BOREHOLE SEISMIC VELOCITY LOGGING
Suspension PS Logging for P- and S-Wave Profiles
Explore suspension P-S logging for downhole compressional and shear-wave velocity profiles, site characterisation, seismic assessment and engineering interpretation.
METHOD OVERVIEW
What Is Suspension PS Logging?
Suspension P-S logging is a borehole seismic method for estimating compressional-wave (Vp) and shear-wave (Vs) velocities over depth intervals using a source and receiver arrangement within a borehole.
A suspension probe generates elastic waves and records their arrival at downhole receivers. Travel-time differences between suitably located receivers are used to calculate local interval velocities. The resulting Vp and Vs profiles help describe the stiffness and seismic behaviour of the materials adjacent to the borehole.
The method is valuable where a vertical velocity profile is needed for dynamic site response, ground characterisation or comparison with laboratory, in-situ and surface-wave results. It does not directly measure strength, bearing capacity or liquefaction resistance.
Specify
Define target depths, needed Vp/Vs information and decision purpose.
Prepare
Confirm borehole geometry, probe compatibility, access and fluid conditions.
Acquire
Collect repeatable waveforms with controlled depth and traceability.
Interpret
Pick arrivals, review uncertainty and reconcile results with ground logs.
MEASUREMENT AND OUTPUTS
What Does the Method Measure?
The useful deliverable is a depth-referenced velocity profile with a defensible record of how each interval value was obtained.
| Output | Engineering use | Important qualification |
|---|---|---|
| Shear-wave velocity, Vs | Small-strain stiffness assessment and seismic site response inputs. | Wave velocity is not the same as shear strength. |
| P-wave velocity, Vp | Compressional behaviour, stratigraphic contrasts and supplementary stiffness interpretation. | P-wave response can be affected by saturation and fluid conditions. |
| Waveforms and depth tags | Traceability, arrival selection and quality review. | Depth control and repeat measurements are necessary. |
| Interpreted zones | Comparison with borehole geology and other geophysics. | Abrupt changes need corroboration, not automatic lithology labels. |
ENGINEERING APPLICATIONS
Where Suspension PS Logging Adds Value
Use borehole velocity information to answer defined geotechnical and seismic questions, not as a generic substitute for all site investigation.
Seismic ground response
Develop a velocity profile that can contribute to site-specific dynamic analysis when combined with other inputs.
Foundation and ground models
Compare elastic-wave velocity changes against borehole strata, ground improvement zones and other testing.
Quality verification
Investigate variations in the condition of an improved ground mass, subject to method resolution and site validation.
For infrastructure sites with limited surface access, a suitable borehole may offer a useful alternative to certain surface seismic layouts. Feasibility depends on the borehole and tool requirements.
SURVEY PLANNING
Field Conditions and Measurement Workflow
Well-conceived field preparation often matters more than collecting extra traces without a clear interpretation objective.
- Record borehole coordinates, casing, diameter, total depth, inclination and any changes in borehole construction.
- Confirm tool-specific borehole-fluid and casing requirements with the qualified logging provider; do not assume every cased or dry borehole is suitable.
- Choose a suitable logging interval, depth reference, tool centralisation procedure and repeatability checks.
- Retain raw and processed waveforms, picking basis, depth intervals and instrument metadata.
- Cross-check the velocity profile against stratigraphy, downhole/crosshole measurements, surface-wave results and relevant laboratory tests where available.
METHOD SELECTION
Suspension PS vs Downhole and Crosshole Testing
These are related seismic methods, but their source–receiver geometry, field access and resolution are not identical.
| Method | Typical geometry | Selection factor |
|---|---|---|
| Suspension PS | Source and receivers deployed inside one suitable borehole. | A single-borehole local interval velocity profile is needed. |
| Conventional downhole | Surface source with receiver(s) at successive borehole depths. | Surface access and ray-path interpretation are feasible. |
| Crosshole seismic | Separate source and receiver boreholes at comparable depths. | Lateral travel paths and multiple boreholes are available. |
The preferred technique should follow site geometry, required depth coverage, geological complexity and the uncertainty that matters to the design.
LIMITATIONS
What the Data Cannot Tell You on Their Own
P-S velocities provide a measurement of elastic-wave propagation, not a complete geotechnical ground model.
- Poor borehole conditions, signal-to-noise ratio and inconsistent depth referencing can distort picked arrivals.
- Strong heterogeneity, weak signal quality or mode conversions can make some intervals difficult to interpret.
- Dynamic small-strain stiffness inferred from velocity is not equivalent to large-strain design modulus without an appropriate model.
- Values depend on physical conditions and must not be translated into strength, density or lithology by a single universal correlation.
- The method is not a substitute for qualified geological logging, sampling and independent engineering interpretation.
DATA QUALITY
QA/QC Checks Before Engineering Use
Assess whether each velocity interval is supported by repeatable waveforms and a reliable borehole depth record.
- Review waveform clarity, polarity and P/S arrival separation.
- Check repeated readings and unusual jumps in interval velocity.
- Document assumptions about depth, tool spacing and borehole deviation.
- Flag invalid intervals rather than smoothing them into apparently precise values.
- Preserve original records, instrument settings and interpretation revision history.
PRACTICAL QUESTIONS
Suspension PS Logging FAQs
Answers to common selection and reporting questions.
Is a borehole always required?
Yes. Suspension P-S logging uses an appropriate borehole. The actual borehole construction and conditions must meet the tool and procedure requirements.
Does Vs automatically establish allowable bearing pressure?
No. Vs informs small-strain stiffness and seismic characteristics. Bearing resistance requires a separate geotechnical design assessment.
Can suspension P-S data be compared with MASW?
Yes, as complementary information. Differences in measurement volume, geometry, frequency content and inversion should be considered.
REFERENCES
Technical References and Related Methods
The external sources below explain related seismic-logging applications and the need to interpret the results in engineering context.
TECHNICAL ENQUIRY
Discuss a Borehole Velocity Logging Requirement
Share the borehole details and the engineering question before selecting the survey method.
GEOOE approaches this topic through engineering-led method selection, monitoring data quality and technology collaboration. For a project-specific discussion, share the asset or site type, the engineering question, available records and the expected deliverable.