---
title: "Field identification criteria of fault and fold"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:field-identification-criteria-of-fault-and"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/field-identification-criteria-of-fault-and
site: BCT Engineering
---

# Field identification criteria of fault and fold

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2080 Bhadra, 4 marks; 2079 Bhadra, 4 marks (asked 2 times)
- Video: [Criteria for Recognition in Field - Structural Geology and Stratigraphy - Engineering Geology](https://www.youtube.com/watch?v=MHa4lh1Eifo) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/field-identification-criteria-of-fault-and
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

Describe the criteria for identification of fault and fold in the field.

## Short answer

Faults show offset beds, slickensides, breccia, fault scarps, linear valleys, and line of springs. Folds show repetition of beds in reverse order, opposite dips on either side of an axis, older beds in anticline cores, and V-shaped outcrop patterns.

## Answer

#### Fault
**Direct evidences**
- Displacement or offset of beds, dykes, veins, streams, roads or ridges.
- Repetition or omission (missing) of beds in a sequence.
- Slickensides (polished, grooved surfaces) and striations on the fault plane showing the direction of movement.
- Fault breccia, fault gouge or mylonite along the fault zone.
- Drag folds (bending of beds near the fault plane).

**Physiographic (topographic) evidences**
- Fault scarps (straight steep cliffs) and triangular facets.
- Linear valleys, straight stream courses and sudden changes in stream direction.
- Offset or beheaded streams, waterfalls and rapids along a straight line.
- Line of springs and seepages, and a sharp line of vegetation change.
- Alignment of sag ponds, lakes and hot springs.
- Abrupt change of rock type across a straight line, and earthquake epicentres in a line.

#### 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. Evidence of fault?
   A. Reversed repeat
   B. Axial cleavage
   C. Opposite dips
   D. Slickensides and breccia
   Answer: D. Fold evidences differ. (Key point: Fault evidence)

2. Fold shows beds?
   A. Repeated in reverse order about axis
   B. Missing
   C. Offset
   D. Same order
   Answer: A. ABCDCBA. (Key point: Fold bed repeat)

3. Anticline core?
   A. Younger
   B. Older beds
   C. Same
   D. Igneous
   Answer: B. Syncline younger. (Key point: Anticline core)

4. Anticline dips?
   A. Converging
   B. Same
   C. Diverging
   D. Vertical
   Answer: C. Syncline converging. (Key point: Dips)

## Related in Engineering Geology I

- [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×
- [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
- [Fold, fault, joint, thrust in tunnelling](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Afold-fault-joint-thrust-in) — Engineering Geology I, chapter 5
- [Fold, fault and joint; attitude](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Afold-fault-and-joint-attitude) — Engineering Geology I, chapter 5
- [Identify fold in the field](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aidentify-fold-in-the-field) — Engineering Geology I, chapter 5, asked 2×

## Related in other subjects

- [Field identification of fine-grained soils](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Afield-identification-clay-silt) — Soil Mechanics, chapter 3, asked 4×