Quest for a mantle plume under Réunion Island, western Indian Ocean: results of the RHUM-RUM experiment
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jeudi 18 janvier 2018, 11h00, Sophia, salle de conférence du bât. 1
Karin Sigloch, Univ. of Oxford
The French-German RHUM-RUM experiment (Réunion Hotspot and Upper Mantle–Réunions Unterer Mantel) aims to clarify the presence or absence of a mantle plume under La Réunion, an intra-plate volcanic hotspot that emerged
65 Ma ago with the eruption of the Deccan flood basalts on India, has since burned a 5,500-km long hotspot track into the Indian Ocean seafloor, and remains among the most active volcanoes on earth. For 13 months in 2012-2013, RHUM-RUM deployed 57 broadband ocean bottom stations at 2500 to 5400 m depth and over an area of 2000 × 2000 km2, centered on La Réunion Island. The stations were equipped with broadband, three-component seismometers (corner frequencies of 60, 120, or 240 s and sampling rates of 50–100 Hz), and with broadband hydrophones (corner period 100 s, cutoff frequency 8 Hz, and sampling rates of 50–100 Hz). The network was complemented by 30 RHUM-RUM land stations that operated for 2-3 years on Reunion, Mauritius, Madagascar, the Seychelles, and the Iles Eparses. I will review the project results, in terms of mantle structure imaged from the surface to the core, but also in terms of serendipitous scientific byproducts, which mostly fall in the category of marine environmental seismology, such as tracking of tropical storms using OBS, first detection of the seismic hum on OBS, successful long-range cross-correlation of microseismic noise on OBS, and the detection and identification of hydroacoustic phases, whales, and passing ships.
Apéro Congrès 2018
jeudi 25 janvier 2018, de 09h00 à 14h00, Géoazur - Salle de conférences du bâtiment 1
sur les participations à des congrès au cours de l'année 2017.
Shallow megathrust earthquake ruptures betrayed by their outer-trench aftershocks signature Shallow megathrust earthquake ruptures betrayed by their outer-trench aftershocks signature Shallow megathrust earthquake ruptures betrayed by their outer-trench a
jeudi 1er février 2018, 11h00, Salle de Conférence du Bâtiment 4
Anthony Sladen, Géoazur
For some megathrust earthquakes, the rupture extends to the solid Earth's surface, at the ocean floor. This unexpected behaviour holds strong implications for the tsunami potential of subduction zones and for
the physical conditions governing earthquakes, but such ruptures occur in underwater areas which are hard to observe, even with current instrumentation and imaging techniques. Here, we evidence that aftershocks occurring ocean-ward from the trench are conditioned by near-surface rupture of the megathrust fault. Comparison to well constrained earthquake slip models further reveals that for each event the number of aftershocks is proportional to the amount of shallow slip, a link likely related to static stress transfer. Hence, the spatial distribution of these specific aftershock sequences could provide independent constrains on the coseismic shallow slip of future events. It also offers the prospect to be able to reassess the rupture of many large subduction earthquakes back to the beginning of the instrumental era.
Tout public Géoazur
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jeudi 8 février 2018, 11h00, Géoazur, Sophia-Antipolis, salle de conférence Bât.4
L'observatoire éducatif vise à faciliter l’utilisation des données issues de capteurs pour l’enseignement dans le secondaire et le supérieur. Ce projet (2017-2021) est mis en place dans le cadre de l’IDEX
JEDI de Université Côte d’Azur. Il est piloté par la cellule Education de l’UMR Géoazur. Il prévoit la mise en oeuvre d'une interface basée sur les données de recherche en géosciences concernant le bassin méditerranéen et orienté vers l’éducation au risque naturel pour le grand public et notamment les lycéens et les étudiants.
L'équipe Education de Géoazur vous attend pour vous présenter l'état d'avancement du projet, les différentes opérations en cours.
Mechanical instabilities : From faults to slope instabilities
jeudi 15 février 2018, 11h00, Salle de conférence du Bâtiment 4 Sophia
Virginie Durand, IPGP
The lithosphere is a system that deforms at different scales. In this presentation, I will be considering two of them: a large one, with faults, and a small one with slope
instabilities, and more particularly rockfalls. One of the signatures of the deformation of these two different systems is the seismicity they produce. We therefore use it as a deformation indicator. Earthquake interactions and nucleation are a subject under discussion. Indeed, two different mechanisms are proposed to explain them: cascade triggering, or existence of a transient deformation. First, analysing the seismicity and comparing it with displacement measurements, we look at large scale earthquake interactions in Turkey and Greece, two seismically active regions. Second, we study earthquake nucleation, in a systematic way. Our observations in these two cases give signs in support of the existence of a transient deformation triggering seismic activity. Though, on one hand, large earthquakes (M>6) can trigger a slow deformation episode which, propagating, can generate seismic activity at large distances (over 100km), after a few months or years of delay. On another hand, large interplate earthquakes are preceded by an acceleration of slow slip on the plate interface, leading to the main shock. I am also interested in smaller mechanical instabilities, studying rockfalls happening in the crater of Piton de la Fournaise Volcano, in La Réunion island. Indeed, the rockfalls, being much smaller than the faults, can be more easily instrumented. Furthermore, we can also directly observe them, thanks to cameras. The aim of the study is to investigate the link between the different external forcing mechanisms, and more particularly with the eruptions. The forcings in the case of the Piton de la Fournaise volcano are the volcanic seismicity, the cone deformation, and the rainfalls. The complexity of the interactions of the rockfalls with all these different forcing makes it difficult to decipher the influence of each of them. Volcanic seismicity and cone deformation seem to trigger rockfalls with bigger volumes (over 1000m3), and rain appears to make the slope material more sensitive, but doesn't look sufficient to trigger big rockfalls. Therefore, the destabilization of the slopes of the crater in response to the eruptions appears to generate rockfalls with bigger volumes. Furthermore, these bigger volumes are generally located on the side of the crater closer to the next eruption.
Electromagnetism from space and mantle conductivity, temperature and composition
jeudi 22 février 2018, 11h00, Sophia, salle de conférence du bât
Erwan Thébault, univ. Nantes
Tout public Géoazur
Mon TPE en 300 secondes
jeudi 19 avril 2018, 11h00, Géoazur, Sophia-Antipolis, salle de conférence Bât.4
Jean-Luc Berenguer et les lycéens du CIV
Des lycéens viennent présenter leur Travaux Personnels Encadrés (TPE) de l'année réalisés autour des géosciences aux chercheurs.
300 secondes, le temps pour chaque groupe de lycéens d'évoquer leur TPE, premier