[S-GD01] Geodesy and Global Geodetic Observing System

[SGD01-P01] Absolute gravity measurements at Matsushiro in June 2023 and sensitivity calibration of superconducting gravimeters CT #036 and iGrav #028

*Yuichi Imanishi¹, Ryuichi Nishiyama¹, Ryo Honda², Taiki Marufuji³, Kazunari Nawa³ (1.Earthquake Research Institute, The University of Tokyo, 2.Mount Fuji Research Institute, Yamanashi Prefectural Government, 3.National Institute of Advanced Industrial Science and Technology)

Keywords:Matsushiro, absolute gravity measurement, superconducting gravimeter, sensitivity calibration

In June 2023, we conducted a tour of absolute gravity measurements visiting three stations: Mt. Fuji (Yamanashi prefecture), Matsushiro (Nagano prefecture), and Kamioka (Gifu prefecture), with the aim of tracking long-term gravity changes after the 2011 Tohoku earthquake. At the Matsushiro station, we were able to obtain very high-quality data over a total of four days, thanks to the good weather conditions. The effective number of drops was 24,580, and the drop-to-drop scatter was 4.25 µGal. The gravity acceleration at 130 cm above the floor was estimated to be 979,772,780.975 ± 0.027 µGal. We believe that this is one of the most precise results ever obtained in Japan for absolute gravity measurements at a single point.

Using this absolute gravity measurement data, we calibrated the sensitivity of two superconducting gravimeters (CT #036 and iGrav #028) currently operating simultaneously at the same location. The estimated scale factors (expressed as positive values) were 1134.47 ± 0.70 µGal/V for CT #036 and 2042.6 ± 1.2 µGal/V for iGrav #028, respectively, achieving a relative accuracy of approximately 0.06%.