High‐speed friction of disaggregated ultracataclasite in rotary shear: Characterization of frictional heating, mechanical behavior, and microstructure evolution

Abstract

[1] To understand the frictional behavior of natural faults at seismic slip rates, high-speed rotary shear experiments were conducted on disaggregated ultracataclasite from the Punchbowl fault. The experimental gouge layers were sheared at normal stresses of 0.2-1.3 MPa and velocities of 0.1-1.3 m/s to total displacements of 1.3-84 m. We employ thermomechanical FEM models and microstructural observations to consider spatial and temporal variation of normal stress and temperature in the samples and understand microprocesses. Four distinct gouge units form during shear. A slightly sheared starting material (Unit 1) and a strongly sheared and foliated gouge (Unit 2) are produced when frictional heating is insignificant and the coefficient of sliding friction is 0.4-0.6. A random fabric gouge with rounded prophyroclasts (Unit 3) and an extremely fine, microfoliated layer (Unit 4) develop when significant frictional heating occurs at greater velocity and normal stress, and the coefficient of sliding friction drops to approximately 0.2. Unit 3 forms at the critical temperature for vaporization of water and is associated with localization of slip to Unit 4 and elevation of temperature. The critical displacement for dynamic weakening in the rotary configuration can be understood as a consequence of the progressive inward migration of the friction-generated thermal front and the weaker localized slip surface and associated fluidized zone.Citation: Kitajima, H., J. S. Chester, F. M. Chester, and T. Shimamoto (2010), High-speed friction of disaggregated ultracataclasite in rotary shear: Characterization of frictional heating, mechanical behavior, and microstructure evolution,

Earthquake faulting in subduction zones: insights from fault rocks in accretionary prisms

“…In fact, high-velocity (1.3 m/s) friction experiments on natural fault gouges successively reproduced fluidization-related microstructures found in nature, during which the apparent coefficient of friction (ratio of shear to normal stress) decreased to approximately 0.1 to 0.2 (Mizoguchi et al 2009;Kitajima et al 2010;Ujiie and Tsutsumi 2010). Mizoguchi et al (2009) reported folding and fluttering structures in the gouge after high-velocity friction experiments under dry (room humidity) conditions.…”

From field geology to earthquake simulation: a new state-of-the-art tool to investigate rock friction during the seismic cycle (SHIVA)

“…Moreover, the differential speed across the sample affects the thermal evolution of the slipping zone: at the sample edge, where the slip rate is higher, the temperature increases faster than at the sample center. This results in uneven thermal dilatancy and normal stress distribution of the specimens, which affects the measured friction (e.g., Kitajima et al 2010). It follows that the utilization of larger in size and ring-shaped samples will yield more accurate experimental data.…”

The Role of Adsorbed Water on the Friction of a Layer of Submicron Particles

“…Although the breakdown of carbonates requires temperatures in excess of 800°C, similar dehydration reactions are likely to occur in some phyllosilicates at more modest temperatures of 150-200°C. These dehydration reactions have been proposed as a weakening mechanism in high-speed rotary shearing experiments of disaggregated ultracataclasite from the Punchbowl fault in Southern California (KITAJIMA et al 2010). In that study, slip velocities ranged from 0.1 to 1.3 m/s at normal stresses between 0.2 and 1.5 MPa and total displacements of 1.5-84 m. They reported a significant reduction in the coefficient of sliding friction when the slip velocity and normal stress were sufficiently high to generate calculated temperatures in excess of about 150°C.…”

“…In microstructural studies of radial sections from their deformed samples, KITAJIMA et al (2010) identified four distinct structural units. The first, a compacted, slightly sheared and modified starting material, and the second, a well-foliated and sheared gouge, were similar to those observed in other lowspeed experiments that produce friction coefficients near 0.6.…”