D.C. resistivity surveys of the Broadlands geothermal region, New Zealand

Risk, G. F.; Macdonald, W. J. P.; Dawson, G. B.

doi:10.1016/0375-6505(70)90027-1

Cited by 38 publications

(19 citation statements)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…As the electric field vectors produced by the three sources are not independent, the third measurement is used to provide a check on data consistency and quality. For most dc measurements, apparent resistivity is defined by comparing the measured electric field strength vector E with the theoretical current density vector J for a uniform half-space [Risk et al, 1970;Zohdy, 1978]. However, the most general form for expressing the relationship between these two vector fields is as an apparent resistivity tensor 1/ defined by E = l/J.…”

Section: Shallow Resistivity Structure Of the Tvzmentioning

confidence: 99%

Electrical resistivity image of the upper crust within the Taupo Volcanic Zone, New Zealand

Bibby¹,

Caldwell²,

Risk³

1998

J. Geophys. Res.

View full text Add to dashboard Cite

Abstract. The Taupo Volcanic Zone (TVZ) forms a region of back-arc extension within the continental crust of New Zealand and is notable for its caldera volcanism, high rate of magmatic production, and high heat flow. On the eastern side of the TVZ, volcanism terminates abruptly along a linear margin. We present the interpretation of three multiple-source bipoledipole resistivity surveys across this margin. The major features of the measured data can be reproduced by using two-dimensional models of the resistivity in the upper 10 km of the crust. Along the margin the high-resistivity graywacke basement (300 f•m increasing to 1300 f•m) is downfaulted to the west across a zone about 6 km wide, with a total vertical offset of approximately 2 km. The easternmost fault is overlain by an unbroken 0.24 Ma ignimbrite sheet, suggesting the fault has been inactive for this period. Further to the west, at depths greater than 2 kin, a conductive zone about 15 km wide and of total conductance 180-280 S has been identified. This conductive zone can be modeled by using a range of resistivities (40-3 f•m) and thicknesses (8-2 kin). Models incorporating resistivities less than 15 f•m require the low-resistivity zone to be wedge shaped, so that conductance increases to the west. The low resistivity is believed to be caused by the presence of clay alteration within volcanoclastic rocks. The large volume of volcanic rocks at depth can be linked to a series of caldera-forming eruptions that have taken place along the eastern side of the TVZ.

show abstract

Section: Shallow Resistivity Structure Of the Tvzmentioning

confidence: 99%

Electrical resistivity image of the upper crust within the Taupo Volcanic Zone, New Zealand

Bibby¹,

Caldwell²,

Risk³

1998

J. Geophys. Res.

View full text Add to dashboard Cite

show abstract

“…Although such a feature is not generally eommon in nature, it is relevant for mapping in geothermal regions, as the boundary of a geothermal field is often modelled as a vertical diseontinuity in resistivity (e.g., Risk et al 1970). Theoretieal expressions for the apparent resistivity for this situation are given by Van Nostrand & Cook (1966).…”

Section: Apparent Anisotropymentioning

confidence: 99%

“…Portions of the data from this map have previously been published in studies ofsome of the geothermal areas that lie within the map sheet (Maedonald 1966;Risk et al 1970;Dawson et al 1981;Bennie 1983;Risk et al 1984). Eaeh of these have been studies of small areas, and data outside the specifie region of interest have been ignored.…”

mentioning

confidence: 99%

Electrical resistivity mapping in the Central Volcanic Region of New Zealand

Bibby¹

1988

New Zealand Journal of Geology and Geophysics

View full text Add to dashboard Cite

Over 17 000 electrical resistivity measurements have been made in the Central Volcanic Region ofNew Zealand since 1963. Both the Wenner and Schlumberger electrode configurations have been used although the Schlumberger array has been used exclusively since 1970. Improved instrumentation and measurement techniques have led to much improved quality of more recently acquired data, and the incorporation of self consistency tests allow suspect data to be identified. These electrical resistivity data are now being published as a map series, based on the NZMS 260 topographie maps, on ascale of 1:50 000. For each map sheet, two contour maps are issued, one incorporating data with a nominal Schlumberger array spacing of 500 m, the other with nominal spacing of 1000 m. Measurements made with the Wenner configuration, with electrode spacing 1800 ft (549 m) and 3600 ft (1097 m) are used to augment the data for each of these maps, respectively. Because the Wenner data are not directly compatible with the Schlumberger data, reduced weighting is applied to the Wenner data in the contouring process so that they become important only in regions where other data are not available. Contour intervals for the apparent resistivity are logarithmically spaced with six contours per decade. This reflects the approximately logarithmic distribution of apparent resistivity. Maps also show measurement sites at which electrical resistivity soundings data are available. The contours shown on the maps are based on computed contours, but modifications have been made so as to improve the representation of important short wavelength features, and to allow the compiler to include some interpretation. Received26 May 1987, accepled18 January 1988The first map of the series is sheet U17-Wairakei, which includes a number of important geothermal areas.

show abstract

“…The bipole-dipole survey, undertaken over a 3 week period in late 1991 , employed the multiple-source bipole-dipole technique in the format developed in New Zealand primarily for geothermal exploration in 1968 (RISK et al, 1970;BIBBY and RISK, 1973). The sources were sited in forested land on the Kaingaroa Plateau (site shown in Fig.…”

Section: Multiple-source Bipole-dipole Measurementsmentioning

confidence: 99%

“…This study was followed by several investigations made using deep penetration direct current bipole-dipole surveying, from which the modern multiple-source bipole-dipole surveying was developed. The only published accounts of these surveys (RISK et al, 1970;RISK, 1973, 1992;BIBBY et al, 1984;RISK, 1984) deal mostly with geothermal resource investigations, but the data also reflect information about deep structures. Several studies have also been made using natural field methods, including magnetotelluric studies (HURST, 1974;MIDHA, 1979;INGHAM, 1987INGHAM, , 1991.…”

Section: Introductionmentioning

confidence: 99%