MASW Test: Procedure, Shear Wave Velocity (Vs30) and Seismic Site Classification

The MASW test is a fast, non-invasive way to measure how stiff the ground is with depth. It has become a standard part of site investigation for buildings, bridges, industrial plants and any structure designed for earthquake loads.

MASW full form and what it measures

MASW stands for Multichannel Analysis of Surface Waves. When the ground is struck, part of the energy travels as surface (Rayleigh) waves. Low-frequency waves penetrate deeper than high-frequency waves, so they travel at different speeds depending on the stiffness of each layer. By analysing this dispersion, MASW produces a profile of shear wave velocity (Vs) against depth.

Shear wave velocity is directly related to the small-strain stiffness of soil and rock, which is why it is so valuable in seismic and dynamic design.

MASW test procedure

1. Geophone spread: typically 12 to 48 low-frequency geophones are laid out in a straight line at equal spacing.
2. Source: a sledgehammer striking a steel plate (active MASW) is the most common source. Several shots are stacked to improve signal quality.
3. Recording: a multichannel seismograph records the arrivals at all geophones at once.
4. Passive option: ambient noise from traffic and the environment can be recorded to extend the depth of investigation where needed.
5. Processing: the records are transformed into a dispersion image, the fundamental-mode curve is picked, and an inversion produces the 1D Vs profile. Multiple shot points along a line can be combined into a 2D Vs section.

The method works well in noisy urban environments where boreholes alone are slow, and it does not require drilling.

Vs30 and seismic site classification

Vs30 is the average shear wave velocity of the top 30 metres. It is the key parameter for site classification in international codes such as ASCE 7 and Eurocode 8, and it is widely used in site-specific seismic hazard and ground response studies in India.

In Indian practice, IS 1893 (Part 1) governs earthquake-resistant design and classifies sites by soil type. Shear wave velocity from MASW supports this classification, especially where SPT data are limited, and is essential for site-specific response spectrum studies on important structures.

Other uses of MASW

• Mapping depth to rock and the stiffness of fill.
• Locating soft zones and voids between boreholes.
• Machine foundation design (dynamic soil properties).
• Checking ground improvement before and after treatment.
• Assessing liquefaction susceptibility together with SPT and grain size data.

MASW vs seismic refraction survey

A seismic refraction survey uses the first arrivals of compression (P) waves to map layer boundaries, especially depth to rock. It needs velocity to increase with depth. MASW measures shear wave velocity and can handle stiff-over-soft layering better. The two are often recorded with the same equipment and combined in one survey for a fuller picture.

Limitations to know

MASW gives an averaged profile beneath the spread, so very thin layers may not be resolved, and results should be calibrated against boreholes where possible. Interpretation needs experience, particularly where higher modes dominate the dispersion image.

MASW is part of our geophysical survey service and is often paired with borehole soil testing and ERT.

Frequently asked questions

Talk to our team

Need shear wave velocity or Vs30 for seismic design? Call +91 98718 04288, email contact@geowingseng.com or send your site details and we will reply within one working day.