3.2.2 Viscoelastic Relaxation Simulation
Although afterslip is likely to be the dominant process in the early
period of the post-seismic deformation, for an Mw8.2 event it is
necessary to consider the viscoelastic contribution to the observed
post-seismic signal as well (Sun and Wang, 2015. However, it is known to
be difficult to separate the two post-seismic processes in the early
time period Sun and Wang, 2015. Therefore, we consider a range of
viscoelastic relaxation models based on different assumed viscoelastic
structures, subtract these from the data, and then estimate the
best-fitting afterslip model for each.
The numerical simulation we use is the software package VISCO2.5D, which
imposes source and domain boundary conditions on a 2-D structure to
approximate the 3-D equations of quasi-static equilibrium by the
spectral element method (Pollitz, 2014). We use the Slab2.0 slab
geometry at the center of the coseismic rupture and assume a laterally
homogeneous viscosity structure (Figure 4a, b). The elastic slab
separates the sub-oceanic asthenosphere from the mantle wedge. We vary
the viscosity in the mantle wedge, and include a 90km thick elastic slab
(including its mantle lithosphere). We also varied the continental
lithosphere thickness and the presence of a cold nose to the mantle
wedge (e.g., Luo and Wang, (2021)). All of these model assumptions
affect our model predictions (see section 4.2).
(a) (b)