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The Tunisian domain is formed following the convergence between Nubia and Eurasia which is responsible for folding and still active faulting. We used 62 earthquake focal mechanisms to constrain the present stress field of the Tunisian domain. The results show that the tectonic regime is compressional with a dominant direction NW-SE maximum horizontal principal stress direction. The focal depth distribution indicates that Northern Tunisia is an area of convergence with a thin crust and a shallow Moho. However, in the central and southern Atlas, the presence of focal mechanisms with strike-slip faulting shows that this zone is a deep seismogenic area with a thick crust.These results are consistent with the neotectonic and seismotectonic stress field determined by other studies. The neotectonic deformations of Tunisia are like the past deformations guided by the convergence between the African and the Eurasian plates. [ABSTRACT FROM AUTHOR]

The present work tests the use of hypsometric integral (HI) in identifying neotectonic and lithology signals in the Utica-Mateur basin (north-eastern Tunisia), a region recognised by low deformation rates. We computed HI values using three digital elevation models (DEMs) of 10, 30 and 90 m pixel resolution. We extracted maximum, minimum and mean elevations from each DEM. The obtained results reveal that the HI spatial distributions did not demonstrate clear spatial patterns and did not correlate with geological substrates. We also find that the distribution of HI is independent of the DEM resolution, but are influenced by the size of the moving window. By applying the hot spot analysis (Gi*-statistics) on extracted HI data, we find two main clusters with high (hot spots) and low (cold spots) HI values. These hot spots correspond mainly to active faults and coincide with shallow earthquake clusters in the study area. [ABSTRACT FROM AUTHOR]

An electrical resistivity tomography survey has been conducted along the eastern coast of the Gulf of Aqaba in order to assess the salinity of the coastal shallow aquifer. The study area is extended from Ra's Shikh Humayd to the town of Maqnah, northwest of Saudi Arabia. Eight electrical profiles were conducted using the Wenner-Schlumberger configuration. The total length of each profile was 360 m providing an expected maximum depth of penetration of about 50 m. All electrical profiles were conducted perpendicular to the coast and directed in the west-east direction. The inversion of the electrical data provided a clear two-dimensional image of the subsurface in the area that reflected the variations in the resistivity of the shallow aquifer system. The subsurface is composed of three layers: the upper layer corresponds to the dry alluvial and gravel deposits that have resistivity values in the range between 40 and 1400 Ω m. The second layer is the saturated zone of the alluvial sediments which represents the coastal aquifer in the study area. The resistivity value of the saturated zone is in the range of 0.15 to 25 Ω m. The lower layer in the subsurface stratification is the resistive bedrock which has resistivity values of more than 100 Ω m. It is composed of Pleistocene-Miocene sediments. The extension of saline water body has been mapped along all electrical profiles. The interpretation of the resistivity models shows that the salinity of the groundwater in the area is strongly related to three main factors: (1) the closeness to the coast; (2) closeness to wadis and low areas which allow saline surface water to infiltrate into the shallow aquifer and; (3) the abundance of gypsum outcrop in the vicinity. This last factor emphasizes the important effect of the local geological setting on the salinity of groundwater; the abundant supply of leached gypsum contributes to the salinity of the shallow aquifer. [ABSTRACT FROM AUTHOR]

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Detailed gravity data integrated with geological data and mining well data are analysed to constrain the shape of the Triassic evaporitic body at Jebel El Mourra (northern Tunisian Atlas) and the mechanism of its emplacement at the surface. The gravity data analysis included the construction of a gravity anomaly maps, and synthetic and forward 2.5D gravity models. The complete Bouguer and residual gravity anomaly maps indicate a positive amplitude gravity anomaly over the Triassic evaporitic outcrops and prominent NE–SW-trending features associated with the boundary of the Triassic rocks and surrounded layers. A NW–SE-trending gravity model that crosses the Triassic evaporitic outcrop at Jebel El Mourra shows that the positive gravity anomaly can be explained by a deep-rooted salt diapir. Conventional models of salt dome formation suggest that they produce negative gravity anomalies; however, this study shows that this model is not universal. The studied area is an example of a diapir expressed by positive gravity anomaly and this result is supported by synthetic gravity models at different stages of salt piercing. [ABSTRACT FROM AUTHOR]

Bouguer gravity and aeromagnetic data are analyzed to determine the extent of Miocene magmatism in the Nefza and Tabarka regions of northwestern Tunisia. Construction of magnetic intensity and enhanced analytic signal (EAS) maps indicated the existence of at least two regions containing probable subsurface igneous bodies that correlate to the small scattered igneous outcrops in the Nefza and Tabarka regions. Because of the lack of lateral resolution of the EAS techniques, 3-D magnetic and 2.5-D gravity models were constructed over the anomalies at Nefza and Tabarka. The final models indicate that the maximum depths of the igneous bodies are between 2.5 and 2.7 km with maximum widths between 15 and 22 km. The final models also indicate that the bodies are tabular with a combination of laccolithic and lopolithic shapes and were probably emplaced in the shallow levels of the crust (at least 3 km). These widths greatly expand the region of known Miocene magmatism in northwestern Tunisia. Combined with geochemical and petrological data of the surface volcanic rocks, the gravity and magnetic models imply a wider range of Miocene volcanic activity in northern Tunisia, probably related to a subduction zone. [Copyright &y& Elsevier]

Bouguer gravity data were analysed to determine the general crustal and upper-mantle structure in northern Tunisia. Residual gravity anomalies were determined by removing the gravitational effect of crustal thickness variations imaged by regional seismic experiments. Residual gravity anomalies contain short-wavelength anomalies superimposed on a long-wavelength component that decreases in amplitude northward towards the Tunisian coastline. An edge-enhancement analysis (e.g. enhanced analytic signals) of the short-wavelength anomalies suggests a previously unknown east west-trending gravity anomaly south of 37°N with source depths of between 3 and 7 km. Modelling of residual and Bouguer gravity anomalies indicate that there are two possible solutions for the residual gravity decrease in northern Tunisia: (1) thickening of Cenozoic and Mesozoic sediments north of a strike-slip fault or (2) a crustal and uppermantle low-density zone interpreted as being crustal material of the remnant subducted African Plate. The latter result is favoured based on seismic tomographic images of the Mediterranean region, which implies that subducting material exists under the African coast, geological interpretations suggesting that the Tell Atlas may be a thrust wedge accreted by underplating of the African continental crust and seismic refraction models, indicating a thinning of sediments in northern Tunisia. The east-west-trending gravity anomalies south of 37°N correspond to an important structural feature that may be related to either a structural boundary (e.g. a transform fault) or subduction beneath the African Plate. [ABSTRACT FROM AUTHOR]