Ultralow Friction of Carbonate Faults Caused by Thermal Decomposition

Abstract

High-velocity weakening of faults may drive fault motion during large earthquakes. Experiments on simulated faults in Carrara marble at slip rates up to 1.3 meters per second demonstrate that thermal decomposition of calcite due to frictional heating induces pronounced fault weakening with steady-state friction coefficients as low as 0.06. Decomposition produces particles of tens of nanometers in size, and the ultralow friction appears to be associated with the flash heating on an ultrafine decomposition product. Thus, thermal decomposition may be an important process for the dynamic weakening of faults.

Fault roughness and strength heterogeneity control earthquake size and stress drop

“…The strength and corresponding stress drop of an asperity may greatly exceed the respective mean values for the whole rupture surface-depending on asperity size relative to rupture area of the earthquake [e.g., Somerville et al, 1999;Mai and Beroza, 2002;Ripperger and Mai, 2004;Kanamori and Brodsky, 2004;Konca et al, 2008;Mai and Thingbaijam, 2014]. Indeed, the inferred coseismic stress drops on those asperities [e.g., Ripperger and Mai, 2004;Mai and Thingbaijam, 2014] compare well with stress drops suggested by high-speed laboratory friction experiments [e.g., Kanamori and Brodsky, 2004;Han et al, 2007;Di Toro et al, 2011]. We conclude that laboratory friction experiments portray "only" the rupture behavior of strength asperities.…”

“…The corresponding values of Δτ are centered at 3-4 MPa and do not change systematically with earthquake size, which is taken as evidence for self-similar earthquake scaling [e.g., Kanamori and Anderson, 1975;Hanks, 1977;Allmann and Shearer, 2009]. On the other hand, laboratory friction experiments indicate an almost complete breakdown in frictional resistance during sliding when coseismic slip velocities are reached [e.g., Han et al, 2007;Di Toro et al, 2011]. The observed large change in friction (typically Δμ ≥ 0.5) in such experiments, combined with effective normal stresses at seismogenic depths (σ eff ), yields coseismic stress drops Δτ = Δμσ eff that exceed those derived from seismological observations by multiples of 10.…”

Flash weakening is limited by granular dynamics

“…One of the most important findings in such experiments is the remarkable weakening due to mechano-chemical effects by frictional heating [Tullis, 2007]. Consequently, the following mechanisms have been proposed as contributing to weaker fault strength: melting, silicagel formation, thermal decomposition, moisture absorption/ desorption, and flash heating [Tsutsumi and Shimamoto, 1997;Goldsby and Tullis, 2002;Di Toro et al, 2004;Han et al, 2007;Mizoguchi et al, 2006].…”

Rock‐and‐soil avalanches: Theory and simulation

“…These mechanisms are thermal pressurization of pore fluid (thermal expansion), degradation of microcontacts by flash heating, thermal decomposition of rock minerals, lubrication by silica gel, and shear melting [e.g., Lin et al, 2001;Di Toro et al, 2004;Rice, 2006;Han et al, 2007]. These all involve heating of the shear zone and hence are plausible only under dynamic conditions (i.e., high slip velocity).…”

“…[87] Thermal decomposition results from frictional heating of rock minerals within narrow fault zones that are sheared at high velocities (i.e., 1 m/s [Han et al, 2007]). Very low friction appears to be associated with flash heating of an ultrafine decomposition product composed of nanometric particles, which exhibit degraded microcontacts.…”