Rupture and Afterslip Controlled by Spontaneous Local Fluid Flow in Crustal Rock

Aben, Frans M.; Brantut, Nicolas

doi:10.1029/2023jb027534

Cited by 3 publications

(2 citation statements)

References 53 publications

(88 reference statements)

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“…However, structural observations show the samples are undergoing the same processes of dilation, microcrack coalescence, and fracture localization that occurs during typical brittle failure, albeit at a slower rate. Overall, our findings agree with previous studies of low‐porosity crystalline rocks which show similar behaviors of fault stabilization as a result of high pore fluid pressure (Aben & Brantut, 2021, 2023; Brace & Martin, 1968; Brantut, 2020; French & Zhu, 2017; Martin, 1980). We posit that apparent frictional sliding reflects transient sliding of geometrically complex faults and not a dilatant hardening process, as evidenced by the lack of a stress drop over durations lasting minutes to hours.…”

Section: Discussionsupporting

confidence: 92%

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Effects of Dilatant Hardening on Fault Stabilization and Structural Development

Williams,

French

2024

Geophysical Research Letters

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Dilatant hardening is one proposed mechanism that causes slow earthquakes along faults. Previous experiments and models show that dilatant hardening can stabilize fault rupture and slip in several lithologies. However, few studies have systematically measured the mechanical behavior across the transition from dynamic to slow rupture or considered how the associated damage varies. To constrain the processes and scales of dilatant hardening, we conducted triaxial compression experiments on cores of Crab Orchard sandstone and structural analyses using micro‐computed tomography imaging and petrographic analysis. Experiments were conducted at an effective confining pressure of ∼10 MPa, while varying confining pressure (10–130 MPa) and pore fluid pressure (1–120 MPa). Above 15 MPa pore fluid pressure, dilatant hardening slows the rate of fault rupture and slip and deformation becomes more distributed amongst multiple faults as microfracturing increases. The resulting increase in fracture energy has the potential to control fault slip behavior.

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Section: Discussionsupporting

confidence: 92%

“…Periods of constant strength over such long durations have not been observed in previous studies of dilatant hardening. However, it is possible that some of our shorter duration periods of apparent frictional sliding are analogous to the stable failure events identified by Aben and Brantut (2023).…”

Section: Discussionmentioning

confidence: 88%

Effects of Dilatant Hardening on Fault Stabilization and Structural Development

Williams,

French

2024

Geophysical Research Letters

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Opposite Variations for Pore Pressure on and off the Fault During Simulated Earthquakes in the Laboratory

Liu,

Brantut,

Aben

2024

JGR Solid Earth

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We measured the spatiotemporal evolution of pore pressure on‐ and off‐fault during failure and slip in initially intact Westerly granite under triaxial conditions. The pore pressure perturbations in the fault zone and the surrounding bulk presented opposite signs upon shear failure, resulting in large pore pressure gradients over small distances (up to 10 MPa/cm). The on‐fault pore pressure dropped due to localized fault dilation associated with fracture coalescence and fault slip, and the off‐fault pore pressure increased due to bulk compaction resulting from the closure of dilatant microcracks mostly parallel to the maximum compression axis. We show that a reduction in bulk porosity and relatively undrained conditions during failure are necessary for the presence of the off‐fault pore pressure elevation. Considering this phenomenon as a consequence of a main shock, we further show that off‐fault pore pressure increase has the potential to trigger neighboring fault instabilities. In nature, we expect the phenomenon of off‐fault pore pressure increase to be most relevant for misoriented faults, where the pre‐rupture stresses can be large enough to reach the dilatancy threshold in the wall rocks.

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Permeability Development During Fault Growth and Slip in Granite

Aben,

Farsi,

Brantut

2024

JGR Solid Earth

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In tight crystalline rocks faults are known to be substantially more hydraulically conductive than the rock matrix. However, most of our knowledge relies on static measurements, or before/after failure data sets. The spatio‐temporal evolution of the permeability field during faulting remains unknown. Here, we determine at which stage of faulting permeability changes most, and the degree of permeability heterogeneity along shear faults. We conducted triaxial deformation experiments in intact Westerly granite, where faulting was stabilized by monitoring acoustic emission rate. At repeated stages during deformation and faulting we paused deformation and imposed macroscopic fluid flow to characterize the overall permeability of the material. The pore pressure distribution was measured along the prospective fault to estimate apparent hydraulic transmissivity, and propagation of the macroscopic shear fault was monitored by locating acoustic emissions. We find that average permeability increases dramatically (by two orders of magnitude) with increasing deformation up to peak stress, where the fault is not yet through‐going. Post‐peak stress, overall permeability increases by a factor of three. However, at this stage we observed local heterogeneities in permeability by up to factors of eight, ascribed to a partially connected fracture network. This heterogeneity decreases with fault completion at residual shear stress. With further slip on the newly formed fault, the average hydraulic transmissivity remains mostly stable. Our results show that permeability enhancement during shear rupture mostly occurs ahead of the rupture tip, and that strongly heterogeneous permeability patterns are generated in the fault cohesive zone due to partial fracture connectivity.

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Rupture and Afterslip Controlled by Spontaneous Local Fluid Flow in Crustal Rock

Cited by 3 publications

References 53 publications

Effects of Dilatant Hardening on Fault Stabilization and Structural Development

Effects of Dilatant Hardening on Fault Stabilization and Structural Development

Opposite Variations for Pore Pressure on and off the Fault During Simulated Earthquakes in the Laboratory

Permeability Development During Fault Growth and Slip in Granite

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