APPLICATION OF 2D HOMOGENEOUS FUNCTION METHOD TO STUDY THE SUBSURFACE GEOLOGIC SECTION IN THE NORTHWESTERN PART OF THE KHARGA OASIS AREA, WESTERN DESERT, EGYPT.

Abstract

The present study represents an application of 2D homogeneous function method to investigate the subsurface geologic section and detect depth and thickness of Nubia aquifer in the northwestern part of El-Kharga Oasis area. A simple inversion of refraction travel times (GOOGRAF software) is used for the automatic determination of 2D velocity field models, and interface structures of the subsurface geologic section in the study area. In this method the homogeneous function automatically inverts the first arrival refractions to derive a 2D velocity distribution which involves the seismic boundaries. A complex set of observed refracted traveltimes along three seismic profiles (about 1200 m length each) is used to construct refraction time field sections t(x, l) and 2D velocity field sections. Such kind of sections allows seeing complex layered structure of the subsurface section and allocation of the boundaries and the faults. Moreover, the interpreted geoseismic sections, where the interfaces between different seismic zones, faults and contact between the different blocks of rocks are traced according to their own gradient velocity range are also introduced. The resultant models were in consistent with the study objectives. They provided the required details on the delineation and mapping the geometries of the inversion boundary of the deduced five seismic zones with velocities ranging from 200 to more than 4400m/s in which the significant structural complexities where large fault blocks were interpreted. Besides, two aquifers of two different levels were also delineated. The locations of the interfaces between the seismic zones and also the two saturated zones everywhere were found to be completely compatible with knowledge about identified boundaries supplied by the nearby borehole. So, the inversion has proved very effective in confirming and imaging the accurate setting of the interfaces of the subsurface sedimentary succession including aquifers and structural complexities and providing valuable deeper information about the fault morphology.