Swansea's urban fabric stretches from the Tawe river corridor across perched valleys carved into Pennant sandstone, but the near-surface geology tells a more complicated story. Glacial till and soft estuarine silts blanket much of the city centre and SA1, creating abrupt stiffness transitions that catch out generic ground models. A standard borehole log won't capture the shear wave velocity profile — and that's where the MASW method earns its place. We run 24-channel linear arrays across the site, recording Rayleigh wave dispersion to invert a 1D VS profile down to 30 metres. The output is the VS30 value that Eurocode 8 demands for seismic site class. In our experience across South Wales, this parameter flips a design from ground type D to C more often than desk-study assumptions would suggest, directly reducing seismic load factors for footings and structural frames.
A 50 m/s difference in VS30 can change your seismic site class — and your Improvement budget — before the first pile is designed.
