Tectonic and sedimentary processes of the southeast Alaska margin

Strike-slip tectonics dominate the southeast Alaska margin. The Queen Charlotte-Fairweather Fault transform system extends ~1200 km from southern Canada north to Yakutat Bay, Alaska, accommodating nearly 4.5 cm/yr of dextral offset between the Pacific and North American plates. This dissertation aims to better characterize the transform plate boundary by examining the accommodation of oblique transpression, crustal structure, seismogenic faults, and tectonic influence on regional sedimentary processes. We address fundamental tectonic questions utilizing a suite of geophysical data including multichannel seismic (MCS) reflection, bathymetry, magnetics, gravity, and earthquake data. A 2011 MCS survey reveals subsurface channel deposits related to the development of the deep-sea Baranof sedimentary fan in the Gulf of Alaska. We find that Baranof Fan channels have avulsed consistently southward, affected by the changing position of channel heads relative to sediment sources along the shelf edge due to strike-slip motion along the Queen Charlotte Fault (QCF). Baranof Fan sediments sit atop a flexural depression in the Pacific crust near the QCF, which developed between ~6 Ma and ~2 Ma. We interpret the flexure to be an artifact of oblique convergence along the southern QCF, preserved by sedimentary loading in part from the Baranof Fan. ~150 km of the QCF near the Pacific flexural depression ruptured in January 2013, producing a M [subscript]w 7.5 earthquake near Craig, Alaska. A tomographic inversion of Craig aftershock data reveals a low velocity zone on the Pacific side of the plate boundary at seismogenic depths, which may indicate the contrast of a warm, young Pacific crust along the older, colder North American crust. These results have relevance for rupture directionality and future seismic hazard along the QCF. Finally, we revisit seismic hazard associated with the 10 September 1899 Mw 8.2 earthquake at the northern termination of the transform system near Yakutat Bay, Alaska. We quantify uncertainty on coseismic uplift measurements and integrate various geophysical data, including a 2012 MCS survey, to provide an updated fault map and tectonic model of the Yakutat Bay region. Our results support a subduction-related rupture of the 10 September event with limited slip along the transpressive termination of the Fairweather Fault.