---
title: "Indirect methods of surface investigation"
subject: "Engineering Geology II"
chapter: 4
key: "semester_4/engineering_geology_ii:indirect-surface-methods"
source: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/indirect-surface-methods
site: BCT Engineering
---

# Indirect methods of surface investigation

Engineering Geology II · Chapter 4: Engineering geology in site selection, investigation & construction/excavation

- Asked in: 2076 Baisakh, 3 marks
- Video: [Electrical Resistivity and Seismic Method of Geological Investigation - Engineering Geology](https://www.youtube.com/watch?v=j1U-u_Tb7I0) — Ekeeda
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_4/engineering_geology_ii/indirect-surface-methods
- Whole chapter: https://www.bctengineer.com/md/semester_4/engineering_geology_ii/chapter-4

## Question

Describe the indirect methods of surface site investigation.

## Short answer

Indirect surface methods gather subsurface information without direct contact, using topographic and geological maps, aerial photo interpretation, satellite imagery, GIS, and surface geophysics (seismic refraction, resistivity). They are cheap, rapid, and guide direct investigation planning.

## Answer

Indirect surface methods get information without direct contact with the ground, by use of maps, images and instruments.

1. **Study of existing maps and records:** topographic, geological, soil and hydrological maps, previous reports, rainfall and flood data.
2. **Aerial photo interpretation:** stereo pairs show lithology, lineaments, faults, landslides, drainage patterns, and land forms.
3. **Remote sensing and satellite imagery** (Landsat, Sentinel, Google Earth), DEM, LiDAR, used for large areas, landslide inventory and structure mapping.
4. **GIS analysis:** overlay of slope, geology, land use and rainfall for hazard zoning.
5. **Surface geophysical methods:**
   - Seismic refraction: depth of bed rock and layer velocity.
   - Electrical resistivity: groundwater, clay and bed rock.
   - Magnetic and gravity methods.
   - Ground penetrating radar.
6. **Local knowledge and interviews** about floods, past slides and springs.

Advantages: cheap, quick, cover wide areas, guide the planning of direct investigation. Limit: interpretations must be checked in the field.

## Check yourself

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

1. Aerial photo interpretation shows
   A. Core recovery
   B. Bearing capacity
   C. Lithology, lineaments, faults, landslides and drainage patterns
   D. Lugeon values
   Answer: C. Stereo pairs reveal terrain features. (Key point: Aerial photos)

2. GIS is used to
   A. Drill cores
   B. Take undisturbed samples
   C. Run plate loads
   D. Overlay slope, geology, land use and rainfall for hazard zoning
   Answer: D. It is an indirect analysis tool. (Key point: GIS)

3. What is a limit of indirect methods?
   A. Interpretations must be checked in the field
   B. They are costly
   C. They cover small areas
   D. They are slow
   Answer: A. They are cheap and wide-ranging but need verification. (Key point: Advantage and limit)

## Related in Engineering Geology II

- [Indirect sub-surface methods: tunnel and dam](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Aindirect-subsurface-tunnel-dam) — Engineering Geology II, chapter 4
- [Direct methods of sub-surface investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Adirect-subsurface-methods) — Engineering Geology II, chapter 4, asked 3×
- [Surface versus sub-surface investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asurface-vs-subsurface-investigation) — Engineering Geology II, chapter 4, asked 3×
- [Purposes of site investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asite-investigation-purposes) — Engineering Geology II, chapter 4, asked 7×
- [Types and methods of site investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Asite-investigation-methods) — Engineering Geology II, chapter 4, asked 7×
- [Detail stage of EG site investigation](https://www.bctengineer.com/question.md?key=semester_4%2Fengineering_geology_ii%3Adetail-stage-investigation) — Engineering Geology II, chapter 4

## Related in other subjects

- [Methods of surface and subsurface site investigation](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Amethods-of-surface-and-subsurface) — Engineering Geology I, chapter 1, asked 4×
- [Site investigation for dam and reservoir](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Asite-investigation-for-dam-and) — Engineering Geology I, chapter 1, asked 2×
- [Contents of site investigation report](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Asite-investigation-report) — Foundation Engineering, chapter 2, asked 5×
- [Engineering geological map and site investigation](https://www.bctengineer.com/question.md?key=semester_3%2Fengineering_geology_i%3Aengineering-geological-map-and-site) — Engineering Geology I, chapter 1, asked 3×