No abstract

In this study, a new approach for the computation of coseismic gravity gradient changes in a spherically symmetric Earth model is presented. We derived the mathematical expressions of gravity gradient changes based on the Green's functions for four independent seismic sources. The results obtained from numerical computations and those calculated using the flat‐Earth model are in good agreement within a near field, verifying that our computing scheme is valid, while the differences in the far field show the advantages of the spherical model. Furthermore, the proposed method was applied to analyze the coseismic gravity gradient changes caused by the 2011 Tohoku‐Oki earthquake. The theoretical gravity gradient changes agree well with the Gravity Recovery and Climate Experiment observations, indicating that the proposed dislocation theory is important and can be used to efficiently interpret seismic deformations. In addition, the contribution of seawater was discussed.

The Earth’s synthetic density and gravitational models can be used to validate numerical methods for global (or large-scale) gravimetric forward and inverse modelling formulated either in the spatial or spectral domains. The Preliminary Reference Earth Model (PREM) density parameters can be adopted as a 1-D reference density model and further refined using more detailed 2-D or 3-D crust and mantle density models. Alternatively, the AK135-F density parameters can be used for this purpose. In this study, we investigate options for a refinement of the Earth’s synthetic density model by assessing the accuracy of available 1-D density models, specifically the PREM and AK135-F radial density parameters. First, we use density parameters from both models to estimate the Earth’s total mass and compare these estimates with published results. We then estimate the Earth’s gravity field parameters, particularly the geoidal geopotential number W0 and the mean gravitational attraction and compare them with published values. According to our results, the Earth’s total mass from the two models (the PREM and the AK135-F) differ less than 0.02% and 0.01%, respectively, when compared with the value adopted by the International Astronomical Union (IAU). The geoidal geopotential values of the two models differ from the value adopted by the IAU by less than 0.1% and 0.04%, respectively. The values of the mean gravitational attraction of the two models differ less than 0.02% and 0.08%, respectively, when compared with the value obtained from the geocentric gravitational constant and the Earth’s mean radius. These numerical findings ascertain that the PREM and AK135-F density parameters are suitable for defining a 1-D reference density model.