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991.
Raimundo Delgado Aníbal Costa António Arêde Nelson Vila Pouca João Guedes Xavier Romão Pedro Delgado Patrício Rocha 《Bulletin of Earthquake Engineering》2010,8(1):181-199
Research on seismic safety assessment has been the centre of great interest among the scientific community in recent years.
Although the devastating impact of earthquakes on current society should be incentive enough to increase research, the development
of more realistic mechanical behaviour models and the continuous enhancement of computation capabilities are paramount factors
contributing a great deal to the increase of such interest. In this context, three research areas can be identified as currently
leading to important developments: code related research, especially in Europe where new design codes are in the implementation
process; risk analysis, namely concerning the definition of methodologies for safety assessment that involve the evaluation
of the failure probability and could be included in future generations of codes; and experimental characterization of constitutive
laws which provides support for the development and calibration of accurate and realistic numerical models for seismic analysis
and for the adequate characterization of limit state capacities. The paper will present some of the current scientific research
trends on these three seismic safety assessment related topics. Studies addressing the seismic safety assessment of structures,
either probabilistically or based on code provisions, and that consider realistic nonlinear mechanical behaviour models will
be focussed. Reference will also be made to experimental research on the seismic behaviour of structural elements, emphasizing
its crucial role to support the development of numerical models simulating the effects of different seismic strengthening
techniques. Finally, given the development of studies leading to new trends and perspectives for performance based earthquake
engineering, a possible scenario for seismic design in the future is presented, emphasizing the key issues for its implementation. 相似文献
992.
Luis Manuel de Vries Jesus Carrera Oriol Falivene Oscar Gratacós Luit Jan Slooten 《Mathematical Geosciences》2009,41(1):29-42
Simulation of flow and solute transport through aquifers or oil reservoirs requires a precise representation of subsurface
heterogeneity that can be achieved by stochastic simulation approaches. Traditional geostatistical methods based on variograms,
such as truncated Gaussian simulation or sequential indicator simulation, may fail to generate the complex, curvilinear, continuous
and interconnected facies distributions that are often encountered in real geological media, due to their reliance on two-point
statistics. Multiple Point Geostatistics (MPG) overcomes this constraint by using more complex point configurations whose
statistics are retrieved from training images. Obtaining representative statistics requires stationary training images, but
geological understanding often suggests a priori facies variability patterns. This research aims at extending MPG to non-stationary
facies distributions. The proposed method subdivides the training images into different areas. The statistics for each area
are stored in separate frequency search trees. Several training images are used to ensure that the obtained statistics are
representative. The facies probability distribution for each cell during simulation is calculated by weighting the probabilities
from the frequency trees. The method is tested on two different object-based training image sets. Results show that non-stationary
training images can be used to generate suitable non-stationary facies distributions. 相似文献
993.
Ramón Luna Carlos Millán Manuel Domingo Miguel Ángel Satorre 《Astrophysics and Space Science》2008,314(1-3):113-119
CO2 ices are known to exist in different astrophysical environments. In spite of this, its physical properties (structure, density,
refractive index) have not been as widely studied as those of water ice. It would be of great value to study the adsorption
properties of this ice in conditions related to astrophysical environments. In this paper, we explore the possibility that
CO2 traps relevant molecules in astrophysical environments at temperatures higher than expected from their characteristic sublimation
point. To fulfil this aim we have carried out desorption experiments under High Vacuum conditions based on a Quartz Crystal
Microbalance and additionally monitored with a Quadrupole Mass Spectrometer. From our results, the presence of CH4 in the solid phase above the sublimation temperature in some astrophysical scenarios could be explained by the presence of
several retaining mechanisms related to the structure of CO2 ice. 相似文献
994.
Nguyen Dinh Chau Paweł Jodłowski Stefan J. Kalita Paweł Olko Edward Chruściel Adam Maksymowicz Michał Waligórski Paweł Bilski Maciej Budzanowski 《Acta Geophysica》2008,56(2):505-517
The doses of gamma radiation, concentrations of radium isotopes in water and sediments, radon concentration and concentration
of alpha potential energy of radon decay products in the copper ore mine and in the mining region in the vicinity of Lubin
town in Poland are presented. These data served as a basis for the assessment of radiological hazard to the mine workers and
general public. The results of this assessment indicate that radiological hazard in the region does not differ substantially
from typical values associated with natural radiation background. The calculated average annual effective dose for copper
miners is 1.48 mSv. In general, copper ore mines can be regarded as radiologically safe workplaces. 相似文献
995.
Eleazar Padrón Gladys Melián Rayco Marrero Dácil Nolasco José Barrancos Germán Padilla Pedro A. Hernández Nemesio M. Pérez 《Pure and Applied Geophysics》2008,165(1):95-114
Significant changes in the diffuse emission of carbon dioxide were recorded in a geochemical station located at El Hierro,
Canary Islands, before the occurrence of several seismic events during 2004. Two precursory CO2 efflux increases started thirteen and nine days before two seismic events of magnitude 2.3 and 1.7, which took place near
El Hierro Island, Canary Islands, on March 23 and April 15, reaching a maximun value of 51.1 and 46.2 g m−2 d−1, respectively, five and eight days before the two seismic events. Other similar increases started thirteen and five days
before the occurrence of two seismic events of magnitude 1.3 and 1.5 which took place on October 15 and 21 respectively, reaching
the maximum values four and one day before the earthquakes. These changes were not related to variations in atmospheric or
soil parameters. The Material Failure Forecast Method (FFM), which analyzes the rate of precursory phenomena, was successfully
applied to forecast the first seismic event that took place in El Hierro Island in 2004. 相似文献
996.
Belén Oliva-Urcia Inma Gil-Peña Ruth Soto José María Samsó Borja Antolín Emilio L. Pueyo 《Studia Geophysica et Geodaetica》2018,62(2):291-322
Magnetic fabric allows to unravel the petrofabrics of sedimentary rocks and to assess their deformational history. The use of this technique, in addition to classical structural field observations in the limbs of seven asymmetric folds in the Pyrenees, helps to determine the differences of internal deformation as well as the folding kinematics. Three folds developed during the Variscan Orogeny in Ordovician and Devonian rocks, and four folds developed during the Pyrenean Orogeny in Eocene rocks, are studied. Folds show a variety of structural locations, in different thrust sheets of the Southern Central Pyrenees, different cleavage development, age, geometry and lithology. Sampling follows an equivalent lithological layer in the two limbs, except for one case, of the selected folds. Results show a modified tectonic magnetic fabric in most sites with the magnetic lineation on the tectonic foliation plane. A larger scattering of the magnetic lineation (maximum magnetic anisotropy axis) and a higher intensity of the preferred orientation of minerals (eccentricity of the anisotropy of magnetic susceptibility - AMS ellipsoid) is better observed in the overturned (short) limb of the asymmetric Variscan folds than in the normal (long) limb. On the other hand, the shape parameter in Alpine folds is generally larger in the overturned (short) limb then in the normal (long) one. A good clustering of the minimum magnetic anisotropy axes is observed in all limbs. The combination of the AMS data with the structural data helps to understand and better constrain the deformation degree in these asymmetric folds and to unravel the deformational history. 相似文献
997.
Margaret?E.?HartleyEmail authorView authors OrcID profile Enik??Bali John?Maclennan David?A.?Neave S?mundur?A.?Halldórsson 《Contributions to Mineralogy and Petrology》2018,173(2):10
The 2014–2015 Holuhraun eruption, on the Bárðarbunga volcanic system in central Iceland, was one of the best-monitored basaltic fissure eruptions that has ever occurred, and presents a unique opportunity to link petrological and geochemical data with geophysical observations during a major rifting episode. We present major and trace element analyses of melt inclusions and matrix glasses from a suite of ten samples collected over the course of the Holuhraun eruption. The diversity of trace element ratios such as La/Yb in Holuhraun melt inclusions reveals that the magma evolved via concurrent mixing and crystallization of diverse primary melts in the mid-crust. Using olivine–plagioclase–augite–melt (OPAM) barometry, we calculate that the Holuhraun carrier melt equilibrated at 2.1?±?0.7 kbar (7.5?±?2.5 km), which is in agreement with the depths of earthquakes (6?±?1 km) between Bárðarbunga central volcano and the eruption site in the days preceding eruption onset. Using the same approach, melt inclusions equilibrated at pressures between 0.5 and 8.0 kbar, with the most probable pressure being 3.2 kbar. Diffusion chronometry reveals minimum residence timescales of 1–12 days for melt inclusion-bearing macrocrysts in the Holuhraun carrier melt. By combining timescales of diffusive dehydration of melt inclusions with the calculated pressure of H2O saturation for the Holuhraun magma, we calculate indicative magma ascent rates of 0.12–0.29 m s?1. Our petrological and geochemical data are consistent with lateral magma transport from Bárðarbunga volcano to the eruption site in a shallow- to mid-crustal dyke, as has been suggested on the basis of seismic and geodetic datasets. This result is a significant step forward in reconciling petrological and geophysical interpretations of magma transport during volcano-tectonic episodes, and provides a critical framework for the interpretation of premonitory seismic and geodetic data in volcanically active regions. 相似文献
998.
The Devonian-Carboniferous contact in southern South America, characterized by a sharp unconformity, has been related to the Late Devonian-Early Carboniferous Eo-Hercynian orogeny. The Calingasta-Uspallata basin of western Argentina and the Sauce-Grande basin (Ventana Foldbelt) of eastern Argentina have been selected to characterize this unconformity. The Eo-Hercynian movements were accompanied in western Argentina by igneous activity related to a Late Devonian—Early Carboniferous magmatic arc mainly exposed today along the Andean Cordillera. This magmatic activity is partly reflected also in eastern Argentina (Ventana Foldbelt), where isotopic dates suggest a thermal event also related to the intrusions present to the west in the North Patagonian Massif and Sierras Pampeanas. The scarcity of Lower Carboniferous deposits in the stratigraphic record of southern South America suggests that the Early Carboniferous was a time interval dominated by uplift and erosion followed by widespread subsidence during the Middle and Late Carboniferous. The origin of the Eo-Hercynian orogeny can be linked with the convergence between the Arequipa Massif, and its southern extension, and the South American continent. Its effects are best represented along the Palaeo-Pacific margin, although distant effects are discernible in the cratonic areas of eastern South America.
Correspondence to: O. R. López-Gamundí 相似文献
999.
Federico M. Ledesma Silvina Van der Molen Pedro J. Barón 《Journal of Sea Research》2010,63(3-4):213-216
The European green crab Carcinus maenas is a widely spread invasive species. Studying the most recently introduced population of the species in the Atlantic coast off Patagonia, it became apparent to us that carapaces (the dorsal cover of the visceral-cavity detaching from the rest of the exoskeleton after ecdysis) accumulated on the intertidal may be used as a valuable complementary material to analyze the size structure of crabs. However, since growth rate (and consequently size at instar) of crabs differs between males and females, finding a method to distinguish crab sex by observation of carapace morphology was necessary to allow the construction of independent size frequency distributions for each sex. In this work, we examined the shape of the carapaces from both sexes of C. maenas, and using Elliptical Fourier Analysis successfully identified sexual dimorphism. Thus, a reliable method to identify sexes by visual observation of the carapace was developed. Based on our results, we discuss the evolutionary significance of carapace form differentiation of both sexes. 相似文献
1000.
Jorge García-Girón Camino Fernández-Aláez Alejandro Nistal-García Margarita Fernández-Aláez 《Journal of Paleolimnology》2018,60(4):495-509
Macrofossils are known as a useful tool in reconstructing their original plant communities. However, most studies have been focused on comparing the composition and distribution of living plant communities and their remains in temperate lakes. Mediterranean shallow lakes have been historically far less studied and little is known about the relationships between Mediterranean macrophyte communities and their remains. The aim of our study is to assess how contemporary aquatic macrophyte communities are represented by their sedimentary remains in terms of composition, distribution and concordance between the contemporary and the subfossil assemblages in a procrustean superimposition space, and to determine which surface sediment cores, collected along a depth gradient, may represent best the whole-lake macrofossil assemblage. These analyses were carried out for both species and macrophyte growth forms (submerged hydrophytes, floating-leaved hydrophytes, helophytes and charophytes) in order to check which of the two (species and growth forms) were represented best by their macro-remains. The most abundant present-day species (Myriophyllum alterniflorum DC. and Potamogeton trichoides L.) were under-represented while Characeae and some floating-leaved hydrophytes (Polygonum amphibium L. and Ranunculus peltatus Schrank) were over-represented in sedimentary samples. Additionally, macro-remains of submerged hydrophytes and helophytes were generally found in the central areas and in close proximity to contemporary vegetation, whereas floating-leaved hydrophytes distributed close to the near-shore. Notwithstanding some disparities between contemporary vegetation and their macrofossil assemblages, we found a good agreement between present-day and sedimentary datasets for both species and macrophyte growth forms. Furthermore, our study suggests that sediment cores from deep areas are more likely to represent best the whole-lake macrofossil assemblage because of their high diversity, equitability and heterogeneity. We conclude that aquatic macrophyte subfossils from the central areas of the basin can be a very useful tool in tracking the species composition and structure of the original macrophyte communities in shallow Mediterranean lakes. Additionally, when considering the use of macro-remains to reconstruct the composition and structure of macrophyte growth forms, we recommend a multicore approach that uses transects running from the shore to the lake center. 相似文献