Viscoelastic relaxation and afterslip following the 2008 Mw 7.9 Wenchuan earthquake

Post-seismic deformation following big earthquakes can help to better analyze the rheological structure of the lithosphere and geodynamic processes. The extensive and long-lasting post-seismic deformation following the 2008 M_w7.9 Wenchuan earthquake offers a unique opportunity. This study constructed a three-dimensional (3D) viscoelastic finite element model of the eastern Tibetan Plateau and calculate the post-seismic deformations of the 2008 M_w7.9 Wenchuan earthquake using four rheological models (Maxwell, Kelvin, Poynting-Thomson, and Burgers). The results show that among these four viscoelastic models, the Burgers model provides the best fit to the post-seismic deformation of the Wenchuan earthquake, but there is still a lack of early deformation near the co-seismic rupture zone. We then also analyze the impact of the afterslip on post-seismic deformation using three different afterslip models. The results show that afterslip plays a dominant role in the early post-seismic deformation, especially in the near field of the rupture zone. The optimal Burgers model combined with afterslip can better explain the post-seismic deformation of the Wenchuan earthquake. The optimal steady-state viscosities for the middle-lower crust and upper mantle of the Songpan-Ganzi block are 7 × 10¹⁸ Pa·s and 6 × 10¹⁹ Pa·s, respectively.