There are two major classes of geologic fault, dip/slip faults, like the one shown in Karen's illustration, and a strike/slip.

Dip/slip faults show a vertical change: one wall, usually called the hanging wall, is higher than the lower surface, or footwall. Dip/slip faults can be caused by compression, which can force one side up above the other, or by tearing forces, in which the separate sides of the fault move apart.

Strike/slip faults show horizontal change, as compressive or tearing forces displace each side of the fault laterally. Faults can exhibit both characteristics, as well, with both vertical and horizontal displacement. Faults are well-known for their interrelationship with earthquakes and some—like the San Andreas fault in southern California—lie under populated areas and are the subject of constant and intense study.