Magnetotelluric sounding of the Hikurangi Margin, New Zealand

Abstract

Magnetotelluric soundings from 30 sites on the Hikurangi Margin have been used to image the electrical resistivity structure associated with the subduction of the Pacific Plate beneath the Australian Plate along the east coast of the North Island of New Zealand. The data are generally 2-D in nature and exhibit a strike orientation that is compatible with the observed tectonic strike of the margin. 1-D inversions of invariant impedance responses from sites on a transect parallel to this orientation yield an electrical structure that correlates with both the near-surface geology and the results of a seismic refraction profile. 2-D inversion and forward modelling of responses from a transect across the margin not only clearly identify surface conductive sediments associated with the outer forearc region but also suggest the possibility of a thin conductive zone immediately above the plate interface. The conductive layer is coincident with a low-velocity region identified by seismic results and has been interpreted as being due to subducted sediments.