High-resolution P- and S-wavefield seismic investigations of a quick-clay site in southwest of Sweden

Seismic investigations were performed at a site in the southwest of Sweden where major quick-clay landslides have occurred in the past. Given the potential high risk of the area and the presence of medium infrastructures, the site posed a need for detailed investigations in a wide depth range and in high resolution. A high-fold seismic survey was designed and conducted along two profiles using a 1-2 m receiver and shot spacing in order to retrieve both P- and S-wavefield seismic images from vertical component data. The data were analysed by combining first-break traveltime tomography and surface-wave analysis as well as P- and S-wavefield reflection seismic imaging. Using the first breaks, P-wave velocity (VP) models were estimated, indicating the bedrock topography along the profiles and the sediment characteristics. The S-wave velocity (Vs) models were estimated from the surface waves and indicated areas of low shear strength. Combined with VP and Vs models, this permits the estimation of VP/VS, a parameter that can indicate areas with high water content, significant for the detection of quick clays and possible liquefaction issues. The results are integrated with the P- and S-wave reflection seismic images and compared with other geophysical investigations, such as magnetic and gravity data that were collected along the profiles.