Evaluating subsurface structures and stratigraphic units using 2D electrical and magnetic data at the area north Greater Cairo, Egypt

Abstract 2D dipole–dipole resistivity data and ground magnetic survey are used in combination with available data from boreholes and surface geology to detect subsurface structures and stratigraphic units and to study the ability of the site area (located at north Grater Cairo) for a building construction. Five 1-km length dipole–dipole profiles were measured using electrode spacing of 5 m. The data from these profiles, which were carried out parallel (125 m apart) and in E–W direction, have been inverted using a 2D regularization algorithm. The geoelectrical models obtained from inversion of the field data allowed the characterization of different geological units such as mud, alluvium, sandy clay and sand and sandstone deposits. Two hundred and twenty seven stations of ground magnetic data have been measured in a grid of 50 m × 50 m using two automatic proton precession magnetometers with an accuracy of 1 nT. The results showed that the depth of the basaltic basement varies between 24 and 122 m and it is affected by several fault elements trending NW–SE and crossing the southwestern part of the study area. These faults seem to control the distribution of the sedimentary cover. Fifteen boreholes drilled in the area with depths ranging from 50 to 202 m have been used to define the thickness of the different lithological units and the depth of the top of the basaltic sheet. The results of the boreholes logging indicate that the depth of basaltic sheet ranges from 23.7 m, in the western part of the study area, to 122 m in the central part.