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Abstract Shear wave splitting is often assumed to be caused by mantle flow or preexisting lithospheric fabrics. We present 2,389 new SKS shear wave splitting observations from 384 broadband stations deployed in Alaska from January 2010 to August 2017. In Alaska, splitting appears to be controlled by the absolute plate motion (APM) of the North American and Pacific plates, the interaction between the two plates, and the geometry of the subducting Pacific‐Yakutat plate. Outside of the subduction zone's influence, the fast directions in northern Alaska parallel the North American APM direction. Fast directions near the Queen Charlotte‐Fairweather transform margin are parallel to the faults and are likely caused by the strike‐slip deformation extending throughout the lithosphere. In the mantle wedge, fast directions are oriented along the strike of the slab with large splitting times and are caused by along‐strike flow in the mantle wedge as the slab provides a barrier to flow. South of the Alaska Peninsula, the fast directions are parallel to the trench regardless of sea floor fabric, indicating along strike flow under the Pacific plate. Under the Kenai Peninsula, the complex flat slab geometry may cause subslab flow to be parallel to Pacific APM direction or to the North America‐Pacific relative motion.
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Local- S shear wave splitting along the length of the Alaska–Aleutian subduction zone
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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- Award ID(s):
- 1949210
- PAR ID:
- 10502740
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Geophysical Journal International
- Volume:
- 237
- Issue:
- 3
- ISSN:
- 0956-540X
- Format(s):
- Medium: X Size: p. 1567-1574
- Size(s):
- p. 1567-1574
- Sponsoring Org:
- National Science Foundation
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