---
title: "Strike of limestone bed directed N20°E, dip 45°"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:strike-of-limestone-bed-directed"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/strike-of-limestone-bed-directed
site: BCT Engineering
---

# Strike of limestone bed directed N20°E, dip 45°

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2081 Baisakh, 4 marks
- 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-of-limestone-bed-directed
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

A limestone bed is directed towards N20°E with a dip angle of 45°. Find out the strike of the limestone bed.

## Short answer

Strike is 90° from dip direction. With a dip towards N20°E, the strike is N70°W (S70°E).

## Answer

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

**Given**: Limestone bed directed (dipping) towards N20°E with a dip of 45°. Dip direction = N20°E, azimuth = 20°.

$$
\begin{aligned} \text{Strike} &= \text{dip direction} \pm 90° \\ &= 20° - 90° = 290° \ \text{or}\ 20° + 90° = 110° \end{aligned}
$$

These two azimuths (290° and 110°) are the two ends of one line, so the strike is **N70°W (S70°E)**.

```text
                    N
         N70W \     |     / dip N20E
                \   |   /
                  \ | /
  W ----------------+--------------------- E
                    | \
                    |   \
                    |     \ S70E
                    S
   ( \ = strike line N70W-S70E,  / = dip direction N20E, at 90 deg to strike )
```

**Answer: Strike = N70°W (S70°E).**

## 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 is at 90° to the dip direction
   D. Strike equals the dip amount
   Answer: C. 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 N20°E?
   A. 160°
   B. 70°
   C. 340°
   D. 20°
   Answer: D. Convert the quadrant bearing to an azimuth measured clockwise from north. (Key point: Azimuth conversion)

3. What is the strike for dip direction N20°E?
   A. N70°W (S70°E)
   B. N20°W (S20°E)
   C. N70°E (S70°W)
   D. N20°E (S20°W)
   Answer: A. 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 inclined east at 45°](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-of-limestone-bed-inclined) — Engineering Geology I, chapter 5
- [Strike of quartzite bed towards S20°W](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-of-quartzite-bed-towards) — Engineering Geology I, chapter 5
- [Strike of quartzite bed, dip 70° towards S20°E](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-of-quartzite-bed-dip) — Engineering Geology I, chapter 5
- [Strike of quartzite bed, dip 80° towards N10°E](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-of-quartzite-bed-dip-80) — Engineering Geology I, chapter 5
- [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
- [Strike of limestone bed dipping S55°E](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-of-limestone-bed-dipping) — Engineering Geology I, chapter 5

## Related in other subjects

- [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