Anisotropy Variations in the Alaska Subduction Zone Based on Shear-Wave Splitting From Intraslab Earthquakes
Abstract
Shear‐wave splitting observations can provide insight into mantle flow, due to the link between the deformation of mantle rocks and their direction‐dependent seismic wave velocities. We identify anisotropy in the Cook Inlet segment of the Alaska subduction zone by analyzing splitting parameters of S waves from local intraslab earthquakes between 50 and 200 km depths, recorded from 2015–2017 and emphasizing stations from the Southern Alaska Lithosphere and Mantle Observation Network experiment. We classify 678 high‐quality local shear‐wave splitting observations into four regions, from northwest to southeast: (L1b) splitting measurements parallel to Pacific plate motion, (L1a) arc‐perpendicular splitting pattern, (L2) sharp transition to arc‐parallel splitting, and (L3) splitting parallel to Pacific plate motion. Forward modeling of splitting from various mantle fabrics shows that no one simple model fully explains the observed splitting patterns. An A‐type olivine fabric with fast direction dipping 45° to the northwest (300°)—aligned with the dipping slab—predicts fast directions that fit L1a observations well, but not L2. The inability of the forward model fabrics to fit all the observed splitting patterns suggests that the anisotropy variations are not due to variable ray angles, but require distinct differences in the anisotropy regime below the arc, forearc, and subducting plate.
Additional Information
© 2021 American Geophysical Union. Issue Online: 14 May 2021; Version of Record online: 14 May 2021; Accepted manuscript online: 07 May 2021; Manuscript accepted: 02 May 2021; Manuscript revised: 13 April 2021; Manuscript received: 01 December 2020. We acknowledge helpful reviews from Jun Nakajima and an anonymous reviewer. C. Tape thanks Doug Christensen and Melissa Moore for leading the SALMON seismic deployment. This work was supported by NSF Grants EAR‐1251971 (Tape), EAR‐1829447 (Tape), and EAR‐1829440 (Abers). Data Availability Statement: All waveforms used in this study are publically avaialable at IRIS. All splitting measurement data can be found in Richards (2020b). Further analysis and figures from this study, beyond the supplementary material, can be found in Richards (2020a).Attached Files
Published - 2020GC009558.pdf
Supplemental Material - 2020gc009558-sup-0001-supporting_information_si-s01.pdf
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Additional details
- Eprint ID
- 109121
- Resolver ID
- CaltechAUTHORS:20210513-140501367
- EAR-1251971
- NSF
- EAR-1829447
- NSF
- EAR-1829440
- NSF
- Created
-
2021-05-13Created from EPrint's datestamp field
- Updated
-
2021-11-01Created from EPrint's last_modified field
- Caltech groups
- Seismological Laboratory, Division of Geological and Planetary Sciences