Hanging wall movement determines the geometric classification of faulting. One can distinguish between “dip-slip” and “strike-slip” hanging-wall movements.
Dip slip- Dip-slip – movement occurs when the hanging wall moved predominantly up or down relative to the footwall.
- If the motion was down, the fault is called a normal fault, if the movement was up, the fault is called a reverse fault.
- Downward movement is “normal” because we normally would expect the hanging wall to slide downward along the foot wall because of the pull of gravity.
- Moving the hanging wall up an inclined fault requires work to overcome friction on the fault and the downward pull of gravity.
Strike slip–When the hanging wall moves horizontally, it’s a strike-slip
- If the hanging wall moves to the left, the earthquake is called right-lateral, if it moves to the right, it’s called a left-lateral fault.
- The way to keep these terms straight is to imagine that you are standing on one side of the fault and an earthquake occurs.
- If objects on the other side of the fault move to your left, it’s a left-lateral fault, if they move to your right, it’s a right-lateral fault.
Oblique slip-When the hanging wall motion is neither dominantly vertical nor horizontal, the motion is called oblique-slip. Although oblique faulting isn’t unusual, it is less common than the normal, reverse, and strike-slip movement.
