Radiomagnetotelluric Measurements on the Lake Mälaren along a Planned New Motorway in Stockholm, Sweden

In this study we have tested a new technique with RMT measurements on water which we call Marine Tensor RMT. The measurements were performed on the Lake Mälaren close to the city of Stockholm along a planned new motorway “E4 The Stockholm bypass”. The RMT system was slightly modified to be adapted for marine applications and part of the equipment was placed on a float that was dragged behind a small motorboat. The first results from the two test profiles on the Lake Mälaren are very promising. It was possible to make the measurements in a continuous way with an approximate speed of 2 km/hour. This makes it ten times faster compared to measurements on land. With this technique large areas can be covered with parallel profiles within a short period of time. The results from the 2D inversions show a good correlation with the results from the refraction seismic investigations in the same area. Moreover the resolution is fairly good even at greater depth and the resistivity models can give additional quantitative information about the bedrock quality at depth down to 60 m which is the depth for the planned road tunnel.