Abstract Postseismic displacements associated with the 2001 Mw 8.4 Arequipa earthquake have been observed on a continuous GNSS timeseries in Arequipa for over two decades (∼30 cm on horizontal components). Using Finite Element Method (FEM), we explore the rheological properties of the South Peru subduction zone to model this temporal evolution, and we quantify the effects of the postseismic processes on the interseismic coupling assessment with viscoelastic Green’s functions. Using one continuous and eight survey GNSS timeseries as constraints, we found that a Burgers rheology in the asthenosphere (Maxwell viscosity ηM ${\eta }{M}$ = 9 × 1018 Pa·s, Kelvin viscosity ηK ${\eta }{K}$ = 5 × 1018 Pa·s) with an elastic cold‐nose fits best the pattern. The postseismic processes affect the interseismic coupling distribution and moment deficit rate, raising their values by 9% over the South Peru segment and up to 24% in the vicinity of the 2001 Arequipa earthquake rupture. These values remain within the uncertainties from Lovery, Chlieh, et al. (2024, https://doi.org/10.1029/2023jb027114).

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