A thin-sheet model of electromagnetic induction in northern England and southern Scotland

Abstract

Electric currents induced in the seas surrounding the British Isles influence the electromagnetic fields observed on land. Observational data suggest that , at certain periods, anomalous currents concentrate in a thin­ sheet comprising the shallow seas and onshore sedimentary sequences. The block and basin structure of northern England and southern Scotland provides a physical basis for the implementation of a thin-sheet approximation in quantitative electromagnetic modelling studies of the region. The model comprises a non-uniform thin-sheet at the surface of a layered half. space. The solution to this problem , as formulated by Vasseur & Weidelt, has been applied to a regional thin-sheet model of northern England and southern Scotland. A regional observational data set, comprising the anomalous vertical field at a period of 750s, is used to constrain possible models. Geological and geophysical observations are used to provide a realistic model for the major sedimentary basin of the region and the results obtained are compared with observations. The results suggest that such a basin is capable of establishing a substantial onshore perturbation in the anomalous vertical field, of similar geometry to that observed. Although the present study is necessarily limited in its depth resolution , it is suggested that other models presented go some way to defining the lateral extent of the conductive configuration for the region.