Present‐Day Vertical Land Motion of Australia From GPS Observations and Geophysical Models

Abstract

The secular rate of Australia's vertical surface deformation due to past ice‐ocean loading changes is not consistent with present vertical velocities observed by a previously sparse network of Global Positioning System (GPS) sites. Current understanding of the Earth's rheology suggests that the expected vertical motion of the crust should be close to zero given that Australia is located in the far field of past ice sheet loading. Recent GPS measurements suggest that the vertical motion of the Australian continent at permanent sites is between 0 and −2 mm/year. Here we investigate if vertical deformation due to previous ice sheet loading can be recovered in the time series of Australian GPS sites through enlarging the number of sites compared to previous studies from ~20 to more than 100 and through the application of improved data filtering. We apply forward geophysical models of elastic surface displacement induced by atmospheric, hydrologic, nontidal ocean, and ice loading and use independent component analysis as a spatiotemporal filter that includes multivariate regression to consider temporally correlated noise in GPS. Using this approach, the common mode error is identified, and subsequent multivariate regression leads to an average reduction in trend uncertainty of ~35%. The average vertical subsidence of the Australian continent is substantially different to vertical motion predicted by glacial isostatic adjustment and surface mass transport models.

Vertical Deformation and Residual Altimeter Systematic Errors around Continental Australia Inferred from a Kalman-Based Approach

“…The average uncertainties from our approach at GPS and TG sites were 0.65 and 0.71 mm/yr, respectively, comparable with 0.83 and 0.87 mm/yr inferred from Hector-derived (at GPS) and GPS-Krig (at TG) uncertainties, respectively. The GPS-inferred VLM field showed that the Australian plate is largely subsiding with weighted mean rates of -0.10, -0.38, -0.95 and -0.62 mm/yr in the NW, NE, SW and SE regions, respectively, in general agreement with previous GPS estimates of subsidence (Hammond et al, 2021;Riddell et al, 2020). The estimates at TGs revealed localized VLM trends around the continent that are not completely consistent with the GPS-Krig interpolations.…”

“…GPS observations of VLM across Australia suggest the continent is subsiding overall (Hammond et al, 2021;King et al, 2012;Riddell et al, 2020). Recent work by Riddell et al (2020) using GPS time series showed the widespread pattern of subsidence cannot be fully explained by GIA.…”

“…GPS observations of VLM across Australia suggest the continent is subsiding overall (Hammond et al, 2021;King et al, 2012;Riddell et al, 2020). Recent work by Riddell et al (2020) using GPS time series showed the widespread pattern of subsidence cannot be fully explained by GIA. Earlier work also suggested subtle subsidence from spatially interpolating linear GPS rates to many Australian TGs (e.g., Burgette et al, 2013;White et al, 2014).…”

Modeling Seasonal Variations in Vertical GPS Coordinate Time Series Using Independent Component Analysis and Varying Coefficient Regression

“…Gruszczynska et al [ 30 ] used multichannel singular spectrum analysis (MSSA) to model the common seasonal signals in GPS observations in different regions around the world and without influencing the high frequency part of the spectra. Some other data-driven mathematical methods have been proposed to be used in modeling the geophysical signals from regional geodetic time series, e.g., principle component analysis (PCA) and independent component analysis (ICA), which have been widely used in smoothing and modeling GPS time series [ 15 , 23 , 31 , 32 , 33 , 34 , 35 , 36 , 37 ]. ICA has especially been widely used in the separation of potential sources of seasonal signals in vertical GPS coordinate time series, and the main independent components (ICs) were thought to be consistent with some of the geophysical signals [ 32 , 33 , 34 ].…”

Characteristics of seasonal variations and noises of the daily double-difference and PPP solutions

“…Continuous GNSS (Global Navigation Satellite System) time series has been extensively used in Earth surface motion monitoring (e. g., plate tectonics [1,2], sea-level variation [3,4], polar research [5] and other [6,7]). Multi-year combination dense GNSS network solutions of the EPN weekly SINEX files [8] play an important role in providing accurate stations' positions and velocities in the European territory.…”