Hi all,

I used box with lithosphere boundary indicators build a 3D continental extension model. Now I want to prescribe the right lithosphere extends at 5mm/yr, and set the normal direction of the front and back lithosphere boundaries to free slip, so that material can flow in and out

according to the flow induced by the moving plate. I tried to prescribe the y component to be zero traction. But the model cannot converge. The model boundary conditions are set as follows:

```
####### boundary condition #######
# 0:left, 1:right, 2:front, 3:back, 4:bottom, 5:top, 6:left lithosphere, 7:right lithosphere, 8:front lithosphere, 9:back lithosphere
subsection Boundary velocity model
set Tangential velocity boundary indicators = 0, 1, 2, 3, 4, 6
set Prescribed velocity boundary indicators = 7 x:function
subsection Function
set Variable names = x,y,z
set Function constants = v=0.005
set Function expression = v; \
0; \
0
end
end
subsection Boundary traction model
set Prescribed traction boundary indicators = 8 y:zero traction, 9 y:zero traction
end
subsection Boundary composition model
set Fixed composition boundary indicators = 8, 9
set List of model names = initial composition
end
```

I want to know if there are any issues with such a setup, and how I could improve my model. This is my complete prm file.

test_extension_3D_decoupling_1.prm (11.9 KB)