Seismic noise-based methods for soft-rock landslide characterization

International audienceIn order to better understand the mechanics and dynamic of landslides, it is of primary interest to image correctly their internal structure. Several active geophysical methods are able to provide the geometry of a given landslide, but were rarely applied in 3 dimensions in the past. The main disadvantages of methods like seismic reflection or electrical tomographies are that there are heavy to set up, require for some heavy processing tools to implement, and consequently are expensive and time consuming. Moreover, in the particular case of soft-rock landslides, their respective sensitivity and resolution are not always adequate to locate the potential slip surfaces. The passive methods, which require lighter instrumentation and easier processing tools, can represent an interesting alternative, particularly for difficult accessible landslides. Among them, the seismic noise based methods have shown increasing applications and developments, in particular for seismic hazard mapping in urban environment. In this paper, we present seismic noise investigations carried out on two different sites, a mudslide and a translational clayey landslide where independent measurements (geotechnical and geophysical tests) were performed earlier. Our investigations were composed of H/V measurements, which are fast and easy to perform in the field, in order to image shear wave contrasts (slip surfaces), and seismic noise array method, which is heavier to apply and interpret, but provides S-waves velocity profile versus depth. The comparisons between geophysical investigations and geotechnical information proved the applicability of such passive methods in 3D complexes, but also some limitations. Indeed interpretation of these measurements can be tricky in rough and non-homogeneous terrains

Sensibiliser pour mieux prévenir : une approche sensible des risques dans le quartier du Bas de la Rivière, à la Réunion

Global warming is causing unprecedented weather phenomenon and threatening our regions in unpredictable ways. The uncertain intensity and constant recurrence of these hazards calls into question our risk management policies, those that were created based on the basis of scientific research. These programmatic policies, which are operating in all regions, increase the vulnerability of these areas, notably due to the lack of communication and accessibility of their content to the general public. We need to rethink our approach and communication with regards to risks in order to create a more integrated policy in line with the issues at stake in each territory. To achieve this we need to design a policy that is closer to the people and aims to consolidate their risk culture by borrowing methods from the social sciences. The study presented in this PFE examines the risk culture of the inhabitants of the Bas de la Rivière district on Reunion Island. Once the residents' perceptions of risk have been collected, they serve as the basis for the creation of a new communication tool focusing on the neighborhood's natural hazards in the form of a detailed map. The aim of this tool is to raise residents' awareness of current issues and strengthen their risk culture awareness.Le réchauffement climatique intensifie les phénomènes météorologiques extrêmes, menaçant nos territoires de manière imprévisible. L’intensité et la récurrence incertaines de ces aléas, remet en question nos politiques de gestion des risques, initialement fondées sur la maîtrise des éléments naturels grâce aux savoirs des sciences dures. Ces politiques programmatiques, transposables à toutes les échelles et sur tous les territoires, augmentent la vulnérabilité de ces espaces, notamment par le manque de communication et d’accessibilité au grand public de leur contenu. Repenser l’approche et la communication autour des risques semble nécessaire pour créer une politique plus intégrée, en phase avec les enjeux de chaque territoire. Pour ce faire, il convient de concevoir une politique plus proche des populations qui a pour visée de consolider leur culture du risque par l’emprunt de méthode des sciences sociales. L’étude présentée dans ce PFE, questionne la culture du risque des habitants du quartier du Bas de la Rivière à la Réunion. Une fois que les perceptions des risques des habitants sont recueillies, elles servent de base à la création d'un nouvel outil de communication axé sur les aléas naturels du quartier, prenant la forme d’une carte sensible. L'objectif de cet outil est de sensibiliser davantage les habitants afin de renforcer leur culture du risque

Vers une méthode de conception de cours pour l'enseignement à distance. Une méthode basée sur le parcours personnalisé de l'apprenant

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First results of the 2005 seismology - geodesy monitoring campaign for volcanic crustal deformation in the Reykjanes Peninsula, Iceland

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