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Evaluation of electrical methods, seismic refraction and ground‐penetrating radar to identify clays below sands ‐ Two case studies in SW Sweden
- Source: Near Surface Geophysics, Volume 3, Issue 2, Jan 2005, p. 59 - 70
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- 01 Feb 2003
- 01 Jan 2005
- 01 Jan 2005
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Abstract
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.