CRUSTAL STRUCTURE MODELING FOR THE NORTHERN PART OF THE ASWAN LAKE AREA USING SEISMIC-WAVES GENERATED BY EXPLOSIONS AND LOCAL EARTHQUAKES

In this work, two types of seismic waves generated from explosions and local earthquakes were used as wave sources to model the crust and upper mantle structure of the Aswan area. Two reserved refraction profiles oriented N-S were carried out in the northern part of the Aswan Lake area across the E-W fault trends. Interpretation of seismic explosion data shows the crust beneath the Aswan reservoir area to be characterized by three major refractors below the sedimentary cover. P- and S-Wave velocities and depths of these layers respectively are; 5.3 and 3.0 km/s from the base of the Nubian sandstone to a depth of 4.7 km; 6.2 and 3.5 km/s to a depth of 16 km and 6.9 and 3.7 km/s for depths greater than 16 km. The uppermost mantle P velocity is 8.1 km/s which is deduced from the old Aswan Dam explosion, as a P(m)P phase. Near the reservoir area, the sediments comprise a single layer with V(p1) of 2.2 km/s and V(s1) of 1.25 km/s with varying thickness from 250 m at the northern shot (Khor Kurkur) to 350 m at the southern shot (Garf Hussein) west of Gebel Marawa; along the Sinn El-Kaddab profile, however, it shows two different velocity layers having V(p2) of 2.2 km/s and V(p1) of 1.22 km/s for the first layer and V(p2) of 3.6 km/s and V(s2) of 1.98 km/s for the second with thickness of 250 m and 450 m, respectively. A remarkable slowing of Pg at Gebel Marawa is due to abundant faults and fractures. Local earthquake data indicate that the velocity variations in the Aswan crust are similar to those deduced from the refraction explosion experiment. The P-wave (P*) velocity of 6.9 km/s for the lower crust was extended to a depth of 30 km by introducing a P(n) velocity of 8.1 km/s for the upper mantle, this significantly improved the RMS residuals. The relative station correction derived from the velocity inversion of local earthquakes reflects the local variations in the crustal structure combined with local sedimentary inhomogeneities and variation in thickness.