Surrey’s rapid vertical expansion—adding over 9,800 new residential units in 2023 alone—has pushed foundation design into increasingly complex glacial and alluvial deposits south of the Fraser River. When a 30-storey tower goes up in Whalley or a mid-rise lands on the silty clays of Cloverdale, the National Building Code of Canada (NBCC 2020) demands a site-specific shear wave velocity average in the upper 30 metres, known as VS30. We deploy a 24-channel seismograph with 4.5 Hz geophones in linear arrays spaced at 2 to 4 metres, capturing Rayleigh wave dispersion down to 30–35 metres depth. The surface-based MASW method avoids drilling altogether while delivering the VS30 value that directly determines Site Class C, D, or E—the single most consequential parameter for base shear calculations. In a city where the unconsolidated Sumas till can mask a stiff contact at 18 metres, assuming a default Class D without measured VS30 frequently overestimates seismic demand by 15–20%.
A measured VS30 of 240 m/s versus an assumed 180 m/s often drops a Surrey site from Class E to Class D, cutting spectral acceleration by 20%.
