Engineering Rock Mechanics

Points to remember 439

Rotate the tracing paper so that the

tick for N” is on the E-W line, and

count in to get the rotated normal

N”. In effect, we have modelled the

rotation of the core.

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N”

BH

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N

BH
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145/73

Now put the point BH on

the E-W line, and move the

point N” along the small

circle by the same amount

but in the opposite direc-

tion to that used in step 2.

This puts the projection

back to its starting position,

and N” moves to NR: the

rotated normal.

Put NRon the E-W line, count across

90°, and mark DR Measure the dip

of DR and mark its azimuth. Finally,

put the tracing paper back to the

datum and measure the azimuth of

DR. Thus, we see that the apparent

orientation of the discontinuity is

187/58.

BH

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Points to remember

1. Never write on the projection itself: you should always write on the


2. Use pencil, not pen, as you will make mistakes that need to be erased.


3. Adopt-and use always-a simple but clear naming convention for

tracing paper.