Geology Reference
In-Depth Information
Fig. 1.31.
Fault separation terminology
or the intersection line between bedding and a dike (Fig. 1.30). The displacement of
dipping beds on faults oblique to the strike of bedding leads to complex relationships
between the displacement and the slip in a specific cross-section direction, such as
parallel to the dip of bedding. A strike-slip component of displacement is never visible
on a vertical cross section.
1.6.2
Separation
Fault separation is the distance between any two parts of an index plane (e.g., bed or
vein) disrupted by a fault, measured in any specified direction (Dennis 1967). The
separation directions commonly important in mapping are parallel to fault strike,
parallel to fault dip, horizontal, vertical and perpendicular to bedding. It should be
noted that the definitions of the terms for fault separation and the components of
separation are not always used consistently in the literature. Stratigraphic separation
(Fig. 1.31) is the thickness of strata that originally separated two beds brought into
contact at a fault (Bates and Jackson 1987) and is the stratigraphic thickness missing
or repeated at the point, called the fault cut (Tearpock and Bischke 2003), where the
fault is intersected. The amount of the fault cut is always a stratigraphic thickness.
Throw and heave (Fig. 1.31) are the components of fault separation most obvious
on a structure contour map. Both are measured in a vertical plane in the dip direction
of the fault. Throw is the vertical component of the dip separation measured in a vertical
plane (Dennis 1967). Stratigraphic separation is not equal to the fault throw unless the
marker horizons are horizontal (see Sect. 5.5.3). Heave is the horizontal component of the
dip separation measured in a vertical plane normal to the strike of the fault (Dennis 1967).
1.6.3
Geometrical Classifications
A fault is termed normal or reverse on the basis of the relative displacement of the
hangingwall with respect to the footwall (Fig. 1.32). For a normal fault, the hangingwall
is displaced down with respect to the footwall, and for a reverse fault the hangingwall
is displaced up with respect to the footwall. The relative displacement may be either a
slip or a separation and the use of the term should so indicate, for example, a
normal-
