MASW / VS30 Testing in Mississauga — Shear Wave Velocity Profiles

The Halton Till sits right under Mississauga. That dense clay-silt mix, with pockets of sand and gravel, means your site class can shift from C to D within a few hundred metres. If you're designing according to NBCC 2020, you cannot guess the Vs30 value. The 2020 code update tightened the rules for site-specific shear wave velocity measurements, especially on deep soil sites. We run the MASW survey with a 24-channel seismograph and 4.5 Hz geophones. The array picks up Rayleigh wave dispersion down to 30 metres, sometimes deeper if the background noise is low. This gives you the Vs30 number that your structural engineer needs for the seismic load calculation. For a tight soil profile like the one at Square One or along the 403 corridor, we often combine the surface wave data with a CPT test to anchor the velocity model to a measured tip resistance log.

A MASW line costs less than a single borehole and gives you the Vs30 number that directly feeds the seismic base shear calculation.

How we work

Mississauga has two very different soil stories. North of the 401, near Meadowvale, the till is shallow and the shale bedrock is close to the surface. A Vs30 of 400-600 m/s is common there. South of the QEW, in Port Credit or Clarkson, the overburden deepens and the shear wave velocity drops below 300 m/s. That's the difference between Site Class C and D. Our field crew lays out the geophone spread, hits the sledgehammer plate, and records the surface waves. The dispersion curve is inverted to get the 1D Vs profile. You get the results in a format ready for the structural model. Before you start the foundation design, talk to your geotechnical consultant about running a seismic refraction line too—it helps map the top of rock when the till cover is variable.

Site-specific factors

A six-storey condo project in Streetsville hit a problem in 2022. The geotechnical report assumed Site Class C based on one deep borehole. The city reviewer flagged it and asked for a measured Vs30. We ran the MASW line across the footprint. The real Vs30 came back at 260 m/s—Site Class D. The structural design had to be revised. The base shear increased by roughly 15%. That meant larger footings and more rebar in the shear walls. The developer lost four weeks redoing the permit drawings. The cost of the MASW survey was a fraction of the redesign fee. If the shear wave velocity had been measured from day one, the project would have stayed on schedule.

Technical data

Parameter	Typical value
Measurement depth	30 m below ground surface
Array length	46 to 92 m (24-channel spread)
Geophone frequency	4.5 Hz vertical component
Source type	Sledgehammer on aluminum plate
Sampling rate	0.5 ms to 1.0 ms
Reported parameter	Vs30 in m/s per NBCC 2020
Data format	SEG-2, CSV, and graphical profile
Typical survey time on site	2 to 4 hours

Associated technical services

Standard Vs30 Survey

One MASW line across the building footprint. You get the Vs30 value, the 1D shear wave velocity profile, and the NBCC Site Class determination. Suitable for low-rise and mid-rise buildings.

2D MASW Cross-Section

Multiple parallel lines or a rolling spread to map lateral variation in Vs. Used for larger footprints, irregular foundations, or when the till thickness changes across the site.

Combined MASW + Downhole Seismic

We run the surface MASW line and pair it with a downhole seismic test in the same borehole. The downhole data calibrates the Vs profile at one point, and the MASW extends it across the entire site.

Regulatory framework

NBCC 2020 (National Building Code of Canada), CSA A23.3-19 (Design of Concrete Structures), ASTM D5777-18 (Standard Guide for Using the Seismic Refraction Method), ASTM D7400-19 (Standard Test Methods for Downhole Seismic Testing), MTO LS-700 (Ontario Ministry of Transportation — Geophysical Methods)

Frequently asked questions

How much does a MASW survey cost in Mississauga?

For a standard single-line Vs30 survey on a typical residential or small commercial lot in Mississauga, the cost ranges from CA$2,180 to CA$3,910. The final price depends on the line length, site access, and whether we need traffic control on a public road. We provide a fixed-price quote after a site visit.

How do you get the Vs30 from the surface wave data?

We record Rayleigh waves with a 24-channel linear array. The dispersion curve—phase velocity versus frequency—is extracted from the shot gather. Then we run an inversion algorithm to find the 1D shear wave velocity profile that matches the measured dispersion. Vs30 is the time-averaged Vs over the top 30 metres, calculated directly from that profile.

Is MASW accepted by the City of Mississauga for building permits?

Yes. The City of Mississauga building division accepts MASW-derived Vs30 values when the survey is conducted and reported by a qualified geotechnical engineer. The report must reference the NBCC 2020 site classification procedure and include the raw dispersion data and the inversion model. We stamp every report with a licensed professional engineer in Ontario.

How long does a MASW test take on site?

The field work for one MASW line takes between two and four hours. That includes laying out the geophone cable, recording multiple shot points, and packing up. You get the preliminary Vs30 number within 24 hours. The full stamped report with the dispersion curves and the Vs profile is delivered in three to five business days.