---
title: "Engineering evaluation of hazard"
subject: "Engineering Geology II"
chapter: 5
key: "semester_4/engineering_geology_ii:hazard-evaluation-absolute"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/hazard-evaluation-absolute
site: BCT Engineering
---

# Engineering evaluation of hazard

Engineering Geology II · Chapter 5: Geological Hazards

- Asked in: 2074 Bhadra, 3+2 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/hazard-evaluation-absolute
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-5

## Question

Classify the engineering evaluation of hazard. How is absolute hazard assessment carried out?

## Short answer

Hazard evaluation is classified as absolute (quantitative probability or factor of safety) and relative (ranking). Absolute assessment uses deterministic factor-of-safety calculations or probabilistic analysis of historical event frequencies to compute annual probability and design magnitudes, producing numerical hazard maps.

## Answer

#### Classification of engineering evaluation of hazard
Hazard can be evaluated in two ways.
1. **Absolute hazard evaluation:** the hazard is given a **numerical value** of probability (for example, a 1 in 100 year event) or a quantity such as factor of safety, annual probability, expected displacement, magnitude. It is quantitative and used in design.
2. **Relative hazard evaluation:** areas are ranked as high, moderate or low **by comparison** with each other, without absolute probability; qualitative or semi-quantitative (hazard zoning maps).

#### Absolute hazard assessment (how it is done)
1. **Collect data:** past events (inventory), geology, slope, rainfall, earthquake records, geotechnical parameters.
2. **Deterministic method:** compute the **factor of safety** of the slope, for example

$$
F = \frac{cA + W\cos\beta\tan\phi}{W\sin\beta}
$$

   with $F<1$ meaning failure.
3. **Probabilistic method:** use frequency of past events to calculate return period $T$ and annual probability $P = 1/T$; probability of occurrence in $n$ years is $1-(1-1/T)^n$.
4. **Define the design event** (design earthquake, 100-year flood) and compute magnitude, runout distance or displacement.
5. **Present results** as hazard maps with numerical values and use them in design and risk calculation.

## Check yourself

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

1. What is absolute hazard evaluation?
   A. Listing past events without numbers
   B. Giving the hazard a numerical probability or quantity
   C. Ranking areas as high, moderate or low
   D. A purely qualitative opinion
   Answer: B. It is quantitative and used in design. (Key point: Absolute hazard)

2. If return period is T years, annual probability is?
   A. 1 - T
   B. T^2
   C. 1/T
   D. T
   Answer: C. P = 1/T. (Key point: Probability)

3. What does F < 1 indicate in deterministic assessment?
   A. Stable slope
   B. A safe slope
   C. No driving force
   D. Failure
   Answer: D. Resisting force is less than driving force. (Key point: Factor of safety)

4. How does relative differ from absolute evaluation?
   A. It ranks areas by comparison without absolute probability
   B. It gives exact probability
   C. It computes F
   D. It uses return periods
   Answer: A. Relative hazard evaluation is qualitative or semi-quantitative. (Key point: Relative evaluation)

## Related in Engineering Geology II

- [Hazard versus risk](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Ahazard-vs-risk) — Engineering Geology II, chapter 5, asked 6×
- [Define hazard, risk, vulnerability](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Ahazard-risk-vulnerability) — Engineering Geology II, chapter 5, asked 2×
- [Relative hazard](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Arelative-hazard) — Engineering Geology II, chapter 5

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