The Impact of Rheology on the Transition From Stick‐Slip to Creep in a Semibrittle Analog

Birren, Thomas; Reber, Jacqueline E.

doi:10.1029/2018jb016914

Cited by 18 publications

(21 citation statements)

References 40 publications

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“…Such classical wing cracks are typically found in laboratory experiments and as subsidiary cracks in nature (e.g. Lee et al, 2016;Birren and Reber, 2019;Mutlu and Pollard, 2008;Willemse and Pollard, 1998). In the following we briefly attempt to link our model observations with the theory of wing cracks and normal and reverse faults in nature.…”

Section: Wing Crack Transition and Relation To Normal And Reverse Faumentioning

confidence: 87%

Characteristics of earthquake ruptures and dynamic off-fault deformation on propagating faults

Dinther¹,

Preuss²,

Ampuero³

et al. 2020

Preprint

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Abstract. Natural fault networks are geometrically complex systems that evolve through time. The evolution of faults and their off-fault damage pattern are influenced by both dynamic earthquake ruptures and aseismic deformation in the interseismic period. To better understand each of their contributions to faulting we simulate both earthquake rupture dynamics and long-term deformation in a visco-elasto-plastic crust subjected to rate-and-state-dependent friction. The continuum mechanics-based numerical model presented here includes three new features. First, a 2.5-D approximation to incorporate effects of a viscoelastic lower crustal substrate below a finite depth. Second, we introduce a dynamically adaptive (slip-velocity-dependent) measure of fault width to ensure grid size convergence of fault angles for evolving faults. Third, fault localization is facilitated by plastic strain weakening of bulk rate-and-state friction parameters as inspired by laboratory experiments. This allows us to for the first time simulate sequences of episodic fault growth due to earthquakes and aseismic creep. Localized fault growth is simulated for four bulk rheologies ranging from persistent velocity-weakening to velocity-strengthening. Interestingly, in each of these bulk rheologies, faults predominantly localize and grow due to aseismic deformation. Yet, cyclic fault growth at more realistic growth rates is obtained for a bulk rheology that transitions from velocity-strengthening friction to velocity-weakening friction. Fault growth occurs under Riedel and conjugate angles and transitions towards wing cracks. Off-fault deformation, both distributed and localized, is typically formed during dynamic earthquake ruptures. Simulated off-fault deformation structures range from fan-shaped distributed deformation to localized Riedel splay faults. We observe that the fault-normal width of the outer damage zone saturates with increasing fault length due to the finite depth of the seismogenic zone. We also observe that dynamically and statically evolving stress fields from neighboring fault strands affect primary and secondary fault growth and thus that normal stress variations affect earthquake sequences. Finally, we find that the amount of off-fault deformation distinctly depends on the degree of optimality of a fault with respect to the prevailing but dynamically changing stress field. Typically, we simulate off-fault deformation on faults parallel to the loading direction. This produces a 6.5-fold higher off-fault energy dissipation than on an optimally oriented fault, which in turn has a 1.5-fold larger stress drop. The misalignment of the fault with respect to the static stress field thus facilitates off-fault deformation. These results imply that fault geometries bend, individual fault strands interact and that optimal orientations and off-fault deformation vary through space and time. With our work we establish the basis for simulations and analyses of complex evolving fault networks subject to both long-term and short-term dynamics.

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Section: Wing Crack Transition and Relation To Normal And Reverse Faumentioning

confidence: 87%

Characteristics of earthquake ruptures and dynamic off-fault deformation on propagating faults

Dinther¹,

Preuss²,

Ampuero³

et al. 2020

Preprint

View full text Add to dashboard Cite

show abstract

“…Nonetheless, the dominant shear component alludes to a transition or an approximation to a wing crack rather than the development of a classical wing crack. Such classical wing cracks are typically found in laboratory experiments and as subsidiary cracks in nature (e.g., Lee et al, 2016;Birren and Reber, 2019;Mutlu and Pollard, 2008;Willemse and Pollard, 1998). In the following we briefly attempt to link our model observations with the theory of wing cracks and normal and reverse faults in nature.…”

Section: Wing Crack Transition and Relation To Normal And Reverse Faumentioning

confidence: 90%

“…However, changes in other frictional parameters or material parameters (e.g., shear modulus) with plastic strain are not taken into account in our simulations despite the fact that they can be expected in natural fault systems. Our model is a simplification in that it ignores anisotropy, poroelasticity and dilatant volume changes, which are typically observed in natural faults (e.g., Woodcock et al, 2007;Brace et al, 1966;Peacock and Sanderson, 1992;Rawling et al, 2002). Our choice of parameters results in a Poisson's ratio of 0.125.…”

Section: Width Of the Off-fault Fanmentioning

confidence: 99%

Characteristics of earthquake ruptures and dynamic off-fault deformation on propagating faults

Preuss¹,

Ampuero²,

Gerya³

et al. 2020

Solid Earth

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Abstract. Natural fault networks are geometrically complex systems that evolve through time. The evolution of faults and their off-fault damage patterns are influenced by both dynamic earthquake ruptures and aseismic deformation in the interseismic period. To better understand each of their contributions to faulting we simulate both earthquake rupture dynamics and long-term deformation in a visco-elasto-plastic crust subjected to rate- and state-dependent friction. The continuum mechanics-based numerical model presented here includes three new features. First, a 2.5-D approximation is created to incorporate the effects of a viscoelastic lower crustal substrate below a finite depth. Second, we introduce a dynamically adaptive (slip-velocity-dependent) measure of fault width to ensure grid size convergence of fault angles for evolving faults. Third, fault localization is facilitated by plastic strain weakening of bulk rate and state friction parameters as inspired by laboratory experiments. This allows us to simulate sequences of episodic fault growth due to earthquakes and aseismic creep for the first time. Localized fault growth is simulated for four bulk rheologies ranging from persistent velocity weakening to velocity strengthening. Interestingly, in each of these bulk rheologies, faults predominantly localize and grow due to aseismic deformation. Yet, cyclic fault growth at more realistic growth rates is obtained for a bulk rheology that transitions from velocity-strengthening friction to velocity-weakening friction. Fault growth occurs under Riedel and conjugate angles and transitions towards wing cracks. Off-fault deformation, both distributed and localized, is typically formed during dynamic earthquake ruptures. Simulated off-fault deformation structures range from fan-shaped distributed deformation to localized splay faults. We observe that the fault-normal width of the outer damage zone saturates with increasing fault length due to the finite depth of the seismogenic zone. We also observe that dynamically and statically evolving stress fields from neighboring fault strands affect primary and secondary fault growth and thus that normal stress variations affect earthquake sequences. Finally, we find that the amount of off-fault deformation distinctly depends on the degree of optimality of a fault with respect to the prevailing but dynamically changing stress field. Typically, we simulate off-fault deformation on faults parallel to the loading direction. This produces a 6.5-fold higher off-fault energy dissipation than on an optimally oriented fault, which in turn has a 1.5-fold larger stress drop. The misalignment of the fault with respect to the static stress field thus facilitates off-fault deformation. These results imply that fault geometries bend, individual fault strands interact, and optimal orientations and off-fault deformation vary through space and time. With our work we establish the basis for simulations and analyses of complex evolving fault networks subject to both long-term and short-term dynamics.

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“…Velocity‐strengthening parts of a subduction interface can produce an SSE by damping an otherwise unstable rupture initiating in velocity‐weakening material (Luo & Ampuero, ; Skarbek et al, ). Analog models show that slow stick‐slip events can occur in a macroscopically homogeneous viscoplastic material likely due to reorganization of microgel force chains (Birren & Reber, ; Reber et al, ). These analog models showed that microscopically these events are related to reorganization of force chains, while macroscopically they correspond to episodic opening of tensile fractures, which grade into shear fractures and viscous deformation accommodating overall simple shear.…”

Section: Introductionmentioning

confidence: 99%

Fracture and Weakening of Jammed Subduction Shear Zones, Leading to the Generation of Slow Slip Events

Beall

Fagereng

Ellis

2019

Geochem Geophys Geosyst

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Geodetic data have revealed that parts of subduction interfaces creep steadily or transiently. Transient slow slip events (SSEs) are typically interpreted as aseismic frictional sliding. However, SSEs may also occur via mixed viscobrittle deformation, as observed in shear zones containing mixtures (mélange) of strong fractured clasts embedded in a weak viscobrittle matrix. We test the hypothesis that creep in a subduction mélange occurs through distributed matrix deformation, where flow is intermittently impeded by load‐bearing clast networks (jamming). Our numerical models demonstrate that bulk mélange rheology can be dominated by the strong clasts in the absence of fracturing, while at high driving stresses or low frictional strength, clast fracturing redistributes deformation into the matrix, leading to high bulk strain rates. Because mélange stress is heterogeneous, fracturing of clasts occurs throughout jammed mélange when the driving stresses are only ∼20% of the clast yield strength. The effective rheology of jammed mélange can be characterized by a logarithmic dependence of stress on strain rate, which is used to explore strain rate transients caused by temporal variation in clast friction. Clasts must weaken significantly (∼75%) in order to increase strain rate by 8 times. Spring‐block slider models with a more idealized viscobrittle rheology also demonstrate that strain rate transients can be generated when rate‐and‐state friction is incorporated. We outline a model where high bulk strain rates are generated when pervasive fracturing occurs, but further slip is limited by viscous processes. Incorporating such viscous damping into models may widen the conditions under which SSEs can occur while preventing development of seismic slip.

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The Impact of Rheology on the Transition From Stick‐Slip to Creep in a Semibrittle Analog

Cited by 18 publications

References 40 publications

Characteristics of earthquake ruptures and dynamic off-fault deformation on propagating faults

Characteristics of earthquake ruptures and dynamic off-fault deformation on propagating faults

Characteristics of earthquake ruptures and dynamic off-fault deformation on propagating faults

Fracture and Weakening of Jammed Subduction Shear Zones, Leading to the Generation of Slow Slip Events

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