Study of tidal gravimetric factors in Chinese mainland based on three-dimensional Earth model

Tides are the Earth's response to the gravitational attraction of the Sun, the Moon, and other stars, and tidal gravimetric factors vital for revealing the Earth's interior structure. The tidal potential can be decoupled into several components, among which M2 and O1 are semi-diurnal and diurnal components, respectively, with the largest amplitudes caused by the attraction of the Moon. The China Earthquake Administration and the Chinese Academy of Sciences deployed the first gravimeters in the 1980s to study the spatial distribution characteristics of solid tides in Chinese mainland, and have developed a gravity observation network of >50 stations. In the current study, we utilized these observations, combined with tidal theory, considering the effects of lateral inhomogeneity and three-dimensional Earth models, such as GyPSuM, SPani, SEISGLOB2, SGLOBE-rani, and SAW642ANb, to construct a tidal gravimetric factor model of the M2 and O1 components in Chinese mainland and its adjacent zones. The effect of the lateral inhomogeneity on the tidal gravimetric factor was estimated using the perturbation method. The amplitude ranges of effects of the P-wave velocity perturbation, S-wave velocity perturbation, density perturbation, and their summation effects on the M2 component were −0.12% to 0.14%, −0.19% to 0.17%, −0.08% to 0.06%, and −0.09% to 0.11%, respectively (the effects on the O1 component were −0.13% to 0.28%, −0.27% to 0.15%, −0.12% to 0.10%, and −0.15% to 0.05%, respectively). For the M2 and O1 factors, the West Region Block, southwestern Xizang Block, northwestern South China Block, and central North China Block were attributed negative values, whereas the other regions were attributed positive values. For the M2 factor, the Himalayan orogenic belt (negative values) and southeastern margin of Cathaysia (positive values) were most significantly affected by lateral inhomogeneity, reflecting the special tectonics of these regions. There was no obvious maximum value for the O1 factor. The least-square-collocation method based on the idea of "remove-recovery" was utilized to combine the observed and theoretical tidal gravimetric factors. The magnitude of the gravimetric factor of the M2 component in Chinese mainland and its adjacent zones ranged from 1.130 to 1.175, with low values around and high values in the center. The magnitude of the gravimetric factor of the O1 component ranged from 1.145 to 1.195, showing a gradual increase from the northwest to southeast. The above outcomes can provide references for related studies of tidal gravimetric factors and Earth models in Chinese mainland and neighboring areas. The difference between the observed and theoretical M2 factors peaked at the southeastern margin of Cathaysia. The average difference was approximately 0.01, three to four times larger than the variation range of the theoretical M2 factor. This difference corresponds to the deviation between the real Earth and the Earth models. The difference between the superconducting gravimeter stations varied from 0.001 to 0.004. However, the difference at the gPhone stations commonly exceeded 0.01. The results show that setting up more high-precision gravimeters is expected to improve the tidal gravimetric factor model for Chinese mainland.