[1] Shear localization is a process of primary importance for the
onset of subduction and the evolution of plate tectonics on Earth. In
this paper we focus on a model in which shear localization is initiated
through shear heating. The rheology employed is linear Maxwell
viscoelastic with von Mises plasticity and an exponential dependence of
viscosity on temperature. Dimensional analysis reveals that four
nondimensional (0-D) parameters control the initiation of shear zones.
The onset of shear localization is systematically studied with 0-D, 1-D,
and 2-D numerical models, both under constant stress and under constant
velocity boundary conditions. Mechanical phase diagrams demonstrate that
six deformation modes exist under constant velocity boundary conditions.
A constant stress boundary condition, on the other hand, exhibits only
two deformation modes ( localization or no localization). Scaling laws
for the growth rate of temperature are computed for all deformation
modes. Numerical and analytical solutions demonstrate that diffusion of
heat may inhibit localization. Initial heterogeneities are required to
initiate localization. The derived scaling laws are applied to
Earth-like parameters. For a given heterogeneity size, stable
(nonseismic) localization only occurs for a certain range of effective
viscosities. Localization is inhibited if viscosity is smaller then a
minimum threshold, which is a function of the heterogeneity size. The
simplified rheological model is compared with a more realistic and more
complex model of olivine that takes diffusion, power law, and Peierls
creep into account. Good agreement exists between the models. The
simplified model proposed in this study thus reproduces the main physics
of ductile faulting. Two-dimensional late stage simulations of
lithospheric-scale shear localization are presented that confirm the
findings of the initial stage analysis.