Effective bulk rheology of a two‐phase subduction shear zone: insights from micromechanics‐based modeling and implications for subduction interface slow slip events

Lu, Lucy Xi, Beall, Adam and Fagereng, Åke ORCID: https://orcid.org/0000-0001-6335-8534 2024. Effective bulk rheology of a two‐phase subduction shear zone: insights from micromechanics‐based modeling and implications for subduction interface slow slip events. Geophysical Research Letters 51 (20) , e2024GL110830. 10.1029/2024gl110830

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Abstract

Subduction interfaces exhibit various slip styles, including slow slip events (SSEs). We use a micromechanics‐based approach to calculate the effective rheology of a shear zone containing ellipsoidal amphibolite clasts deforming by dislocation creep within an interconnected linear‐viscous phyllosilicate‐dominated matrix. Frictional failure occurs if local stress exceeds Mohr‐Coulomb yield strength. At moderate fluid overpressure, mixed‐frictional‐viscous behavior emerges at ∼ ${\sim} $ 350–560 ° ${}^{\circ}$ C, consistent with a broad zone of mixed fault slip behavior without requiring extreme fluid overpressures. Increasing stress in this transition zone promotes local frictional failure and raises bulk strain rate. If, however, the bulk strain rate increases by more than one order of magnitude, system‐wide frictional sliding becomes preferable. This strain rate increase is insufficient to explain the slip rates observed in geophysically detectable SSEs. Therefore, viscous matrix flow as modeled here cannot explain SSEs without either invoking dynamic weakening within a frictional‐viscous flow or a mechanism switch to dominantly frictional sliding.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Earth and Environmental Sciences
Additional Information:	License information from Publisher: LICENSE 1: URL: http://creativecommons.org/licenses/by/4.0/
Publisher:	Wiley
ISSN:	0094-8276
Date of First Compliant Deposit:	22 October 2024
Date of Acceptance:	8 October 2024
Last Modified:	22 Oct 2024 08:45
URI:	https://orca.cardiff.ac.uk/id/eprint/173236

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