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