Geomagnetic variation anomalies in northern England: processing and presentation of data from a non-simultaneous array

The block and basin structure of northern England has been investigated by an array of 35 magnetometer stations over a grid with a spacing of 10km. Recordings at these sites were made simultaneously with those at a reference site. Using the common reference data, transfer function analysis enables the three anomalous field components to be estimated at each site, for the period range 10–104s. Using the transfer functions obtained, maps of the anomalous field components may be generated across the array, and used for interpretation of electrical conductivity structure. Maps thus obtained from the non-simultaneous array data in northern England are used to illustrate the advantages of the method, and provide evidence of an east-west current flow concentrated along the southern margin of the Northumberland Trough. The limitations of the procedure, although slight, are considered. The errors which arise in the method are deduced and techniques for their removal are suggested.