1 Introduction
The Queen Charlotte–Fairweather Fault System—the fastest slipping
ocean-continent strike-slip fault on Earth (Molnar and Dayem, 2010;
Brothers et al., 2020)—defines the western North America plate
boundary in southeastern Alaska and western Canada. The Fairweather
fault traces the northern 250 km of this fault system and accommodates
>90% of the 53 mm/yr motion between the North America
plate and the Yakutat block (Plafker et al., 1978; Brothers et al.,
2020; Elliott and Freymueller, 2020). The Yakutat block, an
overthickened oceanic plateau (Plafker, 1987; Lahr and Plafker, 1980;
Bruns, 1983), is tectonically coupled to the Pacific Plate along the
Transition fault (Eberhart-Phillips et al., 2006; Christeson et al.,
2010) and both plates collide into southern Alaska (Figure 1).
Transpression along the northeastern margin of the Yakutat block, where
Cretaceous-Cenozoic sedimentary rocks obliquely collide with Chugach
metamorphic rocks of the Fairweather Range, focuses extreme rates of
horizontal and vertical deformation west of the Fairweather fault.
The 1958 moment magnitude (Mw) 7.8 Fairweather
earthquake nucleated at 16±4 km depth just north of Cross Sound (Doser
and Lomas, 2000; Doser, 2010) near the southern end of the Fairweather
fault where the plate boundary bends ~20° offshore to
the Queen Charlotte fault (Figures 1 and 2). The fault ruptured toward
the northwest through a restraining double bend (terminology after
Crowell (1974)) between Icy Point and Crillon Lake (Witter et al.,
2021), and continued breaking >260 km of the Fairweather
fault to at least the latitude of Yakutat Bay (Doser, 2010). The 1958
focal mechanism indicates a steep (88°E) fault plane striking 340°
northwest, similar to the 337° strike of the linear Queen Charlotte
fault trace in the seafloor (Brothers et al., 2020). Fault rupture
stepped on land at Icy Point and induced 3.5–6.5 m right-lateral
surface displacements on near-vertical faults striking 318°–322°
(Tocher, 1960) through