Definitions

Fault: a surface along which appreciable displacement has taken place; this surface may be planar or curviplanar.

Fault zone: a zone containing a number of parallel or anastomosing faults.

Echelon faults: relatively short, parallel faults of a zone which display an overlapping or staggered pattern.

Shear zone: a zone across which two blocks have been displaced in fault-like manner, but without development of visible fractures.

Footwall: the surface bounding the body of rock immediately below a non-vertical fault. The body of rock itself is called the footwall block.

Hangingwall: the surface bounding the body of rock immediately above a non-vertical fault. The body of rock itself is called the hangingwall block.

Cut-off line: the trace of a displaced plane on the fault surface; these lines occur in pairs, one on the footwall and one on the hangingwall.

Slip: the relative displacement of formerly adjacent points (Fig. 8.1a); also called the net slip. It is represented by the relative slip vector, usually of the hangingwall block relative to the footwall block. Dip slip and strike slip are components. This total displacement is the result of the accumulation of a number of small slip events, which are not necessarily parallel to the slip vector.

Separation: the distance between two displaced planes. It may be measured on the fault perpendicular to the cut-off lines, but more commonly in the strike or dip directions (Fig. 8.1b).