The geophone array is laid out north of the Speed River, near the historic Galt core. A 24-channel seismograph records surface waves while a sledgehammer source sends energy through glacial till and outwash. In Cambridge, seismic microzonation starts with understanding what lies beneath the drumlin fields and buried valleys. The city sits on complex Quaternary deposits — tills, glaciolacustrine silts, and sandy outwash — that amplify ground motion differently from block to block. A VS30 measurement on one lot can shift site class by two categories compared to a property three streets over. We run active MASW lines and passive microtremor arrays, then invert dispersion curves to shear-wave velocity profiles. The NBCC 2020 requires a site class for seismic design, and the default assumption of Site Class C can be dangerously unconservative where soft sediments exceed 30 metres. Our equipment is calibrated to ASTM D4428 and we log every shot with GPS-tagged metadata so the city’s building officials can trace the survey footprint. Before finalizing a site class, we often cross-check the velocity model with MASW data collected at multiple azimuths to rule out lateral variability beneath the proposed footprint.
A site class shift from C to E under NBCC 2020 can double the design spectral acceleration — and in Cambridge, that shift is more common than most engineers assume.
Scope of work in Cambridge Ontario
Critical ground factors in Cambridge Ontario
Cambridge lies within the Western Quebec Seismic Zone, with a 2% probability of exceedance in 50 years for ground motions that can damage unreinforced masonry. The 2010 Val-des-Bois earthquake — magnitude 5.0, centred near the Ottawa River — produced perceptible shaking here and reminded the region that moderate events at distance still carry low-frequency energy efficient at exciting soft soil basins. The buried bedrock valley trending northwest–southeast through the city acts as a two-dimensional basin, trapping body waves and converting them to surface waves that travel laterally and increase duration. This basin-edge effect is poorly captured by the NBCC’s one-dimensional site factors. A microzonation study that includes 2D modelling along critical transects — such as the corridor near the 401 interchange — can reveal amplification zones that a simple VS30 map would miss. Liquefaction susceptibility in the sandy outwash deposits along the Speed and Grand Rivers adds a second hazard layer during prolonged shaking, particularly where the groundwater table sits within three metres of grade.
Our services
The microzonation report is only part of the seismic picture. We pair it with complementary site characterization services that feed directly into foundation and structural design.
Site-Specific Response Spectrum
We generate a design spectrum from measured shear-wave velocities, applying NBCC site factors and, where warranted by basin geometry, one-dimensional equivalent-linear analysis to capture nonlinear soil behaviour at higher strain levels.
Liquefaction Triggering Analysis
Using SPT or CPT data calibrated to the microzonation VS profile, we run cyclic stress ratio evaluations per Youd & Idriss (2001) and compute post-liquefaction settlement and lateral spread displacement for the design earthquake scenario.
Frequently asked questions
What does a seismic microzonation study cost in Cambridge?
Costs range from CA$5,930 to CA$19,640 depending on the number of measurement points, array type, and whether passive HVSR or active MASW is required. A single-lot site class determination with one MASW line and HVSR runs toward the lower end. A multi-block microzonation with 2D basin modelling and a design response spectrum approaches the upper range.
How does microzonation differ from a standard site class determination?
A standard site class determination measures VS30 and assigns a letter category. Microzonation goes further: it maps spatial variations in ground response across a neighbourhood or corridor, identifies basin-edge effects, and produces site-specific spectra that the structural engineer can use directly in dynamic analysis rather than relying on generic NBCC amplification factors.
Can frozen ground affect the VS30 measurement in Cambridge?
Yes, frozen near-surface soils can increase VS30 by 10–15% because ice binds soil particles and stiffens the matrix. We schedule winter surveys around thaw cycles or apply a correction based on soil type and frost depth. The Grand River Conservation Authority’s groundwater monitoring data helps us confirm whether conditions are representative of the design case.