Tectonic block motion and glacial isostatic adjustment in southeast Alaska and adjacent Canada constrained by GPS measurements

We use data from campaign and continuous GPS sites in southeast Alaska and the neighboring region of Canada to constrain a regional tectonic block model that estimates block angular velocities and derives a self-consistent set of fault slip rates from the block motions. Present-day tectonics in southeast Alaska is strongly influenced by the collision of the Yakutat block. Our model predicts a velocity of 50.3 +/- 0.8 mm/a toward N22.9 +/- 0.6 degrees W for that block. Our results suggest that the eastern edge of the Yakutat block is deforming. Along this edge, the Fairweather fault accommodates a large portion of the Pacific-North America relative plate motion through 42.9 +/- 0.9 mm/a of dextral slip. Further south along the Queen Charlotte fault, our model predicts an average of 43.9 +/- 0.6 mm/a of dextral slip and a southward increasing amount of transpression. Strain from the Yakutat collision is transferred far to the east of the strike-slip system. This strain transfer causes the region north of Glacier Bay to undergo a clockwise rotation. South of Glacier Bay and inboard of the Queen Charlotte fault, a smaller but clearly defined clockwise rotation is observed. The heterogeneous block motion north and south of Glacier Bay may indicate the area is undergoing internal deformation and could explain regional patterns of diffuse seismicity. The Northern Cordillera of Canada displays a small northeasterly motion. Our block model suggests that the entire southeastern Alaska-northwestern Canada margin is mobile.