Geology Reference
In-Depth Information
pointing vertical line and the plane. The hade angle is the complement of the dip
(90° -
). The attitude of a plane may also be given as the azimuth and plunge of the
dip vector, written as dip amount, dip direction. By this convention, the previous atti-
tude is given as 22, 070, indicated by the map symbol of Fig. 2.9e. This is the form that
is usually used in this topic because it is short and convenient for numerical calcula-
tions. The dip vector will occasionally be written in short form as
δ
, where the bold
type indicates a vector. The attitude of a plane may also be represented by the orien-
tation of its pole, a line perpendicular to the plane (Fig. 2.8).
The orientation of a line is given by its trend and plunge. The trend is the angle,
δ
,
between north and the vertical projection of the line onto a horizontal plane (Fig. 2.10).
The plunge is the angle,
p
, in the vertical plane between the line and the horizontal. The
orientation of a line is written as plunge amount, azimuth of trend, for example 30, 060 is
a line plunging 30° toward the azimuth 060°. On a map the orientation of a line is repre-
sented by the same type of symbol as the azimuth and plunge of the dip (Fig. 2.9b) which
is also a line. The two symbols could be differentiated on a map by means of line weight.
Given the
xyz
coordinates of two points, it is possible to calculate the trend and
plunge of the line between them (Fig. 2.11). If subscript 1 represents the higher of the
two points, the plunge of the line determined from the following equations will be
downward. The preliminary value of the azimuth
β
θ
' and plunge
δ
of the line between
points 1 and 2 are (from Eqs. 12.11 and 12.12)
θ
'=arctan(
∆
x
/
∆
y
) ,
(2.7)
δ
=arcsin[(
z
2
-
z
1
)/
L
] ,
(2. 8)
where
Fig. 2.10.
Trend and plunge of a line in
the
shaded
surface
Fig. 2.11.
Trend and plunge of a line
between two points
