A comparative of ocean tide loading displacements modeling and GPS observations in Australia

Accurate observations of ocean tide loading (OTL) displacements can serve as valuable constraints on the Earth′s shallow structure. We use a decade of GPS data from 403 stations across Australia to estimate tidal displacements for the M2 and O1 constituents using a static precise point positioning method. These GPS-observed tidal displacements are then compared with modeled OTL displacements computed from different Earth models and global tidal models. Our results show that the TPXO10-atlas global tidal model provides the most accurate representation of OTL displacements in Australia. The residuals between GPS-observed and modeled OTL displacements exhibit continent-scale spatial coherence, which may be attributed to errors in the a priori body tide model and systematic errors related to Earth′s deep internal structure. To investigate the impact of shallow crust and upper mantle structure on OTL modeling errors, we apply a thin-plate spline function to fit and remove the residuals using inland stations data. After accounting for the body tide model and other systematic errors, the root mean square (RMS) misfits for the M2 constituent at coastal stations decrease from 0.49 mm, 0.47 mm, and 0.50 mm to 0.12 mm, 0.17 mm, and 0.41 mm in the east, north, and vertical components, respectively. For the O1 constituent, the RMS misfits decrease from 0.19 mm, 0.44 mm, and 0.45 mm to 0.08 mm, 0.06 mm, and 0.18 mm, respectively. However, residuals at coastal stations still display regional coherence, primarily caused by the deficiencies of the Earth model in the upper mantle and crust. In particular, the modeled OTL displacements for the vertical component of the M2 constituent are the most sensitive to the Earth model. When considering the effects of anelastic dissipation in the asthenosphere, vertical M2 residuals are reduced by up to 0.65 mm, corresponding to a 22% decrease in RMS misfit. Further incorporating the CRUST1.0 model into OTL displacement modeling for southeastern Australia yields an additional reduction in vertical M2 residuals by up to 0.27 mm, with an 11% decrease in RMS misfit. Despite these refinements, residuals in all three components for both the M2 and O1 constituents still exhibit regional consistency, suggesting that they are largely attributable to unmodeled features in Earth′s shallow structure in this region.