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Abstract Rock friction tests have made profound contributions to our understanding of earthquake processes. Most rock friction tests focused on fault strength evolution during velocity steps or at specific slip rates and the characteristics during stick‐slip events such as dynamic rupture propagation and the transition from stable sliding to instability, with little attention paid to the transient acceleration and deceleration periods. Here, we present Westerly Granite fault friction test results using a unique pneumatically powered apparatus with high acceleration of up to 50 g, focusing on the transient stages of fast fault acceleration and deceleration during both high‐speed sliding and stick‐slip events. Our data demonstrates the dominating velocity‐weakening behavior at transient stages of fault acceleration and deceleration, with a 1/V dependence for peak friction and deceleration lobe consistent with the flash‐heating model but with the acceleration lobe consistently deviating from the 1/V dependence. Our analysis of velocity‐dependent friction between dynamic rupture events, stick‐slips, and high‐speed friction tests reveals the significance of high acceleration in influencing transient fault weakening during dynamic weakening. We further demonstrate that the deviation of the friction‐velocity curve from the 1/V trend during fault acceleration is associated with the contribution of the dynamic rupturing process during the initiation of fault slip.
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Stick-slip Dynamics in Penetration Experiments on Simulated Regolith
Abstract The surfaces of many planetary bodies, including asteroids and small moons, are covered with dust to pebble-sized regolith held weakly to the surface by gravity and contact forces. Understanding the reaction of regolith to an external perturbation will allow for instruments, including sensors and anchoring mechanisms for use on such surfaces, to implement optimized design principles. We analyze the behavior of a flexible probe inserted into loose regolith simulant as a function of probe speed and ambient gravitational acceleration to explore the relevant dynamics. The EMPANADA experiment (Ejecta-Minimizing Protocols for Applications Needing Anchoring or Digging on Asteroids) flew on several parabolic flights. It employs a classic granular physics technique, photoelasticity, to quantify the dynamics of a flexible probe during its insertion into a system of bi-disperse, centimeter-sized model grains. We identify the force chain structure throughout the system during probe insertion at a variety of speeds and for four different levels of gravity: terrestrial, Martian, lunar, and microgravity. We identify discrete, stick-slip failure events that increase in frequency as a function of the gravitational acceleration. In microgravity environments, stick-slip behaviors are negligible, and we find that faster probe insertion can suppress stick-slip behaviors where they are present. We conclude that the mechanical response of regolith on rubble-pile asteroids is likely quite distinct from that found on larger planetary objects, and scaling terrestrial experiments to microgravity conditions may not capture the full physical dynamics.
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- Award ID(s):
- 2104986
- PAR ID:
- 10326381
- Date Published:
- Journal Name:
- The Planetary Science Journal
- Volume:
- 2
- Issue:
- 6
- ISSN:
- 2632-3338
- Page Range / eLocation ID:
- 243
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/PSJ/ac3de2
