The contrast between the stiff glacial till underlying Point Grey and the deep soft sediments of the Fraser River delta in Richmond is a stark reminder that Vancouver cannot be treated as a single seismic zone. A site on the UBC campus can experience half the spectral acceleration of a site near Marine Drive station during a crustal event, simply because of the impedance contrast at the till-bedrock interface. Our seismic microzonation work quantifies these differences block by block, integrating shear-wave velocity profiles from MASW and downhole surveys with the NBCC 2020 hazard model to produce site-specific ground motion parameters that go well beyond the default Site Class C assumption still used in too many preliminary designs across the Lower Mainland.
Two sites 800 metres apart in Vancouver can differ by two NBCC site classes, and ignoring that gradient puts long-period structures at risk of resonant amplification.
