HR: 16:30h
AN: G14A-03    [Abstracts]
TI: Accommodation of Plate-Boundary Strain in the Northern Cordillera of NW Canada and E Alaska from Earthquake Statistics and GPS
AU: * Leonard, L J
EM: lleonard@nrcan.gc.ca
AF: School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055 STN CSC, Victoria, BC V8W 3P6, Canada
AU: * Leonard, L J
EM: lleonard@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada, 9860 West Saanich Road, Sidney, BC V8L 4B2, Canada
AU: Mazzotti, S
EM: smazzotti@nrcan.gc.ca
AF: School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055 STN CSC, Victoria, BC V8W 3P6, Canada
AU: Mazzotti, S
EM: smazzotti@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada, 9860 West Saanich Road, Sidney, BC V8L 4B2, Canada
AU: Hyndman, R D
EM: rhyndman@nrcan.gc.ca
AF: School of Earth and Ocean Sciences, University of Victoria, P.O. Box 3055 STN CSC, Victoria, BC V8W 3P6, Canada
AU: Hyndman, R D
EM: rhyndman@nrcan.gc.ca
AF: Pacific Geoscience Centre, Geological Survey of Canada, 9860 West Saanich Road, Sidney, BC V8L 4B2, Canada
AB: Current collision of the Yakutat block with N. America is accommodated over a large region of the Canada-Alaska Northern Cordillera. We investigate this plate-boundary strain distribution using continuous and campaign Global Positioning System (GPS) data and deformation rates estimated from earthquake catalog statistics. Seismic deformation estimates have significant uncertainties, but generally agree with other estimates (GPS, geological, plate models) and provide useful first-order constraints on local long-term tectonics and seismic hazard. Our GPS data infer that the relative Yakutat/N. America motion is accommodated to the east by near-field right- lateral motion (~ 40 mm/yr), mainly on the Fairweather fault, and minor shortening (~ 6 mm/yr). To the north, collision is taken up by fold-and-thrust belt shortening (~ 31 mm/yr), with westward extrusion and possible counter-clockwise rotation of the Yakutat block and Alaskan forearc facilitated by ~ 23 mm/yr distributed dextral shear. We estimate that 50-75% of the relative plate motion is taken up by earthquakes on the Yakutat/N. America boundaries. The remainder must be accommodated by lateral crustal extrusion, other far-field strain, and possibly aseismic creep. Significant seismic strain occurs throughout E. Alaska, Yukon and W. Northwest Territories, inferring that plate- boundary deformation is far-reaching. GPS data enable the extent of this deformation to be mapped, thereby defining the NW edge of "stable" N. America. GPS sites in SW Yukon show motion of 3-10 mm/yr to the NE, confirming strain transfer at least 400 km from the Yakutat collision. We calculate dextral slip at 5-10 mm/yr on the Denali fault system in Alaska, similar to late Pleistocene/Holocene rates from geomorphic offsets. Right-lateral motion bypasses the Denali fault in easternmost Alaska and westernmost Yukon, passing along the Totschunda and Duke River fault systems. Significant seismic deformation (in cases higher than suggested by GPS) occurs throughout the N. Cordillera, where pre-existing faults have a strong control on the pattern and mechanisms of current deformation.
DE: 1243 Space geodetic surveys
DE: 7230 Seismicity and tectonics (1207, 1217, 1240, 1242)
DE: 8150 Plate boundary: general (3040)
DE: 9350 North America
SC: Geodesy [G]
MN: 2007 Fall Meeting