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).