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1. Mayotte seismic crisis: building knowledge in near real-time by combining land and ocean-bottom seismometers, first results

Author

Jérôme Vergne, Jean Battaglia, Louis Géli, Stephan J. Jorry, Jérôme Van der Woerd, Anthony Dofal, Jean-Marie Saurel, Hélène Jund, Marie Paule Bouin, Arnaud Gaillot, Alison Colombain, Ronan Apprioual, Nicolas Mercury, Sophie Lambotte, Valérie Ferrazzini, Cécile Doubre, Yves Fouquet, Philippe Kowalski, Simon Besançon, Océane Foix, Cyprien Griot, Céleste Broucke, Mickaël Roudaut, Claudio Satriano, Grégoire Dectot, Isabelle Thinon, Rémi Dretzen, Lise Retailleau, Tom Dumouche, Nicolas Desfete, Félix Léger, Pierre Guyavarch, Didier Bertil, Aude Lavayssière, Philippe Fernagu, Aline Peltier, Fabrice R. Fontaine, Frédéric Lauret, Arnaud Lemarchand, Emmanuel Rinnert, Chastity Aiken, Pascal Pelleau, Wayne C Crawford, Marc Grunberg, Frédéric Tronel, Roser Hoste-Colomer, Soumya Bodihar, Emmanuel Maros, Christophe Brunet, R. Daniel, Eric Jacques, Kevin Canjamale, Emre Güzel, Patrice Boissier, Anne Lemoine, Agathe Roullé, Philippe Catherine, Maxime Bes de Berc, Nathalie Feuillet, Angèle Laurent, Institut Terre Environnement Strasbourg (ITES), École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES)-Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Institut de Physique du Globe de Paris (IPGP (UMR_7154)), Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), Observatoire Volcanologique du Piton de la Fournaise (OVPF), Institut de Physique du Globe de Paris (IPG Paris), Laboratoire GéoSciences Réunion (LGSR), Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris), Ecole et Observatoire des Sciences de la Terre (EOST), Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement et la société-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA), Faculty of Electrical and Electronics Engineering [Istanbul], and Istanbul Technical University (ITÜ)

Subjects
Volcano monitoring, Seismometer, 010504 meteorology & atmospheric sciences, Population, Magnitude (mathematics), Context (language use), Induced seismicity, 010502 geochemistry & geophysics, 01 natural sciences, Remote sensing of volcanoes, Geochemistry and Petrology, education, Indian Ocean, 0105 earth and related environmental sciences, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, education.field_of_study, geography, geography.geographical_feature_category, Volcano seismology, Geophysics, Volcano, Africa, Submarine pipeline, Geology, Seismology, Channel (geography)
Abstract

SUMMARYThe brutal onset of seismicity offshore Mayotte island North of the Mozambique Channel, Indian Ocean, that occurred in May 2018 caught the population, authorities and scientific community off guard. Around 20 potentially felt earthquakes were recorded in the first 5 d, up to magnitude Mw 5.9. The scientific community had little pre-existing knowledge of the seismic activity in the region due to poor seismic network coverage. During 2018 and 2019, the MAYOBS/REVOSIMA seismology group was progressively built between four French research institutions to improve instrumentation and data sets to monitor what we know now as an on-going exceptional submarine basaltic eruption. After the addition of 3 medium-band stations on Mayotte island and 1 on Grande Glorieuse island in early 2019, the data recovered from the Ocean Bottom Seismometers were regularly processed by the group to improve the location of the earthquakes detected daily by the land network. We first built a new local 1-D velocity model and established specific data processing procedures. The local 1.66 low VP/VS ratio we estimated is compatible with a volcanic island context. We manually picked about 125 000 P and S phases on land and sea bottom stations to locate more than 5000 events between February 2019 and May 2020. The earthquakes outline two separate seismic clusters offshore that we named Proximal and Distal. The Proximal cluster, located 10 km offshore Mayotte eastern coastlines, is 20–50 km deep and has a cylindrical shape. The Distal cluster start 5 km to the east of the Proximal cluster and extends below Mayotte's new volcanic edifice, from 50 to 25 km depth. The two clusters appear seismically separated, however our data set is insufficient to firmly demonstrate this.

Published
2021
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2. A Cagey Approach to Speedy and Safe Seafloor Deployments

Author

Pascal Pelleau, Ronan Apprioual, Antony Ferrant, and Daniel Aslanian

Subjects
General Earth and Planetary Sciences
Abstract

Researchers devised a simple way to deliver ocean bottom seismometers accurately to the seafloor to study ongoing seismic and volcanic activity near the islands of Mayotte.

Published
2022
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3. Birth of a large volcanic edifice offshore Mayotte via lithosphere-scale dyke intrusion

Author

Angèle Laurent, Philippe Kowalski, R. Daniel, Eric Jacques, Patrick Bachèlery, Raphaël Grandin, Manuel A. Moreira, Aline Peltier, Valérie Ballu, Nathalie Feuillet, François Beauducel, Jean-Pierre Donval, Arnaud Gaillot, Didier Bertil, Yves Fouquet, Vivien Guyader, Fabien Paquet, Arnaud Lemarchand, Cecile Cathalot, Simon Besançon, Emmanuel Rinnert, Chastity Aiken, Carla Scalabrin, Wayne C Crawford, Isabelle Thinon, Jean Marie Saurel, Océane Foix, Anne Lemoine, Pascal Pelleau, Christine Deplus, Louis Géli, Stephan J. Jorry, J. Gomez, Claudio Satriano, Pascal Bernard, Jérôme Van der Woerd, Institut de Physique du Globe de Paris (IPG Paris), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM), LIttoral ENvironnement et Sociétés (LIENSs), La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA), Institut Terre Environnement Strasbourg (ITES), École Nationale du Génie de l'Eau et de l'Environnement de Strasbourg (ENGEES)-Université de Strasbourg (UNISTRA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS), French Ministries of Environment, Research and Overseas under a research project to N.F. (proposal INSU-CT3 TELLUS SISMAYOTTE2019)., Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPC), Institut des Sciences de la Terre d'Orléans - UMR7327 (ISTO), Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de Paris, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS), Magma - UMR7327, Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Institut national des sciences de l'Univers (INSU - CNRS)-Université d'Orléans (UO)-Centre National de la Recherche Scientifique (CNRS)-Bureau de Recherches Géologiques et Minières (BRGM) (BRGM)-Observatoire des Sciences de l'Univers en région Centre (OSUC), Institut des Sciences de la Terre (ISTerre), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de recherche pour le développement [IRD] : UR219-Université Savoie Mont Blanc (USMB [Université de Savoie] [Université de Chambéry])-Centre National de la Recherche Scientifique (CNRS)-Université Gustave Eiffel-Université Grenoble Alpes (UGA), LIttoral ENvironnement et Sociétés - UMR 7266 (LIENSs), Institut national des sciences de l'Univers (INSU - CNRS)-La Rochelle Université (ULR)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Magmas et Volcans (LMV), Institut national des sciences de l'Univers (INSU - CNRS)-Institut de Recherche pour le Développement et la société-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Observatoire de Physique du Globe de Clermont-Ferrand (OPGC), Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Université Clermont Auvergne (UCA), Institut de physique du globe de Strasbourg (IPGS), Institut national des sciences de l'Univers (INSU - CNRS)-Université Louis Pasteur - Strasbourg I-Centre National de la Recherche Scientifique (CNRS), Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS)-Université de Paris (UP), LIttoral ENvironnement et Sociétés - UMRi 7266 (LIENSs), and Université de La Rochelle (ULR)-Centre National de la Recherche Scientifique (CNRS)

Subjects
[SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, geography, geography.geographical_feature_category, 010504 meteorology & atmospheric sciences, Lava, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, 010502 geochemistry & geophysics, 01 natural sciences, Seafloor spreading, Submarine eruption, Volcano, [SDU]Sciences of the Universe [physics], Lithosphere, Asthenosphere, Magma, General Earth and Planetary Sciences, Caldera, 14. Life underwater, Petrology, Geology, 0105 earth and related environmental sciences
Abstract

International audience; Volcanic eruptions shape Earth’s surface and provide a window into deep Earth processes. How the primary asthenosphericmelts form, pond and ascend through the lithosphere is, however, still poorly understood. Since 10 May 2018, magmaticactivity has occurred offshore eastern Mayotte (North Mozambique channel), associated with large surface displacements,very-low-frequency earthquakes and exceptionally deep earthquake swarms. Here we present geophysical and marine datafrom the MAYOBS1 cruise, which reveal that by May 2019, this activity formed an 820-m-tall, ~5 km³ volcanic edifice on the seafloor.This is the largest active submarine eruption ever documented. Seismic and deformation data indicate that deep (>55 kmdepth) magma reservoirs were rapidly drained through dykes that intruded the entire lithosphere and that pre-existing subverticalfaults in the mantle were reactivated beneath an ancient caldera structure. We locate the new volcanic edifice at the tip ofa 50-km-long ridge composed of many other recent edifices and lava flows. This volcanic ridge is an extensional feature insidea wide transtensional boundary that transfers strain between the East African and Madagascar rifts. We propose that the massiveeruption originated from hot asthenosphere at the base of a thick, old, damaged lithosphere.

Published
2021
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4. Birth of a large volcanic edifice through lithosphere-scale dyking offshore Mayotte (Indian Ocean)

Author

Nathalie Feuillet, Stephan Jorry, Wayne Crawford, Christine Deplus, Isabelle Thinon, Eric Jacques, Jean-Marie Saurel, Anne Lemoine, Fabien Paquet, Claudio Satriano, Chastity Aiken, Océane Foix, Philippe Kowalski, Angèle Laurent, Emmanuel. Rinnert, Cecile Cathalot, Jean.Pierre Donval, Vivien Guyader, Arnaud Gaillot, carla scalabrin, Manuel Moreira, Aline Peltier, François Beauducel, Raphaël Grandin, Valérie Ballu, Romuald Daniel, Pascal Pelleau, Simon Besancon, Louis Geli, Pascal Bernard, Patrick Bachelery, Yves Fouquet, Didier Bertil, Arnaud Lemarchand, and Jerôme Van der Woerd

Published
2021
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5. Innovative optical geophysical instruments at the end of plurikilometric fibers for monitoring volcanic and seismic hazard in harsh environment

Author

Bernard P., Romain Feron, Guy Plantier, Mathieu Feuilloy, Philippe Menard, Nercessiane, A., Julien Couteau, Anthony Sourice, Brunet C., Boyer D., Stéphane GAFFET, Louis Géli, Pascal Pelleau, ESEO-GSII (GSII), ESEO-Tech, Université Bretagne Loire (UBL)-Université Bretagne Loire (UBL), Laboratoire d'Acoustique de l'Université du Mans (LAUM), Centre National de la Recherche Scientifique (CNRS)-Le Mans Université (UM), Institut de Physique du Globe de Paris (IPGP), Université Pierre et Marie Curie - Paris 6 (UPMC)-Institut national des sciences de l'Univers (INSU - CNRS)-IPG PARIS-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), Géoazur (GEOAZUR 6526), Institut de Recherche pour le Développement (IRD)-Université Pierre et Marie Curie - Paris 6 (UPMC)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), and Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER)

Subjects
[SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, ComputingMilieux_MISCELLANEOUS
Abstract

International audience

Published
2019

6. Onland and Offshore Extrinsic Fabry–Pérot Optical Seismometer at the End of a Long Fiber

Author

D. Boyer, Frederick Boudin, Romain Feron, Han Cheng Seat, Louis Géli, Anthony Sourice, Alexandre Nercessian, Guy Plantier, Julien Couteau, Michel Cattoen, Christophe Brunet, Mathieu Feuilloy, Stéphane Gaffet, Jean Chéry, Patrick Chawah, Pascal Bernard, Pascal Pelleau, Institut de Physique du Globe de Paris (IPGP), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), ESEO-GSII (GSII), ESEO-Tech, Université Bretagne Loire (UBL)-École supérieure d'électronique de l'ouest [Angers] (ESEO)-Université Bretagne Loire (UBL)-École supérieure d'électronique de l'ouest [Angers] (ESEO), Laboratoire d'Acoustique de l'Université du Mans (LAUM), Le Mans Université (UM)-Centre National de la Recherche Scientifique (CNRS), Équipe Optoélectronique pour les Systèmes Embarqués (LAAS-OSE), Laboratoire d'analyse et d'architecture des systèmes (LAAS), Université Toulouse Capitole (UT Capitole), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université Toulouse - Jean Jaurès (UT2J), Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Université Toulouse Capitole (UT Capitole), Université de Toulouse (UT), Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), Laboratoire Souterrain à Bas Bruit (LSBB), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Laboratoire Interdisciplinaire de Recherche Impliquant la Géologie et la Mécanique (LIRIGM), Université Joseph Fourier - Grenoble 1 (UJF), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), ANR-16-CE04-0008,HIPERSIS,Sismomètre Optique à Haute Performance(2016), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), Université Bretagne Loire (UBL)-Université Bretagne Loire (UBL), Centre National de la Recherche Scientifique (CNRS)-Le Mans Université (UM), Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Aix Marseille Université (AMU)-Avignon Université (AU)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse 1 Capitole (UT1)-Université Toulouse - Jean Jaurès (UT2J)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse 1 Capitole (UT1)-Université Toulouse - Jean Jaurès (UT2J), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), and Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER)

Subjects
Seismometer, Optical fiber cable, Heterodyne, Optical fiber, 010504 meteorology & atmospheric sciences, [SDU.STU.GP]Sciences of the Universe [physics]/Earth Sciences/Geophysics [physics.geo-ph], Ambient noise level, [SDU.STU]Sciences of the Universe [physics]/Earth Sciences, Geophone, 010502 geochemistry & geophysics, 7. Clean energy, 01 natural sciences, Noise floor, law.invention, [SPI.TRON]Engineering Sciences [physics]/Electronics, Interferometry, Geophysics, 13. Climate action, law, [SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing, Geology, 0105 earth and related environmental sciences, Remote sensing
Abstract

We report here the design, performance, and in situ demonstration, on‐land and offshore, of an innovative high‐resolution low‐cost optical (laser) seismometer. The instrument was developed within the Laser Interferometry for Earth Strain project (French Agence Nationale de la Recherche [ANR] program), and first tested at the low‐noise underground laboratory Laboratoire Souterrain à Bas Bruit (LSBB, France). It is based on Fabry–Pérot optical interferometry between the extremity of a probing optical fiber and a reflecting mirror secured to the mobile mass of a passive 2 Hz geophone. The detection technique is based on the wavelength modulation of the laser diode (1310 nm), which allows the separation of the optical power into two signals in quadrature, thanks to an heterodyne technique. The relative displacement of the mobile mass is retrieved in real time by the phase unwrapping of these two signals. At LSBB, the fiber was 3 km long. It recorded many teleseismic earthquakes and a few regional ones, and resolves the low‐seismic noise of the Earth for periods up to 6 s, presenting an acceleration noise floor lower than 1 ng/Hz in the 0.3–5 Hz range. A three‐component version of this fiber‐based interferometric 2 Hz geophone has been recently constructed, shielded in a hyperbaric container, and installed offshore for test in Brittany (France) in April 2018, with an improved control system. Its record of the marine ambient noise matches those of a collocated commercial broadband seismometer for periods up to 50 s. This opens promising perspectives for large‐scale ocean bottom instrumentation with up to 50‐kilometer‐long optical lines; an installation is planned for 2020, off Guadeloupe, with a 5‐kilometer‐long fiber cable. It may also prove useful for installations in other challenging and exposed environments, such as deep hot boreholes, active volcanoes, unstable landslides, for real‐time monitoring in regions with high natural hazard, but also for seismic monitoring of geoindustries.

Published
2019
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7. Lithospheric structuration onshore-offshore of the Sergipe-Alagoas passive margin, NE Brazil, based on wide-angle seismic data

Author

L. Morvan, Z. Mokeddem, Danielle Porcari Alves, J. P. G. Soares, Y. Biari, Pascal Pelleau, Maryline Moulin, A. Cupertino, Afonso Loureiro, Walter R. Roest, D. Pierre, Nuno Dias, C. Ducatel, J. Crozon, P. Barros Junior, J.M. Pinheiro, Flora Gallais, João C. Duarte, Adriano R. Viana, D. Le Piver, Caesar Augusto Rigoti, Marina Rabineau, M. Roudaut-Pitel, Massinissa Benabdellouahed, Inês Rio, Alexandra Afilhado, M. Roudaut, P. Fernagu, Carlos Corela, Frauke Klingelhoefer, Mikael Evain, Agnès Baltzer, R. A. Fuck, Daniel Aslanian, C. Falcão, Philippe Schnurle, P. Mazé, Unité de recherche Géosciences Marines (Ifremer) (GM), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Instituto Superior de Engenharia de Lisboa (ISEL), Instituto Dom Luiz, Universidade de Lisboa (ULISBOA), Petrobras [Rio de Janeiro], Laboratoire Géosciences Océan (LGO), Centre National de la Recherche Scientifique (CNRS)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Université de Bretagne Sud (UBS), Littoral, Environnement, Télédétection, Géomatique UMR 6554 (LETG), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-Université de Nantes (UN)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Brest (UBO)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-École pratique des hautes études (EPHE), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (IGARUN), and Université de Nantes (UN)-Université de Nantes (UN)

Subjects
010504 meteorology & atmospheric sciences, Passive margins, Crustal structure, 010502 geochemistry & geophysics, 01 natural sciences, South Atlantic ocean, Tectonic Inheritance, Passive margin, Lithosphere, Oceanic crust, [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, Sergipe-Alagoas Basin, 14. Life underwater, Tectonic inheritance, Passive Margins, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, 0105 earth and related environmental sciences, Earth-Surface Processes, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, geography, geography.geographical_feature_category, Continental shelf, Continental crust, South Atlantic Ocean, Geology, Crust, Fold (geology), Volcano, 13. Climate action, NE Brazil, Wide-angle refraction seismics, [SDU.STU.PG]Sciences of the Universe [physics]/Earth Sciences/Paleontology, Sergipe-Alagoas basin, Seismology
Abstract

International audience; The structure and nature of the crust underlying the Camamu-Almada-Jequitinhonha-Sergipe-Alagoas basins System, in the NE Brazilian margin, were investigated based on the interpretation of 12 wide-angle seismic profiles acquired during the SALSA (Sergipe ALagoas Seismic Acquisition) experiment in 2014. In this work, we present two 220-km-long NW-SE combined wide-angle and reflection seismic profiles, SL 01 and SL 02, that have been acquired using 15 ocean-bottom-seismometers along each profile, offshore the southern part of the Sergipe Alagoas Basin (SAB), north of the Vaza-Barris Transfer zone. The SL 02 has a 150-km long inland continuation with 20 land-seismic-stations until the Sergipano Fold Belt (SFB). Wide-angle seismic forward modeling allows us to precisely divide the crust in three domains: beneath the continental shelf, a ∼100 km wide necking zone is imaged where the continental crust thins from ∼35 km on the Unthinned Continental Domain, which displays a three-layered crust structure, to less than 8 km on the Oceanic Crust Domain. In the necking zone, the upper and the middle layers thin dramatically and almost disappear, while the Moho discontinuity shows clear PmPs. The Continental-Oceanic Crust Boundary (COB) is located at ∼80 km from the coastline and is marked by intracrustal seismic reflectors and changes in the seismic velocity, showing a sharp transition. On profile SL02, the oceanic crust is perturbed by a volcanic edifice together with an anomalous velocity zone underneath the area.

Published
2018
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8. Imaging exhumed lower continental crust in the distal Jequitinhonha basin, Brazil

Author

Frauke Klingelhöfer, Massinissa Benabdellouahed, P. Barros Junior, D. Pierre, C. Ducatel, Nuno Dias, Jacqueline Cosmo Andrade Pinheiro, J. Crozon, Walter R. Roest, Caesar Augusto Rigoti, Pascal Pelleau, Maryline Moulin, José Antônio Cupertino, Flora Gallais, Marina Rabineau, M. Roudaut-Pitel, Mikael Evain, Inês Rio, J. P. G. Soares, J. L. Duarte, D. Le Piver, Dorismar David Alves, Carlos Corela, Alexandra Afilhado, M. Roudaut, P. Fernagu, Luis Matias, J. P. Mazé, Y. Biari, L. Morvan, Z. Mokeddem, Agnès Baltzer, M. Vinicius Aparecido Gomes de Lima, Afonso Loureiro, R. A. Fuck, Daniel Aslanian, Philippe Schnurle, C. Falcão, Adriano R. Viana, Instituto Dom Luiz, Universidade de Lisboa (ULISBOA), Unité de recherche Géosciences Marines (Ifremer) (GM), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Instituto Dom Luís, Faculdade de Ciências, Laboratory of Microelectronics USP, Universidade de São Paulo (USP), Faculdade de Ciências [Lisboa], Laboratoire Géosciences Océan (LGO), Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Institut Universitaire Européen de la Mer (IUEM), Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), Littoral, Environnement, Télédétection, Géomatique UMR 6554 (LETG), Université de Caen Normandie (UNICAEN), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-Université de Nantes (UN)-École pratique des hautes études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Brest (UBO)-Université de Rennes 2 (UR2), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS), Instituto de Geociências, Universidade de Brasília, Institut de Recherches sur les lois Fondamentales de l'Univers (IRFU), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay, Centro de Geofisica [Lisboa] (CGUL), Thales Research and Technologies [Orsay] (TRT), THALES, Société GéoHyd, Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Bretagne Sud (UBS)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-École pratique des hautes études (EPHE), Université de Rennes (UNIV-RENNES)-Université de Rennes (UNIV-RENNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (IGARUN), Université de Nantes (UN)-Université de Nantes (UN), Universidade de Lisboa = University of Lisbon (ULISBOA), Géosciences Marines (GM), Universidade de São Paulo = University of São Paulo (USP), Université de Bretagne Sud (UBS)-Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER)-Université de Brest (UBO)-Centre National de la Recherche Scientifique (CNRS), Normandie Université (NU)-Normandie Université (NU)-Université d'Angers (UA)-École Pratique des Hautes Études (EPHE), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Université de Brest (UBO)-Université de Rennes 2 (UR2)-Centre National de la Recherche Scientifique (CNRS)-Institut de Géographie et d'Aménagement Régional de l'Université de Nantes (IGARUN), and THALES [France]

Subjects
Seismometer, 010504 meteorology & atmospheric sciences, Passive margins, Structural basin, Crustal structure, 010502 geochemistry & geophysics, 01 natural sciences, Oceanic crust, Passive margin, Refraction (sound), 14. Life underwater, Geomorphology, ComputingMilieux_MISCELLANEOUS, [SDU.STU.OC]Sciences of the Universe [physics]/Earth Sciences/Oceanography, 0105 earth and related environmental sciences, Earth-Surface Processes, [SDU.STU.TE]Sciences of the Universe [physics]/Earth Sciences/Tectonics, PSDM, Continental crust, Sediment, South Atlantic Ocean, Lower continental crust, Geology, Crust, [SDU.STU.ST]Sciences of the Universe [physics]/Earth Sciences/Stratigraphy, NE Brazil, Wide-angle refraction seismic, Cretaceous breakup
Abstract

Twelve combined wide-angle refraction and coincident multi-channel seismic profiles were acquired in the Jequitinhonha-Camamu-Almada, Jacuipe, and Sergipe-Alagoas basins, NE Brazil, during the SALSA experiment in 2014. Profiles SL11 and SL12 image the Jequitinhonha basin, perpendicularly to the coast, with 15 and 11 four-channel ocean-bottom seismometers, respectively. Profile SL10 runs parallel to the coast, crossing profiles SL11 and SL12, imaging the proximal Jequitinhonha and Almada basins with 17 ocean-bottom seismometers. Forward modelling, combined with pre-stack depth migration to increase the horizontal resolution of the velocity models, indicates that sediment thickness varies between 3.3 km and 6.2 km in the distal basin. Crustal thickness at the western edge of the profiles is of around 20 km, with velocity gradients indicating a continental origin. It decreases to less than 5 km in the distal basin, with high seismic velocities and gradients, not compatible with normal oceanic crust nor exhumed upper mantle. Typical oceanic crust is never imaged along these about 200 km-long profiles and we propose that the transitional crust in the Jequitinhonha basin is a made of exhumed lower continental crust.

Published
2018
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9. Cone penetration testing to assess slope stability in the 1979 Nice landslide area (Ligurian Margin, SE France)

Author

Pierre Henry, Pascal Pelleau, Alois Steiner, Achim J Kopf, Ronan Apprioual, and Sylvia Stegmann

Subjects
Sub-seafloor modeling, Geology, Landslide, Numerical slope stability, Free gas, Oceanography, Mbsf, Seafloor spreading, Finite element method, Penetration test, Weak zone, Geochemistry and Petrology, Cone penetration test, Slope stability, Dynamic penetrometer, Geotechnical engineering, Slope stability analysis, Geomorphology
Abstract

In the landslide-prone area near the Nice international airport, southeastern France, an interdisciplinary approach is applied to develop realistic lithological/geometrical profiles and geotechnical/strength sub-seafloor models. Such models are indispensable for slope stability assessments using limit equilibrium or finite element methods. Regression analyses, based on the undrained shear strength (su) of intact gassy sediments are used to generate a sub-seafloor strength model based on 37 short dynamic and eight long static piezocone penetration tests, and laboratory experiments on one Calypso piston and 10 gravity cores. Significant strength variations were detected when comparing measurements from the shelf and the shelf break, with a significant drop in su to 5.5 kPa being interpreted as a weak zone at a depth between 6.5 and 8.5 m below seafloor (mbsf). Here, a 10% reduction of the in situ total unit weight compared to the surrounding sediments is found to coincide with coarse-grained layers that turn into a weak zone and detachment plane for former and present-day gravitational, retrogressive slide events, as seen in 2D chirp profiles. The combination of high-resolution chirp profiles and comprehensive geotechnical information allows us to compute enhanced 2D finite element slope stability analysis with undrained sediment response compared to previous 2D numerical and 3D limit equilibrium assessments. Those models suggest that significant portions (detachment planes at 20 m or even 55 mbsf) of the Quaternary delta and slope apron deposits may be mobilized. Given that factors of safety are equal or less than 1 when further considering the effect of free gas, a high risk for a landslide event of considerable size off Nice international airport is identified.

Published
2015
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10. Hydrogeology and its effect on slope stability along the coastal aquifer of Nice, France

Author

Pascal Pelleau, Ronan Apprioual, Sylvia Stegmann, Achim J Kopf, and Nabil Sultan

Subjects
geography, Hydrogeology, geography.geographical_feature_category, Groundwater flow, Piezometer, Geology, Landslide, Aquifer, Oceanography, Pore water pressure, Geochemistry and Petrology, Slope stability, Geomorphology, Groundwater
Abstract

Along the Ligurian continental margin off Nice (Western Mediterranean) a considerable portion of the sediments is affected by pore pressure transients resulting from groundwater charging by the nearby river Var, and also from leaching clay-mineral bearing deposits, which results in sensitive, weak clays. In 1979 the area suffered a tsunamigenic landslide that generated several casualties and material damage to the coastal zone. The seafloor presently shows evidence for soft sediment deformation and pore water freshening. In this paper, we present the first comprehensive in situ pore pressure data set collected over space and time between 2006 and 2009 in a landslide-prone area. Using piezometers (IFREMER Brest, France) and dynamic cone penetrometers (FF-CPTu, MARUM Bremen, Germany) as well as a simple modelling approach, we illuminate what governing factors control strength and pore pressure in marine slope sediments affected by the Var aquifer. Our results attest (i) a strong link between pore pressure transients and local precipitation over a period of 11 months; (ii) overpressure at levels where groundwater flow occurs (coarse intervals containing sand and gravel); and (iii) fluidised fractures and channels that indicate high pore pressures at least temporarily. In essence, seepage and repeated pore pressure fluctuations weaken the sediment effectively, so that it cannot be ruled out that the currently stable portion adjacent to Nice Airport may fail in the near future.

Published
2011
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11. Microseismicity and faulting in the southwestern Okinawa Trough

Author

Shu Kun Hsu, J. Crozon, Pascal Pelleau, Jean-Claude Sibuet, Cheng-Horng Lin, Yves Auffret, Jing Yi Lin, Frauke Klingelhoefer, and Chao Shing Lee

Subjects
Seismometer, geography, geography.geographical_feature_category, Ocean bottom, Trough (geology), Magma chamber, Fault (geology), Induced seismicity, Geophysics, Volcano, Passive seismic, Geology, Seismology, Earth-Surface Processes
Abstract

In November 2003, 15 ocean bottom seismometers were deployed in the southwestern Okinawa Trough. More than 3300 microearthquakes were located during the 10-days passive seismic experiment. The earthquake activity is characterized by the ceaseless occurrence of small earthquakes in the vicinity of all the instruments. The seismicity is essentially restricted to the central part of the Southwestern Okinawa Trough, except for one cluster of events situated in the southern part of it (cluster 2). The seismic activity terminates abruptly against the NE–SW trending prolongation of the Lishan fault. Most of the microearthquakes are aligned along the E–W trending normal faults, showing where the present-day active normal faulting occurs and how it accounts for the N–S extension in the Okinawa Trough. According to the P-wave velocity spectra estimated from some deep earthquakes located beneath the cross backarc volcanic trail area, the existence of a lower crustal/upper mantle magma chamber is confirmed by the presence of low frequency earthquakes in the 3–10 Hz bandwidth.

Published
2009
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12. Structure et évolution récente de l’éventail turbiditique du Zaïre : premiers résultats scientifiques des missions d’exploration Zaïango1 & 2 (marge Congo–Angola)

Author

Renaud Cagna, Michel Séranne, M. Voisset, Philippe Saget, Tania Marsset, Bruno Savoye, Helmuth Kuhn, Jean-Charles Ennes, Michel Cremer, Jean-François Bourillet, Alban Crusson, Jean-Claude Sibuet, Paul Beuzart, Sébastien Migeon, Marie Guiomar, Michel Lopez, Francois Harmegnies, Eliane Le Drezen, Valérie Bellec, Roger Tofani, René Kerbrat, Jean-Yves Landure, Hélène Ondréas, Pascal Pelleau, Pierre Cochonat, Olivier Bain, Jean-Pierre Le Formal, Caroline Lasnier, Benoît Loubrieu, Blandine Klein, Agnès Baltzer, Gilbert Floch, Daniel Diebler, Bernard Dennielou, Laurence Droz, Alain Normand, Ronan Apprioual, and Hervé Nouzé

Subjects
geography, geography.geographical_feature_category, Amazon rainforest, Central africa, Submarine, Ocean Engineering, Channel geometry, Water depth, Paleontology, Oceanography, River mouth, Submarine pipeline, Ecology, Evolution, Behavior and Systematics, Geology
Abstract

Two scientific submarine exploration cruises were realised in 1998 offshore Congo and Angola within the ZaiAngo project. The main goal of the project is the study of the present and recent Zaire submarine fan. The survey followed the present channel down to its distal end, 760 km from the river mouth at a water depth of 4 800 m. Preliminary results indicate that it feeds a distal lobe complex. Only one turbiditic channel is active at one time. The channels are highly meandering in their upper course. More than 80 palaeochannels have been identified both south and north of the present channel. The estimated area of the Zaire deep-sea fan is close to those of the Amazon fan.

Published
2000
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13. Premières observations sur la morphologie et les processus sédimentaires récents de l’Éventail celtique

Author

Gilbert Floch, Bruno Savoye, Jean-François Bourillet, M. Voisset, Sylvie Bourquin, Benoît Loubrieu, Laurence Droz, G. A. Auffret, Bernard Dennielou, Sébastien Zaragosi, Agnès Baltzer, Alain Coutelle, Nicolas Weber, and Pascal Pelleau

Subjects
Turbidité, Paléoclimat, 010504 meteorology & atmospheric sciences, Aquatic Science, Palaeoclimate, 010502 geochemistry & geophysics, Oceanography, 01 natural sciences, Deep sea fan, Quaternaire, Turbidity, Quaternary, Phanerozoic, 14. Life underwater, Glacial period, 0105 earth and related environmental sciences, Forestry, Eventail profond, Turbidite, Western europe, Interglacial, Sediment, Cenozoic, Geology, Sédiment
Abstract

During the SEDIFAN 1 cruise we surveyed the bathymetry and the acoustic properties of the surface sediment of the Celtic Deep Sea Fan. We also collected Kullenberg cores in order to study recent sedimentary processes. From the bathymetry survey it is relatively easy to recognize the main areas of modern fan. The upper fan included a large sedimentary ridge which constitutes the right levee of the prominent meandering Whittard valley. After its confluence with the Shamrock valley the course of the Whittard valley is abruptly deflected to the south. At a short distance to the south the valley divides into two upper-fan channels, the Celtic channel to the west being the deeper one. This point constitutes the centre of a radiating pattern which is developed on a 150 degrees quadrant and a radius of about 100 km. The acoustic imagery displays contrasted features, related to change in lithology within the first metre beneath the sea bottom and to the sea floor roughness. The Austell ridge exhibits a contrasted pattern of elongated areas with high and low acoustic backscattering levels. This pattern is related to the development of abyssal dunes, the amplitude of which is of metric order. Particularly remarkable is a lobe-shaped low back-scattering area in the western part of the middle fan, also noteworthy are a lineated facies to the west and a braided facies to the east of the fan. The laminated silty-clayey sequences deposited on the Whittard ridge and on the Trevelyan levee were deposited during the deglaciation. We interpret these as turbidity currents overflow deposits from the Whittard valley. At the end of isotopic stage 3 and during stage 2, the English Channel was a large plain flooded by the Channel River. During this period a broad delta developed at 100 m below the present-day depth and a wide spectrum of material was bound to be supplied to the deep sea and contributed particularly to the deposition of the Whittard ridge silty-clayey sequences. The stage 2 deposits are characterized by rhythmic levels enriched in monosulfides. These types of deposits are common in areas affected by fluvial discharges. Excluding the sedimentary ridge and the channel levees the surface deposits sampled with the Kullenberg corer are sandy. These sands are deposited in various contexts on the interfluve between the western and eastern channels and at channel mouths. They were emplaced during high sea level stands as a result of high energy gravity processes. The precise sources of these sands have not yet been identified, however benthic foraminifers from included ooze pebbles have living depths of between 500 and 1 000 m. The gravity processes which eroded this marry ooze may have been triggered on the upper slope. The Celtic shelf is presently a high energy platform where the conjunction of storms and spring tides call lead to enhanced sediment transport from near-shore to the deep sea. The relict or palimpsest deposits of the glacial delta also constitute a large reservoir of sandy material which can also be subject to reworking., Le programme Enam 2 (European North Atlantic Margin) concerne l'étude des processus sédimentaires quaternaires du Spitzberg au golfe de Gascogne. Dans le cadre de ce programme, la reconnaissance de l'Éventail profond celtique était l'objectif de la campagne Sedifan 1 au cours de laquelle nous avons établi la morphologie de l'éventail et obtenu une image acoustique des fonds sédimentaires. La morphologie permet de mettre en évidence une organisation en éventail. On note aussi le développement remarquable d'une ride sédimentaire au niveau de l'éventail supérieur. Les sédiments prélevés révèlent la présence de dépôts sableux, témoins d'une activité récente qui pourrait être liée à l'importance de l'hydrodynamisme sur les Grands Bancs de la plate-forme celtique.

Published
2000
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14. A Long-term Monitoring Array for Landslide Precursors: A Case Study at the Ligurian Slope (Western Mediterranean Sea)

Author

Achim J Kopf, Ronan Apprioual, Nabil Sultan, Sebastien Garziglia, Matthias Zabel, Sylvia Stegmann, and Pascal Pelleau

Subjects
Mediterranean sea, Oceanography, Climatology, Long term monitoring, Landslide, Geology
Abstract

Abstract The Nice Slope, situated in the French part of the Ligurian Margin, representsa landslide-prone area, where different factors favour slope instability:Seismicity up to ~M6,rapid sediment deposition in the Var fluvial system,groundwater discharge along the coastal aquifer,creeping ofsensitive clay layers, andhuman activity (land reclamation, construction). In 1979, a catastrophic failure occurred in the Var pro-delta, that destroyedthe Nice new harbour extension, mobilised ~8.7×106 m3 material, and initiated atsunami wave of 2–3m. This event led extensive research efforts first directedat understanding the triggers of the failure. In later years, some furtherstudies allowed to detect the occurrence of mechanically weak sediments outsidethe area that failed in 1979. This, along with the detection of freshened porewater and excess pore pressure development raised concerns as to the presentday and future slope stability. Hence, at present, progressive weakening of the shallow sediment is monitoredusing a long-term array in collaboration between Ifremer Brest and MARUMBremen. It comprises two multi-level pore pressure probes (Ifremer piezometers, one installed in the 1979 scar, one in the unaffected slope further E) as wellas a tilt-meter instrument (Ifremer) that will observe the deformation rate ofthe upper 8 m of sediment in real-time. In addition, an osmotically drivenfluid sampling-lance (MARUM) collects pore fluids for geochemical studies atthe levels of the pore pressure ports of the piezometers to identifyground-water discharge. With temporary OBS installations and onshoreseismometers in place, the array will allow us to distinguish between thevarious factors that are presently affecting the stability of the NiceSlope.

Published
2012
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17. High resolution passive optical seismometer connected to a long fiber for onland and offshore remote applications

Author

Pascal Bernard, Romain Feron, Guy Plantier, Alexandre Nercessian, Julien Couteau, Mathieu Feuilloy, Anthony Sourice, Michel Cattoen, Han Cheng Seat, Patrick Chawah, Jean Chery, Christophe Brunet, Frédéric Boudin, Daniel Boyer, Stéphane GAFFET, Louis Geli, Pascal Pelleau, Institut de Physique du Globe de Paris (IPGP), Centre National de la Recherche Scientifique (CNRS)-Université de La Réunion (UR)-Université Paris Diderot - Paris 7 (UPD7)-IPG PARIS-Institut national des sciences de l'Univers (INSU - CNRS), ESEO-Tech, Université Bretagne Loire (UBL), Laboratoire d'Acoustique de l'Université du Mans (LAUM), Centre National de la Recherche Scientifique (CNRS)-Le Mans Université (UM), ESEO-GSII (GSII), Université Bretagne Loire (UBL)-Université Bretagne Loire (UBL), Équipe Optoélectronique pour les Systèmes Embarqués (LAAS-OSE), Laboratoire d'analyse et d'architecture des systèmes (LAAS), Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse 1 Capitole (UT1)-Université Toulouse - Jean Jaurès (UT2J)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse 1 Capitole (UT1)-Université Toulouse - Jean Jaurès (UT2J), Géosciences Montpellier, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Centre National de la Recherche Scientifique (CNRS)-Université des Antilles (UA), École normale supérieure - Paris (ENS Paris), Laboratoire Souterrain à Bas Bruit (LSBB), Université Nice Sophia Antipolis (... - 2019) (UNS), Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Observatoire de la Côte d'Azur, Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris Diderot - Paris 7 (UPD7)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS), Université Bretagne Loire (UBL)-École supérieure d'électronique de l'ouest [Angers] (ESEO)-Université Bretagne Loire (UBL)-École supérieure d'électronique de l'ouest [Angers] (ESEO), Le Mans Université (UM)-Centre National de la Recherche Scientifique (CNRS), Université Toulouse Capitole (UT Capitole), Université de Toulouse (UT)-Université de Toulouse (UT)-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Université de Toulouse (UT)-Institut National des Sciences Appliquées (INSA)-Université Toulouse - Jean Jaurès (UT2J), Université de Toulouse (UT)-Université Toulouse III - Paul Sabatier (UT3), Université de Toulouse (UT)-Centre National de la Recherche Scientifique (CNRS)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université de Toulouse (UT)-Université Toulouse Capitole (UT Capitole), Université de Toulouse (UT), École normale supérieure - Paris (ENS-PSL), Université Paris sciences et lettres (PSL), Université Nice Sophia Antipolis (1965 - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Avignon Université (AU)-Aix Marseille Université (AMU)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Université Côte d'Azur (UCA)-Centre National de la Recherche Scientifique (CNRS), Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées-Université Fédérale Toulouse Midi-Pyrénées-Centre National de la Recherche Scientifique (CNRS)-Université Toulouse III - Paul Sabatier (UT3), Université Fédérale Toulouse Midi-Pyrénées-Institut National des Sciences Appliquées - Toulouse (INSA Toulouse), Institut National des Sciences Appliquées (INSA)-Institut National des Sciences Appliquées (INSA)-Institut National Polytechnique (Toulouse) (Toulouse INP), Université Fédérale Toulouse Midi-Pyrénées-Université Toulouse - Jean Jaurès (UT2J)-Université Toulouse 1 Capitole (UT1), Université Fédérale Toulouse Midi-Pyrénées, Institut national des sciences de l'Univers (INSU - CNRS)-Université de Montpellier (UM)-Université des Antilles (UA)-Centre National de la Recherche Scientifique (CNRS), Centre National de la Recherche Scientifique (CNRS)-Observatoire de la Côte d'Azur, COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-COMUE Université Côte d'Azur (2015-2019) (COMUE UCA)-Université Côte d'Azur (UCA)-Aix Marseille Université (AMU)-Avignon Université (AU)-Université Nice Sophia Antipolis (... - 2019) (UNS), COMUE Université Côte d'Azur (2015-2019) (COMUE UCA), and Institut Français de Recherche pour l'Exploitation de la Mer - Brest (IFREMER Centre de Bretagne)

Subjects
[SPI]Engineering Sciences [physics], [SDU]Sciences of the Universe [physics], [SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology, [SPI.SIGNAL]Engineering Sciences [physics]/Signal and Image processing
Abstract

International audience; In many areas with high telluric hazard (earthquakes, tsunamis, landslides etc.), our understanding of seismogenic and mechanical processes and our ability to properly asses the related hazard is still very limited by the difficulty or the impossibility to deploy arrays of high performance seismometers in areas with harsh and challenging environment (far offshore, hot/deep boreholes, mountainous regions, etc.), due to the high installations and maintaining costs, and to the risk of loss (lightning, eruptions, rock falls, power failure, etc.) or even to the absence of suitablecommercial technology (high temperature). These last few years, innovative, high-resolution, low-cost optical seismometers have been developed to provide a real-time monitoring solution for regions of interest. The application fields of these significant advances are multiple: natural areas with a high telluric hazard, geo-industries (oil and gas production, geothermy, gas or waste storage), monitoring of structures, etc.The IPGP, the ESEO Group and their partners Geosciences Montpellier and the Laboratory of Analysis and Architecture Systems (LAAS) of Toulouse developed an on-land and offshore, high resolution, low-cost optical (laser) seismometer (french ANR LINES). Campaigns have been conducted in order to test and qualify their first prototype of 2 Hz - optical seismometers, at the Low Noise Underground Laboratory (LSBB) of Rustrel (France). This allowed a first validation of all opto-mechanical functions of the involved sensors, including the dedicated signalprocessing. Thus, the acceleration floor noise level of the sensor is lower than 1ng.Hzˆ-1/2 in the 0.3-5Hz range andremains under 10ng.Hzˆ-1/2 in the 0.15-20Hz range. One of the current fields of investigation, co-financed by the Technology Transfer Accelerator Office (SATT) Ouest Valorisation, consists in adapting these technologies to the design of a 3 components remote underwater seismometer. In this campaign, the integration of optical components, electronics for analog signal conditioning and digital signal processing has significantly improved the sensor performances and allowed an important reduction of power consumption (by a factor of ten). This autonomous device has been deployed during the past 6 months directly on a platform in the Brest harbour, collaborating with IFREMER and the Sea Test Base of ISEN. Our optical geophones were packaged in a hyperbaric chamber, buried in the seafloor, 500 meters away from the platform and at a depthof about 10 meters. This presentation aims to show the results and observations collected during these campaigns, and discuss aboutthe short and long term perspectives.

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