Salt Geometry Influence on Present-Day Stress Orientations in the Nile Delta: Insights from Numerical Modeling
The offshore Nile Delta displays sharply contrasting orientations of the maximum horizontal stress, SH, in regions above Messinian evaporites (suprasalt) and regions below Messinian evaporites (subsalt). Published stress orientation data predominantly show margin-normal suprasalt SH orientations but a margin-parallel subsalt SH orientation. While these data sets provide the first major evidence that evaporite sequences can act as mechanical detachment horizons, the cause for the stress orientation contrast remains unclear. In this study, 3D finite element analysis is used to investigate the causes for stress re-orientation based on two different hypotheses. The modeling study evaluates the influence of different likely salt geometries and whether stress reorientations are the result of basal drag forces induced by gravitational gliding or whether they represent localized variations due to mechanical property contrasts. The modeling results show that when salt is present as a continuous layer, gravitational gliding occurs and basal drag forces induced in the suprasalt layers result in the margin-normal principal stress becoming the maximum horizontal stress. With the margin-normal stress increase being confined to the suprasalt layers, the salt acts as a mechanical detachment horizon, resulting in different SH orientations in the suprasalt compared to the subsalt layers. When salt is present as isolated bodies localized stress variations occur due to the mechanical property contrasts imposed by the salt, also resulting in different SH orientations in the suprasalt compared to the subsalt layers. The modeling results provide additional quantitative evidence to confirm the role of evaporite sequences as mechanical detachment horizons.
A. Eckert and W. Zhang, "Salt Geometry Influence on Present-Day Stress Orientations in the Nile Delta: Insights from Numerical Modeling," Journal of African Earth Sciences, vol. 114, pp. 96-109, Elsevier Ltd, Feb 2016.
The definitive version is available at https://doi.org/10.1016/j.jafrearsci.2015.11.014
Geosciences and Geological and Petroleum Engineering
Center for High Performance Computing Research
Keywords and Phrases
Finite Element Method; Geometry; Messinian; Numerical Model; Salt; Salt Tectonics; Stress; Three-Dimensional Modeling; Egypt; Nile Delta
International Standard Serial Number (ISSN)
Article - Journal
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