Analysis of Superconducting Gravimeter measurements at MunGyung station, Korea

In 2005, Korea’s first Superconducting Gravimeter (SG) was installed at MunGyung (MG). For the installation of the SG, a new measuring hut with a grounded pier was built. The SG has been successfully recording since April 2005. To monitor the groundwater level changes around the SG, a borehole was drilled in September 2005. For analyzing the gravity data, the SG calibration factor of −64.548 μgal/V (μgal = 10−8 m/s2) was determined by a parallel registration with an absolute gravimeter. The noise magnitude (NM) at the MG site was determined and compared with other SG stations and the New Low Noise Model. The MG site can be classified within the NM of other SG stations. Additionally, noise caused by misaligned instrumental tilt has been investigated and spectrally analyzed. Covering the instrument with a polystyrene box has resulted in a decrease of this noise. After preprocessing, the tidal analysis has been performed and compared with the Wahr–Dehant tidal model parameters. Non-tidal gravity variations, caused by atmospheric pressure and ground water level variations, were calculated. According to the FES2002 ocean tide model, the ocean loading at MG site was calculated. All known gravity effects (i.e. solid Earth tides, polar motion, atmospheric pressure and ground water level induced gravity variations, and the ocean loading gravity effect) were then subtracted from the SG measured gravity data. The remaining gravity variations (gravity residuals) were spectrally analyzed for detection of unknown gravity effects. Co-seismic gravity changes were detected by the SG for earthquakes with epicenters within a distance of about 100 km from the MG station. The largest detected co-seismic gravity change was 0.06 μgal.