The type of stress placed on a normal fault is tensional stress. In normal faulting, tensional stress gradually weakens the Earth's crust until the rock cracks, with one crustal block moving downwards relative to its adjacent fault block.
A fault along the Earth's crust is identified by the corresponding type of stress that caused its formation. In geology, a stress is defined as the amount of force exerted on a unit of surface area. Generally, shear stress forms transform faults, compressive stress creates reverse faults and tensional stress produces normal faults.
Tensional stress usually occurs along divergent plate boundaries, where the Earth's massive crustal plates move in opposite directions. As the plates move away from each other, tensional stress builds up on the surface of the Earth. The principal stress direction exerted by tensional stress is along the vertical direction, while the least compressive stresses or the intermediary stresses are along the horizontal direction. When the crust finally fractures, the normal fault forms a less than 45-degree-angle with the principal stress direction. One fault block begins to slide along the fault, while the other block remains in its original position. Tensional stresses have a local lengthening effect on the Earth's terrain.