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Title: Effect of pore pressure buildup on slowness of rupture propagation

Pore fluid pressure is known to play an important role in brittle fracture initiation and propagation, yet the underlying mechanisms remain unclear. We conducted triaxial experiments on saturated porous sandstones to investigate effects of pore pressure buildup on the slowness of shear rupture propagation at different confining pressures. At low to intermediate confinements, rocks fail by brittle faulting, and pore pressure buildup causes a reduction in rock’s shear strength but does not induce measurable differences in slip behavior. When the confinement is high enough to prohibit dynamic faulting, rocks fail in the brittle-ductile transitional regime. In the transitional regime, pore pressure buildup promotes slip instability on an otherwise stably sliding fracture. Compared to those observed in the brittle regime, the slip rate, stress drop, and energy dissipated during rupture propagation with concurrent pore pressure buildup in the transitional regime are distinctively different. When decreasing confining pressure instead, the slip behavior resembles the ones of the brittle regime, emphasizing h ow the observed slowness is related to excess pore pressure beyond the effective pressure phenomenon. Analysis of the mechanical data using existing theoretical models confirms these observations. Quantitative microstructural analyses reveal that increasing pore pressure lessens the dilatancy hardening during failure,more » thus enhances slip along the localized zone in the transitional regime. Lastly, our experimental results suggest that pore pressure buildup induces slow slip in the transitional regime, and slip rates along a shear fracture may vary considerably depending on effective stress states.« less
Authors:
 [1] ;  [2]
  1. Univ. of Maryland, College Park, MD (United States); British Geological Survey, Nottingham (United Kingdom)
  2. Univ. of Maryland, College Park, MD (United States)
Publication Date:
Grant/Contract Number:
FG02-07ER15916
Type:
Accepted Manuscript
Journal Name:
Journal of Geophysical Research. Solid Earth
Additional Journal Information:
Journal Volume: 120; Journal Issue: 12; Journal ID: ISSN 2169-9313
Publisher:
American Geophysical Union
Research Org:
Univ. of Maryland, College Park, MD (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; shear fracture; brittle‐ductile transition; rock physics; lab experiments; porous rocks; slow slips
OSTI Identifier:
1468400
Alternate Identifier(s):
OSTI ID: 1402159

Ougier-Simonin, Audrey, and Zhu, W. Effect of pore pressure buildup on slowness of rupture propagation. United States: N. p., Web. doi:10.1002/2015JB012047.
Ougier-Simonin, Audrey, & Zhu, W. Effect of pore pressure buildup on slowness of rupture propagation. United States. doi:10.1002/2015JB012047.
Ougier-Simonin, Audrey, and Zhu, W. 2015. "Effect of pore pressure buildup on slowness of rupture propagation". United States. doi:10.1002/2015JB012047. https://www.osti.gov/servlets/purl/1468400.
@article{osti_1468400,
title = {Effect of pore pressure buildup on slowness of rupture propagation},
author = {Ougier-Simonin, Audrey and Zhu, W.},
abstractNote = {Pore fluid pressure is known to play an important role in brittle fracture initiation and propagation, yet the underlying mechanisms remain unclear. We conducted triaxial experiments on saturated porous sandstones to investigate effects of pore pressure buildup on the slowness of shear rupture propagation at different confining pressures. At low to intermediate confinements, rocks fail by brittle faulting, and pore pressure buildup causes a reduction in rock’s shear strength but does not induce measurable differences in slip behavior. When the confinement is high enough to prohibit dynamic faulting, rocks fail in the brittle-ductile transitional regime. In the transitional regime, pore pressure buildup promotes slip instability on an otherwise stably sliding fracture. Compared to those observed in the brittle regime, the slip rate, stress drop, and energy dissipated during rupture propagation with concurrent pore pressure buildup in the transitional regime are distinctively different. When decreasing confining pressure instead, the slip behavior resembles the ones of the brittle regime, emphasizing h ow the observed slowness is related to excess pore pressure beyond the effective pressure phenomenon. Analysis of the mechanical data using existing theoretical models confirms these observations. Quantitative microstructural analyses reveal that increasing pore pressure lessens the dilatancy hardening during failure, thus enhances slip along the localized zone in the transitional regime. Lastly, our experimental results suggest that pore pressure buildup induces slow slip in the transitional regime, and slip rates along a shear fracture may vary considerably depending on effective stress states.},
doi = {10.1002/2015JB012047},
journal = {Journal of Geophysical Research. Solid Earth},
number = 12,
volume = 120,
place = {United States},
year = {2015},
month = {11}
}