Surface Wave Isotropic and Azimuthally Anisotropic Dispersion Across Alaska and the Alaska-Aleutian Subduction Zone

Comprehensive observations of surface wave anisotropy across Alaska and the Aleutian subduction zone are needed to improve understanding of its tectonics, mantle dynamics, and earthquake risk. We produce such observations, using stations from the USArray Transportable Array and regional networks across Alaska and the Alaska Amphibious Community Seismic Experiment in the Alaska-Aleutian subduction zone both onshore and offshore. Our data include Rayleigh and Love wave phase dispersion from earthquakes (28-85 s) and ambient noise two- and three-station interferometry (8-50 s). Compared with using two-station interferometry alone, three-station interferometry significantly improves the signal-to-noise ratio and approximately doubles the number of measurements retained. Average differences between both isotropic and anisotropic tomographic maps constructed from different methods lie within their uncertainties, which is justification for combining the measurements. The composite tomographic maps include Rayleigh wave isotropy and azimuthal anisotropy from 8 to 85 s both onshore and offshore, and onshore Love wave isotropy from 8 to 80 s. In the Alaska-Aleutian subduction zone, Rayleigh wave fast directions vary from trench parallel to perpendicular and back to parallel with increasing periods, apparently reflecting the effect of the subducted Pacific Plate. The tomographic maps provide a basis for inferring the 3-D anisotropic crustal and uppermost mantle structure across Alaska and the Aleutian subduction zone.