Voids and Rock Friction at Subseismic Slip Velocity

Abstract

Abstract-We found that the amplitudes of transmitted waves across the sliding surfaces are inversely correlated to high slip rate friction, especially when the interfaces slide fast ([ 10 -3 m/s). During the rock-rock friction experiments of metagabbro and diorite at sub-seismic slip rate (* 10 -3 m/s), friction does not reach steady state but fluctuates within certain range. The amplitudes of compressional waves transmitted across the slipping interfaces decrease when sliding friction becomes high and it increases when friction is low. Such amplitude variation can be interpreted based on the scattering theory; small amplitudes in transmitted waves correspond to the creation of large-scale (* 50 lm) voids and large amplitudes correspond to the smallscale (* 0.5 lm) voids. Thus, large-scale voids could be generated during the high-friction state and low-friction state was achieved by grain size reduction caused by a comminution process. This was partly confirmed by the experiments with a synthetic gouge layer. The result can be interpreted as an extension of force chain theory to high-velocity sliding regime; force chains were built during the high friction and they were destroyed during the low friction. This mechanism could be a microscopic aspect of friction evolution at sub-seismic slip rate.

Origin of the Co‐Seismic Variations of Elastic Properties in the Crust: Insight From the Laboratory

“…Fukuyama et al. (2018) studied amplitude variation during high‐velocity friction experiments. Moreover, Shreedharan et al.…”

“…Scuderi et al (2016) explored the complete spectrum of failure modes, from slow to fast earthquakes, showing that not only co-seismic changes but also precursory variations of P-wave velocity occur for each mode of failure. Fukuyama et al (2018) studied amplitude variation during high-velocity friction experiments. Moreover, Shreedharan et al (2021) showed clear precursory P-wave amplitude variations occurring with the instability nucleation phase and precursory P-wave velocity variations distorted by the presence of the surrounding bulk material.…”

Apparent Dependence of Rate- and State-Dependent Friction Parameters on Loading Velocity and Cumulative Displacement Inferred from Large-Scale Biaxial Friction Experiments

“…Figure 1a shows a schematic diagram of the apparatus. A pair of rock specimens made of Indian metagabbro (see Fukuyama et al 2016 for its mineral composition) was used. The lower specimen moved with the shaking table and the upper specimen was fixed to the outer base of the shaking table by a reaction force bar.…”