Problem: Dipping planes show a different dip depending on the orientation of the viewer: this dip is known as the apparent dip and is NOT the true dip. The "true" dip of the plane is the maximum dip. Often you may not be able to measure the true dip but you can estimate the true dip if you have two apparent dips

Question: Graphically derive the true dips from the following apparent trends and plunges (lines)?

1. N60E/20 N75E/32

2. N60E/67 N4W/34

3. N40W/35 N85W/15

4. N75E/28 S70E/43

5. S70E/43 S2W/25

6. S35W/24NW S15W/13
 
 

Problem: A plane can also be defined provided that the position of three points on the plane are known. The plane that is common to all three is unique.

(a) Calculate the strike and dip of the gas-bearing sand layer with the following information

Three land wells (Echidna-1, Emu-2 and Pollard) located at the same height have drilled through the same layer of methane-bearing sand. Emu-2 lies 200 m from Echidna-1 along an azimuth of 050°. Pollard is found 240 m from A along an azimuth of 160°

Following are the different depths at which the gas-bearing sand were found in each well:

Echidna-1: 120 m

Emu-2: 180 m

Pollard: 320 m

I recommend you use a scale on your work of 1:2,000

(b) Using the attached Map (#15) calculate the strike and dip of the coal seam.