---
title: "Earthquake terminology and seismic construction"
subject: "Engineering Geology I"
chapter: 2
key: "semester_3/engineering_geology_i:earthquake-terminology-and-seismic-construction"
source: https://www.bctengineer.com/q/semester_3/engineering_geology_i/earthquake-terminology-and-seismic-construction
site: BCT Engineering
---

# Earthquake terminology and seismic construction

Engineering Geology I · Chapter 2: Basic Reviews of the Earth

- Asked in: 2064 Jestha (old course), 4+4 marks
- Video: [Basic Earthquake Terms, Definitions - Civil Engineering](https://www.youtube.com/watch?v=-4tc07xJUMY) — TOT - The Online Tutor
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_3/engineering_geology_i/earthquake-terminology-and-seismic-construction
- Whole chapter: https://www.bctengineer.com/md/semester_3/engineering_geology_i/chapter-2

## Question

Describe the different terminologies of earthquake with necessary diagram. Describe the points that should be taken into consideration for the construction of civil engineering structures in seismic areas.

## Short answer

Focus is the underground rupture point, epicentre is directly above. Magnitude measures energy (Richter), intensity measures damage (Mercalli). Seismic construction: avoid faults and soft soils, follow codes, use symmetrical plans, ductile detailing, bands, uniform foundation, light materials, and separation gaps.

## Answer

#### Earthquake terminology
```text
        Epicentre (E)
 ground ------*--------------------
              |  \  seismic waves
              |   \
              |    \
  depth h     |     \
              * Focus (F)
```
- **Focus (hypocentre)**: the point inside the Earth where the rock first ruptures and energy is released.
- **Epicentre**: the point on the surface vertically above the focus.
- **Focal depth**: vertical distance from focus to epicentre. Shallow (0-70 km), intermediate (70-300 km), deep (300-700 km).
- **Epicentral distance**: distance from the observation station to the epicentre.
- **Magnitude**: measure of energy released (Richter scale), a single value.
- **Intensity**: measure of effects and damage at a place (Modified Mercalli scale, I to XII).
- **Isoseismal lines**: lines joining points of equal intensity.
- **Seismograph / seismogram**: instrument and record of ground motion.
- **Foreshocks and aftershocks**: smaller shocks before and after the main shock.
- **Seismic waves**: P, S, Love and Rayleigh waves.

#### Points to consider for construction in seismic areas
1. Avoid sites on active faults, soft or loose saturated soils (liquefaction), steep unstable slopes and landslide areas; prefer hard rock or firm soil.
2. Follow the earthquake code (Nepal National Building Code NBC 105 and IS 1893), using the seismic zone factor.
3. Use simple, symmetrical plans and regular elevations, and avoid large overhangs and soft storeys.
4. Provide ductile detailing, tie beams, bands (plinth, lintel, roof) and vertical reinforcement in masonry.
5. Make the foundation uniform and at one level; use a raft or tie beams, and avoid mixed foundation types.
6. Use light roofing and light materials; avoid heavy parapets.
7. Provide adequate separation between adjacent buildings to prevent pounding.
8. Use good quality materials and workmanship, proper mortar and anchorage.
9. For dams and bridges, use flexible joints, adequate freeboard and proper shear keys.
10. Use base isolation or dampers for important structures.

## Check yourself

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

1. Which pairing of measure and scale is correct?
   A. Magnitude measures damage (Mercalli); intensity measures energy (Richter)
   B. Magnitude measures energy released (Richter); intensity measures effects at a place (Modified Mercalli, I to XII)
   C. Both are measured on the Mercalli scale
   D. Magnitude is the distance to the epicentre; intensity is the focal depth
   Answer: B. Magnitude is a single energy-based value; intensity describes local effects. (Key point: Magnitude vs intensity)

2. What do isoseismal lines join?
   A. Points of equal magnitude
   B. Points of equal focal depth
   C. Points of equal intensity
   D. Stations that recorded the same P-wave arrival time
   Answer: C. Isoseismal lines connect places that experienced the same intensity. (Key point: Isoseismal lines)

3. Which site is best for building in a seismic area?
   A. Loose saturated sand near a river
   B. Hard rock or firm soil, away from active faults and landslide areas
   C. A steep slope with unstable soil
   D. Directly on an active fault for good foundation contact
   Answer: B. Soft, loose saturated soils risk liquefaction; faults and unstable slopes should be avoided. (Key point: Site selection)

4. Which design practice is recommended in seismic areas?
   A. Simple symmetrical plans, regular elevation and adequate separation between adjacent buildings
   B. Large overhangs and soft storeys for flexibility
   C. Heavy parapets and heavy roofing for stability
   D. Buildings touching each other for mutual support
   Answer: A. Regular, symmetric buildings with separation prevent torsion, soft-storey failure and pounding. (Key point: Building configuration)

## Related in Engineering Geology I

- [Earthquake occurrence, terminology, causes, effects](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aearthquake-occurrence-terminology-causes-effects) — Engineering Geology I, chapter 2
- [Seismic waves and earthquake mechanism](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aseismic-waves-and-earthquake-mechanism) — Engineering Geology I, chapter 2
- [Earthquake intensity, magnitude, seismic waves](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aearthquake-intensity-magnitude-seismic-waves) — Engineering Geology I, chapter 2
- [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
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