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SUMMARY The Alaska–Aleutian subduction zone represents an ideal location to study dynamics within a mantle wedge. The subduction system spans several thousand kilometres, is characterized by a slab edge, and has ample seismicity. Additionally, the majority of islands along the arc house broad-band seismic instruments. We examine shear wave splitting of local-S phases originating along the length of the subduction zone. We have dense measurement spacing in two regions, the central Aleutians and beneath Alaska. Beneath Alaska, we observe a rotation in fast splitting directions near the edge of the subducting slab. Fast directions change from roughly trench perpendicular away from the slab edge to trench parallel near the boundary. This is indicative of toroidal flow around the edge of the subducting Alaska slab. In the central Aleutians, local-S splitting is primarily oriented parallel to, or oblique to, the strike of the trench. The local-S measurements, however, exhibit a depth dependence where deeper events show more consistently trench-parallel directions indicating prevalent trench-parallel mantle flow. Our local-S shear wave splitting results suggest trench-parallel orientation are likely present along much of the subduction zone excited by the slab edge, but that additional complexities exist along strike.
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Seismic Azimuthal Anisotropy Beneath the Alaska Subduction Zone
Abstract We estimate depth‐dependent azimuthal anisotropy and shear wave velocity structure beneath the Alaska subduction zone by the inversion of a new Rayleigh wave dispersion dataset from 8 to 85 s period. We present a layered azimuthal anisotropy model from the forearc region offshore to the subduction zone onshore. In the forearc crust, we find a trench‐parallel pattern in the Semidi and Kodiak segments, while a trench‐oblique pattern is observed in the Shumagins segment. These fast directions agree well with the orientations of local faults. Within the subducted slab, a dichotomous pattern of anisotropy fast axes is observed along the trench, which is consistent with the orientation of fossil anisotropy generated at the mid‐ocean ridges of the Pacific‐Vancouver and Kula‐Pacific plates that is preserved during subduction. Beneath the subducted slab, a trench‐parallel pattern is observed near the trench, which may indicate the direction of mantle flow.
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- Award ID(s):
- 1952209
- PAR ID:
- 10525951
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 51
- Issue:
- 14
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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