Which fault type forms when Earth’s crust is pulled apart?

A normal fault forms when Earth’s crust is pulled apart.

In extension, the block of crust above the inclined fault plane, called the hanging wall, moves downward relative to the block below it, called the footwall. This movement accommodates stretching and commonly produces fault-bounded valleys, tilted blocks, and rift structures.

Normal faults are widespread at divergent plate boundaries, including mid-ocean ridges and continental rifts. They can also occur in regions where the crust is being stretched for other reasons. The East African Rift contains many active normal faults as the African continent undergoes extension.

A reverse fault has the opposite sense of movement: compression pushes the hanging wall upward. A thrust fault is a low-angle reverse fault. A strike-slip fault mainly involves horizontal movement, as along the San Andreas Fault. Real faults can combine vertical and horizontal motion, but their dominant movement determines the usual classification.