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Shear wave splitting of teleseismic core phases such as SKS is commonly used to constrain mantle seismic anisotropy, a proxy for convective deformation. In plate boundaries, sharp lateral variations of splitting measurements near transform faults are often linked to deformation within a lithospheric shear zone below, but potential seismic waveform effects from heterogeneous structure on small scales may influence the interpretation. Here, we explore possible finite frequency effects on shear wave splitting near fault zones in a fully three‐dimensional anisotropic setting. We find that shear zones wider than 80 km, a scale set by the Fresnel zone, can be clearly detected, but narrower zones are less distinguishable. Near the edge of the shear zone, the combined effect of anisotropy and scattering generates false splitting measurements with large delay times and fast axis orientation approaching the back‐azimuth, a bias which can only be identified when records from different back‐azimuths are analyzed together. This substantiates that back‐azimuthal variations of splitting can arise not just from vertical layering but also lateral changes of anisotropic media. We also test the effects of shear zone edge geometry, epicentral distance, filtering frequency, crustal thickness, and sediment cover. Our study delineates the ability of shear wave splitting to resolve and investigate fault zones, and emphasizes the importance of good azimuthal coverage to correctly interpret observed anisotropy. Based on revisiting previous shear wave splitting and lithospheric deformation studies, we infer that many crustal fault zones are underlain by lithospheric shear zones at least 20 km wide. 

Azimuthal variations in receiver function conversions can image lithospheric structural contrasts and anisotropic fabrics that together compose tectonic grain. We apply this method to data from EarthScope Transportable Array in Alaska and additional stations across the northern Cordillera. The best-resolved quantities are the strike and depth of dipping fabric contrasts or interfaces. We find a strong geographic gradient in such anomalies, with large amplitudes extending inboard from the present-day subduction margin, the Aleutian arc, and an influence of flat-slab subduction of the Yakutat microplate north of the Denali fault. An east–west band across interior Alaska shows low- amplitude crustal anomalies. Anomaly amplitudes correlate with structural intensity (density of aligned geological elements), but are the highest in areas of strong Cenozoic deformation, raising the question of an influence of current stress state. Imaged subsurface strikes show alignment with surface structures. We see concentric strikes around arc volcanoes implying dipping magmatic structures and fabric into the middle crust. Regions with present-day weaker deformation show lower anomaly amplitudes but structurally aligned strikes, suggesting pre-Cenozoic fabrics may have been overprinted or otherwise modified. We observe general coherence of the signal across the brittle-plastic transition. Imaged crustal fabrics are aligned with major faults and shear zones, whereas intrafault blocks show imaged strikes both parallel to and at high angles to major block-bounding faults. High-angle strikes are subparallel to neotectonic deformation, seismicity, fault lineaments, and prominent metallogenic belts, possibly due to overprinting and/or co-evolution with fault-parallel fabrics. We suggest that the underlying tectonic grain in the northern Cordillera is broadly distributed rather than strongly localized. Receiver functions thus reveal key information about the nature and continuity of tectonic fabrics at depth and can provide unique insights into the deformation history and distribution of regional strain in complex orogenic belts.