Characterizing the Spatial Patterns of Vertical Crustal Deformations Over the South American Continent Based on GNSS Imaging

Aiming to characterize the spatial patterns of vertical crustal motions over the South American continent, the position time series of 601 GNSS sites located in this region are analyzed. Firstly, we model the time-series through a combination of long-period linear trends, periodic seasonal variations, co- and post-seismic effects, obtaining an estimate of the vertical velocity. Then, we image the vertical velocities and annual signals implementing a Median Spatial Filtering (MSF) procedure with an empirical Spatial Structure Function (SSF) to reveal the spatial patterns of vertical crustal motions in the South American continent. Meanwhile, in order to better explore the vertical crustal motions, we also estimate the surface mass changes over this region based on Gravity Recovery and Climate Experiment (GRACE). For the image of annual signals, the large values are focused on the Amazon basin, and the region with larger amplitudes is located near the Amazon River. Compared with the image of annual signals, the spatial patterns of the image of vertical velocities over the South American continent are relatively complex. The result indicates that large-scale subsidence occurs at two regions (i.e., Amazon basin and Pampas steppe), and three regions (i.e., southern Brazilian Plateau, Chile, and Gran Chaco Plain) exhibit large-scale uplift. By combining the GNSS-derived velocity field with the surface mass changes determined by GRACE, we speculate the large-scale subsidence with rates ranging from 1 to 3.3 mm/yr can be attributed to the long-term gain of surface mass. Meanwhile, the subduction of Nazca plate is the dominant factor of the significant crustal uplift in most regions of Chile. As for the southern Chile, the small-scale anomalous uplift is mainly due to the serious surface mass loss induced by the glaciers melting in the Patagonian Icefield.