Manioc : Portail | resultats 1 - 20 pour la recherche: Amer Geophysical Union

Tectonic inheritance and Pliocene-Pleistocene inversion of the Algerian margin around Algiers: Insights from multibeam and seismic reflection data
Auteur(s) : Strzerzynski, Pierre Deverchere, Jacques Cattaneo, Antonio Domzig, Anne Yelles, Karim De Lepinay, Bernard Mercier Babonneau, Nathalie Boudiaf, Azzedine

Éditeur(s) : Amer Geophysical Union
Résumé : The Algerian margin has originated from the opening of the Algerian basin about 25-30 Ma ago. The central margin provides evidence for large-scale normal faults of Oligo-Miocene age, whereas transcurrent tectonics characterizes the western margin. A set of NW-SE oriented dextral transform faults was active during basin opening and divided the 600 km long central margin into segments of similar to 120-150 km. The upper Miocene, Plio-Quaternary, and present-day tectonic setting is, however, compressional and supports the occurrence of a margin inversion, a process still poorly documented worldwide. We show that the central Algerian margin represents a rare example of inverted margin, where the process of subduction inception is particularly well expressed and helps understand how extensional and transtensive structures are involved in margin shortening. Using multibeam bathymetry and multichannel seismic reflection sections from the MAR-ADJA 2003 and 2005 cruises, we evidence Pliocene-Pleistocene shortening with contrasting styles along the margin between west (Khayr Al Din bank) and east (Boumerdes-Dellys margin) of Algiers. Pre-Miocene structures such as basement highs and transform faults appear to control changes of the deformation pattern along this part of the margin, resulting in different widths, geometries, and relative positions of folds and faults. Plio-Quaternary and active blind thrust faults do not reuse Oligo-Miocene normal and transform faults during inversion, but instead grow within the continental margin (as testified for instance by the 21 May 2003 M-w 6.8 Boumerdes-Zemmouri earthquake), at the foot of the continental slope and at the northern sides of basement highs interpreted as stretched continental blocks of the rifted margin. The inherited structures of the margin appear, therefore, to determine this deformation pattern and ultimately the earthquake and tsunami sizes offshore. The complex geometry of the fault system along the Algerian margin suggests a process of initiation of subduction in its central and eastern parts.
Tectonics (0278-7407) (Amer Geophysical Union), 2010-03 , Vol. 29 , N. TC2008 , P. 1-22

Droits : 2010 American Geophysical Union
http://archimer.ifremer.fr/doc/00008/11883/9286.pdf
http://archimer.ifremer.fr/doc/00008/11883/9287.pdf
DOI:10.1029/2009TC002547
http://archimer.ifremer.fr/doc/00008/11883/

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Oligocene-Miocene spreading history of the northern South Fiji Basin and implications for the evolution of the New Zealand plate boundary
Auteur(s) : Herzer, R. H. Barker, D. H. N. Roest, Walter Mortimer, N.

Éditeur(s) : Amer Geophysical Union
Résumé : A tectonic model of the evolution of the northern half of the South Fiji Basin, including the Minerva Triple Junction and Cook Fracture Zone, is developed from regional gravity, multibeam bathymetry, and a new interpretation of magnetic anomalies pinned to radiometric dates of oceanic crust in the basin. The geometry and age of a portion of the Minerva Triple Junction and the Cook-Minerva spreading center (the connection from the triple junction to the Cook Fracture Zone, which accommodated coeval opening of the Norfolk Basin), are resolved with multibeam bathymetry and magnetics. The South Fiji Basin opened from about 34 to 15 Ma in an anticlockwise sweep about an Euler pole located at the northern end of the present Lau Ridge. This rotation and a rigidly straight southeastward motion of the Three Kings Ridge were accommodated by the configuration of the triple junction changing from ridge-fault-fault to ridge-ridge-fault to ridge-ridge-ridge. During this evolution the southeastern arm of the system, the Julia Fracture Zone, underwent several transformations and the Cook-Minerva spreading center experienced repeated ridge jumps. The kinematics of the northern South Fiji Basin dictate, to a large extent, the evolution of the southern South Fiji Basin and the Norfolk Basin. This in turn leads to the interpretation of a complex trench-trench-double transform fault framework at the northern New Zealand margin, which explains most aspects of the geology, structure, and arc volcanic history of the margin and provides a radical new setting for the origin of the Northland Allochthon.
Geochemistry Geophysics Geosystems (1525-2027) (Amer Geophysical Union), 2011-02 , Vol. 12 , N. Q02004 , P. 1-20

Droits : 2011 American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00030/14112/11362.pdf
DOI:10.1029/2010GC003291
http://archimer.ifremer.fr/doc/00030/14112/

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The 2010 Haiti earthquake: A complex fault pattern constrained by seismologic and tectonic observations
Auteur(s) : De Lepinay, Bernard Mercier Deschamps, Anne Klingelhoefer, Frauke Mazabraud, Yves Delouis, Bertrand Clouard, Valerie Hello, Yann Crozon, Jacques

Éditeur(s) : Amer Geophysical Union
Résumé : After the January 12, 2010, Haiti earthquake, we deployed a mainly offshore temporary network of seismologic stations around the damaged area. The distribution of the recorded aftershocks, together with morphotectonic observations and mainshock analysis, allow us to constrain a complex fault pattern in the area. Almost all of the aftershocks have a N-S compressive mechanism, and not the expected left-lateral strike-slip mechanism. A first-order slip model of the mainshock shows a N264 degrees E north-dipping plane, with a major left-lateral component and a strong reverse component. As the aftershock distribution is sub-parallel and close to the Enriquillo fault, we assume that although the cause of the catastrophe was not a rupture along the Enriquillo fault, this fault had an important role as a mechanical boundary. The azimuth of the focal planes of the aftershocks are parallel to the north-dipping faults of the Transhaitian Belt, which suggests a triggering of failure on these discontinuities. In the western part, the aftershock distribution reflects the triggering of slip on similar faults, and/or, alternatively, of the south-dipping faults, such the Trois-Baies submarine fault. These observations are in agreement with a model of an oblique collision of an indenter of the oceanic crust of the Southern Peninsula and the sedimentary wedge of the Transhaitian Belt: the rupture occurred on a wrench fault at the rheologic boundary on top of the under-thrusting rigid oceanic block, whereas the aftershocks were the result of the relaxation on the hanging wall along pre-existing discontinuities in the frontal part of the Transhaitian Belt. Citation: Mercier de Lepinay, B., et al. (2011), The 2010 Haiti earthquake: A complex fault pattern constrained by seismologic and tectonic observations, Geophys. Res. Lett., 38, L22305, doi:10.1029/2011GL049799.
Geophysical Research Letters (0094-8276) (Amer Geophysical Union), 2011-11 , Vol. 38 , N. L22305 , P. 7 p.

Droits : 2011 by the American Geophysical Union
http://archimer.ifremer.fr/doc/00054/16557/14071.pdf
DOI:10.1029/2011GL049799
http://archimer.ifremer.fr/doc/00054/16557/

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Seasonal dynamics of sea surface salinity off Panama: The Far Eastern Pacific fresh pool
Auteur(s) : Alory, Gael Maes, Christophe Delcroix, Thierry Reul, Nicolas Illig, Serena

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Multiple widespread landslides during the long-term evolution of a volcanic island: Insights from high-resolution seismic data, Montserrat, Lesser Antilles
Auteur(s) : Lebas, E. Le Friant, A. Boudon, G. Watt, S. F. L. Talling, P. J. Feuillet, Nathalie Deplus, Christine Berndt, C.

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Hypercanes: A possible link in global extinction scenarios
Auteur(s) : Emanuel, Kerry A Speer, Kevin Rotunno, Richard Srivastava, Ramesh Molina, Mario

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From seismic noise to ocean wave parameters: General methods and validation
Auteur(s) : Ardhuin, Fabrice Balanche, Abel Stutzmann, E. Obrebski, Mathias

Éditeur(s) : Amer Geophysical Union
Résumé : Seismic noise is an indirect source of information on ocean waves. Using a model of noise generation and propagation, seismic stations can be separated into those that are mostly sensitive to local sea states, and those that integrate sources from a large oceanic area. The model also provides a classification of noise-generating sea states into three classes. The analysis of Central California seismic noise data, well correlated with local waves, reveals that class I events dominate in summer, caused by a single wind-sea system, and for which ocean wave spectral levels are proportional to seismic spectral levels to an exponent b similar or equal to 0.9. In winter, noise is dominated by class II generation, for which coastal reflection is important, with a wave spectral density roughly proportional to the seismic spectral density to an exponent b similar or equal to 0.7. Sporadic events of class III probably produce some of the strongest noise events in Central California and need to be properly screened. These events are caused by opposed wave systems that are usually the wind-sea and a swell. This noise classification can be used to improve on the correlation between measured and estimated wave heights(up to r = 0.93 for daily averages). For other locations, where remote oceanic sources are recorded, a significant wave height estimated from the seismic noise compares well with area-averaged satellite data or wave model results(r > 0.85 for daily averages). These analyses pave the way for quantitative uses of seismic records, including the reconstruction of past wave climates, and the calibration of wave hindcasts.
Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2012-05 , Vol. 117 , N. C05002 , P. 19 pp.

Droits : 2012 AGU
http://archimer.ifremer.fr/doc/00083/19443/17051.pdf
DOI:10.1029/2011JC007449
http://archimer.ifremer.fr/doc/00083/19443/

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Multiphased tectonic evolution of the Central Algerian margin from combined wide-angle and reflection seismic data off Tipaza, Algeria
Auteur(s) : Lepretre, Angelique Klingelhoefer, Frauke Graindorge, David Schnurle, Philippe Beslier, M. O. Yelles, K. Deverchere, Jacques Bracene, R.

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The provenance of sediments in the Gulf of Lions, western Mediterranean Sea
Auteur(s) : Revillon, Sidonie Jouet, Gwenael Bayon, Germain Rabineau, Marina Dennielou, Bernard Hemond, Christophe Berne, Serge

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SMOS salinity in the subtropical north Atlantic salinity maximum: 1. Comparison with Aquarius and in situ salinity
Auteur(s) : Hernandez, Olga Boutin, Jacqueline Kolodziejczyk, Nicolas Reverdin, Gilles Martin, Nicolas Gaillard, Fabienne Reul, Nicolas Vergely, J. L.

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Haline hurricane wake in the Amazon/Orinoco plume: AQUARIUS/SACD and SMOS observations
Auteur(s) : Grodsky, Semyon A. Reul, Nicolas Lagerloef, Gary Reverdin, Gilles Carton, James A. Chapron, Bertrand Quilfen, Yves Kudryavtsev, Vladimir N.

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Refining benthic foraminiferal Mg/Ca-temperature calibrations using core-tops from the western tropical Atlantic: Implication for paleotemperature estimation
Auteur(s) : Tisserand, Amandine A. Dokken, Trond M. Waelbroeck, Claire Gherardi, Jeanne Marie Scao, Vincent Fontanier, Christophe Jorissen, Frans

Éditeur(s) : Amer Geophysical Union
Résumé : Benthic foraminiferal Mg/Ca has been shown to have great potential as a proxy for reconstructing deep water temperatures. However, the exact relationship between Mg uptake in benthic foraminifera and temperature is still ambiguous, and further exploration and refinement is much needed to reduce uncertainties associated with the method. Here, we present new core-top Mg/Ca data from benthic foraminiferal species from the lower part of the thermocline in the western tropical Atlantic (northern Brazilian margin). This area is unusual in that the changes in carbonate chemistry along the transect are very small, making it an ideal region for isolating and studying the role of temperature in the incorporation of Mg into the benthic shells. Our results show that benthic foraminiferal Mg/Ca largely reflects temperature in this area. Our data are combined with previously published data to produce new and improved Mg/Ca calibration equations for a number of benthic foraminiferal species within the Atlantic Ocean. Our study provides the first C. wuellerstorfi Mg/Ca data for the 46 degrees C temperature range and indicates that C. wuellerstorfi Mg/Ca is strongly controlled by temperature. As a result, the newly established C. wuellerstorfi calibration over the entire 06 degrees C temperature range is significantly improved with respect to previously published C. wuellerstorfi calibrations limited to the coldest part between 0 and 4 degrees C. Other benthic species (Cibicidoides kullenbergi, Globocassidulina subglobosa, Uvigerina peregrina, and Oridorsalis umbonatus) have also been studied, although these results are less conclusive.
Geochemistry Geophysics Geosystems (1525-2027) (Amer Geophysical Union), 2013-04 , Vol. 14 , N. 4 , P. 929-946

Droits : 2013. American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00181/29191/27596.pdf
DOI:10.1002/ggge.20043
http://archimer.ifremer.fr/doc/00181/29191/

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Observations of intermittent deep currents and eddies in the Gulf of Mexico
Auteur(s) : Kolodziejczyk, Nicolas Ochoa, Jose Candela, Julio Sheinbaum, Julio

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The Mw=6.3, November 21, 2004, Les Saintes earthquake (Guadeloupe): Tectonic setting, slip model and static stress changes
Auteur(s) : Feuillet, Nathalie Beauducel, F. Jacques, E. Tapponnier, P. Delouis, B. Bazin, S. Vallee, M. King, G. C. P.

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Comparison of spaceborne measurements of sea surface salinity and colored detrital matter in the Amazon plume
Auteur(s) : Fournier, Severine Chapron, Bertrand Salisbury, J. Vandemark, Douglas Reul, Nicolas

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Deep circulation in the equatorial Atlantic Ocean
Auteur(s) : Gouriou, Y Andrie, C Bourles, B Freudenthal, S Arnault, S Aman, A Eldin, G Du Penhoat, Y

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Spatial and temporal coherence between Amazon River discharge, salinity, and light absorption by colored organic carbon in western tropical Atlantic surface waters
Auteur(s) : Salisbury, J. Vandemark, D. Campbell, J. Hunt, C. Wisser, D. Reul, Nicolas Chapron, Bertrand

Éditeur(s) : Amer Geophysical Union
Résumé : The temporal evolution and spatial distribution of surface salinity and colored detrital matter (cdm) were evaluated within and adjacent to the Amazon River Plume. Study objectives were as follows: first, to document the spatial coherence between Amazon discharge, salinity, cdm, and the nature of the salinity-cdm relationship; second, to document the temporal and spatial variability of cdm along the trajectory of the low-salinity Amazon Plume, and third, to explore the departure of cdm from conservative mixing behavior along the plume trajectory into the open ocean. Time series (2003-2007) of surface salinity estimated using the Advanced Microwave Scanning Radiometer-Earth Observing System and corresponding satellite cdm absorption (acdm) data documented a plume of freshened, colored water emanating from the Amazon. Salinity and acdm were generally coherent, but there were regions in which spatial patterns of salinity and acdm did not coincide. Salinity was oppositely phased with discharge, whereas acdm was in phase but lagged discharge and typically remained high after maximum discharge. Along the river plume trajectory, acdm was inversely correlated with salinity, yet there was considerable deviation from conservative mixing behavior during all seasons. Positive anomalies in a linear relationship between salinity and acdm corresponded to areas of enhanced satellite-retrieved net primary productivity, suggesting the importance of phytoplankton biomass or its subsequent remineralization as a source of cdm. Negative anomalies tended to predominate at the distal sections of the plume trajectories, an observation consistent with the process of photo-oxidation of cdm over observed time scales of days to weeks.
Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2011-07 , Vol. 116 , N. C00H02 , P. 14 p.

Droits : 2011 American Geophysical Union. All Rights Reserved.
http://archimer.ifremer.fr/doc/00041/15218/12593.pdf
DOI:10.1029/2011JC006989
http://archimer.ifremer.fr/doc/00041/15218/

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From the western boundary currents to the Pacific Equatorial Undercurrent: Modeled pathways and water mass evolutions
Auteur(s) : Grenier, Melanie Cravatte, Sophie Blanke, Bruno Menkes, Christophe Koch-larrouy, Ariane Durand, Fabien Melet, Angelique Jeandel, Catherine

Éditeur(s) : Amer Geophysical Union
Résumé : The hydrological and geochemical properties of the waters constituting the Pacific Equatorial Undercurrent (EUC) determine the properties of the equatorial cold tongue. Understanding and quantifying the various EUC origins is therefore of prime importance. For this purpose, a high-resolution (1/4 degrees) interannual oceanic simulation was analyzed from the western tropical Pacific boundaries to 140 degrees W, using a Lagrangian framework. Waters from the Low-Latitude Western Boundary Currents (LLWBCs) transiting from Vitiaz Strait (the main contributor), from Solomon Strait, and via the Mindanao Current were identified as the principal sources to the EUC. Waters conveyed by the interior ocean off equator are negligible till 180 E. The LLWBCs' waters represent 87% of the EUC transport at 156 degrees E out of which the New Guinea Coastal Undercurrent (NGCU) is as large as 47%. The EUC meridional distribution suggests that the waters originating from Solomon Strait and Mindanao Current mostly remain in the hemisphere from which they originate. Contrastingly, Vitiaz Strait waters are found in both hemispheres. The vertical EUC distribution shows that the lower layer of the EUC is mainly composed of Vitiaz Strait waters. Finally, the source transport distributions were characterized, at their origin and within the EUC, as a function of density. These distributions showed that waters flowing through Vitiaz Strait at densities higher than those of the EUC (down to sigma(theta) = 27.2 kg m(-3)) undergo a diapycnal mixing and lighten during their journey to join the EUC. This lightening supports the suggestion that the NGCU is a major source for the EUC geochemical enrichment.
Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2011-12 , Vol. 116 , N. C12044 , P. 16 p.

Droits : 2011 by the American Geophysical Union
http://archimer.ifremer.fr/doc/00060/17105/14621.pdf
DOI:10.1029/2011JC007477
http://archimer.ifremer.fr/doc/00060/17105/

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Tectonic context of moderate to large historical earthquakes in the Lesser Antilles and mechanical coupling with volcanoes
Auteur(s) : Feuillet, Nathalie Beauducel, Francois Tapponnier, Paul

Éditeur(s) : Amer Geophysical Union
Résumé : The oblique convergence between North American and Caribbean plates is accommodated in a bookshelf faulting manner by active, oblique-normal faults in the northern part of the Lesser Antilles arc. In the last 20 years, two M > 6 earthquakes occurred along a large, arc parallel, en echelon fault system, the 16 March 1985 in Redonda and 21 November 2004 in Les Saintes. A better understanding of active faulting in this region permit us to review the location and magnitude of historical earthquakes by using a regional seismic attenuation law. Several others moderate earthquakes may have occurred along the en echelon fault system implying a strong seismic hazard along the arc. These faults control the effusion of volcanic products and some earthquakes seem to be correlated in time with volcanic unrest. Shallow earthquakes on intraplate faults induced normal stress and pressure changes around neighboring volcano and may have triggered volcanic activity. The Redonda earthquake could have initiated the 1995 eruption of Montserrat's Soufriere Hills by compressing its plumbing system. Conversely, pressure changes under the volcano increased Coulomb stress changes and brought some faults closer to failure, promoting seismicity. We also discuss the magnitude of the largest 11 January 1839 and 8 February 1843 megathrust interplate earthquakes. We calculate that they have increased the stress on some overriding intraplate faults and the extensional strain beneath several volcanoes. This may explain an increase of volcanic and seismic activity in the second half of the 19th century culminating with the devastating, 1902 Mount Pelee eruption.
Journal Of Geophysical Research-solid Earth (0148-0227) (Amer Geophysical Union), 2011-10 , Vol. 116 , N. B10308 , P. 1-26

Droits : Copyright 2011 by the American Geophysical Union
http://archimer.ifremer.fr/doc/00200/31097/29515.pdf
DOI:10.1029/2011JB008443
http://archimer.ifremer.fr/doc/00200/31097/

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Bundled turbidite deposition in the central Pandora Trough (Gulf of Papua) since Last Glacial Maximum: Linking sediment nature and accumulation to sea level fluctuations at millennial timescale
Auteur(s) : Jorry, Stephan J. Droxler, Andre W. Mallarino, Gianni Dickens, Gerald R. Bentley, Sam J. Beaufort, Luc Peterson, Larry C. Opdyke, Bradley N.

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