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International audience; From 10 May 2018 to 1 November 2022 (time of writing), an unprecedented seismic activity is observed east of Mayotte Island (France), related to the largest submarine eruption ever recorded with offshore geophysical studies. Using signals from regional and local seismic stations, we build a comprehensive catalog of the local seismicity for the first ten months of the sequence. This catalog includes a total of 2874 events of magnitude (Mlv) ranging from 2.4 to 6.0, with 77% of them relocated using a double difference location procedure. The hypocentral locations over this period are highly dependent on the small seismic network available. Therefore we compare the locations of later events using a similar network and those estimated from a local ocean bottom seismometer (OBS) network installed since March 2019. Based on the time space evolution and characteristics of the seismicity, five distinct phases can be identified, corresponding to the successive activation of two deep seismic swarms, related to the lithospheric-scale magma ascent up to the seafloor, along with progressive deepening of the seismicity interpreted as decompression of a 40 km deep reservoir.

SUMMARYThe brutal onset of seismicity offshore Mayotte island North of the Mozambique Channel, Indian Ocean, that occurred in May 2018 caught the population, authorities and scientific community off guard. Around 20 potentially felt earthquakes were recorded in the first 5 d, up to magnitude Mw 5.9. The scientific community had little pre-existing knowledge of the seismic activity in the region due to poor seismic network coverage. During 2018 and 2019, the MAYOBS/REVOSIMA seismology group was progressively built between four French research institutions to improve instrumentation and data sets to monitor what we know now as an on-going exceptional submarine basaltic eruption. After the addition of 3 medium-band stations on Mayotte island and 1 on Grande Glorieuse island in early 2019, the data recovered from the Ocean Bottom Seismometers were regularly processed by the group to improve the location of the earthquakes detected daily by the land network. We first built a new local 1-D velocity model and established specific data processing procedures. The local 1.66 low VP/VS ratio we estimated is compatible with a volcanic island context. We manually picked about 125 000 P and S phases on land and sea bottom stations to locate more than 5000 events between February 2019 and May 2020. The earthquakes outline two separate seismic clusters offshore that we named Proximal and Distal. The Proximal cluster, located 10 km offshore Mayotte eastern coastlines, is 20–50 km deep and has a cylindrical shape. The Distal cluster start 5 km to the east of the Proximal cluster and extends below Mayotte's new volcanic edifice, from 50 to 25 km depth. The two clusters appear seismically separated, however our data set is insufficient to firmly demonstrate this.

Designing a seismic source model based on the most complete description of potentially active faults and on the kinematics of their latest movements is an essential requirement in seismic hazard studies, at regional and local scales. A study to characterize active faults in the Hispaniola island (today’s Haiti and Dominican Republic) has been conducted in the framework of the probabilistic seismic hazard assessment for Santo Domingo (capital of the Dominican Republic). In this work, we present a seismotectonic map of Hispaniola and its surroundings, based on a compilation and synthesis of geological, geophysical, geodetic and seismological data. Based on these data, distinct seismic zone sources are proposed and classified as either intercrustal domains, major active faults or subduction zones. Each seismic source is described according to several parameters, including its mechanism and current rate of deformation, the associated seismicity and its estimated maximal magnitude. These results constitute an essential database for a homogeneous evaluation of the seismic hazards of Hispaniola.

Since the 2000s, local seismic hazard studies have shown that Mayotte Island presented superficial geological formations prone to lithological site effects. The seismic sequence initiated in May 2018 confirmed the importance of such effects, both in terms of intensity and spatial extension. The analysis of the recorded strong motions showed that weathered volcanic formations are prone to significant site effects with mean amplification factors for peak ground acceleration (PGA) between 1.4 and 4.9 and that a complex combination of lithological and topographic site effects is in action. We thus implement a regional scale map of site effects for the fast calculation of strong motion and damage maps for crisis management purposes. We also provide a first estimate of key site parameters for eight stations: surface geology, resonance frequency, an amplification factor proxy for PGA, a value, if available, and an estimated EC8 soil class.; Depuis les années 2000, les études d’aléa sismique local réalisées à Mayotte ont montré que les formations géologiques superficielles présentes sur l’île étaient susceptibles de présenter des effets de site lithologiques. La séquence sismique initiée en mai 2018 a confirmé l’importance de ces effets, aussi bien en termes d’intensité que d’étendue spatiale. L’analyse des enregistrements des mouvements forts a montré notamment que les formations volcaniques altérées pouvaient être soumises à des effets de site significatifs avec des facteurs d’amplification moyens du PGA compris entre 1,4 et 4,9, et que ces effets résultaient probablement d’une combinaison complexe d’effets lithologiques et topographiques. Nous avons ensuite produit une carte d’effets de site à l’échelle régionale pour permettre le calcul en temps réel de cartes de mouvements forts et de dommages à des fins de gestion de crise. Enfin, pour les 8 sites de stations sismologiques étudiés dans cet article, nous proposons une première estimation des paramètres de sites clefs, à savoir : la géologie superficielle, la fréquence de résonance, un facteur d’amplification du PGA, une valeur du paramètre , si disponible, et une estimation de la classe de sol EC8 au site.

International audience; Volcanic eruptions shape Earth’s surface and provide a window into deep Earth processes. How the primary asthenosphericmelts form, pond and ascend through the lithosphere is, however, still poorly understood. Since 10 May 2018, magmaticactivity has occurred offshore eastern Mayotte (North Mozambique channel), associated with large surface displacements,very-low-frequency earthquakes and exceptionally deep earthquake swarms. Here we present geophysical and marine datafrom the MAYOBS1 cruise, which reveal that by May 2019, this activity formed an 820-m-tall, ~5 km³ volcanic edifice on the seafloor.This is the largest active submarine eruption ever documented. Seismic and deformation data indicate that deep (>55 kmdepth) magma reservoirs were rapidly drained through dykes that intruded the entire lithosphere and that pre-existing subverticalfaults in the mantle were reactivated beneath an ancient caldera structure. We locate the new volcanic edifice at the tip ofa 50-km-long ridge composed of many other recent edifices and lava flows. This volcanic ridge is an extensional feature insidea wide transtensional boundary that transfers strain between the East African and Madagascar rifts. We propose that the massiveeruption originated from hot asthenosphere at the base of a thick, old, damaged lithosphere.

International audience; In recent years, the French seismological, geodetic and gravimetric community has been structured within RESIF (French seismological and geodetic network). In addition to instrumental developments, RESIF has structured the work on French seismicity (metropolitan and overseas) within the RESIF transverse seismicity action (ATS). The purpose of this article is to present the ATS and the way it is structured to propose to the community different products: seismicity bulletin and catalogue, historical and instrumental macroseismicity data, shakemaps. The places where these products can be found are indicated, as well as the way they are realized and the improvements in progress for a better realization and availability. The link with EPOS (European plate observing system) is also underlined.; Ces dernières années, la communauté sismologique, géodésique et gravimétrique française s'est structurée au sein de RESIF (Réseau sismologique et géodésique français). Outre les développements instrumentaux, RESIF a structuré les travaux sur la sismicité française (métropole et outre-mer) au sein de l'Action transverse sismicité (ATS) de RESIF. L'objet de cet article est de présenter l'ATS et la manière dont elle est structurée pour proposer à la communauté différents produits : bulletin et catalogue de sismicité, données historiques et instrumentales de macrosismicité, shakemaps. Les endroits où ces produits peuvent être trouvés sont indiqués, ainsi que la façon dont ils sont réalisés et les améliorations en cours pour une meilleure réalisation et disponibilité. Le lien avec EPOS (European plate observing system) est également souligné.

International audience; The Mayotte seismic sequence that started on 10 May 2018, with a main shock of magnitude Mw 5.9 on May 15, followed by a major offshore volcanic activity, raises several questions of seismovolcanic hazards in the Comoros region. The unexpected size and duration of the crisis is an opportunity to reassess the distribution and magnitude of the seismicity near Mayotte Island, but also regionally. We present a comprehensive seismicity catalogue of the region including the Mozambique Channel, the Mozambique coast and Madagascar, based partly on previously published data in the region and partly on unpublished data from local catalogues for the Comoros and Madagascar. Our catalogue extends from 1900 onward with a completeness of magnitude 5.5 until 1980s and decreasing only recently to 4.5 after 2010. It comprises the events of magnitude Mlv ≥3.5 for the seismic sequence of Mayotte from May 2018 to October 2020 as the crisis is still ongoing. Present knowledge of the seismicity, largely partial in distribution and magnitude before 1980, makes the seismic sequence of 2018-2020 an exceptional and unprecedented seismo-volcanic event in the region. We discuss the distribution of seismicity in time and space within the context of the south eastward propagation of the East African rift system towards Madagascar.

Instrumental catalogues of earthquakes in the subduction zone of the Lesser Antilles are produced by local observatories and the International Seismological Centre. But none of these catalogues merge all arrival times of the first regional phases available; in addition, they have a magnitude of completeness relatively high for the entire Lesser Antilles area. As part of the Antilles Seismological Data Centre project, we produced a unified catalogue of known earthquakes from 1972 to 2012, with optimal constraints on the hypocentre locations. We re-evaluated the hypocentres with the method used in local observatories and a probabilistic method improving the distributions of arrival time residuals. We developed a simple method to select the preferred hypocentre independently of the localization algorithm, and we offer a complete catalogue including 46,703 earthquakes. Compared to other existing catalogues, we provide additional arrival times for 24,528 earthquakes. Our results highlight the variabilities of the magnitude of completeness and of the seismicity suggesting how the future analysis could infer the mechanisms of heterogeneous seismic coupling and intermediate-depth triggering., Comptes Rendus Geoscience, 353 (S1), ISSN:1778-7025, ISSN:1631-0713

SUMMARYOn 10 May 2018, an unprecedented long and intense seismic crisis started offshore, east of Mayotte, the easternmost of the Comoros volcanic islands. The population felt hundreds of events. Over the course of 1 yr, 32 earthquakes with magnitude greater than 5 occurred, including the largest event ever recorded in the Comoros (Mw = 5.9 on 15 May 2018). Earthquakes are clustered in space and time. Unusual intense long lasting monochromatic very long period events were also registered. From early July 2018, Global Navigation Satellite System (GNSS) stations and Interferometric Synthetic Aperture Radar (InSAR) registered a large drift, testimony of a large offshore deflation. We describe the onset and the evolution of a large magmatic event thanks to the analysis of the seismicity from the initiation of the crisis through its first year, compared to the ground deformation observation (GNSS and InSAR) and modelling. We discriminate and characterize the initial fracturing phase, the phase of magma intrusion and dyke propagation from depth to the subsurface, and the eruptive phase that starts on 3 July 2018, around 50 d after the first seismic events. The eruption is not terminated 2 yr after its initiation, with the persistence of an unusual seismicity, whose pattern has been similar since summer 2018, including episodic very low frequency events presenting a harmonic oscillation with a period of ∼16 s. From July 2018, the whole Mayotte Island drifted eastward and downward at a slightly increasing rate until reaching a peak in late 2018. At the apex, the mean deformation rate was 224 mm yr−1 eastward and 186 mm yr−1 downward. During 2019, the deformation smoothly decreased and in January 2020, it was less than 20 per cent of its peak value. A deflation model of a magma reservoir buried in a homogenous half space fits well the data. The modelled reservoir is located 45 ± 5 km east of Mayotte, at a depth of 28 ± 3 km and the inferred magma extraction at the apex was ∼94 m3 s−1. The introduction of a small secondary source located beneath Mayotte Island at the same depth as the main one improves the fit by 20 per cent. While the rate of the main source drops by a factor of 5 during 2019, the rate of the secondary source remains stable. This might be a clue of the occurrence of relaxation at depth that may continue for some time after the end of the eruption. According to our model, the total volume extracted from the deep reservoir was ∼2.65 km3 in January 2020. This is the largest offshore volcanic event ever quantitatively documented. This seismo-volcanic crisis is consistent with the trans-tensional regime along Comoros archipelago.

Volcanic eruptions are foundational events shaping the Earth’s surface and providing a window into deep Earth processes. We document here an ongoing magmatic event offshore Mayotte island (Western Indian Ocean) unprecedented in terms of emitted volume of lava and duration of the seismic crisis.This event gave birth to a deep-sea volcanic edifice 820m tall and ~ 5 km3 in volume, located 50 km from Mayotte. A plume with distinct chemical signatures compared to open-ocean seawater emanated from the edifice, generating an exceptional 1900m-high vertical acoustic anomaly in the water column. Noble gas analyses in the vesicles from a popping rock dredged on the flank of the edifice, indicate rapid magma transfer from the asthenosphere. The edifice is located at the tip of a WNW-ESE–striking volcanic ridge composed of many other edifices, cones and lava flows constructed by past eruptions. Starting in May 2018 thousand of earthquakes were triggered by the magmatic event. The space-time distribution of the seismicity suggests that magma below the center of the ridge was transported to the new edifice over a few weeks in dikes that penetrated the brittle mantle a result of a lithosphere-scale extensional episode accommodating motion along a transfer zone between the East-African rifts and Madagascar. Since the eruption’s onset, the seismicity is mostly concentrated closer to the island, in an exceptionally deep zone (25-50 km) overlain by a zone of enigmatic, very low frequency, tremors.

International audience

p. 715-736, Tras el terremoto de Haití de 2010 dio comienzo una iniciativa para tratar de entender mejor los efectos de los terremotos en la República Dominicana, en particular en la ciudad de Santiago de los Caballeros, segunda más importante del país. Santiago ha sufrido varios terremotos devastadores, en 1562 la ciudad fue reconstruida en un nuevo sitio al sur de la falla responsable. El daño debido a un terremoto ocurre asociado a un conjunto de factores, entre ellos, la aceleración del suelo, que por lo general se señala como el principal o como la clave para explicar la mayor parte de los efectos. La aceleración del suelo varía dependiendo principalmente de la distancia al epicentro, de las propiedades del suelo y de la topografía. En cuanto a la distancia, es de esperar menor aceleración conforme aumenta la distancia al epicentro. De otra parte, suelos con diferentes características dan lugar a diferentes respuestas. Los efectos de la topografía aún no se comprenden bien. El efecto de la atenuación de la distancia en un radio de unos pocos kilómetros suele ser mucho menos relevante que el efecto de la variación en las propiedades de los suelos. Este artículo recoge los resultados obtenidos de los estudios de peligro sísmico y microzonificación sísmica en la ciudad de Santiago de los Caballeros: i) cuantificación del peligro sísmico regional debido a la falla septentrional; ii) un nuevo mapa geológico y iii) la cartografía de zonas de respuesta sísmica homogénea y susceptibilidad a la licuefacción, Instituto Geológico y Minero de España, España, Bureau de recherches géologiques et minières, Francia, Servicio Geológico Nacional, República Dominicana, Departamento de Geología, Universidad de Atacama, Chile

The Lesser Antilles, in the eastern Caribbean, is prone to a large seismic hazard due to the subduction of the Atlantic lithosphere beneath the Caribbean plate, with a slow convergence rate of 2 cm/yr (Demets et al. 2000; Mann et al. 2002). The largest historical earthquake in the region, in 1843 between Guadeloupe and Antigua, had a magnitude estimate of 7.5 to 8 (Bernard and Lambert 1988), but historical seismicity covers too short a period of time (less than three and one-half centuries) to estimate the recurrence time of strong events or their plausible maximum magnitude. The latest destructive earthquake, Les Saintes in Guadeloupe in 2004, had a magnitude 6.3 (Institut de Physique du Globe de Paris 2004; Bertil et al. 2004). To better understand the regional geodynamics and assess the related seismic hazard, we must improve our knowledge and our understanding of the area's present seismicity. Since the 1950s, several regional research institutes have monitored local seismicity. The Institut de Physique du Globe de Paris (IPGP) and Bureau de Recherches Geologiques et Minieres (BRGM) have set up various seismological and accelerometric arrays to monitor the French islands of Guadeloupe and Martinique. As a consequence, several large datasets with very different formats and time spans exist, scattered among several sites. Providing a more integrated database for the seismicity of the Lesser Antilles arc was the primary motivation for creating the French Antilles Seismological Data Base (Centre de Donnees Sismologiques des Antilles, CDSA). The aim of this paper is to introduce the newly created CDSA and to illustrate its capacity for improving our knowledge of the region's seismicity. In the first part of this study, we present the various arrays, waveform databases, and seismicity catalogs used by the CDSA. In the second part, we present and discuss new …

International audience; Strong-motion networks have been operating in the Caribbean region since the 1970s, however, until the mid-1990s only a few analogue stations were operational and the quantity of data recorded was very low. Since the mid-1990s, digital accelerometric networks have been established on islands within the region. At present there are thought to be about 160 stations operating in this region with a handful on Cuba, 65 on the French Antilles (mainly Guadeloupe and Martinique), eight on Jamaica, 78 on Puerto Rico (plus others on adjacent islands) and four on Trinidad. After briefly summarising the available data from the Caribbean islands, this article is mainly concerned with analysing the data that has been recorded by the networks operating on the French Antilles in terms of their distribution with respect to magnitude, source-to-site distance, focal depth and event type; site effects at certain stations; and also with respect to their predictability by ground motion estimation equations developed using data from different regions of the world. More than 300 good quality triaxial acceleration time-histories have been recorded on Guadeloupe and Martinique at a large number of stations from earthquakes with moment magnitudes larger than 4.8, however, most of the records are from considerable source-to-site distances. From the data available it is found that many of the commonly-used ground motion estimation equations for shallow crustal earthquakes poorly estimate the observed ground motions on the two islands; ground motions on Guadeloupe and Martinique have smaller amplitudes and are more variable than expected. This difference could be due to regional dependence of ground motions because of, for example, differing tectonics or crustal structures or because the ground motions so far recorded are, in general, from smaller earthquakes and greater distances than the range of applicability of the investigated equations.

Le 12 janvier 2010, la capitale d'Haïti, Port-au-Prince, a subit un des plus violents séismes qu'elle ait connu au cours de ces derniers siècles. Soutenue par le PNUD et l'Etat haïtien (LNBTP et BME), une étude de microzonage sismique sur Port-au-Prince a alors été engagée. La connaissance géologique locale et les données topographiques constituent des préalables essentiels dans le processus de réalisation d'un microzonage sismique. Dans ce cadre, les images Pléiades et le MNT (dérivé de ces images PLEIADES et calculé par le SERTIT/CNES dans le cadre du projet KalHaiti) ont été utilisés pour l'étude géologique et l'analyse morphologique de la région de Port-au-Prince. L'étude lithostratigraphique montre un substratum marno-calcaire d'âge miocène à pliocène, caractéristique de dépôts en milieu profond à sublittoral. Ces dépôts sont entrecoupés de dépôts détritiques d'origine tectonique liée au jeu des failles bordières sud de la plaine de Port-au-Prince. La carte des failles actives réalisée est directement intégrée à la carte du microzonage sismique. Les résultats géologiques ont constitué des éléments essentiels pour l'évaluation des aléas mouvements de terrain (effets induits) et des effets de site lithologiques et topographiques du microzonage sismique.

Instrumental seismic activity in Madagascar over a 16-years period, as well as the largest earthquakes experienced over the last century, are studied using seismic signal recordings and the archives of the Antananarivo Geophysical Observatory (Institut et Observatoire de Geophysique d'Antananarivo). Earthquakes occur in most of the island. The known focal mechanisms indicate a general E–W extension, consistent with the stretching currently observed in the Mozambique channel and on the eastern edge of the African continent. Seismic areas cover the main Pliocene–Quaternary tectonic formations. Other events are located near Pan-African tectonics structures, preferentially reactivated within the Precambrian basement complex. A regional origin of stresses cannot explain completely the spatial distribution of all the earthquakes in the central highlands of Madagascar. An other possible stress origin can be a thermal bulge on which the main Pliocene Quaternary tectonic and volcanic structures of this region are situated. The current tectonic phase of extension seems to correspond to an early stage of reactivation. Madagascar could be part of the E–W extension zone associated with diffuse seismicity affecting East Africa south of the Equator.

International audience; Epistemic uncertainties can be classified into two major categories: parameter and model. While the first one stems from the difficulties in estimating the values of input model parameters, the second comes from the difficulties in selecting the appropriate type of model. Investigating their combined effects and ranking each of them in terms of their influence on the predicted losses can be useful in guiding future investigations. In this context, we propose a strategy relying on variance-based global sensitivity analysis, which is demonstrated using an earthquake loss assessment for Pointe-à-Pitre (Guadeloupe, France). For the considered assumptions, we show: that uncertainty of losses would be greatly reduced if all the models could be unambiguously selected; and that the most influential source of uncertainty (whether of parameter or model type) corresponds to the seismic activity group. Finally, a sampling strategy was proposed to test the influence of the experts' weights on models and on the assumed coefficients of variation of parameter uncertainty. The former influenced the sensitivity measures of the model uncertainties, whereas the latter could completely change the importance rank of the uncertainties associated to the vulnerability assessment step.

The inclusion of epistemic uncertainties, generally via logic trees (Kulkarni et al. , 1984), within probabilistic seismic‐hazard assessments (PSHAs) is becoming standard for all types of studies (commercial, governmental, or research; site specific, national, regional, or global). Consequently many studies publish expected ground motions for a given annual frequency of exceedance (AFE) or return period derived from the hazard curves for the mean, median, and various fractiles (percentiles). The spread of these values represents the uncertainty captured in the results (the greater the spread the higher the uncertainty). For example, Figure 1 shows the distribution of AFE for a peak ground acceleration (PGA) of 0.25 g obtained in the study for the Washington Nuclear Plant (WNP)‐2 nuclear power plant (Hanford Reservation, Washington State) reported by Kulkarni et al. (1984). Distributions of ground‐motion levels for a given AFE are now most commonly reported in recent PSHAs rather than distributions of AFEs for a certain ground‐motion level. Figure 1. Example distribution of annual frequency of exceedance (AFEs) for a considered peak ground acceleration (PGA) of 0.25 g for the WNP‐2 nuclear power plant (Hanford Reservation, Washington State) (Kulkarni et al. , 1984, Reprinted with permission from Earthquake Engineering Research Institute). Woo (2002) calls for the epistemic uncertainty to be overlaid on seismic hazard maps, although this is rarely, if ever, done. Giardini et al. (2004, their fig. 34) present the relative uncertainty in the Swiss National Seismic Hazard Map showing that parts of the map are associated with considerable uncertainty (more than 40%) because of doubts over the seismic source zones and b ‐values. A recent detailed study of epistemic uncertainties in a PSHA is by Bradley et al. (2012), who rank the impact of various uncertainties on hazard results for two New Zealand cities (Wellington and Christchurch). There are, however, no studies to our knowledge …

International audience; The main objective of this work is to compare the potential direct economic losses between two different hazards in Guadeloupe (French Antilles), earthquakes and storm surges, for different return periods. In order to validate some hypotheses which are done concerning building typologies and their insured values a comparison between real economic loss data and estimated ones is done using a real event. In 2004 there was an earthquake in Guadeloupe, Mw 6.3, in a little archipelago in the south of Guadeloupe called Les Saintes. The heaviest intensities were VIII in the municipalities of Les Saintes and decreases from VII to IV in the other municipalities of Guadeloupe. The CCR, French Reinsurance Organism, has provided data about the total insured economic losses estimated per municipality (in a situation in 2011) and the insurance penetration ratio, it means, the ratio of insured exposed elements per municipality. Some other information about observed damaged structures is quite irregular all over the archipelago, being the only reliable one the observed macroseismic intensity per municipality (field survey done by BCSF). These data at Guadeloupe's scale has been compared with results coming from a retro damage scenario for this earthquake done with the vulnerability data from current buildings and their mean economic value of each building type and taking into account the local amplification effects on the earthquake propagation. In general the results are quite similar but with some significant differences. The results coming from scenario are quite correlated with the spatial attenuation from the earthquake intensity; the heaviest economic losses are concentrated within the municipalities exposed to a considerable and damageable intensity (VII to VIII). On the other side, CCR data show that heavy economic damages are not only located in the most impacted cities but also in the most important municipalities of the archipelago in terms of economic activity (industry, commerce and tourism), even if in these municipalities intensities were quite smaller (V to VI in EMS98 scale). It seems that damage scenario cannot consider completely this situation and the greater complexity of industrial and commercial areas. The next work is to compare seismic risk and storm surge risk in a little scale (for 3 municipalities in Pointe à Pitre area, the capital of Guadeloupe), in terms of potential direct economic losses for different return periods. The methodology therefore relies on (i) a probabilistic hazard assessment, (ii) a loss ratio estimation for the exposed elements and (iii) an economic estimation of these assets. Seismic hazard assessment was done for return periods of 100, 475, 1000 and 5000 years. Storm surge hazard assessment is based on the selection of relevant historical cyclones and on the simulation of the associated wave and cyclonic surge. The combined local sea elevations, called "set-up", are then fitted with a statistical distribution in order to obtain its time return characteristics. Several run-ups are then extracted, the inundation areas are calculated and the relative losses of the affected assets are deduced. Current building vulnerability was adapted for each single risk, vulnerability indices (RISK-UE method) for seismic risk and vulnerability functions for storm surge. State of art of available vulnerability functions in storm surge and floods in tropical context has been done (CAPRA software, HAZUS software) even if these functions do not consider explicitly the local context in Guadeloupe. Damages caused by wind are not considered. The past storm surge events in French Antilles data are not enough to build new vulnerability functions. The results have been achieved in the project MATRIX (http://matrix.gpi.kit.edu/), funded by the European Commission in the Seventh Framework Programme (FP7/2007-2013), under grant agreement n 265138.

International audience; Over recent years, many studies devoted to large-scale seismic risk analyses have been carried out in different regions and by various research teams. A wide variety of software is available to perform these analyses: they are more or less flexible and use different levels of precision to model ground motion and vulnerability of the built environment. All are based on risk calculation through the convolution of hazard and vulnerability. This article presents a seismic risk analysis tool, Armagedom, implemented over the past five years on a variety of urban seismic contexts: Bouzareah (Algeria), four provinces in Iran, the French Departments lying along the French/Spanish border, and Overseas Departments in the French Antilles. The objectives and requirements of these studies differed with respect to the level of precision that was sought and the surface areas examined. In order to meet differing project targets, three levels of seismic risk assessment were defined based on the macroseismic and mechanical approaches for vulnerability and damage estimation presenting different levels of precision: Level N0 estimates seismic risk on a regional territorial scale based on the macroseismic approach and existing statistical data; Level N1 yields the seismic risk at a district level based on the macroseismic approach and on visual evaluation of the vulnerability of structures over an itinerary in the area to be analyzed; and Level N2 also establishes the seismic risk at a district level, but the hazard description is represented by a spectrum and vulnerability is estimated based on mechanical models. The software, with a modular design, was developed in order to optimize computation time and automate execution of the three levels of analysis. In this article, the software modules are illustrated by maps derived from the seismic risk analyses performed. We further use the available event information to test, validate, and update the methods and software presented in this article.

International audience; A unified probabilistic seismic hazard assessment (PSHA) for the Pyrenean region has been performed by an international team composed of experts from Spain and France during the Interreg IIIA ISARD project. It is motivated by incoherencies between the seismic hazard zonations of the design codes of France and Spain and by the need for input data to be used to define earthquake scenarios. A great effort was invested in the homogenisation of the input data. All existing seismic data are collected in a database and lead to a unified catalogue using a local magnitude scale. PSHA has been performed using logic trees combined with Monte Carlo simulations to account for both epistemic and aleatory uncertainties. As an alternative to hazard calculation based on seismic sources zone models, a zoneless method is also used to produce a hazard map less dependant on zone boundaries. Two seismogenic source models were defined to take into account the different interpretations existing among specialists. A new regional ground-motion prediction equation based on regional data has been proposed. It was used in combination with published ground-motion prediction equations derived using European and Mediterranean data. The application of this methodology leads to the definition of seismic hazard maps for 475- and 1,975-year return periods for spectral accelerations at periods of 0 (corresponding to peak ground acceleration), 0.1, 0.3, 0.6, 1 and 2 s. Median and percentiles 15% and 85% acceleration contour lines are represented. Finally, the seismic catalogue is used to produce a map of the maximum acceleration expected for comparison with the probabilistic hazard maps. The hazard maps are produced using a grid of 0.1°. The results obtained may be useful for civil protection and risk prevention purposes in France, Spain and Andorra.

In numerous regions, the focal depths are not precisely determined from standard location methods because of the poor azimuthal coverage by the seismic network or because of the important geological complexity. In this study, we attempt to refine the determination of the focal depth of some events by analyzing the waveforms of the seismograms and the relative amplitude of the crustal phases. The discrete wave number representation method is used to compute synthetics corresponding to sources at various depths. We present three examples of events which occurred in southeast France in different geological units. We conclude that the waveforms are not very sensitive to slight changes of the crustal model or quality factors, but are very dependent on the focal depth. If a convenient crustal model is used in the computations, the numerical simulations constrain the depth in a better way than standard location methods using arrival times. In our examples, when the path from source to station crosses different structures, the best fit of the envelope of the seismograms by synthetics computed in a flat-layered model is reached for a crustal model corresponding to the source region.

National audience; Experience of past earthquakes as well as "earthquake" civil-protection’s exercises underlines the need for crisis managers to have at their disposal rapid-response tools able to assess consequences caused by earthquakes, even for moderate events. BRGM and its partners have developed tools to meet these operational needs, in order to automatically and quickly produce maps of seismic ground-motions, as well as sectorized assessments of damages. To go further in taking account operational requirements related to the management of seismic crisis, work is being done in order to provide the authorities with a quick assessment of the human tolls that may control their actions, structured within reports dedicated to civil-protection teams. Exploratory tracks are also being considered in order to enrich the information feedback from the field by using techniques of "crowd-sourcing", thanks to the use of distributed "citizen" sensors or of social-networks.; L’expérience acquise après séismes ainsi que dans le cadre d’exercices « séisme » de sécurité-civile montre que les gestionnaires de crise ont besoin de disposer d’outils pour identifier rapidement l’ampleur des conséquences occasionnées, y-compris dans le cas d’évènements modérés. Le BRGM et ses partenaires ont mis en place des outils visant à répondre à ces besoins opérationnels, permettant notamment la cartographie rapide et automatique de l’ampleur des secousses sismiques, ainsi que l’estimation sectorisée des dommages. Afin d’aller encore plus loin dans la prise en compte des besoins opérationnels liés à la gestion de crise sismique, des travaux sont menés dans le but de fournir aux autorités une évaluation rapide de bilans essentiels au dimensionnement de leur réponse opérationnelle, structurée selon des communiqués directement appropriables par les services concernés. Des pistes exploratoires sont par ailleurs à l’étude dans le but d’enrichir la remontée d’information terrain en ayant recours aux techniques de « crowd-sourcing », par la mobilisation de capteurs « citoyens » distribués ou par l’usage des réseaux sociaux.