If the south side of a fault is up relative to the north side, what fault type does this indicate?

• A. Normal fault
• B. Strike-slip fault
• C. Reverse fault
• D. Oblique-slip fault

Answer: (C)

Movement where the block above the fault plane (the hanging wall) rises relative to the block below (the footwall) indicates compression along the fault, which is a reverse fault. In a reverse fault, the hanging wall moves up relative to the footwall, whereas a normal fault has the hanging wall moving down due to extension, a strike-slip fault involves mostly horizontal (lateral) movement with little vertical offset, and oblique-slip faults combine vertical and horizontal movement but not a clean up-motion of one side as described. So the observed up-motion of the southern side relative to the northern side best identifies a reverse fault.