Geomagnetic induction studies in Scandinavia. II. Geomagnetic depth sounding, induction vectors and coast-effect

In this paper an event of very favourable structure for induction purposes, which was observed by the Scandinavian magnetometer array, is discussed and analysed in detail. The responses derived, in both the time and frequency domains, display a large coast effect at all coastal stations, both on the sea coasts and on the Gulf of Bothnia. Two relatively large inland anomalies are also delineated. The more significant of the two, the Storavan anomaly, is apparent using all the analysis techniques employed, and may be associated with a remnant of the Svionian island arc system. The less dominant anomaly, in the vicinity of Mieron, has no obvious correlation with geology or tectonic formations, and appears to be polarisation sensitive - it is only energised by E-W magnetic fields. First approximation modeling of the coast effect observed by the NW stations illustrated that the responses are well satisfied by the conductivity contrast between sea and land. Finally, the validity of the derived induction vectors, and the possible effects of induction for source field studies, are discussed.-Author