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  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