Electromagnetic induction in the New Zealand South Island

Abstract

Laboratory magnetic field measurements for a scaled analogue model of New Zealand and the surrounding oceans are used to provide induction arrows for simulated geomagnetic variations of 5–120 min periods for a series of traverses over the South Island. As the island is relatively narrow, the field responses for all on-land locations show significant effects of the surrounding oceans. The model simulates a uniformly resistive island, the oceans, and a conductive asthenosphere at depth, and thus discrepancies between the model and field results for sites on the island are attributed to anomalous geological structures not simulated in the model. Removing the coast effects before interpretation, by subtracting the model induction arrows from the field site arrows at Eyrewell permits an obvious reinterpretation that attributes a significant component of the field responses to the nearby Alpine and Marlborough Faults, rather than to the channelled current in Cook Strait.