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11.
Eva De Boever Marijke Huysmans Philippe Muchez Lyubomir Dimitrov Rudy Swennen 《Marine and Petroleum Geology》2009,26(8):1580-1591
Up to 10 m in length and >1 m in diameter tubular, calcite-cemented sandstone concretions are hosted by the faulted Dikilitash unconsolidated sands and sandstones. These structures document shallow subsurface pathways of Early Eocene methane seepage in the Balkan Mountains foreland (NE Bulgaria). Their exceptional exposure allowed a unique study of the factors governing the morphology and spatial distribution of such fossilized fluid conduits. The large dimensions and subvertical, cylindrical shape of the most common tube type primarily reflects the buoyancy-driven, vertical path of an ascending gas-bearing fluid through permeable, mainly unconsolidated sandy host sediments. Tube morphology was also influenced by local stratigraphic anisotropies and might as well document differences in former seepage conditions. Mapping of >800 tubular concretions showed the NNW–NNE elongation and alignment of tube clusters and massive cemented sandstone structures. This suggests that Paleogene fault systems played a major role in directing the movement of fluids. However, within a single tube cluster, tubes are preferentially aligned, over distances up to 50 m along directions at an angle between 10° and 36° with respect to the inferred NNW–NNE, cluster parallel fault traces. In addition, cylindrical tubes of analogue dimensions are aligned over distances >100 m along N15° to N25°-oriented directions. It is hypothesized that this spatial geometry of tubular concretions reflects the complex geometry of deformations structures in fault damage zones along which fluids were preferentially channelled. 相似文献
12.
David Arnas Daniel Casanova Eva Tresaco 《Celestial Mechanics and Dynamical Astronomy》2017,128(2-3):197-219
The aim of the time distribution methodology presented in this paper is to generate constellations whose satellites share a set of relative trajectories in a given time, and maintain that property over time without orbit corrections. The model takes into account a series of orbital perturbations such as the gravitational potential of the Earth, the atmospheric drag, the Sun and the Moon as disturbing third bodies and the solar radiation pressure. These perturbations are included in the design process of the constellation. Moreover, the whole methodology allows to design constellations with multiple relative trajectories that can be distributed in a minimum number of inertial orbits. 相似文献
13.
High‐pressure phase transitions of α‐quartz under nonhydrostatic dynamic conditions: A reconnaissance study at PETRA III 下载免费PDF全文
Eva‐Regine Carl Ulrich Mansfeld Hanns‐Peter Liermann Andreas Danilewsky Falko Langenhorst Lars Ehm Ghislain Trullenque Thomas Kenkmann 《Meteoritics & planetary science》2017,52(7):1465-1474
Hypervelocity collisions of solid bodies occur frequently in the solar system and affect rocks by shock waves and dynamic loading. A range of shock metamorphic effects and high‐pressure polymorphs in rock‐forming minerals are known from meteorites and terrestrial impact craters. Here, we investigate the formation of high‐pressure polymorphs of α‐quartz under dynamic and nonhydrostatic conditions and compare these disequilibrium states with those predicted by phase diagrams derived from static experiments under equilibrium conditions. We create highly dynamic conditions utilizing a mDAC and study the phase transformations in α‐quartz in situ by synchrotron powder X‐ray diffraction. Phase transitions of α‐quartz are studied at pressures up to 66.1 and different loading rates. At compression rates between 0.14 and 1.96 GPa s?1, experiments reveal that α‐quartz is amorphized and partially converted to stishovite between 20.7 GPa and 28.0 GPa. Therefore, coesite is not formed as would be expected from equilibrium conditions. With the increasing compression rate, a slight increase in the transition pressure occurs. The experiments show that dynamic compression causes an instantaneous formation of structures consisting only of SiO6 octahedra rather than the rearrangement of the SiO4 tetrahedra to form a coesite. Although shock compression rates are orders of magnitude faster, a similar mechanism could operate in impact events. 相似文献
14.
15.
M. Boccaletti M. Coli C. Eva G. Ferrari G. Giglia A. Lazzarotto F. Merlanti R. Nicolich G. Papani D. Postpischl 《Tectonophysics》1985,117(1-2)
The Northern Apennines have been subdivided into homogeneous zones, on the basis of recent structural evolution and crustal structure, in which the earthquake distribution can find a coherent framework. These zones, whose physiography is in strict connection with their structure, are: the Internal Peri-Tyrrhenian Belt; the External or Main Belt; the Buried Belt; and the Pede-Alpine Homocline. Earthquake activity has a tendency to cluster along well-defined bands, particularly in the easternmost border of the Peri-Tyrrhenian Belt, as well as along the zone between the External Belt and the Buried Belt, i.e. along the Padanian margin of the Northern Apennines.A minimum of seismic activity seems to be correlated with some zones of the External Belt, as well as with the Late Tertiary and Quaternary magmatic province of Tyrrhenian Southern Tuscany.The fault-plane solutions are coherent with the structural picture.A tentative seismotectonic model of the Northern Apennines is discussed. 相似文献
16.
Ivana Nemešová Eva Smítková Reviewer O. Zikmunda 《Studia Geophysica et Geodaetica》1982,26(2):176-186
Summary A model of a building cumulus structure is described. The one-stage model published in[1] was used to describe ascent of two cloudy parcels that a cloud is supposed to be formed of. The other ascent is assumed to take place after the first cloud element sinks back as a result of evaporative cooling. The numerical results and their evaluation are given for various rates of mixing at the cloud top level of the first cloud volume. 相似文献
17.
Eva Falck 《Polar research》2001,20(2):193-200
Measurements of nitrate and phosphate taken in the Northeast Water Polynya (NEWP) during the summer of 1993 have been used to identify the contribution of waters of Atlantic and Pacific origin in the polynya. Since waters from the northern Pacific exhibit a deficit in nitrate relative to phosphate due to denitrification in low oxygen waters, the relationship between nitrate and phosphate can be used to distinguish between oceanic waters of Pacific and Atlantic origin. The Pacific Water enters the Arctic Ocean through Bering Strait and flows along the northern coasts of Alaska and Canada. Some of this water exits through Fram Strait and may therefore enter the polynya which is situated above the continental shelf off the north-eastern coast of Greenland. Compared to data from the Greenland Sea, which only show a N–P relationship of typical Atlantic Water, the data from the Northeast Water Polynya show that the upper waters of the polynya bear a clear signal of waters of Pacific origin. In the surface mixed layer an average of about 90% is found to have Pacific N–P characteristics. Below the surface mixed layer the amount of Pacific derived water decreases through the halocline and from about 150 m to the bottom only typical Atlantic Water is found. 相似文献
18.
Fabrizio Eva 《GeoJournal》2001,52(4):295-301
Discussion of the future of Europe continues to be a marginal political issue, partly because of the resistance of states, on both the practical (bureaucratic) and conceptual levels, created by the government leaders and heads of state. In turn, the nation-states are challenged from within by independent and separatist movements that have laid bare the fundamental hypocrisy of rhetorical discussions of the principle regarding the self-determination of peoples; interfering with states (and their borders) has proven to be a taboo for Europe. The growing flexibility of the globalised economy should be paralleled by a growing flexibility in the conception of the division and political organisation of territory, but this is not the case. Further inflexibility stems from the socio-economic inequity that we accept in our daily lives as normal, in particular as regards inequality in the use and division of territory. Equality, or better egaliberté (equality and liberty), is a sufficiently dynamic and flexible concept to be taken as a point of reference in envisaging the society, Europe, and world of tomorrow. It is only through the concept of egaliberté that we can imagine a Europe based on relations between regions that are conceived and organised on multiple scales and not as region-nations conceived on the basis of ethnicity or in the name of supposed cultural homogeneity. 相似文献
19.
Eva Fediuková 《Mineralogy and Petrology》1971,15(4):249-257
Summary In granulites of South-Bohemia not only the usually occurring Al2SiO5 polymorphs, kyanite and sillimanite, were found but also andalusite. Its presence indicates that the metamorphic development of these granulites is characterized by a high PT-gradient. The granulitic rocks of the Bohemian Massif can be regarded as a facies series ranging from the granulite facies through the amphibolite facies to the hornblende-hornfels facies. The lower limit of the PT-conditions of this series should be placed below the position of the triple point of Al2SiO5.
With 5 Figures 相似文献
Andalusit in Granuliten der Böhmischen Masse
Zusammenfassung In den Mineralparagenesen der südböhmischen Granulite wurde neben den üblicherweise auftretenden Al2SiO5-Modifikationen, Disthen und Sillimanit, auch Andalusit gefunden. Seine Anwesenheit weist darauf hin, daß die metamorphe Entwicklung der erwähnten Granulite durch einen ausgeprägten PT-Gradienten gekennzeichnet wurde. Die Granulitgesteine der Böhmischen Masse kann man als eine Faziesserie ansehen, die von der Granulitfazies über die Amphibolitfazies bis in die Hornblende-Hornfelsfazies reicht. Die untere Grenze der PT-Bedingungen dieser Serie ist unter die Lage des Tripelpunktes von Al2SiO5 zu setzen.
With 5 Figures 相似文献
20.
The use of logic trees in probabilistic seismic hazard analyses often involves a large number of branches that reflect the uncertainty in the selection of different models and in the selection of the parameter values of each model. The sensitivity analysis, as proposed by Rabinowitz and Steinberg [Rabinowitz, N., Steinberg, D.M., 1991. Seismic hazard sensitivity analysis: a multi-parameter approach. Bull. Seismol. Soc. Am. 81, 796–817], is an efficient tool that allows the construction of logic trees focusing attention on the parameters that have greater impact on the hazard.In this paper the sensitivity analysis is performed in order to identify the parameters that have the largest influence on the Western Liguria (North Western Italy) seismic hazard. The analysis is conducted for six strategic sites following the multi-parameter approach developed by Rabinowitz and Steinberg [Rabinowitz, N., Steinberg, D.M., 1991. Seismic hazard sensitivity analysis: a multi-parameter approach. Bull. Seismol. Soc. Am. 81, 796–817] and accounts for both mean hazard values and hazard values corresponding to different percentiles (e.g., 16%-ile and 84%-ile). The results are assessed in terms of the expected PGA with a 10% probability of exceedance in 50 years for rock conditions and account for both the contribution from specific source zones using the Cornell approach [Cornell, C.A., 1968. Engineering seismic risk analysis. Bull. Seismol. Soc. Am. 58, 1583–1606] and the spatially smoothed seismicity [Frankel, A., 1995. Mapping seismic hazard in the Central and Eastern United States. Seismol. Res. Lett. 66, 8–21]. The influence of different procedures for calculating seismic hazard, seismic catalogues (epicentral parameters), source zone models, frequency–magnitude parameters, maximum earthquake magnitude values and attenuation relationships is considered. As a result, the sensitivity analysis allows us to identify the parameters with higher influence on the hazard. Only these parameters should be subjected to careful discussion or further research in order to reduce the uncertainty in the hazard while those with little or no effect can be excluded from subsequent logic-tree-based seismic hazard analyses. 相似文献