Diagram and graphs from the paper.
(Top) Experimental Setup. Two PMMA blocks are pressed together and sheared to produce stick-slips. Thick blue line marks an imposed barrier of high fracture energy. The interface is illuminated by a sheet of light and the transmitted light proportional to the real area of contact, A (x, z, t), is observed at each spatial location. (Bottom) Arrest and re-nucleation experiments. Contact area A normalized by initial contact area A0, highlights region where fault is still locked (red) or has already slipped (blue). Rupture is arrested at “barrier” at location x=100 mm. Five arrested ruptures (x100 mm). Duration of nucleation, t, is inversely related to the velocity of the first rupture front (Varr) which scales with the stress at re-nucleation point. Credit: Gvirtzman and Fineberg [2023], Figure 1a and 3a
Editors’ Highlights are summaries of recent papers by AGU’s journal editors.
Source: Journal of Geophysical Research: Solid Earth

Linear elastic fracture mechanics (LEFM) predicts that once a small but stably growing nucleus of fault slip reaches a critical length, the rupture front will accelerate and transition into an unstable dynamic slip, causing earthquakes. Scientists have captured this transition in laboratory earthquake studies since the 1990s, demonstrating the success of LEFM in describing the mechanics of earthquake faults. However, the detailed process by which this nucleus of fault slip grows has been challenging to observe due to its small size and spontaneity in location.

In their laboratory earthquake experiments, Gvirtzman and Fineberg [2023] overcome these obstacles by purposely arresting and re-nucleating dynamic ruptures at a controlled location and tracking the 2D growth of the nucleus of fault slip at sub-millimeter resolution. The arrested rupture is also cleverly designed to produce quantifiable stress fields around the next nucleation point which can be related to the kinematics of the re-nucleation process. The nucleus was found to grow at speeds proportional to the applied shear stress, self-similar scaling in temporal growth was also observed, both inaccessible by traditional LEFM. Fault roughness plays a role governing where, when, and in what form nucleation will take place. The study lays groundwork for future experimental studies and challenges existing theories that predict the critical transition length between stable to dynamic fault slip.

Citation: Gvirtzman, S., & Fineberg, J. (2023). The initiation of frictional motion—The nucleation dynamics of frictional ruptures. Journal of Geophysical Research: Solid Earth, 128, e2022JB025483. https://doi.org/10.1029/2022JB025483

—Hiroki Sone, Associate Editor, JGR: Solid Earth

Text © 2023. The authors. CC BY-NC-ND 3.0
Except where otherwise noted, images are subject to copyright. Any reuse without express permission from the copyright owner is prohibited.