Seismic Tomography (Refraction/Reflection) in Regina, SK

Compliance with the National Building Code of Canada (NBCC 2020) in Regina requires more than a standard borehole when deep glacial till and compressible lacustrine clays govern site response. The seismic tomography survey, combining refraction and reflection methodologies, maps shear-wave velocity profiles across the Wascana Plain, where post-glacial Lake Regina sediments reach over 15 meters in thickness. Our team executes high-resolution P-wave and S-wave tomography lines to image bedrock topography, detect buried channels, and delineate the stiff till surface that controls bearing capacity and seismic site class. For complex stratigraphy near Wascana Creek or the Trans-Canada Highway corridor, this dataset feeds directly into the geotechnical model, reducing uncertainty in footings design and deep excavations where water-bearing sands interbed with clay.

A seismic tomography line images what a drill rig misses—buried valleys and abrupt till surface drops that change the foundation strategy across a single building footprint.

Methodology and scope

A recent warehouse expansion north of Victoria Avenue encountered a 9-meter drop in bedrock elevation over a 60-meter transect—a buried preglacial valley invisible to conventional drilling alone. We deployed a 48-channel seismic refraction spread with a 5-meter geophone spacing, stacked with a weight-drop source to penetrate ambient noise from nearby rail traffic. The resulting tomogram resolved the paleovalley geometry, pinpointing where the stiff glacial till pinches out and the overlying silty clay thickens. Integrating this model with CPT test data allowed the structural engineer to adjust pile lengths by segment, eliminating the risk of differential settlement across the building footprint. For reflection surveys, we utilize high-frequency geophones and a land streamer system that accelerates data acquisition across paved or gravel surfaces, capturing stratigraphic detail down to 60 meters—sufficient for most Regina mid-rise developments. The velocity model also supports MASW cross-calibration, improving Vs30 estimates for seismic site classification under NBCC 2020.

Local geotechnical context

The costliest mistake we see in Regina is relying on sparse borehole logs to infer bedrock continuity across a site—then hitting a soft-filled buried channel during excavation that triggers a slope failure or foundation redesign. The seismic tomography survey eliminates that blind spot. Without it, a contractor working in the Ross Industrial Area might assume uniform till at grade only to discover a 6-meter pocket of saturated, unconsolidated sediment that destabilizes a retaining wall or delays a mat foundation pour by weeks. Another common error is misclassifying the seismic site class because Vs30 was estimated from blow counts rather than measured with a refraction survey—leading to overly conservative or dangerously unconservative seismic load assumptions per NBCC 2020. On sites with high groundwater, the tomographic velocity model also reveals low-velocity zones that correlate with liquefaction susceptibility in water-bearing sands, a concern in parts of the Regina region underlain by the Empress Group.

Typical values

Parameter	Typical value
Survey depth range (refraction)	5 to 40 m (weight drop / accelerated hammer)
Survey depth range (reflection)	10 to 80 m (land streamer + high-frequency source)
Geophone spread	24 to 72 channels, 2–10 m spacing
Seismic source	Accelerated weight drop, sledgehammer, or Betsy gun
Primary deliverables	P-wave and S-wave velocity tomograms, bedrock contour map, Vs30 profile
Site class determination	NBCC 2020 Table 4.1.8.4.A (Vs30-based)
Typical line length	115 to 345 m (varies by target depth)

Related services

P-Wave Refraction Tomography

Generates a continuous compressional-wave velocity model of the subsurface, primarily used to map bedrock topography and the top of competent glacial till. Ideal for foundation feasibility studies and cut-fill analysis across large industrial lots in the Regina area.

S-Wave Refraction (MASW Cross-Calibration)

Delivers shear-wave velocity profiles and the Vs30 value required for NBCC 2020 site classification. We deploy low-frequency horizontal geophones to capture dispersion data that constrain the shallow velocity structure, critical for seismic design of schools, healthcare facilities, and mid-rise structures.

High-Resolution Seismic Reflection

Resolves stratigraphic layering at higher resolution than refraction, identifying thin sand seams, clay-silt transitions, and buried channel margins. Applied with a towed land streamer for rapid coverage on paved surfaces or compacted gravel, minimizing disruption to site operations.

Applicable standards

NBCC 2020 – Division B, Article 4.1.8.4 (Seismic Site Classification), CSA A23.3-19 – Design of Concrete Structures (seismic provisions), ASTM D5777-18 – Standard Guide for Using the Seismic Refraction Method, ASTM D7128-18 – Standard Guide for Using the Seismic Reflection Method, Canadian Geotechnical Society – Canadian Foundation Engineering Manual, 4th ed.

Common questions

What is the typical cost of a seismic tomography survey in Regina?

Budget between CA$3,360 and CA$6,620 for a standard refraction line with 48 geophone channels, including field acquisition, processing, and a signed engineering report. The final figure depends on survey length, source type (weight drop vs. explosive), and whether S-wave data is required for Vs30 determination.

How does seismic tomography help with NBCC 2020 site classification?

The NBCC classifies sites from A (hard rock) to E (soft soil) based on the average shear-wave velocity in the upper 30 meters (Vs30). Seismic tomography measures Vs directly rather than relying on correlations from blow counts. A refraction survey provides a velocity model that yields the Vs30 value and the velocity profile shape, both of which influence the site period and seismic design spectrum.

Can you perform surveys on paved industrial sites with heavy truck traffic?

Yes. We use a land streamer with built-in geophones that can be towed across asphalt or compacted gravel, and we schedule acquisition windows to avoid peak traffic hours. For high-ambient-noise environments near railways or the Ring Road, we stack multiple source impacts per shot point to improve signal-to-noise ratio without compromising data quality.

What depth of investigation should we expect in Regina's soil conditions?

Refraction tomography typically reaches 20 to 40 meters depth with a 115-meter spread and a weight-drop source, which covers the glacial till and the transition to bedrock in most Regina locations. Reflection surveys can image deeper—up to 80 meters—useful for mapping the Judith River Formation contact or deep paleochannel structures beneath the city.