Ground deformation monitoring of the eruption offshore Mayotte

In May 2018, the Mayotte island, located in the Indian Ocean, was affected by an unprecedented seismic crisis, followed by anomalous on-land surface displacements in July 2018. Cumulatively from July 1, 2018 to December 31, 2021, the horizontal displacements were approximately 21 to 25 cm eastward, and subsidence was approximately 10 to 19 cm. The study of data recorded by the on-land GNSS network, and their modeling coupled with data from ocean bottom pressure gauges, allowed us to propose a magmatic origin of the seismic crisis with the deflation of a deep source east of Mayotte, that was confirmed in May 2019 by the discovery of a submarine eruption, 50 km offshore of Mayotte ([Feuillet et al., 2021]). Despite a non-optimal network geometry and receivers located far from the source, the GNSS data allowed following the deep dynamics of magma transfer, via the volume flow monitoring, throughout the eruption

Shear-wave velocity structure beneath the Dinarides from the inversion of Rayleigh-wave dispersion

Highlights • Rayleigh-wave phase velocity in the wider Dinarides region using the two-station method. • Uppermost mantle shear-wave velocity model of the Dinarides-Adriatic Sea region. • Velocity model reveals a robust high-velocity anomaly present under the whole Dinarides. • High-velocity anomaly reaches depth of 160 km in the northern Dinarides to more than 200 km under southern Dinarides. • New structural model incorporating delamination as one of the processes controlling the continental collision in the Dinarides. The interaction between the Adriatic microplate (Adria) and Eurasia is the main driving factor in the central Mediterranean tectonics. Their interplay has shaped the geodynamics of the whole region and formed several mountain belts including Alps, Dinarides and Apennines. Among these, Dinarides are the least investigated and little is known about the underlying geodynamic processes. There are numerous open questions about the current state of interaction between Adria and Eurasia under the Dinaric domain. One of the most interesting is the nature of lithospheric underthrusting of Adriatic plate, e.g. length of the slab or varying slab disposition along the orogen. Previous investigations have found a low-velocity zone in the uppermost mantle under the northern-central Dinarides which was interpreted as a slab gap. Conversely, several newer studies have indicated the presence of the continuous slab under the Dinarides with no trace of the low velocity zone. Thus, to investigate the Dinaric mantle structure further, we use regional-to-teleseismic surface-wave records from 98 seismic stations in the wider Dinarides region to create a 3D shear-wave velocity model. More precisely, a two-station method is used to extract Rayleigh-wave phase velocity while tomography and 1D inversion of the phase velocity are employed to map the depth dependent shear-wave velocity. Resulting velocity model reveals a robust high-velocity anomaly present under the whole Dinarides, reaching the depths of 160 km in the north to more than 200 km under southern Dinarides. These results do not agree with most of the previous investigations and show continuous underthrusting of the Adriatic lithosphere under Europe along the whole Dinaric region. The geometry of the down-going slab varies from the deeper slab in the north and south to the shallower underthrusting in the center. On-top of both north and south slabs there is a low-velocity wedge indicating lithospheric delamination which could explain the 200 km deep high-velocity body existing under the southern Dinarides

Crustal Thinning From Orogen to Back-Arc Basin: The Structure of the Pannonian Basin Region Revealed by P-to-S Converted Seismic Waves

We present the results of P-to-S receiver function analysis to improve the 3D image of the sedimentary layer, the upper crust, and lower crust in the Pannonian Basin area. The Pannonian Basin hosts deep sedimentary depocentres superimposed on a complex basement structure and it is surrounded by mountain belts. We processed waveforms from 221 three-component broadband seismological stations. As a result of the dense station coverage, we were able to achieve so far unprecedented spatial resolution in determining the velocity structure of the crust. We applied a three-fold quality control process; the first two being applied to the observed waveforms and the third to the calculated radial receiver functions. This work is the first comprehensive receiver function study of the entire region. To prepare the inversions, we performed station-wise H-Vp/Vs grid search, as well as Common Conversion Point migration. Our main focus was then the S-wave velocity structure of the area, which we determined by the Neighborhood Algorithm inversion method at each station, where data were sub-divided into back-azimuthal bundles based on similar Ps delay times. The 1D, nonlinear inversions provided the depth of the discontinuities, shear-wave velocities and Vp/Vs ratios of each layer per bundle, and we calculated uncertainty values for each of these parameters. We then developed a 3D interpolation method based on natural neighbor interpolation to obtain the 3D crustal structure from the local inversion results. We present the sedimentary thickness map, the first Conrad depth map and an improved, detailed Moho map, as well as the first upper and lower crustal thickness maps obtained from receiver function analysis. The velocity jump across the Conrad discontinuity is estimated at less than 0.2 km/s over most of the investigated area. We also compare the new Moho map from our approach to simple grid search results and prior knowledge from other techniques. Our Moho depth map presents local variations in the investigated area: the crust-mantle boundary is at 20–26 km beneath the sedimentary basins, while it is situated deeper below the Apuseni Mountains, Transdanubian and North Hungarian Ranges (28–33 km), and it is the deepest beneath the Eastern Alps and the Southern Carpathians (40–45 km). These values reflect well the Neogene evolution of the region, such as crustal thinning of the Pannonian Basin and orogenic thickening in the neighboring mountain belts

Station sismologique CHMF de Charmoille (Doubs)

The seismological station CHMF of Charmoille (Doubs) is installed in a gallery that housed a water pipe supplying a village below. As in abandoned mines, this type of location is ideal because the sensor is placed on a flat concrete surface cast on the rock and temperature and pressure variations are low. Here, to ensure perfect insulation, the gallery was closed with a double-glazed window surrounded by concrete. In the foreground on the left is the electrical cabinet housing the rest of the station's instruments. This photo was taken during a monitoring visit to the station by the team from the Seismological Observatory of North-East France (Eost-Obsnef). The station is integrated into the national Résif research infrastructure, dedicated to the observation and understanding of the structure and dynamics of the Inner Earth. Résif is based on high-tech observation networks, composed of seismological, geodetic and gravimetric instruments deployed in a dense manner throughout France. These data make it possible to study with high spatial and temporal resolution the deformation of the ground, surface and deep structures, seismicity on a local and global scale and natural hazards, and more particularly seismic hazards, on French territory. Résif is integrated into European (EPOS - European Plate Observing System) and global systems of instruments for imaging the Earth's interior as a whole and studying many natural phenomena.La station sismologique CHMF de Charmoille (Doubs) est installée dans une galerie qui abritait une conduite d'eau alimentant un village en contrebas. Comme dans les mines désaffectées, ce type d'emplacement est idéal car le capteur y est posé sur une surface plane en béton coulée à même le rocher et les variations de température et de pression y sont faibles. Ici, pour assurer une isolation parfaite, la galerie a été fermée par une fenêtre à double vitrage entourée de béton. On voit, au premier plan à gauche, l'armoire électrique abritant le reste des instruments de la station. Cette photo a été prise lors d'une visite de contrôle de la station par l'équipe de l'Observatoire sismologique du Nord-Est de la France (Eost-Obsnef). La station est intégrée à l'infrastructure nationale de recherche Résif, 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. Ces données 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

La station sismologique MANO de Manonville (Meurthe-et-Moselle), installée en forage

Seismological stations may have to be buried to areas where conditions are stable so that the recorded data are not affected by external disturbances. This is why the drilling technique is used. In this photo, we see the seismological station MANO of Manonville (Meurthe-et-Moselle). It was drilled in a former abandoned quarry. In the foreground is the cabinet housing the scientific equipment, except for the sensor which is at the bottom of the 6-metre deep shaft (in the background). The solar panels are used to supply power to the assembly while waiting for an electrical connection. We also distinguish (yellow box) the temporary station installed beforehand for the test and which is dismantled during the final installation. This station, installed by the team of the Seismological Observatory of North-East France (Eost-Obsnef), is part of the national Résif research infrastructure, dedicated to the observation and understanding of the structure and dynamics of the Inner Earth. Résif is based on high-tech observation networks, composed of seismological, geodetic and gravimetric instruments deployed in a dense manner throughout France. These data make it possible to study with high spatial and temporal resolution the deformation of the ground, surface and deep structures, seismicity on a local and global scale and natural hazards, and more particularly seismic hazards, on French territory. Résif is integrated into European (EPOS - European Plate Observing System) and global systems of instruments for imaging the Earth's interior as a whole and studying many natural phenomena.Les stations sismologiques doivent parfois être enterrées jusqu'à des zones où les conditions sont stables afin que les données enregistrées ne soient pas affectées par des perturbations extérieures. C'est pourquoi on a recours à la technique du forage. Sur cette photo, on voit la station sismologique MANO de Manonville (Meurthe-et-Moselle). Elle a été installée en forage dans une ancienne carrière désaffectée. On voit au premier plan l'armoire abritant les équipements scientifiques, à l'exception du capteur qui est au fond du puits de 6 mètres de profondeur (au second plan). Les panneaux solaires servent à l'alimentation électrique de l'ensemble dans l'attente d'un raccordement électrique. On distingue également (boitier jaune) la station temporaire installée préalablement pour le test et qui est démontée lors de l'installation définitive. Cette station, installée par l'équipe de l'Observatoire sismologique du Nord-Est de la France (Eost-Obsnef), est intégrée à l'infrastructure nationale de recherche Résif, 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. Ces données 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

Entrée de la station sismologique WLS à Welschbruch (Bas-Rhin)

The seismological station WLS is located in the municipality of Welschbruch (Bas-Rhin). This picture shows the entrance to the seismological cellar in the forest. The site is equipped with a Trillium-40 velocimetric sensor, which is integrated in the Permanent Broadband Network (RLBP) of the national research infrastructure Résif, dedicated to the observation and understanding of the structure and dynamics of the Inner Earth. Résif is based on high-tech observation networks, composed of seismological, geodetic and gravimetric instruments deployed in a dense manner throughout France. The data collected make it possible to study with high spatial and temporal resolution the deformation of the ground, surface and deep structures, seismicity on a local and global scale and natural hazards, and more particularly seismic events, on French territory. Résif is part of the European (EPOS - European Plate Observing System) and global systems of instruments used to image the Earth's interior as a whole and to study many natural phenomena.La station sismologique WLS se situe sur la commune de Welschbruch (Bas-Rhin). Sur cette photo, on voit l’entrée de la cave sismologique qui se trouve en forêt. Le site possède un capteur vélocimétrique Trillium-40, qui s’intègre au Réseau large bande permanent (RLBP) de l’infrastructure de recherche nationale Résif, l’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

Installation d’une station temporaire sur un site du réseau de mesure GNSS à Djibouti

Pictured here is the Ashtech Geodetic IV GNSS antenna and GPSMob tripod used during a measurement campaign in Djibouti in 2010. These instruments belong to the National Mobile GNSS Park (GPSMob), which is part of Résif, a national research infrastructure dedicated to the observation and understanding of the structure and dynamics of the internal Earth. Résif is based on high-tech observation networks, composed of seismological, geodesic and gravimetric instruments deployed densely over 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.On peut voir sur la photo l'antenne GNSS Ashtech Geodetic IV et le trépied GPSMob utilisés pendant une campagne de mesure à Djibouti en 2010. Ces instruments appartiennent au Parc national GNSS mobile (GPSMob), qui 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