الفهرس 
INTRODUCTION & AIM OFTHEWORKOnly 14 pages are availabe for public view
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Abstract
The northern Red Sea Rift including the Suez Rift constitutes an active rift in the ”last stages of continental rifting which is beginning to undergo to oceanic seafloor spreading. The main targets of this work are studying the local active seismic zones of the northern Red Sea region and their focal mechanism solutions for some selected large recent earthquakes. A high-resolution 3-dimensional gravity and magnetic modeling supplemented with the seismic information has been used to establish a possible crustal thickness and density distribution between the upper part of the crystalline basement and the Moho. Moreover, the magnetic evidence for understanding the sea floor spreading process along the Northern Red Sea Rift is discussed.
According to the epicentral distributions of earthquakes and the related tectonic setting, the Red Sea region is subdivided into major seismic trends or zones (Levant Aqaba and Northern Red Sea Rift). The seismic activity, focal mechanisms are studied for each zone.
In both the northern Red Sea and the Gulf of Suez zones, the mechanisms are composed of normal and strike slip components and in the Gulf of Aqaba most of solutions are normal faulting with large component of strike-slip movement.
The 3- dimensional gravity modeling reveals the evolution of the low-density upper mantle from the Suez Rift in the north to the Northern Red Sea in the south. The Bouguer anomalies along the axial portion of the rift floor, as deduced from the results of the regional and residual separation, are mainly caused by the deep-seated structures and upper mantle. The lateral extent of the anomalous upper mantle under the Northern Red Sea of the rift is larger than the one under the Gulf of Suez.
Because of the asthenospheric uplift and, hence the anomalous upper mantle, the Moho-depth map of the Red sea region, as obtained from the 3-dimensional gravity modeling, exhibits various crustal thickness distribution. The Red Sea Hills exhibit a maximum Moho depth of 35 km and gradually decrease to 20 km parallel to the Red Sea coast. The crust along the Red Sea coast is continental and about 20-22 km thick, where the crustal thikness is over 33 km under most parts of Sinai Plateau, where the basement complex is cropping out.
The Moho depth to the continental crust decreases towards Suez Rift (18 km). The crust (oceanic) under the main Red Sea axial depression is, however, thinner than the normal continental crust of the adjoining Red Sea Hills and Sinai Mountains. The shallowest depth to
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,·
.,,
the top of the Moho is relatively :<::; 13 km in the southern part of the northern Red Sea Rift. The rate of rifting in the northern Red Sea is greater than that in the southern half of the Gulf of Suez which in turn suffered more rifting than the northern half of the Gulf.
Ten magnetic profiles (having the same coordinates of the .
modeled gravity planes) were also modeled using 3-D magnetic modeling across the northern Red Sea. Both the gravity and magnetic modeling reveal suitable information for the investigated deep and shallow structures, respectively.
The magnetic anomalies along the axial portion of the rift floor,
as deduced from the results of the regional and residual separation and the 3-D magnetic modeling, are mainly caused by the oceanic crust structures and I or anomalous upper mantle beneath the graben. In particular, the maximum magnetic anomaly of the northern Red Sea axial rift floor due to the sea floor spreading coincides with the high magnetic
/ · susceptibility of oceanic crust. Moreover, the observed magnetic profiles
r·
’ · show that the spreading rates are found to decrease progressively
;;·
’’· northwards, from 0.7 crnlyr at profile 29 down to 0.5 crnlyr at profile 20....