New Zealand gravity reference stations 2020: history and development of the gravity network

Gravity surveys using relative gravity meters are often tied to accessible, accurate and stable gravity reference stations. Since 1947 gravity reference networks have included pendulum gravity stations, New Zealand Primary Gravity Network stations, stations at geodetic benchmarks, base stations established by GNS Science and absolute gravity stations (since 1995). New Zealand Gravity Reference Stations 2020 is a revision of earlier gravity networks and includes precise observations made with relative meters since the 1970s that for the first time are referenced to absolute gravity measured in New Zealand. Currently there are 1710 gravity reference sites with 1475 sites classed as usable. The gravity across the network has been combined in a set of least squares calculations with an estimated uncertainty for gravity at geodetic benchmarks and GNS Science base stations of ± 0.3 µN/kg, and ± 0.6 µN/kg at New Zealand Primary Gravity Network stations. Gravity stations affected by large earthquakes since 1990 have been resurveyed, and gravity changes due to long term variations in elevation, local fluctuations in groundwater level and alteration to nearby topography from erosion and roadworks are estimated at < ± 0.3 µN/kg