Progressive flash heating and the evolution of high‐velocity rock friction

Chen, Jiangzhi; Rempel, A. W.

doi:10.1002/2013jb010631

Cited by 12 publications

(45 citation statements)

References 50 publications

(137 reference statements)

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“…With increasing slip rates accompanying the onset of stick-slip, time is insufficient for heat diffusion, resulting in increased temperatures, and potentially, melting of asperity contacts. If this occurs, the shear strength of the contact can transition from frictional sliding to being governed by the viscous properties of the melt (Chen & Rempel, 2014;Rempel & Weaver, 2008), although many classic models assume that the weakened state has no shear strength (Rice, 1999(Rice, , 2006. Laboratory specimens are commonly inferred to have asperity contact sizes between~1 and 25 μm, based on extrapolation of direct observations made at low normal stresses (σ N < 20 MPa; Dieterich & Kilgore, 1994) and assuming a purely elastic asperity model (Greenwood & Williamson, 1966;Harbord et al, 2017;Nielsen et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Rheological Controls on Asperity Weakening During Earthquake Slip

et al. 2019

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Evolution of fault strength during the initial stages of seismic slip plays an important role in the onset of velocity‐induced weakening, which in turn, leads to larger earthquake events. A key dynamic weakening mechanism during the early stages of slip is flash heating, where stress concentrations at contacts on the interface lead to the rapid generation of heat. Although potential weakening from flash heating has been extensively modeled, there is little recorded microstructural evidence of its physical manifestations. We present results of a series of triaxial experiments on synthetic faults in quartz sandstone. Samples were subjected to a variety of normal stresses and ambient temperatures, to induce a range of slip event sizes and sliding velocities. We show the microstructural evolution of asperity interactions from the onset of flash heating through to the formation of grain‐scale areas of sheared melt. Using microstructural observations and mechanical data from the experiments, we model temperature and the viscoelastic behavior of the glass. Results suggest that, in the earliest stages of slip asperity contacts melt, but temperatures remain too low for viscous shear to occur within the melt layer. Instead melted asperities behave as glassy solids, facilitating continued frictional heating. With further slip, increased asperity temperatures allow the transition to viscous shear within the melt layer, facilitating weakening. These results highlight the dynamic evolution of the viscoelastic properties of the melt and resulting effects on asperity strength. Such complexity has, to‐date, not been fully addressed in modeling of flash heating.

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Section: Introductionmentioning

confidence: 99%

Rheological Controls on Asperity Weakening During Earthquake Slip

et al. 2019

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“…Seismologists have proposed thermal dynamic weakening mechanisms (where sliding friction τ slide < < τ fail ) for rock with enough physical detail that application to icequakes is feasible (e.g., Acosta et al, ; Bizzarri & Cocco, , ; Beeler et al, ; Bizzarri, ; Brantut & Mitchell, ; Brantut & Platt, ; Brantut & Viesca, ; Chen & Rempel, , ; Passelègue et al, ; Rempel & Weaver, ; Rice, , ; Sleep, ). The generic term “flash heating” is highly misleading and conflates two processes: (1) thermal weakening occurs at the micron‐scale asperity tips of real contact on the fault surface.…”

Section: Review Of Dynamic Weakening Mechanisms During Earthquakesmentioning

confidence: 99%

“…A major inconsistency arises with the assumption in equation that the strength of the model contact vanishes once the weakening displacement D weak is achieved (Acosta et al, ; Chen & Rempel, ; Rempel & Weaver, ; Sleep, ). No frictional heat is subsequently generated.…”

Section: Thermal Weakening Of Asperity Tips In Icementioning

confidence: 99%

“…The cooled contact should then strengthen, which is inconsistent with the assumption that its strength is near zero. Instead, the thin weakened zone of the tip self‐organizes so that its heat generation balances the heat lost by conduction (Acosta et al, ; Chen & Rempel, ; Rempel & Weaver, ; Sleep, ). Sleep () derived an easily evaluated self‐consistent formula for macroscopic shear traction for thermal weakening at asperity tips,

τ_{\mod} = P_{eff} μ_{RS} ([], 2 {(\frac{V_{weak}}{V_{slip}})}^{1 / 2} - ((), \frac{V_{weak}}{V_{slip}}))

…”

Section: Thermal Weakening Of Asperity Tips In Icementioning

confidence: 99%

“…In this model, the local strength of the contact rapidly decreases when the contact temperature change exceeds Δ T weak , which precludes the temperature from greatly exceeding Δ T weak . Rempel and Weaver () and Chen and Rempel () presented an analytical model where latent heat is important. However, it is difficult to compute the shear stress from their model.…”

Section: Thermal Weakening Of Asperity Tips In Icementioning

confidence: 99%

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Friction in Cold Ice Within Outer Solar System Satellites With Reference to Thermal Weakening at High Sliding Velocities

Sleep

2019

JGR Planets

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The icy shells of Enceladus and Europa consist from top down of cold (~100 K) ice at low (<0.1 MPa) pressure, cold ice at high pressure up to ~10 MPa, and warm ice near 273 K the base. The pressure ~10 MPa and temperature near 273 K of basal ice within Enceladus and Europa are similar to that within terrestrial glaciers that are known to have seismicity (icequakes). Warm ice easily melts during sliding so its icequakes are qualitatively explained and expected on these satellites if the macroscopic strain rates are comparable to those within terrestrial glaciers subjected to oceanic tides. However, cold ice at high pressures does not readily macroscopically melt during sliding. A dynamic weakening mechanism for crustal faults in rock may be applicable to Enceladus and Europa. Micron‐scale real contacts support ~0.4‐GPa shear tractions and normal tractions on rapidly sliding ice faults. At sliding velocities above ~0.1 m/s, the asperity tips of the contacts become hot and weak in ice. The macroscopic friction depends on the average strength of the asperity tips during the lifetimes of contact. The strength of the asperity tips self‐organizes so that frictional heating balances the heat lost from the asperity tip by conduction. The macroscopic coefficient of friction at coseismic sliding velocities decreases to a modest fraction of the low‐velocity coefficient of friction, but does not approach zero. This velocity‐weakening mechanism likely allows major icequakes within the cold interiors of Europa and Enceladus.

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Shear zone broadening controlled by thermal pressurization and poroelastic effects during model earthquakes

Chen

Rempel

2015

JGR Solid Earth

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As a result of the comminution that takes place over numerous earthquake cycles, mature faults are characterized by thick layers of pulverized gouge with finite porosity that is saturated with water at seismogenic depths. The heat generated during earthquakes raises the gouge temperature and thermal expansion of the pore fluid, and surrounding solids produce elevated pore pressures that cause fault strength to decrease in the process known as thermal pressurization. Building upon this framework, we describe a model that imposes a plane-strain configuration and shows that the stress variations caused by porothermoelasticity promote the Mohr-Coulomb failure of previously undeformed regions. Except in special cases where the friction is rate strengthening, we find that the frictional strength must vary throughout the post-failure region, which we identify in our model with the shear zone. We introduce a strain rate function that describes the overall influence of distributed slip on energy dissipation and fault strength as the shear zone thickness expands. Using typical fault parameters at 7 km depth, the shear zone reaches several millimeters of thickness after 1 s sliding at an overall rate of 1 m/s. The expansion of the shear zone limits the temperature rise to several hundred degrees Celsius, and the average fault strength falls to about a tenth of the static frictional strength.

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Progressive flash heating and the evolution of high‐velocity rock friction

Cited by 12 publications

References 50 publications

Rheological Controls on Asperity Weakening During Earthquake Slip

Rheological Controls on Asperity Weakening During Earthquake Slip

Friction in Cold Ice Within Outer Solar System Satellites With Reference to Thermal Weakening at High Sliding Velocities

Shear zone broadening controlled by thermal pressurization and poroelastic effects during model earthquakes

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