Fault lubrication during earthquakes

Abstract

The determination of rock friction at seismic slip rates (about 1 m s(-1)) is of paramount importance in earthquake mechanics, as fault friction controls the stress drop, the mechanical work and the frictional heat generated during slip(1). Given the difficulty in determining friction by seismological methods(1), elucidating constraints are derived from experimental studies(2-9). Here we review a large set of published and unpublished experiments (similar to 300) performed in rotary shear apparatus at slip rates of 0.1-2.6 ms(-1). The experiments indicate a significant decrease in friction (of up to one order of magnitude), which we term fault lubrication, both for cohesive (silicate-built(4-6), quartz-built(3) and carbonate-built(7,8)) rocks and non-cohesive rocks (clay-rich(9), anhydrite, gypsum and dolomite(10) gouges) typical of crustal seismogenic sources. The available mechanical work and the associated temperature rise in the slipping zone trigger(11,12) a number of physicochemical processes (gelification, decarbonation and dehydration reactions, melting and so on) whose products are responsible for fault lubrication. The similarity between (1) experimental and natural fault products and (2) mechanical work measures resulting from these laboratory experiments and seismological estimates(13,14) suggests that it is reasonable to extrapolate experimental data to conditions typical of earthquake nucleation depths (7-15 km). It seems that faults are lubricated during earthquakes, irrespective of the fault rock composition and of the specific weakening mechanism involved

Voids and Rock Friction at Subseismic Slip Velocity

“…The frequency of oscillation seems dependent on the amount of slip displacement as well as on the rock type. We could see a similar behavior at subseismic slip velocity in Reches and Lockner (2010), Di Toro et al (2011), and Goldsby and Tullis (2011). According to Goldsby and Tullis (2011), such friction instability seems typical for gabbro and granite rocks.…”

“…At slow slip velocity (* 10 -6 m/s), friction follows the Byerlee's law (Byerlee 1978). But, as slip velocity increases, the coefficient of friction decreases, primarily due to the generation of heat (Di Toro et al 2011). By looking at the experimental results closely, the coefficient of friction fluctuates at a subseismic slip velocity (* 10 -3 m/s) (e.g., Tsutsumi and Shimamoto 1997;Mizoguchi and Fukuyama 2010;Di Toro et al 2011).…”

Extreme hydrothermal conditions at an active plate-bounding fault

“…Experimental studies of dynamic friction confirm that slip weakening by up to one order of magnitude is common as the slip rate approaches values inferred for large earthquakes, though the mechanisms of weakening are debated 13,14 . The evolution of the coefficient of friction on a fault surface during and after an earthquake is time-dependent 15 .…”

“…The evolution of the coefficient of friction on a fault surface during and after an earthquake is time-dependent 15 . Of particular importance is the stability of phyllosilicate phases with low dynamic friction 16 , thermal expansion and the generation of physicochemical reaction products produced during slip 13 , and the presence of low-permeability mineral cements LETTER RESEARCH that enhance dynamic fluid pressurization mechanisms 17 . Temperature and fluids within fault zones are primary controls on material properties and slip-weakening mechanisms, and hence they strongly influence earthquake processes.…”

Additional shear resistance from fault roughness and stress levels on geometrically complex faults

“…[5] Extreme dynamic weakening at coseismic slip rates has been widely observed in high-velocity friction experiments [e.g., Tsutsumi and Shimamotom, 1997;Di Toro et al, 2004;Hirose and Shimamoto, 2005;Beeler et al, 2008;Goldsby and Tullis, 2011;Di Toro et al, 2011]. Planar faults governed by strongly rate-weakening friction laws support self-sustaining slip-pulse ruptures at background stress levels b around a critical stress level pulse 0.25 eff [Cochard and Madariaga, 1996;Beeler and Tullis, 1996;Zheng and Rice, 1998;Lapusta and Rice, 2003;Lykotrafitis et al, 2006;Noda et al, 2009], even with off-fault plasticity [Dunham et al, 2011a;Gabriel et al, 2013].…”