Breakdown of Scaling and Friction Weakening in Intermittent Granular Flow

Area of Science:

• Geophysics and Materials Science
• Focuses on granular matter dynamics and geological hazard triggers.

Background:

• Granular materials are ubiquitous, and their behavior under shear stress is critical for understanding geological events like landslides and earthquakes.
• Granular systems flow via intermittent avalanches at low shear rates, with expected universal velocity profiles.

Purpose of the Study:

• To investigate the scaling behavior of avalanche velocity in granular systems under shear stress.
• To identify the underlying mechanisms responsible for any observed deviations from universal scaling laws.

Main Methods:

• Analysis of data from long-duration experiments on granular material behavior.
• Examination of frictional response across different slip durations and regimes.

Main Results:

• A breakdown in the expected self-similar and symmetric velocity scaling was observed for longer slips.
• Shorter slips exhibited self-similar and symmetric velocity profiles, consistent with theoretical expectations.
• The scaling breakdown was traced to the onset of dynamically-induced friction weakening.

Conclusions:

• The study reveals a critical deviation from universal scaling in granular avalanche dynamics.
• Dynamical friction weakening amplifies instabilities in granular systems, particularly during longer slip events.
• These findings are crucial for understanding and mitigating risks associated with natural hazards like earthquakes and landslides.