The trace of a fault is the line that the fault plane makes with a surface (often the surface of the ground, sometimes a bedding surface). Faults are classified as normal, reverse, or strike-slip, depending on the relative motion along the fault plane; see Figure F-3. A fourth type of fault, associated with plate movement, is a transform fault (q.v.). A hinge or scissors fault is produced by rotation of the blocks across the fault about an axis perpendicular to the fault plane so that throw varies along the fault trace. Primary faults may produce secondary stresses that produce secondary faults (which may be of different type). Thus thrusting may produce tensions that cause secondary normal faults. Faulting and folding are common responses to the same stresses; see Figure F-17. Faulting during sediment deposition (growth faulting) often affects the stratigraphy such that beds may abruptly thicken and become more sandy downthrown at a normal growth fault.
Evidences of faults in seismic data are principally by: