=== Benchmark 3 ===
Viscoelastic relaxation of stresses resulting from an imposed simple shear strain. No body forces are imposed.

''Benchmark 3a:'' Solve using a Maxwell viscoelastic material rheology

''Benchmark 3b:'' Solve using a Burger's body rheological description

''Benchmark 3c:'' Solve using a power-law material description

==== GOALS ====
  * Test relevant constitutive relations
  * Verify timing of output in specific codes (i.e., is output written at the beginning or end of the step).
==== DETAILED DESCRIPTION ====
  * Model size: 24 km by 24 km by 24 km (0 km ≤ x; y ≤ 24 km; -24 km ≤ z ≤ 0 km)
  * Elastic material properties: Poisson solid, G = 30 GPa
  * Maxwell viscoelastic material properties: η = 10^18^ Pa-s
  * Burger's body material properties: Maxwell element as above, Kelvin-Voigt element has G,,KV,, = 10 GPa, η,,M,, = 10^17^ Pa-s
  * Power-law material properties: η,,ref,, = 10^18^ Pa-s and σ,,ref,, = 10^5^ Pa. (Note: This value is chosen because the maximum initial elastic stress is of order 10^6^ Pa; although all of that is deviatoric, the deviatoric stress decreases with time.)
  * Density and Gravity: None
  * Boundary conditions: Bottom pinned [[br]]
     Sides pinned in y and z; free in x [[br]]
     Top pinned in y and z; 1 m of displacement imposed in x
  * Coarse mesh node spacing: dx = dy = dz = 2 km
==== REQUESTED OUTPUT AND RESULTS ====
Mesh Variations: As memory, time, and patience allow, run models at 1/2, 1/4, and 1/8, etc. the original coarse mesh spacing, investigate variable mesh spacing, and/or employ a variety of element types.

For All Benchmark Variations:

  * Stresses along a path through (0,0,-24) and (24,24,0) at t = 0, 1, 5, and 10 years.
  * Displacements along a path through (0,0,-24) and (24,24,0) at t = 0, 1, 5, and 10 years.
  * CPU time, wallclock time, memory usage info, compiler info, and platform info
==== TRUTH ====
Analytical solutions for each material rheology will be posted at geoweb.mit.edu/fe. 
==== ADDITIONAL NOTES ==== 
None.