Analysis of fault initiation and fault spacing in elasto-plastic sedimentary materials

In elasto-plastic sedimentary materials a fault appears as a thin, plastic softening zone (shear band) that is bounded by broader elastic zones consisting of material points that have unloaded. Associated with a certain prescribed incremental strain an incremental “elasto-plastic” stress (in the case of plastic yielding) and an incremental “elastic” stress (after unloading) can be determined. The ratio of these two stresses is identified to be the quantity that controls the initiation and spacing of the faults. Faults form when this ratio is sufficiently large and the fault spacing increases with this ratio. The results obtained are verified numerically for a Drucker-Prager type yield condition.