High-resolution imaging of the Pyrenees and Massif Central from the data of the PYROPE and IBERARRAY portable array deployments

International audienceThe lithospheric structures beneath the Pyrenees, which holds the key to settle long-standing controversies regarding the opening of the Bay of Biscay and the formation of the Pyrenees, are still poorly known. The temporary PYROPE and IBERARRAY experiments have recently filled a strong deficit of seismological stations in this part of western Europe, offering a new and unique opportunity to image crustal and mantle structures with unprecedented resolution. Here we report the results of the first tomographic study of the Pyrenees relying on this rich data set. The important aspects of our tomographic study are the precision of both absolute and relative traveltime measurements obtained by a nonlinear simulated annealing waveform fit and the detailed crustal model that has been constructed to compute accurate crustal corrections. Beneath the Massif Central, the most prominent feature is a widespread slow anomaly that reflects a strong thermal anomaly resulting from the thinning of the lithosphere and upwelling of the asthenosphere. Our tomographic images clearly exclude scenarios involving subduction of oceanic lithosphere beneath the Pyrenees. In contrast, they reveal the segmentation of lithospheric structures, mainly by two major lithospheric faults, the Toulouse fault in the central Pyrenees and the Pamplona fault in the western Pyrenees. These inherited Hercynian faults were reactivated during the Cretaceous rifting of the Aquitaine and Iberian margins and during the Cenozoic Alpine convergence. Therefore, the Pyrenees can be seen as resulting from the tectonic inversion of a segmented continental rift that was buried by subduction beneath the European plate

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

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

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

Intégration des données de sismomètres fond de mer dans Résif

International audienceFew seismic seabed experiments are currently available at EIDA data centres, partly because of the difficulty in preparing their data and metadata for data centres, including: 1) Non-standard data loggers that are not referenced in the Nominal Response Library (NRL) and have non-standard data formats; 2) The inability to synchronize the sensor clock with GPS while on the seabed; 3) The lack of standards for OBS-specific parameters. We present a three-part harmonized approach to simplify data and metadata preparation and standardize results according to FAIR (Findable, Accessible, Interoperable, Reusable) principles. This poster was presented at the Résif Scientific and Technical Meetings held in Biarritz in November 2019. Résif is 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, geodetic and gravimetric instruments deployed in a dense manner throughout the French territory. The data collected allow the study of ground deformation, surface and deep structures, local and global seismicity and natural hazards, particularly seismic, on the French territory with a high spatio-temporal resolution. Résif is integrated into the European (EPOS - European Plate Observing System) and worldwide instruments that allow to image the Earth's interior in its entirety and to study many natural phenomena.Peu d'expériences de sismomètres fond de mer sont actuellement disponibles dans les centres de données EIDA, en partie à cause de la difficulté à préparer leurs données et métadonnées pour les centres de données, notamment : 1) Les enregistreurs de données non standard qui ne sont pas référencés dans la bibliothèque de réponses nominales (NRL) et qui ont des formats de données non standard ; 2) L'incapacité de synchroniser l'horloge du capteur avec le GPS lorsqu'il est en fond marin ; 3) L'absence de normes pour les paramètres spécifiques aux OBS. Nous présentons une approche harmonisée en trois parties pour simplifier la préparation des données et des métadonnées et normaliser les résultats selon les principes FAIR (Findable, Accessible, Interoperable, Reutilisable). Ce poster a été présenté aux Rencontres scientifiques et techniques Résif qui se sont déroulées à Biarritz en novembre 2019. Résif est 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

Ambient noise tomography of the Pyrenees and the surrounding regions: Inversion for a 3-D Vs model in the presence of a very heterogeneous crust

The lithospheric architecture of the Pyrenees is still uncertain and highly debated. Here, we provide new constraints from a high-resolution 3-D S-wave velocity model of the Pyrenees and the adjacent foreland basins. This model is obtained from ambient noise tomography on records of temporary and permanent seismic arrays installed in southwestern France and northern Spain. We first computed group velocity maps for Rayleigh waves in the 5 to 55 s period range using noise correlation stacks at 1500-8500 station pairs. As the crust is very heterogeneous, poor results were obtained using a single starting model in a linearized inversion of group velocity dispersion curves for the shear wave structure. We therefore built a starting model for each grid node by full exploration of the model space. The resulting 3-D shear wave velocity model is compared to data from previous geophysical studies as a validation test. Despite the poor sensitivity of surface waves to seismic discontinuities, the geometry of the top of the basement and the Moho depth are retrieved well, except along the Cantabrian coast. Major reflectors of the ECORS deep seismic sounding profiles in the central and western Pyrenees coincide with sharp velocity gradients in our velocity model.We retrieve the difference between the thicker Iberian crust and the thinner European crust, the presence of low-velocity material of the Iberian crust underthrust beneath the European crust in the central Pyrenees, and the structural dissymmetry between the South Pyrenean Zone and the North Pyrenean Zone at the shallow crustal level. In the Labourd-Mauléon-Arzacq region (western Pyrenees), there is a high S-wave velocity anomaly at 20-30 km in depth, which might explain the positive Bouguer anomaly of the Labourd Massif. This high-velocity lower crust, which is also detected beneath the Parentis area, might be an imprint of the Albian-Aptian rifting phase. The southeastern part of the Massif Central has an unusual velocity structure, with a very shallowMoho (21-25 km) above an uppermost mantle with anomalously low shear wave velocity.We thank all participants in the fieldwork, and the municipalities and landlords that hosted a PYROPE temporary station. We also acknowledge SISMOB, the French seismic mobile pool (a com- ponent of the RESIF Research Facility), for providing us with the seismological instrumentation for the temporary deployments. We used data from the FR and RD (RESIF), G (Geoscope) and CA (‘Institut Cartogr ` afic i Geol ` ogic de Catalunya’) permanent net- works. RESIF ( http://portal.resif.fr/ ) is a national Research Infras- tructure, recognized as such by the French Ministry of Higher Education and Research. RESIF is managed by the RESIF Con- sortium, composed of 18 Research Institutions and Universities in France. RESIF additionally supported by a public grant overseen by the French National Research Agency (ANR) as part of the «Investissements d’Avenir» program (reference: ANR-11-EQPX- 0040)andtheFrenchMinistryofEcology,SustainableDevelopment and Energy. The PYROPE experiment was supported by the French Research Agency “ANR blanc” program (project PYROPE, ANR-09-BLAN-0229). This is a contribution of the Team Consolider-Ingenio 2010 TOPO-IBERIA (CSD2006–00041). CPeer reviewe

Résif-SI Grenoble : Résif-DC, Rap, Sismob

The Résif seismological data center (CD-Résif, also called 'knot B', DOI:10.17616/R37Q06) is hosted by the University of Grenoble Alpes and co-operated by the UMS GRICAD and the Osug data center. Résif data services are developed, deployed and maintained by the Résif team at ISTerre. The Résif data centre ensures the security and distribution of validated data and metadata. This poster highlights the new services offered by the Résif data centre to the community and shows the statistics of the data centre. It also shows how the data centre can respond to new current challenges (intensive computing, dense network data, ...). This poster was presented during the Résif Scientific and Technical Meetings that took place in Biarritz in November 2019. Résif is 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, geodetic and gravimetric instruments deployed in a dense manner throughout the French territory. The data collected allow the study of ground deformation, surface and deep structures, local and global seismicity and natural hazards, particularly seismic, on the French territory with a high spatio-temporal resolution. Résif is integrated into the European (EPOS - European Plate Observing System) and worldwide instruments that allow to image the Earth's interior in its entirety and to study numerous natural phenomena.Le centre de données sismologiques Résif (CD-Résif, dit aussi 'noeud B', DOI:10.17616/R37Q06) est hébergé par l'Université Grenoble Alpes et co-exploité par l'UMS GRICAD et le centre de données de l'Osug. Les services de données Résif sont développés, déployés et maintenus par l'équipe Résif d'ISTerre. Le centre de donnée Résif assure la mise en sécurité et la distribution des données validées et des métadonnées. Ce poster met en évidence les nouveaux services proposés par le centre de données Résif à la communauté et montre les statistiques du centre de données. Il montre aussi comment le centre de donnée peut répondre aux nouveaux enjeux actuels (calcul intensif, données des réseaux denses, …). Ce poster a été présenté lors des Rencontres scientifiques et techniques Résif qui se sont déroulées à Biarritz en novembre 2019. Résif est 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

SeedPSD : Un nouvel outil pour le contrôle de la qualité des données sismologiques

International audienceLe Centre de données sismologiques annonce la naissance de SeedPSD, un nouveau service ouvert à la communauté sismologique. Cet outil a été développé afin de répondre aux attentes des utilisateurs scientifiques. Il est capable de générer à la demande des PDFs ("Probability Density Functions") et des spectrogrammes. Cela permet de visualiser le niveau de bruit d'une série temporelle produite par un capteur d'une station sismologique et ainsi d'estimer la qualité de chaque site instrumental

La distribution des données sismologiques par Résif

National audienceLa Système d'Information Résif-SI est une action transverse de l'Infrastructure de Recherche Résif, dont l'objectif est de distribuer de manière libre et gratuite, dans les meilleurs délais possibles et sur le long terme, les données acquises par Résif et les métadonnées associées. Résif-SI couvre la distribution des données sismologiques et géodésiques (GNSS et gravimétriques). La refonte du système de distribution des données sismologiques est une priorité pour Résif depuis son démarrage ; le présent texte se focalise ainsi sur les données sismologiques. Pour simplifier la lecture, Résif-SI désigne dans cet article seulement la partie sismologique du Système d'Information de Résif