Elevated stresses and creep rates beneath the brittle‐ductile transition caused by seismic faulting in the upper crust

Abstract

Large faults in the brittle upper continental crust are envisaged to terminate near the brittle‐ductile transition zone, at a depth that is a complex function of material properties, temperature, stress, and strain rate. Here we investigate the effect of coseismic displacement along a fault in the upper crust on the adjacent middle and lower crust using a two‐dimensional numerical model of faulting within an elastic‐frictional‐viscous rheology. Results demonstrate that a major displacement event can cause a dramatic increase in differential stress and creep strain rates in the crust near and below the lower termination of the fault, a transient deflection of the brittle‐ductile transition zone, and a zone of elevated strain rates down to the base of the crust. The perturbation decays over timescales consistent with postseismic relaxation. The stresses and strain rates predicted in such models are in accord with those inferred from microstructural damage analysis of exhumed metamorphic rocks, indicating short‐term deformation at decaying stress and strain rates.