Mapping the Pre-Holocene Surface of an Infilled Valley in the East Kent Fens, UK, with a Shear-Wave Seismic Refraction Survey

In a study of the Holocene sediments in the Hacklinge-Deal area of the East Kent Fens, Southeastern England, hand-coring data has shown that the pre-Holocene surface in this area is incised by one or more valley features, now infilled with unconsolidated Holocene sediments. A shear-wave seismic refraction survey was carried out along profiles where hand-coring had failed to penetrate to bedrock in an attempt to define the detailed form of the pre-Holocene surface. The seismic refraction work was successful because of the large velocity contrast for seismic shear-waves between the Holocene sediments and the Cretaceous chalk bedrock. The seismic data showed that the maximum depth to chalk in the area was almost 20 m, and the results obtained from one profile were subsequently confirmed by hand-coring to a depth of 9 m. Hand-coring, seismic, and Ordnance Survey spot height data have been combined to produce a first estimation of the three-dimensional form of the pre-Holocene surface in the study area