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Anisotropy-revealed change in hydration along the Alaska subduction zone

Colton Lynner
Anisotropy-revealed change in hydration along the Alaska subduction zone
Geology (Boulder) (June 2021) 49 (9): 1122-1125

Abstract

Megathrust earthquake behavior in subduction zones is controlled by a variety of factors including the hydration state of the subducting slab. Increased hydration reduces the occurrence of great, damaging earthquakes by diminishing the strength of the material along the interface between tectonic plates. Understanding variations in hydration in subductions zones is necessary for properly assessing the overall hazard posed by each region. Fortunately, seismic anisotropy is strongly dependent upon hydration of the subducting crust and lithosphere. I present shear-wave splitting measurements that illuminate changes in anisotropy, and therefore hydration, of the subducting Pacific plate beneath the Alaska subduction zone (northern Pacific Ocean). Variations in shear-wave splitting directly correlate to changes in the behavior of great, megathrust earthquakes. My measurements show that the Shumagin seismic gap is characterized by a hydrated subducting slab, explaining the long-term lack of great earthquakes. Observations in the immediately adjacent Semidi segment, which experiences great events regularly, indicate a far less hydrated slab. These results are driven by the preferential alignment of paleo-spreading fabrics of the Pacific plate. Where fabrics are more closely aligned with the orientation of the trench, outer-rise faulting and plate hydration is enhanced. These results highlight the importance of changes in preexisting slab structures and subsequent hydration in the production of great, damaging earthquakes.


ISSN: 0091-7613
EISSN: 1943-2682
Coden: GLGYBA
Serial Title: Geology (Boulder)
Serial Volume: 49
Serial Issue: 9
Title: Anisotropy-revealed change in hydration along the Alaska subduction zone
Author(s): Lynner, Colton
Affiliation: University of Delaware, Department of Earth Sciences, Newark, DE, United States
Pages: 1122-1125
Published: 20210603
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 34
Accession Number: 2021-071876
Categories: SeismologySolid-earth geophysics
Document Type: Serial
Bibliographic Level: Analytic
Annotation: NSF Grant OCE-19492010
Illustration Description: illus. incl. geol. sketch map
N54°00'00" - N60°00'00", W156°00'00" - W152°00'00"
N52°00'00" - N57°00'00", W160°00'00" - W156°00'00"
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2022, American Geosciences Institute. Reference includes data from GeoScienceWorld, Alexandria, VA, United States. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 202150
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