Abstract: Time-varying gravity field is an important means to study the physical properties of the earth. In this paper, a field source inversion method which is suitable for the time-varying gravity signals obtained from ground flow gravity measurements is proposed. The method uses hexahedral elements in spherical coordinate system to simulate the field source media and is suitable for constructing equivalent source models of large-scale seismic flow gravity measurements. In this method, the high-frequency components of time-varying gravity signals are suppressed by introducing a first-order smoothing priori, which can be used to extract long-period signals related to earthquake preparation. The theory and model experiments prove that the algorithm is reliable and stable. We also used the campaign gravity survey of the southern section of the north-south seismic zone from 2014 to 2017 for inversion. And the time-varying apparent density signal of the equivalent field source in the crust was obtained, which was within ±0.7‰ of the normal crust density, and its spatial morphology was controlled by the boundary of the Sichuan-Yunnan block. The results of this paper can be applied to the interpretation of time-varying gravity field model and the extraction of deep field source characteristics, which can provide a complete method for seismic gravity precursor signal analysis and related research.

Key words: Time-varying gravity field, Potential field inversion, Campaign gravity survey, Equivalent source, Density variation