5.4 Constraints on the Updip Coseismic Slip Distribution and
Postseismic Mechanisms
The updip portion of the published coseismic slip models varies
considerably (Figures 2, 7), and it remains un which model better
resolves the up-dip portion of the coseismic slip. The Ye et al. (2022)
and Liu et al. (2023) models used tsunami data to iteratively adjust the
coseismic model. These models differ from the Elliott et al. (2022), Liu
et al. (2022) and Mulia et al. (2022) model in having a distinct slip
patch that has very large slip magnitude (~ 10m) and a
rake of 45 degree under Chirikof island. Aside from that shallow patch,
the Ye et al. (2022) and Liu et al. (2023) models overall restrict slip
to greater depths than do the Elliott et al. (2022) model, or the models
shown here. However, the solutions fit the tsunami data are not unique.
Liu et al., (2023) Figure S7 shows that the Elliott et al., (2022)
model, which has about ~1m slip extending slightly
beyond the continental shelf break, also fits the tsunami data well.
Brooks et al. (2023) modeled the coseismic (and 2.5 month postseismic)
displacement from a GNSS-Acoustic site seaward of the Chignik rupture
and have also argued for greater slip extending to shallower depths than
some of the models proposed, although the slip could be in the form of
rapid shallow afterslip.
Its more difficult to constrain the up-dip post-seismic slip compared to
the downdip portion. The main limitation is that we only have one GPS
continuous site, AC13, at the updip end of the coseismic rupture area.
Stress-driven afterslip models do not predict the very large postseismic
displacement at AC13, unless they include a large coseismic slip patch
very close to AC13 (like the Ye et al., (2022) and Liu et al., (2023)
models). However, considering the magnitude of this earthquake and the
location of site AC13, the effects of poroelastic relaxation, depth
variations in the frictional parameters (e.g., Tian et al. (2023)), the
potential existence of a weak sub-slab oceanic mantle layer could also
affect the model prediction. Thus, there could be considerable
non-uniqueness in the model. Due to the limited number of GPS sites
located at the updip end of the coseismic rupture, it is difficult to
fully separate the postseismic mechanisms, making it also difficult to
assess the exact contribution of shallower afterslip and the shallower
portion of coseismic slip of this event. A significant expansion of
seafloor geodesy will be required to answer those remaining questions.