[CIG-SHORT] material model for landers/hector mine benchmark

[Eric Andreas Hetland]

> That is why I thought breaking it up into 10-12 layers
> with only small jumps in elastic properties between layers without
> remeshing would probably work okay.

Forgive the interjection (that may be way off base), but can't it be
possible to just figure out the depth of the center of each element, then
"look-up" what the material properties for that element should be based on
an interpolation of the material property model Brad H built? Of course,
this would only work for depths with smooth gradients in the material
property model. And as pointed out, property discontinuities should be
preserved in the FE mesh by forcing element boundaries to fall onto the
discontinuity in material properties.

It does not seem necessary to re-generate the material property model nor
the FE mesh (unless the discontinuities in the FE mesh and material model do
not correspond). I am probably missing something, but it just does not seem
that FE meshes should have to follow layers in a material property model,
unless there are discontinuities in property across those layers.

- Eric.