الفهرس 
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Abstract
Seismic methods represent one of the most effective methods of geophysical prospecting where it can provide important information about the subsurface condition including structure and distribution of rock types when it used in conjunction with other geophysical, borehole, and geological data and with concept of physics and geology, can provide important information about the subsurface condition including structure and distribution of rock types. Theoretical study: The theoretical study aims to drive a new 2D forward modeling code and to evaluate the performance of tomographic software with various synthetic models representing different geological scenarios. For seismic tomography, the assumption of straight ray path propagation is not valid when high-contrast seismic anomalies occur. In such cases the extended inversion algorithm based on curved ray path in needed. So, the present new 2D seismic tomographic forward modeling code is based on curved raypath. The curved traveltime integral is derived from the solution of Eikonal equation. We applied the 2D forward code on a various synthetic models representing different geological scenarios. The resulting time from the 2D forward code (calculated time) was taken as an observed time and interpreted using 2D tomographic inversion algorithm (SeisImager 2D). The results of 2D tomographic inversion algorithm for the different synthetic models show that: 1) The non-uniform depths of the sections are due to non-uniform penetration of seismic rays which are calculated during the solution of the inverse problem, 2) The inversion examples indicate that the performance of the iterative tomographic code for the different synthetic models matches to the true model in geometry but the velocities are under estimated and 3) The values of the obtained velocities are under estimated because of using smoothing matrix in inversion solution. Applied study: The applied study was included application of the 2D seismic refraction tomography in Wadi Beda El Atshan area, near Quseir city in the Eastern Desert, Egypt. The study area (about 4 Km2) is occupied the southern part of Wadi Beda El Atshan to the south of Quseir–Qift road, about 12 km west of the coastal town of Quseir city between latitudes 260 02′ and 260 03′ N and longitudes 340 11′ and 340 12′ E. This area is characterized by excellent exposure of tilted basement blocks and their Cretaceous to Tertiary sedimentary covers and including complex different structures represents proper example for constructing the 2D structural models. The goals of this work are; constructing the 2D structural models of seismic refraction data, inferring the downward extension of the observed surface faults, obtaining more information about the subsurface fault morphology and detecting the depth to the basement complex with delineation of its relief. To achieve these goals, shallow seismic refraction method was used. Five shallow seismic refraction profiles were conducted; four of them are oriented WSW-ENE perpendicular to the main stream of the valley each with one spread with varied lengths, and the other one is oriented NW- SE parallel to the main direction of the valley and contains two spreads. These profiles were conducted with two end shots (forward and reverse) and with 10 m geophone spacing. The measurements were made by 12 channel-signal enhancement seismograph (model EG & G ES-1225) and ultra-portable 24 channel seismograph recorder (seismic geode model 5842) which manufactured by Geometrics. The seismic refraction data were interpreted automatically using a 2D refraction tomographic inversion algorithm (GODOGRAF and SeisImager 2D) to obtain subsurface models of the geoseismic layers and their velocities and thicknesses. The results from the two different algorithms were compared. The quantitative results of the shallow seismic refraction data were presented as time-distance curves, 2D velocity sections, structural sections and geoseismic sections. They show that: 1) The 2D velocity models which obtained from both used algorithms (GODOGRAF and SeisImager 2D) everywhere were found to be completely compatible in images, depth, thicknesses of the velocity zones, location, attitudes, and displacements of the most detected faults, 2) The calculated P-waves velocities ranging from 1000 m/sec to 7000 m/sec within the time interval of about 500 m sec, 3) The maximum depth reached more than 300 m in some areas, 4) The distribution of these velocities proved that the studied subsurface sections seem to have strong anisotropic medium in both vertical and lateral directions and 5) The lithology of the subsurface sections within the study area display significant structural complexities where large fault blocks are interpreted.