Analysis of Shear Wave Splitting Patterns in Alaska: Evidence for Strong Intra‐Slab Anisotropy

Abstract Shear wave splitting (SWS) patterns at subduction zones are often interpreted by complex mantle flow above or below the slab. However, our recent previous work shows dipping anisotropic slabs can explain observed patterns in Japan. Here, we extend this analysis to the Alaska subduction zone, using 2,567 high‐quality teleseismic SWS measurements from 195 broadband stations. As was found in Japan, the observed SWS patterns in Alaska depend on earthquake backazimuth. The fast‐S polarization directions are either trench parallel or perpendicular in southeastern Alaska and form a prominent circular pattern in central Alaska. We found that a dipping anisotropic slab following the Slab 2.0 geometry, with 30% shear anisotropy, and exhibiting tilted transverse isotropy with a symmetry axis normal to the slab interface, predicts both the fast‐S polarizations and delay times ( δt = 1.0–1.5 s). This suggests that intra‐slab anisotropy can be the primary control on SWS, without requiring complex mantle flow.