Evolution of fault systems at a strike‐slip plate boundary: A viscoelastic model

Abstract

A viscoelastic model of crustal deformation suggests that the formation and evolution of strike‐slip fault systems are strongly influenced by rheologic contrasts between the upper and lower crust. When deformation is driven by a narrow zone of high shear in the mantle, the presence of a low‐viscosity lower crustal layer underlying a primarily elastic upper crust widens the deformation zone with time and promotes the formation of a broadly distributed network of interacting faults within the upper crust. In contrast, the deformation zone in a primarily elastic crust is narrow, encompassing a single, plate‐bounding fault. Patterns of surface strain rate and seismicity are thus significantly more complex in the presence of a low‐viscosity lower crust, due to interactions between faulting in the upper crust at short time scales and viscous behavior in the lower crust at long time scales.