---
title: "True dip versus apparent dip"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:true-dip-versus-apparent-dip"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/true-dip-versus-apparent-dip
site: BCT Engineering
---

# True dip versus apparent dip

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2064 Jestha (old course), 4 marks; 2069 Chaitra, 2 marks (asked 2 times)
- Video: [Structural Geology Lesson 2: Apparent Dip](https://www.youtube.com/watch?v=-TPje1Ef-x4) — Blake Splitter
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/true-dip-versus-apparent-dip
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

Differentiate between true dip and apparent dip.

## Short answer

True dip is the maximum inclination of a bed measured perpendicular to strike. Apparent dip is measured in any other direction and is always less, given by tan(δ_a)=tan(δ)×sin(α) where α is the angle between the section and strike.

## Answer

| Point | True dip | Apparent dip |
|---|---|---|
| Definition | Maximum inclination of a bed measured in a direction perpendicular to the strike | Inclination of the bed measured in any direction other than perpendicular to the strike |
| Direction | At 90° to the strike | At any angle between 0° and 90° to the strike |
| Value | Greatest dip of the plane | Always less than the true dip (zero along strike) |
| Seen in | Section perpendicular to the strike | Cuts, boreholes and sections oblique to the strike |
| Relation | True dip is a constant for a plane | $\tan \delta_a = \tan \delta \times \sin\alpha$, where $\alpha$ is the angle between the section and the strike |

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. True dip measured?
   A. Perpendicular to strike
   B. Along strike
   C. Any
   D. 45 deg
   Answer: A. Max. (Key point: True dip)

2. Apparent dip compared to true?
   A. Greater
   B. Always less
   C. Equal
   D. Double
   Answer: B. Zero along strike. (Key point: Value)

3. True dip seen in?
   A. Oblique sections
   B. Any
   C. Section perpendicular to strike
   D. Along strike
   Answer: C. Else apparent. (Key point: Section)

4. Relation?
   A. tan(apparent)=tan(true)/sin(alpha)
   B. apparent=true+alpha
   C. sin(apparent)=tan(true)
   D. tan(apparent) = tan(true) x sin(alpha)
   Answer: D. Alpha angle between section and strike. (Key point: Formula)

## Related in Engineering Geology I

- [Calculating apparent dip from true dip](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Acalculating-apparent-dip-from-true) — Engineering Geology I, chapter 5, asked 2×
- [Fold classification, strike, true and apparent dip](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Afold-classification-strike-true-and) — Engineering Geology I, chapter 5
- [Strike-dip relationship and apparent dip](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrikedip-relationship-and-apparent-dip) — Engineering Geology I, chapter 5, asked 2×
- [Apparent dip in cross-section drawing](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aapparent-dip-in-crosssection-drawing) — Engineering Geology I, chapter 5

## Related in other subjects

- [True dip from two apparent dips](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Atrue-dip-from-apparent-dips) — Engineering Geology II, chapter 6
- [Reserve: limestone dip 30, apparent 20 m](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areserve-limestone-dip-30) — Engineering Geology II, chapter 7
- [True thickness from apparent thickness 210 m](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Abh-quartzite-thickness-210-attitude) — Engineering Geology II, chapter 6
- [Reserve: quartzite apparent dips 1:9 and 1:12, 2.7 x 3.1 km](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areserve-quartzite-apparent-dips-terrain) — Engineering Geology II, chapter 7, asked 2×