SEISMIC SURVEYS IN THE NORTHERN RED-SEA - ASYMMETRIC CRUSTAL STRUCTURE

Wide angle reflection and refraction seismic (WARRS) surveys at key sections of the Northern Red Sea and adjacent areas enabled a better definition of the crust and upper mantle structure. A fundamental asymmetry of the region was revealed by the results of profiles, which cover both flanks of the Red Sea main trough, the coastal plains and the bordering Precambrian shields. This asymmetry is clearly expressed by the presence of different crustal types on both flanks: the western flank shows oceanised crust within only 20 km off the African coast, while the whole eastern flank is underlain by a continental type of crust. Likewise, the shape of the continent-ocean transitions differs significantly on both flanks: the Arabian margin extends almost into the centre of the Red Sea and shows considerable stretching and attenuation of the continental crust, while the African margin, on the other hand, even thickens towards the escarpment and appears very abrupt. The influence of the Red Sea opening, as reflected by the decrease of seismic velocities and the increase of Poisson's ratio in the upper mantle due to partial melting, is strictly limited to the area seaward of the Egyptian escarpment. The asymmetry in the Northern Red Sea is regarded to be the expression of strike-slip processes in the initial stages of Red Sea evolution.