Anisotropic Pn Tomography of Alaska and Adjacent Regions

Abstract

Abstract We use Pn tomography with coordinate rotation to image in Alaska and adjacent areas and obtain a new Pn velocity and anisotropy model. The observed Pn velocities correlate well with the local geological structures. Low Pn velocities are observed beneath the Aleutian volcanic arc, which may reveal partial melting related to plate dehydration. However, it is separated by a distinct high‐velocity anomaly, suggesting a slab tear. The slightly low Pn velocities beneath the Denali volcanic gap suggest that a small amount of magma is produced but is insufficient to form surface volcanoes. We observe sharp bending of the fast directions on the two sides of the northeast edge of the Yakutat Plate, which reveals the plate’s bending. Large‐scale low velocities are observed beneath the northwestern Cordillera, which may be due to the upwelling of hot material from the deep mantle. The Pn fast directions are parallel to the Queen Charlotte‐Fairweather fault system, consistent with the shear strain direction of the faults, reflecting that the influence of the plate boundary is far‐reaching and that the deformation of the crust and the upper mantle is coupled. Our study provides new constraints on the complex deformation beneath Alaska and adjacent areas.