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41.
Jean-Loup Guyot Jean-Marie Jouanneau Jorge Quintanilla Jean-Gabriel Wasson 《Geodinamica Acta》2013,26(4):233-241
RésuménLe Rio Béni est l’un des principaux formateurs andins du Rio Madeira, le plus important des affluents méridionaux de l’Amazone. La station hydrométrique de “Angosto del Bala” sur le Rio Béni contrôle un bassin andin de 67500 km2, aux caractéristiques géomorpho-climatiques très contrastées.Afin de connaître l’évolution temporelle des teneurs relatives des éléments des phases dissoutes et particulaires, un suivi hydrologique et hydrogéochimique a été réalisé à cette station en mars 1988, période de hautes eaux où une crue de fréquence annuelle a été observée. Les résultats obtenus montrent l’existence d’une grande variabilité temporelle des concentrations, mais présentant un cortège hydrogéochimique stable au cours de la crue.Enfin, l’importance quantitative de cette période de hautes eaux sur le bilan moyen annuel des flux exportés est souligné. 相似文献
42.
43.
The Canterbury earthquake sequence beginning with the 2010 M W 7.2 Darfield earthquake is one of the most notable and well-recorded crustal earthquake sequences in a low-strain-rate region worldwide and as such provides a unique opportunity to better understand earthquake source physics and ground motion generation in such a tectonic setting. Ground motions during this sequence ranged up to extreme values of 2.2 g, recorded during the February 2011 M W 6.2 event beneath the city of Christchurch. A better understanding of the seismic source signature of this sequence, in particular the stress release and its scaling with earthquake size, is crucial for future ground motion prediction and hazard assessment in Canterbury, but also of high interest for other low-to-moderate seismicity regions where high-quality records of large earthquakes are lacking. Here we present a source parameter study of more than 200 events of the Canterbury sequence, covering the magnitude range M W 3–7.2. Source spectra were derived using a generalized spectral inversion technique and found to be well characterized by the ω ?2 source model. We find that stress drops range between 1 and 20 MPa with a median value of 5 MPa, which is a factor of 5 larger than the median stress drop previously estimated with the same method for crustal earthquakes in much more seismically active Japan. Stress drop scaling with earthquake size is nearly self-similar, and we identify lateral variations throughout Canterbury, in particular high stress drops at the fault edges of the two major events, the M W 7.2 Darfield and M W 6.2 Christchurch earthquakes. 相似文献
44.
Hugues Leroux Guy Libourel Laurence Lemelle Franois Guyot 《Meteoritics & planetary science》2003,38(1):81-94
Abstract— An analytical transmission electron microscopy (ATEM) study was undertaken in order to better understand the formation conditions of dusty olivines (i.e., olivines containing abundant tiny inclusions of Fe‐Ni metal) in primitive meteorites. Dusty olivines from type I chondrules in the Bishunpur chondrite (LL3.1) and from synthetic samples obtained by reduction of San Carlos olivines were examined. In both natural and experimental samples, micron size metal blebs observed in the dusty region often show preferential alignments along crystallographic directions of the olivine grains, have low Ni contents (typically <2 wt%), and are frequently surrounded by a silica‐rich glass layer. These features suggest that dusty olivines are formed by a sub‐solidus reduction of initially fayalitic olivines according to the following reaction: Some volatilization of SiOgas may account for the apparent excess of metal relative to silica‐rich glass observed in both experimental and natural samples. Comparison with experimentally produced dusty olivines suggests that time scales of the order of minutes usually inferred for chondrule formation are also adequate for the formation of dusty olivines. These observations are in agreement with the hypothesis that at least part of the metal phase in chondrites originated from reduction during chondrule formation. 相似文献
45.
Germanate olivines Mg2GeO4, Ca2GeO4 and CaMgGeO4 have been studied by high-pressure X-ray Diffraction and high-pressure X-ray Absorption Spectroscopy. The three compounds were compressed, in the 0–30 GPa pressure range, at room temperature in a diamond-anvil cell, silicon oil being used as the pressure transmitting medium. Values of K0 are 166 ± 15, 117 ± 15 and 152 ± 14 GPa for Mg2GeO4, Ca2GeO4 and CaMgGeO4 respectively. These olivines all exhibit compression anisotropy, the a axis being the least compressible. Crystal to crystal phase transitions have been observed in Mg2GeO4 and Ca2GeO4 above 12 GPa and 6 Gpa respectively. The nature of these structural changes remains unclear yet. The onset of amorphization has been observed in Mg2GeO4 and Ca2GeO4 at pressures above about 22 and 11 GPa respectively. These phase transitions and amorphization processes do not involve any detectable increase in the coordination number of germanium atoms. At higher pressure (P >23 GPa), we report the onset of a transition from a phase with fourfold coordinated germanium to a phase with higher germanium coordination number in CaMgGeO4. 相似文献
46.
Va?rie Malavergne Julien Siebert Fra?ois Guyot Laurent Gautron Tahar Hammouda Dan Frost 《Geochimica et cosmochimica acta》2004,68(20):4201-4211
High-pressure high-temperature experiments have been carried out up to 25 GPa and 2200°C in a multianvil press on assemblages made of silicates and iron-silicon alloys. At 20 GPa, silicon is extracted from the metal phase, forming stishovite reaction rims around metal grains. The silicon content in metal has been measured by analytical electron microscopy and electron microprobe. In contrast with earlier experiments, the present data were obtained by using silicon-rich metal alloys as starting materials instead of studying incorporation of silicon in initially silicon-free metal. As in most of previous studies carried out below 25 GPa, the silicon content in liquid metal increases with increasing pressure and with decreasing oxygen fugacity. The oxygen fugacity in most experiments was calculated by using two independent buffers: iron/?stite (IW) and SiO2/Si, allowing to link consistently the Fe contents in silicates, the Si contents in metal and the temperatures of the experiments. At oxygen fugacities 4 log units below IW, silicates are in equilibrium with Si-rich metallic alloys (up to 17 wt% of Si in metal at 20 GPa and 2200°C). Extrapolation to 2 log units below IW leads to less than 0.1 wt% Si in the metal phase. Presence of several wt% of silicon in the Earth’s core thus requires highly reduced initial materials that, if equilibrated at conditions relevant to small planets, should already contain significant amount of silicon dissolved in metal. 相似文献
47.
Ca2SiO4 dicalcium silicate has been transformed at high pressure in a diamond-anvil cell (DAC) coupled with a YAG laser heater, in order to study the high-pressure modifications of this compound. Starting material was the olivine form of Ca2SiO4 (γ-polymorph). Several samples have been synthesized at loading pressures of 4.5, 10 and 15 GPa respectively, at room temperature. Other samples have been obtained at pressures ranging between 4.5 and 45 GPa and temperatures estimated to be about 2500 °C. The study of the quenched high pressure and/or high temperature phases has been performed using analytical transmission electron microscopy (ATEM) and X-ray diffraction (XRD). All the polymorphs of Ca2SiO4 usually produced with high temperatures, including α-Ca2SiO4, have been observed in the samples recovered from the high-pressure experiments. The α′-Ca2SiO4 and α-Ca2SiO4 polymorphs have been obtained at ambient conditions for the first time without stabilizing impurities. A new modification of α′-Ca2SiO4 has also been synthesized. Finally, the breakdown at high-pressure and temperature of Ca2SiO4 into CaSiO3 and CaO is reported. 相似文献
48.
E. Gautier D. Brunstein P. Vauchel M. Roulet O. Fuertes J. L. Guyot J. Darozzes L. Bourrel 《地球表面变化过程与地形》2007,32(2):230-248
The Andean Cordillera and piedmont significantly influence river system and dynamics, being the source of many of the important rivers of the Amazon basin. The Beni River, whose upper sub‐catchments drain the Andean and sub‐Andean ranges, is a major tributary of the Madeira River. This study examines the river in the south‐western Amazonian lowlands of Bolivia, where it develops mobile meanders. Channel migration, meander‐bend morphology and ox‐bow lakes are analysed at different temporal and spatial scales. The first part of this study was undertaken with the aim to link the erosion–deposition processes in the active channel with hydrological events. The quantification of annual erosion and deposition areas shows high inter‐annual and spatial variability. In this study, we investigate the conditions of sediment exportation in the river in relation to three hydrological parameters (flood intensity, date of discharge peak and duration of the bank‐full stage level). The second part of this study, focusing on the abandoned meanders, analyses the cutoff processes and the post‐abandonment evolution during 1967–2001. This approach shows the influence of the active channel behaviour on the sediment diffusion and sequestration of the abandoned meanders and allows us to build a first model of the contemporary floodplain evolution. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
49.
Adrien Oth Friedemann Wenzel Hillel Wust-Bloch Ellen Gottschämmer Zvi Ben-Avraham 《Pure and Applied Geophysics》2007,164(1):23-37
3-D simulations of elastic wave propagation generated by earthquakes with magnitudes between 5.5 and 7.0 are used to parameterize
strong ground motion attenuation relations for the Dead Sea Rift (DSR) graben structure. The results show that standard attenuation
relations with an isotropic distance parameter are inadequate for a graben structure with a deep sedimentary trough. A new
strategy is devised for the parameterization of attenuation relations in graben structures by looking at the statistical properties
of 53 simulated earthquakes of variable magnitudes located at various sites along the western boundary fault of the DSR graben.
An exemplary attenuation relation is designed from the synthetics for the 1 Hz spectral acceleration, modifying the Joyner-Boore-type
parametrization by adding coefficients suited for three different source-to-sensor configurations: within the graben, beyond
the graben and path unaffected by the graben structure. 相似文献
50.
Socié Adrien Dubois Frédéric Monerie Yann Perales Frédéric 《Computational Geosciences》2021,25(5):1473-1491
Computational Geosciences - In the context of long-term degradation of porous media, the coupling between fracture mechanics and reactive transport is investigated. A reactive transport model in a... 相似文献