Question:
The figure shows stereographic projections of the axial plane and the hinge line of a fold. Which one of the following folds is represented in the figure?
The figure shows stereographic projections of the axial plane and the hinge line of a fold. Which one of the following folds is represented in the figure?
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In fold classification, "plunging" refers to the tilt of the fold axis, while "non-plunging" indicates a horizontal fold axis.
Updated On: Dec 11, 2025
- Upright plunging
- Upright non-plunging
- Reclined
- Recumbent
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The Correct Option is B
Solution and Explanation
Step 1: Understanding Stereographic Projections.
Stereographic projections of folds show the orientation of the axial plane and hinge line. An upright fold has its axial plane vertical and a non-plunging hinge line, meaning the fold axis remains horizontal.
Step 2: Analyzing the options.
(A) Upright plunging: Incorrect — A plunging fold would have a hinge line that dips.
(B) Upright non-plunging: Correct — This fold has a vertical axial plane and a horizontal hinge line, consistent with the figure.
(C) Reclined: Incorrect — A reclined fold has an inclined axial plane, not consistent with the figure.
(D) Recumbent: Incorrect — A recumbent fold has a nearly horizontal axial plane.
Step 3: Conclusion.
The correct answer is (B) Upright non-plunging, as the figure shows a fold with a vertical axial plane and a horizontal hinge line.
Stereographic projections of folds show the orientation of the axial plane and hinge line. An upright fold has its axial plane vertical and a non-plunging hinge line, meaning the fold axis remains horizontal.
Step 2: Analyzing the options.
(A) Upright plunging: Incorrect — A plunging fold would have a hinge line that dips.
(B) Upright non-plunging: Correct — This fold has a vertical axial plane and a horizontal hinge line, consistent with the figure.
(C) Reclined: Incorrect — A reclined fold has an inclined axial plane, not consistent with the figure.
(D) Recumbent: Incorrect — A recumbent fold has a nearly horizontal axial plane.
Step 3: Conclusion.
The correct answer is (B) Upright non-plunging, as the figure shows a fold with a vertical axial plane and a horizontal hinge line.
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