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/ | Partager |
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/ | Partager |
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/ | Partager |
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 Éditeur(s) : Amer Geophysical Union Résumé : The freshest surface waters in the tropical Pacific are found at its eastern boundary. Using in situ observations, we depict the quasi-permanent presence of a far eastern Pacific fresh pool with Sea Surface Salinity (SSS) lower than 33, which is confined between Panama's west coast and 85W in December and extends westward to 95W in April. Strong SSS fronts are found at the outer edge of this fresh pool. We investigate the seasonal dynamics of the fresh pool using complementary satellite wind, rain, sea level and in situ oceanic current data at the surface, along with hydrographic profiles. The fresh pool appears off Panama due to the strong summer rains associated with the northward migration of the ITCZ over Central America in June. During the second half of the year, the eastward-flowing North Equatorial Counter Current keeps it trapped to the coast and strengthens the SSS front on its western edge. During winter, as the ITCZ moves southward, the north-easterly Panama gap wind creates a south-westward jet-like current in its path with a dipole of Ekman pumping/eddies on its flanks. As a result, upwelling in the Panama Bight brings to the surface cold and salty waters which erode the fresh pool on its eastern side while both the jet current and the enhanced South Equatorial Current stretch the fresh pool westward until it nearly disappears in May. New SMOS satellite SSS data proves able to capture the main seasonal features of the fresh pool and monitor its spatial extent. Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2012-04 , Vol. 117 , P. - Droits : 2012 AGU http://archimer.ifremer.fr/doc/00072/18311/16581.pdf DOI:10.1029/2011JC007802 http://archimer.ifremer.fr/doc/00072/18311/ | Partager |
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. Éditeur(s) : Amer Geophysical Union Résumé : New high-resolution multichannel seismic data (GWADASEIS-2009 and JC45/46-2010 cruises; 72 and 60 channels, respectively) combined with previous data (AGUADOMAR-1999 and CARAVAL-2002; 6 and 24 channels, respectively) allow a detailed investigation of mass-wasting processes around the volcanic island of Montserrat in the Lesser Antilles. Seven submarine deposits have sources on the flanks of Montserrat, while three are related to the nearby Kahouanne submarine volcanoes. The most voluminous deposit (similar to 20 km(3)) within the Bouillante-Montserrat half-graben has not been described previously and is probably related to a flank instability of the Centre Hills Volcano on Montserrat, while other events are related to the younger South Soufriere Hills-Soufriere Hills volcanic complex. All deposits are located to the south or southeast of the island in an area delimited by faults of the Bouillante-Montserrat half-graben. They cover a large part of the southeast quarter of the surrounding seafloor (similar to 520 km(2)), with a total volume of similar to 40 km(3). Our observations suggest that the Bouillante-Montserrat half-graben exerts a control on the extent and propagation of the most voluminous deposits. We propose an interpretation for mass-wasting processes around Montserrat similar to what has happened for the southern islands of the Lesser Antilles. Geochemistry Geophysics Geosystems (1525-2027) (Amer Geophysical Union), 2011-05 , Vol. 12 , N. 5 , P. Q05006 Droits : Copyright 2011 by the American Geophysical Union http://archimer.ifremer.fr/doc/00200/31100/29510.pdf DOI:10.1029/2010GC003451 http://archimer.ifremer.fr/doc/00200/31100/ | Partager |
Hypercanes: A possible link in global extinction scenarios Auteur(s) : Emanuel, Kerry A Speer, Kevin Rotunno, Richard Srivastava, Ramesh Molina, Mario Éditeur(s) : Amer Geophysical Union Résumé : Bolide impacts and large-scale volcanic eruptions have been proposed as possible causes of the massive extinction of life that has occurred episodically in Earth's history. In spite of the catastrophic disruption of the local environment that accompanies bolide impacts and volcanic eruptions, it has been difficult to explain why these events sometimes lead to global extinction of species. We propose that, in some cases, the missing link may be provided by hypercanes, runaway hurricanes that are capable of injecting massive amounts of water and aerosols into the middle and upper stratosphere, where they may have profound effects on atmospheric chemistry and radiative transfer. Hypercanes are theorized to occur when the sea surface temperature exceeds a critical threshold, which may occur when sea water is locally heated by bolide impact, shallow-sea volcanism, or possibly, by overturning of superheated brine pools formed by underwater volcanic activity. Simulations using a convection-resolving nonhydrostatic, axisymmetric numerical model show that hypercanes can indeed develop when the sea surface temperature is high, and that they inject large amounts of mass into the stratosphere. Journal Of Geophysical Research-atmospheres (2169-897X) (Amer Geophysical Union), 1995-07 , Vol. 100 , N. D7 , P. 13755-13765 Droits : 1995 by the American Geophysical Union. http://archimer.ifremer.fr/doc/00258/36966/35611.pdf DOI:10.1029/95JD01368 http://archimer.ifremer.fr/doc/00258/36966/ | Partager |
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/ | Partager |
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. Éditeur(s) : Amer Geophysical Union Résumé : The origin of the Algerian margin remains one of the key questions still discussed in the Western Mediterranean sea, due to the imprecise nature and kinematics of the associated basin during the Neogene. For the first time, the deep structure of the Maghrebian margin was explored during the SPIRAL seismic survey. In this work, we present a N-S transect off Tipaza (west of Algiers), a place where the margin broadens due to a topographic high (Khayr-al-Din Bank). New deep penetration seismic profiles allow us to image the sedimentary sequence in the Algerian basin and the crustal structure at the continent-ocean boundary. Modeling of the wide-angle data shows thinning of the basement, from more than 15km in the continental upper margin to only 5–6km of oceanic-type basement in the Algerian basin, and reveals a very narrow or absent transitional zone. Analysis of the deep structure of the margin indicates features inherited from its complex evolution: (1) an oceanic-type crust in the deep basin, (2) similarities with margins formed in a transform-type setting, (3) a progressive deepening of the whole sedimentary cover, and the thickening of the Plio-Quaternary sediments at the margin foot, coeval with (4) a downward flexure of the basement in the basin. These features argue for a multiphased evolution of the margin, including (1) an early stage of rifting and/or spreading, (2) a late transcurrent episode related to the westward migration of the Alboran domain, and (3) a diffuse Plio-Quaternary compressional reactivation of the margin. Journal Of Geophysical Research-solid Earth (0148-0027) (Amer Geophysical Union), 2013-08 , Vol. 118 , N. 8 , P. 3899-3916 Droits : 2013. American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00152/26333/24412.pdf DOI:10.1002/jgrb.50318 http://archimer.ifremer.fr/doc/00152/26333/ | Partager |
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 Éditeur(s) : Amer Geophysical Union Résumé : In this study, we undertook a reconnaissance study of sediments provenance in the Gulf of Lions focusing over the last 16 ka. We used geochemical and isotopic tracers to determine the source of sediments and give insight into the weathering conditions prevailing. Sediments samples were selected both onshore and offshore from the western, eastern, and central part of the Gulf of Lions. We analyzed bulk sediments, coarse and fine silt, and clay fractions. Elemental and Nd isotope compositions appeared to differ from one grain size fraction to another one. These are interpreted in terms of zircon addition in the coarse silt fraction for the elemental concentrations and variable sources influences for the Nd isotope compositions. Our results indicate that sediments in the Gulf of Lions mainly originated from the Rhone River watershed although a contribution of Saharan dust is seen in one sample. Influence of Pyrenean small rivers is minor in these samples. Some Sr isotope compositions shifts are interpreted as reflecting variable amounts of chemical weathering that are consistent with published paleoclimatic reconstructions. Geochemistry Geophysics Geosystems (1525-2027) (Amer Geophysical Union), 2011-08 , Vol. 12 , N. Q08006 , P. 20 p. Droits : 2011 by the American Geophysical Union http://archimer.ifremer.fr/doc/00043/15376/12734.pdf DOI:10.1029/2011GC003523 http://archimer.ifremer.fr/doc/00043/15376/ | Partager |
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. Éditeur(s) : Amer Geophysical Union Résumé : Sea surface salinity (SSS) measured from space by the Soil Moisture and Ocean Salinity (SMOS) mission is validated in the subtropical North Atlantic Ocean. 39 transects of ships of opportunity equipped with thermosalinographs (TSG) crossed that region from 2010 to 2012, providing a large database of ground truth SSS. SMOS SSS is also compared to Aquarius SSS. Large seasonal biases remain in SMOS and Aquarius SSS. In order to look at the capability of satellite SSS to monitor spatial variability, especially at scales less than 300 km (not monitored with the Argo network), we first apply a monthly bias correction derived from satellite SSS and In Situ Analysis System (ISAS) SSS differences averaged over the studied region. Ship SSS averaged over 25 km is compared with satellite and ISAS SSS. Similar statistics are obtained for SMOS, Aquarius and ISAS products (root mean square error of about 0.15 and global correlation coefficient r of about 0.92). However, in the above statistics, SSS varies due to both large scale and mesoscale (here, for scales around 100 km) variability. In order to focus on mesoscale variability, we consider SSS anomalies with respect to a monthly climatology. SMOS SSS and Aquarius SSS anomalies are more significantly correlated (r > 0.5) to TSG SSS anomaly than ISAS. We show the effective gain of resolution and coverage provided by the satellite products over the interpolated in situ data. We also show the advantage of SMOS (r=0.57) over Aquarius (r=0.52) to reproduce SSS mesoscale features. Journal Of Geophysical Research-oceans (0148-0027) (Amer Geophysical Union), 2014-12 , Vol. 119 , N. 12 , P. 8878-8896 Droits : 2014. American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00210/32150/34082.pdf DOI:10.1002/2013JC009610 http://archimer.ifremer.fr/doc/00210/32150/ | Partager |
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. Éditeur(s) : Amer Geophysical Union Résumé : At its seasonal peak the Amazon/Orinoco plume covers a region of 10^6 km2 in the western tropical Atlantic with more than 1m of extra freshwater, creating a near-surface barrier layer (BL) that inhibits mixing and warms the sea surface temperature (SST) to >29oC. Here new sea surface salinity (SSS) observations from the Aquarius/SACD and SMOS satellites help elucidate the ocean response to hurricane Katia, which crossed the plume in early fall, 2011. Its passage left a 1.5psu high haline wake covering >10^5 km2 (in its impact on density, the equivalent of a 3.5oC cooling) due to mixing of the shallow BL. Destruction of this BL apparently decreased SST cooling in the plume, and thus preserved higher SST and evaporation than outside. Combined with SST, the new satellite SSS data provide a new and better tool to monitor the plume extent and quantify tropical cyclone upper ocean responses with important implications for forecasting. Geophysical Research Letters (0094-8276) (Amer Geophysical Union), 2012-10 , Vol. 39 , N. L20603 , P. 1-8 Droits : 2012. American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00094/20540/18943.pdf DOI:10.1029/2012GL053335 http://archimer.ifremer.fr/doc/00094/20540/ | Partager |
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/ | Partager |
Observations of intermittent deep currents and eddies in the Gulf of Mexico Auteur(s) : Kolodziejczyk, Nicolas Ochoa, Jose Candela, Julio Sheinbaum, Julio Éditeur(s) : Amer Geophysical Union Résumé : Intense currents having speeds between 10 and 40 cm.s(-1) from 1000 m below the surface to the bottom have been measured in the Loop Current (LC) region and in the Western Gulf of Mexico (WGM). The observations come from moored current meters sampling from the near-surface to the bottom at 3300-3500 m and from August 2008 to August 2010. Ten intermittent intensified currents are documented. These events last 10 to 30 days and take place in the region just between the surface-intensified anticyclonic-cyclonic features, as deduced from altimetry and measured currents. In the WGM, they occur between the cores of anticyclone-cyclone pairs. In the Eastern Gulf of Mexico (EGM), they occur in the Loop Current edge between its anticyclonic circulation and a neighboring cyclone. During each event, the analysis shows an increase in the barotropic contribution to the current. In the Loop Current region, these events are often associated with intensification of cyclonic vorticity in the deep layer. Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2012-09-14 , Vol. 117 , N. C09014 , P. 20p. Droits : 2012. American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00099/20994/18626.pdf DOI:10.1029/2012JC007890 http://archimer.ifremer.fr/doc/00099/20994/ | Partager |
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. Éditeur(s) : Amer Geophysical Union Résumé : On November 21, 2004, a magnitude 6.3 earthquake occurred offshore, 10 km south of Les Saintes archipelago in Guadeloupe (French West Indies). There were more than 30000 aftershocks recorded in the following two years, most of them at shallow depth near the islands of the archipelago. The main shock and its main aftershock of February 14, 2005 (M-w = 5.8) ruptured a NE-dipping normal fault (Roseau fault), mapped and identified as active from high-resolution bathymetric data a few years before. This fault belongs to an arc-parallel en echelon fault system that follows the inner edge of the northern part of the Lesser Antilles arc, accommodating the sinistral component of oblique convergence between the North American and Caribbean plates. The distribution of aftershocks and damage (destruction and landslides) are consistent with the main fault plane location and attitude. The slip model of the main shock, obtained by inverting jointly global broadband and local strong motion records, is characterized by two main slip zones located 5 to 10 km to the SE and NW of the hypocenter. The main shock is shown to have increased the Coulomb stress at the tips of the ruptured plane by more than 4 bars where most of the aftershocks occurred, implying that failures on fault system were mainly promoted by static stress changes. The earthquake also had an effect on volcanic activity since the Boiling Lake in Dominica drained twice, probably as a result of the extensional strain induced by the earthquake and its main aftershock. Journal Of Geophysical Research-solid Earth (0148-0227) (Amer Geophysical Union), 2011-10 , Vol. 116 , N. B10301 , P. 1-25 Droits : Copyright 2011 by the American Geophysical Union. http://archimer.ifremer.fr/doc/00200/31099/29511.pdf DOI:10.1029/2011JB008310 http://archimer.ifremer.fr/doc/00200/31099/ | Partager |
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 Éditeur(s) : Amer Geophysical Union Résumé : Large rivers are key hydrologic components in oceanography, particularly regarding air-sea and land-sea exchanges and biogeochemistry. We enter now in a new era of Sea Surface Salinity (SSS) observing system from Space with the recent launches of the ESA Soil Moisture and Ocean Salinity (SMOS) and the NASA Aquarius/Sac-D missions. With these new sensors, we are now in an excellent position to revisit SSS and ocean color investigations in the tropical northwest Atlantic using multi-year remote sensing time series and concurrent in situ observations. The Amazon is the world's largest river in terms of discharge. In its plume, SSS and upper water column optical properties such as the absorption coefficient of colored detrital matter (acdm) are strongly negatively correlated (<-0.7). Local quasi-linear relationships between SSS and acdm are derived for these plume waters over the period of 2010-2013 using new spaceborne SSS and ocean color measurements. Results allow unprecedented spatial and temporal resolution of this coupling. These relationships are then used to estimate SSS in the Amazon plume based on ocean color satellite data. This new product is validated against SMOS and in situ data and compared with previously developed SSS retrieval models. We demonstrate the potential to estimate tropical Atlantic SSS for the extended period from 1998 to 2010, prior to spaceborne SSS data collection. Journal Of Geophysical Research-oceans (0148-0227) (Amer Geophysical Union), 2015-05 , Vol. 120 , N. 5 , P. 3177-3192 Droits : 2015. American Geophysical Union. All Rights Reserved. http://archimer.ifremer.fr/doc/00255/36610/35742.pdf DOI:10.1002/2014JC010109 http://archimer.ifremer.fr/doc/00255/36610/ | Partager Voir aussi Amazon-Orinoco river plume SMOS SSS conservative mixing ocean color salinity satellite oceanography Télécharger |
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 Éditeur(s) : Amer Geophysical Union Résumé : In the Atlantic Ocean, the northward export of warm surface water is compensated by a southward flow of cold North Atlantic Deep Water (NADW). The NADW is transported southward along the American continental margin within the Deep Western Boundary Current (DWBC). Some tracer and float observations have shown that part of the DWBC water flows eastward along the equator. Here we present three meridional velocity sections which give an instantaneous image of the top-to-bottom zonal circulation along the equatorial Atlantic. They reveal the presence of Equatorial Deep Jets (EDJs) between 1 degrees 30'N and 1 degrees 30'S, alternating eastward-westward currents with short vertical scale, surrounded by columns of eastward currents (the Extra Equatorial Jets or EEJs) at 2 degreesN and 2 degreesS. In addition to direct velocity measurements, tracer distributions give indications of water-mass feeding of the EDJs and EEJs by the DWBC. Geophysical Research Letters (0094-8276) (Amer Geophysical Union), 2001-03 , Vol. 28 , N. 5 , P. 819-822 Droits : 2001 AGU http://archimer.ifremer.fr/doc/00000/10369/9567.pdf http://archimer.ifremer.fr/doc/00000/10369/ | Partager |
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/ | Partager |
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/ | Partager |
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/ | Partager |
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. Éditeur(s) : Amer Geophysical Union Résumé : Since Last Glacial Maximum (23-19 ka), Earth climate warming and deglaciation occurred in two major steps (Bolling-Allerod and Preboreal), interrupted by a short cooling interval referred to as the Younger Dryas (12.5-11.5 ka B. P.). In this study, three cores (MV-33, MV-66, and MD-40) collected in the central part of Pandora Trough (Gulf of Papua) have been analyzed, and they reveal a detailed sedimentary pattern at millennial timescale. Siliciclastic turbidites disappeared during the Bolling-Allerod and Preboreal intervals to systematically reoccur during the Younger Dryas interval. Subsequent to the final disappearance of the siliciclastic turbidites a calciturbidite occurred during meltwater pulse 1B. The Holocene interval was characterized by a lack of siliciclastic turbidites, relatively high carbonate content, and fine bank-derived aragonitic sediment. The observed millennial timescale sedimentary variability can be explained by sea level fluctuations. During the Last Glacial Maximum, siliciclastic turbidites were numerous when the lowstand coastal system was located along the modern shelf edge. Although they did not occur during the intervals of maximum flooding of the shelf (during meltwater pulses 1A and 1B), siliciclastic turbidites reappear briefly during the Younger Dryas, an interval when sea level rise slowed, stopped, or perhaps even fell. The timing of the calciturbidite coincides with the first reflooding of Eastern Fields Reef, an atoll that remained exposed for most of the glacial stages. Journal Of Geophysical Research-earth Surface (0148-0227) (Amer Geophysical Union), 2008-03-29 , Vol. 113 , N. F01S19 , P. 1-15 Droits : Copyright 2008 by the American Geophysical Union. http://archimer.ifremer.fr/doc/00079/19014/16592.pdf DOI:10.1029/2006JF000649 http://archimer.ifremer.fr/doc/00079/19014/ | Partager |