Strength of Strained Two-Phase Mixtures: Application to Rapid Creep and Stress Amplification in Subduction Zone Mélange

Adam Beall, Åke Fagereng, Susan Ellis

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51 Citations (Scopus)


Aseismic creep may occur by distributed deformation in mélange shear zones comprising weak matrix and stronger clast materials. Slow slip events or steady tectonic displacement can be distributed over <100-m thick shear zones if weak matrix controls bulk shear zone deformation. We use 2-D numerical models to quantify the rheology of moderately strained (shear strain <1.75) mélange for various volumetric proportions of competent clasts. Mélange deformation with <50% clasts is matrix dominated and can accommodate steady creep. At higher clast proportions mélange viscosity increases more than tenfold after small strains, because strong clasts interact and form force chains. Clast shear stress is amplified above the imposed shear stress, by a factor of <14 where force chains develop. Slow slip events may occur due to a temporary absence of force chains, while localized regions of high shear stress generate coincident fracturing and potentially tremor events.

Original languageEnglish
Pages (from-to)169-178
Number of pages10
JournalGeophysical Research Letters
Issue number1
Publication statusPublished - 16 Jan 2019
Externally publishedYes


  • brittle-ductile deformation
  • mélange
  • numerical modeling
  • shear zones
  • slow slip
  • subduction zones

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