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The electrical conductivity structure of the Baltic Shield in Finland has been studied by magnetovariational (MV) and magnetotelluric (MT) work. First magnetometer arrays revealed the crustal Oulu conductivity anomaly which consists of a crustal conductive zone and a conductivity boundary. Since 1983 the magnetotelluric technique has been used to study the Oulu anomaly in more detail. The information obtained from the induction vectors of the MV and MT data are compared. 1 D and 2D models of the Oulu anomaly were constructed from MT data using induction vectors as additional information. In the centre of the research area the anomalous body (with a resistivity of 0.5 ohm m) lies below a depth of 4-7 km. Its width is about 25 km and its length is more than 100 km. To the south-west of this anomaly a low-resistive crustal layer exists at a depth of 14 km, whereas to the north-east no crustal layer was identified in the very resistive Karelidic realm.           ARK: https://n2t.net/ark:/88439/y097907 Permalink: https://geophysicsjournal.com/article/229 &nbsp

In 1981 and 1982 four arrays of 30 or 31 magnetometers were operated on the Baltic Shield in central and south-eastern Finland to measure the natural magnetic field variations. These measurements were used to deduce some information about the lateral variation of the electrical conductivity within the Earth's crust. The stations were situated between latitudes 56° and 64° geomagnetic north. As substorms often extend over this area, most magnetic disturbance events have strong external spatial gradients and are not suitable for determining the electrical conductivity distribution inside the Earth. Some magnetic disturbance events with only smooth external spatial gradients could be selected and used for further analysis. For 11 of these events (2–6 h long), the horizontal spatial wavenumber k has been calculated. The product of the wavenumber k and the inductive scale length C was then used as an acceptance criterion and as a weighting function in the calculation of single station transfer functions. Most of the data were not acceptable for the criterion k · |C| < 0.3 for periods longer than 500 s. Because of the small number of acceptable data the statistical significance was not sufficient for all sites. Despite these problems induction vectors and conducted hypothetical vertical field maps could be used to locate conductivity anomalies. Intensive induction was found in three zones in the area under investigation.           ARK: https://n2t.net/ark:/88439/y036023 Permalink: https://geophysicsjournal.com/article/223 &nbsp