Figure 1. Tectonic setting of the Alaska-Aleutian subduction zone. The gray shaded patches with dashed lines indicate the historical rupture regions. The light blue dashed line shows the tsunami source model of the 1938 Mw8.2 earthquake determined by Freymueller et al. (2021). The blue dashed line show an alternative rupture area of the 1938 Mw8.2 earthquake. The blue and red shadowed region indicate the coseismic rupture areas of the 2020 Mw7.8 Simeonof event (Xiao et al., 2022) and 2021 Mw 8.2 Chignik event, respectively. The two stars and two beach balls indicate the epicenters and GCMT solutions of the 2020 event (blue) and 2021 event (red), respectively. The orange cycles scaled by magnitude show the 30-day aftershocks following the 2021 event. The red cycles show the location of the GPS continue sites used in this study. Dashed light grey lines outlines the depth contours from the Slab2 model (Hayes et al., 2018). The white barbed line shows the plate boundary between the Pacific plate and the North American plate. The black arrow shows the Pacific plate velocity relative to the North American plate (DeMets et al., 2010).
Several coseismic rupture models have been published for the July 29, 2021, Mw8.2 Chignik earthquake (Elliott et al., 2022; Ye at al., 2022; Liu et al.,2022; Mulia et al., 2022), using different inversion assumptions and regularization methods, and slightly different coseismic observation data sets. Therefore, it is difficult to determine which coseismic model better recovers the actual slip distribution by using the coseismic observations only. Ye et al. (2022) argued that their model better resolv the up-dip portion of the coseismic slip distribution because they added tsunami data as an additional constraint, but for the down-dip portion of the coseismic rupture, each published model seems to do equally well in terms of fitting the coseismic observations. Despite the similarity in fit, the shape of the slip distributions of those models vary considerably at the down-dip end (Figure 2).