If a bed dips 5 degrees in the opposite direction to the regional dip, the map-measured thickness is likely to be:

If a bed dips 5 degrees in the opposite direction to the regional dip, the map-measured thickness is likely to be:

• A. Less than true thickness
• B. Greater than true thickness
• C. Equal to true thickness
• D. Not determinable

Answer: (B)

The key idea is how a bed’s dip affects what you measure on a map. Thickness you measure on a map is a projection of the true, perpendicular thickness onto the horizontal plane of the map. When a bed is dipping, this horizontal projection makes the distance between the top and bottom surfaces appear slightly larger than the true thickness, because you’re viewing a tilted slab end-on rather than straight on. Mathematically, the apparent thickness on the map is about the true thickness divided by the cosine of the dip angle. With a dip of 5 degrees, cos 5° is about 0.996, so the apparent thickness is 1/cos 5° ≈ 1.0038 times the true thickness. That means the map-measured thickness is slightly greater than the true thickness. Whether the bed dips opposite to the regional dip doesn’t change this small geometric effect—the tilt still causes a tiny exaggeration in the map thickness. So the best answer is that the map-measured thickness is greater than the true thickness.

The key idea is how a bed’s dip affects what you measure on a map. Thickness you measure on a map is a projection of the true, perpendicular thickness onto the horizontal plane of the map. When a bed is dipping, this horizontal projection makes the distance between the top and bottom surfaces appear slightly larger than the true thickness, because you’re viewing a tilted slab end-on rather than straight on.

Mathematically, the apparent thickness on the map is about the true thickness divided by the cosine of the dip angle. With a dip of 5 degrees, cos 5° is about 0.996, so the apparent thickness is 1/cos 5° ≈ 1.0038 times the true thickness. That means the map-measured thickness is slightly greater than the true thickness.

Whether the bed dips opposite to the regional dip doesn’t change this small geometric effect—the tilt still causes a tiny exaggeration in the map thickness. So the best answer is that the map-measured thickness is greater than the true thickness.