The impact of brittle clast failure within a viscous matrix on deformation dynamics: A 3D experimental approach
Date
2022-12
Authors
McLafferty, Shae
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Reber, Jacqueline E
Iverson, Neal R
Michael, James B
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Abstract
Transient slip events such as tectonic tremor, low-frequency earthquakes, and slow slip events can occur along the interface of subduction megathrusts over a wide range of pressures and temperatures. These transient events take place downdip of the frictionally dominated seismogenic zone and updip of the viscously creeping aseismic zone within an environment of rheological heterogeneity. In this zone of transition between the brittle and viscous regimes, simultaneous brittle and viscous deformation, or semi-brittle deformation, accommodates stress. Semi-brittle deformation can occur over a wide range of scales, temperatures, pressures and within geological environments beyond subduction zones. Many observations of semi-brittle deformation record deformation of brittle clasts encompassed by a viscous matrix that flows. Here, we investigate controls on semi-brittle deformation to better understand the changes in slip dynamics from a viscous end member to a brittle end member, including semi-brittle deformation. To this end, we deform analog materials within a 3D ring shear apparatus and record both force signals and in situ observations of deformation dynamics. In our experiments, a visco-elasto-plastic polymer, Carbopol®, acts as the viscous phase, and elasto-plastic HydroOrbs that are able to break represent the brittle phase. When the two phases are combined, they behave in a semi-brittle manner where both brittle and viscous deformation occur simultaneously. The volume percent of the brittle phase, brittle phase particle size, and matrix viscosity are found to impact deformation dynamics across all experiment types. Failure of the brittle phase occurs not only in semi-brittle experiments with 64% brittle phase volume but also in experiments with 32% brittle phase volume indicating the viscous phase is able to support sufficient stress to cause brittle failure. Our experiments illustrate a possible mechanism for brittle clast failure in a viscous matrix observed in many geological environments.
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