From One-Dimensional to Three-Dimensional: Effect of Lateral Inhomogeneity on Tidal Gravity Derived by Analytical Expression
- Institute of Earthquake Forecasting, China Earthquake Administration, Beijing 100036, China
Abstract. Lateral inhomogeneity in Earth’s mantle affects the tidal response. In this study, the analytical method for determining the effect of lateral inhomogeneity on tidal gravity, presented by Molodenskiy (1980), is introduced. Moreover, the current study reformulates the expressions for estimating the lateral inhomogeneity effects with respect to the unperturbed Earth and supplements some critical derivation process to enhance the method. The effects of lateral inhomogeneity are calculated using several real Earth models. By considering the collective contributions of seismic wave velocity disturbance and density disturbance, the global theoretical changes of semidiurnal gravimetric factor are obtained, which vary from −0.22 % to 0.17 % compared with those in a layered Earth model, no more than 1/3 of the ellipticity’s effect. The gravity changes caused by laterally-inhomogeneous disturbance are also computed, and turn out to be up to 0.16 % compared with the changes caused by tide-generating potential. The current study tests the importance of lateral inhomogeneity and other factors. The results indicate that the rotation, ellipticity, and inelasticity on tidal gravity are the most dominant factors, the ocean tide loading is the moderate one, and the lateral inhomogeneity is the least but not negligible factor, because the three-dimensional effect is comparable with ocean tide loading at some locations. Moreover, the amplitude of tidal gravity caused by lateral inhomogeneity is noticeable larger than the precision of superconducting gravimeters.
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