Post-seismic motion after 3 Chilean megathrust earthquakes: a clue for a linear asthenospheric viscosity

Over the last decade, three major subduction earthquakes, Maule M-w 8.8 (2010), Illapel M-w 8.3 (2015) and Iquique M-w 8.1 (2014), occurred in Chile and generated significant post-seismic deformations. These large scale and long lasting deformations can be quantified with modern GNSS precise positioning and highlight viscoelastic processes in the asthenosphere. Here, we calculate the ratios of cumulative post-seismic displacements after 5 yr over the coseismic offsets. We find that at any distance from the trench, ratios are similar for the three earthquakes despite their different magnitudes which imply induced stresses that are more than one order of magnitude apart. This observation suggests that the post-seismic deformation is related to the same effective viscosity for the three earthquakes, indicating Newtonian rheology, rather than power-law rheology in the asthenosphere.