Difference electromagnetic induction arrow responses in New Zealand

Abstract

Geomagnetic observations in New Zealand are expected to include ocean effects owing to geomagnetic induction in the surrounding oceans. In this work, these unwanted effects in the observations at each of 34 field sites are removed by subtracting laboratory model ocean effect induction arrows from geomagnetic induction arrows to yield difference arrows. The difference arrows at sites in the central region of North Island can be accounted for by induction primarily in conductive structure in the Central Volcanic Region (CVR), whereas in the southern regions the arrows appear to include additional components that would be consistent with conductive structures at depth associated with the Wellington Fault system and the subducting Pacific Plate. In the northern and southern regions of South Island the arrows could be accounted for in part by conductive structures associated with the Dun Mountain Ophiolites and Haast Schists, and in part by the conductive structures in the Alpine Fault system, whereas in the central regions conductive structures beneath the Southern Alps and the Canterbury Plains would appear to play the major role.