Razor-Sharp Edge—The Yakutat Slab Dissecting South-Central Alaska

The tectonics of south-central Alaska are dominated by subduction of the Pacific plate, the Yakutat oceanic plateau, and evolution of the major continental fault system, the Denali fault. Our new structural images show the razor-sharp edge and extent of the Yakutat slab as it subducts beneath the North American plate with remarkable detail. Thousands of small, previously undetected earthquakes form a prominent linear cluster that illuminates the precise edge of the subducted Yakutat microplate and defines the location of changing slab morphology reflecting the change in stress state. Our new seismic images and refined locations of down-dipping seismicity further elucidate the lack of mantle wedge below the Denali volcanic gap and the northeastern margin of the subducted Yakutat microplate, imaged here to be directly below the curved section of the Denali fault. We suggest these features have controlled the nucleation of the 2002 Mw 7.9 Denali fault earthquake and the position of recently onset volcanic fields.