Regional structural mapping using a combined geological and geophysical approach – A preliminary study at Cairo-Suez district, Egypt. (August 2018)

• Record Type: Journal Article
• Authors: Attwa, Mohamed; Henaish, Ahmed
• Is Part Of: Journal of African earth sciences. Volume 144(2018)
• Page Start: 104
• Page End: 121
• Publication Date: 2018-08
• Subjects: Structural mapping -- DCR inversion -- Electrical resistivity tomography -- Uncertainty reduction -- Cairo-suez district; Earth sciences -- Africa -- Periodicals; Earth sciences -- Middle East -- Periodicals; Geology -- Africa -- Periodicals; Geology -- Middle East -- Periodicals; Sciences de la terre -- Afrique -- Périodiques; Sciences de la terre -- Moyen-Orient -- Périodiques; Géologie -- Afrique -- Périodiques; Géologie -- Moyen-Orient -- Périodiques; Earth sciences; Geology; Africa; Middle East; Periodicals; Electronic journals; 556.05
• DOI: 10.1016/j.jafrearsci.2018.04.010
• Languages: English
• ISSNs: 1464-343X

Abstract

Abstract: Contrary to the usual application of individual geological and/or geophysical surveys, this paper represented a sequential use of surface structural mapping and DCR method to afford a sensible structural model in a cost effective way. Understanding the geological setting of a non-mapped area at the central part of Cairo-Suez District (CSD), Egypt, is an immediate engineering concern due to its complex deformation history. Field work is carried out to measure stratigraphic sections and establish structural characteristics of the rock units. Surface geophysical DCR sounding and electrical resistivity tomography (ERT) surveys are performed. To overcome the non-uniqueness problem of DCR interpretation, the available borehole data, detailed surface geological measurements and a sequential use of linear and non-linear inversion algorithms are applied. The practical benefits of detailed surface structural mapping are demonstrating in considering all geological parameters to a conceptual subsurface model, which would have not been identified or misinterpreted otherwise. In an integrative approach, such detailed surface data allow us to confirm the uncertain inferred regional subsurface structures based on DCR data inversion. For detailed subsurface structural characterization, the results of ERTs using coarse triangular mesh and iteratively reweighted algorithm show a good agreement with prior known surface and underground structural features. Additionally, ERTs significantly resolve the complex geological features, which constitute uncertain structures in the surface structural model. The main impact of presented integrative approach is to (i) constraint the DCR data interpretation and (ii) inform a preliminary study plan of regional structural investigation, which can be used as a platform for engineering decision–making and/or further detailed geophysical and geotechnical investigations. Graphical abstract: (a) Google Earth satellite image © 2016 CNES/Astrium of the fault scarp at the Upper Eocene rocks of Gebel Yahmoum Yahmoum El-Asmar, Cairo-Suez District. (b) Field photo of the fault scarp of structural high, looking towards ESE. (c) Electrical resistivity tomogram obtained from 2D inversion of 2D profile P1 and oriented mostly perpendicular to the major surface structures and DCR sounding location No. 23. (d) A correlation between the deduced structures along 2D-ERT P1, inversion results of DC sounding No. 23 and the constructed geological cross-section (X-X'). Highlights: An integrated approach is presented to create a high-resolution subsurface structural mapping. 1D models are generated from the sounding data by the hybrid genetic algorithm. A 2D cell model is derived by using conventional inversion method. The study shows that this integrative approach reduces the uncertainty of the resultant structural model. The present approach is a platform for further in-situ geophysical and geotechnical investigations.