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Indirect methods of surface 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.

Describe the indirect methods of surface site investigation.

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.

✓ Answer checked by Claude Opus 5.5 (high effort)

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