Question

The width of the outcrop of a fault zone on a flat surface is 100 m. A vertical borehole through the fault zone measured its vertical thickness to be 80 m. The true thickness of the fault zone is ________ m. (Round off to two decimal places.)
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Hint:

For dipping beds: True thickness = Vertical thickness / cos(dip angle).

Answer 1

Correct Answer: 70

Step 1: Geometry of the problem.
Outcrop width (horizontal) = 100 m. Vertical thickness = 80 m.
Step 2: True thickness.
True thickness (T) = Vertical thickness × cos(dip). If outcrop width > vertical thickness, dip = tan\textsuperscript{–1}(80/100) = 38.66°. T = 80 / cos(38.66°) = 80.0 m (approx).
Step 3: Conclusion.
True thickness ≈ 80.00 m.