New GPS constraints on the motion of the Yakutat block

Abstract

Global Positioning System (GPS) measurements were made at Yakutat, on the Yakutat terrane of southern Alaska, to investigate the motion of the Yakutat block with respect to the North American plate and to help constrain motion along the Fairweather fault. The velocity of Yakutat derived from the GPS data is 44.1 +/- 1.9 mm/yr toward N37°+/- 4°W relative to stable North America. The magnitude of this velocity is similar to that of the Pacific plate predicted by NUVEL1A, although there is a significant difference in the azimuth of these two vectors. The motion of Yakutat relative to North America is almost exactly parallel to the strike of the Fairweather fault, suggesting that most deformation inboard of Yakutat is right-lateral strike slip on the Fairweather fault or faults parallel to it, and that significant motion normal to the Fairweather fault occurs offshore of Yakutat. The GPS velocity at Yakutat is also used to help constrain the slip rate and locking depth of the Fairweather fault.