HR: 0800h
AN: S41A-0951    [Abstracts]
TI: Rate- and State Friction Behaviour of Simulated Fault Rocks: Influence of Phyllosilicate and Pressure Solution
AU: * Niemeijer, A R
EM: niemeyer@geo.uu.nl
AF: HPT Laboratory, Faculty of Geosciences, Utrecht University, Budapestlaan 4, Utrecht, 3508 TA Netherlands
AU: Peach, C J
EM: cpeach@geo.uu.nl
AF: HPT Laboratory, Faculty of Geosciences, Utrecht University, Budapestlaan 4, Utrecht, 3508 TA Netherlands
AU: Spiers, C J
EM: cspiers@geo.uu.nl
AF: HPT Laboratory, Faculty of Geosciences, Utrecht University, Budapestlaan 4, Utrecht, 3508 TA Netherlands
AB: Rate and State Friction (RSF) laws are widely used to describe experimental rock friction results and to model seismogenic processes. The empirical RSF parameters a and b as determined in rock friction experiments give realistic results when used in models for the seismogenic cycle. However, the critical slip distance parameter, D$_{c}$, has to be arbitrarily scaled up from laboratory values of 10 $\mu$m to around 1 m. Recent evidence indicates that fault healing by solution-transfer processes may contribute to the discrepancy between laboratory and natural fault behaviour. Such processes are known to be strongly influenced by phyllosilicates. To examine the effects of phyllosilicates, we report results from slide-hold-slide experiments on wet, simulated, phyllosilicate-bearing faults (salt-muscovite gouge mixtures), performed under conditions where pressure solution is active. At low (\leq 1 $\mu$m/s) sliding velocities, results show that shearing of the gouge involves slip on the foliation, accomodated by pressure solution of the intervening halite grains. This leads to velocity-strengthening behaviour and a mylonitic microstructure. At high sliding velocities (\geq 1 $\mu$m/s) pressure solution is too slow to accommodate all the imposed shear and the foliation is destroyed, resulting in a microstructure that resembles that of a cataclasite. In this regime, the gouge shows strong velocity-weakening behaviour. Control experiments performed on pure halite, pure muscovite and dry halite-muscovite mixtures showed little or no velocity-weakening effect. Significantly, slide-hold-slide on wet halite-muscovite mixtures show a major increase in healing rate with increasing sliding velocity in the velocity-weakening field. The maximum healing rate measured at 10 $\mu$m/s is an order of magnitude higher than healing rates from room-dry experiments, and the displacement required to establish new steady state sliding (D$_{c}$) increases with increasing hold time and increasing sliding velocity, reaching a value of ~ 400 $\mu$m. Taken together, our results suggest that the combined effects of phyllosilicates and pressure solution may provide an explanation for both stable creep and unstable seismic slip on mature phyllosilicate-bearing faults. A physical model to scale the RSF empirical parameters to natural conditions should take the operation of pressure solution and the effects of phyllosilicates into account.
DE: 7299 General or miscellaneous
DE: 8123 Dynamics, seismotectonics
DE: 5112 Microstructure
DE: 5120 Plasticity, diffusion, and creep
SC: Seismology [S]
MN: 2004 AGU Fall Meeting