynamique des massifs granitiques. Appliquée à la distribution spatiale de la séquence de répliques du séisme d'Arudy de 1980 (M=5.1, Pyrénées Orientales), la méthodologie précédente a permis d'identifier des plans potentiels de rupture. La combinaison de ces résultats avec les mécanismes au foyer disponibles et avec les marqueurs géologiques et géomorphologiques a conduit à proposer et valider un modèle tectonique local sous la forme d'une terminaison en queue de cheval d'orientation E-W. Les perspectives ouvertes par ce mémoire laissent présager d'un champ énorme de développement d'outils et de réflexions nouvelles. Même si les problèmes abordés dans cette thèse ont concerné exclusivement des données mono-dimensionnelles et des données binaires (noir et blanc) bi-dimensionnelles, la voie est ouverte pour étendre les méthodologies précédentes à des données bidimensionnelles non-binaires (couleur) et tri-dimensionnelles.

Well-logging techniques provide a preferential way of investigating deep geological formations, not directly observable. They measure on a continuous basis and in situ numerous petrophysical parameters, as well as oxide contents in 7 major (Si, Ca, Fe, Al, S, K, Ti) and 3 (U, Th, Gd) trace chemical elements. A thorough knowledge of the physics underlying tool operation and the calibration steps is needed to estimate the uncertainty on the measurement. This uncertainty is mainly due to tool operating conditions (borehole diameter and irregularities,, operating speed). When good quality data are available, multivariate clustering techniques, such as k-means, are used as a first approach to visualize the variables provided by well-logging tools. One can also choose linear and non linear inversion methods to infer an accurate enough mineralogical log so it may be used in geological and petrophysical modeling. Wireline logging techniques are typically carried out during oceanic and continental scientific drilling programs, but are almost useless in such unstable geological environments as sedimentary structures associated with tectonic plates convergence zones. The improved state-of-the-art method of Logging-While-Drilling gives a best quality measurement before the borehole conditions worsen. Geological, petrophysical and textural interpretation of well-logging data gives valuable information on sedimentation type, as well as hints on possible mineralogical transformations. The in situ criterion pertaining to the well-logging measurement allows fluids dynamics modeling as well as variation and orientation of tectonic stress, often characterizing these geological environments.; Les techniques de diagraphies sont un moyen privilégié pour étudier les formations géologiques profondes, inaccessibles à l'observation directe. Elles mesurent en continu et in situ de nombreux paramètres pétrophysiques, ainsi que les concentrations en 7 éléments majeurs (Si, Ca, Fe, Al, S, K, Ti) et 3 éléments traces (U, Th et Gd). Une connaissance préalable des différents modes de fonctionnement des outils et de leur calibration permet d'évaluer la précision de la mesure. Celle-ci est surtout fonction des conditions de mesure (diamètre et rugosité du puits, vitesse de mesure). Lorsque les données sont de bonne qualité, les méthodes de classification multivariée, comme la méthode des nuées dynamiques ou le k-means, sont employées comme premier outil de visualisation des grandeurs mesurées par diagraphie. En parallèle ou en complément, à l'aide de méthodes d'inversion linéaire ou non-linéaire, il est possible de calculer une minéralogie en continu avec une précision suffisante pour être utilisée dans des modèles pétrophysiques et géologiques. Les zones de convergence de plaques lithosphériques sont des environnements géologiques instables, dans lesquels les techniques de diagraphie par cable, classiquement utilisée dans les forages scientifiques océaniques ou continentaux, ne permettent pas d'obtenir des données de bonne qualité. La nouvelle méthode de Logging-While-Drilling, ne laisse pas à l'environnement de mesure le temps de se déteriorer et donne une mesure utilisable. L'interprétation géologique, minéralogique et faciologique des données de diagraphies apportent des indications précieuses sur la dynamique sédimentaire, ainsi que sur les éventuelles transformations minéralogiques. Le caractère in situ de la mesure rend possible la modélisation de la dynamique des fluides ou de la variation et de l'orientation des champs de contrainte, dont les environnements étudiés sont souvent le siège.

International audience; We acquired continuous series of microgravity measurements using several Scintrex CG-3M gravity meters for several weeks in 1997. The meters with 1 mGal resolution were installed side by side in a stable reference station at the ORSTOM research centre to perform identical data acquisition. We present and compare the instrumental responses obtained for the various gravity meters (measurement series of gravity field, standard deviation, internal temperature, tilts) and analyse their correlation with simultaneous recordings of meteorological parameters. The data have been processed in order to (1) establish the mid-to long-term relative stability and the accuracy of the instruments, (2) estimate the contribution of instrumental effects to gravity data measurements and (3) quantify the amplitude of the time variations of the gravity field that might be detected with such instruments. This study emphasizes the sensitivity of some instrumental responses of the Scintrex CG-3M gravity meters (such as internal temperature or tilt) to local atmospheric-pressure variations. This sensitivity can lead to non-negligible perturbations of the gravity measurements through automatic corrections applied in real-time mode by the integrated software. We show that most of these instrumental artefacts can be easily removed in data post-processing by using simultaneous atmospheric-pressure data. After removal of an accurate Earth tide model, the instrumental drift and the instrumental effects, the temporal series are compared by computing differential signals. These residual signals obtained over a period of several weeks exhibit the following characteristics: (1) the gravity residuals have a maximum amplitude ranging from 5 to 10 mGal and from 10 to 15 μGal for filtered and unfiltered data, respectively; and (2) the standard error, tilts and internal temperature measurements of the various gravity meters are very consistent; their respective residual amplitudes are ±2 mGal, ±3 arcsec and ±0.05 mK. In order to calibrate the gravity meters precisely in the measurement range used in this study, we have measured a calibration line established in the framework of the fourth intercomparison of absolute and relative gravity meters. This calibration was achieved with an accuracy of 5 μGal. This result is consistent with other field tests already performed with such gravity meters. In addition, we also checked the accuracy of the tilt sensors by increasing the electronic read-out by a factor of 10. The tilt response of the whole gravity meter to a small induced inclinometric variation indicates that the precision of the tilt measurements is about a few tenths of an arc second. This study reveals that temporal variations of the gravity field could potentially be detected in the field with an accuracy of about 5–15 mGal by permanent networks of Scintrex CG-3M gravity meters set up a few kilometres apart. This result is of particular interest in field surveys of temporal gravity changes related to some environmental or geodynamical processes, where the expected gravity variations are greater than a few tens of mGal. In particular, in volcanological applications, the continuous monitoring of active volcanoes with such permanent networks of gravity meters co-located with subcentimetre-accuracy GPS receivers should be very helpful to understand internal magmatic processes better and to detect possible gravity and inclinometric signals occurring during pre-eruptive phases. In this field, continuous microgravity recordings associated with classical reiteration networks will probably improve hazard mitigation in the near future

The aim of this work is the determination of the neotectonic activity of the Jura mountains. Alluvial terraces are a good index of mountain uplift. Our hypothesis is to use the terrace base as a reference. With the age and altitude variations, we could also calculate the uplift velocity variations during the last hundred thousand years. Then a test of DC electric and TDEM measurements was carried out in the Seille valley (french Jura) for mapping alluvial terraces.

International audience

Time domain electromagnetic (TDEM) and tensor audiomagnetotelluric (AMT) data have been acquired at several locations on the eastern flank of Piton de la Fournaise volcano (Reunion Island) within a depressed area called Grand Brulé, interpreted as a collapse structure. The survey objectives were to provide a geophysical estimate of the subsurface structure and to evaluate the possibility of detecting aquifers in a volcanic environment not very known. The TDEM and the AMT data collected along two E-W traverses orthogonal to coastline on the northern and southern edges of Grand Brulé were interpreted with one-dimensional layered models. From the surface downward, the geoelectrical sections reveal two major units : very resistive, young lava flows (dry) and a shallow conductor (< 500 m) which is probably primarily attributable to a clayey, poorly permeable base. A notable exception to this pattern is seen at sites close to the coast, where we found three-layered structures. There is an intermediate layer of resistivity of about 100-200 ohm m between the top resistive layer and bottom conductive layer that represents a probable freshwater lens in the southern part and an alluvial fan with resistivities substantially higher (200 ohm m) in the northern part of Grand Brulé. It is suggested that the 200 ohm layer, interpreted as a buried paleoriver, corresponds to a drainage structure. (Résumé d'auteur)

International audience; An audiomagnetotelluric survey has been performed along an inactive flank of La Fournaise volcano massif in Reunion island, to study the subsurface resistivity structure. One-dimensional modelling of the AMT data at each site revealed an extensive low-resistivity (less than 10 ω m) zone at a few hundred meters below the surface. The significance of this unexpected conductive substratum is discussed in relation with the proposed impact of volcano-tectonic processes (caldera and landslides collapses), and a new interpretation of the geological structure is proposed. Moreover, it is likely that these conductors are poorly permeable argilaceous materials; then they coincide with a limit in permeability and determine groundwater behavior.