Coulomb subduction zone wedge mechanics

Wedge mechanics derives the stress status of a wedge due to the basal friction, gravitational force and boundary forces, and thus helps to quantitatively analyze the relationship between the fault strength and rock properties and the stability of the wedge. This paper summarizes analytical stress solutions in wedges with different rock materials. Then it introduces the dynamic Coulomb wedge theory based on an analytical solution of an elastic perfectly-plastic Coulomb subduction zone wedge. Seismic reflection profiles have indicated that the frontal forearc near the trench has a steeper surface slope and undergoes complicated permanent plastic deformation (outer wedge). The farther landward features flatter surface slope and smooth horizontal sedimentary layers and generally has sediment basins (inner wedge). The dynamic Coulomb wedge theory postulates that the contrasts of the geometry and deformation pattern between the outer and inner wedges may be due to the difference in the basal frictional property. The basal fault underlying the inner wedge is seismogenic, and the inner wedge may undergo mostly elastic deformation in earthquake cycles. However, the outer wedge overlies stable-sliding portion of the fault and may undergo plastic failure with permanent deformation.