The first angle, called strike , is measured as a compass direction from north. Strike is the angle from north of the line made by the intersection of the fault plane with a horizontil surface. The other angle, dip , is the angle between the horizontil and the fault plane measured perpendicular to the strike. The two blocks of rock on either side of the fault are the footwall, below the fault plane, and the hanging wall, above the fault plane. The amount of relative movement between the two blocks is called the throw of the fault.
Normal faults are common in regions of extension, such as rifts and spreading ridges.
In reverse faults, the footwall drops relative to the hanging wall. Reverse faults are common in regions of compression such as convergent plate margins. In such regions, a special type of reverse fault, called a thrust fault, is common. Another type of fault is shown in the two diagrams at right. These faults are called strike-slip faults and are characterized by movement of the two fault blocks past one another in the horizontil plane.