A magnetotelluric investigation of the North Island volcanic plateau

Abstract

A magnetotelluric field station was successfully established and operated in the southern part of the North Island Volcanic Plateau. Data was recorded during February and August 1968. Both visual correlation and power spectral analyses of the graphic records were used to determine apparent resistivities and phase differences, for periods in the range 3 to 350 seconds. Interpretation of the plotted resistivities suggests that the geoelectric section is divided into three principal layers. The layer nearest the surface has a resistivity of 36.5 ohm-metres. The next layer, beginning at a depth of about 4.3 km, has a resistivity of 3750 ohm-metres, and extends to a depth of 86 km. The resistivity of the lowest layer is 3.75 ohm-metres. Evidence of an anisotropy and/or inhomogeneity with an axis of least resistivity running north-east was found, which parallels many important geological features.