---
title: "Strike of quartzite bed dipping S25°E"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:strike-of-quartzite-bed-dipping"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/strike-of-quartzite-bed-dipping
site: BCT Engineering
---

# Strike of quartzite bed dipping S25°E

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2081 Baisakh (new course), 2 marks; 2081 Bhadra, 2 marks (asked 2 times)
- 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-dipping
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

A quartzite rock bed dips towards S25°E. Find its strike direction with a figure (the 2081 Bhadra paper gave a sandstone bed with the same direction and asked for a net diagram).

## Short answer

Strike is perpendicular to dip direction. For a bed dipping S25°E, strike is N65°E (also S65°W).

## Answer

The strike is always at 90° to the dip direction.

**Given**: dip direction = S25°E, which is azimuth $180° - 25° = 155°$.

$$
\begin{aligned} \text{Strike azimuth} &= 155° - 90° = 65° \\ \text{(or } 155° + 90° &= 245° \text{)} \end{aligned}
$$

So the strike is **N65°E** (the same line is S65°W).

```text
               N
               |        strike N65E
               |     /
               |   / 65
        W -----+-/---------- E
               | \
               |  \ 25
               |   v  dip direction S25E
               S
```

The strike line and dip direction are perpendicular: the strike is 25° north of east and the dip direction is 65° south of east (25° + 65° = 90°).

**Answer: Strike = N65°E (S65°W).** For the sandstone bed with the same dip direction in the net-diagram version, mark the strike N65°E-S65°W as a diameter of the stereonet. The great circle of the bed joins the two strike ends and bows towards S25°E (the dip direction); its pole plots on the opposite side, along N25°W. The dip amount fixes how far the great circle bows in from the primitive circle.

## Check yourself

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

1. Strike relative to dip direction?
   A. At 90 deg
   B. Parallel
   C. 45 deg
   D. Opposite
   Answer: A. Perpendicular. (Key point: Rule)

2. S25E in azimuth?
   A. 205 deg
   B. 155 deg
   C. 25 deg
   D. 115 deg
   Answer: B. 180-25=155. (Key point: Azimuth)

3. Strike?
   A. N25E
   B. N65W
   C. N65E (S65W)
   D. N155E
   Answer: C. 155-90=65. (Key point: 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 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 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 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
- [Strike of limestone bedrock dipping N31°W](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Astrike-of-limestone-bedrock-dipping) — 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

## Related in other subjects

- [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×
- [Reserve: quartzite apparent dips 1:9 and 1:12, 4.6 km2](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Areserve-quartzite-apparent-dips-area) — Engineering Geology II, chapter 7, asked 2×
- [Principal MI, direction and position of section (2080 Bhadra)](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Aprincipal-mi-2080b) — Strength of Materials, chapter 2