With a population approaching 145,000, Saguenay sits in one of Canada's most active seismic zones, making the 1988 magnitude 5.9 earthquake a permanent reference point for local construction. The city spans thick sequences of Laflamme Sea clays, glacial tills, and bedrock outcrops that vary sharply between Jonquière and Chicoutimi, so a uniform foundation assumption simply does not work here. We run active and passive MASW surveys to deliver VS30 profiles that anchor the NBCC seismic site classification—moving the conversation from generic code assumptions to measured ground response. Because the Saguenay graben imposes real amplification risks, the shear wave velocity data feeds directly into the structural engineer's dynamic analysis and often reduces the seismic design category when stiff soils are proven at depth. For deeper verification in variable overburden, the S-wave refraction survey provides a complementary tomographic image that helps map the bedrock interface across the site.
A measured VS30 profile in Saguenay can shift a site from Site Class D to Site Class C, reducing the design spectral acceleration by 20 to 30 percent and unlocking substantial savings in the structural frame.
Quick answers
What does a MASW / VS30 survey cost for a typical Saguenay building site?
For a standard VS30 determination on a single-family or small commercial lot in the Saguenay region, the fee typically ranges from CA$2.440 to CA$3.740 depending on array length, site access, and whether passive-source recording is needed to reach the full 30-metre depth. We provide a fixed-price proposal after reviewing the site location and any existing borehole data.
How does the Saguenay soil affect the seismic site class?
The Laflamme Sea clays and interbedded silts that dominate the low-lying areas of Chicoutimi and Jonquière often produce VS30 values in the 180 to 300 m/s range, placing them in Site Class D or E. However, where glacial till or bedrock lies within a few metres of the surface—common on the terraces and toward Laterrière—the measured VS30 can exceed 360 m/s and qualify for Site Class C, which significantly reduces the design base shear.
Can you perform the survey on a site with existing structures or limited space?
Yes. While the ideal setup uses a straight 46-metre or 92-metre line, we adapt the array geometry for constrained urban lots in Saguenay by using shorter spreads combined with passive microtremor recording and the SPAC method. This hybrid approach lets us extract a reliable dispersion curve even when the available clearance is under 20 metres, provided we have enough ambient noise to process the low-frequency band passively.
