---
title: "Strike of quartzite bed towards S20°W"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:strike-of-quartzite-bed-towards"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/strike-of-quartzite-bed-towards
site: BCT Engineering
---

# Strike of quartzite bed towards S20°W

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2079 Bhadra, 2 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-quartzite-bed-towards
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

A quartzite bed is directed towards S20°W with a dip angle of 45°. Find out the strike of the quartzite bed.

## Short answer

Dip direction S20°W (azimuth 200°). Strike = 200° ± 90°, giving 110° (S70°E) and 290° (N70°W). Strike is S70°E (N70°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**: Quartzite bed directed (dips) towards S20°W with a dip of 45°. Dip direction = S20°W, azimuth = 200°.

$$
\begin{aligned} \text{Strike} &= \text{dip direction} \pm 90° \\ &= 200° - 90° = 110° \ \text{or}\ 200° + 90° = 290° \end{aligned}
$$

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

```text
                    N
         N70W \     |
                \   |
                  \ |
  W ----------------+--------------------- E
                  / | \
                /   |   \
     dip S20W /     |     \ S70E
                    S
   ( \ = strike line N70W-S70E,  / = dip direction S20W, at 90 deg to strike )
```

**Answer: Strike = S70°E (N70°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 at 90° to the dip direction
   B. Strike is parallel to the dip direction
   C. Strike is at 45° to the dip direction
   D. Strike equals the dip amount
   Answer: A. 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 S20°W?
   A. 160°
   B. 200°
   C. 20°
   D. 250°
   Answer: B. Convert the quadrant bearing to an azimuth measured clockwise from north. (Key point: Azimuth conversion)

3. What is the strike for dip direction S20°W?
   A. N20°W (S20°E)
   B. N70°E (S70°W)
   C. S70°E (N70°W)
   D. S20°W (N20°E)
   Answer: C. Azimuth +/- 90° gives the two ends of one line, which is the strike. (Key point: Strike result)

## Related in Engineering Geology I

- [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 limestone bed directed N20°E, dip 45°](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-of-limestone-bed-directed) — 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 quartzite bed dipping S25°E](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-of-quartzite-bed-dipping) — Engineering Geology I, chapter 5, asked 2×
- [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 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