Structure of Rock - Rock Mechanics Based on an Anisotropic Jointed Rock Model - page 23

nuity system”. The individual discontinuities of a set are characterized by parameters
describing orientation, appearance and persistence.

Orientation
The three-dimensional orientation of a discontinuity is well-defi ned by two angles (Fig.
2.25). The so-called “angle of strike” (strike angle) is measured from the north in a

clockwise direction until the intersection of the discontinuity and the horizontal (con-
tour line). The angle

α

between the horizontal and the line of dip of the discontinuity
is referred to as the “angle of dip” (Fig. 2.25). According to this defi nition, the angular
range of

β

α and β is as follows:

(2.1)

(2.2)

Alternatively, instead of α d can be used, which describes the angle

between north and the projection of the line of dip on the horizontal being defi ned (Fig.
2.25) as

α the “dip direction”

(2.3)

Figure 2.25 Orientation of a discontinuity (Wittke 1990)

With the aid of the equal-area projection of the lower hemisphere, the orientation of dis-
continuities as subsequently outlined can be represented in a two-dimensional diagram.
This method was fi rst developed as a tool for use in structural geology and then extended