There are two fundamentally different ways to approach fault modeling.
When we talk about “Prehistoric Fault Modeling” we want to take the following steps:
1. Build the geologic model the way that it was before the faulting occurred.
2. Establish one side of the model as the Reference Side, (that does not move) and the other as the Displacement Side (that does move)
3. Cut the model with the fault surface and keep the Reference Side
4. Transform the model (translations and/or rotations) and cut the model with the fault surface and keep the Displacement Side.
5. OPTIONAL: Cut away any displaced blocks that are protruding above ground surface.
6. Display both sides in the viewer.
The advantage of Prehistoric Fault Modeling is that when we build the geologic model, we can use data from both sides of the fault surface to build a single unified geologic model. This creates the best possible model, especially in the regions adjacent to the fault surface.
Though it seems complicated, if we know the displacements at the fault surface, all we need to do to build the “Prehistoric Fault Model” is to modify the data on the Displacement Side so that boring logs or horizon picks are translated to their correct locations before the faulting occurred. This is usually a simple operation in Excel. When we have multiple fault blocks, we may have multiple “Displacement Zones”, each with their own unique translations, but this also is just a matter of careful bookkeeping.
The other approach could be referred to as Contemporary Fault Modeling. In this case we take the following steps:
1. Build a separate geologic model for each fault block using only the data within that displacement zone.
2. Cut each fault block with the fault surface(s)
3. Display all blocks in the viewer
Generally, this approach is much simpler, but the disadvantage is that the geologic model for each block (zone) is built using only the data from that zone. borings that might be “just” on the other side of the fault surface, cannot be used! The quality of the model(s) suffers, especially in the regions near the fault surface(s).