2 Seismotectonic and geologic setting
2.1 A transpressional plate boundary in southeast Alaska
The Fairweather fault juxtaposes the Yakutat block and the North America plate along >250 km of the curvilinear plate boundary that extends from Icy Point north-northwest to the vicinity of Yakutat Bay (latitude range 58.4°–60.0°N) (Plafker et al., 1978) (Figure 1). Witter et al. (2021) determined a Holocene slip rate of ≥49 mm/yr for the Fairweather fault at Crillon Lake (29 km north-northwest of Icy Point) from analyses of multiple offset fluvial channels cut into till and outwash, which is similar to the ~53 m/kyr slip rate estimate for the offshore Queen Charlotte fault 50 km to the southeast (Brothers et al., 2020). Elliott and Freymueller (2020) used horizontal crustal velocities from satellite geodesy to devise a block model that implies 44-46 mm/yr of right-lateral strike-slip motion between the Yakutat block and North America accommodated on the Fairweather fault. This decadal slip rate amounts to >90% of the strike-slip motion along the eastern margin of the Yakutat block. Block model results of Elliott and Freymueller (2020) also imply convergence normal to the plate boundary on reverse faults that build topography immediately west of the Fairweather fault.