Impact of Spontaneous Generation of Splay Faults on Stress Heterogeneity in Accreting Sediments

ABSTRACT: We model the progressive generation and propagation of faults in accreting sediments and study how this process affects stress and deformation in the accretionary wedge. We develop large-scale evolutionary drained geomechanical models. We simulate sediment behavior using a porous elasto-plastic constitutive formulation that incorporates the effect of both mean and shear stress to compaction. We integrate a FEM-DEM framework that enables faulting when the deviatoric plastic strain exceeds a specified threshold over a specified length. New faults are introduced to the mesh as contact surfaces with a friction angle lower than that of the intact sediment. We find that the weaker faults lead to a decrease in sediment differential stress in zones that extend several hundred meters away from the fault. This introduces a significant heterogeneity in both stress and strength within the accretionary wedge. The heterogeneity propagates seaward as the wedge evolves and new faults are generated. We also explore the effect of fault frictional strength through parametric analyses. We find that weaker faults result in more extensive areas of low differential stress and delay the generation of the next set of faults at the toe of the wedge. Our results offer a significant improvement over previous models of continuum wedge sediments that predict Coulomb failure throughout the wedge. Our study provides insights into the state of stress in faulted accretionary wedges, highlighting the spatial heterogeneity of stress and its potential impact on factors influencing seismic cycles in subduction zones.