3-D seismic endoscopy: multiscale analysis and dynamic azimuthal filtering of borehole waves     

Henri Pierre Valero  Ginette Saracco 《Geophysical Journal International》2005,161(3):813-828

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Geochemical morphology of the North Mid-Atlantic Ridge, 10°–24°N: Trace element-isotope complementarity     

Laure Dosso  Henri Bougault  Jean-Louis Joron 《Earth and Planetary Science Letters》1993,120(3-4):443-462

The new data presented here from a 10–24°N segment of the North Mid-Atlantic Ridge show that this segment is the most depleted of the 10–70°N ridge section. They also show the existence of: (1) a geochemical gradient from the 14°N anomaly to 17°10′N; (2) a very depleted mantle source (the lowest Sr isotopic ratios found so far in the North Atlantic); and (3) a geochemical limit located at about 17°10′N without any obvious relation with any structural feature. The 15°20′N fracture zone does not show any relationship with respect to this gradient. The basalts located north of 17°10′N have very homogeneous features, which allow their characteristics to be averaged (i.e., ⁸⁷Sr/⁸⁶Sr= 0.70238 ± 0.00004, (Nb/Zr)_N = 0.28 ± 0.1) and they are defined as normal mid-ocean ridge basalts. The basaltic glasses located south of 17°10′N present a wide spectrum of isotopic compositions and extended rare earth element patterns (from depleted to enriched). Despite this, they have a constant K/Nb of 233 ± 9 (1s_M, n = 18) whereas this ratio is 344 ± 29 north of 17°10′N. These observations illustrate the strong coherence of behaviour between K and Nb (Ta) during the petrogenic processes involved in the generation of these mid-ocean ridge basalts and also their fractionation during previous mantle processes. Possible interpretations of mixing processes are discussed and sources at the ridge segment scale are favoured. However, when looking in detail, local heterogeneities are still common and can even be traced back off-axis to 115 my.

Placed in the context of the North Atlantic Ridge from 10° to 70°N, the Sr isotopic ratios reveal the Azores superstructure (23–50°N), whereas the trace element ratios (La/Sm-Nb/Zr) trace the second-order structures (33–40°N, 42–48°N) superimposed on the superstructure. This study illustrates the complementarity of information given by certain well chosen trace element ratios on the one hand and by isotopic ratios on the other. Since there is evidence of decoupling between isotopic ratios and/or trace element ratios, it introduces the notion of complementary “chemical memory” as recorded by a given type of trace element ratio or a given type of isotopic ratio  相似文献   

Rectified flow along a vertical coastline     

Xiuzhang Zhang  Don L. Boyer  Gabriel Chabert d'Hires  Denis Aelbrecht  Henri Didelle 《Dynamics of Atmospheres and Oceans》1993,19(1-4)

Laboratory experiments are conducted on a physical system in which an oscillatory, along-shore, free stream flow of a homogeneous fluid occurs in the vicinity of a long coastline with vertical slope; the model sea-floor is horizontal. Particular attention is given to the resulting rectified (mean) current which is along the coastline with the shore on the right, facing downstream. In the lateral far field region defined by (1), where y is the offshore coordinate and H is the depth of the fluid, the motion field is approximately independent of the lateral distance from the coast. The vertical structure of the cross-stream motion in this region consists of Ekman layers near the sea-floor and interior adjustment flows, both periodic in time. In the near field, defined by (1), the motion is strongly dependent on the cross-stream coordinate as well as time, and rectified currents are observed. The mechanism responsible for the rectification is a complex nonlinear coupling between laterally directed adjustment flows driven by the transport in the bottom Ekman layers, and the free stream motion field. The rectified current is found to be substantially wider than the Stewartson layer thickness but much narrower than the Rossby deformation radius. The characteristic width, δ_y, of the rectified current is shown to scale as , where Ro is the Rossby number Ro_t is the temporal Rossby number and E is the Ekman number. Experiments are presented which support this scaling.  相似文献   

Utilisation d'un microdébitmètre à haute résolution pour les mesures de turbulence par avion     

Aimé Druilhet  Henri Bardeau 《Pure and Applied Geophysics》1990,132(3):457-479

Résumé Nous avons décrit dansBardeau et al. (1987), la réalisation, le fonctionnement et les tests d'un microdébitmètre basé sur l'anémométrie à fil chaud. Il a été particulièrement montré que cet appareil était bien adapté aux mesures de pression et pression différentielle avec une grande sensibilité et une très faible constante de temps. Nous présentons ici les applications qui ont été faites de ce capteur aux mesures à haute résolution à bord d'avions instrumentés pour la recherche atmosphérique. L'avion utilisé était spécialement équipé pour les mesures de turbulence et permettait donc l'acquisition d'un grand nombre de paramètres indispensables à l'analyse des données de ce capteur. Dans les applications aéronautiques qui ont été faites, le capteur a surtout été utilisé en tant que variomètre. Les comparaisons avec les mesures standards d'altitude par pression et couplages pression-données inertielles montrent que cet instrument pourrait apporter une contribution intéressante dans le domaine de la mesure à haute fréquence des fluctuations de pression.  相似文献   

Source parameters for the Roermond aftershocks of 1992 April 13-May 2 and site spectra for P and S waves at the Belgian seismic network     

Mihnea-Corneliu Oncescu  Thierry Camelbeeck  Henri Martin 《Geophysical Journal International》1994,116(3):673-682

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Deccan flood basalts at the Cretaceous/Tertiary boundary?   总被引：9，自引：0，他引：9  

Vincent Courtillot  Jean Besse  Didier Vandamme  Raymond Montigny  Jean-Jacques Jaeger  Henri Cappetta 《Earth and Planetary Science Letters》1986,80(3-4):361-374

Joint consideration of new paleomagnetic, paleontological and geochronological data from the Deccan continental flood basalts in India and critical discussion of earlier results lead us to suggest that volcanic activity may have lasted less than 1 Ma, thus possibly ranking as one of the largest volcanic catastrophes in the last 200 Ma. Available data are best satisfied if volcanism spanned the Cretaceous/Tertiary boundary, followed shortly afterwards by rifting of the Arabian Sea. These results point out the need for further work which may help in choosing between “external” and “internal” models of the Cretaceous/Tertiary boundary events.  相似文献   

La double evolution de la lithosphere et de la biosphere     

Henri  Genevieve Termier 《International Journal of Earth Sciences》1986,75(3):863-887

Conclusion L'évolution de la lithosphère ressortit de phénomènes cosmiques, les uns liés au système solaire dans son ensemble, d'autres spécifiques à la Terre (l'atmosphère, l'eau, p.e.). Elle appartient au règne minéral et progresse souvent par cycles. L'évolution de la biosphère est liée à celles des sphères externes de la Terre, mais l'instabilité de la matière vivante et de la vie qui la constituent lui confère une polarité, celle de l'Evolution organique, laquelle procède dans un sens progressif, en laissant de coté les Êtres remplacés par de plus performants. L'évolution de la lithosphère a influé sur celle de la biosphère parce qu'elle lui fournit ses milieux de vie favorables à certains progrès ou hâtant les éliminations. L'évolution synchrone de la biosphère, en influant sur la composition de l'atmosphère et de l'hydrosphère, a joué un rÔle important dans la composition des sédiments et de la surface de la lithosphère.  相似文献   

Petrology of the ocean floor: Roger Hekinian. Elsevier Oceanography Series, 33. Elsevier, Amsterdam, 1982, XIV + 393 pp. 120 fig., 69 tables. Dfl. 200.00/US $93.00, hardcover     

Henri Termier 《Tectonophysics》1984,106(1-2)

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Organic matter in anoxic marine pore water: oxidation effects     

William H. Orem  Henri E. Gaudette 《Organic Geochemistry》1984,5(4):175-181

A series of cores were obtained from the Great Bay Estuary, New Hampshire during 1980 and 1981 in order to investigate the effects on the dissolved organic matter of exposure of anoxic marine pore water to atmospheric oxygen during laboratory handling. Sediment sections from these cores were homogenized and split into two equal parts, one of which was handled in a glove bag under a nitrogen atmosphere, and the other exposed to atmospheric oxygen during laboratory processing. Analysis of the pore water for dissolved organic carbon (DOC) indicated two effects: (1) in the top 15 cm, DOC was lost from the pore water of the oxidized subsections, probably as a consequence of co-precipitation with iron (III) oxi-hydroxides, whereas (2) deeper in the cores, the pore water from the oxidized subsections showed a net increase in DOC, possibly due to oxidation of sedimentary organic matter. In addition, structural changes in the dissolved organic matter in anoxic pore water following oxidation was indicated by high pressure liquid chromatography and ultrafiltration analysis.  相似文献   

Emissions of Polycyclic aromatic hydrocarbons by savanna fires   总被引：2，自引：0，他引：2  

Pierre Masclet  Hélène Cachier  Catherine Liousse  Henri Wortham 《Journal of Atmospheric Chemistry》1995,22(1-2):41-54

Although Polycyclic aromatic hydrocarbons (PAH) are known as anthropogenic compounds arising from the combustion or the pyrolysis of fossil fuels, they may be also emitted by the combustion of vegetation. A field study was carried out in January 1991 at Lamto (Ivory Coast) as part of the FOS DECAFE experiment (Fire Of Savanna). Some ground samplings were devoted to the qualitative and quantitative characterization of atmospheric emissions by savanna fires during prescribed burns and under background conditions. Specific collections for gaseous and particulate PAHs have shown that the African practice of burning the savanna biomass during the winter months is an important source of PAHs. These compounds are emitted mainly in gaseous form but a significant fraction, essentially heavy PAHs, is associated with fine carbonaceous particles and can therefore represent a hazard for human health, since some of these compounds are mutagenic and carcinogenic. Twelve compounds were identified during the fire episodes and in the atmospheric background. The total concentration in the fires is of the order of 10 ng m^–3 for the gas phase and from 0.1 to 1 ng m^–3 in the aerosols. In the atmospheric background the mean concentrations are regular, 0.15 ng m^–3 and 2 pg m^–3, respectively. These concentrations are comparable with what is observed in European rural zones. The particulate emissions of PAHs by the savanna fires are distinguished by the abundance of some compounds which can be considered as tracers, although they are also slightly emitted by fossil fuel sources. These compounds are essentially pyrene, chrysene and coronene. In the gas phase, although no individual PAH may be considered as specific of the biomass combustion emissions, the relative abundances of the main PAHs are characteristic of the biomass burning. The concentrations of pyrene and fluorene are always predominant; these compounds could be considered as characteristic emission products of smoldering and flaming episodes, respectively. In the background the PAH composition shows that in a tropical region the air consists of a mixture coming from the various sources, but the biomass combustion is by far the most important source.The fluxes of total PAH emitted by savanna biomass burning in Africa were estimated to be of the order of 17 and 600 ton yr^–1, respectively, for the particulate PAHs and the gaseous PAHs, respectively.  相似文献