Analytical and numerical modeling of viscous anisotropy: A toolset to constrain the role of mechanical anisotropy for regional tectonics and fault loading

Abstract

Whether mechanical anisotropy is required to explain the dynamics of the lithosphere, in particular near fault zones where it may affect loading stresses, is an important yet open question. If anisotropy affects deformation, how can we quantify its role from observations? Here, we derive analytical solutions and build a theoretical framework to explore how a shear zone with anisotropic viscosity can lead to deviatoric stress heterogeneity as well as non-coaxial principal stress and strain rates. We also develop an open-source finite element approach to explore more complex scenarios in both 2-D and 3-D, and simulate three 3-D scenarios inspired by an anisotropic major strike-slip fault zone, the asthenospheric mantle, and the Leech River Schist above the Cascadia subduction zone. Our findings and new tools may help geoscientists to better understand, detect, and evaluate mechanical anisotropy in natural settings, with potential implications including the transfer of lithospheric stress and deformation including fault loading.