Boundary definition by GEOCUBIT for 2-layer model

I am trying to export the following mesh (with 2 irregular layers: volumes yellow and green) from cubit using geocubit library, but when i got the exported free_or_absorbing_surface_file_zmax file to use in specfem3D, this file does not contain apparently the correct 2D elements at the free surface. I used the following boundary definition,

This is of GEOCUBIT

#… which extracts the bounding faces and defines them into blocks

Is there any suggestions? by the way, the volumes are also merged, so there must not been a problem with it.