Final answer:
A fault where the hanging wall moves downwards in relation to the footwall is known as a normal fault. This occurs because of extensional forces in the Earth's crust that pull it apart.
Step-by-step explanation:
In geology, a fault in which the hanging wall moves downwards relative to the footwall is called a normal fault. This type of fault occurs during extensional forces which pull the crust apart.
Structures associated with such faults include features like the horsts and grabens seen in landscapes subject to this tension.
Normal faults are created when the Earth's crust is stretched and thinned. As the crust is pulled apart, tensional stress leads to the hanging wall moving down with respect to the footwall.
This downward movement is a distinguishing characteristic of normal faults. In contrast, a reverse fault is one where the hanging wall moves upwards due to compressional forces.
A strike-slip fault involves horizontal movement of the walls, and an oblique fault has a component of both dip-slip and strike-slip movement.