Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Three-dimensional P-wave velocity structure of the mantle beneath the South Pacific Superswell is determined through passive broadband seismic experiments on the ocean floor and islands between 2003 and 2005. We collected approximately 1500 relative times of long-period teleseismic P-waves by using a waveform cross-correlation. We analyzed this data set with relative time tomography to depths of 2000 km. The resultant structure shows lateral heterogeneity of approximately +/- 2%, in which a distinct low velocity region is found beneath the center of the Superswell at a depth of 1600 km. At 1200km depth, an elongated low velocity region is found beneath the Society to Pitcairn hotspots. At 800 km depth, two linear low velocity regions are located beneath Tuamotu and Austral islands. Isolated low velocity regions are identified beneath the Society, Marquesas, and Macdonald hotspots at 400 km depth. Our new tomographic images reveal that the large low velocity region rooted in the deep lower mantle is split into two sheets at 1200 km depth and these terminate at approximately 800 km depth. This feature appears to be consistent with the characteristics of a thermo-chemical pile or dome.
ISSN: 0031-9201

hal-00413036
https://hal.archives-ouvertes.fr/hal-00413036
https://hal.archives-ouvertes.fr/hal-00413036/document
https://hal.archives-ouvertes.fr/hal-00413036/file/Tanaka_tomo_PLUME_PEPI2009_hal.pdf
DOI : 10.1016/j.pepi.2008.10.016

Éditeur(s) : American Geophysical Union
Résumé : [1] Extreme weather events such as tropical cyclones are difficult to observe with conventional means. Satellite-based observations provide essential measurements of key parameters governing tropical cyclones. They are critical for short-term forecasting. Radiometers onboard the Defense Meteorological Satellite Program satellite series, WindSat and Tropical Rainfall Measuring Mission satellites, scatterometers onboard the ERS, ADEOS, and QuikScat satellites offer unprecedented synoptic observations of surface wind and atmospheric liquid water content, revealing the storm structures with good accuracy. However, satellite estimates do not provide direct measurements of geophysical parameters and can suffer from limitations linked to the sensors characteristics, such as the signal wavelength and polarization or the measurement incidence angle. For example, measurements at Ku band are strongly affected by rain. Still, each observing system can offer specific information that can be combined with the others. In particular, we highlight the capabilities of dual-frequency altimeter to provide very high resolution measurements of rain rate, surface wind speed, and wave characteristics. A method is proposed to obtain continuous along-track 5 km resolution measurements of these parameters in the tropical cyclone Isabel. The results shows that dual-frequency altimeters can provide useful information to complement and validate the operational fields provided by the atmospheric numerical models and by NOAA observing systems.
Journal of Geophysical Union - Research C - Oceans (0148-0227) (American Geophysical Union), 2006 , Vol. 111 , N. C1 , P. NIL_38-NIL_50

Droits : 2006 American Geophysical Union
http://archimer.ifremer.fr/doc/2006/publication-1033.pdf
DOI:10.1029/2005JC003068
http://archimer.ifremer.fr/doc/00000/1033/

Éditeur(s) : HAL CCSD
Résumé : International audience
This work aims to better understand the physical processes governing the wave propagation in a vertically shearedcurrent and the resulting nearshore circulation patterns. It is based on a high resolution hydro-morphodynamic fieldcampaign, ROUSTY2014, collecting a comprehensive hydro-morphodynamical dataset during a full winter season.The overall analysis highlights three main circulation patterns, largely controled by the bathymetric features and byco-working or competing wind and waves forcings. Regarding the vertical structuration of the circulation, most of fieldobservations shown seaward directed circulation with onshore component close to the air/sea surface whose intensityvaries according to incoming wave conditions. Forth, vertical shear increase when breaking happen close to sensorlocation and orientation of mean circulation depend on wind direction.
35th International Conference on Coastal Engineering
Antalya, Turkey

hal-01426582
https://hal.archives-ouvertes.fr/hal-01426582

Éditeur(s) : HAL CCSD American Geophysical Union (AGU)
Résumé : Mantle xenoliths in Pliocene alkali basalts of the eastern Betics (SE Iberia, Spain) are spinel ± plagioclase lherzolite, with minor harzburgite and wehrlite, displaying porphyroclastic or equigranular textures. Equigranular peridotites have olivine crystal preferred orientation (CPO) patterns similar to those of porphyroclastic xenoliths but slightly more dispersed. Olivine CPO shows [100]-fiber patterns characterized by strong alignment of [100]-axes subparallel to the stretching lineation and a girdle distribution of [010]-axes normal to it. This pattern is consistent with simple shear or transtensional deformation accommodated by dislocation creep. One xenolith provides evidence for synkinematic reactive percolation of subduction-related Si-rich melts/fluids that resulted in oriented crystallization of orthopyroxene. Despite a seemingly undeformed microstructure, the CPO in orthopyroxenite veins in composite xenoliths is identical to those of pyroxenes in the host peridotite, suggesting late-kinematic crystallization. Based on these observations, we propose that the annealing producing the equigranular microstructures was triggered by melt percolation in the shallow subcontinental lithospheric mantle coeval to the late Neogene formation of veins in composite xenoliths. Calculated seismic properties are characterized by fast propagation of P waves and polarization of fast S waves parallel to olivine [100]-axis (stretching lineation). These data are compatible with present-day seismic anisotropy observations in SE Iberia if the foliations in the lithospheric mantle are steeply dipping and lineations are subhorizontal with ENE strike, implying dominantly horizontal mantle flow in the ENE-WSW direction within vertical planes, that is, subparallel to the paleo-Iberian margin. The measured anisotropy could thus reflect a lithospheric fabric due to strike-slip deformation in the late Miocene in the context of WSW tearing of the subducted south Iberian margin lithosphere.
ISSN: 0278-7407

Droits : info:eu-repo/semantics/OpenAccess
hal-01685809
https://hal.archives-ouvertes.fr/hal-01685809
https://hal.archives-ouvertes.fr/hal-01685809/document
https://hal.archives-ouvertes.fr/hal-01685809/file/Hidas_et_al-2016-Tectonics.pdf
DOI : 10.1002/2016TC004165

Éditeur(s) : HAL CCSD Editions Paralia CFL
Résumé : The wave-dominated beach barrier of Villeneuve-Lès-Maguelone extends between Palavas and Frontignan (Gul f of Lions, northernmost Me diterranean Sea), along a slightly natural sandy protected area char acterized by typical and well-expressed morphologies. In the nearshore, the sea bottom shows one or two approximately rectilinear sand bars. In 2010-2011, we pe rformed a 6 month-long monitoring (autumn 2010/late spring 2011) of a 500 meter-long se gment along this sand barrier. We used RTK D-GPS offering centimeter resolution to acquire sets of elevation data on the beach and the upper shoreface. The study is innovative because a full morphologic monitoring was performed each time the wave/ wind conditions changed significantly. These changes were tracked in real-time thanks to a set of hydrodynamic equipments deployed at sea, including well-known DREAL buoys. We identify from well- documented data: (1) a beach reconstruction cycle at the shorelin e after a moderate storm event (wave height at 3-4 m) and (2) how a sand bar in the nearshore migrates to the shoreline and drives the shoreline shift.
ISSN: 1760-8716

hal-00854402
https://hal.archives-ouvertes.fr/hal-00854402
DOI : 10.5150/jngcgc.2012.023-C

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
We report on microstructural data obtained by optical microscopy and transmission electron microscopy concerning the crystallographic relationships of serpentine minerals with their host olivine in two contrasting situations. In the first case, mesh-textured lizardite (liz) is developed in a standard 60% serpentinized oceanic harzburgite from the Oman ophiolite where olivine converts to columnar lizardite. The joined columns are perpendicular to the basal plane (001)(liz), corresponding to the pseudofibres observed optically. The plane (001)(liz) is locally parallel to the narrow boundary ol-liz; thus column orientations register the interface of serpentinization. The ol-liz relationships are not strictly topotactic, but reflect preferred cracking orientations in olivine, parallel to (010)(ol). In the second case, antigorite (atg) develops in a rare sample of antigorite schist in a kimberlite from Moses Rock (Colorado Plateau), representative of a suprasubduction-zone mantle wedge. High-resolution transmission electron microscopy (HRTEM) images along [010](atg) show domains of very regular modulation with a 43 center dot 5 A wavelength (m = 17, where m is the number of silicate tetrahedra along the wave), with few defects, indicative of HP-HT antigorite, and also heavily kinked regions as fingerprints of strong tectonic shear. TEM imaging and electron diffraction patterns reveal two topotactic relationships between antigorite and olivine: [100](atg)//[010](ol) and < 100 >(atg)//< 100 >(ol); the planes in contact are (001)(atg)//(100)(ol) and (001)(atg)//(010)(ol), respectively. The [010](atg)//[001](ol) and antigorite lamellae are parallel to the forsterite b-axis. In both cases, the topography of olivine-serpentine interfaces is controlled by open fluid pathways along microcracks oriented according to the anisotropy of the olivine aggregate. In the cases studied, the serpentine aggregate exhibits a preferred orientation inherited from that of the peridotite. These results have some relevance to the seismic anisotropy of serpentinized mantle. Anisotropy of propagation of seismic waves as a result of the olivine fabric is maintained and reinforced with the development of lizardite. Conversely, the development of antigorite produces a trench-parallel fast S-wave polarization and an anisotropy that is lowered at low degrees of serpentinization and then increased with increasing serpentinization.
ISSN: 0022-3530

hal-00456061
https://hal.archives-ouvertes.fr/hal-00456061
DOI : 10.1093/petrology/egp049

Éditeur(s) : HAL CCSD Institute of Electrical and Electronics Engineers
Résumé : International audience
An effective solution for increasing the exposure uniformity and efficiency of biological samples in in vitro bioelectromagnetic experiments at 60 GHz is proposed by introducing a novel choke ring antenna (CRA). The CRA is optimized to provide a uniform exposure of samples, whose dimensions are equivalent to those of a standard 35-mm Petri dish, positioned close to the antenna aperture, i.e., 10-20 wavelengths. The antenna prototype is fabricated in metallized foam. The realized exposure efficiency of the sample exceeds 55% (if estimated for an exposure uniformity better than - 0.5 dB). To validate the numerical results, the field intensity profiles on the surface of a high-water-content phantom have been experimentally obtained using a high-resolution infrared camera. Compared to the standard open-ended waveguide and horn antennas, typically used for millimeter-wave dosimetry, a twofold advantage of the proposed CRA is demonstrated, namely, the improvement of the exposure efficiency by a factor of 1.5 to 2 with a simultaneous reduction of the exposure distance by a factor of 8-2, respectively, depending on the type of the reference antenna. These advantages make the proposed CRA an excellent candidate for 60-GHz short-range exposure systems for in vitro bioelectromagnetic studies.
ISSN: 0018-9480

hal-00874349
https://hal.archives-ouvertes.fr/hal-00874349
DOI : 10.1109/TMTT.2013.2255619

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
This work presents seismic properties derived from a detailed microstructural study of supra-subduction mantle xenoliths extracted by the active Avacha volcano in the southern Kamchatka arc. These peridotites underwent low-stress deformation and syn- to late-kinematic reactive percolation of hydrous melts or fluids leading to local orthopyroxene enrichment and dispersion of the olivine CPO in the shallow mantle wedge. All samples show an axial [ 100] olivine CPO implying fast S-wave polarization parallel to the flow direction in the mantle. Orthopyroxene-enrichment by reactive fluids/melts percolation lowers the Vp/Vs ratio, but cannot explain the Vp/Vs ratios <1.7 mapped in the Japan and Andes forearc mantle. These low Vp/Vs ratios may however be explained by considering the intrinsic anisotropy of the peridotites.
ISSN: 0094-8276

hal-00512636
https://hal.archives-ouvertes.fr/hal-00512636
DOI : 10.1029/2010GL043450

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
We predict the IR-TO, IR-LO and Raman modes (wave numbers and intensities) of magnesite (MgCO3) up to 50 GPa, at T = 0 K, using the density-functional perturbation theory up to a third order perturbation, under the harmonic assumption. The predicted IR-TO and Raman mode wave numbers, the mode Grüneisen parameters and the Davydov splittings are systematically compared with experimental data for all modes up to the pressures of 10-30 GPa and for some modes up to 50 GPa. Existing experiments allow extending this comparison only to IR-LO wave numbers of the E u (ν3) asymmetric-stretch mode, confirming the odd experimental behavior of this mode at very high pressures. Predicted IR-TO, IR-LO and Raman intensities up to 50 GPa are just tabulated, but data are missing for their comparison with precise experiments. However, the generally good agreement observed between numerical results and experimental data, when their comparison is possible, suggests that first-principles methods are a major help to predict the entire spectrum up to very high pressures.
ISSN: 0342-1791

hal-00527834
https://hal.archives-ouvertes.fr/hal-00527834
DOI : 10.1007/s00269-010-0395-y

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We investigate upper mantle anisotropy beneath the Pyrenean range along three N-S profiles across the mountain belt. The results of a first profile that operated in 1993 in the central part of the belt have been presented elsewhere. We present the results of two other profiles that ran in 1995-1996 and 1996-1997 in the eastern and western part of the belt, respectively and propose an interpretation of the whole results. Teleseismic shear waves (SKS, SKKS, and PKS) are used to determine splitting parameters: the fast polarization direction φ and the delay time δt. Teleseismic shear wave splitting in the eastern Pyrenees displays homogeneous φ values trending N100°E and δt values in the range 1.1 to 1.5 s. A station located in the southern Massif Central, 100 km north of the range, is characterized by different splitting parameters (φ = N70°E, δt = 0.7 s). In the western part of the belt, anisotropy parameters are similar across the whole belt (φ = N110°E and δt = 1.3 to 1.5 s). Most of the measured delay times, including those obtained in the central part of the range, are above the global average of the SKS splitting (around 1 s). At the belt scale, φ is generally poorly correlated with recent estimations of the absolute plate motion, which predicts a fast direction ranging between N50°E and N80°E. Instead, the orientation of φ (N100°E) is parallel to the trend of the Pyrenean belt but also to Hercynian preexisting structures. This parallelism supports an anisotropy primarily related to frozen or active lithospheric structures. We show that a signature related to the Pyrenean orogeny is likely for the stations located in the internal domains of the belt. By contrast, the anisotropy measured at the stations located on the external parts of the belt could reflect a pre-Pyrenean (Hercynian) deformation. We suggest that a late Hercynian strike-slip deformation is responsible for this frozen upper mantle anisotropy and that the Pyrenean tectonic fabric developped parallel to this preexisting fabric. Finally, no particularly strong splitting is related to the North Pyrenean Fault, commonly believed to represent the plate boundary between Iberia and Eurasia.
ISSN: 2169-9313

hal-01388841
http://hal.univ-reunion.fr/hal-01388841
http://hal.univ-reunion.fr/hal-01388841/document
http://hal.univ-reunion.fr/hal-01388841/file/Barruol_Aniso_Pyr_JGR1998.pdf
DOI : 10.1029/98JB02790

Éditeur(s) : Interciencia
Résumé : Zooplankton abundance, biomass and composition were evaluated in various temporal scales in a seasonal coastal upwelling system at Margarita Island, Venezuela. Scales of temporal variation include weeks, months and seasons (relaxation, upwelling and transition). Seasons were delimitated by upwelling index and sea temperature. The sampling period comprise Sept/2002 - July/2003. Zooplankton samplings were made by horizontal trawls (1-10m depth), using 200,mu m nets, 2-6km from the coastal margin. Total abundance show important variation at week scales, with different patterns between locations, while seasonal differences of abundance are marginal. Biomass only shows seasonal variation due significant reduction in the transition season. Zooplankton assemblages show changes at scale of weeks, with different local patterns, and seasonal changes. Changes in assemblage between the relaxation and upwelling seasons include reduction (during upwelling) of abundance in copepods, cladocerans, salpidae, chaetognates, fish and crustacea larvae. Except by cirripedia larvae, those were important in the upwelling assemblages. Transition shows high variation, with reduction of biomass and assemblage composition similar to upwelling, except by an isolated event. Small scale variation in the zooplankton could be related to physical processes at small scales, eg. turbulence, local circulation, small eddies and filaments, and biological response. Additional sources of nutrient input, eg. riverine input and internal waves, could support local plankton productivity and abundance during relaxation. Detection of high variation in zooplankton abundance and composition at small scales, with local interaction, bring a new light over zooplankton estimation in time series in this system.
La abundancia, la biomasa y la composición del zooplancton costero fueron analizadas a varias escalas temporales en un área afectada por surgencia costera estacional (Isla de Margarita, Venezuela); considerando para ello escalas de semanas, meses y periodos, así como la variación local. La estimación del zooplancton fue realizada a partir de arrastres horizontales (1-10m de profundidad) utilizando redes de 200μ entre 2 y 6 km de la línea de costa, entre set/2002 y jul/2003. La abundancia total presentó alta variabilidad a escala de semanas, con patrones diferentes entre localidades, mientras que la diferencia entre periodos es marginal. La biomasa únicamente mostró variación a escala de periodos por una disminución durante el periodo de transición. La composición presentó fluctuaciones a escalas temporales pequeñas, con patrones de variación diferentes localmente, así como a escala de periodos. Los cambios en composición entre el periodo de relajación y el de surgencia incluyen disminución en la abundancia de copépodos, cladóceros, salpas, quetognatos, larvas de peces y crustáceos; excepto por las larvas de cirrípedos que forman un componente importante durante la surgencia. Se postula que procesos físicos a pequeña escala, como la turbulencia, la circulación local o la formación de pequeños giros o filamentos, y los procesos biológicos, condicionan esta elevada variabilidad a escalas pequeñas. La existencia de fuentes de enriquecimiento adicionales como aportes de ríos y ondas internas pudiera condicionar la presencia de elevada abundancia y biomasa, en especial durante periodos de relajación. Los cambios en composición resaltan la importancia del aporte de merozooplancton costero. Palabras clave / Biomasa / Escalas Temporales / Surgencia / Venezuela / Zooplancton Costero /
Interciencia (0378-1844) (Interciencia), 2014-02 , Vol. 39 , N. 2 , P. 122-128

Droits : info:eu-repo/semantics/openAccess
http://archimer.ifremer.fr/doc/00187/29851/28297.pdf
http://archimer.ifremer.fr/doc/00187/29851/

Éditeur(s) : HAL CCSD Seismological Society of America
Résumé : Shear-wave splitting measurements are widely used to analyze orientations of anisotropy. We compare two different shear-wave splitting techniques, which are generally assumed to give similar results. Using a synthetic test, which covers the whole backazimuthal range, we find characteristic differences, however, in fast-axis and delay-time estimates near Null directions between the rotation correlation and the minimum energy method. We show how this difference can be used to identify Null measurements and to determine the quality of the result. This technique is then applied to teleseismic events recorded at station LVZ in northern Scandinavia, for which our method constrains the fast-axis azimuth to be 15° and the delay time 1.1 sec.
ISSN: 0037-1106

hal-00404493
https://hal.archives-ouvertes.fr/hal-00404493
DOI : 10.1785/0120060190

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We present a graphical user interface to facilitate the processing of teleseismic shear-wave splitting observations. In contrast to a fully automated technique, we present a manual, per-event approach that maintains user control during the sequence of processing. The SplitLab environment is intended to undertake the repetitive processing steps while enabling the user to focus on quality control and eventually the interpretation of the results. Pre-processing modules of SplitLab create a database of events and link the corresponding seismogram files. The seismogram viewer tool uses this database to perform the measurement interactively. Post-processing of the combined results of such a project includes a viewer and export option. Our emphasis lies in the application to teleseismic shear-wave splitting analysis, but our code can be extended easily for other purposes. SplitLab can be downloaded at http://www.gm.univ-montp2.fr/splitting/.
ISSN: 0098-3004

hal-00412372
https://hal.archives-ouvertes.fr/hal-00412372
https://hal.archives-ouvertes.fr/hal-00412372/document
https://hal.archives-ouvertes.fr/hal-00412372/file/Wuestefeld_Splitlab_CompGeosc2008_hal.pdf
DOI : 10.1016/j.cageo.2007.08.002

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We report measurements of long-period P wave polarization (P pol) in Australia and Tahiti made by combining modeling of the polarization deviation and harmonic analysis. The analysis of the deviation of the horizontal polarization of the P wave as a function of event back azimuth may be used to obtain information about (1) sensor misorientation, (2) dipping discontinuities, (3) seismic anisotropy, and (4) velocity heterogeneities beneath a seismic station. The results from harmonic analysis and a grid search using Snell's law suggest the presence of a dipping seismic discontinuity beneath stations CTAO and CAN in Australia. These results are consistent with published receiver function studies for these stations. The P pol fast axis orientation is close to the N–S absolute plate motion direction at station TAU (Tasmania), which may be due to plate-motion-driven alignment of olivine crystals in the asthenosphere. Interestingly, measurements of SKS splitting at Tahiti (French Polynesia) show an apparent isotropy, whereas an inversion of P pol observations at PPTL seismic station located in Tahiti suggests the presence of two anisotropic layers. The fast axis azimuth is oriented E–W in the upper layer, and it is close to the NW–SE orientation in the lower layer. Since P pol orientations are used for real-time earthquake locations, especially in poorly instrumented areas such as the South Pacific, we show that the bias from anisotropy and sensor misorientation determined here can be corrected to improve the location accuracy, which yields fundamental data for rapid location necessary for effective tsunami warning.
ISSN: 2169-9313

hal-01389113
http://hal.univ-reunion.fr/hal-01389113
http://hal.univ-reunion.fr/hal-01389113/document
http://hal.univ-reunion.fr/hal-01389113/file/Fontaine_Ppol_JGR2009.pdf
DOI : 10.1029/2008JB005709

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Constraining mantle deformation beneath plate boundaries where plates interact with each other, such as beneath active or halted mountain belts, is a particularly important objective of "mantle tectonics" that may bring a depth extent to the Earth's surface observation. Such mantle deformation can be mapped at scale lengths of several tens of kilometers through the analysis of seismological data and particularly by mapping seismic anisotropy from the splitting analysis of vertically-propagating SKS waves that largely reflect the strain-induced crystal preferred orientations of the rock-forming minerals within the upper mantle. In the present study, we analyse data from approximately 50 broadband seismic stations covering the Western Alps and we provide a coherent picture of upper mantle anisotropy beneath the belt. The large-scale anisotropy pattern is characterized by fast split directions that closely follow the trend of the belt. Moreover, the maximum anisotropy magnitude is not located beneath the internal zones of the belt but instead beneath external units. All suggests that the anisotropy is likely dominated by sublithospheric mantle deformation. We propose that the observed anisotropy pattern can be explained by recent or active mantle flow around the Eurasian slab presently plunging beneath the inner parts of the Alps.
ISSN: 0012-821X

hal-00617828
https://hal.archives-ouvertes.fr/hal-00617828
https://hal.archives-ouvertes.fr/hal-00617828/document
https://hal.archives-ouvertes.fr/hal-00617828/file/Barruol_SKS_Alpes_EPSL2011_hal.pdf
DOI : 10.1016/j.epsl.2010.12.040

Éditeur(s) : Université de Bretagne Occidentale
Résumé : Situé entre la zone de subduction des Nouvelles Hébrides à vergence est présente à l'ouest, et la zone de subduction des Tonga-Kermadec à vergence ouest, à l'est, le bassin Nord Fidjien est un bassin marginal créé, entre les plaques Pacifique et Indo-Australienne, par accrétion océanique en arriére de l'arc Néo Hébridais, du fait de la rotation horaire de ce dernier. La compilation des données bathymétriques, de magnétisme et de sismique réflexion monotrace recueillies lors des campagnes Seapso III, Moana Wave 87 et Kaiyo 87, permet de préciser la structure détaillée du système d'accrétion de la partie centrale du bassin Nord Fidjien, entre 15° et 22°S.

Droits : UBO
http://archimer.ifremer.fr/doc/00034/14529/11825.pdf
http://archimer.ifremer.fr/doc/00034/14529/

Éditeur(s) : HAL CCSD American Physical Society
Résumé : International audience
Absolute M-shell x-ray production cross sections have been measured and calculated for Au and Bi for electron incident energies from close to the ionization threshold up to 38 keV. The experimental cross sections were deduced from M alpha x-ray intensities emitted from ultrathin Au and Bi samples deposited on self-supporting C films. The measurements were performed on an electron microprobe using several wavelength-dispersive spectrometers. The x-ray production cross sections were also evaluated theoretically using ionization cross sections calculated from the plane-wave and the distorted-wave Born approximations. Experimental results are compared with the calculated cross sections and also with the results of two analytical formulas widely used in many applications. Good agreement is found between the measured cross sections and the predictions from the distorted-wave Born approximation, which indicates that this approximation is suited for the calculation of M-shell ionization cross sections of heavy elements.
ISSN: 1050-2947

hal-00411432
https://hal.archives-ouvertes.fr/hal-00411432
DOI : 10.1103/PhysRevA.78.022704

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We have analyzed the microstructures and crystal preferred orientations (CPO), and calculated the seismic properties of 53 mantle xenoliths from four localities within the North Tanzanian Divergence of the East African rift: two within the rift axis and two in the transverse volcanic belt. Olivine OH concentrations were measured in 15 xenoliths.Most samples have harzburgitic to dunitic compositions and high olivine Mg#. Microstructures and olivine CPO patterns vary strongly depending on the location. In-axis peridotites display mylonitic to porphyroclastic microstructures, which record recent deformation by dislocation creep. Highly stretched orthopyroxenes in mylonites indicate that the deformation was initiated under high stress and probably low temperature. Orthopyroxene replacement by olivine in mylonitic and porphyroclastic peridotites suggest syn-kinematic melt–rock reactions and further deformation under near-solidus conditions. Exsolutions in orthopyroxene imply significant cooling between melt-assisted deformation and xenolith extraction. Late metasomatism is evidenced by the occurrence of veins crosscutting the microstructure and interstitial clinopyroxene and phlogopite. Axial-[100] olivine CPOs predominate, suggesting activation of the high temperature, low pressure [100] {0kl} slip systems and, probably, transtensional deformation. In the volcanic belt, Lashaine peridotites display very coarse-granular textures, indicating deformation by dislocation creep under low deviatoric stress conditions followed by annealing. Axial-[010] olivine CPOs are consistent with transpressional deformation or simultaneous activation of the [100](010) and [001](010) slip systems. Intermediate microstructures and CPOs in Olmani suggests heterogeneous deformation within the volcanic belt. Olivine OH concentrations range between 2 and 12 ppm wt. H2O. No systematic variations are observed between in- and off-axis samples. Maximum P wave azimuthal anisotropy (AVp) ranges between 3.3 and 18.4%, and the maximum S wave polarization anisotropy (AVs) between 2.3 and 13.2%. Comparison between seismic properties of in-axis peridotites and SKS splitting data suggests transtensional deformation in the lithospheric mantle beneath the rift.
ISSN: 0040-1951

hal-01121552
https://hal.archives-ouvertes.fr/hal-01121552
DOI : 10.1016/j.tecto.2014.11.011

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : We present a regional surface waveform tomography of the Pacific upper mantle, obtained using an automated multimode surface waveform inversion technique on fundamental and higher mode Rayleigh waves, to constrain the VSV structure down to ∼400 km depth. We have improved on previous implementations of this technique by robustly accounting for the effects of uncertainties in earthquake source parameters in the tomographic inversion. We have furthermore improved path coverage in the South Pacific region by including Rayleigh wave observations from the French Polynesian Pacific Lithosphere and Upper Mantle Experiment deployment. This improvement has led to imaging of vertical low-velocity structures associated with hotspots within the South Pacific Super-Swell region. We have produced an age-dependent averagecross-sectionforthePacificOceanlithosphereandfoundthattheincreaseinVSV with age is broadly compatible with a half-space cooling model of oceanic lithosphere formation. We cannot confirm evidence for a Pacific-wide reheating event. Our synthetic tests show that detailed interpretation of average VSV trends across the Pacific Ocean may be misleading unless lateral resolution and amplitude recovery are uniform across the region, a condition that is difficult to achieve in such a large oceanic basin with current seismic stations.
ISSN: 0956-540X

hal-00105949
https://hal.archives-ouvertes.fr/hal-00105949
https://hal.archives-ouvertes.fr/hal-00105949/document
https://hal.archives-ouvertes.fr/hal-00105949/file/Maggi_Pacif_tomo_GJI2006.pdf
DOI : 10.1111/j.1365-246X.2006.03037.x

Éditeur(s) : HAL CCSD
Résumé : International audience
After defining the High Performance Pre- Computing --referred as HPPC-- concept, the aim of the present study is to develop a prototype whether to approve or not the benefits of this concept. Our application case tries to answer the geophysical issue of coastal flooding. This is an example of an alert system based on the HPPC architecture, thus on pre-computed scenarios. The prototype provides the scientists with an ergonomic and on-demand tool allowing the run of scenarios of any implemented numerical models. These runs are available through a web application which submits the corresponding jobs on the remote french public cluster of HPC@LR. In this study we simulate the waves propagation over a Mediterranean grid using the wave model WaveWatch III⃝R . A reference simulation using usual conditions is approximated using the k-NN algorithm over 12, 98 and then 980 pre-computed scenarios. This simple experiment demonstrates how useful the pre-computing of scenarios is for alert systems as far as enough and relevant scenarios are pre-computed. This is the reason why searches continue in each critical points of the HPPC architecture such as the design of experiment, the approximation of the results by meta-models and the research of the closest scenarios in this big data context.
4th International Conference on Knowledge and Systems Engineering
Danang, Vietnam

lirmm-00736797
https://hal-lirmm.ccsd.cnrs.fr/lirmm-00736797
https://hal-lirmm.ccsd.cnrs.fr/lirmm-00736797/document
https://hal-lirmm.ccsd.cnrs.fr/lirmm-00736797/file/PID2396685.pdf
DOI : 10.1109/KSE.2012.36