The shallow Plio-Quaternary (PQ) water table, present over almost the whole Djerid and Chott El Gharsa basins (southern Tunisia), is used as a complement of oases irrigation, especially in summer season. The simplicity of the Plio-Quaternary lithology is confronted to the complexity of the mineralisation mechanisms and the water origin in this aquifer. An approach combining the use of water-dissolved chemical species and isotopic contents has been used to better understand the PQ behaviour under severe increasing exploitation and to determinate the origin of its different water bodies. In southern Tunisia, the aquifer system is composed of the upper unconfined PQ aquifer, the intermediate semi-confined/confined Complexe Terminal (CT) and the deeper confined Continental Intercalaire (CI). Chemical analyses highlighted an origin of mineralisation in close relationship to the dissolution of both sulphated salts (MgSO4 and Na2SO4) and chlorinated salts (NaCl and MgCl) abundant in the surface and subsurface gypsum crust. Positive correlations between gypsum anhydrite, mirabilite, thenardite and halite saturation indexes with respective mineral species, confirm evaporites dissolutions. Isotopic data showed that in addition of sporadic rainfall events, there is a contribution from the CI and the CT Saharan groundwaters, recharging the PQ aquifer in the study area. Return flow irrigation is partly affected by evaporation, before recharging the shallow aquifer, in oases limits. 相似文献
The most of shallow earthquakes are followed, just after the main shock, by increased residual seismicity known as “aftershocks” or “aftershock sequences”. Because of their disparity in time and space, aftershock sequences are more or less obvious and their productivity is spread out in time. Several studies have been regularly proposed to explain or to understand the mechanisms of the occurrence and the behaviour of these small earthquakes. In a theoretical context, many factors can induce the aftershock triggering: residual friction, subcritical crack growth, pore fluid flow etc. Just after the occurrence of the most destructive main shock of the 21 May 2003 Boumerdes (Algeria) earthquake, a wide sequence of aftershocks was recorded at different geographical locations and with various magnitudes. Based on the fact that the region of Boumerdes (40 km east of the capital Algiers) did not develop major earthquakes in the past, a geostatistical investigation of the data for this aftershock sequence is a valuable input for better seismogeological identification of this area. In the present analysis, after an overview of the geological factors in the likely occurrence of the earthquake, fundamental statistical parameters were chosen: the b value from the Gutenberg–Richter law, the p factor of the extracted respectively from the b value and the fractal variogram defined as a graphic tool to describe the continuity or the roughness of data. Jointly to the geostatistical parameters provided by the variogram like the fractal dimension. The main objective of the calculation and interpretation of these parameters is oriented towards a better understanding of the seismicity of the region of Boumerdes (Algeria) now classified as seismogenic zone. 相似文献
RésuméLa plaine de Segui-Zograta est une cuvette synclinale à remplissage Mio-Plio-Quaternaire où la nappe du Plio-Quaternaire constitue la principale source d’approvisionnement en eau pour l’abreuvement du chaptel et pour l’agriculture. Cette zone présente une hétérogénéité de répartition de la minéralisation des eaux souterraines. L’investigation des outils géochimiques basée sur l’étude des éléments majeurs, des isotopes stables (18O, 2H) et radioactifs (3H, 14C) indique la combinaison de différents processus contrôlant la minéralisation de ces eaux. Dans la partie Ouest, les eaux du Plio-Quaternaire présentent un facies de type sulfato-calco-sodique et des salinités élevées. Elles subissent l’effet de la dissolution des minéraux évaporitiques et résultent du mélange par drainance ascendante des eaux fossi des aquifères les plus profonds, à salinité élevée et à faciès chloruro-sulfato-sodique, à travers la faille d’Om Ali où leur contribution peut atteindre 96%. Dans la partie Est, ces eaux sont de type sulfato-calcique, considérées relativement moins minéralisées que celles de la partie Ouest. Elles sont issues de l’infiltration des eaux de pluie récentes et qui ont subi l’effet de l’évaporation.
Rotational excitation cross sections and rate coefficients of AlF collisions with para-H2 are computed at low temperature, i.e., for T≤70 K. Prior to collisional calculations, a four-dimensional (4D) potential energy surface (PES) for the AlF-H2 system is calculated at the ab initio Coupled-Cluster level of the theory with an aug-cc-pVQZ Gaussian basis set. This 4D-PES is further reduced to a two-dimensional
(2D) PES based on the considerations related to collisional studies with para-H2. The [Al-F] and [H-H] bond lengths are frozen at their experimental equilibrium value re=1.654369 bohr and re=1.4011 bohr respectively. The interaction energy presents a global minimum located ∼63 cm−1 below the AlF-H2 dissociation limit. With this PES, cross sections are determined in the Close-Coupling (CC) approach and rate coefficients
are inferred by averaging the cross sections over a Maxwell-Boltzman distribution of kinetic energies. These quantities are
significantly magnified in comparison with their AlF-He counterparts. The already observed propensity towards ΔJ=1 transitions for AlF-He remains. 相似文献
Precursory stages of failure development in large rock samples were studied and simultaneous observations of the space-time variation of several physical fields were carried out under different stress-strain states. The failure process was studied in detail. A hierarchical structure of discreet rock medium was obtained after loading. It was found that the moisture reduced the rock strength, increased the microcrack distribution and influenced the shape of the failure physical precursors. The rise in temperature up to 400 °C affected the physical precursors at the intermediate and final stages of the failure. Significant variations were detected in the acoustic and electromagnetic emissions. The coalescence criterion was slightly depending on the rock moisture and temperature effect. The possibility of identifying the precursory stage of failure at different strain conditions by means of a complex parameter derived from the convolution of physical recorded data is shown. The obtained results point out the efficiency of the laboratory modelling of seismic processes. 相似文献
A study of thirteen geothermal springs located in the geothermal field of Guelma, northeastern Algeria, was conducted. Samples were collected during the period between January 2014 and February 2016. Geochemical processes responsible for the chemical composition of thermal and mineralized water were evaluated. The hydrochemical analysis shows that the thermal waters are characterized by the presence of two different chemical facies, the first type SO4–Ca in the east, west and south of Guelma, the second type HCO3–Ca in the south. This analysis also attributed to sodium, chlorides, and sulfates to an evaporitic terrigenous origin by the molar ratio Sr2+/Ca2+. The thermal spring waters from Guelma geothermal system have a meteoric origin, and all samples are immature with strong mixing between hot and shallow waters with 19–38.5% rate of mixing. The silica geothermometer shows that these thermal waters have a temperature varying from 84 to 122 °C and that the water came from a depth of 2100–3000 m through a fault system that limits the pull-apart basin of Guelma. Potential environmental effluent from thermal spas could pollute in both the irrigation and drinking waters, and which imposes danger on the health of the inhabitants of the region.
We construct a U-N secular canonical planetary theory of the third order with respect to planetary masses. The Hori-Lie procedure is adopted to solve the problem. Expansions have been carried out by hand, neglecting powers higher than the second with respect to the eccentricity-inclination. We take into account the principal as well as the indirect part of the planetary disturbing function. The theory is expressed in terms of the Poincaré canonical variables, referring to the Jacobi-Radau set of origins. We assume that the 1:2 U-N critical terms and its multiples are the only periodic terms. 相似文献