Final answer:
A normal fault plane is more pristinely exposed than a reverse fault plane because the downward motion of the hanging wall in normal faults leads to a clearer exposure, while reverse faults experience upward motion that can obscure the fault plane.
Step-by-step explanation:
When a fault scarp forms, it reveals the fault plane at the surface. The primary reason a normal fault plane is usually more pristinely exposed than a reverse fault plane is that in a normal fault, the action of extension causes the hanging wall to move downward.
This movement often leads to a more distinct and visible scarp as one side of the fault drops down relative to the other, offering a clear view of the fault plane. In contrast, a reverse fault is created through compression, which pushes the hanging wall upwards.
The nature of this upward movement typically results in less clear exposure of the fault plane, as material can be more easily piled up, obscured, or subjected to subsequent erosion and sedimentation that cover the fault plane.
Erosion plays a key role in the exposure of both normal and reverse faults, but due to the respective movements, normal faults tend to have more pronounced and clean exposures at the surface.