---
title: "Strike when dip direction is N40°W"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:strike-when-dip-direction-is"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/strike-when-dip-direction-is
site: BCT Engineering
---

# Strike when dip direction is N40°W

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2072 Chaitra, 4 marks
- Video: [TRUE DIP AND STRIKE DIRECTION NUMERICAL | geology ii | IOE | TU | EASY METHOD |](https://www.youtube.com/watch?v=6vDE-l2E4vQ) — Bishal Khadka
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/strike-when-dip-direction-is
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

Determine the strike direction of the bedding plane when the dip direction is N40°W.

## Short answer

Dip direction N40°W (320°). Strike = 320° ±90°, giving azimuths 50° (N50°E) and 230° (S50°W). Strike is N50°E (S50°W).

## Answer

The strike is the direction of the horizontal line on the bed and it is always at 90° to the dip direction.

**Given**: Dip direction = N40°W, azimuth = 320°.

$$
\begin{aligned} \text{Strike} &= \text{dip direction} \pm 90° \\ &= 320° - 90° = 230° \ \text{or}\ 320° + 90° = 50° \end{aligned}
$$

These two azimuths (50° and 230°) are the two ends of one line, so the strike is **N50°E (S50°W)**.

```text
                    N
     dip N40W \     |     / N50E
                \   |   /
                  \ | /
  W ----------------+--------------------- E
                  / |
                /   |
         S50W /     |
                    S
   ( / = strike line N50E-S50W,  \ = dip direction N40W, at 90 deg to strike )
```

**Answer: Strike = N50°E (S50°W).**

## Check yourself

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

1. How is strike related to the dip direction?
   A. Strike is parallel to the dip direction
   B. Strike is at 45° to the dip direction
   C. Strike equals the dip amount
   D. Strike is at 90° to the dip direction
   Answer: D. Strike is the horizontal line on the bed, perpendicular to dip direction. (Key point: Strike vs dip direction)

2. What is the azimuth of the dip direction N40°W?
   A. 320°
   B. 40°
   C. 140°
   D. 220°
   Answer: A. Convert the quadrant bearing to an azimuth measured clockwise from north. (Key point: Azimuth conversion)

3. What is the strike for dip direction N40°W?
   A. N40°E (S40°W)
   B. N50°E (S50°W)
   C. N50°W (S50°E)
   D. N40°W (S40°E)
   Answer: B. Azimuth +/- 90° gives the two ends of one line, which is the strike. (Key point: Strike result)

## Related in Engineering Geology I

- [Strike of limestone bed, dip N40°W, 64°](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-of-limestone-bed-dip) — Engineering Geology I, chapter 5
- [Dip direction from strike N55°E, dip 30°](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adip-direction-from-strike-n55e) — Engineering Geology I, chapter 5
- [Primary and secondary structures; strike and dip](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aprimary-and-secondary-structures-strike) — Engineering Geology I, chapter 5, asked 2×
- [Dip amount, strike; fold identification criteria](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adip-amount-strike-fold-identification) — 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×
- [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