Estimation of continental scale vertical crustal velocities using GPS and GRACE

The spatial density of crustal motion observations from continuous Global Positioning System (cGPS) networks continues to increase, providing ever more detailed information about the various processes that deform Earth's surface. The signatures of tectonic and mantle processes of interest to solid earth geophysicists are often obscured by deformation due to anthropogenic sources and hydrological loading, which suggests a need for geodetic datasets with these signals removed. To this end, we produce a vertical velocity field for the continental United States using data from over 1200 cGPS stations in operation from 2007 to 2017, removing the contribution of stations affected by poroelastic deformation and other shallow Earth processes. Since cGPS displacements include Earth's elastic response to long term hydrologic loading, we also correct for hydrological loading effects by calculating and removing expected displacements from surface water mass variability obtained by the Gravity Recovery and Climate Experiment (GRACE). We observe centimeter-level differences in hydrologic load between different GRACE analysis centers and we use this information to estimate uncertainties for the calculated GRACE displacements. We further analyze the spatial patterns of correlation between cGPS and GRACE displacements to understand the spatial scales at which the two datasets can best be used together for extracting solid earth signals. Our re-evaluated displacement data provide a continental-scale vertical velocity field without contributions from hydrology or glacial isostatic rebound, and our analysis shows evidence of long-wavelength deformation that may reflect tectonics and underlying mantle dynamics.