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| Registros recuperados: 29 | |
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| Ker, Stephan; Le Gonidec, Y.; Marie, Louis. |
| Seismic Oceanography is a developing research topic where new acoustic methods allow high-resolution teledetection of the thermohaline structure of the ocean. First implementations to study the Ocean Surface Boundary Layer have recently been achieved but remain very challenging due to the weakness and shallowness of such seismic reflectors. In this article, we develop a multifrequency seismic analysis of hydrographic datasets collected in a seasonally stratified midlatitude shelf by ARGO network floats to assess the detectability issue of shallow thermoclines. This analysis, for which sensitivity to the data reduction scheme used by ARGO floats for the transmission of the profiles is discussed, allows characterizing both the depth location and the... |
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| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00347/45801/45446.pdf |
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| Riboulot, Vincent; Ker, Stephan; Sultan, Nabil; Thomas, Yannick; Marsset, Bruno; Scalabrin, Carla; Ruffine, Livio; Boulart, Cedric; Ion, Gabriel. |
| Gas hydrates, a solid established by water and gas molecules, are widespread along the continental margins of the world. Their dynamics have mainly been regarded through the lens of temperature-pressure conditions. A fluctuation in one of these parameters may cause destabilization of gas hydrate-bearing sediments below the seafloor with implications in ocean acidification and eventually in global warming. Here we show throughout an example of the Black Sea, the world’s most isolated sea, evidence that extensive gas hydrate dissociation may occur in the future due to recent salinity changes of the sea water. Recent and forthcoming salt diffusion within the sediment will destabilize gas hydrates by reducing the extension and thickness of their thermodynamic... |
| Tipo: Text |
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| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00418/52981/53916.pdf |
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| Colin, Florent; Ker, Stephan; Riboulot, Vincent; Sultan, Nabil. |
| Gas hydrate (GH) systems constitute methane sinks sensitive to environmental changes such as pressure, temperature, and salinity. It remains a matter of debate as to whether the large GH system of the Black Sea has reached a steady state since the last glacial maximum (LGM). We report on an irregular free gas distribution in specific sediment layers marking an irregular bottom‐simulating reflector (BSR). This anomalous free gas distribution revealed by very high resolution seismic images, acquired by a deep‐towed multichannel seismic system, might be evidence of an on‐going migration of the base of the GH stability zone (GHSZ). We show that the reequilibrium is not occurring homogeneously as overpressure from hydrate dissociation slows their decomposition... |
| Tipo: Text |
Palavras-chave: Hydrates; Seismic; Very high resolution; Dissociation; Black Sea. |
| Ano: 2020 |
URL: https://archimer.ifremer.fr/doc/00652/76430/77526.pdf |
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| Riboulot, Vincent; Cattaneo, Antonio; Scalabrin, Carla; Gaillot, Arnaud; Jouet, Gwenael; Ballas, Gregory; Marsset, Tania; Garziglia, Sebastien; Ker, Stephan. |
| The Romanian sector of the Black Sea deserves attention because the Danube deep-sea fan is one of the largest sediment depositional systems worldwide and is considered the world's most isolated sea, the largest anoxic water body on the planet and a unique energy-rich sea. Due to the high sediment accumulation rate, presence of organic matter and anoxic conditions, the Black sea sediments offshore the Danube delta is rich in gas and thus shows Bottom Simulating Reflectors (BSR). The cartography of the BSR over the last 20 years, exhibits its widespread occurrence, indicative of extensive development of hydrate accumulations and a huge gas hydrate potential. By combining old and new datasets acquired in 2015 during the GHASS expedition, we performed a... |
| Tipo: Text |
Palavras-chave: Hydrates de gaz; Gaz libre; Panaches de gaz; BSR; Mer Noire; Géomorphologie; Gas hydrates; Free gas; Gas flares; BSR; Black Sea; Geomorphology. |
| Ano: 2017 |
URL: http://archimer.ifremer.fr/doc/00407/51860/53914.pdf |
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| Ker, Stephan; Riboulot, Vincent; Ghass Cruise Team,. |
| The objectives of the GHASS (Gas Hydrates, fluid Activities and Sediment deformations in the western Black Sea) cruise are twofold but interconnected. The first aim is to study the dynamics of gas hydrates and free gas associated with geological and climate processes. The second aim is to identify the factors at the origin of observed sediment deformations and submarine landslides in two areas in the Romanian sector of the Black Sea. For the cruise we use quantitative approaches based on multidisciplinary studies (geochemistry, geology, geophysics and geotechnics). Gas hydrates and free gas were detected using surface and deep-towed HR seismic (SYSIF) techniques and by performing in situ geotechnical and acoustic measurements using the Ifremer penetrometer... |
| Tipo: Text |
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| Ano: 2015 |
URL: http://archimer.ifremer.fr/doc/00300/41141/40329.pdf |
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| Riboulot, Vincent; Cattaneo, Antonio; Sultan, Nabil; Garziglia, Sebastien; Ker, Stephan; Imbert, Patrice; Voisset, Michel. |
| A series of pockmarks observed at the seabed matches well the perimeter of a large submarine landslide, called NG1, located on the outer shelf and continental slope of the Eastern Gulf of Guinea. NG1 extends over 200 km2, is covered by a 120-m thick sedimentary layer which tapers downslope, and has an internal structure clearly identified in 3D seismic data consisting of three adjacent units on the upper continental slope. The pockmarks above NG1 have a diameter of several tens of meters and reveal distinct origins: (1) linked to >500 m deep fluid reservoirs, (2) rooted in NG1 internal discontinuities between NG1 units, and (3) well above NG1, superficially rooted in a regional conformity (D40), which marks the lowest sea level of the Marine Isotope... |
| Tipo: Text |
Palavras-chave: Pockmarks; Fluid seepage; Submarine landslide; Sea-level changes; Piezocone; Niger Delta. |
| Ano: 2013 |
URL: http://archimer.ifremer.fr/doc/00159/27031/31906.pdf |
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| Sultan, Nabil; Marsset, Bruno; Ker, Stephan; Marsset, Tania; Voisset, Michel; Vernant, Antoine-mathieu; Bayon, Germain; Cauquil, Eric; Adamy, J.; Colliat, J. L.; Drapeau, D.. |
| Based on acquired geophysical, geological and geotechnical data and modeling, we suggest hydrate dissolution to cause sediment collapse and pockmark formation in the Niger delta. Very high-resolution bathymetry data acquired from the Niger delta reveal the morphology of pockmarks with different shapes and sizes going from a small ring depression surrounding an irregular floor to more typical pockmarks with uniform depression. Geophysical data, in situ piezocone measurements, piezometer measurements and sediment cores demonstrate the presence of a common internal architecture of the studied pockmarks: inner sediments rich in gas hydrates surrounded by overpressured sediments. The temperature, pressure and salinity conditions of the studied area have allowed... |
| Tipo: Text |
Palavras-chave: Methane gas hydrate; Sea floor; Marine sediments; Pore pressure; Porous media; Continental margin; Clathrate hydrate; Fluid flow; Stability; Slope. |
| Ano: 2010 |
URL: http://archimer.ifremer.fr/doc/00012/12300/9092.pdf |
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| Ker, Stephan; Le Gonidec, Y.; Marsset, Bruno; Westbrook, Graham; Gibert, D.; Minshull, T. A.. |
| In the context of seismic imaging of gas/gas-hydrate systems, the fine-scale structure of subseabed gas-related reflections is assessed by taking advantage of the source signature of the deep-towed high-resolution SYSIF seismic device. We demonstrate the value of an original wavelet-based method and associated multiscale seismic attributes, applied to seismic data recently acquired on the western margin of the Arctic archipelago of Svalbard. From analysis in the wavelet domain, we recognize two types of gas-related reflections associated with submetre-scale distribution of gas. We identify a thin gas-charged layer associated with an apparent normal polarity reflection, and we detect gas patches associated with a reverse-polarity bright spot with... |
| Tipo: Text |
Palavras-chave: Wavelet transform; Gas and hydrate systems; Wave propagation; Acoustic properties; Arctic region. |
| Ano: 2014 |
URL: http://archimer.ifremer.fr/doc/00175/28602/27019.pdf |
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| Sultan, Nabil; Riboulot, Vincent; Ker, Stephan; Marsset, Bruno; Geli, Louis; Tary, Jean-baptiste; Klingelhoefer, Frauke; Voisset, Michel; Lanfumey, Valentine; Colliat, Jean-louis; Adamy, Jerome; Grimaud, S.. |
| Gas hydrates were recovered by coring at the eastern border of a shale-cored anticline in the eastern Niger Delta. To characterize the link between faults and fluid release and to identify the role of fluid flow in the gas hydrate dynamics, three piezometers were deployed for periods ranging from 387 to 435 days. Two of them were deployed along a major fault linked to a shallow hydrocarbon reservoir while the third monitored the fluid pressure in a pockmark aligned above the same major fault. In addition, 10 ocean-bottom seismometers (OBS) were deployed for around 60 days. The piezometers simultaneously registered a prolonged fluid flow event lasting 90 days. During this time, OBS measurements record several episodic fluid release events. By combining and... |
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| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00060/17106/14624.pdf |
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| Ker, Stephan; Le Gonidec, Yves. |
| Multiscale seismic attributes based on the wavelet transform properties have been recently introduced and successfully applied to identify the geometry of a complex seismic reflector in an elastic medium. In the present paper, we extend this quantitative approach to anelastic media where intrinsic attenuation modifies the seismic attributes and thus requires a specific processing to retrieve them properly. The method assumes both an attenuation linearly dependent with the seismic wave frequency and a seismic source wavelet approximated with a Gaussian derivative function. We highlight a quasi-conservation of the Gaussian character of the wavelet during its propagation. We show that this shape can be accurately modeled by a Gaussian derivative function... |
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| Ano: 2018 |
URL: http://archimer.ifremer.fr/doc/00409/52034/52700.pdf |
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| Ker, Stephan; Le Gonidec, Yves; Gibert, Dominique. |
| A wavelet-based method was presented in a previous work to introduce multiscale seismic attributes for high-resolution seismic data. Because of the limited frequency bandwidth of the seismic source, we observed distortions in the seismic attributes based on the wavelet response of the subsurface discontinuities (Le Gonidec et al.). In this paper, we go further in the seismic source-correction by considering L´evy alpha-stable distributions introduced in the formalism of the continuous wavelet transform (CWT). The wavelets are Gaussian derivative functions (GDF), characterized by a derivative order. We show that a high-resolution seismic source, after a classical signature processing, can be taken into account with a GDF. We demonstrate that in the... |
| Tipo: Text |
Palavras-chave: Wavelet transform; Wave propagation; Acoustic properties. |
| Ano: 2012 |
URL: http://archimer.ifremer.fr/doc/00090/20155/17828.pdf |
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| Ballas, Gregory; Garziglia, Sebastien; Sultan, Nabil; Pelleter, Ewan; Toucanne, Samuel; Marsset, Tania; Riboulot, Vincent; Ker, Stephan. |
| The geotechnical properties of clay sediments were investigated using laboratory and in-situ measurements as part of the geohazard assessment in the Romanian sector of the Black Sea affected by landslides and seafloor deformation features. The sediments were characterized as predominantly high plastic silty clay of high compressibility, low undrained shear strength, low cohesion and moderate sensitivity. A shallow increase in shear strength exceeding the general trend could have been reconciled with evidence for the precipitation of iron sulfides and calcium carbonates related to early diagenetic reactions of sulfate reduction (e.g. cryptic sulfur cycle) and anaerobic oxidation of methane. Comparison of the compression behaviour of natural and... |
| Tipo: Text |
Palavras-chave: Lacustrine clay sediment; Structured material; Sulfur cement; Carbonate cement; Early diagenesis; Weak layer. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00439/55064/56545.pdf |
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| Ker, Stephan; Thomas, Yannick; Riboulot, Vincent; Sultan, Nabil; Bernard, Céline; Scalabrin, Carla; Ion, G; Marsset, Bruno. |
| A comprehensive characterization of the gas hydrate system offshore the western Black Sea was performed through an integrated analysis of geophysical data. We detected the Bottom Simulating Reflector (BSR), which marks, in this area, the base of gas hydrate stability. The observed BSR depth does not fit the theoretical steady-state base of gas hydrate stability zone (BGHSZ). We show that the disparity between the BSR and predicted BGHSZ is the result of a transient state of the hydrate system due to the ongoing re-equilibrium since the Last Glacial Maximum. When gas hydrates are brought outside the stability zone due to changes in temperature and sea level, their dissociation generates an increase in interstitial pore pressure. This process is favorable to... |
| Tipo: Text |
Palavras-chave: Gas hydrate; BSR; Excess pore pressure; Black Sea. |
| Ano: 2019 |
URL: https://archimer.ifremer.fr/doc/00474/58531/61081.pdf |
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| Marsset, Bruno; Menut, Eric; Ker, Stephan; Thomas, Yannick; Regnault, Jean-pierre; Leon, Pierre; Martinossi, Henri; Artzner, Laurent; Chenot, Damien; Dentrecolas, Stephane; Spychalski, B.; Mellier, G.; Sultan, Nabil. |
| High Resolution (220–1050 Hz) seismic acquisition performed in deep water using deep-towed systems provides unrivalled lateral resolution when compared to conventional surface seismic. The lateral resolution of these acquisitions is controlled by the width of the first Fresnel zone, taking advantage of their positions close to the sea bottom. No current existing deep towed equipment can benefit from seismic imaging processing techniques to improve this resolution as a consequence of positioning inaccuracies. The technological developments of a digital deep-towed multichannel streamer are presented with a particular attention to positioning: each hydrophone incorporates a pitch, roll and heading sensor in order to monitor the constant deformation of the... |
| Tipo: Text |
Palavras-chave: Deep-towed seismics; Multichannel streamer; Seismic imaging. |
| Ano: 2014 |
URL: https://archimer.ifremer.fr/doc/00206/31745/35690.pdf |
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| Riboulot, Vincent; Sultan, Nabil; Imbert, P.; Ker, Stephan. |
| A review of recent literature shows that two geomorphologically different types of pockmarks, contribute to gas seepage at the seafloor. Type-1 pockmarks are defined as seafloor craters associated to fluid seepage and are the most classical type referred to as “pockmarks” in the literature. In contrast, Type-2 pockmarks reveal a complex seafloor morphology that may result from the formation/decomposition of gas hydrates in underlying sedimentary layers. Interpretation of very-high-resolution seismic data, sedimentological analyses and geotechnical measurements acquired from the Eastern Niger Submarine Delta reveal that Type-2 pockmarks are associated to the presence at depth of a conical body of massive gas hydrates. Based on acquired data, theoretical... |
| Tipo: Text |
Palavras-chave: Pockmarks; Gas hydrates; VHR seismic data; Piezocone; Numerical modelling; Niger Delta. |
| Ano: 2016 |
URL: http://archimer.ifremer.fr/doc/00301/41215/40643.pdf |
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| Ker, Stephan; Le Gonidec, Yves; Marie, Louis; Thomas, Yannick; Gibert, Dominique. |
| Seismic Oceanography is coming of age as an established technique of observation of the thermohaline structure of the ocean. The present paper deals with the seismic reflectivity of the Armorican Shelf seasonal thermocline, west of France, based on two seismic experiments performed with a sparker source. The peak frequency was 500 Hz for the ASPEX experiment, where the thermocline was located at 27 m water depth, and reduced to 400 Hz associated to a higher source level for the IFOSISMO experiment, where the thermocline was 12 m deeper. Despite this settings, only the first experiment could clearly highlight the thermocline reflector, providing the first seismic observation of a shallow oceanic structure. To better understand the limitation of... |
| Tipo: Text |
Palavras-chave: Thermocline; Seismic method; Wavelet analysis; Acoustic. |
| Ano: 2015 |
URL: https://archimer.ifremer.fr/doc/00254/36535/35066.pdf |
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| Marsset, Bruno; Ker, Stephan; Thomas, Yannick; Colin, Florent. |
| The acquisition of high resolution seismic data in deep waters requires the development of deep towed seismic sources and receivers able to deal with the high hydrostatic pressure environment. The low frequency piezoelectric transducer of the SYSIF (SYstème Sismique Fond) deep towed seismic device comply with the former requirement taking advantage of the coupling of a mechanical resonance (Janus driver) and a fluid resonance (Helmholtz cavity) to produce a large frequency bandwidth acoustic signal (220–1050 Hz). The ability to perform deep towed multichannel seismic imaging with SYSIF was demonstrated in 2014, yet, the ability to determine P-wave velocity distribution wasn't achieved. P-wave velocity analysis relies on the ratio between the... |
| Tipo: Text |
Palavras-chave: Deep-towed seismic; Seismic imaging; P-wave velocity distribution. |
| Ano: 2018 |
URL: https://archimer.ifremer.fr/doc/00418/52971/53908.pdf |
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| Ker, Stephan; Le Gonidec, Yves; Gibert, D.; Marsset, Bruno. |
| We propose a wavelet-based method to characterize acoustic impedance discontinuities from a multiscale analysis of seismic reflected waves. Our approach relies on the analysis of ridge functions which contain most of the information of the wavelet transform in a sparse support. This method falls in the framework of the wavelet response (WR) introduced by Le Gonidec et al. which analyses the impedance multiscale behaviour by propagating dilated wavelets into the medium. We further extend the WR by considering its application to broad-band seismic data. We take into account the bandpass filter effect related to the limited frequency range of the seismic source. We apply the method to a deep-water seismic experiment performed in 2008 during the ERIG3D cruise... |
| Tipo: Text |
Palavras-chave: Wavelet transform; Seismic attenuation; Wave propagation; Acoustic properties. |
| Ano: 2011 |
URL: http://archimer.ifremer.fr/doc/00049/15994/13449.pdf |
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| Registros recuperados: 29 | |
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