---
title: "Fault, parts, recognition, engineering problems"
subject: "Engineering Geology I"
chapter: 5
key: "semester_3/engineering_geology_i:fault-parts-recognition-engineering-problems"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/fault-parts-recognition-engineering-problems
site: BCT Engineering
---

# Fault, parts, recognition, engineering problems

Engineering Geology I · Chapter 5: Structural Geology

- Asked in: 2061 Baisakh (old course), 2+3+3 marks
- Video: [Recognition in Field and Engineering Consideration - Structural Geology and Stratigraphy](https://www.youtube.com/watch?v=8fYUsXawwUw) — 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/fault-parts-recognition-engineering-problems
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-5

## Question

Define fault and illustrate the different parts of fault. How is it recognised in the field? What engineering problems are created by the presence of fault?

## Short answer

A fault is a fracture with relative displacement. Its parts: fault plane, hanging wall, foot wall, dip, throw, heave, net slip, fault line. Recognized by offset beds, slickensides, breccia, drag folds, scarps, linear valleys, offset streams, springs, and rock changes. Problems: weak zones cause settlement/failure, leakage, tunnel collapse/inflow, slope instability, differential settlement, seismic hazard, and unreliable exploration.

## Answer

A **fault** is a fracture in the rock mass along which the two blocks have moved relative to each other, parallel to the fracture surface. The displacement may range from a few millimetres to hundreds of kilometres.

#### Parts of a fault
- **Fault plane** - the fracture surface along which movement occurs.
- **Hanging wall** - the block lying above the fault plane.
- **Foot wall** - the block lying below the fault plane.
- **Dip of fault** - the angle between the fault plane and the horizontal.
- **Hade** - the angle between the fault plane and the vertical (90 degrees minus the dip).
- **Throw** - vertical displacement; **heave** - horizontal displacement.
- **Net slip** - the actual relative displacement along the fault plane.
- **Fault line (trace)** - the intersection of the fault plane with the ground surface.

```text
  hanging wall
   ________    fault plane
  |        |  /
  |        | /  <- dip
  |________|/_________
            /   foot wall
   throw (vertical), heave (horizontal)
```

#### Recognition in the field
**Direct evidence**
- 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) evidence**
- Fault scarps (straight, steep cliffs) and triangular facets.
- Linear valleys, straight stream courses and sudden changes in stream direction.
- Offset or beheaded streams, and waterfalls and rapids along a straight line.
- A line of springs and seepages, and a sharp line of vegetation change.
- Alignment of sag ponds, lakes and hot springs.
- An abrupt change of rock type across a straight line, and earthquake epicentres in a line.

#### Engineering problems
- **Weak zone**: crushed, sheared rock (breccia, gouge) has low strength, high compressibility and high permeability, so foundations may settle or fail.
- **Leakage**: a fault zone acts as a channel for water, causing seepage under dams and reservoir leakage.
- **Tunnelling**: sudden inflow of water, roof collapse, squeezing and heavy support requirements when a tunnel crosses a fault.
- **Slope instability**: a fault plane dipping out of the slope gives a ready sliding surface for landslides and rock slides.
- **Differential settlement**: a structure built across a fault may settle unevenly, because the rock properties differ on the two sides.
- **Seismic hazard**: active faults can move again and cause earthquakes and surface rupture, so dams, bridges and buildings must be kept away from them.
- **Uncertainty in exploration**: displaced or missing beds make the correlation of boreholes and the estimation of rock depth unreliable.

## Check yourself

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

1. What do throw and heave measure?
   A. Throw is horizontal; heave is vertical
   B. Both are angles to the horizontal
   C. Throw is vertical displacement; heave is horizontal displacement
   D. Both are widths of the fault zone
   Answer: C. Throw is vertical, heave horizontal. (Key point: Throw and heave)

2. What is the hade of a fault?
   A. The angle between the plane and the horizontal
   B. The vertical displacement
   C. The net slip
   D. The angle between the fault plane and the vertical
   Answer: D. Hade equals 90 degrees minus dip. (Key point: Hade)

3. Which is direct evidence of a fault?
   A. Slickensides, breccia, gouge, or offset beds
   B. Uniform bed thickness everywhere
   C. Absence of any crushed rock
   D. A smooth continuous ridge
   Answer: A. Offsets and polished grooved surfaces plus crushed rock indicate faulting. (Key point: Field evidence)

4. Which is a physiographic evidence of faults?
   A. Repetition of beds in the core
   B. Fault scarps, triangular facets and linear valleys
   C. Basal conglomerate
   D. Cooling columns
   Answer: B. Scarps and facets are topographic features of faulting. (Key point: Scarps)

## Related in Engineering Geology I

- [Unconformity recognition and problems](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aunconformity-recognition-and-problems) — Engineering Geology I, chapter 5
- [Folds: recognition and civil engineering influence](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Afolds-recognition-and-civil-engineering) — Engineering Geology I, chapter 5
- [Engineering significance of fault](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-significance-of-fault) — Engineering Geology I, chapter 5, asked 6×
- [Engineering geological problems in tectonic divisions](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-geological-problems-in-tectonic) — Engineering Geology I, chapter 7, asked 2×
- [Discontinuities and engineering problems in Nepal Himalaya](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Adiscontinuities-and-engineering-problems-in) — Engineering Geology I, chapter 7
- [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×

## Related in other subjects

- [Engineering geological problems of Siwalik zone](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asiwalik-problems) — Engineering Geology II, chapter 2, asked 4×
- [Define soil; soil engineering problems](https://www.bctengineer.com/question.md?key=semester_4%2Fsoil_mechanics%3Adefine-soil-engineering-problems) — Soil Mechanics, chapter 1