GNSS receiver distribution in Chile and Argentina. Cyan crosses denote the location of the GNSS receivers, and the red star denotes the epicenter of the M_w 8.3 EQ, on September 16, 2015. The grid cells (a)–(d) denote four subnetworks with a geographical grid of 10° × 10°. The ocean depth is shown by the cold color map, originating from the Earth observatory of the US NASA blue marble with topography and bathymetry.