Spatial–temporal variations of water vapor content over Ethiopia: a study using GPS observations and the ECMWF model

We characterize the spatial–temporal variability of integrated water vapor (IWV) in Ethiopia from a network of global positioning system (GPS) stations and the European Center for Medium range Weather Forecasting (ECMWF) model. The IWV computed from the ECMWF model is integrated from the height of the GPS stations on 60 pressure levels to take both the actual earth surface and the model orography discrepancies into account. First, we compare the IWV estimated from GPS and from the model. The bias varies from site to site, and the correlation coefficients between the two data sets exceed 0.85 at different time scales. The results of this study show that the general ECMWF IWV trend is underestimation over highlands and overestimation over lowlands for wet periods, and overestimation over high- lands and underestimation over lowlands for dry periods with very few exceptional stations. Second, we observe the spatial variation of the IWV. High values are obtained in those stations that are located in the north-eastern (Afar depression) sites and the south-western part of the country. This distribution is related to the spatial variability of the climate in Ethiopia. Finally, we study the seasonal cycle and inter-annual variability of IWV for all stations over Ethiopia. The main result is the strong inter-annual vari- ability observed for the dry seasons

Multiple mantle upwellings in the transition zone beneath the northern East-African Rift system from relative P-wave travel-time tomography

Mantle plumes and consequent plate extension have been invoked as the likely cause of East African Rift volcanism. However, the nature of mantle upwelling is debated, with proposed configurations ranging from a single broad plume connected to the large low-shear-velocity province beneath Southern Africa, the so-called African Superplume, to multiple lower-mantle sources along the rift. We present a new P-wave travel-time tomography model below the northern East-African, Red Sea, and Gulf of Aden rifts and surrounding areas. Data are from stations that span an area from Madagascar to Saudi Arabia. The aperture of the integrated data set allows us to image structures of 100 km length-scale down to depths of 700– 800 km beneath the study region. Our images provide evidence of two clusters of low-velocity structures consisting of features with diameter of 100–200 km that extend through the transition zone, the first beneath Afar and a second just west of the Main Ethiopian Rift, a region with off-rift volcanism. Considering seismic sensitivity to temperature, we interpret these features as upwellings with excess temperatures of 100 6 50 K. The scale of the upwellings is smaller than expected for lower mantle plume sources. This, together with the change in pattern of the low-velocity anomalies across the base of the transition zone, suggests that ponding or flow of deep-plume material below the transition zone may be spawning these upper mantle upwellings

The AlpArray Seismic Network: A Large-Scale European Experiment to Image the Alpine Orogen

International audienceThe AlpArray programme is a multinational, European consortium to advance our understanding of orogenesis and its relationship to mantle dynamics, plate reorganizations , surface processes and seismic hazard in the Alps-Apennines-Carpathians-Dinarides orogenic system. The AlpArray Seismic Network has been deployed with contributions from 36 institutions from 11 countries to map physical properties of the lithosphere and astheno-sphere in 3D and thus to obtain new, high-resolution geophysical images of structures from the surface down to the base of the mantle transition zone. With over 600 broadband stations Electronic supplementary material The online version of this article (https ://doi. 1 3 operated for 2 years, this seismic experiment is one of the largest simultaneously operated seismological networks in the academic domain, employing hexagonal coverage with station spacing at less than 52 km. This dense and regularly spaced experiment is made possible by the coordinated coeval deployment of temporary stations from numerous national pools, including ocean-bottom seismometers, which were funded by different national agencies. They combine with permanent networks, which also required the cooperation of many different operators. Together these stations ultimately fill coverage gaps. Following a short overview of previous large-scale seismological experiments in the Alpine region, we here present the goals, construction, deployment, characteristics and data management of the AlpArray Seismic Network, which will provide data that is expected to be unprecedented in quality to image the complex Alpine mountains at depth

Ambient-noise tomography of the wider Vienna Basin region

We present a new 3-D shear-velocity model for the top 30 km of the crust in the wider Vienna Basin region based on surface waves extracted from ambient-noise cross-correlations. We use continuous seismic records of 63 broad-band stations of the AlpArray project to retrieve interstation Green’s functions from ambient-noise cross-correlations in the period range from 5 to 25 s. From these Green’s functions, we measure Rayleigh group traveltimes, utilizing all four components of the cross-correlation tensor, which are associated with Rayleigh waves (ZZ, RR, RZ and ZR), to exploit multiple measurements per station pair. A set of selection criteria is applied to ensure that we use high-quality recordings of fundamental Rayleigh modes. We regionalize the interstation group velocities in a 5 km × 5 km grid with an average path density of ∼20 paths per cell. From the resulting group-velocity maps, we extract local 1-D dispersion curves for each cell and invert all cells independently to retrieve the crustal shear-velocity structure of the study area. The resulting model provides a previously unachieved lateral resolution of seismic velocities in the region of ∼15 km. As major features, we image the Vienna Basin and Little Hungarian Plain as low-velocity anomalies, and the Bohemian Massif with high velocities. The edges of these features are marked with prominent velocity contrasts correlated with faults, such as the Alpine Front and Vienna Basin transfer fault system. The observed structures correlate well with surface geology, gravitational anomalies and the few known crystalline basement depths from boreholes. For depths larger than those reached by boreholes, the new model allows new insight into the complex structure of the Vienna Basin and surrounding areas, including deep low-velocity zones, which we image with previously unachieved detail. This model may be used in the future to interpret the deeper structures and tectonic evolution of the wider Vienna Basin region, evaluate natural resources, model wave propagation and improve earthquake locations, among others

Arrival angles of teleseismic fundamental mode Rayleigh waves across the AlpArray

The dense AlpArray network allows studying seismic wave propagation with high spatial resolution. Here we introduce an array approach to measure arrival angles of teleseismic Rayleigh waves. The approach combines the advantages of phase correlation as in the two-station method with array beamforming to obtain the phase-velocity vector. 20 earthquakes from the first two years of the AlpArray project are selected, and spatial patterns of arrival-angle deviations across the AlpArray are shown in maps, depending on period and earthquake location. The cause of these intriguing spatial patterns is discussed. A simple wave-propagation modelling example using an isolated anomaly and a Gaussian beam solution suggests that much of the complexity can be explained as a result of wave interference after passing a structural anomaly along the wave paths. This indicates that arrival-angle information constitutes useful additional information on the Earth structure, beyond what is currently used in inversions

Réalisation du forage de la station sismologique BETHI à Béthincourt (Meuse)

Realization of the drilling of the seismological station BETHI in the commune of Béthincourt (Meuse) near Verdun. The compressed air drill is installed on a former quarry used by the municipality to rebuild the village after the Second World War. The drilling was carried out in several stages in order to verify the absence of old shells in the ground. Beyond a depth of 5 meters, the soil, consisting of a mixture of water and limestone that mixed with the clay of the upper layer, bogged down the compressed air system and complicated the work. The drilling was carried out in October 2021 at a depth of 12m with the equipment of the Bureau de recherches géologiques et minières (BRGM) and its technical team with the assistance of the team of the seismological observatory of the Ecole et Observatoire des Sciences de la Terre (EOST) of Strasbourg. Because of technical problems due to the site conditions, the well was finalized with a depth of 9m. The seismological station BETHI has been integrated into the Permanent Broadband Network (RLBP) in August 2021. The RLBP is part of Résif, a national research infrastructure dedicated to the observation and understanding of the Earth's internal structure and dynamics. Résif is based on high technology observation networks, composed of seismological, geodesic and gravimetric instruments deployed in a dense manner on the whole French territory. The data collected allow to study with a high spatio-temporal resolution the ground deformation, the superficial and deep structures, the seismicity at the local and global scale and the natural hazards, and more particularly the seismic ones, on the French territory. Résif is part of the European (EPOS - European Plate Observing System) and global systems of instruments allowing to image the interior of the Earth in its entirety and to study many natural phenomena.Réalisation du forage de la station sismologique BETHI sur la commune de Béthincourt (Meuse) proche de Verdun. La foreuse à air comprimé est installée sur une ancienne carrière utilisée par la commune pour reconstruire le village après la Seconde Guerre Mondiale. Le forage a été effectué en plusieurs étapes afin de vérifier l’absence d’ancien obus dans le sol. Au delà de 5 mètres de profondeur le sol constitué d’un mélange d’eau et de calcaire qui s’est mélangé avec l’argile de la couche supérieur, a embourbé le système à air comprimé et a compliqué le chantier. Le forage a été réalisé en octobre 2021 sur 12m de profondeur avec le matériel du Bureau de recherches géologiques et minières (BRGM) et son équipe technique avec l’assistance de l’équipe de l’observatoire sismologique de l’Ecole et Observatoire des Sciences de la Terre (EOST) de Strasbourg. A cause de problèmes techniques dus aux conditions du site, le puits a été finalisé avec une profondeur de 9m. La station sismologique BETHI a intégré le Réseau Large Bande Permanent (RLBP) en août 2021. Le RLBP fait partie de Résif, une infrastructure de recherche nationale dédiée à l’observation et la compréhension de la structure et de la dynamique Terre interne. Résif se base sur des réseaux d’observation de haut niveau technologique, composés d’instruments sismologiques, géodésiques et gravimétriques déployés de manière dense sur tout le territoire français. Les données recueillies permettent d’étudier avec une haute résolution spatio-temporelle la déformation du sol, les structures superficielles et profondes, la sismicité à l’échelle locale et globale et les aléas naturels, et plus particulièrement sismiques, sur le territoire français. Résif s’intègre aux dispositifs européens (EPOS - European Plate Observing System) et mondiaux d’instruments permettant d’imager l’intérieur de la Terre dans sa globalité et d’étudier de nombreux phénomènes naturels

Réalisation du forage de la station sismologique BETHI à Béthincourt (Meuse)

Realization of the drilling of the seismological station BETHI in the commune of Béthincourt (Meuse) near Verdun. The compressed air drill is installed on a former quarry used by the municipality to rebuild the village after the Second World War. The drilling was carried out in several stages in order to verify the absence of old shells in the ground. Beyond a depth of 5 meters, the soil, consisting of a mixture of water and limestone that mixed with the clay of the upper layer, bogged down the compressed air system and complicated the work. The drilling was carried out in October 2021 at a depth of 12m with the equipment of the Bureau de recherches géologiques et minières (BRGM) and its technical team with the assistance of the team of the seismological observatory of the Ecole et Observatoire des Sciences de la Terre (EOST) of Strasbourg. Because of technical problems due to the site conditions, the well was finalized with a depth of 9m. The seismological station BETHI has been integrated into the Permanent Broadband Network (RLBP) in August 2021. The RLBP is part of Résif, a national research infrastructure dedicated to the observation and understanding of the Earth's internal structure and dynamics. Résif is based on high technology observation networks, composed of seismological, geodesic and gravimetric instruments deployed in a dense manner on the whole French territory. The data collected allow to study with a high spatio-temporal resolution the ground deformation, the superficial and deep structures, the seismicity at the local and global scale and the natural hazards, and more particularly the seismic ones, on the French territory. Résif is part of the European (EPOS - European Plate Observing System) and global systems of instruments allowing to image the interior of the Earth in its entirety and to study many natural phenomena.Réalisation du forage de la station sismologique BETHI sur la commune de Béthincourt (Meuse) proche de Verdun. La foreuse à air comprimé est installée sur une ancienne carrière utilisée par la commune pour reconstruire le village après la Seconde Guerre Mondiale. Le forage a été effectué en plusieurs étapes afin de vérifier l’absence d’ancien obus dans le sol. Au delà de 5 mètres de profondeur le sol constitué d’un mélange d’eau et de calcaire qui s’est mélangé avec l’argile de la couche supérieur, a embourbé le système à air comprimé et a compliqué le chantier. Le forage a été réalisé en octobre 2021 sur 12m de profondeur avec le matériel du Bureau de recherches géologiques et minières (BRGM) et son équipe technique avec l’assistance de l’équipe de l’observatoire sismologique de l’Ecole et Observatoire des Sciences de la Terre (EOST) de Strasbourg. A cause de problèmes techniques dus aux conditions du site, le puits a été finalisé avec une profondeur de 9m. La station sismologique BETHI a intégré le Réseau Large Bande Permanent (RLBP) en août 2021. Le RLBP fait partie de Résif, une infrastructure de recherche nationale dédiée à l’observation et la compréhension de la structure et de la dynamique Terre interne. Résif se base sur des réseaux d’observation de haut niveau technologique, composés d’instruments sismologiques, géodésiques et gravimétriques déployés de manière dense sur tout le territoire français. Les données recueillies permettent d’étudier avec une haute résolution spatio-temporelle la déformation du sol, les structures superficielles et profondes, la sismicité à l’échelle locale et globale et les aléas naturels, et plus particulièrement sismiques, sur le territoire français. Résif s’intègre aux dispositifs européens (EPOS - European Plate Observing System) et mondiaux d’instruments permettant d’imager l’intérieur de la Terre dans sa globalité et d’étudier de nombreux phénomènes naturels

Maintenance de la foreuse lors de la construction de la station sismologique BETHI située à Béthincourt (Meuse)

Realization of the drilling of the seismological station BETHI in the commune of Béthincourt (Meuse) near Verdun. The compressed air drill is installed on a former quarry used by the municipality to rebuild the village after the Second World War. The drilling was carried out in several stages in order to verify the absence of old shells in the ground. Between 2 and 5m deep the soil is composed of clay, which completely blocked the arm of the drill. The site had to stop for more than a day in order to clean the machine and to recover the spare parts and thus to restore the drill. On this picture, you can see the guide tube, the axis of the drilling machine with its tool, and on both sides the two 6m tubes which will be used as casing for the drilling. The drilling was carried out in October 2021 at a depth of 12m with the equipment of the Bureau de recherches géologiques et minières (BRGM) and its technical team with the assistance of the team of the seismological observatory of the Ecole et Observatoire des Sciences de la Terre (EOST) of Strasbourg. Because of technical problems due to the site conditions, the well was finalized with a depth of 9m. The seismological station BETHI has been integrated into the Permanent Broadband Network (RLBP) in August 2021. The RLBP is part of Résif, a national research infrastructure dedicated to the observation and understanding of the Earth's internal structure and dynamics. Résif is based on high technology observation networks, composed of seismological, geodesic and gravimetric instruments deployed in a dense manner on the whole French territory. The data collected allow to study with a high spatio-temporal resolution the ground deformation, the superficial and deep structures, the seismicity at the local and global scale and the natural hazards, and more particularly the seismic ones, on the French territory. Résif is part of the European (EPOS - European Plate Observing System) and global systems of instruments allowing to image the interior of the Earth in its entirety and to study many natural phenomena.Réalisation du forage de la station sismologique BETHI sur la commune de Béthincourt (Meuse) proche de Verdun. La foreuse à air comprimé est installée sur une ancienne carrière utilisée par la commune pour reconstruire le village après la Seconde Guerre Mondiale. Le forage a été effectué en plusieurs étapes afin de vérifier l’absence d’ancien obus dans le sol. Entre 2 et 5m de profondeur le sol est composé d’argile, celui-ci bloqua complètement le bras de la foreuse. Le chantier a dû se mettre à l’arrêt plus d’une journée afin de nettoyer la machine et récupérer les pièce de rechange et ainsi remettre en état la foreuse. Sur cette photo, on voit le tube guide, l’axe de la foreuse avec son outil, et de part et d’autre les deux tubes de 6m qui devront servir de tubage pour le forage. Le forage a été réalisé en octobre 2021 sur 12m de profondeur avec le matériel du Bureau de recherches géologiques et minières (BRGM) et son équipe technique avec l’assistance de l’équipe de l’observatoire sismologique de l’Ecole et Observatoire des Sciences de la Terre (EOST) de Strasbourg. A cause des problèmes techniques dus aux conditions du site, le puits a été finalisé avec une profondeur de 9m. La station sismologique BETHI a intégré le Réseau Large Bande Permanent (RLBP) en août 2021. Le RLBP fait partie de Résif, une infrastructure de recherche nationale dédiée à l’observation et la compréhension de la structure et de la dynamique Terre interne. Résif se base sur des réseaux d’observation de haut niveau technologique, composés d’instruments sismologiques, géodésiques et gravimétriques déployés de manière dense sur tout le territoire français. Les données recueillies permettent d’étudier avec une haute résolution spatio-temporelle la déformation du sol, les structures superficielles et profondes, la sismicité à l’échelle locale et globale et les aléas naturels, et plus particulièrement sismiques, sur le territoire français. Résif s’intègre aux dispositifs européens (EPOS - European Plate Observing System) et mondiaux d’instruments permettant d’imager l’intérieur de la Terre dans sa globalité et d’étudier de nombreux phénomènes naturels

Maintenance de la foreuse lors de la construction de la station sismologique BETHI située à Béthincourt (Meuse)

Realization of the drilling of the BETHI seismological station in the commune of Béthincourt (Meuse) near Verdun. The compressed air drill is installed on a former quarry used by the municipality to rebuild the village after the Second World War. The drilling was carried out in several stages in order to verify the absence of old shells in the ground. Between 2 and 5m deep the soil is composed of clay, which completely blocked the arm of the drill. The site had to be stopped for more than a day in order to clean the machine and to recover the spare parts and thus restore the drill. The drilling was carried out in October 2021 at a depth of 12m with the equipment of the Bureau de recherches géologiques et minières (BRGM) and its technical team with the assistance of the team of the seismological observatory of the Ecole et Observatoire des Sciences de la Terre (EOST) of Strasbourg. Because of technical problems due to the site conditions, the well was finalized with a depth of 9m. The seismological station BETHI has been integrated into the Permanent Broadband Network (RLBP) in August 2021. The RLBP is part of Résif, a national research infrastructure dedicated to the observation and understanding of the Earth's internal structure and dynamics. Résif is based on high technology observation networks, composed of seismological, geodesic and gravimetric instruments deployed in a dense manner on the whole French territory. The data collected allow to study with a high spatio-temporal resolution the ground deformation, the superficial and deep structures, the seismicity at the local and global scale and the natural hazards, and more particularly the seismic ones, on the French territory. Résif is part of the European (EPOS - European Plate Observing System) and global systems of instruments allowing to image the interior of the Earth in its entirety and to study many natural phenomena.Réalisation du forage de la station sismologique BETHI sur la commune de Béthincourt (Meuse) proche de Verdun. La foreuse à air comprimé est installée sur une ancienne carrière utilisée par la commune pour reconstruire le village après la Seconde Guerre Mondiale. Le forage a été effectué en plusieurs étapes afin de vérifier l’absence d’ancien obus dans le sol. Entre 2 et 5m de profondeur le sol est composé d’argile, celui-ci bloqua complètement le bras de la foreuse. Le chantier a dû se mettre à l’arrêt plus d’une journée afin de nettoyer la machine et récupérer les pièce de rechange et ainsi remettre en état la foreuse. Le forage a été réalisé en octobre 2021 sur 12m de profondeur avec le matériel du Bureau de recherches géologiques et minières (BRGM) et son équipe technique avec l’assistance de l’équipe de l’observatoire sismologique de l’Ecole et Observatoire des Sciences de la Terre (EOST) de Strasbourg. A cause de problèmes techniques dus aux conditions du site, le puits a été finalisé avec une profondeur de 9m. La station sismologique BETHI a intégré le Réseau Large Bande Permanent (RLBP) en août 2021. Le RLBP fait partie de Résif, une infrastructure de recherche nationale dédiée à l’observation et la compréhension de la structure et de la dynamique Terre interne. Résif se base sur des réseaux d’observation de haut niveau technologique, composés d’instruments sismologiques, géodésiques et gravimétriques déployés de manière dense sur tout le territoire français. Les données recueillies permettent d’étudier avec une haute résolution spatio-temporelle la déformation du sol, les structures superficielles et profondes, la sismicité à l’échelle locale et globale et les aléas naturels, et plus particulièrement sismiques, sur le territoire français. Résif s’intègre aux dispositifs européens (EPOS - European Plate Observing System) et mondiaux d’instruments permettant d’imager l’intérieur de la Terre dans sa globalité et d’étudier de nombreux phénomènes naturels

Afar Margin Northern Profile

Profile of 7 x ESPD and 3 x 40TD sensors across the western margin of Afar from near Mekele to Berhale. Aim of the research is to image the lithospheric structure across the rift margin.</span