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SinceMay 2018,Mayotte Island has been experiencing seismo-volcanic activities that could trigger submarine landslides and, in turn, tsunamis. To address these hazards, we use the HySEA numerical model to simulate granular flow dynamics and the Boussinesq FUNWAVE-TVD numerical model to simulate wave propagation and subsequent inundations. We investigate 8 landslide scenarios (volumes from 11.25£106 m3 to 800£106 m3). The scenario posing the greatest threat involves destabilization on the eastern side ofMayotte’s lagoon at a shallowdepth and can generate sea-surface deformations of up to 2 m.We show that the barrier reef surroundingMayotte plays a prominent role in controlling water-wave propagation and in protecting the island. The tsunami travel time to the coast is very short (a few minutes) and the tsunami is not necessarily preceded by a sea withdrawal. Our simulation results provide a key to establishing hazard maps and evacuation plans and improving early-warning systems, Depuis mai 2018, l’île deMayotte connaît une activité sismo-volcanique importante susceptible de déclencher des glissements de terrain sous-marins générant des tsunamis. Pour faire face à ces aléas, nous utilisons deux modèles numériques complémentaires : le modèle HySEA (simulant la dynamique des écoulements granulaires) et le modèle Boussinesq FUNWAVE-TVD (simulant la propagation des vagues et les inondations) pour étudier 8 scénarios de glissements sous-marins potentiels (volumes de 11,25£106 m3 à 800£106 m3). Les scénarios ayant le plus d’impact se situent à proximité de Petite Terre et à faible profondeur. Ils peuvent générer une élévation de la surface de la mer jusqu’à 2 m en zone habitée à Petite Terre. Nous montrons que la barrière de corail entourant Mayotte joue un rôle prépondérant dans le contrôle de la propagation des vagues et dans la protection de l’île. Le temps de trajet du tsunami jusqu’à la côte est très court (quelques minutes) et le tsunami n’est pas nécessairement précédé d’un retrait maritime. De telles observations sont essentielles pour construire des cartes d’aléas précises et des plans d’évacuation afin d’aider la population

International audience; This work focuses on the use of thin-layer models for simulating fast gravitational flows for hazard assessment. Such simulations are sometimes difficult to carry out because of the uncertainty on initial conditions and on simulation parameters. In this study, we aggregate various field data to constrain realistic initial conditions and to calibrate the model parameters. By using the SHALTOP numerical code, we choose a simple and empirical rheology to model the flow (no more than two parameters), but we model more finely the geometrical interactions between the flow and the topography. We can thus model both a rock avalanche, and the subsequent remobilization of the deposits as a high discharge debris flow.Using the Prêcheur river catchment (Martinique, Lesser Antilles) as a case study, we focus on extreme events with a high potential to impact populations and infrastructures. We use geological and geomorphological data, topographic surveys, seismic recordings and granulometric analysis to define realistic simulation scenarios and determine the main characteristics of documented events. The latter are then reproduced to calibrate rheological parameters. With a single rheological parameter and the Coulomb rheology, we thus model the emplacement and main dynamic characteristics of a recent rock avalanche, as well as the travel duration and flooded area of a documented high discharge debris flow. Then, in a forward prediction simulation, we model a possible 1.9x10^6 m^3 rock avalanche, and the instantaneous remobilization of the resulting deposits as a high-discharge debris flow. We show that successive collapses allow to better reproduce the dynamics of the rock avalanche, but do not change the geometry of the final deposits, and thus do not influence the initial conditions of the subsequent debris flow simulation. A progressive remobilization of the materials slows down the debris flow and limits overflow, in comparison to instantaneous release. However, we show that high discharge debris flows, such as the one considered for model calibration, are better reproduced with an instantaneous initiation. The range of travel times measured for other significant debris flows in the Prêcheur river is consistent with our simulation results, with various rheological parameters and the Coulomb or Voellmy rheology.

Depth-averaged thin-layer models are commonly used to model rapid gravity-driven flows such as debris flows or debris avalanches. However, the formal derivation of thin-layer equations for general topographies is not straightforward. The curvature of the topography results in a force that keeps the velocity tangent to the topography. Another curvature term appears in the bottom friction force when frictional rheologies are used. In this work, we present the main lines of the mathematical derivation for these curvature terms that are proportional to the square velocity. Then, with the SHALTOP numerical model, we quan- tify their influence on flow dynamics and deposits over synthetic and real topographies. This is done by comparing simulations in which curvature terms are exact, disregarded or approximated. With the Coulomb rheology, for slopes θ = 10° and for friction coefficients below μ = tan(5°), neglecting the curvature force increases travel times by up to 10% and 30%, for synthetic and real topographies respectively. When the curvature in the friction force is neglected, the travel distance may be increased by several hundred meters on real topographies, whatever the topography slopes and friction coefficients. We observe similar effects on a synthetic channel with slope θ = 25° and μ = tan(15°), with a 50% increase of the kinetic energy. Finally, approximations of curvature in the friction force can break the non-invariance of the equations and decelerate the flow. With the Voellmy rheology, these discrepancies are less significant. Curvature effects can thus have significant impact for model calibration and for overflows prediction, both being critical for hazard assessment.

Several studies have shown that global changes have important impacts in mountainous areas, since they affect natural hazards induced by hydrometeorological events such as landslides. The present study evaluates, through an innovative method, the influence of both vegetation cover and climate change on landslide hazards in a Pyrenean valley from the present to 2100. We first focused on assessing future land use and land cover changes through the construction of four prospective socioeconomic scenarios and their projection to 2040 and 2100. Secondly, climate change parameters were used to extract the water saturation of the uppermost layers, according to two greenhouse gas emission scenarios. The impacts of land cover and climate change based on these scenarios were then used to modulate the hydromechanical model to compute the factor of safety (FoS) and the hazard levels over the considered area. The results demonstrate the influence of land cover on slope stability through the presence and type of forest. The resulting changes are statistically significant but small and dependent on future land cover linked to the socioeconomic scenarios. In particular, a reduction in human activity results in an increase in slope stability; in contrast, an increase in anthropic activity leads to an opposite evolution in the region, with some reduction in slope stability. Climate change may also have a significant impact in some areas because of the increase in the soil water content; the results indicate a reduction in the FoS in a large part of the study area, depending on the landslide type considered. Therefore, even if future forest growth leads to slope stabilization, the evolution of the groundwater conditions will lead to destabilization. The increasing rate of areas prone to landslides is higher for the shallow landslide type than for the deep landslide type. Interestingly, the evolution of extreme events is related to the frequency of the highest water filling ratio. The results indicate that the occurrences of landslide hazards in the near future (2021–2050 period, scenario RCP8.5) and far future (2071–2100 period, scenario RCP8.5) are expected to increase by factors of 1.5 and 4, respectively.

Several studies have shown that global changes have important impacts in mountainous areas, since they affect natural hazards induced by hydro-meteorological events such as landslides. To estimate the capacity of mountainous valleys to cope with landslide hazard under global change (climate change as well as climate- and human-induced land use change), it is necessary to evaluate the evolution of the different components that define this type of hazard: topography, geology and geotechnics, hydrogeology and land cover. The present study evaluates, through an innovative methodology, the influence of both vegetation cover and climate change on landslide hazard in a Pyrenean valley from the present to 2100. Once the invariant features of the studied area, such as geology and topography, were set, we first focused on assessing future land use changes through the construction of four prospective socioeconomic scenarios and their projection to 2040 and 2100. These inputs were then used to spatially model land use and land cover (LUCC) information to produce multi-temporal LUCC maps. Then, climate change inputs were used to extract the water saturation of the uppermost layers, according to two greenhouse gas emissions scenarios. The impacts of land use and climate change based on these scenarios were then used to modulate the hydro-mechanical model to compute the factor of safety (FoS) and the hazard levels over the considered area. The results demonstrate the influence of land use on slope stability through the presence and type of forest. The resulting changes are significant despite being small and dependent on future land use linked to the socioeconomic scenarios. In particular, a reduction in human activity results in an increase in slope stability; in contrast, an increase in anthropic activity leads to an opposite evolution in the region, with some reduction in slope stability. Climate change may also have a significant impact in some areas because of the increase in the soil water content; the results indicate a reduction in the FoS in a large part of the study area, depending on the landslide typology considered. Therefore, even if future forest growth leads to slope stabilization, the evolution of the groundwater conditions will lead to destabilization. These changes are not uniform over the area and are particularly significant under the most extreme climate scenario, RCP 8.5. Compared to the current period, the size of the area that is prone to deep landslides is higher in the future than the area prone to small landslides (both rotational and translational). On the other hand, the increase rate of areas prone to landslides is higher for the small landslide typology than for the deep landslide typology. Interestingly, the evolution of extreme events is related to the frequency of the highest water filling ratio. The results indicate that the occurrences of landslide hazards in the near future (2021–2050 period, scenario RCP 8.5) and far future (2071–2100 period, scenario RCP 8.5) are expected to increase by factors of 1.5 and 4, respectively.

A key point of landslide hazard assessment is the estimation of their runout. Empirical relations linking angle of reach to volume can be used relatively easily, but they are generally associated with large uncertainties as they do not consider the topographic specificity of a given study site. On the contrary, numerical simulations provide more detailed results on the deposits morphology, but their rheological parameters can be difficult to constrain. Simulating all possible values can be time consuming and incompatible with operational requirements of rapid estimations. We propose and compare three operational methods to derive scaling power laws relating the landslide travel distance to the destabilized volume. The first one relies only on empirical relations, the second one on numerical simulations with back-analysis, and the third one combines both approaches. Their efficiency is tested on three case studies: the Samperre cliff collapses in Martinique, Lesser Antilles (0.5 to 4&times, 106 m3), the Frank Slide rock avalanche (36&times, 106 m3) and the Samperre cliff collapses in Martinique, Lesser Antilles (0.5 to 4&times, 106 m3) the Fei Tsui debris slide in Hong Kong (0.014&times, 106 m3). Purely numerical estimations yield the smallest uncertainty, but the uncertainty on rheological parameters is difficult to quantify. Combining numerical and empirical approaches allows to reduce the uncertainty of estimation by up to 50%, in comparison to purely empirical estimations. However, it may also induces a bias in the estimation, though observations always lie in the 95% prediction intervals. We also show that empirical estimations fail to model properly the dependence between volume and travel distance, particularly for small landslides (&lt, 20,000 &lt, 0.02&times, 106 m3).

International audience; In France, in the context of regulatory mapping (PPRNs –Prevention Plans of Natural Risk based on French regulatory rules), landslide hazard assessment follows an empirical approach and uses basic available data. Therefore, the results are closely linked to the quality of the expertise and divergent opinions may arise in some specific cases. In recent years, numerical approaches using GIS, the availability of new databases, the development of new acquisition tools in the field and web visualization services have improved the knowledge of phenomena and different landslide-prone areas. Numerical approaches using GIS, that allow the transparency and traceability of results, have various levels of complexity and require different quantities of input data. However, they are often neglected by experts and new data and tools are not currently used to develop regulatory mapping documents. Numerous scientific examples show that these numerical approaches, web services and new tools can be a significant help in improving knowledge and provide a credible alternative to the expert approach, even in a regulatory context such as a PPRN. Thus, through this synthesis carried out as part of the regulatory mapping of landslide hazards and risks in France, a state-of-the-art spatial assessment of current landslide hazards is performed. The new tools and newly available databases to support this type of analysis are then described. Finally, the perspectives and limitations of alternative approaches and new tools and data are discussed, leading to some considerations for the improvement of the current method of producing landslide hazard maps for PPRNs in France

International audience; Better understanding the pathways through which future socioeconomic changes might influence land use and land cover changes (LULCCs) is a crucial step in accurately assessing the resilience of societies to mountain hazards. Participatory foresight involving local stakeholders may help building fine-scale LULCC scenarios that are consistent with the likely evolution of mountain communities. This paper develops a methodology that combines participatory approaches in downscaling socioeconomic scenarios with LULCC modelling to assess future changes in mountain hazards, applied to a case study located in the French Pyrenees. Four spatially explicit local scenarios are built each including a narrative, two future land cover maps up to 2040 and 2100, and a set of quantified LULCC. Scenarios are then used to identify areas likely to encounter land cover changes (deforestation, reforestation, and encroachment) prone to affect gravitational hazards. In order to demonstrate their interest for decision-making, future land cover maps are used as input to a landslide hazard assessment model. Results highlight that reforestation will continue to be a major trend in all scenarios and confirm that the approach improves the accuracy of landslide hazard computations. This validates the interest of developing fine-scale LULCC models that account for the local knowledge of stakeholders.

International audience

International audience; Mapping subsurface clay minerals is an important issue because they have particular behaviors in terms of mechanics and hydrology that directly affects assets laid at the surface such as buildings, houses, etc. They have a direct impact in ground stability due to their swelling capacities, constraining infiltration processes during flooding, especially when moisture is important. So detecting and characterizing clay mineral in soils serve urban planning issues and improve the risk reduction by predicting impacts of subsidence on houses and infrastruc-tures. High-resolution clay maps are thus needed with accurate indications on mineral species and abundances. Clay minerals, known as phyllosilicates, are divided in three main species: smectite, illite, and kaolinite. The smectite group highly contributes to the swelling behavior of soils, and because geotechnical soil analyses are expensive and time-consuming, it is urgent to develop new approaches for mapping clays' spatial distribution by using new technologies, e.g., ground spectrometer or remote hyperspectral cameras [0.4-2.5 μm]. These technics constitute efficient alternatives to conventional methods. We present in this chapter some recent results we got for characterizing clay species and their abundances from spectrometry, used either from a ground spectrometer or from hyperspectral cameras.

International audience; The investigation and monitoring of shallow hazards due to the presence of underground cavities remain a challenge for geophysical approaches. Thus, seismic surface waves have been tested in several recent research projects in order to detect and localize voids as well as to determine their geometries. Among these works, numerous numerical studies have proved the feasibility of Rayleigh waves to detect cavities. However, most imagery processes adapted to R waves are faced with difficulties when applying them to real data. This limitation points to a major problem: the interactions between Rayleigh waves and a cavity are complex, particularly in the case of dispersing and attenuating surrounding media. Here, a combined approach based on numerical and experimental data obtained in a reduced-scale measurement bench is conducted to better understand the seismic wave propagation phenomena involved in the presence of a cavity and define robust observables that can be used in field measurements. The observables bearing the cavity signature are studied qualitatively and quantitatively on numerical and experimental recordings. The latter take into account all the propagation phenomena involved. The observations are carried out on the vertical and horizontal component of the Rayleigh wave displacement. The selected observables are studied depending on non-dimensional cavity's parameters versus the frequency, that is the wavelength-to-size ratio and the wavelength-to-depth ratio. The effects of the cavity's parameters on the observables show particularities as a function of these components, such as a higher rate of the amplitude on the horizontal component as well as a perturbation of the direct seismic surface wave amplitude above the cavity, also higher on the horizontal component. This latter feature is particularly visible on the variation of the elliptical particle motion recorded at the surface. It can be linked to the mode conversions that occur in the vicinity of the cavity and which predominate on the horizontal component when the signal is normalized.

The Action Database (ADB) was developed during the ESPREssO project (Enhancing Synergies for Disaster Prevention in the European Union) in order to store and analyze relevant ideas emerging during the project to deal with the challenges. It provides the opportunity to formalize discussions and to store their content in a synthetic format, as well as to collect experiences and evaluate the impacts they had at their respective scales of implementation and on different parameters. The major aim of the ESPREssO-ADB tool, and its main innovation, is to deal with multi-hazard and multi-challenge actions, in an international context and notably in a cross-border initiative. The ESPREssO project aimed at contributing to a new strategic vision on Disaster Risk Reduction (DRR) and Climate Change Adaptation (CCA) in Europe. To do so, stakeholders working with CCA and/or DRR in Europe were consulted to identify measures boosting adaptation or societies’ resilience. Each idea, measure or comment was stored and ranked in the ADB using qualitative criteria based on the Sendai Priorities and the SHIELD model proposed by the ESPREssO Team. Each action was assessed through multi-criteria analysis and effectiveness was approached under two different angles. The first one in line with the priorities of the Sendai Framework; and the second one with the SHIELD model. This model incorporate recommendations on how to optimize risk management capabilities through DRR. Positive actions had fed the Vision Paper and Guidelines produced by the project. This paper describes in details the ADB structure and the multi-criteria analysis performed.

Ce numéro de Regards économiques analyse le décret qui organise les inscriptions en première année secondaire en Fédération Wallonie-Bruxelles. Le décret inscription requiert que les parents transmettent une liste de maximum dix établissements dans lesquels ils aimeraient inscrire leur enfant, classés dans l’ordre de leurs préférences. En parallèle, le décret fixe les critères qui sont utilisés pour déterminer à quels enfants donner priorité lorsque la demande pour un établissement excède son nombre de places disponibles. L’allocation des places disponibles est réalisée par un algorithme se basant sur les préférences transmises par les parents et les critères de priorité. Dans la mesure du possible, les élèves souhaiteraient pouvoir s’inscrire dans les établissements qu’ils estiment leur convenir le mieux. Le décret inscription atteint-il cet objectif ? Le rapport 2018 de la Commission Interréseaux des Inscriptions révèle qu’au 11 avril 2018, 91,13% des élèves de la Fédération Wallonie-Bruxelles (FWB) étaient assurés de disposer d’une place dans « l’établissement de leur première préférence ». A Bruxelles, ils étaient 77,85% dans ce cas. Si ces chiffres paraissent encourageants, il convient cependant de les relativiser car ils mesurent le pourcentage d’élèves pouvant s’inscrire dans l’établissement qu’ils ont classé en haut de leur liste. Mais le décret actuel incite les parents à ne pas classer les écoles dans l’ordre de leurs vraies préférences parce qu’il alloue 80% des places disponibles dans une école sur base des premiers choix et parce que la priorité d’un élève augmente dans un établissement qu’il a bien classé. En classant les écoles de manière stratégique, les élèves peuvent parfois obtenir une meilleure affectation qu’en les classant selon l’ordre de leurs préférences. Dès lors, ces chiffres ne nous disent pas vraiment quelle est la proportion d’élèves qui ont obtenu leur école préférée. Nous expliquons dans cet article que les comportements stratégiques des parents entraînent une série de désavantages. Le décret complexifie la tâche des parents, il favorise les élèves les mieux informés au détriment des autres, il constitue une source de stress lors de la réalisation du classement et de remords une fois les résultats connus, il peut conduire la direction d’établissement à influencer le classement choisi par les parents, il peut générer des situations où des échanges d’établissement permettraient aux élèves d’améliorer leur situation, il ne garantit pas à un élève une place dans une école dans laquelle il a une priorité plus élevée qu’un autre élève pouvant s’y inscrire et il favorise les élèves qui ont des options externes au détriment de ceux qui n’en ont pas. Par contre, il peut induire une allocation des élèves telle que ceux qui ont une préférence forte pour un établissement prisé peuvent s’y inscrire parce qu’ils prennent le risque de classer cette école en première position, alors que d’autres optent pour des stratégies sûres. Quelle est l’ampleur de ces comportements stratégiques et surtout quels sont leurs effets ? La réponse à ces questions dépend notamment des tensions entre l’offre et la demande dans les établissements ciblés par les élèves. S’ils avaient la garantie de pouvoir s’inscrire dans une école qu’ils apprécient, même si cette école n’est pas celle qu’ils préfèrent, le décret inscription et les classements stratégiques qu’il induit ne poseraient pas de problèmes. A l’inverse, lorsque tous les établissements dans lesquels des parents souhaiteraient inscrire leur enfant sont fortement demandés, la position de chaque école dans le classement est cruciale. En effet, des élèves peuvent dans ce cas se retrouver sans établissement parce qu’ils ont classé les écoles d’une manière plutôt que d’une autre. Les classements stratégiques sont de ce fait déterminants dans les zones densément peuplées en regard des places qui y sont disponibles (Nord-Est de Bruxelles) ou pour des parents qui veulent absolument inscrire leurs enfants dans un établissement qui a une bonne réputation. Gardons cependant en tête que ces difficultés ne sont pas le résultat de l’utilisation d’un algorithme mais proviennent plutôt d’une offre insuffisante en regard de la demande. Si les effets pervers liés aux classements stratégiques étaient jugés trop importants, il y aurait alors lieu de remplacer le décret inscription par une procédure non manipulable. Notons qu’un tel changement n’implique pas de modifier les critères déterminant les priorités attribuées aux élèves. Par contre, comme expliqué dans Maniquet (2009), changer l’algorithme modifiera la performance de la procédure en termes d’efficacité et de respect des priorités fixées par le décret, que ce soit en l’améliorant ou en la détériorant. Le choix d’une autre procédure peut être éclairé par les résultats des nombreuses études scientifiques qui ont proposé et évalué différentes procédures d’inscription centralisées.

Acceso electrónico sólo desde el IGME, Landslides are one of the most widespread geohazards in Europe, producing significant social and economic impacts. Rapid population growth in urban areas throughout many countries in Europe and extreme climatic scenarios can considerably increase landslide risk in the near future. Variability exists between European countries in both the statutory treatment of landslide risk and the use of official assessment guidelines. This suggests that a European Landslides Directive that provides a common legal framework for dealing with landslides is necessary. With this long-term goal in mind, this work analyzes the landslide databases from the Geological Surveys of Europe focusing on their interoperability and completeness. The same landslide classification could be used for the 849,543 landslide records from the Geological Surveys, from which 36% are slides, 10% are falls, 20% are flows, 11% are complex slides, and 24% either remain unclassified or correspond to another typology. Most of them are mapped with the same symbol at a scale of 1:25,000 or greater, providing the necessary information to elaborate European-scale susceptibility maps for each landslide type. A landslide density map was produced for the available records from the Geological Surveys (LANDEN map) showing, for the first time, 210,544 km2 landslide-prone areas and 23,681 administrative areas where the Geological Surveys from Europe have recorded landslides. The comparison of this map with the European landslide susceptibility map (ELSUS 1000 v1) is successful for most of the territory (69.7%) showing certain variability between countries. This comparison also permitted the identification of 0.98 Mkm2 (28.9%) of landslide-susceptible areas without records from the Geological Surveys, which have been used to evaluate the landslide database completeness. The estimated completeness of the landslide databases (LDBs) from the Geological Surveys is 17%, varying between 1 and 55%. This variability is due to the different landslide strategies adopted by each country. In some of them, landslide mapping is systematic; others only record damaging landslides, whereas in others, landslide maps are only available for certain regions or local areas. Moreover, in most of the countries, LDBs from the Geological Surveys co-exist with others owned by a variety of public institutions producing LDBs at variable scales and formats. Hence, a greater coordination effort should be made by all the institutions working in landslide mapping to increase data integration and harmonization., Earth Observation and Geohazards Expert Group (EOEG), EuroGeoSurveys, the Geological Surveys of Europe, Bélgica, Geohazards InSAR Laboratory and Modeling Group, Instituto Geológico y Minero de España, España, Risk and Prevention Division, Bureau de Recherches Géologiques et Minières, Francia, Engineering Geology Department, Institute of Geology and Mineral Exploration, Grecia, GeoHazard team, Geological Institute of Romania, Rumanía, Geological Survey of Slovenia, Eslovenia, Croatian Geological Survey, Croacia, Italian Institute for Environmental Protection and Research, Geological Survey of Italy, Italia, Swiss Federal Office for the Environment, Suiza, Geological Survey of Austria, Austria, Polish Geological Institute, National Research Institute, Polonia, Geological Survey of Ireland, Irlanda, Czech Geological Survey, República Checa, Federal Institute for Geosciences and Natural Resources, Alemania, Geological Survey of Norway, Noruega, Cyprus Geological Survey, Chipre, Geological Survey of Sweden, Suecia, Institut Cartogràfic i Geològic de Catalunya, España, British Geological Survey, Reino Unido, Geological Survey of Slovakia, Eslovaquia, Geological Survey of Lithuania, Lituania, Federalni zavod za geologiju, Bosnia y Herzegovina, Geological Survey of Estonia, Estonia, Laboratório Nacional de Energia e Geologia, Portugal, Geological Survey of Hungary, Hungría, Norwegian Water and energy Directorate of Norway, Noruega

We analyze experimentally behavior in a finitely repeated public goods game. One of the main results of the literature is that contributions are initially high, and gradually decrease over time. Two explanations of this pattern have been developed: (i) the population is composed of free-riders, who never contribute, and conditional cooperators, who contribute if others do so as well; (ii) strategic players contribute to sustain mutually beneficial future cooperation, but reduce their contributions as the end of the game approaches. This paper contributes to bridging the gap between these views. We analyze preferences and strategic ability in one design by manipulating group composition to form homogeneous groups on both dimensions. Our results highlight the interaction between the two: groups that sustain high levels of cooperation are composed of members who share a common inclination toward cooperation and have the strategic abilities to recognize and reap the benefits of enduring cooperation.

The dynamics of the 2–12 January 2010 effusive eruption at Piton de la Fournaise volcano were examined through seismic and infrasound records, time-lapse photography, SO2 flux measurements, deformation data, and direct observations. Digital elevation models were constructed for four periods of the eruption, thus providing an assessment of the temporal evolution of the morphology, the volume and the extrusion rate of the lava flow. These data were compared to the continuous recording of the seismic and infrasonic waves, and a linear relationship was found between the seismic energy of the tremor and the lava extrusion rate. This relationship is supported by data from three other summit eruptions of Piton de la Fournaise and gives total volume and average lava extrusion rate in good agreement with previous studies. We can therefore provide an estimate of the lava extrusion rate for the January 2010 eruption with a very high temporal resolution. We found an average lava extrusion rate of 2.4 m3s−1 with a peak of 106.6 m3s−1 during the initial lava fountaining phase. We use the inferred average lava extrusion rate during the lava fountaining phase (30.23 m3s−1) to estimate the value of the initial overpressure in the magma reservoir, which we found to range from 3.7×106 Pa to 5.9×106 Pa. Finally, based on the estimated initial overpressure, the volume of magma expelled during the lava fountaining phase and geodetic data, we inferred the volume of the magma reservoir using a simple Mogi model, between 0.25 km3 and 0.54 km3, which is in good agreement with previous studies.

We develop a simple model to analyze the timing of contests. When the odds of winning a contest are exogenously given – we show that if either the players discount the future or if the total cost of contest is smaller in the future – there exist subgame perfect equilibria where both players settle, anticipating a contest in the future. With endogenous efforts, the aggregate efforts expanded in a contest are smaller if the contest occurs in the future when the relative effort productivities remain constant or diverge over time, thus creating scope for delay in contests. When the effort productivities converge over time, the total efforts may be greater under a future contest. As a consequence, players either settle over the two periods, or else they initiate a contest immediately.

World Landslide Forum (4º. 2017. Liubliana, Eslovenia), Exposure to hazards is expected to increase in Europe, due to rapid population growth in urban areas and the escalation of urbanization throughout many countries. In the framework of the European Geological Surveys (EGS), the Earth Observation and Geohazards Expert Group (EOEG) has carried out a survey based enquiry regarding the integration of geohazards (earthquakes, volcanoes, landslides, ground subsidence, floods and others) into urban and land-use planning. Responses from 19 European countries and 5 regions reveal heterogeneous policies across national borders. 17% of the countries have not yet implemented any legal measures to integrate geohazards into urban and land-use plans and half of the participating countries have no official methodological guides to construct geohazard maps. Additionally, there is a scarce knowledge about real social impacts of geohazards and resulting disasters in many of the countries, although they have a significant impact on their national economies. This overview stresses the need for a common legislative framework and homogenization of the national legislations as well as mutual guidelines which adopt the principles applicable to the management of geohazards and explain the process to be followed in the production of hazard documentation. This is especially relevant in case of landslide and subsidence hazards; although those are of great importance in Europe, there are no common guidelines and practices similar to Directive 2007/60/EC on the assessment and management of flood risk. Based on their expertise, EuroGeoSurveys (EGS) have the potential to coordinate this activity in European geohazard guidelines and to promote the interaction among stakeholders., Geohazards InSAR Laboratory and Modeling Group, Instituto Geológico y Minero de España, España, Bureau de Recherches Géologiques et Minières, Francia, Engineering Geology Department, Institute of Geology and Mineral Exploration, Grecia, GeoHazard team, Geological Institute of Romania, Rumanía, Geological Survey of Slovenia, Eslovenia, Croatian Geological Survey, Croacia, Geological Survey of Italy, Italia, Swiss Federal Office for the Environment, Suiza, Geological Survey of Austria, Austria, Polish Geological Institute, National Research Institute, Polonia, Geological Survey of Ireland, Irlanda, Czech Geological Survey, República Checa, Federal Institute for Geosciences and Natural Resources, Alemania, Geological Survey of Norway, Noruega, Cyprus Geological Survey, Chipre, Geological Survey of Sweden, Suecia, Institut Cartogràfic i Geològic de Catalunya, España, British Geological Survey, Reino Unido, Geological Survey of Slovakia, Eslovaquia, Geological Survey of Lithuania, Lituania, Federalni Zavod Za Geologiju, Nigeria, Geological Survey of Estonia, Estonia, Laboratorio Nacional de Energia e Minas, Portugal, Geological Survey of the Republic of Srpska, Bosnia y Herzegovina

International audience; The ANR-SAMCO project aims to develop a proactive resilience framework enhancing the overall resilience of societies on the impacts of mountain risks. The project aims to elaborate methodological tools to characterize and measure ecosystem and societal resilience from an operative perspective on three mountain representative case studies. To achieve this objective, the methodology is split in several points: (1) the definition of the potential impacts of global environmental changes (climate system, ecosystem e.g. land use, socioeconomic system) on landslide hazards, (2) the analysis of these consequences in terms of vulnerability (e.g. changes in the location and characteristics of the impacted areas and level of their perturbation) and (3) the implementation of a methodology for quantitatively investigating and mapping indicators of mountain slope vulnerability exposed to several hazard types, and the development of a GIS-based demonstration platform available on the web. The strength and originality of the SAMCO project lies in the combination of different techniques, methodologies and models (multi-hazard assessment, risk evolution in time, vulnerability functional analysis, and governance strategies) that are implemented in a user-oriented web-platform, currently in development. We present the first results of this development task, architecture and functions of the web-tools, the case studies database showing the multi-hazard maps and the stakes at risks. Risk assessment over several area of interest in Alpine or Pyrenean valleys are still in progress, but the first analyses are presented for current and future periods for which climate change and land-use (economical, geographical and social aspects) scenarios are taken into account. This tool, dedicated to stakeholders, should be finally used to evaluate resilience of mountainous regions since multiple scenarios can be tested and compared.

Open image in new window Global changes would have impacts worldwide, but their effects should be even more exacerbated in areas particularly vulnerable. Mountainous areas are among these vulnerable territories. In order to estimate the capacity of such mountainous valleys to face global changes (climate, but also climate- and human- induced land-use changes), it is necessary to be able to evaluate the evolution of the different threats. The present work shows a methodology to evaluate the influences of both vegetation cover and climate on landslides activities over a whole valley until 2100, to propose adequate solutions for current and future forestry management. Firstly, the assessment of future land use is addressed through the construction of four prospective socio-economic scenarios up to 2040 and 2100, which are then spatially validated and modeled with LUCC models. Secondly, the climate change inputs of the project correspond to 2 scenarios of emission of greenhouse gases. The used simulations were performed with the GHG emissions scenarios RCP 4.5 and RCP 8.5. The impact of land use and climate change is then addressed through the use of these scenarios into hazards computations. For that we use a large-scale slope stability assessment tool ALICE which combines a mechanical stability model, a vegetation module which interfere with the first model, to take into account the effects of vegetation on the mechanical soil properties, and a hydrogeological model. The results demonstrate the influence of the forest on slope stability; the absence of the forest implies an increase of the probability of landslide occurrence, and at the contrary, the presence of forest has a local stability effect on the slope. The results also indicate some future evolution of the land use, leading to significant modifications of the stability of the slopes. Finally the climate change may have noteworthy impact on the occurrence of landslide with the increase of the water content of the soil when regarding future long periods; the results point out a reduction of the SF in a large part of the studied area. These changes are not uniform over the area, and are particularly significant for the worse scenario RCP 8.5.

Evidence suggests that in developing countries, agents rely on mutual insurance agreements to deal with income or expenditure shocks. This paper analyzes which risk-sharing networks can be sustained in the long run when individuals are far- sighted, in the sense that they are able to forecast how other agents would react to their choice of insurance partners. In particular, we study whether the farsightedness of the agents leads to a reduction of the tension between stability and efficiency that arises when individuals are myopic. We find that for extreme values of the cost of establishing a mutual insurance agreement, myopic and farsighted agents form the same risk-sharing networks. For intermediate costs, farsighted agents form efficient networks while myopic agents don't.

Short-wave infrared (SWIR: 1100–2500 nm) reflectance spectra of soil samples, acquired under laboratory-controlled conditions, were used to estimate the swelling potentials of the soils and to use SWIR spectroscopy to improve a part of the swelling-risk map of France. A total of 332 samples were collected to the west of Orléans (France) in various geological formations and swelling-risk areas and along two (eastern and western) transects with different samples spacings. Comparisons between the swelling potentials of the soils and the swelling-risk areas of the map exhibit good correlation in the south of the sampling area; however, there are several inconsistencies in the north of the study area that highlight the necessity of locally redrawing the accepted swelling-risk map of France. The sampling interval (approximately 260 m) along the eastern transect was too sparse and does not appear to have effectively captured the smallest and/or isolated lithologies. The sampling interval along the western transect (approximately 50 m) revealed the presence of an unmapped swelling-potential zone, which was confirmed by several soil samples. The sample interval along the western transect appears to be more suitable for mapping the smallest lithologies. The presence of several samples in close proximity that exhibit the same swelling potential is a robust indication of the presence of a zone with constant swelling potential. A new swelling-risk map of the sampling area was produced based on the soil samples. The map produced by interpolation did not permit the representation of discrete lithological units, introduced spurious swelling-risk zones that however could be representative of tillage in agricultural zones. More samples are therefore needed to produce a reliable map on the scale of the sampling area. According to swelling potential uncertainty related to soil sampling and soil treatment, spectroscopy-based approach proposed here cannot be used to replace the existing swelling-risk map of France. This method permits however the rapid and low-cost estimation of the swell potentials of a large number of samples, which could be used at regional-scale to target areas where doubt remains or where infrastructure damages attributed to swelling behavior are known. At local scale, soil samples need to be properly and laboratory treated to accurately produce local revised and detailed swelling-risk maps.

article i nfo Non-invasive geophysical techniques offer an interesting alternative to traditional soil sampling methods, es- pecially for estimating spatial variations of soil parameters in the landscape. The spectral analysis of seismic surface-waves (MASW) can be used to determine the vertical shear-wave velocity (Vs) model (i.e., vertical variations in Vs with depth). In our study, MASW soundings were determined at each point in a grid spread over a wind-eroded field plot of 15,600 m 2 . Vs was then mapped in terms of the thickness and stiffness of the superficial loamy material horizon, which are called ThickLM and StiffLM, respectively. To relate the Vs values to the soil stiffness, cone resistance (Qd) soundings were also performed using a Dynamic PANDA penetrom- eter. Concurrently, boreholes were used to sample the same horizon for bulk soil density (ρb) measurements. Based on these measurements, large variations in ThickLM were observed. The distribution of Vs values along a 130 m transect allowed for the distinction between two layers corresponding to different mechanical prop- erties. The Vs value of 240 m/s was then used as a limit between the loamy material and the underlying clays. This limit was validated using drilling observations performed on the same transect. Therefore, it was possi- ble to map the ThickLM, which varied between 0.2 and 6.5 m over the entire field. The comparison between the averaged values of Vs and Qd in the loamy material layer showed a significant correlation (R 2 =0.4) such that the mapping of StiffLM was realised from the Vs map and the Vs-Qd relationship. Density comparison be- tween the ρb measured on drill samples and the ρb calculated from Vs was also performed using previously published relationships; however, significant correlations were not observed. The obtained maps of ThickLM and StiffLM were consistent with the expected effects of erosion at the catchment scale and provide indica- tions of historical erosion events. This methodology, which provides a structural and mechanical characteri- sation of subsurface materials, should help to focus conservation measures to the most threatened areas (i.e., the identification of areas that show a reduced ThickLM and increased StiffLM, which are associated with high soil erosion vulnerability and/or high compaction state).

The objective of this work is to present a multitechnique approach to define the geometry, the kinematics, and the failure mechanism of a retrogressive large landslide (upper part of the La Valette landslide, South French Alps) by the combination of airborne and terrestrial laser scanning data and ground-based seismic tomography data. The advantage of combining different methods is to constrain the geometrical and failure mechanism models by integrating different sources of information. Because of an important point density at the ground surface (4. 1 points m−2), a small laser footprint (0.09 m) and an accurate three-dimensional positioning (0.07 m), airborne laser scanning data are adapted as a source of information to analyze morphological structures at the surface. Seismic tomography surveys (P-wave and S-wave velocities) may highlight the presence of low-seismic-velocity zones that characterize the presence of dense fracture networks at the subsurface. The surface displacements measured from the terrestrial laser scanning data over a period of 2 years (May 2008–May 2010) allow one to quantify the landslide activity at the direct vicinity of the identified discontinuities. An important subsidence of the crown area with an average subsidence rate of 3.07 m year–1 is determined. The displacement directions indicate that the retrogression is controlled structurally by the preexisting discontinuities. A conceptual structural model is proposed to explain the failure mechanism and the retrogressive evolution of the main scarp. Uphill, the crown area is affected by planar sliding included in a deeper wedge failure system constrained by two preexisting fractures. Downhill, the landslide body acts as a buttress for the upper part. Consequently, the progression of the landslide body downhill allows the development of dip-slope failures, and coherent blocks start sliding along planar discontinuities. The volume of the failed mass in the crown area is estimated at 500,000 m3 with the sloping local base level method.

International audience; Assessing the effectiveness of elastic full-waveform-inversion (FWI) algorithms when applied to shallow 2D structures in the presence of a complex topography is critically important. By using FWI, we overcome inherent limitations of conventional seismic methods used for near-surface prospecting (acoustic tomography and multichannel spectral analysis of surface waves). The elastic forward problem, formulated in the frequency domain, is based on a mixed finite-element P0-P1 discontinuous Galerkin method to ensure accurate modeling of complex topography effects at a reasonable computing cost. The inversion problem uses an FWI algorithm to minimize the misfit between observed and calculated data. Based on results from a numerical experiment performed on a realistic landslide model inspired from the morphostructure of the Super-Sauze earthflow, we analyzed the effect of using a hierarchical preconditioning strategy, based on a simultaneous multifrequency inversion of damped data, to mitigate the strong nonlinearities coming from the surface waves. This strategy is a key point in alleviating the strong near-surface effects and avoiding convergence toward a local minimum. Using a limited-memory quasi-Newton method improved the convergence level. These findings are analogous to recent applications on large-scale domains, although limited source-receiver offset ranges, low-frequency content of the source, and domination of surface waves on the signal led to some difficulties. Regarding the impact of data decimation on the inversion results, we have learned that an inversion restricted to the vertical data component can be successful without significant loss in terms of parameter imagery resolution. In our investigations of the effect of increased source spacing, we found that a sampling of 4 m (less than three times the theoretical maximum of one half-wavelength) led to severe aliasing.

Geophysical methods such as seismic surveying and electrical resistivity imaging appear to be well-adapted to investigate and understand landslide mechanisms. They allow direct and non-intrusive measurement of acoustic velocity and electrical resistivity, two fundamental parameters used to define the physical properties of the reworked moving materials. Both methods were applied at the Super-Sauze site in the French South Alps, where a typical example of an intra-material earthflow-mudslide can be observed. Measurements were taken simultaneously along two orthogonal profiles: one 325 m in length is perpendicular to the axis of the earthflow; the other 235 m in length is located along the axis of the earthflow. The results show a correlation between the seismic and electrical resistivity data, confirming that the simultaneous use of both methods gives complementary information about landslide mechanisms. The seismic data provide information on fracture density variations, whereas the electrical resistivity data provide information on water content variations. To cite this article: G. Grandjean et al., C. R. Geoscience 338 (2006). Resume Les methodes geophysiques telles que la sismique et l'imagerie electrique apparaissent adaptees a l'etude des mecanismes de glissements de terrain. En effet, ces methodes permettent de realiser des mesures directes et non intrusives de la vitesse acoustique et de la resistivite electrique, parametres essentiels decrivant les proprietes physiques des sols en mouvement. Ces deux methodes ont ete appliquees sur le site de Super-Sauze (Alpes du Sud, France), representatif des phenomenes gravitaires de type glissement-coulee intramateriaux. Les investigations ont ete effectuees simultanement sur deux profils orthogonaux : l'un, de 325 m de longueur, transverse a l'axe du glissement-coulee, l'autre, de 235 m, dans la direction de la pente en long du glissement-coulee. Les premiers resultats, presentant une correlation entre les donnees sismique et electrique, confirment que l'utilisation conjointe de ces deux methodes permet d'obtenir des informations complementaires sur le comportement mecanique de ce type de glissements de terrain a savoir les variations de la densite de fracturation avec la sismique et les variations de l'etat hydrique avec l'electrique. Pour citer cet article : G. Grandjean et al., C. R. Geoscience 338 (2006).

Seismic methods were tested to detect underground cavities in the surroundings of Annet-sur-Marne (Seine-et-Marne, France). Cavities are located in three Ludian gypsum layers, between 30 and 80 m in depth. A high resolution seismic profile 450 m long was carried out so that the first third and the other part are respectively above non-exploited and exploited areas. Data processing highlights a series of reflections related to the marl–gypsum interfaces in the non-exploited area, while these reflections disappear in the exploited area. With the help of numerical simulations, this feature is interpreted as a disorganisation of wave fronts reflected on interfaces because of the presence of cavities. To cite this article: G. Grandjean et al., C. R. Geoscience 334 (2002) 441–447.

National audience; This work focuses on the use of a combined statistical-mechanical approach to predict changes in landslide displacement rates from observed changes in rainfall amounts. The forecasting tool associates a statistical impulse response (IR) model to simulate the changes in landslide rates by computing a transfer function between the input signal (e.g. rainfall) and the output signal (e.g. displacements) and a simple 1D mechanical (MA) model (e.g. visco-plastic rheology) to take into account changes in pore water pressures. The models have been applied to forecast the displacement rates at the Super-Sauze landslide (South East France), one of the most active and instrumented clayey landslide in the European Alps. Results indicate that the three models are able to reproduce the displacement pattern in the general kinematic regime with very good accuracy (succession of acceleration and deceleration phases); at the contrary, extreme kinematic regimes such as fluidization of part of the landslide mass are not being reproduced: this statement, quantitatively characterised by the Root Mean Square Error between the model and the observations, constitutes however a robust approach to predict changes in displacement rates from rainfall or groundwater time series, several days before it happens. The variability of the results, depending in particular on the fluidization events and on the location of displacement data is discussed.

International audience; Landslide analysis is increasingly based on the combination of multiple information sources at different spatial and temporal resolutions, spatial coverage, accuracy and acquired using various airborne and terrestrial platforms and geomorphological, geophysical, and geotechnical methods. Morphological mapping and morphostructure characterization are preliminary steps to analyze the observed and future landslide distributions. The objective of this work is to propose a morpho-structural model of an active landslide complex on the Normandy coast (north-west France) by combining different data sources. The methodology associates field investigation with interpretation of high-resolution topographic and geophysical images. The proposed morpho-structural model highlights the division of the landslide into several morphological features. This division may explain the spatial variability and temporal variability of the slope dynamics.

The paper analyzes the role of the structure of communication - i.e. who is talking with whom - on the choice of messages, on their credibility and on actual play. We run an experiment in a three-player coordination game with Pareto ranked equilibria, where a pair of agents has a profitable joint deviation from the Pareto-dominant equilibrium. According to our analysis of credibility, the subjects should communicate and play the Pareto optimal equilibrium only when communication is public. When pairs of agents exchange messages privately, the players should play the Pareto dominated equilibrium and disregard communication. The experimental data conform to our predictions: the agents reach the Pareto-dominant equilibrium only when announcing to play it is credible. When private communication is allowed, lying is prevalent, and players converge to the Pareto-dominated equilibrium. Nevertheless, at the individual level, players’ beliefs and choices tend to react to messages even when these are non-credible.

International audience; Since the collapse of the Dolomieu crater floor at Piton de la Fournaise Volcano (la Réunion) in 2007, hundreds of seismic signals generated by rockfalls have been recorded daily at the Observatoire Volcanologique du Piton de la Fournaise (OVPF). To study rockfall activity over a long period of time, automated methods are required to process the available continuous seismic records. We present a set of automated methods designed to identify, locate, and estimate the volume of rockfalls from their seismic signals. The method used to automatically discriminate seismic signals generated by rockfalls from other common events recorded at OVPF is based on fuzzy sets and has a success rate of 92%. A kurtosis-based automated picking method makes it possible to precisely pick the onset time and the final time of the rockfall-generated seismic signals. We present methods to determine rockfall locations based on these accurate pickings and a surface-wave propagation model computed for each station using a Fast Marching Method. These methods have successfully located directly observed rockfalls with an accuracy of about 100 m. They also make it possible to compute the seismic energy generated by rockfalls, which is then used to retrieve their volume. The methods developed were applied to a data set of 12,422 rockfalls that occurred over a period extending from the collapse of the Dolomieu crater floor in April 2007 to the end of the UnderVolc project in May 2011 to identify the most hazardous areas of the Piton de la Fournaise volcano summit.

The authors investigate the penetration capabilities of microwaves, particularly at L-band, for the mapping of subsurface heterogeneities such as lithology variations, moisture or sedimentary structures. The experiment site, the Pyla Dune, is a bare sandy area allowing high signal penetration and presenting large subsurface structures (paleosoils) at varying depths. Several radar data sets over this area are available. A polarimetric analysis of airborne synthetic aperture radar (SAR) data as web as the ground penetrating radar (GPR) sounding experiment show that subsurface scattering occurs at several places. The SAR penetration depth is estimated by inverting a scattering model for which the subsurface structure geometric and dielectric properties are determined by the GPR data analysis. These results suggest that airborne radar systems in a lower frequency range (P-band) should be able to detect subsurface moisture down to several meters, leading to innovative Earth observation systems for hydrogeology in arid regions.

A GPR field experiment in the Republic of Djibouti provides evidence for very low radar penetration in arid volcanic materials, in the range 100–500 MHz. This phenomenon is attributed to the high iron oxide and evaporite concentration in soils, which significantly increases the conductivity, thus leading to poor subsurface imaging performances. The geologic context in Djibouti is shown to provide a good terrestrial analogue to Mars geology. Results of this study show that the future sounding radar missions to Mars may not reach the penetration depths previously anticipated.

3D stratigraphic geometries of the intracratonic Meso-Cenozoic Paris Basin were obtained by sequence stratigraphic correlations of around 1 100 wells (well-logs). The basin records the major tectonic events of the western part of the Eurasian Plate, i.e. opening and closure of the Tethys and opening of the Atlantic. From earlier Triassic to Late Jurassic, the Paris Basin was a broad subsiding area in an extensional framework, with a larger size than the present-day basin. During the Aalenian time, the subsidence pattern changes drastically (early stage of the central Atlantic opening). Further steps of the opening of the Ligurian Tethys (base Hettangian, late Pliensbachian;...) and its evolution into an oceanic domain (passive margin, Callovian) are equally recorded in the tectono-sedimentary history. The Lower Cretaceous was characterized by NE–SW compressive medium wavelength unconformities (late Cimmerian–Jurassic/Cretaceous boundary and intra-Berriasian and late Aptian unconformities) coeval with opening of the Bay of Biscay. These unconformities are contemporaneous with a major decrease of the subsidence rate. After an extensional period of subsidence (Albian to Turonian), NE–SW compression started in late Turonian time with major folding during the Late Cretaceous. The Tertiary was a period of very low subsidence in a compressional framework. The second folding stage occurred from the Lutetian to the Lower Oligocene (N–S compression) partly coeval with the E–W extension of the Oligocene rifts. Further compression occurred in the early Burdigalian and the Late Miocene in response to NE–SW shortening. Overall uplift occurred, with erosion, around the Lower/Middle Pleistocene boundary.

International audience; In this study, we demonstrate that cross-correlation gathers of multi-channel and multi-shot configurations provide accurate estimations of shear wave velocity (Vs) perturbations from Rayleigh wave data for the reconstruction of two-dimensional (2D), high-resolution velocity distributions without requiring the systematic calculation of surface wave dispersion, as in the spectral analysis of surface waves (SASW). Data acquisition for cross-correlation analysis is similar to that for a 2D seismic common midpoint reflection survey. The data processing involved is similar to the coda wave interferometry used for seismological data but differs in the sense that the cross-correlation of the original waveform is calculated for active source seismic data. Data processing in cross-correlation analysis consists of the following three steps: First, cross-correlations are calculated for every trace in each shot gather with the same offset trace as a reference shot to flatten the linearly sloping events of surface waves. A common receiver location stack section can then be obtained, which allows for the assessment of lateral variations in the elastic properties of the medium. Second, the maxima of the time-shifted cross-correlation gathers and the maxima of the shot gathers' envelope traces are picked for different frequencies, and trace values having the same receiver location are averaged to calculate Vs perturbations, as described in the theory of coda wave interferometry. Finally, a 2D Vs profile is reconstructed by applying the lateral Vs perturbation to a homogeneous Vs velocity profile obtained by inversion of the surface wave dispersion of the reference shot gather. Analyses of waveform data from numerical modelling and field observations indicate that this new method is valid and greatly improves the accuracy and resolution of near-surface imagery using surface waves and reconstructed subsurface velocity distributions compared with a conventional SASW or multi-channel application.

International audience; Knowledge about soil properties and their variation in space and time is a key challenge for understanding processes in the vadose zone. As we consider more complex models, applied to larger geographical regions, the demand for information on key soil parameters and thus input variables becomes harder to meet. In particular, classical soil maps and soil sampling has limitations in resolution, and information might be subjective. In the face of the new challenges in the context of climate and global change and the increasing need of multidisciplinarity, a more sophisticated use of soil information beyond the "classical" soil information is needed. Predictive soil mapping (Scull et al., 2003) or digital soil function mapping (Ugbemuna and Reuter, 2013) are promising ways to enhance the information content of soil maps. The application of pedometrical approaches, e. g., digital soil mapping (DSM) as one focus of pedometrics, provides the potential to overcome these issues. Today, DSM is well established in soil science, providing tools for improving, advancing, and increasing a more objective collection and spatial analysis of soil data. A broad variety of tools helping to improve the quality of diagnoses, to refine their resolution by using correlations between soil properties, sensor data, and environmental covariates is available and intensively discussed in the soil science community (Adamchuk and Viscarra Rossel, 2010; McBratney et al., 2003; Behrens and Scholten, 2006). However, Carre et al. (2007) asked the DSM community to be much more aware of end-user requirements and coined the term digital soil assessment for the quantitative modeling of soil attributes for assessing soil threats and soil functions. In addition, Grunwald (2009) identified a need for more sophisticated technologies to measure soil properties. Finke (2012) indicated the potential of integration of sensors in making maps and providing model input. Concerning soil moisture, Vereecken et al. (2008) described the need to develop strategies that combine hydrogeophysical measurement techniques with remote sensing methods and, moreover, the development of novel upscaling methods for predicting effective moisture fluxes and disaggregation schemes

We present a processing sequence that attempts to balance geometrical and amplitude analyses in order to recover the maximum information from deep seismic reflection data. The approach, which is guided by the interpretation of other deep geophysical data sets (magnetotellurics, refraction), is applied to Lithoprobe seismic reflection line 28 across the central and northern Abitibi belt. We show, in particular, how amplitude analyses help to quantify the depth of penetration of seismic energy as well as the crustal reflectivity. Apparent lateral variations of deep structures (e.g., the Moho) can be directly related to the high levels of noise that limit the signal penetration depth. We propose a geological model that satisfies all deep geophysical constraints. In this model, the mid crust south of Casa-Berardi tectonic zone consists of imbricated volcanic–plutonic and sedimentary lithologies, which are probably comparable to the mid-crustal section of the Kapuskasing structural zone, and in this paper are referred to as "the Abitibi plate." The lithologies are characterized by high reflectivity, while north of Casa-Berardi tectonic zone the mid crust is dominantly Opatica plutonic lithologies, of lower reflectivity. In this scenario, supracrustal rocks of the Abitibi belt overlie the Opatica plutonic belt, whereas the Abitibi plate extends beneath the Opatica plutonic belt. The boundary between the Opatica plutonic belt and the Abitibi plate is a northward-dipping décollement extending from mid crust in the south to lower crust in the north. The Casa-Berardi tectonic zone appears to be a crustal boundary affecting upper and middle crust down to 20 km, between northern polycyclic terranes and southern monocyclic ones. The uniformity of the lower crust suggests that its formation was decoupled from that of the intermediate to upper crust.

We present velocity models for two seismic wide–angle-refraction profiles across the Archean Abitibi greenstone belt and the Pontiac Subprovince. The seismic profiles are 210 and 220 km long. Traveltime inversion and amplitude forward modelling were used to obtain two-dimensional velocity structure and interface geometry. The main features of the velocity models include (1) three crustal layers; (2) variable velocities (5.6–6.4 km/s) in the upper crust (~0–12 km), with the higher velocities generally associated with mafic metavolcanics and the lower velocities with metasediments and granitic plutons; (3) a relatively uniform middle crust (~12–30 km) with velocities ranging from 6.4 to 6.6 km/s; (4) a velocity increase of 0.3 km/s across the middle crust–lower crust boundary; (5) a lower crust (~30–40 km) with velocities increasing from 6.9 km/s at the top to 7.3 km/s at the base; (6) an average upper mantle velocity of 8.15 km/s; (7) depth to Moho of about 40 km in the north-central Abitibi belt, decreasing southward to 37 km beneath the Pontiac Subprovince; and (8) observed attenuation of seismic energy propagating through the Casa–Berardi deformation zone, suggesting a complex structure in this fault zone. The velocity model is generally consistent with seismic reflection interpretations that suggest that the shallow supracrustal assemblages form an allochthonous veneer, overlying a mid-crustal imbricate sequence of metaplutonic and metasedimentary rocks. The uniform-velocity structure below 12 km depth indicates that the tectonic zones juxtaposing disparate crustal blocks may have limited depth extent. The 40 km thick crust and 10 km thick high-velocity lower crustal layer exceed the thicknesses observed in other studies of Archean crust.

International audience; Characterizing the internal structure of landslides is of first importance to assess the hazard. Many geophysical techniques have been used in the recent years to image these structures, and among them is seismic tomography. The objective of this work is to present a high resolution seismic inversion algorithm of first arrival times that minimizes the use of subjective regularization operators. A Quasi-Newton P-wave tomography inversion algorithm has been developed. It is based on a finite frequency assumption for highly heterogeneous media which considers an objective inversion regularization (based on the wave propagation principle) and uses the entire source frequency spectrum to improve the tomography resolution. The Fresnel wavepaths calculated for different source frequencies are used to retropropagate the traveltime residuals, assuming that in highly heterogeneous media, the first arrivals are only affected by velocity anomalies present in the first Fresnel zone. The performance of the algorithm is first evaluated on a synthetic dataset, and further applied on a real dataset acquired at the Super-Sauze landslide which is characterized by a complex bedrock geometry, a layering of different materials and important changes in soil porosity (e.g. surface fissures). The seismic P-wave velocity and the wave attenuation are calculated, and the two tomographies are compared to previous studies on the site.

International audience; Many studies show that certain geophysical methods, such as seismic and electrical-resistivity imaging, appear to be well adapted for investigating the internal structures of landslides and understanding the related hydro-mechanical mechanisms. These are methods that allow the direct and non-intrusive measurement of acoustic (P) and shear (S) wave velocities and electrical resistivity (ρ), which are three physical parameters considered as essential for estimating the mechanical properties of moving reworked material. We applied these techniques to the La Valette landslide (Southern French Alps), a typical example of an intra-material landslide, carrying out measurements simultaneously along two profiles, 400 m and 300 m long and respectively perpendicular to and along the slide direction. We then used suitable inversion algorithms to estimate both the P- and S-wave velocity fields and the electrical resistivity field from the recorded data. The results, aided by field surface observations, show that a correlation exists between the state of the material and the seismic-velocity and/or electrical-resistivity data, thus confirming that the simultaneous use of the two methods provides complementary information on the geomechanical behavior of the landslide. More particularly, the seismic data provide information on fissure density variations and the presence of shear-bent material, whereas the electrical resistivity data provide information on the groundwater content. To enable a more integrated petrophysical interpretation, we applied a data-fusion strategy based on fuzzy subsets to the geophysical datasets. Through combining the tomograms we identified a surface layer of soft material along the two profiles; the bottom of this layer was also recognized in a borehole. From a methodological point of view, the results show the applicability of adopting geomechanical hypotheses as inputs of geophysical data fusion for identifying areas where sediment mobilization could occur.

International audience; This article appeared in a journal published by Elsevier. The attached copy is furnished to the author for internal non-commercial research and education use, including for instruction at the authors institution and sharing with colleagues. Other uses, including reproduction and distribution, or selling or licensing copies, or posting to personal, institutional or third party websites are prohibited. In most cases authors are permitted to post their version of the article (e.g. in Word or Tex form) to their personal website or institutional repository. Authors requiring further information regarding Elsevier's archiving and manuscript policies are encouraged to visit: a b s t r a c t Bedrock depth provides important information for many environmental and agricultural applications, such as shallow groundwater monitoring, the determination of soil water availability, and the estimation of crop production potential. Direct estimates of bedrock depth from destructive soil observations are discon-tinuous and too expensive to be used in large areas. Geophysical methods are often cited as possible alternatives. However, their ability to provide reliable estimations of bedrock depth is known to depend greatly on local site characteristics. Therefore, combining geophysical methods based on different physical parameters may help to provide better predictions. This study examines the ability of the Spectral Analysis of Surface Waves (SASW) method combined with the classical high resolution Electrical Resistivity Tomography (ERT) method to predict soil depths in a 500 m ranged Mediterranean hillslope (Southern France) with increasing soil depths along the slope. SASW was performed using the data measured in the field with classical seismic equipment (impulse source and geophones distributed along a line). In the same place, eight transects of ERT (Wenner-Schlumberger array, 1 m electrode spaced) were measured under wet and dry conditions. To calibrate the geophysical measurements, 81 boreholes (from two to 5 m deep) were interpreted to determine the bedrock depth, which was defined as the occurrence in the depth of heterogeneous marine Miocene loose sandstone with centimetric laminations. ERT and SASW were found to have highly variable performances for predicting separately the bedrock depth along the hillslope. SASW correctly predicted the bedrock depth in the lower part of the hillslope, whereas the data from ERT were disrupted by shallow permanent groundwater. Conversely, ERT correctly predicted bedrock depth within the upper part of the hillslope, whereas a high variability of SASW data near the topsoil caused difficulties for bedrock depth prediction. From these results, it was possible to define an estimator of bedrock depth according to the presence of shallow groundwater, which varies along the slope, such that more importance is given to ERT estimates in the upper part of the hillslope and more importance is given to SASW in the lower part. This study shows the usefulness of such a sensor combination to estimate soil properties when the uncertainties of making predictions vary according to the geophysical methods.

4 pages; International audience; The aim of this work is to develop a methodology for integrating climate change scenarios into quantitative hazard assessment and especially their precipitation component. The effects of climate change will be different depending on both the location of the site and the type of landslide considered. Indeed, mass movements can be triggered by different factors. This paper describes a methodology to address this issue and shows an application on an alpine test site. The proposed approach is based on coupling a hydrological model (GARDENIA®) with a slope stability model (ALICE®), estimating safety factors spatially. From a DEM, land-cover map, geology, geotechnical data and so forth the program classifies hazard zones depending on geotechnics and different hydrological contexts varying in time. The methodology is applied to the Ubaye valley (France) using present and past climate conditions.