Mantle Flow in the Vicinity of the Eastern Edge of the Pacific-Yakutat Slab: Constraints from Shear Wave Splitting Analyses


To investigate the effects of a slab edge and varying slab geometry on the mantle flow systems beneath south central Alaska, a total of 971 pairs of teleseismic shear wave (SKS, SKKS, and PKS) and 65 pairs of local S wave splitting parameters (fast orientations and splitting times) are measured using data from the USArray and other networks. The Pacific-Yakutat slab edge separates two regions with different characteristics of the splitting measurements. The area to the west of the slab edge has greater splitting times and mostly trench parallel fast orientations, and the area to the east is dominated by smaller splitting times and spatially varying fast orientations. The spatial distribution of the splitting parameters and results of anisotropy layering and depth analyses can be explained by a model involving three flow systems. The sub-slab flow initially entraining with the shallow-dipping Yakutat slab deflects to a trench-parallel direction due to slab retreat and an increase in slab dip, and flows northeastward toward the slab edge, where it splits into two branches. The first branch enters the mantle wedge as a toroidal flow and flows southwestward along the slab, and the second branch continues approximately eastward. The flowlines of the toroidal and continued flow systems are approximately orthogonal to each other in the vicinity of the slab edge, producing the observed small splitting times and spatially varying fast orientations.


Geosciences and Geological and Petroleum Engineering


The study was partially supported by the U.S. National Science Foundation under awards 1830644 to Stephen S. Gao and Kelly H. Liu, and 1919789 to Stephen S. Gao.

Keywords and Phrases

Alaska; Mantle Flow; Seismic Anisotropy; Shear Wave Splitting; Subduction; Yakutat Terrene

International Standard Serial Number (ISSN)

2169-9356; 2169-9313

Document Type

Article - Journal

Document Version


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Publication Date

01 Sep 2021