A NORMAL fault moves because it is under tension.
In geology a fault refers to a planar fracture in a rock volume, which has been displaced as a result of rock mass movement. There are three types of fault, they are: normal, reverse and strike-slip fault.
A normal fault is a type of fault in which the hanging wall has moved downward relative to the foot wall. Normal fault typically occur at points where two rock blocks are pulled apart as a result of tension. Thus, normal fault is always brought about as a result of tension.