NH23B-1882
High-Resolution Geophysical Constraints on Late Pleistocene–Present Deformation History, Seabed Morphology, and Slip-Rate along the Queen Charlotte-Fairweather Fault, Offshore Southeastern Alaska
Tuesday, 15 December 2015
Poster Hall (Moscone South)
Daniel S Brothers1, Peter J Haeussler2, Peter Dartnell3, James E Conrad4, Jared W Kluesner3, Patrick E Hart5, Robert Carleton Witter2, Alicia F Balster-Gee6, Katherine L Maier7, Janet Tilden Watt8 and Amy E East1, (1)USGS Pacific Coastal and Marine Science Center Santa Cruz, Santa Cruz, CA, United States, (2)USGS Alaska Science Center, Anchorage, AK, United States, (3)USGS, Santa Cruz, CA, United States, (4)USGS Western Regional Offices Menlo Park, Menlo Park, CA, United States, (5)USGS California Water Science Center Menlo Park, Menlo Park, CA, United States, (6)Pacific Coastal and Marine Science Center Santa Cruz, Santa Cruz, CA, United States, (7)Organization Not Listed, Washington, DC, United States, (8)USGS California Water Science Center Sacramento, Sacramento, CA, United States
Abstract:
The Queen Charlotte-Fairweather Fault (QCFF) of southeastern Alaska and British Columbia is the dominant fault along the 1200 km-long transform boundary between the Pacific and North American plates. More than 900 km of the QCFF lies offshore where the style and rates of deformation are poorly constrained due to a lack of high-resolution marine geophysical data. In May 2015, the USGS acquired ~900 km2 of high-resolution multibeam bathymetry data and >2000 line-km of high-resolution multichannel seismic reflection profiles between Cross Sound, Yakobi Sea Valley, and Icy Point (the northernmost offshore section of the QCFF) using a 24-ch streamer and 500 Joule minisparker source. During a second cruise in August 2015 we conducted targeted multichannel seismic and subbottom CHIRP profiling in the same region. The new data reveal a single trace of the QCFF expressed as a clear and remarkably straight seafloor lineation for >60 km. Subtle jogs in the fault (<3 degrees) are associated with pop-up structures and en echelon pull-apart basins. The near surface deformation along the fault never exceeds a width of 1.2 km. Northward, as the fault approaches Icy Point and a restraining bend, it splays into multiple strands and displays evidence for uplift and transpression. The fault appears to transition from almost purely strike-slip in the south to oblique-convergence as it steps onshore to the north. The QCFF cuts through the Yakobi Sea Valley and Cross Sound, two elongate bathymetric troughs that were filled with glaciers as recently as 17–19 ka. The southern wall of the Yakobi Sea Valley is offset 890±30 m by the QCFF, providing a late Pleistocene–present slip-rate estimate of 45–54 mm/yr. This suggests that nearly the entire plate boundary slip budget is confined to a single, narrow, strike-slip fault zone, which may have implications for models of plate boundary strain localization.
