Investigación

Lab 4 - The Concept Of Apparent Dip
Q1. Using descriptive geometry
N

Set-up an arbitrary point 1 where the dyke is at the surface.

2

lin

e

4
(e.g. 2cm)

}

p

folding line

3 di

5

Draw a N-S line 2 to represent the cutting, now used as FOLDING LINE for the
apparent dip.
Measure and mark dip line 3 for the apparent dip. NB the dip line must be
inclined to thenorth relative to the folding line.
Select an appropriate depth ‘d’ to dip line measured at a right-angle to the
folding line (= a horizontal) = 4 .

50o

Point 5 represents the place on surface where dyke is depth ‘d’ below surface.
1

N
f.l.

The same procedure is used for the other apparent dip using
the SAME point of origin 1 . Steps 2 through 5 as
applied to the second set ofinform as applied to the
second set of information.

2

045

f.l

.

d.

l.

}

Now have 2 points, ‘Pd’ on map where dyke known to be at
the same depth, i.e. depth d.

Pd

5

Pd

o

d.l.

40

50o

}

4
3

1

(previous depths and dip lines are now omitted for clarity)

dyke s.l. @ d

'd' measured
down from f.l.

(d

.l.)

}

6

Pd

Pd

Dykealso known to be at surface at the point of origin 1 . If it
is assumed that the dyke is planar, the second strike
line MUST be parallel to the first.

9
dyke s.l. @ 0

8

{

1

{

Folding line / dip line construction 9 can then be used to
calculate the dip angle, =50o.

a
(f. d cu
l.) t

7

A second strike line is needed to determine dip angle.

Line passing through originand parallel to depth 'd' strike line,
shown as 8 .

ro

Azimuth of strike given by clockwise angle 7 from north,
=090o.

045

N

(f.l.)

railway cutting
(f.l.)

The 2 points, Pd, can now be linked by a line 6 , which is the
line along which the dyke is at a depth 'd' below the
surface, i.e. a depth 'd' strike line.

map

folding line construction
(or cross-section)

Dipdirection can be determined in different ways:
!direction dip line is inclined with respect to the folding
line, i.e. if viewed from the right, dip line is
inclined to the right, which is north.
!depth of strike lines increase in the down-dip
direction, i.e. north.
!both apparent dips have a northerly component,
impossible to have a south-dipping feature.

NB The dip should be exactly 50oas given for the first
apparent dip because the railway cutting is at a
right angle to strike. Therefore, the apparent
dip observed there, in this case, is the same as
the true dip.

Q2. Using descriptive geometry
Set-up an arbitrary strike line 1 trending 135 representing the coal at the
surface.

.l.
ls
@
0

For a true dip, the folding line 2 must be perpendicular to strike.2

Measure 20o from the folding such that the dip line 3 is inclined to the SE
relative to the folding line.

a
co

6

l.)

a
co

1

(f.

N

o

.l.
ls
@

20

Choose a convenient depth ‘d' 4 measured perpendicularly from the folding line
down to the dip line.

(d.l
.)

d

Point 5 represents the place on the surface along the folding line where the
coal is at adepth 'd' below the surface.

}

d
fro ept
m h 'd
f.l '
.

5

4

A second strike line 6 can now be drawn for the coal at depth 'd'.

3

Now have 2 strike lines for the coal that are going to intersect a N-S
vertical face. All of the previous construction with the
exception of the two strike lines (0 & 'd') are omitted for clarity.

7
P0
8
N

14o

N-S face drawn on map7 will be used as a folding line (for depth=0)
for the apparent dip.
0 strike line hits folding line at P0 8 . In the 'cross-section view' of the
construction, this point remains there as the folding line's
depth is 0.

12
11
a
co
.l.

ls

'd' strike line intersects folding line (or vertical face) at Pd 9 .

}

0

Pd

1

9
a
co

depth 'd'
from f.l.

.l.
ls

Line...