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Anisotropy Variations in the Alaska Subduction Zone Based on Shear-Wave Splitting From Intraslab Earthquakes

Richards, Cole and Tape, Carl and Abers, Geoffrey A. and Ross, Zachary E. (2021) Anisotropy Variations in the Alaska Subduction Zone Based on Shear-Wave Splitting From Intraslab Earthquakes. Geochemistry, Geophysics, Geosystems, 22 (5). Art. No. e2020GC009558. ISSN 1525-2027. doi:10.1029/2020gc009558.

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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.

Item Type:Article
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URLURL TypeDescription
Richards, Cole0000-0002-6625-8317
Tape, Carl0000-0003-2804-7137
Abers, Geoffrey A.0000-0003-0704-2097
Ross, Zachary E.0000-0002-6343-8400
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).
Group:Seismological Laboratory
Funding AgencyGrant Number
Subject Keywords:anisotropy; seismology; shear‐wave splitting; subduction zone
Issue or Number:5
Record Number:CaltechAUTHORS:20210513-140501367
Persistent URL:
Official Citation:Richards, C., Tape, C., Abers, G. A., & Ross, Z. E. (2021). Anisotropy variations in the Alaska subduction zone based on shear‐wave splitting from intraslab earthquakes. Geochemistry, Geophysics, Geosystems, 22, e2020GC009558.
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:109121
Deposited By: Tony Diaz
Deposited On:13 May 2021 21:12
Last Modified:01 Nov 2021 08:05

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