Final answer:
When the hanging wall moves down relative to the footwall with pure dip slip motion, the fault is classified as a normal fault, which is associated with the extension of the Earth's crust.
Step-by-step explanation:
If the hanging wall block moves down relative to the footwall and the motion is pure dip slip, then the fault is a normal fault. In geology, the identification of different types of faults is based on the direction of relative motion along the fault plane. Normal faults are typically associated with areas where the Earth's crust is being extended. When identifying normal faults, geologists observe that the hanging wall, which is the block above the fault plane, has moved downwards in relation to the footwall, which is the block below the fault plane. This downward motion of the hanging wall is a clear indication of a normal fault.