The contrast between a downtown Kingston infill project and a new subdivision out by Collins Bay isn't just about lot size. Downtown, you're often sitting on the limestone of the Gull River Formation, barely a meter below the surface, while out west the overburden thickens into dense glacial till with pockets of softer Leda clay. This matters because the way seismic waves travel through these two profiles is completely different. A standard site class assumption can be off by one or even two letters, and that error flows straight into the structural design loads. We run active and passive surface wave surveys to measure the shear wave velocity profile directly, giving the structural engineer the real VS30 value they need for the NBCC 2020 seismic provisions, not just a conservative guess. For projects in Kingston's nuanced soil landscape, we often pair the MASW data with a targeted seismic refraction line to resolve the top of bedrock when the interface gets complicated near the Frontenac Axis.
A measured VS30 that moves your Kingston project from a default Site Class E to a Class C can reduce seismic base shear by over 30 percent — the MASW survey pays for itself in the foundation alone.
Our approach and scope
Site-specific factors
Kingston's growth spurts, from the limestone boom of the 1840s to the modern expansion north of the 401, have left a patchwork of fill, natural till, and sensitive marine clays across the city. The biggest geotechnical headache we see is a developer who assumes that because the building next door had a Site Class C, theirs will too. That assumption crumbles fast when you hit a buried ravine filled with loose material or a lens of Leda clay that amplifies ground motion like a drum skin. The NBCC and CSA A23.3 are clear: if you don't have measured VS30 data, you default to Site Class E in many cases, which can inflate your seismic design forces by 30 to 50 percent. That's not a code technicality; it's real money in the foundation and lateral system. A single MASW line, calibrated to the local geology and processed with both fundamental and higher-mode Rayleigh wave analysis, turns that expensive assumption into a defensible number.
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Regulatory framework
NBCC 2020 (National Building Code of Canada, seismic provisions Part 4), CSA A23.3-19 (Design of concrete structures, seismic requirements), ASTM D7400-19 (Standard Test Methods for Downhole Seismic Testing, adapted for surface wave)
Related services
MASW for NBCC Site Classification
Complete active and passive surface wave survey with 1D VS profile, VS30 calculation, and formal NBCC 2020 site class letter signed by a professional geoscientist.
Combined MASW and Seismic Refraction
When bedrock depth is uncertain, we run a refraction line alongside the MASW array to independently map the top of rock and constrain the velocity model, critical in the limestone-dominated north end.
2D Shear Wave Velocity Cross-Sections
For larger structures or variable ground, multiple MASW arrays stitched into a 2D VS section showing lateral changes in stiffness, useful for differential settlement and seismic response analysis.
Typical parameters
Common questions
What does a MASW survey actually measure, and how is VS30 calculated?
It measures the speed at which Rayleigh waves travel through the ground at different frequencies. Shorter wavelengths sample shallow material, longer ones go deeper. We record the wavefield with an array of geophones, then transform the data into a dispersion curve — velocity versus wavelength. That curve is inverted into a 1D shear wave velocity profile. VS30 is the time-averaged shear wave velocity for the top 30 meters: we sum the travel time through each layer and divide 30 by that total time. The number drops straight into the NBCC site class table.
How much does MASW testing cost for a typical Kingston building lot?
For a standard single-family or small commercial lot in the Kingston area, a complete MASW survey with NBCC site class letter typically runs between CA$2,310 and CA$3,680, depending on the array length needed to reach the 30-meter depth and whether passive methods are required to constrain deeper layers.
Can you do MASW testing in winter when the ground is frozen?
We can, but the results need careful interpretation. Frozen ground has artificially high shear wave velocity in the top meter or so, and that can bias the VS30 if not corrected. We prefer to work when the frost is out, but for winter construction schedules we apply a frost correction based on local Kingston freeze-depth data and, where possible, use longer passive arrays that are less sensitive to the shallow frozen crust.
What's the difference between MASW and a seismic refraction survey for site class?
Seismic refraction measures P-wave velocity, which in saturated soils is controlled almost entirely by the pore water — you get a number around 1,500 m/s regardless of soil stiffness. Shear wave velocity from MASW is what actually correlates with soil stiffness and what the NBCC requires for site classification. Refraction is excellent for mapping bedrock depth and rippability, but it cannot give you a reliable VS30 or site class on its own.