NBCC 2020 assigns seismic hazard values based on site class, and Burlington's soil profile across the Halton Region makes that classification far from uniform. The city sits on a mix of glaciolacustrine silty clays overlying Ordovician shale, with the Niagara Escarpment cutting through the northern edge. Site class can shift from C to E within a single city block depending on depth to bedrock and shear wave velocity. Our seismic microzonation work targets exactly that variability. We run MASW lines and SPT-based Vs correlations to develop continuous velocity profiles, then produce amplification maps tied to NBCC spectral acceleration values. For sites near the escarpment, we often combine seismic refraction with surface wave methods to confirm bedrock depth where topography complicates the survey.
Two sites 500 metres apart in Burlington can differ by two NBCC site classes, doubling the design spectral acceleration.
