Geostatistics for radiological evaluation: study of structuring of extreme values   总被引：2，自引：2，他引：0  

Y. Desnoyers  J.-P. Chil��s  D. Dubot  N. Jeann��e  J.-M. Idasiak 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(8):1031-1037

Geostatistics applied to radiological evaluation of nuclear premises provides sound methods to estimate radiological activities, together with their uncertainty. Quantification and risk analysis of contaminated areas are initially performed by applying geostatistical methods relying on the multi-Gaussian assumption. However, the application of the classical bi-Gaussian model for disjunctive kriging proves sub-optimal due to the spatial structuring of high and low values. The beta model which pertains to the class of Hermitian isofactorial models is potentially better suited to radiological evaluation as it allows a continuous evolution from a mosaic to a pure diffusive model. In the test case, disjunctive kriging estimates are obtained by applying in turn the beta model and the pure diffusive model. The comparison of estimation outcomes shows rather limited differences, primarily located in and around the homogeneous contaminated areas.  相似文献   

Active surface faulting or landsliding in the Lower Tagus Valley (Portugal)? A solved controversy concerning the Vila Chã de Ourique site     

João Manuel Cabral  Fernando Marques  Paula Figueiredo  Luís Matias 《Journal of Seismology》2011,15(2):215-234

The Lower Tagus Valley has experienced significant (M 6–7) historical seismicity, evidencing the presence of seismogenic faults. These are still deficiently known due to the low strain rates and the recent alluvial sedimentation of the Tagus River that buries most of the structures, though Paleoseismic evidence was allegedly found by a research team in the Tagus valley, at a site 60 km N of Lisbon, near Vila Chã de Ourique (VCO). According to this team, trenching at the VCO site exposed an active thrust fault, evidencing the surface rupture of a large earthquake that occurred in 1531. Our studies performed at this site, comprising field observations with a reappraisal of the trench outcrops previously excavated, borehole drilling, soil mechanics laboratory testing, and seismic reflection acquisition, pointed to the alternative interpretation that the outcropping structures are gravitational and not of tectonic origin. The interpretation of new outcrops crosscutting the structures exposed at the trenches, as well as newly acquired high-resolution seismic reflection data, definitely exclude the active thrust fault explanation and support a gravitational slip model for all the observed structures. Gravitational slip in the river bank slope was promoted by low shear strength clays and high pore water pressure coupled with slope toe river erosion. Gravitational slides must have occurred prior to development of the present sedimentation level of the Tagus alluvial plain, which was attained in the last few thousand years as indicated by borehole data and estimations of sedimentation rates.  相似文献   

Helium irradiation study on zircon     

Lutz Nasdala  Dieter Grambole  Jens Götze  Ulf Kempe  Tamás Váczi 《Contributions to Mineralogy and Petrology》2011,161(5):777-789

Synthetic ZrSiO₄ and (mildly to strongly radiation-damaged) natural zircon samples were irradiated with 8.8 MeV ⁴He²⁺ ions (fluences in the range 1 × 10¹³–5 × 10¹⁶ ions/cm²). For comparison, an additional irradiation experiment was done with 30 MeV ¹⁶O⁶⁺ ions (fluence 1 × 10¹⁵ ions/cm²). The light-ion irradiation resulted in the generation of new (synthetic ZrSiO₄) or additional (mildly to strongly metamict natural samples) damage. The maximum extent of the damage is observed in a shallow depth range approximately 32–33 μm (8.8 MeV He) and ~12 μm (30 MeV O) below the sample surface, i.e. near the end of the ion trajectories. These depth values, and the observed damage distribution, correspond well to defect distribution patterns as predicted by Monte Carlo simulations. The irradiation damage is recognised from the notable broadening of Raman-active vibrational modes, lowered interference colours (i.e. decreased birefringence), and changes in the optical activity (i.e. luminescence emission). At very low damage levels, a broad-band yellow emission centre is generated whereas at elevated damage levels, this centre is suppressed and samples experience a general decrease in their emission intensity. Most remarkably, there is no indication of notable structural recovery in pre-damaged natural zircon as induced by the light-ion irradiation, which questions the relevance of alpha-assisted annealing of radiation damage in natural zircon.  相似文献   

Zooplankton succession during extraordinary drought–flood cycles: A case study in a South American floodplain lake     

Griselda Chaparro  María Cristina Marinone  Ruben J. Lombardo  María Romina Schiaffino  Alice de Souza Guimarães  Inés O’Farrell 《Limnologica》2011,41(4):371-381

We examined the zooplankton abundance and composition of Laguna Grande, a floodplain wetland of the Lower Paraná Basin (Argentina), during an extraordinary drought–flood cycle that affected both the environment and the biological conditions of the lake. Low waters were characterised by remarkably high conductivities and pH values, and high phytoplankton and bacterioplankton abundances with cyanobacterial blooms, while high waters showed opposite features. In relation to zooplankton, the mean abundances of all the taxonomic groups (rotifers, cladocerans, copepods, ciliates, and heterotrophic nanoflagellates) were slightly higher at low waters. Major changes were observed in the specific composition of metazooplankton: the euryhaline species assemblage that dominated in the dry warm period was replaced by several oligohaline littoral and planktonic species characteristic of the Paraná River Basin, when the water level rose. Mean species richness values at high waters doubled those of low waters and were directly correlated to water depth. Most of the rotifers of the genus Brachionus and the cladoceran Moina micrura switched from parthenogenetic to sexual reproduction during low waters, as a response to a harsh environment and crowding. We suggest that the main changes in the environmental conditions in this eutrophic floodplain lake are driven by the hydrology, which regulates the zooplankton succession. The herein described shifts in the zooplankton structure and dynamics of Laguna Grande over an extraordinary drought–flood cycle contribute to the understanding of the processes that might occur under the scenarios predicted by climate change models.  相似文献   

The Ellipsactinia Limestones of the Marsica area (Central Apennines): A reference zonation model for Upper Jurassic Intra-Tethys reef complexes     

G. Rusciadelli  C. Ricci  B. Lathuilière 《Sedimentary Geology》2011,233(1-4):69-87

This study presents a new and innovative distribution model of the main reef builders that thrived on bioconstructed margins of Upper Jurassic Intra-Tethys platforms. The proposed model is based on the zonation of an Upper Jurassic reef complex presently exposed in the central Apennines. Excellent exposures allow the reconstruction of the reef profile across the platform margin. Biota are mainly represented by corals and calcified demosponges, distributed with different amounts and aggregating structures along the reef complex. Microencrusters represent a secondary but important component that actively contributes to the reef construction process. Reef builders are distributed in variable quantities and with variable aggregating structures along the reef complex, revealing a strong reef zonation. Like the biota, the sedimentary features (grain size, sorting and reworking degree, bioerosion, cement crusts and cavities) show a distinctive distribution along the reef complex. Three main zones have been recognized along the studied reef complex: an internal, more protected and deeper zone, corresponding to a relatively deep back-reef/lagoon, is dominated by corals and chaetetids; a central zone (reef flat), where well-preserved coral bioconstructions give rise to a true, but discontinuous framework, and a more external zone, corresponding to the reef crest, characterized by the shallowest depths recorded across the reef complex and dominated by stromatopores. The latter forms mound-shaped structures, playing a role essential for the zoned character of the reef complex. These structures actively contribute to the construction of a moderately high topographic relief in the reef crest.  相似文献   

Innovating resource regimes: Water, wastewater, and the institutional dynamics of urban hydraulic reach in northwest Mexico     

Christopher A. Scott  Nicolás Pineda Pablos 《Geoforum》2011,42(4):439-450

The twin facets of urban hydraulic reach - cities’ appropriation of water from surrounding regions and irrigation use of urban wastewater over a growing rural footprint - form an emerging global policy challenge, especially as democratizing societies seek institutional means to address both urban growth and water scarcity. A central concern of this paper is to demonstrate that policy regionalism, as a process-based understanding of institutions and decision-making, better explains the causes, forms, and outcomes of hydraulic reach than do more structural approaches. Hermosillo, Mexico presents an unfolding case of rural-urban tension for control over rivers and aquifers as well as the infrastructure for water capture, storage, conveyance, and wastewater release. The analysis employs process documentation of water transfer and wastewater negotiations through interviews, review of primary documents, and field observations. Hermosillo’s recourse to negotiated agreements and quasi-market transactions, led by an emerging group of public sector innovators, advances understanding of water policy in Mexico by moving beyond prevailing concerns with the water reform’s neoliberal underpinnings to exploration of rapidly changing urban-centered experimentation. We conclude that evolving urban-rural power disparities and water resource landscapes of urban growth will drive continued expansion of hydraulic reach in water-scarce regions globally.  相似文献   

Impact of mining activities on sediments in a semi-arid environment: San Pedro River, Sonora, Mexico     

Agustín Gómez-Álvarez  Jesús L. Valenzuela-García  Diana Meza-Figueroa  Margarita de la O-Villanueva  Jorge Ramírez-Hernández  Javier Almendariz-Tapia  Efrén Pérez-Segura 《Applied Geochemistry》2011,26(12):2101-2112

A study of the San Pedro River (SPR), which is located in a semi-arid region in Sonora, Mexico, was conducted to evaluate the chemical, spatial and temporal (mobilization) trends of potentially harmful metals in its sediment in the rainy and dry seasons. High total concentrations of metals were detected in the following order: Fe > Cu > Mn > Zn > Pb > Cd. All studied metals except for Pb were increased during the dry season showing the effect of climate on the metal distribution in sediments. The results of sequential extraction indicated that the residual and Fe/Mn oxide fractions were the most important with regard to retaining potentially harmful metals in the sediments. In the exchangeable carbonate and Fe oxide fractions, high concentrations of metals were detected, representing high environmental risk. The geoaccumulation index shows slight to moderate contamination in most samples, and sampling point E4 (related to cattle activity) shows strong contamination for Cd, Cu, Pb and Zn. Enrichment factors (EFs) demonstrate anthropogenic origins for Pb (EF: 3–57), Cd (EF: 6–73) and Cu (EF: 1.5–224). This study shows that sediments are impacted by anthropogenic activities related to the mining industry, untreated wastewater discharges from the city of Cananea and cattle activities. Metal mobility in the SPR can disrupt the development of aquatic species in the river.  相似文献   

Natural tracer profiles across argillaceous formations   总被引：2，自引：0，他引：2  

Martin Mazurek  Peter Alt-EppingAdrian Bath  Thomas Gimmi  H. Niklaus WaberStéphane Buschaert  Pierre De Cannière  Mieke De CraenAndreas Gautschi  Sébastien Savoye  Agnès VinsotIsabelle Wemaere  Laurent Wouters 《Applied Geochemistry》2011,26(7):1035-1064

Argillaceous formations generally act as aquitards because of their low hydraulic conductivities. This property, together with the large retention capacity of clays for cationic contaminants, has brought argillaceous formations into focus as potential host rocks for the geological disposal of radioactive and other waste. In several countries, programmes are under way to characterise the detailed transport properties of such formations at depth. In this context, the interpretation of profiles of natural tracers in pore waters across the formations can give valuable information about the large-scale and long-term transport behaviour of these formations. Here, tracer-profile data, obtained by various methods of pore-water extraction for nine sites in central Europe, are compiled. Data at each site comprise some or all of the conservative tracers: anions (Cl⁻, Br⁻), water isotopes (δ¹⁸O, δ²H) and noble gases (mainly He). Based on a careful evaluation of the palaeo-hydrogeological evolution at each site, model scenarios are derived for initial and boundary pore-water compositions and an attempt is made to numerically reproduce the observed tracer distributions in a consistent way for all tracers and sites, using transport parameters derived from laboratory or in situ tests. The comprehensive results from this project have been reported in Mazurek et al. (2009). Here the results for three sites are presented in detail, but the conclusions are based on model interpretations of the entire data set. In essentially all cases, the shapes of the profiles can be explained by diffusion acting as the dominant transport process over periods of several thousands to several millions of years and at the length scales of the profiles. Transport by advection has a negligible influence on the observed profiles at most sites, as can be shown by estimating the maximum advection velocities that still give acceptable fits of the model with the data. The advantages and disadvantages of different conservative tracers are also assessed. The anion Cl⁻ is well suited as a natural tracer in aquitards, because its concentration varies considerably in environmental waters. It can easily be measured, although the uncertainty regarding the fraction of the pore space that is accessible to anions in clays remains an issue. The stable water isotopes are also well suited, but they are more difficult to measure and their values generally exhibit a smaller relative range of variation. Chlorine isotopes (δ³⁷Cl) and He are more difficult to interpret because initial and boundary conditions cannot easily be constrained by independent evidence. It is also shown that the existence of perturbing events such as the activation of aquifers due to uplift and erosion, leading to relatively sharp changes of boundary conditions, can be considered as a pre-requisite to obtain well-interpretable tracer signatures. On the other hand, gradual changes of boundary conditions are more difficult to parameterise and so may preclude a clear interpretation.  相似文献   

A Semi-classical calculus of correlations     

Yves Colin de Verdière 《Comptes Rendus Geoscience》2011,343(8-9):496-501

The method of passive imaging in seismology has been developped recently in order to image the Earth’s crust from recordings of the seismic noise. This method is founded on the computation of correlations of the seismic noise. In this article, we give an explicit formula for this correlation in the “semi-classical” regime. In order to do that, we define the power spectrum of a random field as the ensemble average of its Wigner measure; this allows phase-space computations: the pseudo-differential calculus and the ray theory. In this way, we get a formula for the correlation of the seismic noise in the semi-classical regime with a source noise which can be localized and non-homogeneous. After that, we show how the use of surface guided waves allows us to image the Earth’s crust.  相似文献   

Modeling aquifer�Criver interactions under the influence of groundwater abstraction in the Mancha Oriental System (SE Spain)     

David Sanz  Santiago Casta?o  Eduardo Cassiraga  Andr��s Sahuquillo  Juan Jos�� G��mez-Alday  Salvador Pe?a  Alfonso Calera 《Hydrogeology Journal》2011,19(2):475-487

The Mancha Oriental System (MOS, 7,260?km²) is one of the largest aquifers within Spain, and is encompassed by the Jucar River Basin. Over the past 30?years, socioeconomic development within the region has been largely due to intensive use of groundwater resources for irrigating crops (1,000?km²). Groundwater pumping (406 million m³/year) has provoked a steady drop in the groundwater level and a reduction of MOS discharge to the Jucar River. The study aims to characterize the river?Caquifer relationship, to determine the influence that groundwater abstraction has on the river discharge. This research has advanced a three-dimensional large-scale numerical groundwater-flow model (MODFLOW 2000) in order to spatially and temporally evaluate, quantify and predict the river?Caquifer interactions that are influenced by groundwater abstraction in MOS. It is demonstrated that although groundwater abstraction increased considerably from the early 1980s to 2000, the depletion of water stored in the aquifer was lower than might be expected. This is mainly due to aquifer recharge from the Jucar River, induced by groundwater abstraction. The area of disconnection between the river and the water table (i.e. where groundwater head is lower than the riverbed) is found to have spread 20?km downstream from its position before pumping started.  相似文献