New absolute gravity measurements in New Zealand
21/09/2016 | 09:15 | Session 4: On the ground and airborne gravimetry
Author(s): Yoichi Fukuda, Hiroshi Takiguchi, Takahito Kazama, Jun Nishijima, Sergei Gulyaev, Tim Natusch, Matt Amos, Vaughan Stagpoole and Christopher Pearson
Yoichi Fukuda, Hiroshi Takiguchi, Takahito Kazama, Jun Nishijima, Sergei Gulyaev, Tim Natusch, Matt Amos, Vaughan Stagpoole and Christopher Pearson
The first absolute gravity (AG) measurements in New Zealand (NZ) were carried out in October 1995 at Godley Head, near Christchurch, using a FG5 (#102 of National Oceanic and Atmospheric Administration), which was on the way to McMurdo Station in Antarctica (Sasagawa, 1995). Since then AG measurements at Godley Head have been occasionally repeated by US, Danish and French groups, usually en route to Antarctica. One notable campaign of AG measurements was conducted by a group from the University of Colorado and the University of Otago using FG5 #111. They made a series of measurements across the NZ Southern Alps in 2000 and reoccupied the AG points in 2015 with the aim studying the formation mechanism of the mountains (Bilham ., 2000; Bilham ., 2015). In February 2015, GNS Science and Land Information New Zealand, collaborating with Geoscience Australia, carried out AG measurements using FG5 #237 at three existing absolute gravity points in South Island and five newly established gravity points in North Island (Stagpoole ., 2015).
To enhance and extend these AG measurements in NZ, we conducted new measurements using a FG5 (#210 of Kyoto University) in January and March 2016. The measurements in North Island were made at two existing points (the Warkworth Radio Astronomy Observatory and Wellington A) and at one newly established point at the Wairakei Research Centre, Taupo. The gravity measurements in South Island were made at five existing AG points; Godly Head, Mt John, University of Otago, Helipad and Bealey Hotel. At each point more than 4000 drops were made and AG values were determined with measurement uncertainties better than 3 ugal (mostly better than 2 ugal) at 130 cm instrument height. The values are compared with the results of the 2015 campaigns. Although the differences of about -10 ugal are observed at Wellington A and Godley Head, the differences at the other points are within 5 ugal. We will further discuss the possible causes of the differences.