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951.
F. Gutiérrez J. P. Galve P. Lucha J. Bonachea L. Jordá R. Jordá 《Environmental Geology》2009,58(5):1107-1122
An active sinkhole around 100 m long has been investigated in the city of Zaragoza (NE Spain). Subsidence activity on this
depression, including the sudden occurrence of a collapse sinkhole 5 m across, led to the abandonment of a factory in the
1990s. At the present time, a building with 100 flats and shallow pad foundations partially built on the sinkhole, is affected
by rapid differential settlement. The development of the sinkhole results from the karstification of the halite- and glauberite-
bearing bedrock and the sagging and collapse of the overlying bedrock and alluvium, more than 30 m thick. GPR and electrical
resistivity profiles have provided information on the distribution and geometry of the subsidence structure. The application
of the trenching technique and geochronological methods (AMS and OSL dating) has allowed us to infer objective and practical
data on the sinkhole including (1) Limits of the subsidence structure, (2) subsidence mechanisms, (3) cumulative subsidence
(>408 cm), (4) subsidence rates on specific failure planes (>1.8 cm/year), (5) episodic displacement regime of some fault
planes. The available information indicates that the progressive deformation recorded in the building will continue and might
be punctuated by events of more rapid displacement. This work illustrates the practicality of the trenching technique for
the study of sinkholes in mantled karst areas. 相似文献
952.
M. Chatterjee J. Canário S. K. Sarkar V. Branco A. K. Bhattacharya K. K. Satpathy 《Environmental Geology》2009,57(5):1125-1134
Mercury concentrations (HgT) in fine-grained fraction (<63 μm) of core sediments of the Hugli–Matla–Bidyadhari estuarine complex, India were analyzed.
Results revealed a wide range of spatial variations (<4–93 ng g−1 dry weight) with a definite enhancement level at the lower stretch of the estuarine complex infested with mangrove plants,
which might act as a sink to HgT. An elevated concentration of Hg was encountered in surface/subsurface layer of the core in majority of the cases resulting
from physical, biogenic and postdepositional diagenetic processes that remobilized and resuspended the metal from deeper sediments.
A strong positive correlation was observed between the Hg and clay fraction content of the sediments, while the correlations
of Hg with Al, Fe and Mn were poor. Based on the index of geoaccumulation (I
geo) and effects range-low (ER-L) value, it is considered that the sediments are less polluted and thus there is less chance
of ecotoxicological risk to organisms living in sediments. 相似文献
953.
Jakob Walcher Brent Groves Tamás Budavári Daniel Dale 《Astrophysics and Space Science》2011,331(1):1-51
Fitting the spectral energy distributions (SEDs) of galaxies is an almost universally used technique that has matured significantly
in the last decade. Model predictions and fitting procedures have improved significantly over this time, attempting to keep
up with the vastly increased volume and quality of available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of multiwavelength data sets, and the methods used to fit model
SEDs to observed galaxy data sets. We touch upon the achievements and challenges in the major ingredients of SED fitting,
with a special emphasis on describing the interplay between the quality of the available data, the quality of the available
models, and the best fitting technique to use in order to obtain a realistic measurement as well as realistic uncertainties.
We conclude that SED fitting can be used effectively to derive a range of physical properties of galaxies, such as redshift,
stellar masses, star formation rates, dust masses, and metallicities, with care taken not to over-interpret the available
data. Yet there still exist many issues such as estimating the age of the oldest stars in a galaxy, finer details of dust
properties and dust-star geometry, and the influences of poorly understood, luminous stellar types and phases. The challenge
for the coming years will be to improve both the models and the observational data sets to resolve these uncertainties. The
present review will be made available on an interactive, moderated web page (), where the community can access and change the text. The intention is to expand the text and keep it up to date over the
coming years. 相似文献
954.
To ascertain the importance of sputtering by solar wind ions on the formation of a sodium exosphere around Mercury and the Moon, we have irradiated with 4 keV He ions, the Na bearing tectosilicates: albite, labradorite, and anorthoclase, as well as adsorbed Na layers deposited on albite and on olivine (a neosilicate that does not contain Na). Sodium at the surface and near surface (<40 Å) was quantified with X-ray photoelectron spectroscopy before and after each irradiation to determine the depletion cross section. We measured a cross section for sputtering of Na adsorbed on mineral surfaces, σs ≈ 1 × 10?15 cm2 atom?1. In addition, mass spectrometric analyses of the sputtered flux show that a large fraction of the Na is sputtered as ions rather than as neutral atoms. These results have strong implications for modeling the sodium population within the mercurian and the lunar exospheres. 相似文献
955.
Javier Alcántara-Carrió Silvia Albarracín Isabel Montoya Montes Germán Flor-Blanco Ángela Fontán Bouzas Jorge Rey Salgado 《Geo-Marine Letters》2013,33(2-3):209-216
The objective of this study is to document and interpret a recently discovered carbonate-cemented coastal barrier on the inner shelf of the Gulf of Valencia (western Mediterranean Sea). The coastal barrier was identified in a high-resolution digital bathymetric model based on a cartographic survey of the study area using a multibeam echosounder. Moreover, radiocarbon dating and petrographic analyses were performed on a rock sample recovered from the seabed. The data reveal the submerged coastal barrier to be approx. 1.7 km wide and 70 km long, and incised by channels of various dimensions. Aligned more or less parallel to the modern coastline, it is interpreted as corresponding to the shoreline of a former sea-level stillstand. The barrier and lagoon system became stranded above sea level in the course of a subsequent forced regression, which also caused the incision of the river courses. Age dating of the cemented rock suggests that the fossil coastal barrier most probably formed during the prolonged Tyrrhenian (Eemian) sea-level highstand, induration taking place by carbonate cementation at the contact between freshwater and seawater (beach-rock formation). The fact that the fossil barrier is today submerged below modern sea level is explained by the sustained subsidence affecting the region. 相似文献
956.
957.
Cantarero S Camino-Sánchez FJ Zafra-Gómez A Ballesteros O Navalón A Vílchez JL Verge C Reis MS Saraiva PM 《Marine pollution bulletin》2012,64(3):587-594
The contamination of aquatic environments has become the focus of increasing regulation and public concern due to their potential and unknown negative effects on the ecosystems. The present work develops a monitoring and statistical study, based on the analysis of variance test (ANOVA) and the multivariable analysis, both for insoluble soap and LAS in order to compare the behavior of different anionic surfactants in this environmental compartment. First, a novel and successfully validated methodology to analyze insoluble soap in these samples is developed. The matrix effect and the comparison of different extraction techniques were also performed. The optimized analytical methodologies were applied to 48 representative samples collected from the Almeria Coast (Spain) and then a statistical analysis to correlate anionic surfactant concentration and several variables associated with marine sediment samples was also developed. The results obtained showed relevant conclusions related to the environmental behavior of anionic surfactants in marine sediments. 相似文献
958.
Bohuslav R??ek Jaroslava Plomerová Vladislav Babu?ka 《Studia Geophysica et Geodaetica》2012,56(1):107-140
Joint inversion of teleseismic P-waveforms and local group velocities of surface waves retrieved from ambient seismic noise
has been performed to model velocity structure of the crust and uppermost mantle of the Bohemian Massif. We analysed P-waveforms
of 381 teleseismic earthquakes recorded at 54 broadband seismic stations located on the territory of the Czech Republic and
in its close surroundings. Group velocities of Rayleigh and Love surface waves were obtained by cross-correlating long-term
recordings of seismic noise. The basis for waveform inversion is the well-known methodology of P-to-S receiver functions constructed
from converted phases. Due to instabilities in direct inversion of receiver functions caused by the necessity of applying
deconvolution, we propose an alternative formulation to fit observed and calculated radial components of P waveforms. The
joint inversion is transformed into a search for the minimum of the cost function defined as a weighted sum of waveform and
group velocity misfits. With the use of the robust stochastic optimizer (Differential Evolution Algorithm), neither derivatives
nor a starting model are needed. The task was solved for 1D layered isotropic models of the crust and the uppermost mantle.
We have performed a sequence of inversions with models containing one, two, three and four layers above a half-space. By using
statistical criteria (F-test) we were able to select the simplest velocity models satisfying data and representing local geological
structures. Complex crustal models are typical for stations located close to boundaries of major tectonic units. The relatively
low average P to S wave-velocity ratio is in agreement with the generally accepted view that the BM crust is predominantly
felsic. 相似文献
959.
We derive expressions for computing the gravitational field (potential and its radial derivative) generated by an arbitrary
homogeneous or laterally varying density contrast layer with a variable depth and thickness based on methods for a spherical
harmonic analysis and synthesis of gravity field. The newly derived expressions are utilised in the gravimetric forward modelling
of major known density structures within the Earth’s crust (excluding the ocean density contrast) beneath the geoid surface.
The gravitational field quantities due to the sediments and crust components density contrasts, shown in numerical examples,
are computed using the 2 × 2 arc-deg discrete data from the global crustal model CRUST2.0. These density contrasts are defined
relative to the adopted value of the reference crustal density of 2670 kgm−3. All computations are realised globally on a 1 × 1 arc-deg geographical grid at the Earth’s surface. The maxima of the gravitational
signal due to the sediments density contrast are mainly along continental shelf regions with the largest sedimentary deposits.
The corresponding maxima due to the consolidated crust components density contrast are over areas of the largest continental
crustal thickness with variable geological structure. 相似文献
960.
This paper deals with the estimation of peak inelastic displacements of SDOF systems, representative of typical steel structures, under constant relative strength scenarios. Mean inelastic deformation demands on bilinear systems (simulating moment resisting frames) are considered as the basis for comparative purposes. Additional SDOF models representing partially‐restrained and concentrically‐braced (CB) frames are introduced and employed to assess the influence of different force‐displacement relationships on peak inelastic displacement ratios. The studies presented in this paper illustrate that the ratio between the overall yield strength and the strength during pinching intervals is the main factor governing the inelastic deformations of partially‐restrained models and leading to significant differences when compared with predictions based on bilinear structures, especially in the short‐period range. It is also shown that the response of CB systems can differ significantly from other pinching models when subjected to low or moderate levels of seismic demand, highlighting the necessity of employing dedicated models for studying the response of CB structures. Particular attention is also given to the influence of a number of scalar parameters that characterise the frequency content of the ground motion on the estimated peak displacement ratios. The relative merits of using the average spectral period Taver, mean period Tm, predominant period Tg, characteristic period Tc and smoothed spectral predominant period To of the earthquake ground motion, are assessed. This paper demonstrates that the predominant period, defined as the period at which the input energy is maximum throughout the period range, is the most suitable frequency content scalar parameter for reducing the variability in displacement estimations. Finally, noniterative equivalent linearisation expressions based on the secant period and equivalent damping ratios are presented and verified for the prediction of peak deformation demands in steel structures. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献