Risk, G.F.; Groth, M.S.; Rayner, H.H.; Dawson, G.B.; Bibby, H.M.; Macdonald, W.J.P.; Hewson, C.A.Y. 1977 The resistivity boundary of the Broadlands geothermal field. [s.l.]: [s.n.]. Report / Geophysics Division 123 42 p.
Abstract: More than 500 apparent resistivity measurements were made at 50 m intervals along 18 traverse lines straddling the boundary of the Broadlands geothermal field. The current electrodes were kept fixed and arranged so that one electrode was at the centre of the field and the other was about 3 km outside the field. Three pairs of current electrodes were used in turn. As the receiver array was traversed from the inside of the field toward the outside, the apparent resistivity rose from 2 to 5 ohm m up to values of 15 to 50 ohm m. The distance taken for the apparent resistivity to rise to a value of 2.5 times its ambient value on the inside of the field varied from about 100 to 500 m. On some lines, abrupt deflections of the electric field vector, and sometimes, the observation of induced polarisation effects coincide with the zone of increasing apparent resistivity. This zone has been called the resistivity boundary of the field and it is an estimate of the position of the lateral limit of the hot geothermal reservoir to depths of about 1 km. Since all the measurements have been located relative to permanent survey marks, later repeat measurements will enable changes of location of the resistivity boundary due to inflow of cold water or other causes to be monitored
