UNDERSTANDING FAULT ZONE ARCHITECTURE AND PERMEABILITY STRUCTURES IN A RIFT SETTING: NORMAL FAULTS FROM THE ETHIOPIAN PLATEAU, EAST AFRICAN RIFT SYSTEM

The Ethiopian Plateau has undergone intense extensional deformation, developed by tensional forces between the Nubian, the Somalian, and the Arabian Plates. The plateau is characterized by Neoproterozoic basement rocks, and 1.2 km thick succession of Mesozoic rift sediments overlain by ~2km thick Cenozoic flood basalts. These different rocks are deformed by numerous macro-to-micro structures, dominantly normal faults, with offset ranging from less than 10cm to more than 50m. However, the effect of these faults on permeability structures, potential for groundwater and hydrocarbons resources in the plateau and adjacent basins is poorly understood. We used measurements of normal faults collected from the field, and numerical model based on ratios within each fault zone to quantify an architectural index assessing permeability of the plateau. For our numerical model, we used Caine’s scheme of evaluating fault related permeability structure equation F_A=(damage zone width/(core width+damage zone width)) to determine the architectural index based on the ratio between fault damage zone and core widths. We also used field-based quantitative fault orientation data and kinematics in DEM-based 3D models in MOVE structural modeling platform to determine permeable and impermeable fault zones and cluster areas of these zones. Based on our preliminary results, the architectural index values range from 0.5-0.94, propose a combination of conduit and barrier flow, which suggests a high possibility of permeability within the plateau. Assessing permeability within the plateau will aid in better understanding of the fluid flow properties of the fault zones. The quantification of permeability in such a rift system can be applied to other endeavors, such as sourcing and accessing minerals, and geothermal energy while understanding the rift geodynamics.