Electrical resistivity structure of the Canterbury Plains, New Zealand

Abstract

Magnetotelluric (MT) soundings from nine locations across the Canterbury Plains, South Island, New Zealand, are used to deduce the electrical resistivity structure of the Plains down to c. 3 km depth. The Quaternary gravels covering the Plains represent a resistive layer which is inferred to be c. 600 m thick and are underlain by more conductive Tertiary sediments. Over most of the Plains, a rise in resistivity at greater depth cannot be unambiguously identified as greywacke basement, but correlation of the electrical structure with earlier seismic and gravity work suggests that the gravels and Tertiary sediments thin towards the western edge of the Plains where greywacke is very close to the surface, dc resistivity soundings are used as a check on the correction of static‐shift in the MT data and are shown to be compatible with the MT results. Joint interpretation of the dc and MT data allows hydrological implications to be drawn on the porosity and pore fluid resistivity of the layers.