This benchmark attempts to reproduce the results of Buiter et al. 2008:
  Dissipation analysis as a guide to mode selection during crustal  
  extension and implications for the styles of sedimentary basins, 
  Journal of Geophysical Research, v. 113, B06406, 
  doi:10.1029/2007JB005272.

More specifically, the provided input files aim to reproduce two numerical
simulations illustrated in Figure 6, which shows crustal structure after
a 400x35 km box has undergone 10 km of extension at a constant rate of
1 cm/yr. Deformation is localized with a weak brittle seed at the base
and horizontal midpoint of the brittle upper crust. This seed leads to the
formation of conjugate shear bands that form an initially symmetric Horst
and Graben system. 

The four panels in Figure 6 illustrate the effects of varying lower crustal
viscosity, which varies from a value of 1e19 to 1e22 Pa s. Increasing the 
lower crust viscosity produces stronger coupling with the brittle upper crust, 
which produces more widely distributed deformation and less offset along the 
Graben bounding shear bands. At the lowest lower crustal viscosity value 
(1e19 Pa s) deformation largely focuses onto one leading to a highly 
asymmetric crustal structure.

In this benchmark, input files are provided for lower crustal viscosities
of 1e20 and 1e22 Pa s.

Localization of deformation is aided by strain weakening, with the cohesion
and internal angle of friction reducing between plastic finite strain invariant
values of 0.5 and 1.5. Notably, This single measure of the plastic finite strain 
magnitude is commonly used in long-term tectonic simulations, but differs from 
other measures of finite strain magnitude that use/calculate an invariant from 
the full finite strain tensor (see finite strain cookbook and integrated strain 
particle property).   
 
