Function Model Based on Nonlinear Transient Rheology of Rocks: An Analysis of Decadal GNSS Time Series After the 2011 Tohoku-oki Earthquake

The postseismic Global Navigation Satellite System (GNSS) time series after the 2011 Tohoku-oki earthquake is often empirically explained by one or more logarithmic and exponential decay functions. However, a function model with these decay functions struggles to illuminate various deformation mechanisms. Here, we propose a new function model incorporating laboratory-derived constitutive laws (power-law flow and velocity-strengthening friction) utilized in mechanical postseismic models of the last decade. We demonstrated that our function model accurately predicts the decade-long time series of inland GNSS stations, including coastal areas where significant postseismic uplift continues now. Moreover, it decomposes them into displacements due to viscoelastic relaxation and afterslip, similar to results produced by previous stress-dependent postseismic models of the 2011 Tohoku-oki earthquake. This physics-based function model is an effective tool to ease the process of forecasting long-term GNSS time series by dividing them into two dominant mechanisms at the plate interface and the surrounding viscoelastic mantle.