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International audience; On November 11, 2019, a Mw 4.9 earthquake hit the region close to Montelimar (lower Rhône Valley, France), on the eastern margin of the Massif Central close to the external part of the Alps. Occuring in a moderate seismicity area, this earthquake is remarkable for its very shallow focal depth (between 1 and 3 km), its magnitude, and the moderate to large damages it produced in several villages. InSAR interferograms indicated a shallow rupture about 4 km long reaching the surface and the reactivation of the ancient NE-SW La Rouviere normal fault in reverse faulting in agreement with the present-day E-W compressional tectonics. The peculiarity of this earthquake together with a poor coverage of the epicentral region by permanent seismological and geodetic stations triggered the mobilisation of the French post-seismic unit and the broad French scientific community from various institutions, with the deployment of geophysical instruments (seismological and geodesic stations), geological field surveys, and field evaluation of the intensity of the earthquake. Within 7 days after the mainshock, 47 seismological stations were deployed in the epicentral area to improve the Le Teil aftershocks locations relative to the French permanent seismological network (RESIF), monitor the temporal and spatial evolution of microearthquakes close to the fault plane and temporal evolution of the seismic response of 3 damaged historical buildings, and to study suspected site effects and their influence in the distribution of seismic damage. This seismological dataset, completed by data owned by different institutions, was integrated in a homogeneous archive and distributed through FDSN web services by the RESIF data center. This dataset, together with observations of surface rupture evidences, geologic, geodetic and satellite data, will help to unravel the causes and rupture mechanism of this earthquake, and contribute to account in seismic hazard assessment for earthquakes along the major regional Cévenne fault system in a context of present-day compressional tectonics.

This document presents a comparison of the various macroseismic survey forms contained since 1910 in the archives of the French Central Seismological Bureau (BCSF), as well as the forms themselves. These forms have made it possible, and today make it possible for some of them to collect information on seismic effects on a municipal or individual scale in order to estimate the intensity of ground shaking according to the scale used when the form was used.Collection des différents formulaires métropolitains d’enquête macrosismique du Bureau central sismologique français - 1921 à 2021. 2Collection of different metropolitan macroseismic survey forms of the French Central Seismological Office - 1921 to 2021.These forms were successively used by the Central Bureau of Meteorology of France (BCMF), the Institute of Earth Physics in Strasbourg (IPGS), the German Imperial Main Station for Earthquake Research in Strasbourg, the Geological and Mining Research Office (BRGM), or the BCSF.The first versions of the forms were in paper form and distributed by mail, the latest versions are mainly distributed by Internet via a collection interface (www.franceseisme.fr). A few forms in the archives are not presented here, they are mainly forms from third-party institutes used occasionally for specific events (University of Rennes, 1930, University of Bordeaux, 1967, Civil Aviation from 1947 to 1963, etc.)., Ce document présente un comparatif des différents formulaires d’enquêtes macrosismiques contenus depuis 1910 dans les archives du Bureau central sismologique français (BCSF), ainsi que les formulaires eux-mêmes. Ces formulaires ont permis et permettent aujourd’hui pour certains d’entre eux de collecter l’information sur les effets sismiques à l’échelle communale ou individuelle afin d’estimer l’intensité de la secousse au sol selon l’échelle utilisée lors de l’utilisation du formulaire.Ces formulaires ont été successivement utilisés par le Bureau central météorologique de France (BCMF), l’Institut de physique du globe de Strasbourg (IPGS), la station principale impériale allemande pour la recherche sur les tremblements de terre à Strasbourg, le Bureau de recherches géologiques et minières (BRGM), ou le BCSF. Les premières versions des formulaires étaient en papier et diffusées par courrier, les dernières versions sont principalement diffusées par Internet via une interface de collecte (www.franceseisme.fr). Quelques formulaires présents dans les archives ne sont pas présentés ici, il s’agit principalement de formulaires d’instituts tiers utilisés ponctuellement pour des événements spécifiques (Université de Rennes, 1930, Université de Bordeaux, 1967, Aviation civile de 1947 à 1963,…).

The CDGP [https://cdgp.u-strasbg.fr], Data Center for Deep Geothermal Energy, was created in 2016 by the LabEx G-Eau-Thermie Profonde (continuing now in ITI GeoT) [https://geot.unistra.fr/], to archive the high-quality data collected in the Upper Rhine Graben geothermal sites and to distribute them to the scientific community for R activities, taking Intellectual Property Rights into account. It manages seismological (catalogues, waveforms, focal mechanisms), seismic, hydraulic, geological, and other data related to anthropogenic hazard from different phases of a geothermal project. Up to now, data are related to Soultz-sous-Forêts, Rittershoffen, Vendenheim and Illkirch. The CDGP was designed (1) as a store to archive and distribute isolated data and (2) as a gateway to access data handled by another datastore. Indeed, other data can be found elsewhere: in official national stores like Minergies [http://www.minergies.fr/en]or InfoTerre [https://infoterre.brgm.fr/], in academic or project-related stores like BCSF-Renass [https://renass.unistra.fr] or GFZ Data Services [https://dataservices.gfz-potsdam.de/portal/], or even using an internal data service like the one provided by the EOST’ seismological data center CDS [https://eost.unistra.fr/plateformes/cds]. A major objective is to give access to data – even outside the CDGP; they are described in metadata records, where links to the resource are set. Access rights can be controlled and granted either by the destination store, or - if requested - by the CDGP. In this latter case, access rules are defined by the center providing data, and access is validated by the CDGP and request is made only if it is granted. Another advantage is to avoid data duplication and therefore disk space, follow-up of updates, access rights management. If possible, these remote data are also provided as the local data to the EPOS Anthropogenic Hazard platform [https://tcs.ah-epos.eu/] This feature is useful for users who do not need to search for data on several different sites. It is also useful for data providers and centers who wish to make their data known while keeping control of data access, or need to do special actions before giving access to their data.

The earthquake of magnitude Mb(RENASS)=3.7 and 3.8 ML(CEA-LDG), occurred on 19 February 2020 at 20 h 20 min UT (22 h 20 min in local time). The epicentre is to the east of Brest according to data from the BCSF-RéNaSS , the CEA-LDG places the epicentre further east (6.5 km). This earthquake is therefore located close to the east-west oriented fault system of the western part of the North Armorican Shear. With the aim of estimating the severity level of the ground shaking of the 19 February earthquake, a macro-seismic survey to collect the seismic effects was launched by the BCSF-RéNaSS in the 277 communes of Finistère., Le séisme de magnitude Mb(RENASS)=3,7 et 3,8 ML(CEA-LDG), s’est produit le 19 février 2020 à 20 h 20 min TU (22 h 20 min en heure locale). L’épicentre se trouve à l’est de Brest selon les données du BCSF-RéNaSS , le CEA-LDG place cet épicentre plus à l’est (6,5 km). Ce séisme est donc localisé à proximité du système de faille orienté estouest de la partie ouest du Cisaillement Nord Armoricain. Dans l’objectif de l’estimation du niveau de sévérité de la secousse au sol du séisme du 19 février, une enquête macrosismique permettant de collecter les effets sismiques a été lancée par le BCSF-RéNaSS dans les 277 communes du Finistère.

On November 11, 2019 at 10:52 a.m., an earthquake of magnitude 5.2 shook the village of Le Teil, located a few kilometers from Montélimar. The Macro-seismic Intervention Group (G.I.M.) led by the French Central Seismological Office (BCSF) was mobilized in the field to estimate the macro-seismic intensities (EMS98 scale) in the epicentral zone. The EMS98 scale is a European scale, which makes it possible to measure the intensity of an earthquake as well as its severity and nature, here in the epicentral zone, i.e. in the land surface where the earthquake was most intense. This mission took place in the field from 18 to 22 November 2019. This G.I.M. preliminary report presents the context of the mission, the data and observations collected, and a map of the macro-seismic intensities of the earthquake.; Le 11 novembre 2019 à 10h52, un séisme de magnitude 5.2 secoue le village du Teil, situé à quelques kilomètres de Montélimar. Le Groupe d’Intervention Macrosismique (G.I.M.) piloté par le Bureau central sismologique français (BCSF) s’est mobilisé sur le terrain afin d’estimer les intensités macrosismiques (échelle EMS98) dans la zone épicentrale. L’échelle EMS98 est une échelle européenne, qui permet de mesurer l’intensité d’un séisme ainsi que sa gravité et sa nature, ici dans la zone épicentrale, c’est-à-dire dans la surface terrestre où le séisme a été le plus intense. Cette mission s’est déroulée sur le terrain du 18 au 22 novembre 2019. Ce rapport préliminaire du G.I.M. présente le contexte de la mission, les données et observations recueillies, et une carte des intensités macrosismiques du séisme.

The earthquake of magnitude ML(RENASS)=4.8 and ML(CEA-LDG) 5.2 occurred on 21 June 2019 at 6 h 50 min UT 8. h 50 min in local time). The moment magnitude (Mw) is calculated between 3.9 and 4.0. The mechanism at the focus is essentially stalling. Waveform inversion indicates a preferential depth between 5 and 7 km. The epicentre is located 6 km SW of Tancoigné in the south of the department of Maine-et-Loire according to BCSF-RENASS data not far from those calculated by the CEA-DASE Detection and Geophysics Laboratory and Geoazur. This earthquake is located in the zone classified as moderate seismicity. In order to estimate the severity level of the ground shaking of the 21 June earthquake (intensity EMS98), a macro-seismic survey to collect the seismic effects was launched by BCSF-RENASS on 1204 communes around the epicentre in nine departments., Le séisme de magnitude ML(RENASS)=4,8 et ML(CEA-LDG) 5,2 s’est produit le 21 juin 2019 à 6 h 50 min TU 8h 50 min en heure locale). La magnitude de moment (Mw) est calculée entre 3.9 et 4.0. Le mécanisme au foyer est essentiellementdécrochant. L’inversion des formes d’onde indique une profondeur préférentielle entre 5 et 7 km. L’épicentre se trouve à 6 km au SW de Tancoigné au sud du département de Maine-et-Loire selon les données du BCSF-RENASS non loin de ceux calculés par le Laboratoire de Détection et de géophysique du CEA-DASE et de Géoazur. Ce séisme est localisé dans la zone règlementairement classée en sismicité modéré. Dans l’objectif de l’estimation du niveau de sévérité de la secousse au sol du séisme du 21 juin (intensité EMS98), une enquête macrosismique permettant de collecter les effets sismiques a été lancée par le BCSF-RENASS sur 1204 communes autour de l’épicentre dans neuf départements.

The EPOS TCS-AH brings together a broad community interested in Anthropogenic Hazards (AH) related to induced seismicity. It is designed as a functional e-research infrastructure that provides access to a large set of relevant data and allows free experimentations in a virtual laboratory, promoting interdisciplinary collaborations between stakeholders (the scientific community, industrial partners and society). The platform provides datasets as Episodes, which comprehensively describe AH cases for infrastructures, people and/or environment. They are grouped in several categories of subsurface exploitations: CO2 sequestration, conventional hydrocarbon extraction, geothermal energy production, reservoir impoundment, unconventional hydrocarbon extraction, underground gas storage, underground mining, and wastewater injection. They gather datasets relevant for the considered hazards (e.g. seismic, air/water quality), industrial data (e.g. well path, injection rates, mining front advance, gas production, water level), and other geodata (e.g. geological section, velocity model, faults, shear wave velocity, bathymetric map). Two local data centers (eNodes: IG-PAS/Poland and CDGP-EOST/France) provide metadata and data to the TCS-AH platform in commonly used standards and formats (e.g. miniSEED, GeoTIFF, and .mat). A registration/authorization is mandatory to access some data covered by restriction imposed by data industry providers or shared data embargoed by running projects. The platform grants access to an application portfolio, designed for the AH area, and addressing: (1) basic services for data integration and handling; (2) services for physical models of stress/strain changes over time and space as driven by geo-resource production; (3) services for analyses of geophysical signals; (4) services to extract the relation between technological operations and observed induced seismic/deformation; (5) services to quantitative probabilistic assessments of anthropogenic seismic hazard - statistical properties of anthropogenic seismic series and their dependence on time-varying anthropogenesis; ground motion prediction equations; stationary and time-dependent probabilistic seismic hazard estimates, related to time-changeable technological factors inducing the seismic process; (6) simulator for multi-hazard/multi-risk assessment in exploration/exploitation of georesources (MERGER) - numerical estimate of the occurrence probability of chains of events or processes impacting the environment.

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International audience

This report is based on data provided by the services responsible for seismic monitoring in France (RéNaSS for the CNRS and the Universities, the ISTerre and Géoazur laboratories for the Universe Science Observatories, LDG for the CEA).The earthquake of April 7, 2014 occurred at 19:27 UT (21:26:59 local time) in the Alpes-de-Haute-Provence. Its epicentre is located approximately 6 km west southwest of the commune of Saint-Paul-sur-Ubaye and 11 km north of Barcelonnette, near the border of the departments of Alpes-de-Haute-Provence and Hautes-Alpes (Figure 1). The initiation of the rupture (hypocentre) is estimated at a depth of 11km below sea level (about 13km below the surface).This earthquake had an impact on the south-eastern quarter of France, i.e. 18 departments plus the Principality of Monaco. It has been noted by many residents as the strongest felt in the region in many years. At La Motte-en-Champsaur (yet 55 km from the epicentre) or Puy-Saint-Eusebe (22km) all the inhabitants went out to the village square to comment on this event, also fearing a more important replica.The mission of the French Central Seismological Office is to collect data on earthquakes felt in France, to collect useful information and to facilitate its dissemination to stakeholders concerned by seismic risk or conducting studies or research requiring the use of these observations., Ce rapport s'appuie sur les données communiquées par les services chargés de la surveillance sismique du territoire français (RéNaSS pour le CNRS et les Universités, les laboratoires ISTerre et Géoazur pour les observatoires des Sciences de l’Univers, LDG pour le CEA).Le séisme du 7 avril 2014 s’est produit à 19h27 TU (21h 26min 59sec heure locale) dans les Alpes- de-Haute-Provence. Son épicentre est situé à environ 6 km à l’Ouest Sud-Ouest de la commune de Saint-Paul-sur-Ubaye et 11km au Nord de Barcelonnette, à proximité de la limite des départements des Alpes-de-Haute-Provence et des Hautes-Alpes (figure 1). L’initiation de la rupture (hypocentre) est estimée à une profondeur de 11km sous le niveau de la mer (environ à 13 km de profondeur sous la surface du sol).Ce séisme a impacté par ses effets le quart sud-est de la France, soit 18 départements plus la Principauté de Monaco. Il a été noté par de nombreux habitant comme étant le plus fort jamais ressenti dans la région depuis de nombreuses années. À La Motte-en-Champsaur (pourtant à 55 km de l’épicentre) ou encore à Puy-Saint-Eusebe (22km) l’ensemble des habitants est sorti sur la place du village pour commenter cet événement, craignant aussi une réplique plus importante.Le Bureau Central Sismologique Français a pour mission de collecter les données sur les séismes ressentis en France, de rassembler les informations utiles et de faciliter leur diffusion vers les acteurs concernés par le risque sismique ou menant des études ou recherches nécessitant l’usage de ces observations.

LPSC14037; Scientific data collected with modern sensors or dedicated detectors exceed very often the perimeter of the initial scientific design. These data are obtained more and more frequently with large material and human efforts. A large class of scientific experiments are in fact unique because of their large scale, with very small chances to be repeated and to superseded by new experiments in the same domain: for instance high energy physics and astrophysics experiments involve multi-annual developments and a simple duplication of efforts in order to reproduce old data is simply not affordable. Other scientific experiments are in fact unique by nature: earth science, medical sciences etc. since the collected data is "time-stamped" and thereby non-reproducible by new experiments or observations. In addition, scientific data collection increased dramatically in the recent years, participating to the so-called "data deluge" and inviting for common reflection in the context of "big data" investigations. The new knowledge obtained using these data should be preserved long term such that the access and the re-use are made possible and lead to an enhancement of the initial investment. Data observatories, based on open access policies and coupled with multi-disciplinary techniques for indexing and mining may lead to truly new paradigms in science. It is therefore of outmost importance to pursue a coherent and vigorous approach to preserve the scientific data at long term. The preservation remains nevertheless a challenge due to the complexity of the data structure, the fragility of the custom-made software environments as well as the lack of rigorous approaches in workflows and algorithms. To address this challenge, the PREDON project has been initiated in France in 2012 within the MASTODONS program: a Big Data scientific challenge, initiated and supported by the Interdisciplinary Mission of the National Centre for Scientific Research (CNRS). PREDON is a study group formed by researchers from different disciplines and institutes. Several meetings and workshops lead to a rich exchange in ideas, paradigms and methods. The present document includes contributions of the participants to the PREDON Study Group, as well as invited papers, related to the scientific case, methodology and technology. This document should be read as a "facts finding" resource pointing to a concrete and significant scientific interest for long term research data preservation, as well as to cutting edge methods and technologies to achieve this goal. A sustained, coherent and long term action in the area of scientific data preservation would be highly beneficial.

In order to be efficient during seismic crisis management, authorities need to dispose of rapid assessment of the earthquake impacts. To answer to this need as well as to ensure quick information of the public, one can usually appeal to empirical relations allowing conversion of ground-motion parameters to intensity values and vice-versa: the so-called "GMICEs" (Ground Motion to Intensity Conversion Equations). Now, the problem is that GMICEs are usually derived from instrumental and macroseismic data independently collected within different geological contexts. These data allow producing only limited correlations, as the observed effects of earthquakes are not directly related to a corresponding seismic record. In that context, it appears essential to dispose of both types of data (instrumental and macroseismic) for close and homogeneous recording/observation sites in order to reduce uncertainty of GMICEs. As to do that, BRGM and BCSF are conducting an original and unique pilot experiment allowing a regular acquisition of macroseismic data close to permanent seismic sensors in French West-Indies (Caribbean): the SISMOTem-Antilles project. The innovative proposed approach consists in setting up a network of voluntary witnesses frequently present very close to seismic sensors, coupled to an online testimony process feeding into a database. This approach seems to be particularly well adapted to French West-Indies where many seismic sensors are located directly in administrative or educational buildings or in the vicinity of habitations. Regular presence of many peoples may facilitate constitution of such a network of witnesses. Theses data will improve research on GMICEs and their utilization.

La communication concerne la thématique Sciences de la Terre, mais ni atmosphère, climat, hydrologie, ni sismologie stricto-sensu; Le traitement sismique sur la grille et sa communauté d'utilisateurs EGEODE

International audience; Although the Upper Rhine Graben (URG) has been studied extensively for years, the origin of some of its first-order structures is still under debate, particularly the relatively young uplift of the Vosges Mountains (VM) and Black Forest Mountains (BFM). Their uplift appears to be temporally related to the change of the URG into a continental transform, the rapid subsidence of its deep northern basin, and the onset of erosional and nondepositional phase south of the Northern Basin. Recent observations from newly released seismic reflection data, coupled with older geologic and seismic observations, are used to explain this correlation. We suggest that when the URG turned into a continental transform during the early Miocene, not only was its northern basin transtensionally subsiding as previously suggested, but the VM and BFM were transpressionally uplifted. Transpression became weaker with growing distance from the Alpine front, and north of Baden-Baden the transpression is expressed only by down-buckling of the sediments, forming a deep, elongated syncline. The largest uplifts and erosion associated with this event occurred along both boundaries of the southern URG. However, the center of the graben was also affected to some extent, causing widespread erosion of pre-early Miocene sediments and subsequent nondeposition. The arcuate Vosges and Black Forest fault systems, which formed the boundary faults of the URG during the Oligocene, became mechanically unfavorable during the Miocene transpressional regime. Instead, more linear normal faults took over as the dominant boundary faults, forming the western and eastern Rhine Fault systems and assuming a strike-slip component of motion.

With the aim of increasing the density and speed of earthquake testimonies, the BCSF has chosen to diversify its data collection tools, thus creating SismoCom, the first application for collecting data from quick testimonies on smartphones. Available free of charge on the IOS system (Apple mobile system on iPodTouch, iPhone, iPad), the BCSF's SismoCom application has also been developed for other mobile computers on the market (Android and Blackberry systems, etc.) - The application will be operational at the BCSF from 2010 to 2016. (www.franceseisme.fr), Dans l’objectif de densifier plus encore les témoignages sur les séismes et d’en augmenter la rapidité ,le BCSF a choisi de diversifier ses outils de collecte.Ainsi est née SismoCom, première application pour la collecte des données de témoignages rapides sur smartphone. Disponible gratuitement sur système IOS(système Apple mobile sur iPodTouch, iPhone, iPad),l’application SismoCom du BCSF a été élaborée également pour les autres ordinateurs mobiles du marché (systèmes Androïd et Blackberry ...) - L'application a été mise en fonctionnelle au BCSF de 2010 à 2016. (www.franceseisme.fr)

SismoCom war die erste Smartphone-Anwendung (April 2010), die es ermöglichte, anhand einer Auswahl von Vorschaubildern Aussagen über die Stärke des bei einem Erdbeben gefühlten Tremors (Intensität) zu treffen. Das Zeugnis wurde an das BCSF (Französisches Seismologisches Zentralbüro) zur wissenschaftlichen Nutzung und schnellen Bestimmung der Erschütterungsintensitäten geschickt. Mit SismoCom war es auch möglich, die aus allen erhaltenen Aussagen abgeleiteten Intensitäten zu visualisieren, eine Liste der letzten lokalisierten Weltbeben zu erhalten, auf aktuelle Tsunamiwarnungen zuzugreifen und sich über Maßnahmen zur Prävention von Erdbebenrisiken zu informieren. Diese Anwendung wurde im Jahr 2016 eingestellt, um eine responsive Version des Formulars zu implementieren, SismoCom was the first smartphone application (april 2010) that allowed to testify about the strength of the tremor (intensity) felt during an earthquake from a selection of thumbnails. The testimony was sent to the BCSF (French Central Seismological Bureau) for scientific use and rapid determination of the shaking intensities. SismoCom also made it possible to visualise the intensities deduced from all the testimonies obtained, to obtain a list of the latest localised world earthquakes, to access current tsunami alerts and to be informed about seismic risk prevention measures. This application was discontinued in 2016 in order to set up a responsive version of the form., SismoCom fue la primera aplicación para teléfonos inteligentes (abril de 2010) que permitió dar testimonio de la fuerza del temblor (intensidad) sentido durante un terremoto a partir de una selección de miniaturas. El testimonio fue enviado a la BCSF (Oficina Central Sismológica de Francia) para su uso científico y la determinación rápida de las intensidades de las sacudidas. SismoCom también permitió visualizar las intensidades deducidas de todos los testimonios obtenidos, obtener una lista de los últimos terremotos mundiales localizados, acceder a las alertas de tsunami actuales y estar informado sobre las medidas de prevención del riesgo sísmico. Esta aplicación se dejó de usar en 2016 para implementar una versión responsiva del formulario., SismoCom était la première application smartphone (avril 2010) qui permettait de témoigner sur la force de la secousse (intensité) ressentie lors d'un séisme à partir d'une sélection d'imagette. Le témoignage était envoyé au BCSF (Bureau central sismologique français) pour un usage scientifique et la détermination rapide des intensités de secousse. SismoCom permettait aussi de visualiser les intensités déduites de tous les témoignages obtenus, d'obtenir la liste les derniers séismes mondiaux localisés, d'accéder aux alertes tsunami en cours et d'être informé sur les mesures de prévention du risque sismique. Cette application a été abandonnée en 2016 pour la mise en place d'une version responsive du formulaire., SismoCom è stata la prima applicazione per smartphone (aprile 2010) che ha permesso di testimoniare la forza del tremore (intensità) sentito durante un terremoto da una selezione di miniature. La testimonianza è stata inviata al BCSF (Ufficio Centrale Sismologico Francese) per un uso scientifico e una rapida determinazione delle intensità di scuotimento. SismoCom ha anche permesso di visualizzare le intensità dedotte da tutte le testimonianze ottenute, di ottenere una lista degli ultimi terremoti mondiali localizzati, di accedere agli attuali avvisi di tsunami e di essere informati sulle misure di prevenzione del rischio sismico. Questa applicazione è stata interrotta nel 2016 per implementare una versione responsive del modulo.

International audience; A contribution to the definition of the structural pattern of the Soultz-sous-Forêts EGS (Enhanced Geothermal System) is presented here. After reprocessing, the PHN84J seismic reflection profile highlights the tilted blocks of the Merkwiller-Péchelbronn oilfield. In the Soultz-sous-Forêts horst, complex fault patterns are observed: the Hermerswiller normal fault flattens at depth and is rooted in decollements occurring in Triassic salt or clay series, while other steep normal faults affect underlying sedimentary formations and basement. Some methods for the exploitation of a seismic diffraction recorded by multi-component Vertical Seismic Profiling (VSP) are also illustrated to locate the diffractor without specific data processing. Polarisation and travel time analysis of a diffraction event recorded in the GPK1 borehole are analysed, and its exploitation combined with seismic reflection helps defining a tilted block geometry.

The structure and evolution of the Southern Kerguelen Plateau, located in the Southern Indian Ocean, are determined from high-quality multichannel seism ic rejlection daca collected during the Marion-Dufresne cruise MD 47 (January-February 1986). The sedimentary sequences over the Raggau Basin, a major feature of the central part of the Southern Kerguelen Plateau, are more than 3 km thick and are divided into two megasequences. The lower megasequence appears very thick in the cent.rai part of the basin and thins towards the SE due to erosion at its top. The upper megasequence is about 1.5 km thick. A discordance at the lower part of the megasequence marks an episode of tectonic extension, characterized by normal faulting, which probably corresponds to the breakup between the Kerguelen Plateau and Broken Ridge., Les profils sismique rénexion multitraces recueillis par le N. O. Marion-Dufresne au cours de la campagne MD47 (1986) permettent d'esquisser l'évolution du domaine sud du plateau de Kerguelen (océan Indien austral) . Le bassin de Raggatt, situé dans la partie centrale du plateau, est caractérisé par un remplissage sédimentaire épais de plus de 3 km, constitué par deux mégaséquences. La mégaséquence inférieure, sans doute très épaisse au centre du bassin, apparaît relativement uniforme. Son toit a subi une érosion très intense dans la moitié sud du bassin, ce qui ·se trad uit par une discordance majeure. La mégaséquence supérieure a une épaisseur moyenne de 1,5 km; elle a été déformée par un épisode de tectonique extensive qui pourrait traduire la séparation entre le plateau de Kerguelen et Broken Ridge.