Brighton’s geology has a habit of keeping you on your toes. You might start with solid chalk near the racecourse, then hit loose Head deposits or thick raised beach gravels just a few hundred metres downslope toward the seafront — and that shift changes the site class completely. We have seen projects where the VS30 value dropped from class B to class D simply because the chalk was more weathered than the boreholes suggested. That is where a surface-wave survey earns its keep. The MASW method gives you a continuous shear-wave velocity profile without the gaps that SPT or CPT leave between test depths, which matters when the formation boundary is uneven. For sites near the Brighton Marina or along the A23 corridor, combining MASW with an SPT drilling campaign is often the most pragmatic way to calibrate velocity against direct penetration resistance, particularly where the chalk is fractured and the seismic signal can scatter.
In Brighton, a VS30 value measured on dry chalk in August can differ from the same location in February — saturation affects Rayleigh wave velocity in the upper 3 metres more than most people expect.
