An Analysis to Observations of the Superconducting Gravimeter at the Jiufeng Seismic Station, Wuhan

Abstract

AbstractThe relationship between the mass transfer in the Earth and vertical deformation can be studied using continuous relative gravimetry and continuous GPS observations. Compared to mobile relative gravimetry and absolute gravimetry, continuous relative gravimetry permits to monitor the whole process of gravity changes and mass transfer, avoiding the problems from low measurement precision and temporal resolution. In this paper, more than 13000 hours gravity data recorded at the Jiufeng seismic station using the superconducting gravimetry (SGC053) are analyzed along with the data of co‐located absolute gravimetry, air pressure, vertical displacement of surrounding GPS stations, WUHN IGS site and WHJF site, GRACE monthly time‐variable gravity and two global continental water storage models (GLDAS, CPC). Gravity variations affected by solid earth tide, air pressure, pole tide and continental water loading are corrected using the harmonic analysis method, atmospheric pressure admittance model, pole tide model and the correlation analysis with GRACE results and/or water storage models, then instrument drift is also corrected using co‐located absolute gravity measurements. Based on the above processing, the relationship between the residual gravity time series and GPS vertical deformation is addressed. The harmonic analysis result for SGC053 gravity records, spanning about one and half years, shows that the white noise is about (1.14~1.40)×10–8 m·s–2 and the tidal factor error of dominant tidal groups reach about 0.10/00. Compared to ocean tide loading (3×10–8 m·s–2), the gravity due to air pressure (12×10–8 m·s–2) and pole tide (10×10–8 m·s–2) is much large. The drift of SGC053, about 2.18×10–8(m·s–2)/a, is estimated using 4 absolute gravity co‐located records of FG5‐232. The result shows that the residual gravity caused by continental water loading in summer and autumn is about (6~8) × 10–8 m·s–2, by comparing residual gravity variations with both GARCE result and global continental water loading (GLDAS, CPC). Gravity variations corrected by water loading show a perfect negative correlation with the vertical deformation of the GPS station, about 15 km away from SGC053, so as to data in spring and winter. And the vertical crustal deformation is subsidence and the gravity change rate is about 1.79×10–8 (m·s–2)/a. The ratio of the changes in gravity and altitude related to the local vertical crustal movement is about –354×10–8 (m·s–2)/m.