Velocity dependence of dynamic rock friction in high-speed friction and stick-slip tests

Xiaofeng Chen, & Frederick M. Chester

Published September 8, 2024, SCEC Contribution #14011, 2024 SCEC Annual Meeting Poster #158 (PDF)

The evolution of rock friction during earthquakes is a fundamental question in earthquake science, and the dependence of rock friction on fault slip rate plays a crucial role. Experimental studies on the velocity dependence of rock friction typically investigate fault strength evolution in velocity-controlled conditions such as constant slip rate or velocity steps. On the other hand, earthquakes and laboratory stick-slip events are more concerned about friction evolution in changing velocity conditions resulting from spontaneous energy dissipation. Here, we investigate the friction response of experimental faults in a double-direct-shear configuration using a unique pneumatically powered apparatus with high acceleration (up to 50 g) and fast loading response, focusing on the velocity dependence during both high-speed sliding and stick-slip events. The experiments are conducted under normal stress of up to 30 MPa at a maximum slip velocity of up to 3 m/s.

Experimental data demonstrate the dominating velocity weakening behavior with a clear 1/V dependence for the peak friction coefficient and the overall friction-velocity history during the fault deceleration stage, consistent with the flash-heating model prediction. The fault strength evolution and fault motion during dynamic weakening in our tests scales well with other rock friction tests and natural earthquakes. The results demonstrate the broad applicability of the 1/V dependence of rock friction as described by the flash-heating model for different rock friction experiments.

During dynamic weakening, the velocity dependence of fault friction consistently deviates from the 1/V trend and becomes more pronounced under high normal stresses with larger fault acceleration. The similarity of the velocity dependence between our tests during dynamic weakening and dynamic rupturing tests, as well as the lack of significant frictional heat production observed by a fast infrared camera, led us to interpret such a modified friction-velocity relationship because of the involvement of fracturing processes during rupture propagation at the initiation of fault slip.

Future tests are underway to study the progressive fault surface damage using optical profilometry and SEM combined with in-situ fault surface temperature monitoring using a fast infrared camera to further explore the micro-mechanical processes involved.

Key Words
high-speed friction, stick-slip, rupture

Citation
Chen, X., & Chester, F. M. (2024, 09). Velocity dependence of dynamic rock friction in high-speed friction and stick-slip tests. Poster Presentation at 2024 SCEC Annual Meeting.

Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)