This is used to define sub-surface ground types and layers (sub-horizons). This dialog is accessible from Sub Horizons Assignments by pressing the plus (+) button next to Ground Layers.
Layer 1, 2, 3
Ground Type (drop list)
Pick the material found in this layer.
Use Surface (check box)
This is only available if the Ground Type for the layer below is defined and there is a reference Terrain that can be used as a sub-surface. To create a Reference Terrain, use Corridor - Reference Surfaces.
Depth from TOPO (edit box or drop list)
Use these controls to define the depth from TOPO surface to the layer below. These controls are disabled unless the ground type for the layer below is defined.
If Use Surface is not checked (or not visible), then the depth is defined by a an edit box. Note that a zero depth or thickness is allowed.
If Use Surface is checked, then the depth is defined by a Reference Terrain surface (TIN). Note that the sub-surface terrain does not have to be defined everywhere; the layer will be zero thickness if the surface can't can't be found.
The bottom layer is assumed to be infinitely deep so no depth control is required.
