Brighton sits on a complex geological boundary where the White Chalk Subgroup of the South Downs meets Quaternary Coombe deposits and raised beach terraces. The sudden change from stiff, fractured chalk to softer, saturated silty clays over distances of less than 200 metres creates abrupt variations in site response during seismic events. A generic seismic hazard map cannot capture this granularity. Our seismic microzonation work for Brighton projects maps VS30 and fundamental site period (T0) at the parcel scale, directly feeding into BS EN 1998-1 ground type determination and the selection of appropriate elastic response spectra for structural design. When working on the London Road viaduct redevelopments or coastal regeneration schemes east of the Palace Pier, we integrate MASW testing to resolve shear-wave velocity profiles through the variable cover, and seismic refraction to delineate the chalk bedrock surface where it dips beneath Holocene alluvium.
Two sites on the same Brighton postcode can fall into ground types B, C, or D depending on cover thickness over chalk, and that difference shifts the design spectrum by up to 40%.
