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1.
Jérôme Nomade Emmanuel Chapron Marc Desmet Jean-Louis Reyss Fabien Arnaud Vincent Lignier 《地学学报》2005,17(4):350-357
Sediment archives from a mountain lake are used as indicators of seismotectonic activity in the Grenoble area (French western Alps, 45°N). Sedimentological analysis (texture and grain-size characteristics) exhibits several layers resulting from instantaneous deposits in Lake Laffrey: six debris flow events up to 8 cm thick can be attributed to slope failure along the western flank of the basin. Dating with 210Pb and 137Cs gamma counting techniques and the reconnaissance of historical events, provide a constrained age-depth model. Over the last 250 years, five of such debris flow deposits could be related to historical earthquakes of MSK intensities greater than VI over an area of <60 km. One debris flow deposit triggered at the beginning of the last century can be related to an historical landslide possibly triggered by the artificial regulation of the lake level. 相似文献
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In an attempt to discover planetary eclipses, we observed the open cluster NGC 7086. On one night we observed the cluster and standard stars through the B and V filters, enabling us to make a colour-magnitude diagram. Plots of the differential magnitudes were inspected for variability, but no planetary eclipses were found. New variable stars were discovered and their light curves show some of them to be eclipsing binary stars. The location on the colour-magnitude diagram of some of the variable stars is consistent with cluster membership. 相似文献
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In the northern limb of the 2.06-Ga Bushveld Complex, the Platreef is a platinum group elements (PGE)-, Cu-, and Ni-mineralized
zone of pyroxenite that developed at the intrusion margin. From north to south, the footwall rocks of the Platreef change
from Archaean granite to dolomite, hornfels, and quartzite. Where the footwall is granite, the Sr-isotope system is more strongly
perturbed than where the footwall is Sr-poor dolomite, in which samples show an approximate isochron relationship. The Nd-isotope
system for samples of pyroxenite and hanging wall norite shows an approximate isochron relationship with an implied age of
2.17 ± 0.2 Ga and initial Nd-isotope ratio of 0.5095. Assuming an age of 2.06 Ga, the ɛNd values range from −6.2 to −9.6 (ave.
−7.8, n = 17) and on average are slightly more negative than the Main Zone of the Bushveld. These data are consistent with local
contamination of an already contaminated magma of Main Zone composition. The similarity in isotope composition between the
Platreef pyroxenites and the hanging wall norites suggests a common origin. Where the country rock is dolomite, the Platreef
has generally higher plagioclase and pyroxene δ
18O values, and this indicates assimilation of the immediate footwall. Throughout the Platreef, there is considerable petrographic
evidence for sub-solidus interaction with fluids, and the Δ
plagioclase–pyroxene values range from −2 to +6, which indicates interaction at both high and low temperatures. Whole-rock and mineral δD values suggest that the Platreef interacted with both magmatic and meteoric water, and the lack of disturbance to the Sr-isotope
system suggests that fluid–rock interaction took place soon after emplacement. Where the footwall is granite, less negative
δD values suggest a greater involvement of meteoric water. Consistently higher values of Δ
plagioclase–pyroxene in the Platreef pyroxenites and hanging wall norites in contact with dolomite suggest prolonged interaction with CO2-rich fluid derived from decarbonation of the footwall rocks. The overprint of post crystallization fluid–rock interaction
is the probable cause of the previously documented lack of correlation between PGE and sulfide content on the small scale.
The Platreef in contact with dolomite is the focus of the highest PGE grades, and this suggests that dolomite contamination
played a role in PGE concentration and deposition, but the exact link remains obscure. It is a possibility that the CO2 produced by decarbonation of assimilated dolomite enhanced the process of PGE scavenging by sulfide precipitation. 相似文献
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We describe recent mechanical andeelectronic modifications to the Cambridge Ocean Bottom Hydrophone system, enabling it to record in addition three geophone channels from a deployed, disposable geophone package. Examples of data from seismic refraction experiments show good correspondence between records of ground motion detected by the hydrophone and the vertical geophone. Seismic signals are undistorted by noise from instrument related sources. Clear examples of P to S conversions just below the receiver are observed. Improved recording conditions are achieved by deploying the geophones in a small pressure vessel as far away as possible from the main instrument package. 相似文献
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Intensive partial reflection drift observations were made at Adelaide (35°S) for a seven day period in June 1973. The results have been analysed to isolate the prevailing motion and oscillations of various time scales: planetary, 24 hr, 12 hr and gravity waves. Each is discussed in turn with particular emphasis on the variability of energy from day to day and as a function of height. Evidence is presented for the local generation of planetary waves, the presence of the evanescent S?21 mode in the 24 hr oscillation, the influence of the S42 mode in the 12 hr oscillation and a definite polarization of gravity waves. The energies of all the forms of motion are shown to decay exponentially with increasing height and the deposition of energy and momentum in the upper mesosphere and lower thermosphere is discussed. 相似文献
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Hydraulic flow and transport (heat and solute) within crystalline rocks is dominated by the fracture systems found within
them. In situ stress conditions have a significant impact on the hydraulic, mechanical and thermal coupled processes, and
quantification of these processes provides a key to understanding the often transient time-dependent behaviour of crystalline
rocks. In this paper, a geomechanical model is presented which describes fracture closure as a function of effective stress
and the changes in parameters such as storage, permeability, porosity and aperture. Allowing the fracture closure to be defined
by the change in normal effective stress provides a link to the numerical consideration of parametrical changes due to rock
stress alterations caused for example by changes in fracture fluid pressure, stress release, tectonic stress, thermal stress,
orientation of the natural fracture in the pervasive stress system and local changes in a rock mass due to stress alteration.
The model uses geometrical considerations based on a fractal distribution of apertures on the fracture surface, and applies
well-established analytical elastic deformation solutions to calculate the deformation response to changes in effective stress.
Analysis of the fractal generation method allows a standard normal distribution of fracture apertures to be predicted for
all common fractal dimensions relating to a 2D surface. Changes in the fracture aperture are related to hydraulic functions
such as permeability, storage and porosity of the fracture. The geomechanical model is experimentally validated against laboratory
scale experimental data gained from the closure of a fractured sample recovered at a depth of 3,800 m from the KTB pilot borehole.
Parameters for matching the experimental data were established externally, the only fitting parameters applied were the minimum
and maximum contact area between the surfaces and the number of allowable contacts. The model provides an insight into the
key processes determining the closure of a fracture, and can act as a material input function for numerical models linking
the effects of changes in the stress field, hydraulic or thermal conditions, to the flow and transport parameters of a fractured
system.
Résumé L’écoulement et le transport (chaleur et soluté) dans les roches cristallines sont dominés par les systèmes de fracture. Les conditions de stress in-situ ont un impact significatif sur l’hydraulique, les processus couplés de mécanique et thermique et la quantification de ces processus apportent une clé pour comprendre le comportement transitoire des roches cristallines. Dans cet article un modèle géomécanique est présenté, modèle qui décrit la fermeture des fractures comme une fonction de la contrainte effective et des changements de paramètres tels le coefficient d’emmagasinement, la perméabilité, la porosité et l’ouverture. En s’accordant que la fermeture des fractures est définit par les changements de la contrainte effective normale, on apporte le lien avec la considération numérique des changements paramétriques dus aux altérations de la contrainte des roches, causés par exemple par des variations de la pression des fluides dans les fractures, du dégagement de la contrainte, des contraintes tectoniques et thermiques, des orientations des fractures naturelles dans le système de contraintes pénétrantes, et des changements locaux dans un massif de roches dus à l’altération des contraintes. Le modèle utilise des considérations géométriques basées sur une distribution fractale des ouvertures à la surface des fractures, et permet d’établir des solutions analytiques de la déformation élastique pour calculer la réponse de la déformation à la contrainte effective. L’analyse de la méthode par génération fractale permet de prédire une distribution normale standard de l’ouverture des fractures, pour toutes les dimensions fractales en relation avec les surfaces 2D. Les changements dans l’ouverture des fractures sont mis en relation avec les fonctions hydrauliques tels la perméabilité, l’emmagasinement et la porosité de la fracture. Le modèle géoméchanique est expérimentalement validé à l’échelle du laboratoire sur un échantillon fracturé récupéré à une profondeur de 3,800 mètres sur le puits du site pilote KTB. Les paramètres du calibrage des données expérimentales ont été établies extérieurement, les seuls paramètres utilisés étant les surfaces de contact minimum et maximum, et le nombre de contacts permis. Le modèle apporte une connaissance perspicace sur le processus clé déterminant la fermeture des fractures, et peut servir de fonction input dans les modèles numériques reliant les effets des variations de la contrainte du terrain, les conditions hydrauliques ou thermales, les paramètres de l’écoulement et du transport et les systèmes de fracture.
Resumen El flujo hidráulico y transporte (de calor y solutos) dentro de rocas cristalinas está dominado por los sistemas de fracturas que se encuentran en ellas. Las condiciones de esfuerzos in-situ tienen un impacto significativo en los procesos aparejados termales, mecánicos e hidráulicos y la cuantificación de estos procesos aporta una clave para entender el frecuente comportamiento transitorio dependiente de las rocas cristalinas. En este artículo se presenta un modelo geomecánico que describe el cierre de fracturas en función del esfuerzo efectivo y los cambios en parámetros tal como almacenamiento, permeabilidad, porosidad y apertura. El definir el cierre de fractura mediante el cambio en esfuerzo normal efectivo aporta un vínculo con la consideración numérica de cambios paramétricos ocasionados por alteraciones de esfuerzos en la roca causadas, por ejemplo, por cambios en presión de fluidos en fractura, liberación de esfuerzo, esfuerzo tectónico, esfuerzo termal, orientación de fracturas naturales en el sistema de esfuerzos penetrante, y cambios locales en una masa rocosa ocasionados por alteración de esfuerzos. El modelo utiliza consideraciones geométricas basadas en la distribución fractal de aperturas en la superficie de fractura y aplica soluciones analíticas bien establecidas de deformación elástica para calcular la respuesta de deformación a cambios en el esfuerzo efectivo. Los análisis del método de generación fractal permiten predecir una distribución normal standard para la distribución de aperturas de fracturas para todas las dimensiones fractales comunes que se relacionan con una superficie 2D. Los cambios en la apertura de fractura se relacionan con funciones hidráulicas tal como permeabilidad, almacenamiento y porosidad de la fractura. El modelo geomecánico se ha validado experimentalmente en contra de datos experimentales a escala de laboratorio obtenidos a partir del cierre de una muestra fracturada recuperada a una profundidad de 3,800 m en el pozo piloto KTB. Se establecieron externamente parámetros que se ajustan a los datos experimentales, con los parámetros de ajuste aplicados que fueron el área máxima y mínima de contacto entre las superficies y el número de contactos permisibles. El modelo arroja luz sobre los procesos clave que determinan el cierre de una fractura y puede actuar como un material de función de entrada para modelos numéricos que vinculan los efectos de cambios en el campo de esfuerzos, condiciones termales o hidráulicas, con los parámetros de flujo y transporte de un sistema fracturado.相似文献
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