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1 doi: /nature09838 (A) N330 (Instron 8500) V = m/s σ n = 5 MPa HVR381c (Kyoto Univ.) V = m/s σ n = 5 MPa Fig. A. Experiments performed with nov aculite (99.9% quartz) in the Instron 8500 rotary shear at Brown University (N330, Di Toro et al., 2004) and in the rotary shear apparatus designed by T. Shimamoto at Kyoto Univerisity (HVR381c, Hirose & Di Toro, unpublished). Novaculite had a similar frictional behavior (and steady-state value) under similar deformation conditions (normal stress of 5 MPa and slip rate of about 5-7 cm/s). The similarity of the experimental results allows to compare mechanical data obtained from the two apparatus as we did in Fig. 1. (B) Fig. B. Under similar deformation conditions (slip rate from 1 to 1.5 m/s and normal stress from 4 to 5.8 MPa), aluminum had a different mechanical behavior (slip strengthening) and higher friction values at steady-state ( µ ss > 1) compared to those achieved by rocks (slip weakening and µ ss < 0.2, respectively) (Han et al., unpublished data). These experiments rule out that the mechanical data reported in the main text in Fig. 1-4 (e.g., low friction coefficient) are the result of the experimental apparatus used. We conclude that the mechanical data reported in the paper correspond to the actual frictional behavior of the rocks. 1

2 Section 2 Data for steady-state friction coefficient vs. slip rate plotted in Figure 3 Quartz (Novaculite) N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 HVR381C Hirose and Di Toro, unpubl. HVR381C Hirose and Di Toro, unpubl. Quartz (Novaculite) HVR Di Toro et al., 2006b HVR Di Toro et al., 2006b Quartz sandstone σ n V μ ss Ref E Dieterich, E Dieterich, E Dieterich,

3 E Dieterich, E Dieterich, 1978 Serpentinite HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 HVR Hirose and Bystricky, 2007 Granite σ n V μ ss Ref Dieterich, Dieterich, Dieterich, Dieterich, Dieterich, Dieterich, Dieterich, Dieterich, 1978 Granite W Di Toro et al., 2004 W Di Toro et al., 2004 W Di Toro et al., 2004 W Di Toro et al., 2004 W Di Toro et al., unpubl. W Di Toro et al., unpubl. W Di Toro et al., unpubl. W Di Toro et al., unpubl. W Di Toro et al., unpubl. 3

4 W Di Toro et al., unpubl. W Di Toro et al., unpubl. W Di Toro et al., unpubl. W Di Toro et al., unpubl. W Di Toro et al., unpubl. Tonalite and tonalitic cataclasite HVR Di Toro et al., 2006a HVR Di Toro et al., 2006a HVR Di Toro et al., 2006a HVR379 (To-Cc) Di Toro et al., 2006b HVR371 (Cc-Cc) Di Toro et al., 2006b Peridotite HVR Di Toro et al., 2006b HVR Di Toro et al., 2006b HVR Di Toro et al., 2006b HVR Di Toro et al., 2006b HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR652* Del Gaudio et al., 2009 Second velocity step HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 Third velocity step HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 Fourth Velocity step HVR Del Gaudio et al.,

5 Gabbro HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 Monzodiorite 5

6 HVR Mizoguchi et al., unpubl. HVR Mizoguchi et al., unpubl. HVR Mizoguchi et al., unpubl. HVR Mizoguchi et al., unpubl. HVR Mizoguchi et al., unpubl. HVR Mizoguchi et al., unpubl. HVR Mizoguchi et al., unpubl. HVR Mizoguchi et al., unpubl. HVR Mizoguchi et al., unpubl. Nojima fault clay-rich dry gouge HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2009 HVR Mizoguchi et al., 2009 HVR Mizoguchi et al., 2007 Vaiont landslide clay-rich dry gouge HVR Ferri et al., HVR Ferri et al., 2010 HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. Anhydrite dry gouge S1 An_ De Paola et al. unpubl. S5 An_ De Paola et al. unpubl. S9 An_ De Paola et al. unpubl. S11 An_ De Paola et al. unpubl. S26 An_ De Paola et al. unpubl. S21 An_ De Paola et al. unpubl. S8 An_ De Paola et al. unpubl. S32 An_ De Paola et al. unpubl. 6

7 S27 An_ De Paola et al. unpubl. S19 An_ De Paola et al. unpubl. S39 An_ De Paola et al. unpubl. S33 An_ De Paola et al. unpubl. Dolomite dry gouge S15 Do_ De Paola et al S37Do_ De Paola et al S24 Do_ De Paola et al S38 Do_ De Paola et al S22 Do_ De Paola et al S35Do_ De Paola et al S28 Do_ De Paola et al S7 Do_ De Paola et al S20 Do_ De Paola et al S18 Do_ De Paola et al S16 Do_ De Paola et al S12 Do_ De Paola et al S13 Do_ De Paola et al Dolomite saturated gouge S30 Do wet_ De Paola et al. unpubl. S17 Do wet_ De Paola et al. unpubl. S25 Do wet_ De Paola et al. unpubl. S4 Do wet_ De Paola et al. unpubl. Dolomite gouge σ n V μ ss Ref E Shimamoto and Logan, E Shimamoto and Logan, E Shimamoto and Logan, 1981 Dolomite σ n V μ ss Ref E Weeks and Tullis, E Weeks and Tullis, 1985 Dolomite HVR Han et al., 2010 HVR Han et al., 2010 HVR Han et al.,

8 Marble (calcite) HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 Calcite (cohesive) C302A Di Toro et al., unpubl. C302B Di Toro et al., unpubl. Calcite gouge σ n V μ ss Ref E Shimamoto and Logan, E Shimamoto and Logan, E Shimamoto and Logan, 1981 Calcite gouge σ n V μ ss Ref E Morrow et al.,

9 S2_1360 gy De Paola et al. unpubl. S3_1361 gy De Paola et al. unpubl. S5_1362 gy De Paola et al. unpubl. S6_1363 gy De Paola et al. unpubl. S7_1364 gy De Paola et al. unpubl. S16_1383 gy De Paola et al. unpubl. S17_1384 gy De Paola et al. unpubl. S19_1386 gy De Paola et al. unpubl. S8_1365 gy De Paola et al. unpubl. S10_1367 gy De Paola et al. unpubl. S11_1368 gy De Paola et al. unpubl. 9

10 References The published experimental data reported in Fig. 3 are from: Del Gaudio, P., Di Toro, G., Han, R., Hirose, T., Nielsen, S., Shimamoto, T., Cavallo, A., Frictional melting of peridotite and seismic slip. Journal of Geophysical Research, 114, doi: 1029/2008JB De Paola, N., Hirose, T., Mitchell, T., Di Toro, G., Togo, T., Shimamoto, T Fault lubrication and earthquake propagation in thermally unstable rocks. Geology, 39, Dieterich, J. H., Time-dependent friction and the mechanics of stick slip. Pure and Applied Geophysics, 116, Di Toro, G., D. L. Goldsby, and T. E. Tullis, Friction falls towards zero in quartz rock as slip velocity approaches seismic slip rates. Nature, 427, Di Toro, G., Hirose, T., Nielsen, S., Pennacchioni, G., Shimamoto, T., 2006a. Natural and experimental evidence of melt lubrication of faults during earthquakes. Science, 311, Di Toro, G., Hirose, T., Nielsen, S., Shimamoto, T., 2006b. Relating high-velocity rock friction experiments to coseismic slip. In Radiated Energy and the Physics of Faulting, Eds. Abercrombie, R., McGarr, A., Di Toro, G., Kanamori, H., Geophysical Monograph Series Vol. 170 (American Geophysical Union, Washington, D.C.), pp Ferri F., Di Toro G., Hirose T., Shimamoto T Evidences of thermal pressurization in high velocity friction experiments on smectite-rich gouges. Terra Nova, 22, pp Han, R., T. Shimamoto, T. Hirose, J.-H., Ree, and J. Ando, Ultralow friction of carbonate faults caused by thermal decomposition. Science, 316, Han, R., Hirose, T. and Shimamoto, T Strong velocity-weakening and powder lubrication of simulated carbonate faults at seismic slip-rates. J. Geophys. Res.,115, doi: /2008jb Hirose, T., and M. Bystricky, Extreme dynamic weakening of faults during dehydration by coseismic shear heating, Geophys. Res. Lett., 34, L14311, doi: /2007gl Mizoguchi, K., T. Hirose, T. Shimamoto, and E. Fukuyama, Reconstruction of seismic faulting by high-velocity friction experiments: An example of the 1995 Kobe earthquake, Geophys. Res. Lett., 34, L01308, doi: /2006gl027931, Mizoguchi, K., Hirose, T., Shimamoto, T, Fukuyama, E., High-velocity frictional behavior and microstructure evolution of fault gouge obtained from Nojima fault, southwest Japan, Tectonophysics 471, Morrow, C. A., D.E. Moore, and D.A. Lockner, The effect of mineral bond strength and adsorbed water on fault gouge frictional strength, Geophys. Res. Lett., 27,

11 Nielsen, S., Di Toro, G., Hirose, T., Shimamoto, T., Frictional Melt and Seismic Slip, Journal of Geophysical Research vol. 113 B01308, doi: /2007jb Shimamoto, T., and J. M. Logan, Effects of simulated fault gouge on the sliding behavior of Tennessee sandstone: nonclay gouges, J. Geophys. Res., 86, Weeks, J. D, and T. E. Tullis, Frictional sliding of dolomite: a variation in constitutional behavior, J. Geophys. Res., 90,

12 Supplemental Information 3 Summary of the weakening mechanisms activated in the high velocity rock friction experiments Here we summarize the inferred weakening mechanisms activated during seismic slip and the measured and estimated temperatures achieved in the slipping zone. For V > 0.03 m/s, quartz-built rocks (novaculite) exhibited a dramatic decrease in friction (Di Toro et al., 2004), attributed to the production of silica-gels (silica-gel lubrication, Goldsby and Tullis, 2002). Gel formation should be aided by solid state amorphization of quartz in the presence of water derived from room humidity, fluid inclusions and other pore. The maximum temperature measured with thermocouples and estimated with FEM modeling was about 150 o C (Di Toro et al., 2004). For silicate-built rocks such as tonalites (Di Toro et al., 2006) peridotite (Del Gaudio et al., 2009) and gabbros (Hirose and Shimamoto, 2005; Nielsen et al., 2008), dramatic weakening occurred once a continuous layer of melt (melt lubrication) separated the sliding surfaces. The maximum temperature measured with thermocouples and estimated with FEM modeling was comprised between 1000 and 1800 o C, depending on rock type (Del Gaudio et al., 2009). Further experiments and theoretical work confirmed the non-linear dependence of shear stress with normal stress ( τ ) (Nielsen et al., 2008), which is typical of lubrication operated by fluids (Persson, 2000). For antigorite-bearing serpentinite, a hydrated rock, dramatic weakening (μ = 0.1) was 0.25 σ n concurrent to emission of H 2 O from the slipping zone (Hirose and Bystricky, 2007). The maximum estimated temperature by means of FEM modeling was about 250 o C. Since dehydration of serpentinite occurs at T > 550 o C, Hirose and Bystricky (2007) proposed that flash heating (Rice 2006) at the asperity contacts was responsible for dehydration reactions and weakening. 12

13 For calcite-built rocks such as marbles, dramatic weakening (μ = 0.1) was concurrent to emission of CO 2 from the slipping zone and production of nanometric particles of lime and portlandite (Han et al., 2007). The maximum measured average temperature was about 900 o C, which is consistent with the breakdown temperature for CaCO 3 CaO + CO 2. Han et al. (2007; 2010) attributed weakening to thermal decomposition and production of nanopowders. For dolomite-bearing gouges, dramatic weakening (μ = 0.1) was concurrent to emission of CO 2 from the slipping zone and production of nanometric particles of periclase and Mg-rich calcite (De Paola et al., 2008). The maximum estimated temperature was about 550 o C, which is consistent with the breakdown temperature of dolomite (CaMg(CO 3 ) 2 (Ca,Mg)CO 3 + MgO + CO 2 ). Since the samples were confined by Teflon rings, De Paola et al. (2011) attributed the observed weakening as due to the combination of flash heating, nanopowder lubrication and thermal pressurization caused by overpressured CO 2. For gypsum-bearing gouges, dramatic weakening (μ = 0.1) was contemporaneous with emission of H 2 O from the slipping zone and production of nanoparticles of bassanite (CaSO 4 (0.5)H 2 O) and anhydrite (CaSO 4 ). For atmospheric low pressures, gypsum partial dehydration (CaSO 4 2H 2 O CaSO 4 (0.5)H 2 O (calcium sulphate hemihydrate) H 2 O) initiates at the breakdown temperature of about 100 o C and gypsum total dehydration (CaSO 4 0.5H 2 O CaSO 4(calcium sulphate anhydrite) + 0.5H 2 O) is completed at the temperature of about 200 o C (see SI section 5). These temperatures are in the range of the estimated temperatures achieved in the slipping zone (see SI section 4). The actual weakening mechanisms are under investigation, though a combination of flash heating, thermal pressurization and nanopowder lubrication seems likely. For anhydrite gouges, dynamic weakening might result by a combination of flash heating and nanopowder lubrication (De Paola et al., 2011). In fact, the melting temperature for anhydrite at the 13

14 investigated experimental conditions is 1460 o C, which is well above the temperature achieved in the experiments. Activation of nanopowder lubrication has been invoked also for experiments performed on marble (Han et al., 2007; 2010) and granite (Reches & Lockner, 2010). For kaolinite-bearing clay-rich fault gouges, dramatic weakening (Mizoguchi et al., 2007; 2009) was concomitant to emission of H 2 O and production of metakaolinite (Brantout et al., 2008). The maximum measured temperature was < 350 o C, which is consistent with the breakdown temperature for Kln Meta-Kln + H 2 O. The actual weakening mechanism remains unknown although it may result from a combination of flash heating and weakening, thermal pressurization and nanopowder lubrication (Ferri et al., 2010). References Brantut, N., Schubnel, A., Rouzaud J.-N., Brunet, F. & Shimamoto T. High-velocity frictional properties of a clay bearing fault gouge and implications for earthquake mechanics. J. Geophys. Res. 113, B10401, doi: /2007jb (2008). Del Gaudio, P. et al. Frictional melting of peridotite and seismic slip. J. Geophys. Res. 114, doi: 1029/2008JB (2009). De Paola, N., et al. Fault lubrication and earthquake propagation in thermally unstable rocks. Geology 39, (2011). Di Toro, G., Goldsby, D.L. & Tullis, T.E. Friction falls towards zero in quartz rock as slip velocity approaches seismic rates. Nature 427, (2004). Di Toro, G., Hirose, T. Nielsen, S., Pennacchioni, G. & Shimamoto, T. Natural and experimental evidence of melt lubrication of faults during earthquakes. Science 311, (2006). Ferri, F., Di Toro, G., Hirose, T. & Shimamoto, T. Evidences of thermal pressurization in high velocity friction experiments on smectite-rich gouges. Terra Nova, 22, (2010). 14

15 Goldsby, D. & Tullis, T. E. Low frictional strength of quartz rocks at subseismic slip rates. Geophys. Res. Lett. 29, doi: /2002gl (2002). Han, R., Shimamoto, T., Hirose, T., Ree, J-H & Ando, J. Ultralow friction of carbonate faults caused by thermal decomposition. Science 316, (2007). Han, R., Hirose, T. & Shimamoto, T. Strong velocity weakening and powder lubrication of simulated carbonate faults at seismic slip rates. J. Geophys. Res., 115, doi: /2008jb00613 (2010). Hirose, T. & Shimamoto, T. Growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting, J. Geophys. Res. 110, B05202, doi: /2004jb (2005). Hirose, T. & Bystricky M. Extreme dynamic weakening of faults during dehydration by coseismic shear heating. Geophys. Res. Lett. 34, doi: /2007gl (2007). Mizoguchi, K., Hirose, T., Shimamoto, T. & Fukuyama, E. Reconstruction of seismic faulting by highvelocity friction experiments: An example of the 1995 Kobe earthquake, Geophys. Res. Lett. 34, L01308, doi: /2006gl02793 (2007). Mizoguchi, K., Hirose, T., Shimamoto, T. & Fukuyama, E. High-velocity frictional behavior and microstructure evolution of fault gouge obtained from Nojima fault, southwest Japan. Tectonophysics 471, (2009). Nielsen, S., Di Toro, G., Hirose, T. & Shimamoto T. Frictional melt and seismic slip. J. Geophys. Res. 113 B01308, doi: /2007jb (2008). Persson, B.N.J. Sliding Friction: Physical Principles and Applications (Springer, Heidelberg, Germany, 2000). Reches, Z. & Lockner, D.A. Fault weakening and earthquake instabilty by powder lubrication. Nature 467, (2010). 15

16 Section 4 Data for power densities plotted in Figure 4 plus estimates for W b and ΔT LOW TO HIGH VELOCITY EXPERIMENTS Quartz-Novaculite, cohesive (gelification) m MPa MW m -2 MJ m -2 o C N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 N Di Toro et al., 2004 Dolomite, cohesive (decarbonation) m MPa MW m -2 MJ m -2 o C HVR Han et al., 2010 HVR Han et al., 2010 HVR Han et al., 2010 Calcite, cohesive (decarbonation and nanopowder lubrication) m MPa MW m -2 MJ m -2 o C HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al.,

17 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 HVR Han et al., 2007 Peridotite, cohesive (melting) m MPa MW m -2 MJ m -2 o C HVR Di Toro et al., 2006b HVR Di Toro et al., 2006b HVR Di Toro et al., 2006b HVR Di Toro et al., 2006b HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR Del Gaudio et al., 2009 HVR652* Del Gaudio et al., 2009 Gabbro, cohesive (melting) m MPa MW m -2 MJ m -2 o C HVR Nielsen et al., 2008 HVR Nielsen et al., 2008 Tonalite, cohesive (melting) m MPa MW m -2 MJ m -2 o C HVR Di Toro et al., 2006a HVR Di Toro et al., 2006a 17

18 HVR Di Toro et al., 2006a HVR379 (To-Cc Di Toro et al., 2006b HVR371 (Cc-Cc Di Toro et al., 2006b Monzodiorite, cohesive (melting) m MPa MW m -2 MJ m -2 o C HVR Mizoguchi & Hirose, unpub HVR Mizoguchi & Hirose, unpub Nojima Fault clay-rich dry gouge, non-cohesive (nanopowder lubr., flash heating, dehydration and therm. press.) m MPa MW m -2 MJ m -2 o C HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2007 HVR Mizoguchi et al., 2009 HVR Mizoguchi et al., 2009 m MPa MW m -2 MJ m -2 o C HVR Ferri et al., 2010 HVR Ferri et al., 2010 HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. HVR Ferri et al., unpubl. Anhydrite dry gouge, non cohesive (nanopowders lubrication and flash heating) m MPa MW m -2 MJ m -2 o C S1 An_ De Paola et al. unpubl. S5 An_ De Paola et al. unpubl. S9 An_ De Paola et al. unpubl. S11 An_ De Paola et al. unpubl. S26 An_ De Paola et al. unpubl. S21 An_ De Paola et al. unpubl. 18

19 S8 An_ De Paola et al. unpubl. S32 An_ De Paola et al. unpubl. S27 An_ De Paola et al. unpubl. S19 An_ De Paola et al. unpubl. S39 An_ De Paola et al. unpubl. S33 An_ De Paola et al. unpubl. Dolomite dry gouge, non-cohesive (nanopowders lubrication, decarbonation, thermal press. and flash heating) m MPa MW m -2 MJ m -2 o C S15 Do_ De Paola et al S37Do_ De Paola et al S24 Do_ De Paola et al S38 Do_ De Paola et al S22 Do_ De Paola et al S35Do_ De Paola et al S28 Do_ De Paola et al S7 Do_ De Paola et al S20 Do_ De Paola et al S18 Do_ De Paola et al S16 Do_ De Paola et al S12 Do_ De Paola et al S13 Do_ De Paola et al Gypsum dry gouge, non-cohesive (nanopowders lubrication, dehydration, thermal press. and flash heating) m MPa MW m -2 MJ m -2 o C S2_1360 gy De Paola et al. unpubl. S3_1361 gy De Paola et al. unpubl. S5_1362 gy De Paola et al. unpubl. S6_1363 gy De Paola et al. unpubl. S7_1364 gy De Paola et al. unpubl. S16_1383 gy De Paola et al. unpubl. S17_1384 gy De Paola et al. unpubl. S19_1386 gy De Paola et al. unpubl. S8_1365 gy De Paola et al. unpubl. S10_1367 gy De Paola et al. unpubl. S11_1368 gy De Paola et al. unpubl. LOW VELOCITY EXPERIMENTS Dolomite m MPa MW m -2 MJ m -2 o C E E-05 Weeks and Tullis, E E-06 Weeks and Tullis,

20 Calcite gouge m MPa MW m -2 MJ m -2 o C E E-05 Morrow et al.,2000 Granite m MPa MW m -2 MJ m -2 o C E E-04 Dieterich, E E-04 Dieterich, E E-06 Dieterich, E E-06 Dieterich, E E-06 Dieterich, E E-06 Dieterich, E E-07 Dieterich, E E-07 Dieterich, 1978 Dolomite gouge m MPa MW m -2 MJ m -2 o C E E-04 Shimamoto & Logan, E E-04 Shimamoto & Logan, E E-04 Shimamoto & Logan, 1981 Dolomite gouge m MPa MW m -2 MJ m -2 o C E E-04 Shimamoto & Logan, E E-04 Shimamoto & Logan, E E-04 Shimamoto & Logan, 1981 Quartz sandstone m MPa MW m -2 MJ m -2 o C E E-10 Dieterich, E E-09 Dieterich, E E-08 Dieterich, E E-07 Dieterich, E E-06 Dieterich,

21 Section 5 Thermal and reaction kinetics properties Thermal properties Density Thermal capacity Thermal conductivity Thermal diffusivity (*) Breakdown Temperature (at 1-atm) ρ c p Κ κ T b kg m -3 J kg -1 K -1 W m -1 K m 2 s -1 K Minerals anhydrite 2950 (1) 721 (2) 5.36 (3) (melting) calcite 2710 (1) 833 (2) 3.50 (3) (decarb.) dolomite 2900 (1) 858 (2) 4.78 (3) (1 st decarb.) gypsum 2350 (1) 1050 (2) 3.16 (3) (1 st dehydr.) kaolinite quartz 2650 (1) 752 (2) 8.00 (3) (melting) Rocks (**) cataclasite (Adamello, Italy) 2746 (4) 765 (4) 3.78 (4) 1.8 clay-rich gouge 2500 (2) gabbro (India) 3242 (5) 755 (5) 3.70 (5) 1.5 peridotite (Balmuccia, Italy) 3363 (6) 843 (6) 5.10 (6) 1.8 tonalite (Adamello, Italy) 2795 (4) 754 (4) 3.8 (4) 1.8 All properties at 300 K (*) κ = K/(ρ c p ) (**) rock properties derived from mineral properties and based on mineral modal content 21

22 Reaction kinetics properties Type of reaction Pre-exponential factor Activation energy Ref. s -1 J mol -1 calcite decarbonation (7) dolomite decarbonation (8) gypsum dehydration (9) kaolinite dehydration (10) 22

23 References thermal properties and reaction kinetics (1) Deer, W.A., Howie, R.A., Zussman, J., An Introduction to the Rock-Forming Minerals. Longman, Harlow. (2) Holland, T.B., Powell, R., An enlarged and updated internally consistent thermodynamic dataset with uncertainties and correlations: the system K2O-Na2O-CaO-MgO-MnO-FeO-Fe2O3-Al2O3-TiO2-SiO2- C-H2-O2. Journal of Metamorphic Geology 8, (3) Clauser, C., Huenges, E., Thermal conductivity of Rocks and Minerals. In: Aherens J.T. (Ed.), Rock Physics and Phase Relations. A Handbook of Physical Constants. AGU Reference Shelf 3, pp (4) Di Toro, G., Pennacchioni, G., Superheated friction-induced melts in zoned pseudotachylytes within the Adamello tonalites (Italian Southern Alps). Journal of Structural Geology 26, (5) Hirose, T., Shimamoto, T., Growth of molten zone as a mechanism of slip weakening of simulated faults in gabbro during frictional melting. Journal of Geophysical Research 110, B05202, doi: /2004jb003207, (6) Del Gaudio, P., Di Toro, G., Han, R., Hirose, T., Nielsen, S., Shimamoto, T., Cavallo, A., Frictional melting of peridotite and seismic slip. Journal of Geophysical Research 114, doi: 1029/2008JB (7) Yue, L., Shui, M. & Xu, Z. The decomposition kinetics of nanocrystalline calcite. Thermochimica Acta 335, (1999). (8) Gunasekaron, S., Anbalagan, G., Thermal decomposition of natural dolomite. Bullettin Material Sciences 30, No. 4, (9) Hudson-Lamb,D.L., Strydoma, C.A., Potgieter, J.H., The thermal dehydration of natural gypsum and pure calcium sulphate dihydrate (gypsum). Thermochimica Acta 282/283, (10) Bellotto, M., Gualtieri, A., Artioli, G., Clark, S.M., Kinetic Study of the Kaolinite-Mullite Reaction Sequence. Part I: Kaolinite Dehydroxylation. Physics and Chemestry of Minerals 22,

24 Note on the Activation Energies of mechanically-activated reactions As discussed in the main text, the work rate can be so intense to grind and mill the rock (producing nanometric in size particles) and to trigger mechanically-and thermally-activated chemical reactions. It follows that we should use the activation energy for chemical reactions involving nanoparticles. In the case of calcite, when the grain size decreases from 2-5 micron to 40 nm (grain size typically found in the experiments by Han et al., 2007, 2010), the activation energy for the decarbonation reaction decreases from 200 kj/mol to 130 kj/mol (see Table 1 below from Yue et al., 1999). Table 1. The reference calcium carbonate (CaCO3) refers to particles of 2-5 micron in size. The nano-particle calcium carbonate referes to particles of 40 nm in size. The activation energy for decarbonation of nanoparticles of calcite is 40% lower than that for micron is size particles (From Yue et al., 1999). In the study by Yue et al. (1999), the nanoparticles were produced by means of chemical precipitation, so the particles were not plastically deformed as the nanoparticles produced during high-velocity friction experiments. In the case of nanoparticles produced by chemical precipitation, the diminution of the activation energy is usually attributed to the excessive energy stored in the surface of the nano-material (Yue et al., 1999). But the internal plastic deformation induced by milling during frictional sliding might further reduce the activation energy of the reaction (Fisher, 1988). A review of the mechanochemistry literature shows that: 1) the activation energy of a mechanically-activated reaction is lower than the activation energy of the same but thermally-activated reaction (e.g., Fisher, 1988). For instance, in the case of quartz, the alpha quartz-cristobalite transition occurs for lower activation energy for mechanically treated quartz (Table 2 from Steinike and Tkáčová, 2000): 24

25 Table 2. The activation energy for the reaction alpha quartz-cristobalite decreases of more than 50% after mechanical treatment by milling: the reaction occurs at lower temperature (from Steinike and Tkáčová, 2000). 2) given the same mechanically-activated reaction, the activation energy during comminution (Fig. 1 of this supplemental information, curve b) is lower (and, as a consequence, the reaction rate higher) for a given temperature, than the activation energy of a compound previously deformed and then heated (Fig. 1 of this supplemental information, curve a). Fig. 1. Temperature dependence of the mechanically-activated formation of Ni(CO)4 in the case of (a) previously deformed nickel and (b) nickel deformed during compound formation. From Hienicke et al., 1967 in Fox In Fig. 4B of the main text we used the reaction rate curves for calcite decarbonation using the activation energy for nano-particles of calcium carbonate from Yue et al. (1999): the large decrease in friction is almost concomitant to the large increase of the reaction rate constant. However, we expect the activation energy for this reaction to be even smaller than the one we used because of the internal plastic deformation of the grains induced during milling. References Heinicke, G., Harentz, H., Sigrist, K.D. Z. Anorg. Allegem. Chem. 352, 168 (1967). Heinicke, G. Tribochemistry. Munich Carl-Hanser Verlag (1984) Fox, P. G. Mechanically initiated chemical reactions in solids. J. Mat. Sci. 10, (1975). Fisher, T.E. Tribochemistry. Ann. Rev. Mater. Sci (1988). Steinike, U., Tkáčová, K. Mechanochemistry of Solids Real Structure and Reactivity. J. Mater. Syn. Process. 8, (2000). Yue, L., Shui, M. & Xu, Z. The decomposition kinetics of nanocrystalline calcite. Thermochimica Acta 335, (1999). 25