Numerical investigation of dip-slip fault propagation effects on offshore seabed sediments

An enhanced understanding of the phenomenon of dip-slip fault propagation through young, unconsolidated offshore sediments is essential for the evaluation of the response of shallow offshore structures and subsea oil/gas pipelines. Substantial and permanent seafloor deformation constitutes a severe geohazard for these marine structures and associated offshore elements/components. This paper addresses the response of seabed sand deposits subjected to underlying dip-slip fault movement. The resulting propagation of the faulting offset in seabed sediments is explored using 2D finite element modeling in Abaqus©, while accounting for nonlinear soil behavior with strain softening. A 2D plain strain FEM seabed model is adopted to investigate the effect of different seabed soil properties and layer thicknesses on the extent and magnitude of seabed surface deformation induced by normal and reverse faults with different dip angles. The results indicate that (1) the adoption of sand properties that depend on depth is necessary to realistically model the fault propagation mechanism, particularly for fault propagation through thick and dense sand deposits, (2) the presentation of fault propagation results in a normalized manner (with respect to sand cover thickness) does not eliminate the dependency on the actual layer thickness, and (3) the deformation of the beds in the cover as a result of basement faulting can be modeled realistically using trishear kinematic approaches.