Dynamic weakening of serpentinite gouges and bare surfaces at seismic slip rates

Abstract

To investigate differences in the frictional behavior between initially bare rock surfaces of serpentinite and powdered serpentinite (“gouge”) at subseismic to seismic slip rates, we conducted single-velocity step and multiple-velocity step friction experiments on an antigorite-rich and lizardite-rich serpentinite at slip rates (V) from 0.003 m/s to 6.5 m/s, sliding displacements up to 1.6 m, and normal stresses (σn) up to 22 MPa for gouge and 97 MPa for bare surfaces. Nominal steady state friction values (μnss) in gouge at V = 1 m/s are larger than in bare surfaces for all σn tested and demonstrate a strong σn dependence; μnss decreased from 0.51 at 4.0 MPa to 0.39 at 22.4 MPa. Conversely, μnss values for bare surfaces remained ∼0.1 with increasing σn and V. Additionally, the velocity at the onset of frictional weakening and the amount of slip prior to weakening were orders of magnitude larger in gouge than in bare surfaces. Extrapolation of the normal stress dependence for μnss suggests that the behavior of antigorite gouge approaches that of bare surfaces at σn ≥ 60 MPa. X-ray diffraction revealed dehydration reaction products in samples that frictionally weakened. Microstructural analysis revealed highly localized slip zones with melt-like textures in some cases gouge experiments and in all bare surfaces experiments for V ≥ 1 m/s. One-dimensional thermal modeling indicates that flash heating causes frictional weakening in both bare surfaces and gouge. Friction values for gouge decrease at higher velocities and after longer displacements than bare surfaces because strain is more distributed.Key PointsGouge friction approaches that of bare surfaces at high normal stressDehydration reactions and bulk melting in serpentinite in < 1 m of slipFlash heating causes dynamic frictional weakening in gouge and bare surfaces

Development of a Material-Testing Machine for Study of Friction: Experimental Analysis of Machine Dynamics and Friction of Rock

“…Experimental studies of high-speed friction in rock have focused on the microscopic processes responsible for dynamic weakening. A number of mechanisms have been proposed in the literature to explain the observations of weakening in rock, such as flash heating [5,47,48], pore fluid pressurization [5], chemical decomposition [49], nano-powder lubrication [19], and melt generation [16]. Dynamic weakening by flash heating is expected for high-speed sliding along bare rock interfaces, such as in the preliminary experiments conducted with the HSLS.…”

“…However, if the sliding velocity is higher than the critical velocity for initiation of weakening, V w , then temperature of the asperity reaches T w , and τ c is reduced to τ cw resulting in macroscopic weakening. The average shear strength of the asperity can be determined from the transient temperature of the contact area over the lifetime of the asperity, and by considering some simplifications, a relation between the steady state friction and the sliding velocity is derived as follows (see [5,47,49] for more details),…”

Dislocation Motion and the Microphysics of Flash Heating and Weakening of Faults during Earthquakes

“…We selected Carrara marble (s769, 99% calcite) as representative of the 20% of sedimentary carbonate-bearing rocks where intra-plate earthquakes occur. Serpentinite (s735, 90% antigorite with minor magnesite and magnetite [12]) a quite common hydrated silicate-bearing mantle rock. Microgabbro (s699, plagioclase 35%-45%, clinopyroxene 25%-35%, feldspathoids 10% and titanomagnetite 5%-15%), a common silicate-bearing rock ( [13,14]) which constitutes most of the lower oceanic and part of the continental crust.…”

“…Theoretical and experimental investigations [5,[7][8][9][10][11][12][13][14][15] on silicate-bearing rocks (gabbro, granite, peridotite, etc.) suggested that such frictional heat initiates at highly stressed microscopic asperities, a process termed flash heating.…”

Towards an improved understanding of the mechanical properties and rheology of the lithosphere: an introductory article to ‘Rock Deformation from Field, Experiments and Theory: A Volume in Honour of Ernie Rutter’

“…On-going experimental, microstructural and theoretical studies on these minerals (e.g. Hildyard et al 2011;Brantut et al 2012;Fusseis et al 2012;Llana-Funez et al 2012;Wheeler 2014) and on serpentinite (Llana-Funez et al 2007;Rutter et al 2009;Proctor et al 2014), one of the main minerals in subduction zones, are aimed at underpining micro-physical parameters that may be used to construct predictive models of the interaction between deformation and metamorphism.…”