Development of branching brittle and ductile shear zones: A numerical study

Meyer, Sven; Kaus, Boris; Passchier, Cees W.

doi:10.1002/2016gc006793

Cited by 27 publications

(35 citation statements)

References 130 publications

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“…Irregular movement of such blocks can lead to both relative rotation and variation in principal stress directions within blocks, which could explain the difference in preserved shortening direction observed in the low‐strain area II in Figure . Numerical studies have shown that due to the interaction of individual shear zone strands, the principal shortening direction inside the shear zones may rotate and lead to further stress perturbations (Meyer et al, ).…”

Section: Discussionmentioning

confidence: 99%

Weak and Slow, Strong and Fast: How Shear Zones Evolve in a Dry Continental Crust (Musgrave Ranges, Central Australia)

et al. 2019

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The strike-slip Davenport Shear Zone in Central Australia developed during the Petermann Orogeny (~550 Ma) in an intracontinental lower crustal setting under dry subeclogite facies conditions (~650°C, 1.2 GPa). This approximately 5-km-wide mylonite zone encloses several large low-strain domains, allowing a detailed study of the initiation of shear zones and their progressive development. Quartzo-feldspathic gneisses and granitoids contain compositional layers, such as quartz-rich pegmatites, mafic bands, and dykes, which should preferentially localize viscous deformation if favorably orientated. This is not observed, except for long, continuous, and fine-grained dolerite dykes. Instead, many shear zones, typically a few millimeters to centimeters in width but extending for tens of meters, commonly exploited pseudotachylytes and are sometimes parallel to a network of little overprinted fractures. The recrystallized mineral assemblage in the sheared pseudotachylyte is similar to that in the host gneiss, without associated hydration due to fluid-rock interaction. Lack of localization in quartz-rich, coarser-grained (typically >50 μm) rocks compared to mafic dykes, precursor fractures, and pseudotachylytes implies that localization in the dry lower crust preferentially occurs along elongate, planar fine-grained layers. Transient high stress repeatedly initiated fractures, providing finer-grained, weaker, planar precursors that localized subsequent ductile shear zones. This intimate interplay between brittle and ductile deformation suggests a local source for lower crustal earthquakes, rather than downward migration of earthquakes from the shallower, usually more seismogenic part of the crust.Shear zone nucleation and strain localization in the lower crust have a major impact on the architecture of mountain belts, and the study of these processes yields insights into the rheology of the Earth's crust. Shear zone nucleation develops from an initial perturbation in rock viscosity, with strain localization being HAWEMANN ET AL.219

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Section: Discussionmentioning

confidence: 99%

Weak and Slow, Strong and Fast: How Shear Zones Evolve in a Dry Continental Crust (Musgrave Ranges, Central Australia)

et al. 2019

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“…The maximum compressive stress σ 1 is initially oriented at an angle of 45 • to the imposed shear direction, indicated by the light green arrows in Fig. [2] (e.g., Meyer et al, 2017). Values of the reference model parameters (Table 1) are set largely in accordance with Lapusta et al (2000), with differences in the choice of V 0 and the initial mean stress P B .…”

Section: Model Setupmentioning

confidence: 99%

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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“…In this area diverse fault patterns and fault networks are found. Analog experiments, structural geology and fracture mechanics define a variety of different secondary fault structure types: branching faults, one-sided horsetail splay faults, synthetic and antithetic Riedel faults, splay cracks, wing cracks, and mixed modes (e.g., Cooke, 1997;Hubert-Ferrari et al, 2003;Kim et al, 2004;Mitchell and Faulkner, 2009;Aydin and Berryman, 2010;Perrin et al, 2016b, Fig. 1b, c, d).…”

Section: Introductionmentioning

confidence: 99%

“…Field observations indicate that the damage fan width scales with accumulated fault displacement (Perrin et al, 2016b, a). At a smaller distance from each fault, an inner damage zone of microfractures also develops, whose width does saturate at a few hundred meters for larger displacements (Mitchell and Faulkner, 2009;Savage and Brodsky, 2011;Ampuero and Mao, 2017). During an earthquake, energy is dissipated in the damage zone over large distances from the fault (Cappa et al, 2014;Ampuero and Mao, 2017).…”

Section: Introductionmentioning

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.

show abstract

Development of branching brittle and ductile shear zones: A numerical study

Cited by 27 publications

References 130 publications

Weak and Slow, Strong and Fast: How Shear Zones Evolve in a Dry Continental Crust (Musgrave Ranges, Central Australia)

Weak and Slow, Strong and Fast: How Shear Zones Evolve in a Dry Continental Crust (Musgrave Ranges, Central Australia)

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

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

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