Integrated structural, geophysical and remote sensing data for characterizing extensional linked fault systems and related land deformation hazards at Cairo-Suez District, Egypt

Abstract

A tiered framework has been developed to map and characterize extensional linked fault systems at Cairo-Suez District, Egypt to better understand seismic and land deformation hazards. As a test site, the present tiered approach is applied on the Cairo-Suez District (CSD), Egypt, which is considered as an active seismogenic zone that encompasses complex deformation settings. Tier 1, which involves outcrop observations and structural mapping, reveals four geometries belonging to soft- and hard-linkage transfer zones (TZs). Considering the mapped TZs, the near-surface heterogeneity is characterized using a 2D-electrical resistivity tomography (2D-ERT) technique at “tier 2” applying an advanced inversion scheme (AIS). Inversion results of the 2D-ERT profiles indicate a subsurface continuity of the mapped surface geological and structural features including shale smears of fault zones and shale layer distributions. At “tier 2”, we particularly identify a highly deformed shale bed of 15-m thick, that accommodate fault slips as indicated by internal gouge zones. We further represent all local hazard factors including slope, drainage density, land use/land cover and displacement maps using the “Fuzzy-Shannon Entropy Model”. Overall, our findings show that most of the delineated deformation hazards in the test site are related to hard-linked TZs. At “tier 3”, we ultimately provide our recommendation for regional and site-specific engineering mitigation and to avoid active faults by defining setback-zone buffer (i.e., no build zone) correlated with the local fault activity and near-surface geometry. For Egypt, an economically developing country, this approach represents a major advancement from conventional geologic and geotechnical investigations through introducing a tiered framework for risk-relevant characterization of the extensional linked fault systems to apply adequate procedures/precautions by engineers for urban planning.