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Abstract:
Large subduction earthquakes induce complex postseismic deformation, primarily driven by afterslip
and viscoelastic relaxation, in addition to interplate relocking processes. However, these signals
are intricately intertwined, posing challenges in determining the timing and nature of relocking.
Here, we use six years of continuous GNSS measurements (2015–2021) to study the spatiotemporal
evolution of afterslip, seismicity and locking after the 2015 Illapel earthquake ( M w 8.3). Afterslip is
inverted from postseismic displacements corrected for nonlinear viscoelastic relaxation modeled
using a power‑law rheology, and the distribution of locking is obtained from the linear trend of GNSS
stations. Our results show that afterslip is mainly concentrated in two zones surrounding the region
of largest coseismic slip. The accumulated afterslip (corresponding to M w 7.8) exceeds 1.5 m, with
aftershocks mainly occurring at the boundaries of the afterslip patches. Our results reveal that the
region experiencing the largest coseismic slip undergoes rapid relocking, exhibiting the behavior
of a persistent velocity weakening asperity, with no observed aftershocks or afterslip within this
region during the observed period. The rapid relocking of this asperity may explain the almost regular
recurrence time of earthquakes in this region, as similar events occurred in 1880 and 1943.
