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  • 1
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    Frictional Melt and Seismic Slip (2007)
    Details
    Publication Date: 2017-04-04
    Description: Abstract. Frictional melt is implied in a variety of processes such as seismic slip, ice skating and meteorite combustion. A steady-state can be reached when melt is continuously produced and extruded from the sliding interface, as shown recently in a number of laboratory rock friction experiments. A thin, low viscosity, high temperature melt layer is formed resulting in low shear resistance. A theoretical solution describing the coupling of shear heating, thermal diffusion and extrusion is obtained, without imposing a-priori the melt thickness. The steady-state shear traction can be approximated at high slip-rates by the theoretical form: τss = σ1/4 n A √ R? log(2V/W) V/W under a normal stress σn, slip rate V , radius of contact area R (A is a dimensional normalizing factor and W a characteristic rate). Although the model offers a rather simplified view of a complex process, the predictions are compatible with experimental observations. In particular, we consider laboratory simulations of seismic slip on earthquake faults. A series of high velocity rotary shear experiments on rocks, performed for σn in the range 1-20 MPa and slip rates in the range 0.5-2 m/s, is confronted to the theoretical model. The behavior is reasonably well reproduced, though the effect of radiation loss taking place in the experiment somewhat alters the data. The scaling of friction with σn, R and V in the presence of melt suggests that extrapolation of laboratory measures to real Earth is a highly non-linear, non-trivial exercise.
    Description: In press
    Description: 10-18
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: friction ; pseudotachylite ; frictional melt ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: manuscript
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  • 2
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    Frictional Melt and Seismic Slip (2008)
    AGU
    Details
    Publication Date: 2017-04-04
    Description: Frictional melt is implied in a variety of processes such as seismic slip, ice skating,and meteorite combustion. A steady state can be reached when melt is continuously produced and extruded from the sliding interface, as shown recently in a number of laboratory rock friction experiments. A thin, low-viscosity, high-temperature melt layer is formed resulting in low shear resistance. A theoretical solution describing the coupling of shear heating, thermal diffusion, and extrusion is obtained, without imposing a priori the melt thickness. The steady state shear traction can be approximated at high slip rates by the theoretical form : tau=sn^[1/4] (A/sqrt[R]) sqrt[ log[2 V/W] / (V/W) ] under a normal stress sn, slip rate V, radius of contact area R (A is a dimensional normalizing factor and W is a characteristic rate). Although the model offers a rather simplified view of a complex process, the predictions are compatible with experimental observations. In particular, we consider laboratory simulations of seismic slip on earthquake faults. A series of highvelocity rotary shear experiments on rocks, performed for sn in the range 1–20 MPa and slip rates in the range 0.5–2 m/s, is confronted to the theoretical model. The behavior is reasonably well reproduced, though the effect of radiation loss taking place in the experiment somewhat alters the data. The scaling of friction with sn, R, and V in the presence of melt suggests that extrapolation of laboratory measures to real Earth is a highly nonlinear, nontrivial exercise.
    Description: Published
    Description: B01308
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: friction ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 3
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    On the transient behavior of frictional melt during seismic slip (2010)
    American Geophysical Union
    Details
    Publication Date: 2017-04-04
    Description: In a recent work on the problem of sliding surfaces under the presence of frictional melt (applying in particular to earthquake fault dynamics), we derived from first principles an expression for the steady state friction compatible with experimental observations. Building on the expressions of heat and mass balance obtained in the above study for this particular case of Stefan problem (phase transition with a migrating boundary) we propose here an extension providing the full time-dependent solution (including the weakening transient after pervasive melting has started, the effect of eventual steps in velocity and the final decelerating phase). A system of coupled equations is derived and solved numerically. The resulting transient friction and wear evolution yield a satisfactory fit (1) with experiments performed under variable sliding velocities (0.9-2 m/s) and different normal stresses (0.5-20 MPa) for various rock types and (2) with estimates of slip weakening obtained from observations on ancient seismogenic faults that host pseudotachylite (solidified melt). The model allows to extrapolate the experimentally observed frictional behavior to large normal stresses representative of the seismogenic Earth crust (up to 200 MPa), high slip rates (up to 9 m/s) and cases where melt extrusion is negligible. Though weakening distance and peak stress vary widely, the net breakdown energy appears to be essentially independent of either slip velocity and normal stress. In addition, the response to earthquake-like slip can be simulated, showing a rapid friction recovery when slip rate drops. We discuss the properties of energy dissipation, transient duration, velocity weakening, restrengthening in the decelerating final slip phase and the implications for earthquake source dynamics.
    Description: S.N. and G.D.T. were supported by a European Research Council Starting Grant Project (acronym USEMS) and by a Progetti di Eccellenza Fondazione Cassa di Risparmio di Padova e Rovigo. We are grateful to Nick Beeler (and to an anonymous referee) for their constructive reviews and their help to improve the clarity of the manuscript.
    Description: Published
    Description: B10301
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: open
    Keywords: Friction ; Melt ; Earthquake dynamics ; fault mechanics ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Relating High-Velocity Rock-Friction Experiments to Coseismic Slip in the Presence of Melts (2010)
    AGU
    Details
    Publication Date: 2020-02-24
    Description: The dynamic strength (tau_f) of faults during coseismic slip is a major unknown in earthquake mechanics, though it has crucial influence on rupture properties, dynamic stress drop, radiated energy and heat produced during slip. In order to provide constraints on tau_f, High-Velocity Rock Friction Experiments (HVRFE) are conducted on natural rocks with rotary shear apparatuses, reproducing slip (several meters) and slip rate (0.1-3 m/s) typical of large earthquakes. Among the various weakening mechanisms possibly activated during seismic slip, we focus on melt lubrication. Solidified, friction-induced melts (pseudotachylytes) decorate some exhumed seismic faults, showing that melt can occur on natural faults, though its frequency is still a matter of debate. In the presence of melt, tau_f undergoes an initial strengthening stage, followed by a dramatic weakening stage (thermal runaway). Field estimates based on pseudotachylyte thickness and experimental measures of tau_f suggest large stress drops once thermal runaway is achieved. These estimates of tau_f are compatible with large dynamic stress drops and high radiation efficiency, as observed for some earthquakes. Moreover, the threshold for the onset of thermal runaway might explain differences between the mechanics of small (M 〈 4) and large earthquakes. A simple mathematical model coupling melting, extrusion and thermal diffusion reproduces some observed experimental features such as the duration of the weakening stage and the convergence to a steady-state.
    Description: Published
    Description: 121-134
    Description: 3.1. Fisica dei terremoti
    Description: reserved
    Keywords: friction, pseudotachylite, exhumed faults, laboratory experiments, High velocity friction ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: book chapter
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