Introduction

Some locations are described as unusually quiet, unstable, vibrating or physically uncomfortable. A building may sit near a road cut, quarry, railway, pumping station, underground water system or geologically complex terrain. Geophysics provides methods for studying the physical properties of the Earth and the processes that occur beneath and around a site.

This does not mean that geology offers a universal explanation for unusual experiences. It means that investigators should consider the ground and surrounding infrastructure as part of the environment rather than treating a building as an isolated space.

What geophysics studies

Geophysics applies physical principles to the Earth. Depending on the question, it may examine:

  • Seismic waves: vibrations travelling through the ground from earthquakes, quarry blasts, machinery or other sources.
  • Ground composition: differences in soil, rock, fill material and moisture content.
  • Electrical properties: resistivity and conductivity, which vary with geology, water content and dissolved minerals.
  • Magnetic properties: local variations associated with rocks, structures and human-made materials.
  • Groundwater: movement and changing water levels that can influence soil and building conditions.

Different methods answer different questions. A magnetometer does not measure seismic vibration; a seismometer does not identify groundwater chemistry.

Ground vibration and building response

Ground motion can be transmitted into a structure through foundations. The resulting movement depends on frequency, amplitude, soil conditions, foundation design and the building's natural modes of vibration. Nearby traffic, heavy vehicles, trains, industrial machinery and construction can all produce measurable vibration.

A building can amplify some frequencies and attenuate others. Loose objects, windows, pipes and suspended components may rattle in response. A witness may hear a sound without recognising the external source.

The correct investigation compares the timing and frequency of a reported event with measured vibration and nearby activity. A correlation is a lead, not automatic proof of causation.

Seismic activity and local context

Earthquakes produce ground motion over a range of frequencies and amplitudes. Small events may be detected by instruments even when many people do not notice them. Regional seismic catalogues can provide context, but a distant event should not be attributed to a local report without checking time, distance, magnitude and expected ground motion.

Human-made events can also appear in vibration data. A seismometer may record footsteps, doors, vehicles or machinery depending on its sensitivity and placement. Instrument logs need to be interpreted with site notes.

Subsurface conditions

Soil type, groundwater and buried infrastructure can influence building behaviour. Settlement, expansive clay, erosion, leaking pipes and changes in groundwater can cause cracking, floor unevenness or intermittent sounds. These are building-condition questions and may require a geotechnical engineer or structural professional.

Investigators should never excavate, drill or enter unstable ground as an informal test.

AERM field protocol

Desk research

  1. Record the site's coordinates only with appropriate permission and privacy safeguards.
  2. Review official geological maps and public seismic catalogues.
  3. Identify nearby roads, railways, quarries, mines, pumping stations and construction.
  4. Review the building's age, foundation information and known repair history where available.
  5. Note uncertainty in map scale and data coverage.

Field measurements

  • Use a suitable vibration meter or geophone with documented bandwidth and calibration.
  • Mount sensors consistently on a stable surface.
  • Record exact sensor placement and orientation.
  • Log event times using synchronised clocks.
  • Record nearby vehicle, machinery and human activity.
  • Repeat measurements at multiple positions if safe and relevant.

Interpretation

A single vibration trace rarely identifies its source. Compare waveform shape, frequency content, timing and spatial distribution. If the question concerns structural safety, refer it to a qualified engineer rather than interpreting a sensor trace as a building diagnosis.

Limits and ethical considerations

Public geological data may be too coarse to describe a specific room or foundation. Consumer devices may not have adequate sensitivity or calibration. A magnetic anomaly does not demonstrate a seismic event, and a seismic event does not explain every sound or sensation reported at a site.

Do not trespass, enter mines or tunnels, approach active quarry faces, or conduct fieldwork during storms or unstable ground conditions.

Conclusion

Geophysical context can improve an investigation by identifying ground vibration, geological conditions and nearby sources of physical disturbance. Its greatest value is methodological: it helps define what was measured, where it was measured and which alternative explanations remain plausible. A location should be studied as a connected environmental system, not as a collection of isolated stories.

AERM Core Principle: No anomaly is considered paranormal until environmental, psychological, technical, and scientific explanations have been systematically evaluated.

References and further reading

  1. US Geological Survey (USGS), educational resources on earthquakes and seismic monitoring.
  2. British Geological Survey, introductory resources on geophysical methods.
  3. Kramer, S. L. Geotechnical Earthquake Engineering. Prentice Hall.
  4. AASHTO, guidance and standards relating to vibration and geotechnical assessment.
  5. International Society for Soil Mechanics and Geotechnical Engineering, educational publications.

About AERM

AERM encourages multidisciplinary investigation and transparent reporting. Geophysical observations are treated as environmental data that must be interpreted within their measurement limits.

Educational and safety disclaimer

This article is not a geological hazard assessment or structural inspection. Consult qualified geologists, geotechnical engineers or structural engineers for site-specific risks. Do not enter restricted or unstable locations.