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The influence of confining stress and preexisting damage on strain localization in fluid-saturated crystalline rocks in the upper crust
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  • Jessica McBeck,
  • Benoit Cordonnier,
  • Yehuda Ben-Zion,
  • François Renard
Jessica McBeck
University of Oslo

Corresponding Author:j.a.mcbeck@geo.uio.no

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Benoit Cordonnier
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Yehuda Ben-Zion
University of Southern California
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François Renard
University of Oslo
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The spatial organization of deformation may provide key information about the timing of catastrophic failure in the brittle regime. In an ideal homogenous system, deformation may continually localize toward macroscopic failure, and so increasing localization unambiguously signals approaching failure. However, recent analyses demonstrate that deformation, including low magnitude seismicity, and fractures and strain in triaxial compression experiments, experience temporary phases of delocalization superposed on an overall trend of localization toward large failure events. To constrain the conditions that promote delocalization, we perform a series of X-ray tomography experiments at varying confining stresses (5-20 MPa) and fluid pressures (zero to 10 MPa) on Westerly granite cores with varying amounts of preexisting damage. We track the spatial distribution of the strain events with the highest magnitudes of the population within a given time step. The results show that larger confining stress promotes more dilation, and promotes greater localization of the high strain events approaching macroscopic failure. In contrast, greater amounts of preexisting damage promote delocalization. Importantly, the dilative strain experiences more systematic localization than the shear strain, and so may provide more reliable information about the timing of catastrophic failure than the shear strain.
28 Apr 2023Submitted to ESS Open Archive
02 May 2023Published in ESS Open Archive