MASW / VS30 Testing in North Bay Ontario

North Bay sits on the Canadian Shield’s edge, where Precambrian bedrock can lie just a few metres under glacial till and glaciolacustrine clays from Lake Nipissing’s old shoreline. A site’s shear wave velocity profile changes fast here—bedrock highs and soft sediment pockets sit side by side. NBCC 2020 classifies most of the city as Site Class C or D, but we regularly find local spots that push into Class E when the clay is thicker than expected. We run the MASW survey with a 24-channel seismograph and active-source sledgehammer, then invert the dispersion curve to get VS30 and a layered velocity model. Before finalizing your foundation design, pairing this data with an SPT drilling program gives you direct soil recovery and N-values that ground-truth the geophysical profile.

VS30 in North Bay can shift from 360 m/s to 210 m/s within the same property—relying on a regional map instead of a site-specific MASW profile is a gamble the code doesn’t support.

Our service areas

Process and scope

The freeze-thaw cycle in northern Ontario is relentless. Ground that reads as competent in August can lose stiffness during April thaw when the upper metre turns to soup. MASW gives you the small-strain stiffness of the soil skeleton—exactly what seismic codes need—without the disturbance that boreholes introduce. We lay out a linear array of 4.5 Hz geophones, typically 48 to 69 metres long depending on target depth, and record Rayleigh wave propagation. The fundamental-mode dispersion curve gets picked manually; no auto-picking algorithm replaces an experienced eye when multiple modes stack up. Processing follows ASTM D7400 guidelines and yields VS30 plus interval velocities that feed into Site Class determination under NBCC 2020 Table 4.1.8.4.A. In downtown North Bay near the escarpment, we often run a shorter array along sidewalks and parking lots to avoid traffic interference. The survey is non-invasive, quiet, and wraps up in a few hours.

MASW / VS30 Testing in North Bay Ontario — Technical reference — North Bay Ontario

Site-specific factors

North Bay’s population passed 52,000 in the last census, and the city keeps pushing development onto the escarpment slopes and former rail yards near the waterfront. Those areas overlay thick deposits of glaciolacustrine silt and clay that amplify ground motion during a seismic event. The Western Quebec Seismic Zone, which produced the 1935 Temiskaming magnitude 6.2 earthquake, sits close enough that NBCC assigns North Bay a non-trivial seismic hazard. Assigning Site Class C by default—the common shortcut when no VS30 data exists—can underestimate spectral acceleration by 30% or more if the actual conditions match Site Class E. That gap translates directly into under-designed lateral systems and foundations. A single MASW line on your parcel replaces the assumption with a measured value and keeps your structural engineer working with real numbers.

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Applicable standards

NBCC 2020 (National Building Code of Canada, seismic provisions), ASTM D7400-19 (Standard Test Methods for Downhole Seismic Testing, adapted for surface MASW), CSA A23.3-19 (Design of Concrete Structures, seismic design references)

Reference parameters

Parameter	Typical value
Method	Active-source MASW (Rayleigh wave, sledgehammer)
Seismograph	24-channel, 24-bit, GPS-synchronized
Geophone frequency	4.5 Hz vertical-component
Array length	48–69 m (adjusted for target depth)
Target depth	Typically 30 m for VS30; deeper profiles on request
VS30 output	Mean shear wave velocity, top 30 m (m/s)
Site Class reference	NBCC 2020, Table 4.1.8.4.A
Processing standard	ASTM D7400-19

Quick answers

What does a MASW survey cost on a typical North Bay lot?

For a single-family residential lot or small commercial parcel, budget between CA$2,570 and CA$4,650 depending on array length, number of lines, and access constraints. We provide a fixed-price proposal after reviewing your site plan.

How long does the field work take and will it damage the property?

One MASW line typically takes 90 minutes to set up, shoot, and pack up. The survey is entirely non-invasive—geophones are planted on spikes that leave no trace, and the energy source is a 10 kg sledgehammer on an aluminum plate. No drilling, no excavation, no cleanup.

Can you run MASW in winter when the ground is frozen?

Yes, with caveats. Frozen ground increases near-surface velocity, which can bias VS30 slightly high. For NBCC Site Class determination, we prefer frost-free months, but winter surveys are feasible if the client accepts the seasonal adjustment we apply during processing.

How many MASW lines does NBCC require for a commercial building?

The code does not prescribe a minimum number of lines—it requires that the Site Class be representative of the building footprint. For a typical commercial box store, we recommend two perpendicular lines crossing at the centre. For irregular footprints or sloping sites, we add a third line to capture lateral variability.

Location and service area

We serve projects in North Bay Ontario and surrounding areas.

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