Sémardi de Jean Lecoulant et Matthieu Olivier

Matthieu Olivier : présentation nouveau doctorant : Modélisation stratigraphique de l’impact des courants tidaux et marins.  Application à la Rade de Brest.

L’objectif principal de ce projet est de mettre en place un modèle stratigraphique capable de retranscrire la sédimentation Holocène de la Rade de Brest. Or la zone d’étude étant un système estuarien bien protégé, des phénomènes hydrodynamiques comme la marée ont une influence qui est supposée importante sur la sédimentation. De plus ces processus de fine échelle temporel sont rarement représentés dans les modèles stratigraphiques.

Pour cela la première partie du travail consiste à définir et quantifier les processus influant sur les dépôts de la rade, via un modèle hydro-sédimentaire (Mars_3D MUSTANG). La validité des observations pourra être vérifiée avec l’aide d’un modèle géologique qui sera construit en parallèle, sur la base de travaux antérieurs.

C’est seulement une fois la dynamique de dépôt identifiée que les observations pourront être adaptées à un modèle stratigraphique. Cependant le changement d’échelle de temps entre les deux types de modélisation représente une des clefs de ce sujet de thèse et est indispensable pour modéliser les dépôts liés aux derniers 10 000ans.

Voir la vidéo

Jean Lecoulant : Génération et propagation modale d’ondes T simulées

Les ondes T sont des ondes émises par les séismes sous-marins. Elles font l’objet d’un intérêt croissant, car leur observation à l’aide d’hydrophones doit permettre de mieux comprendre la dynamique des dorsales médio-océaniques. Dans cette perspective, la connaissance des ondes T peut être améliorée grâce à des simulations numériques, en utilisant un code 3D aux éléments finis spectraux (SPECFEM3D). Nos simulations montrent que les ondes T suivent une propagation modale et elles mettent en évidence les facteurs qui influencent la génération de ces ondes.

voir la vidéo

4 December 2018

EAGER campaign

In search of extreme past events in marine sediments around Taiwan

The EAGER oceanographic cruise aboard the N / O Marion Dufresne from June 5 to 27, 2018, has sampled the sedimentary records of the seabed off the island of Taiwan. Its purpose was to trace the extreme earth events (earthquakes, typhoons, and volcanic eruptions) that occurred during the Quaternary period (over the last hundred thousand years), in order to constrain their cyclicities and variabilities, and thus better to deal with the associated hazards.

It was initiated as part of a Franco-Taiwanese partnership supported by the LIA CNRS D3E (From Deep Earth to Extreme Events), and led by the University of Western Brittany, Nice Sophia Antipolis University, and the National Central University of Taiwan. Forty-nine scientists from eleven different institutions * were on board. Among them, eleven Master students were able to participate in the campaign as part of their curriculum, through the organization of a Floating University.

Taiwan, offers an exceptional setting for the study of extreme telluric events. Indeed, its unique geodynamic context presents a double subduction: that of Ryukyus in the East and that of Manila in the Southwest, leading to seismicity and uplift rates among the highest in the world. In addition, the island is in the axis of the “Typhoon Alley”, subjecting it to an average of 4 typhoons per year. Historically, the region has experienced exceptional events such as the magnitude 7.6 earthquake of Chi-Chi in 1999, or the Meiwa tsunami in 1771, which caused nearly 12,000 casualties, most likely caused by magnitude earthquake ~ 7.5 to 8 off Ryukyu. Finally, Typhoon Morakot in 2009 was one of the most destructive to reach the island, because of the floods and the landslides that it generated.

By definition, these exceptional events are rare, and the instrumental and historical archives too limited. It is therefore essential to establish time series of several thousand years (or more) in order to constrain the recurrence and amplitude of these events, better understand the factors that control them in the long term, and in the end train predictive models of these natural hazards and to improve the prevention of associated risks.

Reading the geological archives is therefore necessary to establish long series. Because of the exceptional erosion occurring on the island, the geological traces on land of these events are limited or incomplete. The marine domain can offer a very good preservation of the history of events: These catastrophic phenomena generate submarine landslides and turbidity currents whose deposits (turbidites) contrast with the slow hemipelagic sedimentation: they are easily identifiable and datable by marine sedimentary cores. The detailed analysis of the sedimentary sequences and their contents can make it possible to go back to source zones, and to propose factors triggering among earthquakes of great magnitude, the leaching by a wave of tsunami, or exceptional floods caused by typhoons.

Thirty-two cores, up to 46 meters long, and fourteen short interface cores were collected during the EAGER campaign for a total of over 600m of deposits. Almost all of the cores at summer have been treated on board (measurements of the physical parameters, opening, description) and makes it possible to propose the following preliminary results:

In the West of the island, the analysis of the superficial deposits shows a stratigraphy a priori compatible with the Pintung earthquake in 2006 of magnitude 7, followed by the typhoon Morakot in 2009. These results are very promising for the study of the deposits older.

To the east, above the subsurface Ryukyus subduction plane, turbidite deposits show a very distinct origin, characterized by reef and continental content reworkings, and suggesting emplacement during tsunamis. . These deposits would thus represent the first marine record of tsunamis documented on land. Future dating will identify these events, and most likely extend the time series on land limited to ~ 2700 years. We also found on several sites for the first time in this region a level of volcanic ash Pleistocene age up to 40cm thick. To date, the volcanic caldera at the origin of this mega-eruption remains enigmatic, and the geochemical analyzes and dating in progress will reveal this mystery.

Finally, at two sites, gas hydrates were recovered in the core cores. This is the first time that gas hydrates have been collected in Taiwanese waters. This discovery represents an important issue in terms of energy resources for Taiwan.

The scientific skills of the participants focused on marine geosciences themes, with various specialties including: marine sedimentology, seismo-tectonics, geodynamics, bio-stratigraphy, paleo-environment, geochemistry, geochronology and geophysics. The oceanographic campaign was also able to host a Floating University organized by IUEM including 11 Masters students from Brest, Nice, Montpellier, and Taiwan from training courses in Geosciences, Biology, and Marine Chemistry. In addition to contributing to the analysis of the data, the students were in charge of the daily organization of seminars and the holding of a science popularization blog.

Contacts: nathalie.babonneau@univ-brest.fr and gueorgui.ratzov@unice.fr

Heads of Mission: Nathalie Babonneau, UMR6538 Geosciences Ocean, Brest, and Georgy Ratzov, UMR7329 GéoAzur, Nice.

Taiwan Scientist: Shu-Kun Hsu, Center for Environmental Studies, National Central University (NCU),

Taiwan Funding: TGIR French Oceanographic Fleet, National Energy Program II project of the Ministry of Science and Technology of Taiwan (NEPII-MOST)

* Institutions: CNRS, University of Western Brittany, University of Nice Sophia-Antipolis, University of Montpellier, University of Perpignan Via Domitia, IFREMER, Grenoble-Alpes University, National Central University (NCU Taiwan), National Taiwan University (NTU), University of the Ryukyus (Japan), National Sun Yat-sen University (Taiwan NSYSU), Taiwan Ocean Research Institute (TORI)

Thematic Days of GT3 / GDR Waves CNRS 2451

May 31st and June 1st, 2018 took place in Grenoble, the Thematic Days of the GT3 / GDR Waves CNRS 2451 on the theme “Magnetic & Electromagnetic Sensors (EM) and Applications”; days co-organized by the LGO (GIM team) and G2Elab (Research Laboratory in Electrical Engineering, Grenoble) Link to the summary sheet of this event

Contact: Jacek.Gieraltowski@univ-brest.fr

FOCUS Kickoff Meeting

Meeting for the FOCUS project, led by Marc-André Gutscher.

Preliminary Program

9:00     coffee – welcome

9:30     Mimmo Palano (INGV, Catania)
             The present-day kinematic pattern of Sicily and Calabria from 23 years of GNSS measurements

10:00   Luciano Scarfi (INGV, Catania)
             Seismic pattern and tomographic images of eastern Sicily and southern Calabria

10:30   Morelia Urlaub (Geomar Kiel)
             Gravitational collapse of Mount Etna’s southeastern flank

11:00   Philippe Jousset (GFZ Potsdam)
            Observing earthquakes with DAS (Distributed acoustic sensing) in Iceland and on Mt. Etna (??)

11:30   Anthony Sladen (GeoAzur Nice)
            SEAFOOD: a Seafloor Fiber-Optic Observatory for Distributed measurements

12:00   Lionel Quetel (IDIL Lannion)
            Demonstration of BOTDR for strain measurements with fiber optic cables

12:30 – 14:00    Lunch  (CROUS Restaurant Universitaire special room and menu)

14:00   Heidrun Kopp (Geomar, Kiel)
            Seafloor monitoring using acoustic ranging networks

14:30   M-A Gutscher (ERC FOCUS – PI)
            FOCUS project, current status and planning for different work topics

15:00  Skype exchange about seafloor operations
(Giorgio Riccobene LNS Catania and Viorel Ciausu Ifremer, Toulon)

15:30  General Discussion

17 :00  End of program

19:00  – 22:00    Dinner at Hostellerie Saint Mathieu (transport in private cars)

ISOTRAPIK Formation

This workshop is a national training action funded by the CNRS for students, technicians, engineers and researchers for the analysis of trace elements and isotopes by ICP-AES, HR- (LA) -ICP-MS, ICP-Q -MS, MC-TIMS, MC-ICP-MS, EA-IRMS, KIEL IV Carbonate-IRMS. The following modules will be covered: operation, maintenance, sample preparation, optimization, analysis, data processing.

More information at the following address: http://www.pso-brest.org/Actualites/ISOTRAPIK