Major element concentrations and stable (δ18O and δ2H) and radiogenic (3H and 14C) isotopes in groundwater have proved useful tracers for understanding the geochemical processes that control groundwater mineralization and for identifying recharge sources in the semi-arid region of Sfax (southeastern Tunisia). Major-ion chemical data indicate that the origins of the salinity in the groundwater are the water–rock interactions, mainly the dissolution of evaporitic minerals, as well as the cation exchange with clay minerals. The δ18O and δ2H relationships suggest variations in groundwater recharge mechanisms. Strong evaporation during recharge with limited rapid water infiltration is evident in the groundwater of the intermediate aquifer. The mixing with old groundwater in some areas explains the low stable isotope values of some groundwater samples. Groundwaters from the intermediate aquifer are classified into two main water types: Ca-Na-SO4 and Ca-Na-Cl-SO4. The high nitrate concentrations suggest an anthropogenic source of nitrogen contamination caused by intensive agricultural activities in the area. The stable isotopic signatures reveal three water groups: non-evaporated waters that indicate recharge by recent infiltrated water; evaporated waters that are characterized by relatively enriched δ18O and δ2H contents; and mixed groundwater (old/recent) or ancient groundwater, characterized by their depleted isotopic composition. Tritium data support the existence of recent limited recharge; however, other low tritium values are indicative of pre-nuclear recharge and/or mixing between pre-nuclear and contemporaneous recharge. The carbon-14 activities indicate that the groundwaters were mostly recharged under different climatic conditions during the cooler periods of the late Pleistocene and Holocene.
An attempt was made to estimate seismic microzonation in Marsa Alam city, Egypt based on the analysis of seismic microtremor
observations. Observations were carried out at 140 sites in the study region. Analysis and processing of microtremor were
divided into two steps; the first one is to measure the horizontal-to-vertical spectral ratios (HVSR) for each site and picked
predominant frequency and its amplitude for each site. The second step is to measure the average shear wave velocity in the
upper 30 m (Vs30) of subsoil using inversion of HVSR technique. The results show well matching of theoretical HVSR and observed
HVSR for body waves in all sites. The Vs30 parameter was used to classify subsoil into classes of soil properties converted
to the slandered European soil code (Eurocode-8 (2002)) as follows; Vs < 180(class D), 180 ≤ Vs < 360 (class C), 360 ≤ Vs < 800
(class B) and Vs ≥ 800 m/s (class A). Our study exhibits that most of Marsa Alam city were covered by B and C classes with
small portions of class D close to the shoreline and class A at the northeastern part of the region. The developed classification
soil map of the study area was correlated with the distribution of the predominant frequency in view of the surface geology
and given a good matching. The results of this study will be useful for planning the Marsa Alam region to be the future tourist
dream for Egypt. The method used in assessment of seismic microzonation in Marsa Alam city could be the fast and inexpensive
technique to measure the Vs30 based on the HVSR of microtremor and would be applied in many other areas in Egypt. 相似文献
This study explored demographic variations among victims injured in the 2008 Wenchuan earthquake. The study analyzed records
of 2,148 patients who were hospitalized with earthquake-related injuries in 14 hospitals between May 12 and May 21 of 2008.
We tested the effects of gender and age on the incidence of fractures and amputations. Although more women than men were hospitalized
as earthquake victims, the results indicated that a higher incidence of pelvic fracture in women was the only statistically
significant injury with regard to gender. Age had a more complex effect on the rate and pattern of fractures. Children younger
than 15 years old were the most likely to sustain skull fractures and amputations. The elderly were the most likely to be
associated with limb fractures. Adult men were the most likely to suffer spine fractures and adult women rib fractures. The
paper concludes with an interpretation of the results in the context of China’s rural conditions and discusses implications
for post-disaster emergency operations and planning. 相似文献
Water in the fissured limestone and dolomite of the Turonian aquifer of Tunisia has been investigated using geochemical (major ions) and isotopic (δ18O, δ2H, 14C) data. To carry out a characterization of aquifer behaviour, 48 representative samples were collected at the end of the humid season. The evolution of chemical composition of groundwater from recharge areas to discharge areas is characterized by increasing sodium, chloride and sulphate contents as a result of leaching of evaporite rock. In the study, three distinct chemical trends in groundwater were identified. The major reactions responsible for the chemical evolution of groundwater in the investigated area fall into three categories: (1) calcite precipitation, (2) gypsum and halite dissolution, and (3) ion exchange. The stable isotope composition of water samples indicates large-scale interaction between the Continental Intercalaire and the Turonian aquifer and the presence of a young local component which probably enters the system via faults and/or fractures. 相似文献
Stable isotopes (??2H, ??18O and ??13C) and radiocarbon (14C) have been used in conjunction with chemical data to evaluate recharge mechanisms and groundwater residence time, and to identify inter-aquifer mixing in the Djeffara multi-aquifer in semi-arid southeastern Tunisia. The southern part of this basin, the Djeffara of Medenine aquifer system, is comprised of two main aquifers of Triassic and Miocene sandstone. The Triassic aquifer presents two compartments; the first one (west of the Medenine fault system) is unconfined with a well-defined isotope fingerprint; the second compartment is deeper and confined. Multi-tracer results show groundwater of different origins, ages and salinities, and that tectonic features control groundwater flows. Fresh and brackish groundwater from the unconfined part of the Triassic aquifer was mostly recharged during the Holocene. The recharge rates of this aquifer, inferred by 14C ages, are variable and could reach 3.5?mm/year. Brackish water of the deep confined part of the Triassic aquifer has stable isotope composition and 14C content that indicates earlier recharge during late Pleistocene cold periods. Brackish to saline water of the Miocene aquifer presents variable isotope composition. Groundwater flowing through the Medenine fault system is mainly feeding the Miocene aquifer rather than the deep confined part of the Triassic aquifer. 相似文献
Detailed hydrogeochemical and isotopic data of groundwaters from the Hammamet–Nabeul unconfined aquifer are used to provide
a better understanding of the natural and anthropogenic processes that control the groundwater mineralization as well as the
sources of different groundwater bodies. It has been demonstrated that groundwaters, which show Na–Cl and Ca–SO4–Cl water facies, are mainly influenced by the dissolution of evaporates, the dedolomitization and the cation-exchange process;
and supplementary by anthropogenic process in relation with return flow of irrigation waters. The isotopic signatures permit
to classify the studied groundwaters into two different groups. Non-evaporated groundwaters that are characterized by depleted
δ18O and δ2H contents highlighting the importance of modern recharge at higher altitude. Evaporated groundwaters with enriched contents
reflecting the significance infiltration of return flow irrigation waters. Tritium data in the studied groundwaters lend support
to the existence of pre-1950 and post-1960 recharge. Carbon-14 activities in shallow wells that provide evidence to the large
contamination by organic 14C corroborate the recent origin of the groundwaters in the study area. 相似文献
Wadi Afara Héouine area (Tahifet, Central Hoggar) is marked by the existence of very diversified lithologies affected by big submeridian accidents, of which Wadi Afara Héouine, who represents a "linear discontinuity" on near 80 km forming a morphological limit which separates, a strongly gneissic domain (Oua Hellèdjène) of a domain with metasedimentary dominant (Aghefsa). Lithologies not described in the former works were defined by the application of specific treatments (color composite, band ratios, and selective PCA). They also allow us to suggest some modifications to the geologic map of Tahifet. Directional filters associated to the previous treatments helped us in the elaboration of lineament map which accentuates the various accidents affecting the region. It seems clearly that treatments applied to the images ETM contribute in an undeniable way to the geologic study of this region especially since a big part of this region is inaccessible 相似文献
This paper describes a vectorized and parallelized implementation of a two-dimensional pseudo-spectralseismic elastic model and of a (frequency-domain)seismic migration algorithm on the (tightly-coupled) vector multiprocessor IBM 3090 VF. Performance data of alternative parallel implementations on an LCAP (loosely coupled system of array processors FPS 164) are also given.The paper reports additionally performance data of a vector/parallel implementation on the IBM 3090 of some characteristicseismic velocity estimation algorithms. The three problems chosen are representative of a wide class of geophysical computations and the results summarized in this paper show their suitability to efficient implementation on the IBM 3090 vector multiprocessor: combined vector/parallel speedups in the range 15–30 are in fact observed. 相似文献
In this paper, the earth pressure distribution acting on a buried pipe with localized support loss is investigated experimentally and numerically in this study. A laboratory setup has been designed to facilitate the simulation of the local wall separation and to track the changes in earth pressure at selected locations along the pipe circumference. Validated by the experimental results, two-dimensional finite element analysis has been conducted to examine the role of soil-pipe interaction on the pressure distribution around the pipe before and after the contact loss is introduced. Experimental and numerical results revealed that the presence of a gap between the pipe wall and the surrounding backfill can lead to significant changes in contact pressure and bending moment in the pipe wall in the immediate vicinity of the gap. This study suggests that efforts to detect and repair areas experiencing support loss should be made before significant changes in pressure develop causing stress concentration in the pipe wall as it may lead to pipe damage. 相似文献