Oblique contraction along the fastest ocean-continent transform plate boundary focuses rock uplift west of the Fairweather fault, southeast Alaska

Abstract

Contraction along the Yakutat–North America plate boundary drives 4.6–9.0 mm/year Holocene rock uplift rates along Earth's fastest slipping (≥49 mm/year) ocean–continent transform fault, the Fairweather Fault. Between Icy Point and Lituya Bay, the near-vertical Fairweather fault focuses rock uplift and rapid right-lateral slip by accommodating both vertical and fault-parallel strain during oblique-slip and separate, predominantly strike-slip ruptures. Unusually high uplift rates, indicated by radiocarbon and luminescence dating, result from a 10-km-wide, asymmetric, positive flower structure along a 20°, ∼30-km-long restraining double bend in the Fairweather fault. The principal reverse fault in the flower structure, the offshore, blind Icy Point–Lituya Bay fault, ruptures no more than every 460–1040 years evidenced by uplifted Holocene shorelines. Maximum 3–5 m coseismic uplifts imply 3.1–10 m dip slip per event and earthquake magnitudes of M w 7.0–7.5. The Yakutat block collides obliquely into North America, and our model entails oblique slip on the Fairweather fault with and without corupture on the reverse fault. Oblique slip is evident by vertically offset (>25 m) fluvial and marine terraces and by the primary Fairweather fault strand that strikes >20° to the west of plate-boundary motion.