A common mistake in Medicine Hat is assuming stiff clay near the surface means a favorable site class without verifying shear wave velocity at depth. The city sits on a complex stack of glacial till, outwash sands, and Bearpaw Formation shale, and the South Saskatchewan River valley cuts through it all, creating abrupt contrasts in sediment thickness. We have seen projects where engineers relied on blow counts alone and missed a velocity inversion that pushed the site into Class D or E under NBCC 2020. Running a MASW survey early removes that uncertainty by delivering a measured VS30 profile, which is what the building official actually needs for the seismic design data report. Combining the surface wave data with a few CPT soundings can further refine the stratigraphy where the till transitions into dense gravel or soft bedrock.
A measured VS30 from an MASW survey in Medicine Hat often yields a more favorable site class than the default assumed Class D, directly reducing seismic design loads.
Our approach and scope
Local considerations
NBCC 2020 assigns default Site Class D to any site lacking a measured VS30, which can impose seismic design forces 20–40% higher than what the actual ground conditions warrant. In Medicine Hat, where much of the residential and commercial development sits on stiff glacial till with VS30 values in the 350–700 m/s range, defaulting to Class D represents an unnecessary structural penalty. The bigger hazard lies in the river valley and tributary coulees, where soft alluvium and a shallow water table can produce VS30 below 180 m/s, triggering Site Class E. This classification increases spectral accelerations and drift limits that affect lateral force-resisting system selection. A single MASW line provides the measured velocity to replace the default assumption, supporting a rational seismic design per CSA A23.3.
Reference standards
NBCC 2020 (National Building Code of Canada, Part 4), CSA A23.3-19 (Design of Concrete Structures – Seismic Provisions), ASTM D5777-18 (Standard Guide for Using the Seismic Refraction Method, for complementary P-wave control), ASTM D7400-19 (Standard Test Methods for Downhole Seismic Testing, for cross-reference)
Complementary services
Single-Location VS30 for Building Permit
One 24-channel MASW spread positioned at the building footprint, processed to a 1D shear wave velocity profile and NBCC site class. Suitable for single-family residential and small commercial projects where the subsurface is laterally uniform.
Multi-Line Grid for Subdivision Classification
Two to four intersecting MASW lines across the development area to map lateral variation in VS30 and identify zones of lower velocity that may require separate foundation design. Delivered as a contoured site class map.
Combined MASW + Downhole Seismic Calibration
Active MASW survey calibrated with a downhole seismic test in a nearby borehole, providing a site-specific transfer function between shear wave velocity and SPT N-value. Ideal for projects where future phases will rely on SPT data alone.
Typical parameters
Common questions
How long does a standard MASW survey take in Medicine Hat?
A single 24-channel line takes about 45 minutes on site once the array is laid out, plus 15 minutes for setup and takedown. Processing the dispersion curve and running the inversion adds two to three hours in the office. We can usually email the VS30 result and site class within one business day of the field work, provided the dispersion data quality is good and no re-shooting is needed.
What does an MASW survey cost for a typical residential lot?
For a standard single-family lot in Medicine Hat, the MASW survey ranges from CA$2,330 to CA$4,280 depending on access conditions, number of shot points required, and whether we need to clear vegetation or work around buried utilities. Multi-line surveys for larger parcels are quoted on a per-line basis after reviewing the site plan.
Does the NBCC accept MASW for site classification?
Yes. NBCC 2020 Table 4.1.8.4.A accepts measured in-situ shear wave velocity as the primary parameter for assigning Site Class A through E. MASW is a standard non-invasive method for obtaining that velocity profile. Our reports include the dispersion curve, the inverted VS profile, the calculated VS30, and the corresponding site class per Table 4.1.8.4.A, which building officials in Alberta recognize for permit submission.