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  • Author or Editor: S. Saleh x
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In the present study the crustal structures of Nile Delta, including Greater Cairo province, and its surroundings, were evaluated using 3D forward gravity and magnetic modeling. The interpretation is also based on the seismic reflection results, well logs data and previous density models. The present results allow to improve the understanding of both the crustal thicknesses and density distributions between the sedimentary cover and the upper mantle in the study area.The high Bouguer anomalies near the Mediterranean coast are mainly caused by deep-seated structures. The crust beneath the Mediterranean coastal region is typically continental, with a thickness of 24 km beneath Rositta and Damitta branches, which increases toward the south. The Greater Cairo province has been modeled with maximum crustal thickness of ca. 34 km. The negative gravity anomalies with minimum values are due to the effect of sedimentary cover and/or basement relief geometry.The main results of this work suggest that the study area could be divided into three different distinctive tectonic zones according to their Moho depth and crustal structures. The southern zone (unstable shelf zone) which covers the Greater Cairo province is characterized by maximum crustal modeled thickness. It also represents the most seismically active tectonic zone in the study area. On the contrary the middle and northern zones show a thinned crustal layer and a correspondingly thicker sedimentary cover.Furthermore, the magnetic anomalies along the Greater Cairo, as deduced from the 3D magnetic modeling, are mainly caused by the upper crustal structures. In particular, the high magnetic anomalies of the southern part of the studied area are interpreted as related to variation in the basement relief near the surface, resulting from block faulting and/or compressional folds.In the northern region near the Mediterranean coastal area the highest magnetic susceptibility anomaly values is affected by the shallow smooth relief of the lower crustal layer. Finally, limited, shallow-seated basaltic intrusions were modeled beneath the western side of Nile Delta. The existence of these basaltic intrusions suggests that the study area was influenced by the opening of the Red Sea and/or Gulf of Suez during the Oligocene time.

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Three-dimensional gravity modeling has been performed for the Eastern Mediterranean including the northeastern Egyptian off-shore area. The gravity models and seismic profiles indicate that a transition from two layer continental crust to a simple layer oceanic crust takes a place along the Levantine margin. The transition along three profiles is located beyond the north African continental margin and it is quite gradual. The crust under the Levantine basin is typically oceanic and slightly thin with 13 km thickness, however it is typical continental under the Egyptian off-shore and having 30 km thickness. The obtained results reflect a large sedimentary sequence of 14 km under the Levantine basin. Since the sediments recovered by the Oceanic Drilling Program Leg160 in the eastern Mediterranean ranged from Pleistocene to Cretaceous, this reflects fairly high sedimentation rate. Distribution of recent earthquake foci indicates that almost all earthquakes occurred along the western and central segments of the Cyprean arc while they completely disappear along the eastern segment. This means that collision between Cyprus and the Eratosthenes seamount is marked by seismic activity and clearly affects the shape of the Cyprean arc. This collision represents a transition zone between active compression and probable subduction in the western segment and diffuse transtension through the eastern part of the arc. Incipient collision between Cyprus and Eratosthenes seamount probably began in Pleistocene time.

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