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

Étude numérique des formes du troisième étage d'Angkor Vat : recherche de l'unité de mesure

Saur Sébastien. Étude numérique des formes du troisième étage d'Angkor Vat : recherche de l'unité de mesure. In: Bulletin de l'Ecole française d'Extrême-Orient. Tome 82, 1995. pp. 301-305

Evolution of the Io footprint brightness I: Far-UV observations

The Io footprint (IFP) is a set of auroral spots and an extended tail resulting from the strong interaction between Io and the Jovian magnetosphere. For the first time, we present measurements of the brightness and precipitated power for each individual spot, using the image database gathered from 1997 to 2009 with the Hubble Space Telescope in the Far-UV domain. We show that the relative brightness of the spots varies with the System III longitude of Io. Moreover, our novel measurement method based on 3D simulations of the auroral features allows to derive the precipitated energy fluxes from images on which the emission region is observed at a slant angle. Peak values as high as 2 W/m² are observed for the main spot, probably triggering a localized and sudden heating of the atmosphere. Additionally, strong brightness differences are observed from one hemisphere to another. This result indicates that the location of Io in the plasma torus is not the only parameter to control the brightness, but that the magnetic field asymmetries also play a key role. Finally, we present new data confirming that significant variations of the spots' brightness on timescales of 2-4 minutes are ubiquitous, which suggests a relationship with intermittent double layers close to Jovian surface

La recherche à l'IGN : activité 2002

Bulletin d'information de l'IGN N°74Ce numéro dresse le bilan de l'activité de recherche en 2002 à l'Institut Géographique National. Outre le bilan des quatre laboratoires de l'IGN, il présente des résultats concernant la restitution automatique des bâtiments en trois dimensions, l'ortho-photographie à grande échelle, le levé laser aéroporté, la prise de vue aérienne numérique en infrarouge, la correction des mesures issues du GPS, l'unification d'informations géographiques, l'ordonnancement puis l'évaluation des outils de généralisation automatique, les logiciels pour l'Internet consacrés à l'information géographique, la mesure du champ de pesanteur terrestre et de la rotation de la Terre ainsi qu'une analyse de risque appliquée au réseau de métro parisie

Does Long-Term GPS in the Western Alps Finally Confirm Earthquake Mechanisms?

International audienceThe availability of GPS survey data spanning 22 years, along with several independent velocity solutions including up to 16 years of permanent GPS data, presents a unique opportunity to search for persistent (and thus reliable) deformation patterns in the Western Alps, which in turn allow a reinterpretation of the active tectonics of this region. While GPS velocities are still too uncertain to be interpreted on an individual basis, the analysis of range-perpendicular GPS velocity profiles clearly highlights zones of extension in the center of the belt (15.3 to 3.1 nanostrain/year from north to south), with shortening in the forelands. The contrasting geodetic deformation pattern is coherent with earthquake focal mechanisms and related strain/stress patterns over the entire Western Alps. The GPS results finally provide a reliable and robust quantification of the regional strain rates. The observed vertical motions of 2.0 to 0.5 mm/year of uplift from north to south in the core of the Western Alps is interpreted to result from buoyancy forces related to postglacial rebound, erosional unloading, and/or viscosity anomalies in the crustal and lithospheric root. Spatial decorrelation between vertical and horizontal (seismicity related) deformation calls for a combination of processes to explain the complex present-day dynamics of the Western Alps