Tout public OCA
Le télescope Schaumasse de l'Observatoire de Nice
mardi 22 mai 2018, NEF - Mont Gros - CION - talk in French - retransmis à Valrose (Salle O. Chesneau)
Matthieu CONJAT - Association Aquila
La coupole Schaumasse abrite l'un des instruments les plus récents du site du Mont-Gros de l'OCA. Il s'agit d'un télescope de 40 cm de diamètre, de type 'Cassegrain', qui est utilisé
depuis 2007 dans le cadre de nombreuses campagnes scientifiques. Je vous parlerai de mesures de diamètres stellaires, d'occultation d'étoiles par des petits corps du système solaire, de découvertes d'astéroïdes doubles et d'étoiles variables, et (un peu) d'imagerie astronomique.
Multidisciplinary studies of earthquakes and tectonics (TBD)
jeudi 24 mai 2018, 11h00, Géoazur, Sophia-Antipolis, salle de conférence Bât.1
Timothy CRAIG (University of Leeds)
Sea Level Change and the Solid Earth: local, regional and global perspectives
jeudi 31 mai 2018, 11h00, Sophia, salle de Conférence du Bâtiment 4
Seismicity, Deformation and Metamorphism in the Western Hellenic Subduction Zone - New Constraints from Tomography
jeudi 7 juin 2018, 11h00, Géoazur, Sophia-Antipolis, salle de conférence Bât.1
Felix HALPAAP (Earth Science, University of Bergen)
jeudi 14 juin 2018, 11h00, Géoazur, Sophia-Antipolis, salle de conférence Bât.4
Mikesell Dylan (Boise State University - USA)
Probing plate boundaries rheology during the seismic cycle using GPS data
en savoir plus...
jeudi 21 juin 2018, 11h00, Géoazur, Sophia-Antipolis, salle de conférence Bât.1
Emilie Klein (UCSD)
2-D and 3-D geophysical imaging of crustal structure at the East Pacific Rise 9°50’N: implications for crustal accretion and hydrothermal circulation
jeudi 28 juin 2018, 11h00, Géoazur, Sophia-Antipolis, salle de conférence Bât.1
Along fast and intermediate spreading centers axial magma lenses (AMLs) are detected beneath much of the ridge axis, and the notion that the AML is the primary melt reservoir for dike
intrusions and magma emplacement on the seafloor (that together build the upper crust) is commonly accepted. However, the physical properties of the AMLs and their role in construction of the lower crust are still elusive. In 2008, a 3D multichannel seismic (MCS) survey was conducted at the East Pacific Rise (EPR), to study physical properties of magmatic system and its relationship with other processes that operate at this MOR system. Here, I will first present results of the analysis focused on examining physical properties of the AML from seismic data: - Magmatic segmentation - Inspection of the AML reflector in seismic data show that this event is disrupted at different length scales. The most of thus mapped fine-scale interruptions in AML are collocated with previously identified higher (third and fourth) order discontinuities in bathymetry, corroborating genetic relationship between magmatic and tectonic segmentation, and supporting the notion of crustal accretion through small magmatic units. - Distribution of melt - Using novel technique developed by oil and gas industry we were able to map variation of melt content within the AML restricted to the innermost zone of the ridge axis. We show that the melt content within the AML varies significantly at spatial scales of several hundreds of meters. - Presence of multiple sills within the lower crust - We identify a series of reflections below the axial magma lens that we interpret as magma lenses in the upper part of the lower crust. From the geometry and amplitude of the reflections in a zone beneath a recent volcanic eruption, we infer that magma drained from a lower lens helped replenish the AML above and, perhaps, contributed to the eruption. Our data indicate that a multi-level complex of magma lenses is present beneath the East Pacific Rise and probably contributes to the formation of both the upper and lower crust. I will then show the results of my recent work focused on the upper crust using elastic 2D and 3D full-waveform inversion techniques : - Signatures of the along-axis hydrothermal circulation - The velocity model reveal a number of low-velocity anomalies, complex in shape, extending down to ~1 km below the seafloor. We attribute them to the presence of hydrothermal flow. Depending on their spatial correlation with the previously identified tectonic discontinuities in bathymetry and presence of venting, we classify them as down-going and up-going pathways, respectively. - Three-dimensional mapping of the upper-crust (ongoing work) - For the first time upper crustal properties are mapped at high-resolution spatial scales in three-dimensions. The layer 2A/ 2B boundary is clearly identified in the resulting model as the base of high velocity gradient and can be followed throughout the entire area included in the inversion; consistency in character of the gradient zone and distinct velocity anomaly near active hydrothermal discharge zones, where the most of the alteration is expected to take place, argue that this boundary is predominantly lithological. Our models corroborate rapid thickening of the basaltic at about 2 km away from the ridge axis, which is in places more abrupt on the Pacific Plate side. In addition, we map the extent of the diking zone, which in width corresponds to the width of the AML. The above strongly argues that the dikes at the EPR are intruded vertically and suggests that the rate of dike subsidence (and thus variation in thickness of extrusives) is highly controlled by the physical properties of the AML.