Integrated 2D modeling and interpretation of geophysical and geotechnical data to delineate quick clays at a landslide site in southwest Sweden

Radio Magnetotellurics (RMT), Electrical Resistivity Tomography (ERT) and high-resolution reflection seismic data were collected along four lines to image the geometry and physical properties of geological structures at a quick-clay landslide site in southwest Sweden. The site is situated in the Göta River valley where the normally consolidated materials mainly consist of glacial and post-glacial sediments. Geotechnical data suggest presence of quick clays above coarse-grained layers. These layers play a key role in the formation of quick clays and landslide triggering. The RMT and ERT data were individually and jointly inverted in 2D to study the resolution of resulting models for each data set. The resistivity models from the joint inversions demonstrate superior resolution and accuracy than individual ones. The geometry and location of shallower structures resolved in the 2D resistivity models from joint RMT+ERT inversions correlate well with those imaged in the reflection seismic data and observed in the existing geotechnical boreholes. The models are poor in resolving deeper resistive bedrock at locations where the thickness of the conductive overburden exceeds a certain limit. However, information from the reflection seismic data could be used to estimate the depth to the top of the bedrock along all the four lines. Comparison between the geotechnical data and the resistivity models suggests that quick clays overlying the coarse-grained layer have higher electrical resistivity than the marine clays. The obtained results were further validated and refined by performing synthetic tests. This study shows that integration of ERT and RMT data with reflection seismic data is ideal for quick-clay landslide studies especially when the clay materials are thick.