Combined electric resistivity tomography and seismic refraction tomography in brackish water in saltsjön in Stockholm

Electrical resistivity tomography (ERT) combined with seismic refraction tomography (SRT) were performed in brackish water in Saltsjön in Stockholm. Results from a test survey with measurements along two lines are presented, whereas a larger survey is in progress at the moment of writing. Geological interpretation of the obtained models fits well with the documentation from drilling, and show that the method works well in practice. As for geophysical surveys on land, the advantage is that you get continuous models that can be linked to variation in soil depth, structures in the rock and hydrogeological conditions. ERT is also a possibility where it is inappropriate to blast or drill because of occurrence of cables, pipelines or archaeological remains on the seabed. The electrical and seismic models from the combined survey complement each other and provide a more reliable overall picture of the variations in sediment depth and rock conditions.