Magnetovariational and Magnetotelluric Investigations in S. Scotland

A two-dimensional array of 20 Gough-Reitzel magnetometers was operated over S. Scotland in 1973 and in 1974–5 magnetotelluric and magnetovariational observations in the period range 10-10,000 s were made in the same region. In this paper, the analyses of the magnetic data from both studies are presented in the form of induction vectors and hypothetical event contours. They suggest that the lateral variations in electrical conductivity structure associated with the Eskdalemuir anomaly are more complex than suggested by earlier studies. A marked discontinuity in electrical structure is apparent in a narrow belt parallel to and south of the S. Uplands fault. This belt is associated with a major gravity anomaly and with steep gradients in the seismic profile at crustal depths. Another discontinuity is indicated near the North umberland Basin. Representative examples of the magnetotelluric analysis and of onedimensional Monte Carlo inversion of the M-T data are presented for the three regions separated by these discontinuities. They show that the conducting zone associated with the Eskdalemuir anomaly is at a depth greater than 24 km, while on either side of this region, there are good conductors within crustal depths.