Seismic Tomography (Refraction/Reflection) for Site...

Q: How much does a seismic tomography survey cost in Coquitlam?

The final number depends on line length, number of spreads, and whether we are running P-wave only or combined P- and S-wave acquisition.

The glacial geology beneath Austin Heights tells a very different story than the Fraser River floodplain near Maillardville. One sits on compact till and bedrock highs. The other overlies deep, compressible sediments. A single borehole can miss the transition zone entirely. Seismic tomography captures these lateral changes across the entire site. P-wave refraction maps bedrock depth. S-wave reflection resolves stiffness contrasts. In Coquitlam, where the Pleistocene stratigraphy shifts abruptly across short distances, this method delivers a continuous profile instead of isolated point data. It is the fastest way to answer the question every geotechnical engineer needs answered: where does competent rock actually begin. We routinely pair the tomographic survey with downhole SPT drilling to ground-truth velocity boundaries with physical samples.

A single refraction line can replace three or four exploratory boreholes when the question is bedrock depth.

Methodology and scope

The 2020 National Building Code of Canada assigns a Site Class based on Vs30, and in Coquitlam that classification can change within a single city block. Hillside lots on Burke Mountain often register Site Class C. Properties closer to the Coquitlam River may drop to Site Class D or E due to loose alluvial deposits. Seismic tomography gives you the spatial resolution to map that boundary. Refraction surveys image compressional wave velocities to depths of 30 meters or more. Reflection surveys, processed with common-midpoint stacking, highlight impedance contrasts at formation interfaces. The ASTM D5777 standard governs field procedures. We use 24-channel or 48-channel seismographs with geophone spacings from 1 to 5 meters depending on target depth. The resulting velocity tomograms show stiff zones, weathered layers, and buried channels that a conventional grid of test pits would likely miss.

Local considerations

Coquitlam’s west side sits on a deep glacial trough. The northeast corner rises into the Coast Mountains in less than four kilometers. That gradient creates two distinct risk profiles. In the lowlands, soft clays and silts amplify ground motion during an earthquake. A Vs30 map derived from seismic tomography identifies zones where the NBCC site factor will drive up structural design loads. On the hillsides, the risk is different. Glacial till can mask a sloping bedrock surface that concentrates groundwater and promotes translational sliding. Reflection tomography images that interface before excavation begins. Skipping the survey on a sloped lot means guessing whether the foundation will bear on till or slide on a clay seam. The cost of a tomographic grid is negligible compared to a retaining wall retrofit.

Technical data

Parameter	Typical value
Survey method	P-wave refraction, S-wave reflection, or hybrid MASW/refraction
Depth of investigation	10 to 60 m (refraction); 15 to 100+ m (reflection)
Geophone array	24- or 48-channel, 1–5 m spacing per ASTM D5777
Seismic source	Sledgehammer, accelerated weight drop, or downhole sparker
Tomographic inversion	Ray-trace or full-waveform inversion (FWI)
Deliverables	P-wave velocity tomogram, Vs30 profile, NBCC Site Class map, bedrock contour
Typical survey duration	1–2 field days for a 5-line grid on a 1-acre lot

Associated technical services

P-Wave Refraction Tomography

Ideal for mapping bedrock depth, rippability, and the thickness of overburden. We deploy 24- or 48-channel spreads with a sledgehammer or weight-drop source. First-arrival picking feeds a ray-trace inversion that produces a continuous 2D P-wave velocity cross-section.

S-Wave Reflection & Vs30 Profiling

Targets shear-wave velocity for NBCC Site Class determination. We use horizontal geophones and a polarized shear source. The processed reflection section reveals stratigraphic boundaries and buried channels, while the interval velocity profile provides the Vs30 value required for structural design.

Quick answers

How much does a seismic tomography survey cost in Coquitlam?

Can seismic tomography replace boreholes on my Coquitlam project?

It reduces the number of boreholes but does not eliminate them entirely. Tomography gives you a continuous velocity profile across the site. A strategically placed SPT borehole then calibrates the velocity-to-strength relationship. Together they provide more complete information than either method alone.

How deep can you see with refraction versus reflection in Coquitlam soils?

Refraction typically reaches 15 to 30 meters with a sledgehammer source, and up to 60 meters with a weight drop. Reflection can image beyond 100 meters because it does not require a velocity increase with depth. In Coquitlam’s glacial sediments, reflection often performs better below 40 meters where refraction signal fades.

What does the final deliverable look like?

You receive a signed engineering report containing 2D P-wave or S-wave velocity tomograms, an interpreted bedrock profile, NBCC Site Class map, and a Vs30 contour plan. All data is delivered in PDF and digital formats compatible with CAD and GIS platforms.

Seismic Tomography (Refraction/Reflection) for Site Characterization in Coquitlam