Relative contribution of afterslip, non-linear viscous, and poroelastic processes to the early postseismic deformation field of the 2010 Maule earthquake

Large earthquakes impose differential stresses in the crust and upper mantle that are transiently relaxed during the postseismic phase mostly due to afterslip on the fault interface, viscoelastic relaxation in the lower crust and upper mantle, and poroelastic rebound in the upper crust. During the last years, the wealth of geophysical and geodetic observations, as well as great effort in forward and inverse modelling have allowed a better comprehension of the role of these mechanisms during the postseismic period. However, it is still an open question to what extent postseismic processes contribute to the surface deformation signal, especially during the early postseismic period. In this study, we use GNSS and InSAR observations collected in the first 48 days following the 2010 Maule earthquake in Chile along with a model approach that integrates afterslip, poroelasticity, and temperature-controlled power-law (non-linear viscosity) rheology. The afterslip distribution is obtained from a geodetic data inversion after removing the poro-viscoelastic component by forward modelling to the geodetic data. We find that our model approach explains the geodetic cumulative signal 14% better than a pure elastic model inverting for afterslip. This improvement is mainly produced by the better fit to the geodetic signal at the volcanic and back-arc regions due to the inclusion of non-linear viscoelastic processes, which can explain > 60% of the observed surface displacements in these regions. We also show that poroelastic processes play a significant role locally, specifically near the region where the coseismic slip was largest. Here, poroelastic processes explain most of the cumulative observed GNSS uplift signal and produce surface landward patterns that affect the horizontal GNSS component by up to 15% in the opposite direction. If poroelastic processes are ignored, our results reveal that the resulting afterslip amplitude is both amplified and suppressed by up to 40% in regions of ~50 x 50 km². Our findings have implications for the calculation of the postseismic slip budget, and therefore the seismic hazard assessment of future earthquakes.