This document discusses methods for describing the orientation of linear geological structures. Plunge describes the angle between a linear structure and the horizontal plane, ranging from 0-90 degrees. Trend refers to the direction of a linear structure projected onto the horizontal plane. Pitch is the angle between a planar structure and the horizontal plane. The document provides an example of how to determine the plunge and pitch of a linear structure given the strike and dip of a planar structure it intersects. A multi-step geometric method is described and illustrated with diagrams.

1. Line Structure
Lecture #16

2. Introduction
• The position of line structure can be presented
with plunge and trend.
• If the line structure on plane structure which the
position known, then the line structure can be
represented by pitch.

4. Plunge
• An angle that form by line structure with
horizontal plane which is measure on the vertical
plane.
• Has range from 0° to 90 °
Shallow 0° – 20°
Moderate 20°- 50°
Steep 50° - 90°

5. Trend
• The direction of line structure projection to the
horizontal plane.
• Line structure and the projection need to be in the
same vertical plane
• Trend able to show the direction of the line
structure.
• Trend to west and trend to east is totally different.

7. Pitch
• The vertical angle between the horizontal plane and
the axis or line of maximum elongation of a feature

8. Solve line structure problem with
geometry descriptive
• In every line structure, the magnitude of plunge
and apparent dip of plane structure is same.
• Example: Determine line structure plunge and
pitch of the plane structure.
a plane structure has strike and dip N45°E/30°SE,
and has line structure with trend N180°E.
Determine the plunge and pitch of the line
structure?

9. 1. Imagine, COED, is the slope plane, Height
differences between CO strike with DE strike is
t. FG line is the projection of DE on the map.
2. Draw strike line on N45°E direction, and draw a
perpendicular line on this strike line and label it
with CI
3. Assume that CI line is the fold line F1, and
rotate the cross section to the map plane. Draw
CJ line with an angle 30° relatively to CI
4. Draw perpendicular line to CI and label it with
KL, this line will cut the CI and CJ line and label
both point with F and D’
- KL line is the projection line from DE strike on
map
- Height differences between CO and DE strike
is FD’ (t)
5. Draw line with direction N180°E from point O
and label the line with OA, the projection to
map.
6. Make OA as the fold line 2, and rotate cross
section into map plane. Draw AB’’ line
perpendicular to OA as many as t.
7. Draw OB’’ line. ˪AOB’’ is the plunge of line
structure.
8. Make CO line as fold line 3, and rotate the
COED plane to map plane. Using Compass draw
arc that connecting D’ to D’’, where D’’ located
along CI line and C as the center of the arc.
Length of CD’’ = CD’
Solution
C
H
D
O
G
A
B
E
F
t
t
9. Draw rectangle COE’D”. This rectangle is slope
plane COED which has been rotated to map
projection. Point B which is on the slope plane also
being rotated on the map plane B’. CO line act as fold
line.
10. Draw OB’ line, which is the OB structure line that
already rotated to map plane. ˪COB is the pitch.

10. Plunge
pitch
G
L
E’
O
B’’
B’
A
t
t D”
D’
J
C
30°
F
I
Draw line with direction N180°E from point O
and label the line with OA, the projection
to map.
K C
H
D
O
G
A
B
E
F
t
t
Draw OB’’ line. ˪AOB’’ is the plunge of line
structure.
Draw OB’ line, which is the OB structure
line that already rotated to map plane.
˪COB is the pitch.

11. Draw perpendicular line to CI and
label it with KL, this line will cut
the CI and CJ line and label both
point with F and D’
- KL line is the projection line
from DE strike on map
- Height differences between CO
and DE strike is FD’ (t)
Assume that CI line is the fold line F1, and
rotate the cross section to the map
plane. Draw CJ line with an angle 30°
relatively to CI
Draw strike line on N45°E direction, and draw a
perpendicular line on this strike line and
label it with CI
Make CO line as fold line 3, and
rotate the COED plane to map
plane. Using Compass draw arc
that connecting D’ to D’’, where
D’’ located along CI line and C as
the center of the arc. Length of
CD’’ = CD’
Draw rectangle COE’D”. This
rectangle is slope plane COED which
has been rotated to map projection.
Point B which is on the slope plane
also being rotated on the map plane
B’. CO line act as fold line.
Make OA as the fold line 2, and rotate cross
section into map plane. Draw AB’’ line
perpendicular to OA as many as t.