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Mechanical data and microstructures of simulated calcite fault gouge sheared at 550°C

Cite as:

Verberne, Berend Antonie; Chen, Jianye; Pennock, Gillian (2017): Mechanical data and microstructures of simulated calcite fault gouge sheared at 550°C. GFZ Data Services. https://doi.org/10.5880/fidgeo.2017.012

Status

I   N       R   E   V   I   E   W : Verberne, Berend Antonie; Chen, Jianye; Pennock, Gillian (2017): Mechanical data and microstructures of simulated calcite fault gouge sheared at 550°C. GFZ Data Services. https://doi.org/10.5880/fidgeo.2017.012

Abstract

The largest magnitude earthquakes nucleate at depths near the base of the seismogenic zone, near the transition from velocity weakening frictional slip to velocity strengthening ductile flow. However, the mechanisms controlling this transition, and relevant to earthquake nucleation, remain poorly understood. Here we present data from experiments investigating the effect of slip rate on the mechanical properties and microstructure development of simulated calcite fault gouge sheared at ~550°C, close to the transition from (unstable) velocity weakening to (stable) velocity strengthening behaviour, reported by Verberne et al. (2015).


We conducted experiments at a constant effective normal stress (σneff) of 50 MPa, as well as σneff-stepping tests employing 20 MPa ≤ σneff ≤ 140 MPa, at constant sliding velocities (v) of 0.1, 1, 10, or 100 µm/s. Samples sheared at v ≥ 1 µm/s showed a microstructure characterized by a single, 30 to 40 μm wide boundary shear, as well as a linear correlation of shear strength (τ) with σneff. Remarkably, electron backscatter diffraction mapping of polygonal shear band grains demonstrated a crystallographic preferred orientation. By contrast, samples sheared at 0.1 µm/s showed a microstructure characterized by homogeneous deformation and plastic flow, as well as a flattening-off of the τ-σneff curve. Our results point to a strain rate dependent frictional-to-viscous transition in simulated calcite fault gouge, and have important implications for the processes controlling earthquake nucleation at the base of the seismogenic zone.

Authors

  • Verberne, Berend Antonie;High Pressure & Temperature Laboratory, Utrecht University
  • Chen, Jianye;High Pressure & Temperature Laboratory, Utrecht University
  • Pennock, Gillian;Structural Geology & Tectonics, Utrecht University

Contact

Contributors

Experimental rock deformation/HPT-Lab (Utrecht University, The Netherlands)

Keywords

EPOS, multi-scale laboratories, rock and melt physical properties, European Plate Observing System, breccia_gouge_series, calcite, carbonate_sedimentary_rock, Powder Mixture, Rock, Friction > Imposed Stress, Strength > Yield Strength, Optical Microscope, Scanning Electrone Microscope, Shear Box, Triaxial, Photography, Strain gauge > Axial strain gauge, Thermocouple, Friction > Imposed Stress, Optical Microscope, Photography, Powder Mixture, Rock, Scanning Electrone Microscope, Shear Box, Strain gauge > Axial strain gauge, Strength > Yield Strength, Thermocouple, Triaxial, breccia_gouge_series, calcite, carbonate_sedimentary_rock

GCMD Science Keywords

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License: CC BY 4.0

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