Etude hydrogéologique des séries triasiques dans la région de Jeffara-Dahar (Sud Tunisien): Apport des diagraphies et de la sismique réflexion

The present study concentrates on the interpretation of well logs and seismic reflection data in the Jeffara- Dahar region (Southeast part of Tunisia) for a better characterization of the Triassic aquifer, a potential target of water supply. Lithological columns and their corresponding well logs reveal that Sidi Stout, Kirchaou and Touareg sandstones as well as Mekraneb and Rehach dolomites are the main reservoirs of the Triassic aquifer. Well log analysis highlights many permeable and fractured layers that could play an important role in the groundwater circulation. The interpreted seismic sections and the resulting isochrone maps show a tectonic influence on the Triassic aquifer geometry in the Jeffara-Dahar region. The normal faulting of E-W and NW-SE accidents created an aquifer compartmentalized by raised and tilted blocks. Seismic cross-sections reveal that this structure controls the depth of permeable formations and the circulation of groundwater. These results will be useful for rationalising the future hydrogeological research that will be undertaken in the Jeffara-Dahar area.[fr] La présente étude concerne l’interprétation des données de la sismique réflexion et celles des puits y compris les enregistrements diagraphiques en vue d’une meilleure caractérisation de l’aquifère triasique de la région de Jeffara-Dahar (Sud-Est de la Tunisie) qui constitue une cible potentielle pour l’alimentation en eau. Les logs lithologiques associés aux enregistrements diagraphiques correspondants montrent que les principaux réservoirs sont les grés de Sidi Stout, Kirchaou et Touareg ainsi que les dolomies de Mekraneb et Rehach. L’interprétation diagraphique met en évidence des niveaux de faible perméabilité et d’autres perméables et bien fracturées qui pourraient jouer un rôle dans l’acheminement des eaux souterraines. Les profils sismiques interprétés et la cartographie élaborée en conséquence mettent en évidence que l’aquifère triasique est compartimenté en blocs soulevés et affaissés. Cette structuration, contrôlée par la réactivation des accidents E-W et NW-SE en failles normales au cours du Trias, influence l’épaisseur des formations perméables ainsi que le sens d’écoulement de la nappe d’eau. Les résultats obtenus seront utiles pour la rationalisation des futures recherches hydrogéologiques dans la région de Jeffara – Dahar

Well dispersed fractal aggregates as filler in polymer-silica nanocomposites: long range effects in rheology

We are presenting a new method of processing polystyrene-silica nanocomposites, which results in a very well-defined dispersion of small primary aggregates (assembly of 15 nanoparticles of 10 nm diameter) in the matrix. The process is based on a high boiling point solvent, in which the nanoparticles are well dispersed, and controlled evaporation. The filler's fine network structure is determined over a wide range of sizes, using a combination of Small Angle Neutron Scattering (SANS) and Transmission Electronic Microscopy (TEM). The mechanical response of the nanocomposite material is investigated both for small (ARES oscillatory shear and Dynamical Mechanical Analysis) and large deformations (uniaxial traction), as a function of the concentration of the particles. We can investigate the structure-property correlations for the two main reinforcement effects: the filler network contribution, and a filler-polymer matrix effect. Above a silica volume fraction threshold, we see a divergence of the modulus correlated to the build up of a connected network. Below the threshold, we obtain a new additional elastic contribution of much longer terminal time than the matrix. Since aggregates are separated by at least 60 nm, this new filler-matrix contribution cannot be described solely with the concept of glassy layer (2nm)

Encéphalite japonaise: risque pour les populations vivant en zones d'endémie et pour les voyageurs [The importance of Japanese encephalitis: for endemic populations and for travellers]

The importance of Japanese encephalitis (JE) in endemic populations and in travellers requires a balanced assessment. This disease represents an important public health problem in some endemic areas, which contrasts with the minimal risk for travellers to endemic areas. This is reflected by high numbers of infections mainly among children in endemic countries and by few case reports among tourists and even expatriates. The total number of case reports between 1978 and 2008 amounts to a risk of one to two cases per year. Nevertheless, some travelling groups may be at higher risk when visiting or working in high risk areas. A new vaccine against Japanese encephalitis will soon be registered in Switzerland. This paper contributes to the scarce data available for decision making whether or not to recommend the vaccination to tourists and expatriates

Encéphalite japonaise: risque pour les populations vivant en zones d’endémie et pour les voyageurs

L’importance de l’encéphalite japonaise (EJ) dans les populations endémiques et chez le voyageur doit être évaluée avec précaution. Cette maladie représente un problème important de santé publique dans certaines régions endémiques comme en témoigne la haute prévalence d’infections chez les enfants, contrastant avec le risque minime encouru par le voyageur et l’expatrié. Le nombre total des cas rapportés entre 1978 et 2008 établit un risque d’une à deux infections par an. Malgré tout, certains groupes de voyageurs peuvent être à plus haut risque suivant les régions qu’ils visitent ou dans lesquelles ils travaillent. Un nouveau vaccin contre l’encéphalite japonaise sera prochainement enregistré en Suisse. Cet article complète les rares données disponibles concernant la recommandation quant à la vaccination chez les touristes ou les expatriés

Deep structure in the Bir M’Chergua region (North-East of Tunisia). Hydrogeological implications

The Bir M’Chergua region, located fifty kilometers from the capital Tunis, is an important economic pole in Tunisia. However, the water shortage resulting from many successive drought periods has led to a significant degradation of the various industrial, tourist and agricultural activities in this region. Groundwater exploitation can alleviate this situation, but it requires a better characterization of aquifers. In this context, the present study aims to provide precisions on the Bir M’Chergua hydrogeological scheme by determining the subsurface structures from gravimetric data interpretation. Residual anomaly, vertical derivative and total horizontal gradient maps are calculated from the Bouguer anomaly to identify and delimit the causative sources. The Euler deconvolution technique is also applied to estimate these sources depth. The structural map resulting from gravimetric interpretation highlights buried structures and discontinuities of different direction and depth that can greatly influence the Bir M’Chergua aquifer system geometry and functioning. In fact, the highlighting of tectonic features at more than 1500 m depth around the Jebel Oust dome explains the origin and the high salinity of the thermal waters in this sector; such tectonic accidents have favored a deep penetration of the recharge water as well as their contact with the Triassic terrains

Hydrogeological study in the Kalaa Khasba plain (Northwestern Tunisia). Contribution of well logging and electrical prospecting

International audienceThe protection of groundwater through the rationalization of its exploitation is crucial in water resources management. However, this rationalization needs a good knowledge of the aquifer system. The present study aimed at the characterization of the Mio-Plio-Quaternary aquifer in Kalaa Khasba plain (northwestern Tunisia) using 250 vertical electrical soundings (VES) and 41 water boreholes. First, well logs consisting of gamma ray, resistivity and spontaneous polarization logs were analyzed to define reservoir layers and follow their lateral evolution in different directions via several correlations. Second, VES data were qualitatively and quantitatively interpreted. Qualitatively, apparent resistivity maps were established for different AB spacings. Quantitatively, theoretical master curves, auxiliary point charts and software were used to determine layer thicknesses and true resistivities. The obtained models were correlated to the lithological columns restored from well logs in the form of geoelectrical cross sections and a three-dimensional representation, the analysis of which elucidated the aquifer geometry. The comparisons and correlations of lithological columns to their corresponding well logs highlighted that the substratum of Mio-Plio-Quaternary deposits near the plain borders consists of Eocene or Cretaceous limestones with marly intercalations. Further, they showed that in most of the boreholes, these deposits contain three lithological units: two clayey units separated by a coarse one which presented its greatest thicknesses (81 and 97 m) in the central part of the plain. The apparent resistivity maps clearly highlighted the richness of this zone in water reservoirs through relatively high resistivity values (15–40 Ωm) for different AB spacings. The geo-electrical cross sections and three-dimensional representation indicated that successive normal faults generated the gradual downwarping of the Eocene and Cretaceous series and the thickening of the Mio-Plio-Quaternary filling within the Kalaa Khasba plain. Moreover, they revealed notable variations in the depth (8–125 m), thickness (28 to > 90 m) and resistivity (15–55 Ωm) of the coarse unit corresponding to the Kalaa Khasba aquifer