The mechanics of lubricated faults: Insights from 3‐D numerical models

Bizzarri, Andrea

doi:10.1029/2011jb008929

Cited by 15 publications

(24 citation statements)

References 106 publications

(164 reference statements)

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τ ()(, S) = ({, \begin{matrix} μ_{static} σ_{eff} + \frac{w}{u} P_{lub}, S_{0} < 1 \\ \frac{w}{u} P_{lub}, S_{0} \geq 1 \end{matrix})

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Section: Discussionmentioning

confidence: 99%

“…The model is parameterized using the Sommerfeld number, which is a measure of the lubrication pressure normalized by the normal stress. The fault shear strength dependence with the Sommerfeld numbers S 0 can be expressed as (Bizzarri, 2012;Brodsky & Kanamori, 2001) Note. κ = thermal conductivity, λ = thermal expansion coefficient, β = compressibility coefficient, η 0 = initial viscosity, ρ = density, C = specific heat, WG = Westerly granite.…”

Section: Fault Weakening Mechanismsmentioning

confidence: 99%

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Effect of Fluid Viscosity on Fault Reactivation and Coseismic Weakening

et al. 2020

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High-viscosity fluids are often used during hydraulic fracking operations in georeservoirs. Here we performed dedicated experiments to study the influence of fluid viscosity on fault reactivation and associated induced earthquakes. Experiments were conducted in the rotary-shear machine Slow to HIgh Velocity Apparatus on experimental fault of Westerly granite saturated by fluids with increasing viscosity (at room temperature) from 0.1 mPa s (water) to 1.2 Pa s (99% glycerol). Fault reactivation was triggered at constant effective normal stress by increasing the shear stress acting on the fault. Our results showed that independent of the viscosity, fault reactivation followed a Coulomb-failure criterion. Instead, fluid viscosity affected the fault weakening mechanism: flash heating was the dominant weakening mechanism in room humidity and water-saturated conditions, whereas the presence of more viscous fluids favored the activation of elasto-hydrodynamic lubrication. Independent of the weakening mechanism, the breakdown work W b dissipated during seismic faulting increased with slip U following a power law (W b ∝ U 1.25 ) in agreement with seismological estimates of natural and induced earthquakes.Plain Language Summary One of the most alarming recent findings in solid earth sciences is the worldwide exponential increase of human-induced seismicity. This is due to engineering operations in deep reservoirs for hydrocarbon production, CO 2 storage, wastewater storage, and exploitation of geothermal resources which result in the reactivation of faults hosted in the reservoirs. While the reactivation of faults due to fluid pressure has been extensively studied, the influence of fluid properties including its viscosity has been overlooked, even if the viscosity of injected fluids spans from the one of water to that of honey. In this study, we discuss the influence of stress perturbations on the reactivation of fluid-permeated experimental faults and on induced earthquakes. Our experimental observations suggest that the viscosity of the fluid does not influence the onset of fault reactivation. Instead, the viscosity of the fluid controls the type of deformation mechanism activated during induced earthquake rupture.

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τ ()(, S) = ({, \begin{matrix} μ_{static} σ_{eff} + \frac{w}{u} P_{lub}, S_{0} < 1 \\ \frac{w}{u} P_{lub}, S_{0} \geq 1 \end{matrix})

…”

Section: Discussionmentioning

confidence: 99%

Section: Fault Weakening Mechanismsmentioning

confidence: 99%

Effect of Fluid Viscosity on Fault Reactivation and Coseismic Weakening

et al. 2020

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“…Further, in our simulations we observed almost equal maximum friction coefficients for dry and saturated samples, while the drops in friction coefficient are larger for saturated case compared to the dry case leading to lower minimum friction after slip event for the saturated case. Similar observations are reported in the numerical and experimental studies [ Bizzarri , ; Scuderi et al ., ].…”

Section: Discussionmentioning

confidence: 99%

On the role of fluids in stick‐slip dynamics of saturated granular fault gouge using a coupled computational fluid dynamics‐discrete element approach

et al. 2017

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The presence of fault gouge has considerable influence on slip properties of tectonic faults and the physics of earthquake rupture. The presence of fluids within faults also plays a significant role in faulting and earthquake processes. In this paper, we present 3‐D discrete element simulations of dry and fluid‐saturated granular fault gouge and analyze the effect of fluids on stick‐slip behavior. Fluid flow is modeled using computational fluid dynamics based on the Navier‐Stokes equations for an incompressible fluid and modified to take into account the presence of particles. Analysis of a long time train of slip events shows that the (1) drop in shear stress, (2) compaction of granular layer, and (3) the kinetic energy release during slip all increase in magnitude in the presence of an incompressible fluid, compared to dry conditions. We also observe that on average, the recurrence interval between slip events is longer for fluid‐saturated granular fault gouge compared to the dry case. This observation is consistent with the occurrence of larger events in the presence of fluid. It is found that the increase in kinetic energy during slip events for saturated conditions can be attributed to the increased fluid flow during slip. Our observations emphasize the important role that fluid flow and fluid‐particle interactions play in tectonic fault zones and show in particular how discrete element method (DEM) models can help understand the hydromechanical processes that dictate fault slip.

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“…the analytical expression of the PR SFV (recall equation (10)). Second, and more importantly, we emphasize that the method of Mikumo et al [2003] has been proven to be adequate in the case of supershear ruptures, but it gives an underestimate of d 0 in the case of subshear events Bizzarri, 2010aBizzarri, , 2012c.…”

Section: Numerical Resultsmentioning

confidence: 89%

“…First, the curve reported in Figure 1 is what it results from the assumption of the two input parameters E G and Δ τ b , which enter directly in the analytical expression of the PR SFV (recall equation (10)). Second, and more importantly, we emphasize that the method of Mikumo et al [2003] has been proven to be adequate in the case of supershear ruptures, but it gives an underestimate of d 0 in the case of subshear events [ Tinti et al , 2004; Bizzarri , 2010a, 2012c]. …”

Section: Numerical Resultsmentioning

confidence: 99%

Analytical representation of the fault slip velocity from spontaneous dynamic earthquake models

Bizzarri¹

2012

J. Geophys. Res.

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[1] We have analyzed the most relevant features of three different analytical representations of the time evolution of the cosesimic slip velocity derived from theoretical basis; the so-called modified Yoffe function (MY), which pertains to a singular crack solution, the solution for a nonspontaneous crack obeying a position-weakening governing equation (PR) and the solution for a 1-D fault model subject to a linear slip-weakening friction law (B). By considering the same input parameters, we quantitatively compare these slip velocity functions (SVF) and we found that the time evolutions of the velocity and the correspondent slip predicted by the MY and B functions are very similar, while the PR predicts a very sharp peak. Correspondingly, the PR SVF is richer in high frequency and the fall off of its spectrum at high frequencies goes roughly as w -1.5 , while those of MY and B more closely follow w -2 . Then we select two spontaneous, 3-D, dynamic, subshear models, representing a crack-like or a pulse-like rupture and we account for both homogeneous and heterogeneous configurations. We then compare the three SVF in order to see how they are able to reproduce the 3-D solutions; we also show how the input parameters of the SVF can be constrained from the results of the dynamic models. In the homogeneous cases our results indicate that the MY and the PR SVF reproduce adequately well the main features of a dynamic solution in the case of a crack-like rupture. The PR function overestimates v peak and the MY SVF predicts a too rapid deceleration. In the case of a pulse-like rupture both the MY and the B SVF tend to underestimate v peak , but all of them capture very well the final cumulated fault slip. Moreover, the B function fits better that the MY the overall behavior of the fault slip. The considered SVF are able to reproduce the spectral fall off of a 3-D solution at intermediate frequencies (for w < 20 Hz), the MY and the PR for a crack-like rupture and the MY and the B SVF for a pulse-like rupture. In particular, for w < 10 Hz the spectral content of the B function is practically indistinguishable from that of the spontaneous pulse-like solution. In the heterogeneous configurations the analytical functions cannot reproduce all the spectral details of the numerical solutions, but we see how it is possible to fit the overall behavior of a single pulse in fault the slip velocity time history. The thorough analysis performed in this work can contribute to the discussion about the debated choice of the source time function to be used in the kinematic models, which in turn is extremely important in the contest of hazard assessment and ground motions generation, although stress heterogeneities, geometrical irregularities, attenuation and free surface effects can definitively smear the details of the analytical functions.Citation: Bizzarri, A. (2012), Analytical representation of the fault slip velocity from spontaneous dynamic earthquake models,

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The mechanics of lubricated faults: Insights from 3‐D numerical models

Cited by 15 publications

References 106 publications

Effect of Fluid Viscosity on Fault Reactivation and Coseismic Weakening

Effect of Fluid Viscosity on Fault Reactivation and Coseismic Weakening

On the role of fluids in stick‐slip dynamics of saturated granular fault gouge using a coupled computational fluid dynamics‐discrete element approach

Analytical representation of the fault slip velocity from spontaneous dynamic earthquake models

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