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Noisy Oceans: Monitoring Seismic and Acoustic Signals in the Marine Environment
No full textMeasuring devices such as ocean bottom seismometers and hydrophones designed to detect earthquakes pick up many other signals. These were previously ignored as background noise from unknown sources, but advanced technology now allows insights into the noise created from icebergs, ships, hydrothermal vents, whales, rain, marine engineering, and more.
Noisy Oceans: Monitoring Seismic and Acoustic Signals in the Marine Environment is a comprehensive guide to non-tectonic marine noise originating from different environmental, biological, and anthropogenic sources.
Volume highlights include:
Overview of marine soundscapes and their sources
Existing and new methods for studying acoustic signals
Case studies from around the world
Spans disciplines from geology and geophysicists to biology
Explores the impacts and implications of marine nois
Une étude des archives sédimentaires et de l’évolution tectonique de l’Atlantique équatorial : implications sur le point triple, rôle de dernier pont terrestre, et potentiel de géo-risque
No full textDu Crétacé à l’Holocène, de la tectonique des plaques à l’océanographie physique en passant par la paléo-climatologie, cette thèse propose un aperçu des impacts climatiques et océanographiques de l’ouverture de l’Atlantique Equatorial. Au Crétacé, pendant le Turonien, la température moyenne de la terre était d’environ 28°C, contre approximativement 15°C actuellement. Ce maximum climatique intervient peu après l’ouverture de l’Océan Atlantique Equatorial, qui constituait le dernier pont terrestre reliant l’Amérique du Sud et l’Afrique, et qui séparait alors l’Atlantique Sud de l’Atlantique Central. Afin d’évaluer l’éventuelle contribution de la rupture de ce pont terrestre à ce maximum climatique, une reconstruction cinématique dédiée au rifting précoce de l’Atlantique Equatorial a été conduite. Cette reconstruction propose une nouvelle segmentation de l’Atlantique Equatorial, dont la partie nord a été affectée par un rifting polyphasé impliquant la formation d’une marge transformante abrupte au niveau du plateau de Demerara. La géométrie escarpée résultant de ce rifting, combinée à la mise en place d’une circulation thermohaline active à l’Oligocène-Miocène, impacte la sédimentation du plateau de Demerara, qui est régulièrement affectée par des glissements sous-marins. Afin de mieux appréhender les risques associes à ces glissements de terrain, une observation multimodale des processus océanographiques à l’oeuvre a également été proposée. La combinaison des données de sismique multi-traces, de sismique grand-angle, de mesure altimétrique, XBT et CTD a révélé un important mélange de la colonne d’eau au niveau du plateau de Demerara ayant de potentiels impacts sur les instabilités sédimentaires du plateau.From the Cretaceous to the Holocene, bridging plate tectonics, physical oceanography, and paleoclimatology, this PhD thesis provides an overview of the climatic and oceanographic impacts of the opening of the Equatorial Atlantic. During the Cretaceous, specifically the Turonian period, Earth’s average temperature was approximately 28°C, compared to around 15°C today.This climatic maximum occurred shortly after the opening of the Equatorial Atlantic Ocean, which served as the last land bridge connecting South America and Africa, thereby separating the South Atlantic from the Central Atlantic. To assess the possible role of the breakup of this land bridge in the Cretaceous climatic maximum, a dedicated kinematic reconstruction focused on the early rifting phase of the Equatorial Atlantic was conducted. This reconstruction proposes a new segmentation of the Equatorial Atlantic, indicating a polyphased rifting pattern that affected its northern part, leading to the formation of a steep transform margin at the Demerara Plateau. The sharp geometry resulting from this rifting, combined with the establishment of active thermohaline circulation during the Oligocene-Miocene, influences sedimentation on the Demerara Plateau, which is frequently affected by submarine landslides. To better understand the risks associated with these landslides, a multimodal observation of the oceanographic processes at play was conducted. The combination of multichannel seismic data, wide-angle seismic surveys, altimetric measurements, XBT, and CTD data revealed significant mixing within the water column over the Demerara Plateau, which may have potential impacts on sediment instability
Seismic and Acoustic Monitoring of Submarine Landslides: Ongoing Challenges, Recent Successes and Future Opportunities
Get PDFSubmarine landslides pose a hazard to coastal communities and critical seafloor infrastructure, occurring on all of the world's continental margins, from coastal zones to hadal trenches. Offshore monitoring has been limited by the largely unpredictable occurrence of submarine landslides and the need to cover large regions. Recent subsea monitoring has provided new insights into the preconditioning and run-out of submarine landslides using active geophysical techniques. However, these tools measure a small spatial footprint and are power- and memory-intensive, thus limiting long-duration monitoring. Most landslide events remain unrecorded. In this chapter, we first show how passive acoustic and seismologic techniques can record acoustic emissions and ground motions created by terrestrial landslides. This terrestrial-focused research has catalyzed advances in characterizing submarine landslides using onshore and offshore networks of broadband seismometers, hydrophones, and geophones. We discuss new insights into submarine landslide preconditioning, timing, location, velocity, and down-slope evolution arising from these advances. Finally, we outline challenges, emphasizing the need to calibrate seismic and acoustic signals generated by submarine landslides. Passive seismic and acoustic sensing has a strong potential to enable more complete hazard catalogs to be built and open the door to emerging techniques (such as fiber-optic sensing) to fill key knowledge gaps
Characterization of the deep structure of the Demerara Plateau, off French Guyana and Surinam
No full textL’exploration des marges continentales a récemment mis en évidence les plateaux marginaux transformants (TMPs). Localisés à la jonction entre deux domaines océaniques différents et associés à une faille transformante, ces plateaux sous-marins présents partout dans le monde sont des noeuds géodynamiques et représentent un des verrous majeurs dans la compréhension de la genèse des marges et des domaines océaniques. Dans ce contexte, cette thèse s’est initiée avec la volonté de comprendre la structure profonde du plateau sous-marin de Démérara, situé au large de la Guyane et du Suriname, et qui constitue un exemple type de TMPs. Ce travail s’appuie sur un jeu de données de sismique lourde issu de la campagne océanographique MARGATS et sur des données de sismique multitrace industrielles. Ce travail a pour but de 1) Déterminer la nature des unités crustales du plateau de Démérara. 2) Déterminer leur géométrie, leurs extensions et leur chronologie. 3) Identifier l’impact des phases tectoniques majeures sur le domaine crustal. 4) Reconstituer l’histoire du plateau et des domaines adjacents. L’ensemble des résultats démontre l’existence d’une marge volcanique Jurassique le long du futur océan Atlantique central, mise en place sous l’influence d’un point chaud, et composée d’un vaste et épais complexe SDRs, de croûte continentale intrudée et de deux unités inférieures sous-plaquées. Cet ensemble est scindé en deux marges conjuguées au Crétacé à l’apparition d’une marge transformante associée au rifting et ouverture de l’océan Atlantique équatorial.The exploration of continental margins has recently highlighted transform marginal plateaus (TMPs). Located at the junction between two different oceanic domains and associated with a transform fault, these submarine plateaus located all over the world’s oceans are geodynamic nodes and represent one of the major barriers to understanding the genesis of continental margins and oceanic domains. In this context, this thesis was initiated with the objective to understand the deep structure of the Demerara plateau, located off the coasts of French Guyana and Suriname, and which constitutes a typical example of TMPs. This work is based on a deep sounding seismic data set from the MARGATS oceanographic campaign and on industrial seismic data.The purpose of this work is to 1) Determine the nature of the crustal units of the Demerara plateau. 2) Determine the geometry of the crustal units, their extensions and their chronology. 3) Identify the impact of the major tectonic phases on the crustal domain. 4) To reconstruct the history of the plateau and adjacent domains. The results demonstrate the existence of a Jurassic volcanic margin set up due to the influence of a hot spot, and composed of a wide and thick SDRs complex, intruded continental crust and two lower units. This ensemble then separated into two conjugate margins during the Cretaceous with the developement of a transform margin associated with the rifting and the opening of the equatorial Atlantic Ocean
Active faulting and deep crustal structure of the Eastern Sicily Margin
No full textLe bassin Ionien, en Méditerranée centrale, abrite une zone de subduction à vergence Nord-Ouest où la plaque Afrique plonge sous les blocs Calabro-Péloritain au Nord-Est de la Sicile. Cette subduction résulte de la lente convergence entre les plaques tectoniques Afrique et Eurasiatique. Bien que de nombreuses campagnes d’exploration scientifique ont été menées dans cette zone particulière, plusieurs questions géodynamiques restent débattues. Tout d’abord la croûte pavant le bassin Ionien pourrait être soit de nature continentale amincie et représenter une extension de la plaque Afrique, soit océanique (Néo-Téthys) faisant de ce bassin l’un des plus anciens domaines océaniques au monde. L’escarpement de Malte représente un vestige de l’ouverture du bassin, mais les mécanismes de rifting et notamment la géométrie d’ouverture du bassin restent débattus. Cette subduction est en retrait vers le Sud-Est depuis les derniers 35 Ma, mais est aujourd’hui confinée à l’étroit bassin Ionien. Afin d’accommoder ce retrait de la plaque plongeante dans le bassin, une grande faille de déchirure lithosphérique de bord de subduction (STEP fault en anglais pour « subduction Transform Edge Propagator ») doit se propager le long de la marge Est-Sicilienne. Cependant, sa position en surface reste difficile à déterminer dans l’épais prisme d’accrétion recouvrant le bassin. Ces questions ont été explorées par modélisation des données de sismique grand angle de la campagne DIONYSUS (Octobre 2014, R/V Meteor) le long de deux profils perpendiculaires à la marge Est-Sicilienne. Des modélisations gravimétriques en 3D ont aussi été réalisées dans le but de localiser la plaque plongeante en profondeur sous les blocs Calabro-Péloritains. La sismicité des trois structures majeures du bassin : l’escarpement de Malte, l’AFS (Alfeo Fault System), et l’IFS (Ionian Fault System) a permis d’étudier leurs activités à l’actuel. Les résultats obtenus permettent d’observer une croûte océanique au fond du bassin. La structure profonde de l’escarpement de Malte est observée comme une zone d’amincissement crustal abrupt, ce qui est caractéristique des marges transformantes. Un profond bassin sédimentaire asymétrique (11 km) est observé au Sud du détroit de Messine. Il s’est probablement ouvert récemment entre les blocs continentaux Péloritain et Calabre. Dans le lobe Ouest du prisme d’accrétion Calabrais, le modèle de vitesse permet d’observer l’indentation du prisme clastique interne dans le prisme évaporitique externe. Des modélisations analogiques utilisant sable et silicone ont permis de démontrer la récente activité de ce lobe. L’interprétation des modèles de vitesse permet de localiser la faille STEP le long de l’AFS sur les deux profils.In the Ionian Sea (central Mediterranean) the slow convergence between Africa and Eurasia results in the formation of a narrow subduction zone. The nature of the crust of the subducting plate remains debated and could represent the last remnants of the Neo-Tethys ocean. The origin of the Ionian basin is also under discussion, especially concerning the rifting mechanisms as the Malta Escarpment could represent a remnant of this opening. This subduction retreats toward the south-east (motion occurring since the last 35 Ma) but is confined to the narrow Ionian basin. A major lateral slab tear fault is required to accommodate the slab rollback.This fault is thought to propagate along the eastern Sicily margin but its precise location remains controversial.This PhD project focussed on the deep sedimentary and crustal structures of the eastern Sicily margin and the Malta Escarpment (ME). Two two-dimensional P wave velocity models were modelled by forward Modelling of wide-angle seismic data, acquired onboard the R/V Meteor during the DIONYSUS cruise in 2014.A 3D gravity model of the region was also performed to constrain the depth of the subducting slab bellow the Calabro-Peloritan backstops. The seismicity of the three structures identified in the velocity models (ME, Alfeo fault System, Ionian Fault System) permits to study their recent activity. The results image an oceanic crust within the Ionian basin as well as the deep structure of the Malta Escarpment, which presents characteristics of a transform margin. A deep and asymmetrical sedimentary basin is imaged south of the Messina strait and seems to have opened between the Calabrian and Peloritan continental terranes. In the western lobe of the Calabrian accretionary prism, the southern velocity model allows to observe the indentation of the internal clastic wedge into the external evaporitic wedge, thus showing the recent activity of this lobe. The interpretation of the velocity models suggests that the major STEP fault is located east of the Malta Escarpment, along the Alfeo Fault System
Paleoseismology and seismogenic potential of the Lesser Antilles Subduction Zone from sediment records
No full textLe segment Sombrero-Barbuda (zone Nord de la subduction des Petites Antilles) présente un gap dans la sismicité récente. Afin de mieux contraindre l’aléa sismique mal défini par la sismicité instrumentale ou historique, une étude de paléosismologie marine basée sur les dépôts marins co-sismiques est initiée à partir de données géophysiques (bathymétrie, réflectivité, sismique HR et THR) et de neuf carottes sédimentaires collectées pendant les campagnes ANTITHESIS et CASEIS. L’établissement d’une carte morphosédimentaire montre que les carottes sont alimentées par plusieurs sources situées principalement au niveau des plateformes carbonatées (systèmes ravines-canyons) et des pentes insulaires (canyons confinés). L’étude multi-proxy des dépôts sédimentaires définit de nombreux faciès sédimentaires gravitaires parfois réunis en séquences de dépôts et/ou megabeds très épais (ex : turbidites amalgamées, complexes HmTu). Le modèle chronostratigraphique identifie 81 évènements répartis dans une à sept carottes pistons. Ces évènements résulteraient de nombreuses déstabilisations gravitaires simultanées de plusieurs sources sédimentaires indépendantes, ce qui mettrait en évidence un déclenchement sismique. Les sept évènements sismiques les mieux définis (notamment par la corrélation de megabeds dans plusieurs carottes) auraient des magnitudes importantes (autour de Mw~8-9). Deux récurrences alternées sont identifiées pour ces évènements, de 9420 +/- 600 ans et 13630 +/- 1300 ans. Certains évènements semblent également se corréler à ceux du segment Antigua-Guadeloupe et mettraient en évidence des méga–évènements ayant une récurrence alternée de ~12 000 ans et ~23 600 ans.The Sombrero-Barbuda segment (Northern Lesser Antilles Subduction Zone) presents a gap in recent seismicity. In order to better estimate the seismic hazard, not well constrained by instrumental or historic seismicity, a marine paleoseismology study based on co-seismic marine deposits has been initiated based on geophysical data (bathymetry, backscatter, HR and VHR seismic) and nine sediment cores collected during ANTITHESIS and CASEIS cruises. The resulting morpho-sedimentary map shows that sediment cores are supplied by numerous sources principally located on the carbonate platforms (gullies-canyons systems) and on insular slopes (confined canyons). The multi-proxy study of sediment deposits defines numerous sediment gravity flow facies often grouped into thick deposit sequences and/or megabeds (ex: amalgamated turbidites, HmTu complexes).The chronostratigraphic model defines 81 events identified in between one up to seven piston cores. These events result from numerous and simultaneous slope destabilizations of different independent sources indicating an origin from seismic triggering. The seven best constrained events (especially by the correlation of megabeds in numerous sediment cores) could have had magnitudes as high as 8 or 9. Two alternate recurrence rates are identified from these events: 9420 +/- 600 years and 13630 +/- 1300 years. Some events also correlate with events from the Antigua- Guadeloupe segment and highlight mega-events with an alternate recurrence of ~12 000 years and ~23 600 years
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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