Because of their geophysical properties, making a detailed interpretation of clay layers beneath surface layers of sand or gravel is sometimes a challenge. We chose two sites in south‐western Sweden where sand over clay has been documented by drilling, to test the effectiveness of four different geophysical methods in mapping the buried clay. We used geoelectrical methods (resistivity and induced polarization), seismic refraction and ground‐penetrating radar. Resistivity was found to be the best method for identifying the presence of the clay layer. Induced polarization (IP), in combination with resistivity, provides additional information but can give erroneous results if IP responses are weak. The seismic refraction method was not effective in detecting the clay layer due to the low contrast in seismic velocities between saturated sand and clay, although the method did give useful constraints on resistivity modelling. With ground‐penetrating radar, it was possible to map the upper boundary of clay with good accuracy.
Ground penetrating radar and shear-wave reflection methods were used to characterize the shallow subsurface. Both methods were compared at a site in south western Sweden. The site, which consists of a [Formula: see text] long profile, was chosen based on existing site information from previous studies. The shallow subsurface consists mainly of sediments of sand and clay. Ground penetrating radar methods, using common-offset and multi-offset techniques, in combination with common midpoint processing, were compared regarding resolution and depth penetration. It is shown that the latter strategy provides more distinct reflections and allows a deeper range of interpretable reflectors. The shear-wave reflection method images overlapping and deeper parts of the section which are below the depth range resolved by the radar waves. The study shows that by combining information from ground penetrating radar and shear-wave reflection surveys, a more complete analysis of subsurface geology can be conducted. Also in conductive environments, the shear-wave reflection method offers a possible alternative to ground-penetrating radar.
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