Frictional Strengthening Explored During Non‐Steady State Shearing: Implications for Fault Stability and Slip Event Recurrence Time

Abstract

On natural faults that host repeating slip events, the inter-event loading time is quite large compared to the slip event duration. Since most friction studies focus on steady-state frictional behavior, the fault loading phase is not typically examined. Here, we employ a method specifically designed to evaluate fault strength evolution during active loading, under shear driving rates as low as 10 −10 m/s, on natural fault gouge samples from the Waikukupa Thrust in southern New Zealand. These tests reveal that in the early stages of loading following a slip event, there is a period of increased stability, which fades with accumulated slip. In the framework of rate-and state-dependent friction laws, this temporary stable phase exists as long as slip is less than the critical slip distance and the elapsed time is less than the value of the state variable at steady state. These observations indicate a minimum earthquake recurrence time, which depends on the field value of the critical slip distance and the background slip rate. We compare estimates of minimum earthquake recurrence times with the recurrence times of repeating large earthquakes on the Alpine Fault in southern New Zealand and repeating small-magnitude earthquakes on the San Andreas Fault system in California. We find that the observed recurrence times are mostly longer than the predicted minimum values, and exceptions in the San Andreas system may be explained by elevated slip rates due to larger earthquakes in this region.

Frictional and Lithological Controls on Shallow Slow Slip at the Northern Hikurangi Margin

“…Few studies have documented a robust velocity dependence of D c . However, our results closely match two cases where this velocity dependence has been documented in quartz gouge (Mair & Marone, 1999) and natural sediment (Ikari, Carpenter, et al., 2020) from the Waikukupa Thrust in southern New Zealand (Figure 6d). Our results demonstrating the velocity dependence of RSF parameters are consistent over a variety of hydration states (humid/saturated) and pore pressures (Figures 6c and 6d).…”

“…Here we discuss the implications of the velocity dependence of the rate-state frictional parameters (a, b and D c ) in our experiments and those of others (Ikari, Carpenter, et al, 2020;Mair & Marone, 1999) for a range of different natural and synthetic fault gouges. A necessary criterion for the emergence of any kind of unstable slip in numerical simulations (Gu et al, 1984;Im et al, 2020) and laboratory experiments (e.g., Leeman et al, 2018Leeman et al, , 2016Shreedharan et al, 2020) is that the critical stiffness criterion be met.…”

Oscillatory Loading Can Alter the Velocity Dependence of Ice‐on‐Rock Friction

“…This concept has also recently been explored by Ikari et al. (2020), who conducted “velocity cycle” tests. They implemented a SHS protocol, but instead of completely stopping the load point, they applied a small driving velocity.…”

“…We propose that multiple loading conditions be considered during experiments to get a full sense of the rate dependence behavior of the material. This concept has also recently been explored by Ikari et al (2020), who conducted "velocity cycle" tests. They implemented a SHS protocol, but instead of completely stopping the load point, they applied a small driving velocity.…”

Weakening behavior of the shallow megasplay fault in the Nankai subduction zone

“…Equation 5 is not derived from the rate-and-state friction formulation (Eqs. 1,2), and is intended to be used as a comparative measurement for shearing that is not necessarily at steady state (Ikari et al 2020). The net change measurement Γ includes the effects of both the velocityand slip-dependence of friction (Fig.…”