Electrical Conductivity Structure of the Eastern Margin of the Central Volcanic Region

Abstract

AMT/MT soundings have now been made at a total of 17 sites along a NE-SW line from the Broadlands- Ohaaki to Wairakei-Tauhara geothermal fields. The data have been modelled in terms of a resistivity structure which shows the geothermal fields to be characterised by very low resistivities (of order 5 ohm-metres) at shallow by resistivities of less than 100 ohm-metres which extend to depths of several kilometres. Between the fields a moderately conductive layer of 10-20 ohm-metres exists at around 1-2 km depth and overlies resistivities of some hundreds of ohm-metres. The extension of this feature to the south-east has been gauged from measurements at four locations on a NW-SE line which crosses the eastern edge of the Central Volcanic Region. These data suggest that, though resistivity values remain relatively low in continental terms, the conductive layer loses its identity some lOkm to the south-east beneath the Kaingaroa Plateau.