SHEAR-WAVE VELOCITY INVESTIGATION
Surface-Wave Seismic Survey Methods
Choose between active and passive surface-wave methods to estimate ground shear-wave velocity, understand uncertainty and complement site investigation.
ENGINEERING OVERVIEW
Choosing a surface-wave approach
Surface-wave seismic surveys investigate how seismic surface waves travel and disperse through the ground. Their frequency-dependent behaviour can be used to infer a shear-wave velocity (Vs) structure. The method family includes active multichannel analysis of surface waves (MASW), passive microtremor array measurements (MAM) and other approaches. This page explains how to select among them rather than duplicating the detailed instructions for any single method.
A design team often asks simply for a “seismic velocity survey”, but the right method depends on whether the needed quantity is P-wave velocity, S-wave velocity, resonance frequency, shallow stiffness or deeper ground structure. Surface-wave methods can help characterise Vs while reducing intrusive work, provided the target, acquisition conditions and interpretation uncertainty are defined.
MEASUREMENT & INTERPRETATION
What the method actually tells you
Surface-wave dispersion
Different wavelengths sample the ground differently; changing phase velocity with frequency creates information for a Vs model.
Active sources
Controlled impacts or vibrators can improve repeatability and acquisition control for selected frequency ranges.
Passive sources
Ambient ground vibration can contribute useful long-wavelength information where a suitable wavefield and array geometry are available.
Interpretation not identity
A Vs section constrains elastic-wave behaviour; it does not uniquely determine geology, strength or all dynamic design parameters.
PRACTICAL SURVEY FLOW
From site question to defensible interpretation
Define engineering question
Identify the required depth interval, design context and evidence needed to support a decision.
Choose active/passive mix
Evaluate access, noise, frequency targets, array aperture and how the data will complement boreholes.
Collect and quality-check
Record geophone geometry, source or ambient-wavefield characteristics and trace repeatability.
Invert with constraints
Interpret dispersion, test alternate Vs models and communicate which depth ranges have reliable support.
WHERE IT ADDS VALUE
Engineering applications and use cases
Seismic site response
Provide Vs evidence for a project-specific understanding of ground response and soil layering.
Foundation and infrastructure corridors
Screen lateral variation in stiffness-related wave velocity and guide selective follow-up investigation.
Ground model integration
Support interpretation alongside boreholes, seismic refraction and electrical/geological evidence.
MEASUREMENT BOUNDARIES
Limitations and conditions of use
Interpretation quality depends as much on survey suitability and independent evidence as on processing software.
- The usable depth interval is not fixed by the method name; it depends on measurable wavelengths, array geometry and ground conditions.
- Surface-wave mode selection and inversion regularisation can produce nonunique profiles.
- Strong lateral variability and three-dimensional features challenge local 1D assumptions.
- Data quality can be reduced by sensor coupling, site noise, limited accessible ground and poor spatial geometry.
METHOD SELECTION
How to choose the right approach
Active MASW
Useful when a controlled source and linear array can be deployed and an interpretable dispersion image obtained.
Passive MAM
Useful when ambient vibration and receiver array geometry support analysis, including potentially complementary lower frequencies.
Seismic refraction
A different method family based on body-wave first arrivals and refracting velocity contrasts, often complementary to Vs surveying.
Choose the surface-wave approach by the engineering quantity sought and the conditions available on site. For robust Vs characterisation, a combined active and passive programme may be more defensible than selecting either method by habit.
ENGINEERING ASSURANCE
Field quality, interpretation and review
A traceable project record should retain the following information where applicable:
- Survey target, frequency/wavelength coverage and expected resolution
- Array layout, instrument coupling, timing and acquisition logs
- Dispersion selections, mode uncertainty and inversion-fit checks
- Independent constraints from boreholes or additional geophysical techniques
PROJECT DELIVERABLES
What a useful technical report should contain
01 · Project output
Method selection and acquisition design rationale
02 · Project output
Field records and dispersion interpretation
03 · Project output
Vs model or site section with constraints and limitations
04 · Project output
Integrated geological interpretation and recommendations for verification
COMMON QUESTIONS
Frequently asked questions
Are surface-wave surveys the same as MASW?
Do passive and active surveys always give the same answer?
Can a surface-wave survey replace drilling?
TECHNICAL REFERENCES
Further technical reading
- USGS — Flexible multimethod seismic site characterisation
- USGS — Multichannel analysis of surface waves
- USGS — MAM/SPAC review
References describe the underlying methods and recommended data-quality principles; interpretation for any particular site must address its own evidence and constraints.
PROJECT ENQUIRIES
Discuss your ground investigation challenge.
GEOOE · GEOORIGIN ENGINEERING LIMITED
Share the site location, investigation objective, expected depth range, available boreholes and decisions the results need to support. We can discuss appropriate technical methods, limitations and project-specific collaboration.