Hunt, T.M. 1984 Repeat gravity measurements at Wairakei geothermal field, 1961-1983: data and measurement techniques. : . Report / Geophysics Division 201 67 p.
Abstract: Repeat gravity surveys made on benchmarks, to examine the effects of mass changes associated with exploitation of the Wairakei Geothermal Field are described, and the data tabulated. Surveys were made in 1961 (59 benchmarks occupied), 1962 (53), 1967 (56), 1968 (64), 1971 (85), 1974 (89), and 1983 (123). The surveys in 1961 and 1962 were made with North American gravity meter AG1-96, and later surveys with La Coste and Romberg meter G-106. Measurements were generally made three times on each benchmark during a survey, and the rms residuals of these measurements were: 0.08 micro N/kg for the 1968 and 1983 surveys; 0.09 micro N/kg for the 1967, 1971, and 1974 surveys; 0.10 micro N/kg for the 1961 survey; and 0.11 micro N/kg for the 1963 survey. Corrections were made to differences in observed gravity, between surveys for the effects of vertical ground movements (up to 11.2 micro N/kg). The gravity effects of changes in shallow groundwater level may be significant (up to 0.45 micro N/kg), but those of horizontal ground movement and changes in temperature of the groundwater are negligible (