Modeling Long-Wavelength Geoid Anomalies from Instantaneous Mantle Flow: Results from Two Recent Tomography Models

Materials in the Earth’s mantle behave as fluids over geological time scales, and this behavior greatly influences geoid anomalies at the Earth’s surface. However, many uncertainties remain regarding the origins of the Earth’s geoid anomalies. Additionally, uncertainties about the viscosity ratios between the upper and lower mantles still exist. Therefore, we model long-wavelength geoid anomalies from instantaneous mantle flow based on the density structure inferred by two recent S-wave tomographic models, SEMUCB_WM1 and S40RTS. In the simulation, we introduce specific viscosity values for certain tectonic regions in the lithosphere and a temperature-dependent viscosity for the mantle beneath the lithosphere. We compute the correlations between the modeled geoid anomalies and observations. Our results show that the geoid anomalies modeled based on the two tomographic models, SEMUCB_WM1 and S40RTS, achieve the best fits with the observations and present correlation coefficients of approximately 0.77 and 0.75 when the viscosity ratios between the lower and upper mantle are 80 and 70, respectively. These values fall toward the end of viscosity contrasts suggested from some previous geodynamic studies, which were 30–100.