The Sudbury Basin’s unique geology—a 1.85-billion-year-old meteorite impact structure rimmed by fractured norite and gabbro—creates sharp lateral contrasts in shear-wave velocity that generic hazard maps simply do not capture. With the city straddling both exposed Archean basement and deep pockets of glaciolacustrine clay along the Ramsey Lake corridor, the amplification potential can vary by a factor of three across a single building lot. Our seismic microzonation work maps these transitions through dense arrays of MASW and downhole measurements, delivering site-specific PGA and response spectra that replace the default NBCC site class with measured Vs30 profiles, an approach that has reduced foundation costs on several Sudbury projects by eliminating over-conservative Class D or E assumptions where competent rock lies within a few meters of grade.
In Sudbury’s impact-altered bedrock, two boreholes 50 meters apart can sit on different site classes—microzonation is the only way to resolve the boundary.
Our approach and scope
Site-specific factors
A common and costly mistake we see in Sudbury is applying a uniform Site Class C across an entire parcel based on a single borehole near the access road, only to discover during excavation that the southern half of the footprint sits on 8 meters of soft varved clay—a Class E profile that was never captured. The consequence is a structural design that underestimates the spectral acceleration at the fundamental period of the building by as much as 40 percent, a discrepancy that can trigger a stop-work order from the city’s building department once the geotechnical report is reviewed against the site plan. We have also encountered cases where the presence of a shallow, weathered norite horizon was mistaken for competent rock at refusal, when in fact the underlying fracture zone—common in the Sudbury Igneous Complex—would amplify short-period motion in a way that only a full Vs profile can quantify. Catching these conditions during the microzonation phase is far less disruptive than revising the lateral system after the permit set has been approved.
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Reference standards
NBCC 2020 (National Building Code of Canada, Part 4, Division B), CSA A23.3-19 (Design of Concrete Structures, seismic provisions), ASTM D7400 / D5777 (downhole and refraction seismic methods), NRC 2015 GMM selection framework for eastern Canada stable continental region
Complementary services
Site-Specific Seismic Hazard Assessment
We combine deterministic and probabilistic seismic hazard analysis with measured Vs profiles to produce uniform hazard spectra (UHS) and design response spectra tailored to the Sudbury site coordinates, accounting for the moderate seismicity of the Western Quebec Seismic Zone and the attenuation characteristics of the Canadian Shield crust.
Vs30 Mapping and Site Classification Grid
For larger parcels and linear infrastructure corridors, we execute multi-line MASW and seismic refraction surveys on a grid geometry that captures the lateral variability of the overburden-bedrock interface, delivering a contoured site class map that the design team can overlay directly with the structural grid to assign foundation-specific ground motion inputs.
Typical parameters
Frequently asked questions
What is the typical budget range for a seismic microzonation study in the Sudbury area?
Based on recent projects in Greater Sudbury, a microzonation study typically falls between CA$5,450 and CA$25,560. A smaller commercial lot with straightforward access and two to three MASW lines sits near the lower end, while a multi-hectare industrial site requiring a dense grid of profiles, downhole verification in boreholes, and full site-response modeling in DEEPSOIL or equivalent software will move toward the upper end. We provide a fixed-scope proposal after reviewing the site plan and any existing geotechnical data.
How does microzonation differ from the site classification in a standard geotechnical report?
A standard report often assigns a single site class based on one or two boreholes and an assumed Vs30 from SPT N-value correlations, which works for simple NBCC compliance on small structures. Microzonation measures Vs directly through surface-wave or borehole methods at multiple locations, creating a spatially resolved model of the subsurface stiffness that captures lateral changes in amplification. For Sudbury sites where rock depth and overburden stiffness can change abruptly—especially near the contact between the norite footwall and the basin fill—the difference in design spectral acceleration between a Class C and a Class E classification can exceed 50 percent at short periods.
What deliverables do we receive at the end of the study?
You receive a stamped geotechnical report containing the measured Vs30 contour map, site-specific response spectra (UHS and design spectra), representative acceleration time histories if required for nonlinear time-history analysis, and a clear tabular summary of the governing site class for each structural zone on the site. The report is prepared in conformance with NBCC 2020 and CSA A23.3 and is ready for direct submission to the City of Greater Sudbury Building Services division as part of the permit application package. More info.