Installation, Calibration, and Data Processing of the Superconducting Gravimeter at the New Deep Underground Lab in Korea

Abstract

Installation, operation, and preliminary analysis of the superconducting gravimeter at the underground Yemi laboratory are presented. In October 2022, a superconducting gravimeter, iGrav#001, was installed at the Yemi laboratory in Korea, located ~ 1008 m below the surface and 118 m below the mean sea level. The ultimate objective of the project is to monitor and analyze earthquake signals to enhance the current early warning systems. The noise analysis revealed that the noise level at YemiLab, particularly within the seismic band, is significantly low and close to the New Low Noise Model. It was found that blasting for mining at least 700 m away from the SG was recorded in the dewar and barometer pressures as well as tilt balance data. However, no effect was recorded in the raw SG data, indicating that the blasting vibration was compensated by the SG tilt system. Through five days of parallel measurements with an FG5 absolute gravimeter, a calibration factor of – 94.38 μGal∙V⁻¹ was estimated. Residual gravity was calculated after removing environmental effects. The spectral analysis reveals several unknown frequencies in the power spectrum density of the residual gravity, which require additional analyses. Co-seismic gravity changes were investigated for an earthquake with 6.2 Mw and 765 km away from the SG station to investigate the sensitivity and capability of the SG for earthquake monitoring. The recorded gravity changes at the arrival time were 0.561 μGal, which gradually decreased and disappeared within half an hour after the first arrival at the SG.