Internal structure of Piton de la Fournaise volcano from seismic wave propagation and earthquake distribution     

Alexandre Nercessian  Alfred Hirn  Jean-Claude Lpine  Martine Sapin 《Journal of Volcanology and Geothermal Research》1996,70(3-4)

Arrival times of seismic waves from local earthquakes are inverted for both locating the source and defining the 3-D velocity heterogeneity of Piton de la Fournaise.The lateral heterogeneity of the 2632 m high edifice is resolved as a high-velocity plug, 1.5 km in diameter, surrounded by a low-velocity ring, which may be interpreted as due to the construction of Fournaise on the flank of the older volcano Piton des Neiges. Wave mode conversion detected on three-component seismograms provides evidence for boundaries of contrasted velocities.Pre-eruptive swarm earthquakes cluster in the high-velocity zone, under the Dolomieu summit crater. Low strength and cohesion of the surrounding material account for the lack of seismicity for the final 1–3 km radial flow of magma to the vents in Enclos Fouqué.Beneath the high-velocity plug the existence of a body with low velocity for P, and even for S, waves is well constrained. However, the walls and base are poorly defined because of the lack of deep earthquakes for sampling. The few earthquakes that are located in this depth region usually occur at a depth of around 1.5 km below sea level in the region of the cone. This can be considered providing the upper constraint on the lower limit of the aseismic part of the low-velocity body. The coincidence in time of their occurrence with the swarms above sea level and the eruptions suggests magmatic activation of the low-velocity aseismic volume 1.5 km below sea level under the high-velocity plug of the cone. Further down, the concentration of seismicity in two swarms, between 2 and 4 km, under the eastern flank does not allow the structure to be sampled effectively.  相似文献   

Effects of granulometric and mineralogical composition on spectral reflectance of soils in a Sahelian area     

Rachida Houssa  Jean-Claude Pion  Hervé Yésou 《ISPRS Journal of Photogrammetry and Remote Sensing》1996,51(6):284-298

During the Hapex-Sahel international investigation, portable radiometers (Barringer and Cimel) were used to study, in the optical domain, the relationship between soil mineralogical and granulometric compositions and radiometric indices: redness index, colour index and texture index. The results show that the granulometric distribution and the mineralogical composition have both important influence on these indices.In this Sahelian area, for soils having more than 1% of hematite, the redness index presents a high correlation with hematite content. For soils with less than 1% of hematite, the redness index depends on the size of the particles and their distribution at the surface.For eolian sandy and ferricrust soils, the colour and texture indices present good correlations, respectively, with iron oxide and kaolinite content. No such correlation is observed for ferruginous soils because of the complex interactions existing between iron oxides, kaolinite and the size of particles.  相似文献   

Tracing and dating recent chemical transfers in weathering profiles by trace-element geochemistry and U---U---Th disequilibria: the example of the Kaya lateritic toposequence (Burkina-Faso)     

Franois Chabaux  Olivier Dequincey  Jean-Jacques Lvque  Jean-Claude Leprun  Norbert Clauer  Jean Riotte  Hlne Paquet 《Comptes Rendus Geoscience》2003,335(16):1219-1231

The paper presents a synthesis of the approach recently developed to constrain the nature and the age of recent element mobility in weathering profiles. The approach relies on a comparison of variations of trace elements and U-series disequilibria in weathering profiles. It is exemplified in the case of old lateritic profiles from the Kaya toposequence, Burkina Faso. Trace elements and ²³⁸U---²³⁴U---²³⁰Th disequilibria have been analysed in whole rock samples from two pits located in very contrasted topographical positions. Trace element data show that the whole toposequence is marked by an intense chemical remobilization, including uranium, from the cap to the lower part of the profiles. ²³⁸U---²³⁴U---²³⁰Th disequilibrium data outline that all the levels of the profiles are affected by recent U---Th fractionations, and that each level of the toposequence is marked by U gains and losses. The chronological approach developed in this paper leads to an age of about 400 kyr for the dismantling of the iron cap, and ages ranging from 0 to 400 kyr for U accumulation in the pink clay horizon of the profiles. The depth repartition of U accumulation in the profile implies that the remobilisation processes in this toposequence varied through time, on time constants similar to those of climatic variations. To cite this article: F. Chabaux et al., C. R. Geoscience 335 (2003).  相似文献   

Reply to the comment on the article "Erosion calderas: origins, processes, structural and climatic control" by Alexandru Szakács and Michael Ort     

Dávid Karátson  Jean-Claude Thouret 《Bulletin of Volcanology》2001,63(4):291-292

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Evidence for recent warming from perturbed geothermal gradients: examples from eastern Canada   总被引：1，自引：0，他引：1  

Jean-Claude Mareschal  Hugo Beltrami 《Climate Dynamics》1992,6(3-4):135-143

Recent variations of the surface temperature of the Earth can be inferred from borehole temperature measurements. Generalized inversion is used to extract the information from the data; the potential of the method is evaluated. Tests were performed with synthetic data to demonstrate the effectiveness of the inversion to recover the gross features of the surface temperature history even when the data are affected by noise and errors. The tests show that it is possible to reconstruct the long term changes in ground temperature during the past 300 years; the resolution decreases with time, in particular if noise and errors must be filtered. Temperature logs, obtained in eastern Canada, and not suspected of being affected by non-climatic factors, have been inverted. The analysis confirms that eastern Canada has experienced warming by 1 to 2°C over the past 100–200 years. The relationship between air and ground temperatures has been examined. In eastern Canada ground temperature follows air temperature closely in summer but stays well above air temperature in winter. The number of days with snow on the ground correlates with the difference between annual mean ground and air temperature.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate-Program  相似文献   

Similarity studies of entrainment in convective mixed layers     

Marie-Agnes Artaz  Jean-Claude Andre 《Boundary-Layer Meteorology》1980,19(1):51-66

A similarity study of entrainment at the top of convectively driven mixed layer is presented. The similarity framework is used for a comparison between various parameterized models of mixed-layer growth rate and between closely related models for the ratio of heat fluxes at ground and inversion levels. These various models are also tested, in dimensionless form, against data from laboratory, field experiments and numerical higher-order-modeling of the convective layer. It is concluded that a rather accurate prediction of mixed-layer growth can be achieved with the simple constant flux ratio model, but that more refined studies of entrainment are required to account for the decrease of the heat flux ratio with increasing convective intensity.List of acronyms CRPE Centre de Recherches en Physique de l'Environnement, Issy-les-Moulineaux, France - EERM Etablissement d'Etudes et de Recherches Météorologiques, Boulogne, France - INRA Institut National de la Recherche Agronomique, Versailles, France - LAMP Laboratoire Associé de Météorologie Physique, Clermont-Ferrand, France - NCAR National Center for Atmospheric Research, Boulder, U.S.A. - NOAA National Oceanic and Atmospheric Administration, Environmental Research Laboratories, Boulder, U.S.A.  相似文献   

Deformation and dynamic recrystallization of K feldspar augen in orthogneiss from Montagne Noire,Occitania, Southern France     

Jean-Luc Vidal  Ladislas Kubin  Pierre Debat  Jean-Claude Soula 《Lithos》1980,13(3):247-255

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Ice action in the lacustrine environment. A review with particular reference to subarctic Quebec,Canada     

Jean-Claude Dionne 《Earth》1979,15(3):185-212

Erosional and depositional features produced by lake ice occur in many lakes of temperate and cold regions. Ice-push ridges, grooves with a boulder at their head, ice-rafted sediments, boulder ridges, stone pavements, beach micro-relief, and destruction of shore vegetation, are features common to many lakes in the James Bay area, subarctic Quebec. However, the ice cover offers good protection against shore erosion by waves, during six months per year, permitting varve sedimentation. Ice-push ridges and grooves with a boulder at their head are the two most common ice-made features: 95 ice-push ridges, up to 7 m high, have been observed in 35 lakes, and grooves, up to 300 m long have been found in 81 sites from 69 lakes. These features resulted from ice movements caused either by ice expansion and wind action, at breakup. A review of the literature indicates that several factors must be considered in any investigation of ice action in the lacustrine environment.  相似文献   

South Armorican shear zone and continental fit before the opening of the Bay of Biscay     

Jean-Claude Sibuet 《Earth and Planetary Science Letters》1973,18(1):153-157

The relative position of continents prior to the opening of the Bay of Biscay can be correctly deduced from reconstruction of the Ibero-Armorican belt only if the extent of the Late-Hercynian horizontal displacement along the south Armorican shear zone and perhaps also along the north Pyrenean fault can be determined.  相似文献   

Les rhyolites hyperalcalines (pantellérites) du lac Tchad. Composition et signification tectonomagmatiqueThe peralkaline rhyolites (pantellerites) of the Lake Chad. Composition and tectonomagmatic significance     

Jean-Paul Vicat  André Pouclet  Yves Bellion  Jean-Claude Doumnang 《Comptes Rendus Geoscience》2002,334(12):885-891

Remnants of rhyolite lava-dome and of alkaline microgranite extrusions emerge, as inselbergs, in the alluvial plain, south of Lake Chad. The peralkaline, arfvedsonite- and acmite-bearing rhyolites are determined as pantellerites. They can be related to a tectonomagmatic stage, dated of the Late Cretaceous, of the western central Africa rift system. They may constitute the NNE extension of a N50° to 30° elongated succession of small alkaline complexes, from the Gulf of Guinea to the North-Cameroon, which initiated the magmatic activity of the Cameroon Line. To cite this article: J.-P. Vicat et al., C. R. Geoscience 334 (2002) 885–891.  相似文献