Flood threat anomaly for the low coastal areas of the English Channel based on analysis of recent characteristic flood occurrences     

Paolo Antonio Pirazzoli  Stéphane Costa  Uwe Dornbusch 《Ocean Dynamics》2007,57(6):501-510

In the English Channel, extreme surge heights did not occur at the time of extreme high tides during the last decades and maximum recorded heights usually do not exceed the maximum astronomical tide by more than a few decimetres. To understand whether this lack of coincidence may be due to specific phenomena or only to chance, we have studied hourly tide records lasting a few decades from nine English and nine French stations as well as air pressure and wind data from nearby meteorological observatories. Among the case studies of moderate flooding at several coastal stations occurring during spring tide, we have selected those of 24–25/10/1980 and of 30/01/1983 to 02/02/1983 as representative of a normal situation without any special chance. The third case study 26–28/02/1990 was potentially more dangerous because of the storm intensity and duration; however, by chance, surge peaks occurred near the low tide. Finally, the propagation of the surge peak of 15–16/10/1987, which reached the maximum height recorded during all the instrumental period at several stations, has been followed all along the English Channel, using the hourly records of 12 tide-gauge stations and of 16 meteorological stations. The surge peak of this great storm, probably the strongest in the last two centuries, occurred everywhere at high tide and spread with the same velocity of the tidal wave. Fortunately, no major flooding occurred because it was the day after a neap tide. In conclusion, some good fortune has saved the low coastal areas of the English Channel from major floods during the last decades. However, the occurrence of the peak of a strong storm surge arriving near the western entrance of the Channel at the time of a great astronomical high tide is a possible event that could be devastating along both sides of the Channel coasts. Main parts of this paper have been presented orally in June 2005 at the joint INQUA–IGCP 495 Meeting “Dunkerque 2005” and in February 2006 at the ASLO-TOS-AGU “Ocean Sciences Meeting” (Honolulu, HI).  相似文献   

Clamshell excavation of a permeable reactive barrier     

Antonio Di Molfetta  Rajandrea Sethi 《Environmental Geology》2006,50(3):361-369

Nowadays, permeable reactive barriers (PRB) are one of the most widespread techniques for the remediation of contaminated aquifers. Over the past 10 years, the use of iron-based PRBs has evolved from innovative to accepted standard practice for the treatment of a variety of groundwater contaminants (ITRC in: Permeable reactive barriers: lessons learned/new directions. The Interstate Technology and Regulatory Council, Permeable Reactive Barriers Team 2005). Although, a variety of excavation methods have been developed, backhoe excavators are often used for the construction of PRBs. The aim of this study is to describe the emplacement of a full-scale PRB and the benefits deriving from the use of a crawler crane equipped with a hydraulic grab (also known as clamshell excavator) in the excavation phases. The studied PRB was designed to remediate a chlorinated hydrocarbons plume at an old industrial landfill site, in Avigliana, near the city of Torino, in Italy. The continuous reactive barrier was designed to be 120 m long, 13 m deep, and 0.6 m thick. The installation of the barrier was accomplished using a clamshell for the excavation of the trench and a guar-gum slurry to support the walls. The performance of this technique was outstanding and allowed the installation of the PRB in 7 days. The degree of precision of the excavation was very high because of the intrinsic characteristics of this excavation tool and of the use of a concrete curb to guide the hydraulic grab. Moreover, the adopted technique permitted a saving of bioslurry thus minimizing the amount of biocide required.  相似文献   

Hydrogeological and hydrochemical features of an area polluted by heavy metals in central Nicaragua     

J. A. Mendoza  T. Dahlin  G Barmen 《Hydrogeology Journal》2006,14(5):777-784

Geophysical and hydrochemical surveys were used to investigate the hydrogeological conditions in one of the Río Sucio microbasins, in central Nicaragua. Zones of vertical structures (i.e. fractures and quartz veins) and weathering were mapped using Continuous Vertical Electrical Soundings (CVES), as such zones are of major importance for groundwater transport. Water from the springs was analysed to determine concentrations of major ions and heavy metals. Low ion concentrations and ¹⁸O analyses indicate that the springs occur close to their recharge areas and there is a relatively rapid groundwater circulation. Mercury (Hg) content in the springs was low, while comparatively high amounts of lead (Pb) were found. The results presented here demonstrate the important function of weathering and tectonics in the occurrence of groundwater systems in the basin. Hg and Pb found in the springs’ water reveal the existence of an increase in pollution sources disseminating in the area. More than 100 years of using mercury in the gold-mining industry and releasing wastes into rivers has affected water quality and ecosystems. Further investigations are needed in this area to determine the groundwater vulnerability to this pollution as this resource may be needed in the future.  相似文献   

Oligocene-early Miocene transgressive cover of the Betic-Rif Internal Zone. Revision of its geologic significance     

Francisco Serrano  Carlos Sanz de Galdeano  Khalil El Kadiri  Antonio Guerra-Merchán  Angel Carlos López-Garrido  Manuel Martín-Martín  Rachid Hlila 《Eclogae Geologicae Helvetiae》2006,99(2):237-253

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Chemical Characterisation of Chromites by XRF Spectrometry     

Maria Fernanda Gazulla  Antonio Barba  María Pilar Gómez  Monica Orduña 《Geostandards and Geoanalytical Research》2006,30(3):237-243

The present study was undertaken to establish and validate a methodology for determining the chemical composition of chromite ores, as no detailed information could be found in the literature. Chromite ores from South Africa, Kazajistan and Mongolia were analysed. X-ray fluorescence (XRF) spectrometry was used for chemical characterisation. Sample preparation in the form of fused beads was optimised in terms of sample:flux ratio, type of flux, type of release agent, fusion temperature and time. Calibration and validation samples were prepared from mixtures of reference materials. The proposed methodology was then used in an interlaboratory test for preparing a new chromite-rich reference material.
L'analyse présentée id a été entreprise afin d'établir et de valider une méthodologie pour déterminer la composition chimique de minerals de chromite, car aucune information détaillée là dessus ne pouvait etre trouvée dans la littérature. Des minerals de chromite d'Afrique du Sud, du Kazakhstan et de Mongolie ont été analysés par spectrométrie de Fluorescence de Rayons X (XRF) afin d'être caractérisés chimiquement. La préparation des échantillons afin d'obtenir des perles fondues a été optimisée en termes du rapport "échantillon/fondant", type de fondant, d'agent mouillant, température et durée de fusion. La calibration et la validation ont été faites à partir de mixtures de matériau de référence. La méthodologie proposée a été ensuite appliquée à un test d'inter-comparaison en vue de préparer un nouveau matériau de référence riche en chromite .  相似文献   

A New Method for Estimating Lengths for Partially Exposed Features     

Clemens A. Visser  Antonio G. Chessa 《Mathematical Geology》2000,32(1):109-126

Length distributions from sedimentary bodies can be measured in outcrop. A common feature in many outcrops is the occurrence of partially exposed bodies, i.e., sedimentary bodies that are cut by either one or both edges of the outcrop. Ignoring these partials while establishing a length distribution leads to a bias toward the smaller length classes. This is because larger bodies have a larger probability to occur as partials than smaller bodies. We present a new method for estimating the expected complete length for a partially exposed feature, based on the theory of conditional probability. The method is demonstrated and tested on a sandstone outcrop exhibiting over 200 interbedded thin silt/shale streaks. It is shown that the method can significantly enlarge both the size and the representativeness of length distributions.  相似文献   

Spatial statistics for urban analysis: A review of techniques with examples   总被引：8，自引：0，他引：8  

Antonio Páez  Darren M. Scott 《GeoJournal》2004,61(1):53-67

Traditionally, urban analysis has been quick to adopt and benefit from developments in technology (e.g., microcomputer, GIS) and techniques (e.g., statistics, mathematical programming). This has not been the case, however, with newer methods of spatial analysis — in particular, spatial statistics. Only recently has this situation started to change. This paper documents the confluence of spatial statistics and urban analysis by first reviewing developments in spatial statistics, and then presenting examples of recent applications in urban analysis. The developments reviewed fall under the rubric of global and local forms of spatial analysis, and cover three major technical issues: spatial association, spatial heterogeneity and the modifiable areal unit problem. The examples highlight the relevance and usefulness of the techniques reviewed for urban transportation and land-use applications. The paper concludes with conjectures concerning future developments at the intersection of spatial statistics and urban analysis.  相似文献   

A linkage criterion for segmented normal faults     

Roger Soliva  Antonio Benedicto 《Journal of Structural Geology》2004,26(12):2251-2267

A detailed field study of 39 centimetre- to metre-scale relay ramps from two outcrops was performed to investigate the development of a linkage criterion for segmented normal faults. We analysed the displacement distribution and the geometry of fault arrays containing three types of relay ramp: open, linked, and fully breached, in order to identify which parameters are relevant to fault linkage, and to establish a linkage criterion. Each relay ramp geometry has a specific graphical field on a relay displacement–separation diagram. The field including all the linked geometries (initiation of linkage) separates open and fully breached relay ramps and is interpreted as a value of relay displacement to separation ratio for which faults link during their overlap. A ‘linkage threshold’, in each studied fault system, is defined as the best-fit linear trend of linked relays. We discuss the scaling and the variability of the linkage criterion using published datasets from a wide variety of settings and scales. The observed linkage threshold is linear, with a slope value varying less than one order of magnitude. This suggests that linking relay ramps have self-similar geometries from centimetre- to kilometre-scale and that normal fault linkage is governed by similar fault interaction across a broad range of scales. The linkage criterion, which can be an effective tool to estimate relay ramp geometry at depth or at the earth surface, could therefore be used to improve investigations in determining fluid entrapment or in the evaluation of potential surface of seismic ruptures.  相似文献   

Stratigraphic architecture of the Pyreneo-Languedocian submarine fan,Gulf of Lions,western Mediterranean Sea     

Antonio Tadeu dos Reis  Christian Gorini  Alain Mauffret  Michelle Mepen 《Comptes Rendus Geoscience》2004,336(2):125-133

The Pyreneo-Languedocian submarine sediment body, located in the western sector of the Gulf of Lions, is an example of a fan-like depositional system essentially controlled by salt tectonics. The area was subjected to a combined effect of overburden subsidence into the evacuated salt layer and a significant distal salt thickening, due to preferential basinward salt migration. This mode of salt migration impacted the Quaternary sea-bottom morphology by creating a large midslope topographic low, providing space accommodation for the Pyreneo-Languedocian fan. At gulf scale, the fan is a unique feature because unchannelized sedimentary environment in the area occurs at slope level, thus in minor water depth in relation to all other deep-water sedimentary systems offshore Gulf of Lions. To cite this article: A.T. dos Reis et al., C. R. Geoscience 336 (2004).  相似文献   

Sr and Nd Characteristics of Brasiliano/Pan-African Granitoid Plutons of the Araçuaí Orogen, Southeastern Brazil: Tectonic Implications     

Veridiana T. de S. Martins  Wilson Teixeira  Carlos M. Noce  Antonio C. Pedrosa-Soares 《Gondwana Research》2004,7(1):75-89

Nd and Sr isotope data were obtained for three plutonic suites (595–505 Ma) and distinct young granitoid intrusions (503 Ma), from the southern part of the Neoproterozoic Araçuaí Orogen. The Sr and Nd isotopes (⁸⁷Sr/⁸⁶Sr, eNd) and TDM values from the plutons and distinct basement rocks are used to constrain the magma genesis of the granitoid plutons. These isotopic parameters, with e_Nd values ranging from −4 to −24 and T_DM ages from 1.3 to 2.8 Ga, for the granitoid suites, and −5 to −40 and 3.5 to 1.5 Ga, for the distinct Archean and Proterozoic basement complexes, suggest that the Jequitinhonha Complex metasediments are the main crustal source for most of these plutons, except for the youngest granitoid intrusions, which may have a protolith similar to the Mantiqueira and Guanhães complexes. Furthermore, the isotope data indicate a minor, but important, participation of Neoproterozoic oceanic lithosphere in the granite genesis, which corroborates with a confined orogenic model and a narrow oceanic consumption (B-subduction) for the Araçuaí Orogen.  相似文献