On the geoelectric structure of the Sphinx Area in Egypt

A three-dimensional model of the electrical resistivity of rocks to a depth of 150 m in the Sphinx and the Pyramid of Khephren (Giza, Egypt) area was built using the results of transient electromagnetic soundings. The technology of the soundings, the data processing, and the design of the media's model as a result of three-dimensional block inversion are described. The boundary of the Paleogene limestones that form the plateau of the pyramids and the underlying structure of the folded Cretaceous are defined based on geological interpretation. The created plateau model indicated the thickness of the slightly inclined Mokattam limestones varied from 25 m to 150 m within a 1000 x 300 m(2) area. Such intense changes in the limestone subface's altitudes were controlled by the folded structure of the underlying Cretaceous carbonates. Cretaceous carbonates show low electrical resistivity, which is typical for fractured rocks saturated with saline water. Dense Mokattam limestone blocks are broken by water-saturated zones with sub-vertical faults in the southwest-northeast direction. The electrical resistivity in the carbonate surface layer, which lies at the base of the pyramids and Sphinx, is heterogeneous with a composition that depends on the clay content and presence of halite.