SUBSURFACE METHODS · ENGINEERING CONTEXT
Geophysical Survey Methods
Understand what seismic, electrical and borehole geophysics can—and cannot—reveal before selecting a method for ground investigation and engineering decisions.
Engineering Overview
Choose the method to fit the geological question
Geophysical surveying measures physical responses of the ground, including seismic wave velocity, electrical resistivity and borehole properties. These responses are interpreted as geological or engineering information with varying degrees of uncertainty. GEOOE, the technology-origin and geo-intelligence platform of GEOORIGIN ENGINEERING LIMITED, provides technical reference material and method-selection context rather than treating any geophysical technique as a universal answer.
Interpretation is strongest when field QC, calibration and independent ground truth are considered together.
PROJECT CHALLENGES
Why Geophysical Results Need Context
Ambiguous interpretation
Different ground materials can produce similar measured responses; one inversion model is not necessarily unique.
Site noise and access
Traffic, vibration, buried services, hard surfacing and restricted offsets can reduce resolution.
Depth versus detail
Greater investigation depth normally changes survey geometry and may compromise near-surface resolution.
Overclaiming certainty
A resistivity or velocity image does not directly establish bearing capacity or groundwater chemistry.
METHOD SELECTION
Compare Geophysical Survey Techniques
Geophysical methods produce indirect observations. Their usefulness depends on acquisition geometry, data quality, inversion assumptions and borehole or other ground truth.
| Method | Measured Response | Possible Engineering Use | Major Limitation |
|---|---|---|---|
| MASW / surface waves | Dispersion of seismic surface waves | Shear-wave velocity profiling for ground stiffness context | Layering, inversion assumptions and usable wavelength range |
| MAM / ambient vibration | Passive array wavefield | Passive Vs assessment where active sources are restricted | Array aperture, noise distribution and inversion uncertainty |
| Seismic refraction | First-arrival travel times | Velocity contrasts and near-surface structure | Hidden low-velocity layers may be poorly resolved |
| VES / electrical resistivity tomography | Electrical potential and apparent resistivity | Electrical contrasts, lateral continuity and saturation indicators | Clay, salinity and moisture can yield non-unique signatures |
| Borehole logging / televiewer | Downhole imaging or geophysical logs | Fractures, lithology and depth-linked interpretation | Borehole condition, calibration and image orientation |
APPLICATIONS
Engineering Uses of Subsurface Geophysics
Infrastructure corridors
Screen broad variations and target subsequent intrusive investigation.
Foundations and rockhead
Provide supporting evidence for geological interfaces and discontinuities.
Groundwater and environmental work
Investigate potential resistivity contrasts alongside sampling and hydrogeology.
Slope and underground projects
Support conceptual ground models with cross-checked field observations.
ENGINEERING WORKFLOW
A Defensible Geophysical Investigation Workflow
01 — Define the question
Clarify target property, expected depth and decision tolerance.
02 — Review conditions
Map access, surface constraints, groundwater and expected geology.
03 — Select a method
Choose survey geometry and a complementary validation method.
04 — Control data quality
Check coupling, noise, repeatability, instrument configuration and inversion assumptions.
05 — Interpret responsibly
Present uncertainty, alternative explanations and recommended ground truth.
DECISION CRITERIA
Method Selection Checklist
Clear objectives, constraints and responsibilities are prerequisites for trustworthy instrumentation and data processing.
- Is the desired output a velocity profile, a resistivity contrast or an actual material sample?
- Does site geometry support sufficient survey line length or array aperture?
- What is the realistic depth of investigation and resolution trade-off?
- Could cultural noise, conductive clays or saline water bias the result?
- How will boreholes, laboratory tests or known features calibrate the interpretation?
- What uncertainty must be reported before the results inform design?
IMPORTANT LIMITATIONS
Interpretation Limits and Ground Truth
No single geophysical method directly replaces boreholes, sampling, field testing or the professional ground model. Methods are complementary and should be chosen by specific engineering objectives.
Geophysical data can inform investigation strategy, but licensing, detailed field delivery and project-specific reporting arrangements must be agreed with the appropriate responsible professionals.
FAQs
Frequently Asked Questions
Can MASW directly provide soil bearing capacity?
Is electrical resistivity a direct measurement of groundwater level?
When is MAM preferable to MASW?
Should a client commission every method?
SOURCES & RELATED PAGES
Technical References and Related Reading
Official and industry sources provide context; related GEOOE pages expand the technical discussion.
Official and Industry References
Related GEOOE Pages
TECHNICAL ENQUIRY
Discuss Your Engineering Challenge with GEOOE
Share the asset type, location, existing instruments, monitoring objective and operational constraints. We can discuss the technical approach and potential collaboration before defining project-specific roles.