Discussion
The apparent thickness of an outcropping bed in 20 m. The bed dips at 30°, what will be the true thickness of the bed ?
Answer: C
The true thickness is 10 m.
On level ground, the apparent thickness of an outcropping bed is the width of its outcrop measured horizontally, perpendicular to strike. The true thickness is measured at right angles to the bedding, so it is the outcrop width times the sine of the dip:
\[ \begin{aligned} t &= w \sin\delta \\ &= 20 \times \sin 30^{\circ} \\ &= 20 \times 0.5 = 10\ \text{m} \end{aligned} \]
20 m would hold only for a vertical bed. True thickness can never exceed the outcrop width, so 30 m is impossible. Using the cosine instead of the sine gives 17.3 m, which is not offered.
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