Quebec City sits just 20 km from the Charlevoix Seismic Zone, the most active earthquake region in eastern Canada, where a magnitude 6.2 event struck as recently as 1925. Any deep foundation or slope design here must account for the complex interface between glacial till, marine clay, and the fractured Appalachian bedrock. Seismic tomography, combining both refraction and reflection techniques, provides a continuous subsurface velocity model that standard boreholes simply cannot match. By measuring P-wave and S-wave travel times from surface-generated energy, we map lithological boundaries and identify potential fault zones that could compromise structural integrity. For projects near the St. Lawrence River, where thick Champlain Sea clay masks the rockhead, this method becomes indispensable. We frequently pair it with a targeted CPT test program to calibrate shear wave velocities against cone resistance data, ensuring the geophysical interpretation matches the geotechnical reality of the site.
A single seismic tomography line can delineate the bedrock depression beneath 300 m of Champlain Sea clay, a feature that scattered boreholes routinely miss.
