Geophysical and Remote-Sensing Constraints on the Fault Controls on Groundwater Accumulation in Basement Rock Aquifers in Sinai, Egypt

Abstract

Aquifers in basement terrains, including fractured basement rocks and superimposed alluvial deposits associated with the dissecting ephemeral streams, are very complex and their groundwater accumulation is significantly affected by their structural settings. However, the distribution and intersection of geologic structures, along with their mechanistic controls on aquifer thickness, depth, and groundwater flow, remain unclear. In this study, an integrated approach is developed that combines fieldwork, remote-sensing data, and geophysical techniques (vertical electrical sounding, seismic refraction, ground-penetrating radar) to characterize, and better understand the role of, geologic structures (e.g., faults and shear zones) in controlling groundwater accumulation in the basement aquifer systems of southern Sinai, Egypt. Three major structural elements were identified in southern Sinai; their spatial distribution and intersections predominantly control groundwater accumulation. A total of 334 locations were identified, in a geographic information system (GIS) environment, at the intersections of two or more fault/shear zone systems, representing optimal aquifer conditions. The intersection of N–S, NE–SW, and NW–SE shear zones and/or the N–S shear zone and ENE–WSW fault resulted in a thicker aquifer unit with a shallow depth to water table, at these sites the faults/shear zones act as barriers for groundwater flow. The intersection of N–S with NW–SE shear zones, N–S shear zones with NE–SW faults, and NE–SW shear zones with NW–SE faults produced a thin aquifer with a greater depth to water table; in these, the faults/shear zones act as channels for groundwater flow. These findings provide valuable new insights into the significance of structural elements and their spatial distribution in controlling groundwater availability in basement rock aquifers. The methodologies employed in this research can be used as a framework for similar studies in other regions with highly fractured basement terrains.

Graphical Abstract