Microcrack populations associated with a propagating shear fracture in granite

Moore, Diane E.

doi:10.3133/ofr93245

Cited by 7 publications

(5 citation statements)

References 19 publications

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“…The Westerly starting material is a granodiorite that consists principally of plagioclase (-40 vol.%), K-feldspar (--25%), quartz (-25%), and biotite (-6%) [Moore, 1993] When the samples were removed from their jackets for examination at the end of an experiment, the two sides of a fracture had to be forcefully separated, indicating induration or welding of fractures. The exposed fracture surfaces showed evidence of both mineral dissolution and crystallization that increased in abundance with temperature and with time.…”

Section: Textural Observationsmentioning

confidence: 99%

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Permeability reduction in granite under hydrothermal conditions

Morrow¹,

Moore²,

Lockner³

2001

J. Geophys. Res.

148

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Abstract. The formation of impermeable fault seals between earthquake events is a feature of many models of earthquake generation, suggesting that earthquake recurrence may depend in part on the rate of permeability reduction of fault zone materials under hydrothermal conditions. In this study, permeability measurements were conducted on intact, fractured, and gouge-bearing In contrast, prefractured samples showed higher rates of permeability decrease at a given temperature. The surfaces of the fractured samples showed evidence of dissolution and mineral growth that increased in abundance with both temperature and time. The experimentally grown mineral assemblages varied with temperature and were consistent with a rock-dominated hydrothermal system. As such mineral deposits progressively seal the fractured samples, their rates of permeability decrease approach the rates for intact rocks at the same temperature. These results place constraints on models of precipitation sealing and suggest that fault rocks may seal at a rate consistent with earthquake recurrence intervals of typical fault zones.

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Section: Textural Observationsmentioning

confidence: 99%

“…The Westerly starting material is a granodiorite that consists principally of plagioclase (-40 vol.%), K-feldspar (--25%), quartz (-25%), and biotite (-6%) [Moore, 1993]; the remainder is a variety of accessory igneous and secondary minerals ( Table 2). Freshly fractured surfaces of Westerly display clean.…”

Section: Textural Observationsmentioning

confidence: 99%

Permeability reduction in granite under hydrothermal conditions

Morrow¹,

Moore²,

Lockner³

2001

J. Geophys. Res.

148

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“…Westerly Granite (WG) originates from the southeast of Rhode Island (USA). The granite is composed of 41 % plagioclase, 25.2 % quartz, 26.3 % potassium feldspar, 6.3 % biotite, and 1.2 % other constituents (Moore 1993). The samples used here have an average grain size of about 0.4 mm, determined with the line-intercept method.…”

Section: Methodsmentioning

confidence: 99%

Evidence for the Heterogeneity of the Pore Structure of Rocks from Comparing the Results of Various Techniques for Measuring Hydraulic Properties

Schepp

Renner

2020

Transp Porous Med

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We applied three oscillatory methods, the previously presented axial pore-pressure and pore-flow methods, and the laboratory application of the radial oscillatory pore-flow method, and performed steady-state flow-through experiments (Darcy tests), for comparison, in experiments on samples of Westerly granite and Wilkeson sandstone. The granite and the sandstone exhibit pore spaces dominated by micro-fractures and by the granular-medium character with a connected porosity of about 1 and 10 %, respectively. Permeability determined by the axial pore-pressure method shows the closest agreement with the results of the Darcy tests. Apparent porosity and drained modulus derived from specific storage capacity deviate from measured connected porosity and reference values, respectively. The observed deviations of the hydraulic properties between methods suggest that they bear information about the structure of the pore space. Only for the sandstone, anisotropy in hydraulic properties appears to contribute to differences between the results of the various methods. We argue that oscillatory testing provides three indicators for heterogeneity, period dependence, the relation between apparent and connected porosity, and the relation between amplitude ratio and apparent penetration depth, calculated from the simple scaling law for homogeneous materials. These indicators consistently classify the samples of Wilkeson sandstone as hydraulically homogeneous and those of Westerly granite as heterogeneous.

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“…Here we argue that any contribution of pore water from the granite in the sample assemblage may be insignificant. Microscopic examinations (e.g., Moore, 1993) show that porosity of undeformed Westerly granite appears as microcracks along grain boundaries. Compressibility measurements under confining pressure showed that the compressibility of Westerly granite rapidly decreases when the confining pressure was raised from 0 to 100 MPa (e.g., Brace, 1965), implying that most micro‐cracks in this rock are eliminated at relatively low pressures.…”

Section: Pore Pressure In Montmorillonitementioning

confidence: 99%

Pore Pressure in Montmorillonite During Frictional Sliding

Chu,

Wang

2023

JGR Solid Earth

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Earth's shallow crust is pervasively breached by fractures and faults that are often filled with saturated clays such as montmorillonite. Pore pressure in montmorillonite is difficult to measure due to its extremely low permeability, resulting in large uncertainties in its friction, which, in turn, may impact our understanding on the mechanical behaviors of the shallow crust. This difficulty motivates us to investigate pore pressure in montmorillonite during frictional sliding. Here we provide a first order understanding on the evolution of pore pressure in montmorillonite during frictional sliding by combining experimental data with an analytical consolidation model. Our result shows large variations in pore pressure in montmorillonite during frictional sliding, which need correction for the evaluation of friction of montmorillonite. We re‐visit this problem with the measured stresses at the end of our slow loading experiments where the modeled pore pressure approaches zero and obtain a new relation that shows a significant cohesive strength. The new relation may be united with our modeled pore pressure with a Biot‐Willis effective stress coefficient of α ∼ 0.5. X‐ray powder diffraction analysis of our samples shows evidence that intense deformation occurred during the frictional sliding with strain‐hardening, consistent with the occurrence of shear localization in the clay matrix following extended frictional sliding (Tembe et al., 2010, https://doi.org/10.1029/2009JB006383). These results suggest that our new relation may represent a constitutive relation for an intensely sheared, saturated montmorillonite in frictional sliding. Our result also suggests that substantial cohesion may appear on some natural clay‐rich faults.

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Microcrack populations associated with a propagating shear fracture in granite

Cited by 7 publications

References 19 publications

Permeability reduction in granite under hydrothermal conditions

Permeability reduction in granite under hydrothermal conditions

Evidence for the Heterogeneity of the Pore Structure of Rocks from Comparing the Results of Various Techniques for Measuring Hydraulic Properties

Pore Pressure in Montmorillonite During Frictional Sliding

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