---
title: "Dip amount, strike; fold identification criteria"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:dip-amount-strike-fold-identification"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/dip-amount-strike-fold-identification
site: BCT Engineering
---

# Dip amount, strike; fold identification criteria

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2081 Kartik (new course), 3 marks
- Video: [Measuring Dip & Strike of a bedding plane using Android App](https://www.youtube.com/watch?v=eIf0o5itR9E) — Geospire
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/dip-amount-strike-fold-identification
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

Define dip amount and strike of a geological plane. Write down the field identification criteria of fold in the field.

## Short answer

Dip amount is the maximum inclination of a plane to the horizontal, measured perpendicular to strike. Strike is the compass bearing of the horizontal line on the plane; it is 90° from the dip direction. A fold is identified by repetition of beds in reverse order, opposite dips across an axis, curved outcrop patterns, older beds in core of an anticline, younger in core of a syncline, drag folds, fan cleavage, and plunging noses on topography.

## Answer

#### Dip amount
The **dip amount (angle of dip)** is the maximum angle that an inclined geological plane makes with the horizontal plane. It is measured in a vertical plane at right angles to the strike, with a clinometer. It ranges from 0° (horizontal) to 90° (vertical). The direction towards which the plane goes down is the dip direction.

#### Strike
The **strike** is the direction (compass bearing) of the horizontal line drawn on an inclined plane, i.e. the line of intersection of that plane with a horizontal plane. It is always perpendicular to the dip direction, for example N30°E.

#### Field identification of fold
- **Repetition of beds** in reverse order on both sides of an axis (A B C D C B A).
- **Opposite dips** on two sides of a line (axis), either converging (syncline) or diverging (anticline).
- **Outcrop pattern** on a map: a series of curved or zig-zag outcrops (V-shaped patterns) with plunge.
- **Age relation**: in an anticline older beds are in the core; in a syncline younger beds are in the core.
- **Drag folds and minor folds** in the small scale, and variation of strike or dip along a traverse.
- **Topography**: ridges and valleys following the folded beds, and plunging noses on hill slopes.
- **Cleavage or joints** (fan or radiating pattern) related to the axial plane.

## Check yourself

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

1. The dip amount is
   A. the angle measured along the strike
   B. the maximum angle a plane makes with the horizontal, measured perpendicular to the strike
   C. the compass bearing of the horizontal line
   D. the angle between two joint sets
   Answer: B. True dip is the maximum inclination, measured at right angles to strike with a clinometer. (Key point: Dip amount)

2. Strike is
   A. the bearing of the horizontal line on an inclined plane, perpendicular to dip direction
   B. the maximum inclination of the plane
   C. parallel to the dip direction
   D. always north-south
   Answer: A. It is the intersection of the plane with a horizontal plane. (Key point: Strike)

3. In the field, older beds in the core of a fold indicate
   A. a syncline
   B. a monocline
   C. a fault
   D. an anticline
   Answer: D. Anticlines have older beds in the core; synclines have younger. (Key point: Age relation in folds)

4. Which observation suggests a fold?
   A. Beds all dipping the same way in uniform order
   B. Absence of any dip
   C. Repetition of beds in reverse order about an axis, with opposite dips
   D. Only horizontal beds with no pattern
   Answer: C. Symmetrical repetition (A B C D C B A) and opposite dips indicate folding. (Key point: Bed repetition)

## Related in Engineering Geology I

- [Field identification criteria of fault and fold](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Afield-identification-criteria-of-fault-and) — 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
- [Field identification criteria of fault](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Afield-identification-criteria-of-fault) — Engineering Geology I, chapter 5, asked 7×
- [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×

## Related in other subjects

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