Delineation of saltwater intrusion zones using the time domain electromagnetic method: the Nabeul–Hammamet coastal aquifer case study (NE Tunisia)     

Fatma Trabelsi  Abdallah Ben Mammou  Jamila Tarhouni  Carlo Piga  Gaetano Ranieri 《水文研究》2013,27(14):2004-2020

The time domain electromagnetic method (TDEM) is applied to monitor, to delineate and to map the saltwater intrusion zones in the Mediterranean Plio‐Quaternary aquifer. Forty‐two TDEM soundings were carried out in the coastal plain of Nabeul–Hammamet region (NE Tunisia). TDEM resistivity data were correlated with the existing borehole logging data to assign them to a particular lithology and to provide information about the position of the freshwater–seawater transition zone. The geoelectric sections showing the vertical configuration of seawater intrusion, with the brackish‐salty‐saturated zones, have a resistivity ranging from ~0.1 to 5 Ω?m and are detected at a depth lower than 1.5 m. The salinized zones are located at Nabeul (Sidi Moussa, Sidi El Mahrsi, Al Gasba and Mrazgua) and at Hammamet (Touristic zone of Hammamet north and south, Baraket Essahel) and reached a distance of 4 km from the coastline, indicating a severe state for the aquifer in these zones. These TDEM results are confirmed by the increase of chloride concentration content in the analysed water samples of monitoring wells. Moreover, in the northeastern part, the presence of a saltwater front located far from the coast and along the NW–SE major surface fault can be explained by two hypothesis: (i) this fault seems to provide a conduit for seawater to move readily towards the water wells and (ii) the clay and gypsum infiltration of marine Messinian deposits through the fault plane leads to low resistivities. Finally, it comes out from this study that TDEM survey has successfully depicted salinized zones of this coastal aquifer. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

The volcanic history of Mars: High-resolution crater-based studies of the calderas of 20 volcanoes     

Stuart J. Robbins  Gaetano Di Achille  Brian M. Hynek 《Icarus》2011,211(2):1179-151

Determining absolute surface ages for bodies in the Solar System is, at present, only possible for Earth and Moon with radiometric dating for both bodies and biologic proxies such as fossils for Earth. Relative ages through cratering statistics are recognized as one of the most reliable proxies for relative ages, calibrated by lunar geologic mapping and Apollo program sample returns. In this work, we have utilized the Mars Reconnaissance Orbiter’s ConTeXt Camera’s images which provide the highest resolution wide-scale coverage of Mars to systematically crater-age-date the calderas of 20 of Mars’ largest volcanoes in order to constrain the length of time over which these volcanoes - and major volcanic activity on the planet, by extension - were active. This constitutes the largest uniform and comprehensive research on these features to date, eliminating unknown uncertainties by multiple researchers analyzing different volcanoes with varied data and methods. We confirm previous results that Mars has had active volcanism throughout most of its history although it varied spatially and temporally, with the latest large-scale caldera activity ending approximately 150 ma in the Tharsis region. We find a transition from explosive to effusive eruption style occurring in the Hesperian, at approximately 3.5 Ga ago, though different regions of the planet transitioned at different times. Since we were statistically complete in our crater counts to sizes as small as ∼60 m in most cases, we also used our results to study the importance of secondary cratering and its effects on crater size-frequency distributions within the small regions of volcanic calderas. We found that there is no “golden rule” for the diameters secondaries become important in crater counts of martian surfaces, with one volcano showing a classic field of secondaries ∼2 crater diameters from the center of its primary but not affecting the size-frequency distribution, and another clearly showing an influence but from no obvious primary.  相似文献   

Measurements of volcanic SO2 and CO2 fluxes by combined DOAS,Multi-GAS and FTIR observations: a case study from Turrialba and Telica volcanoes     

Vladimir Conde  Philippe Robidoux  Geoffroy Avard  Bo Galle  Alessandro Aiuppa  Angélica Muñoz  Gaetano Giudice 《International Journal of Earth Sciences》2014,103(8):2335-2347

Over the past few decades, substantial progress has been made to overcome the technical difficulties of continuously measuring volcanic SO₂ emissions. However, measurements of CO₂ emissions still present many difficulties, partly due to the lack of instruments that can directly measure CO₂ emissions and partly due to its strong atmospheric background. In order to overcome these difficulties, a commonly taken approach is to combine differential optical absorption spectroscopy (DOAS) by using NOVAC scan-DOAS instruments for continuous measurements of crateric SO₂ emissions, and electrochemical/NDIR multi-component gas analyser system (multi-GAS) instruments for measuring CO₂/SO₂ ratios of excerpts of the volcanic plume. This study aims to quantify the representativeness of excerpts of CO₂/SO₂ ratios measured by Multi-GAS as a fraction of the whole plume composition, by comparison with simultaneously measured CO₂/SO₂ ratios using cross-crater Fourier transform infrared spectroscopy (FTIR). Two study cases are presented: Telica volcano (Nicaragua), with a homogenous plume, quiescent degassing from a deep source and ambient temperature, and Turrialba volcano (Costa Rica), which has a non-homogeneous plume from three main sources with different compositions and temperatures. Our comparison shows that in our “easier case” (Telica), FTIR and Multi-GAS CO₂/SO₂ ratios agree within a factor about 3 %. In our “complicated case” (Turrialba), Multi-GAS and FTIR yield CO₂/SO₂ ratios differing by approximately 13–25 % at most. These results suggest that a fair estimation of volcanic CO₂ emissions can be provided by the combination of DOAS and Multi-GAS instruments for volcanoes with similar degassing conditions as Telica or Turrialba. Based on the results of this comparison, we report that by the time our measurements were made, Telica and Turrialba were emitting approximately 100 and 1,000 t day^?1 of CO₂, respectively.  相似文献   

EChO spectra and stellar activity II. The case of dM stars     

Gaetano Scandariato  Giuseppina Micela 《Experimental Astronomy》2015,40(2-3):711-722

EChO is a dedicated mission to investigate exoplanetary atmospheres. When extracting the planetary signal, one has to take care of the variability of the hosting star, which introduces spectral distortion that can be mistaken as planetary signal. Magneticvariability has to be taken into account in particular for M stars. To this purpose, assuming a one spot dominant model for the stellar photosphere, we develop a mixed observational-theoretical tool to extract the spot’s parameters from the observed optical spectrum. This method relies on a robust library of spectral M templates, which we derive using the observed spectra of quiet M dwarfs in the SDSS database. Our procedure allows to correct the observed spectra for photospheric activity in most of the analyzed cases, reducing the spectral distortion down to the noise levels. Ongoing refinements of the template library and the algorithm will improve the efficiency of our algorithm.  相似文献   

Earthquake early warning as a tool for improving society’s resilience and crisis response     

Paolo Gasparini  Gaetano Manfredi  Jochen Zschau 《Soil Dynamics and Earthquake Engineering》2011

Increasing vulnerability of metropolitan areas to earthquake and the very low probability level at which short term earthquake forecasting is possible make earthquake early warning methods (EEW) the main viable alternative for effective risk reduction in cities. Preventive actions, such as retrofitting and building and the diffusion of construction codes, are of course essential. They are not sufficient. A substantial proportion of the population in areas of higher earthquake hazard still reside in buildings that do not meet modern earthquake resistant standards, and cannot currently be strengthened in an economically viable manner. As demonstrated in Japan EEW has the potential of significantly contributing to reduce individual vulnerability of urban population to earthquakes. Future research on EEW should be focused on its implementation to protect lifelines, infrastructures and strategic buildings, and it should include training of administrators and people who can fully exploit the technological advantages offered by EEW systems. In particular it should foresee extensive cost-benefit analysis for each potential application, the identification and solution of legal problems (such as liability in the event of false or missed alarms), education and training, both for mitigation and response, as well as detection and processing within 1 s of the first seismic wave arrivals. Further objectives include the development of people-centred EEW, specialized IT and decision making support systems, integration of sensors, communications and decision making systems, integration into programs of eco-sustainable development, and integration with other EW systems (all hazard systems).  相似文献   

geneGIS: Geoanalytical Tools and Arc Marine Customization for Individual‐Based Genetic Records     

Dorothy M. Dick  Shaun Walbridge  Dawn J. Wright  John Calambokidis  Erin A. Falcone  Debbie Steel  Tomas Follett  Jason Holmberg  C. Scott Baker 《Transactions in GIS》2014,18(3):324-350

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Dioxin Like Compounds Bulk Deposition on Corn (Zea mais) and Alfa Alfa (Medicago sativa): Modelled Levels on Derived Silage and Hay and Their Relevance for Dairy Production     

Gianfranco Brambilla  Stefania Paola De Filippis  Vittorio Esposito  Gaetano Settimo 《洁净——土壤、空气、水》2013,41(2):113-118

Dioxin‐like compounds from regular, occasional or fugitive airborne sources of emission may fall out on fodders close to be harvested for silage and hay production. In this way, a prolonged long‐term intake of contaminated forages in dairy animals may be envisaged, able to determine a rise of the background contamination in milk. We simulated different risk scenarios taking into account the inventoried bulk dry depositions in rural areas of the aforesaid contaminants, silage and hay biomass production per hectare, forages regimen in dairy animals, and the congeners carry‐over rate (COR) from forages to milk. Considering atmospheric depositions >10 pg I‐TE m^?2 day^?1 and accounting for a 30% COR, dairy milk could rise up to the PCDD/F level of 3 pg WHO₁₉₉₈‐TE g^?1 fat. The modelling indicates that in rural areas bulk emissions should be selectively minimised, accounting for the calendar of the different agricultural practices, because of their potential impact on the fodders. Since environmental factors play a non‐negligible role in food production, a stronger harmonisation between I‐TE and WHO_1998–2005‐TE scales with respect to dioxin‐like polychlorobiphenyl congeners inclusion is envisaged. This will allow the prevention of the human indirect exposure to such contaminants when released in the air.  相似文献   

Influence of infill distribution and design typology on seismic performance of low- and mid-rise RC buildings     

Paolo Ricci  Maria Teresa De Risi  Gerardo Mario Verderame  Gaetano Manfredi 《Bulletin of Earthquake Engineering》2013,11(5):1585-1616

A growing attention has been addressed to the influence of infills on the seismic behavior of Reinforced Concrete buildings, also supported by the observation of damage to infilled RC buildings after severe earthquakes (e.g. L’Aquila 2009, Lorca 2011). In this paper, a numerical investigation on the influence of infills on the seismic behavior of four different case study buildings is carried out: four- and eight-storey buildings, designed for seismic loads according to the current Italian technical code or for gravity loads only according to an obsolete technical code, are considered. Seismic capacity at two Limit States (Damage Limitation and Near Collapse) is assessed through static push-over analyses, within the N2 spectral assessment framework. Different infill configurations are considered (Bare, Uniformly Infilled, Pilotis), and a sensitivity analysis is carried out, thus evaluating the influence of main material and capacity parameters on seismic response, depending on the number of storeys and the design typology. Fragility curves are obtained, through the application of a Response Surface Method. Seismic performance is also expressed in terms of failure probability, given a reference time period.  相似文献   

Elastic period of sub-standard reinforced concrete moment resisting frame buildings     

Gerardo M. Verderame  Iunio Iervolino  Gaetano Manfredi 《Bulletin of Earthquake Engineering》2010,8(4):955-972

The fundamental period has a primary role in seismic design and assessment as it is the main feature of the structure that allows one to determine the elastic demand and, indirectly, the required inelastic performance in static procedures. In fact, the definition of easy to manage relationships for the assessment of the elastic period has been the subject of a significant deal of both experimental and numerical/analytical studies, some of which have been acknowledged by codes and guidelines worldwide. Moreover, this kind of information is useful for territorial-scale seismic loss assessment methodologies. In the majority of cases, the assessment of the period is considered as function of the structural system classification and number of storeys or height. Reinforced concrete structures, comprising most of the building stock in Italy and in seismic prone areas in Europe and in the Mediterranean region, were built after the Second World War and are designed with obsolete seismic codes, if not for gravity loads only. Therefore, a class of buildings featuring the same height and/or number of storeys may show a significant variability of the structural system. This, along with the contribution of the stair module, may affect the elastic periods in the two main directions of a three-dimensional building. In the study presented these issues are investigated with reference to a population of existing RC structures designed acknowledging the practice at the time of supposed construction (e.g., simulated design) and with reference to the relative enforced code. The elastic period is evaluated for both main directions of the buildings of the considered sample, and regression analysis is employed to capture the dependency of the elastic dynamic properties of the structures as a function of mass and stiffness.  相似文献   

Effects of suspended sediments from reservoir flushing on fish and macroinvertebrates in an alpine stream     

Giuseppe Crosa  Elena Castelli  Gaetano Gentili  Paolo Espa 《Aquatic Sciences - Research Across Boundaries》2010,72(1):85-95

The downstream ecological consequences of two controlled “free flow” flushing operations designed to remove sediments accumulated in an alpine reservoir are described. The main objectives of the study were (a) to verify to what extent the suspended solid concentration (SSC) in the receiving water course can be controlled by flushing operations, (b) to determine the biological consequences of flushing operations, and (c) to produce technical guidelines for the future planning and monitoring of these activities. We found that the flushing of large volumes of accumulated sediment had clear effects on the stream ecosystem due to the unpredictability of short duration SSC peaks (70–80 g L⁻¹) and the high average SSC (4–5 g L⁻¹) within flushing periods. The main impacts were decreased fish densities (up to 73%) and biomass (up to 66%). A greater mortality recorded for juveniles will likely result in long-term impairment of the age-structures of future fish populations. The zoobenthic assemblages, despite exhibiting a drastic reduction in abundance following the first floods, showed substantial recovery within 3 months of the beginning of flushing operations. Regular sediment removal by yearly flushing is recommended in order to avoid SSC peaks and to facilitate the control of scouring effects caused by the water used to wash out sediments. We also recommend maximum allowable SSCs of 10 g L⁻¹ (daily average) and 5 g L⁻¹ (overall average) for flushing operations carried out in similar environmental contexts.  相似文献