Geology and Geophysical Conditions of Land Platform (Karab) Using Resistivity Imaging and Seismic Refraction Survey, Fashaga Area-Gadaref State, Sudan

Abstract

The purpose of this geophysical investigation is to delineate existence of buried channels filled mainly with natural aggregate (gravel) in the area of proposed dams of Upper Atbara River and Setait River (Fashaga Area). The River Atbara is characterized by a special land platform (badland topography) called the (Karab). The saturation zone in the study area extended under this Karab which needs more investigations. The main objective of the geophysical engineering survey is to determine the surface and subsurface conditions at the proposed site assess the geological engineering condition of proposed site and provide geological engineering data and basis to detailed design. Total of five resistivity profile and three seismic lines were collected and processed. The resistivity imaging coinciding to some extent with the available borehole data drilled in the investigated area, but there is some interference with overlying top soil which has high resistivity value in some profiles. It noticed that from the resistivity imaging investigations the resistivity of gravels or very coarse material can be expected to lie in the range of 300 to 1500 Ohm.m, depending on moisture conditions, and the resistivity values of the Basaltic intrusion lie in the range of 500 to 5000 Ohm.m.so there are some difficulties to differentiate between basaltic intrusion and gravels. Seismic Refraction in Fashaga area shows that the depth to the top of bedrock ranges from 15m to 30m. The interpreted geological section had been made according to geophysical investigation, available borehole data and the geological setting of the area these lines are the dam axis of the Fashaga Area GF02.