The geophone array stretches across the site in a carefully surveyed line, each sensor spiked firmly into the Belfast clay. A sledgehammer strikes the steel plate at the shot point and the seismic pulse races downward, refracting off the sandstone bedrock and reflecting from the clay-till interface. This is seismic tomography in practice—a technique that builds a continuous image of the subsurface from dozens of individual wave paths. In Belfast, where the glacial history has left a chaotic sequence of stiff till, soft clay, and weathered rock, the method reveals the hidden architecture that boreholes alone can miss. The equipment is portable enough to deploy on confined urban plots near the Lagan riverfront, and the data density is high enough to map subtle velocity variations across the 280,000-square-metre footprint of a typical city-centre redevelopment. When combined with targeted SPT drilling for point calibration, the resulting velocity model gives engineers a solid basis for designing foundations that work with the ground rather than against it.
A single seismic line across the Lagan Valley can map bedrock depth, identify buried channels, and deliver the Vs30 profile needed for seismic design—all in one working day.
