Effect of shear zones on post-seismic deformation with application to the 1997 Mw 7.6 Manyi earthquake

We explore the impact of deep ductile shear zones on post-seismic deformation following a finite length strike-slip earthquake. We show that the pattern of post-seismic vertical surface deformation surrounding the fault is a discriminant for the existence of high viscosities immediately below the seismogenic layer, regardless of whether the model contains purely distributed creep or also includes a component of localized creep at subseismogenic depths. Post-seismic deformation characterized by initially fast relaxation followed by a slower relaxation is predicted by models that include both localized creep in a subseismogenic shear zone and distributed creep in the surrounding region, even if they only contain steady Maxwell viscoelasticity. This post-seismic deformation is similar to that in models that approximate the ductile lithosphere and/or asthenosphere with Burgers viscoelasticity. We find that the post-seismic deformation following the 1997 M-w 7.6 Manyi, China, earthquake, is consistent with a post-seismic model composed of a lower Maxwell viscoelastic region with viscosity 10(19) Pa s and a 5 km wide, Maxwell viscoelastic shear zone with viscosity 10(18) Pa s beneath the fault.