Earthquake-like ruptures made in the laboratory broadly followed the path expected by a recently developed two-dimensional theory of frictional slip pulses, according to a new preprint. In the experiments, pulses that grew and pulses that faded tracked an approximately common relationship between pulse size and peak slip rate, with the estimated steady-state point lying between them.
The theory treats the steady-state pulse relation as a dynamic attractor—a pattern that unsteady pulses tend to follow—under fixed prestress. In practical terms, the test asks whether a changing pulse behaves as though it remains organized around the size–speed relationship associated with a steady pulse. The study examined that question across controlled fault conditions.
Inside the laboratory fault
Researchers pressed two quasi-two-dimensional plates of polymethyl methacrylate, or PMMA, together to form a dry, gouge-free, nominally flat fault interface. The experiments controlled prestress and rupture-nucleation conditions and varied roughness amplitude to test the theory across fault conditions.
Ultrahigh-speed photography and digital image correlation measured the rupture field across space and time. The analysis compared an experimental pulse-size quantity, L̃(t), with peak slip rate, ṽmax(t), by plotting their evolving trajectories in the L̃−ṽmax plane. The extracted pulse properties were smoothed with a 10-frame moving average before analysis.
A shared path that shifted
In one tested condition set, growing and decaying pulses approximately followed a common monotonic relation in that plane: their size and peak slip rate changed together in a consistent direction. The estimated steady-state point lay between the growing and decaying subsets. That is the pattern the theory describes as a shared dynamic attractor for unsteady pulses.
The relation also shifted under other tested conditions. Four growing pulses approximately formed a monotonic line shifted upward relative to comparison results in a prestress comparison. On smoother faults, three growing pulses formed a monotonic line shifted upward compared with rougher-fault results.
A prediction about timing
The study also tested the theory’s prediction that pulse size evolves slowly compared with rupture propagation. It evaluated the integral ratio ΔL̃(t)/Δxmax(t), comparing the change in measured pulse size with the distance traveled by the rupture front. The ratio was reported as much less than one for all observed growing pulses, with two representative examples.
This slow-evolution result is consistent with a pulse that travels while its size changes gradually, rather than changing at the same pace as the front. It gives the measured trajectories the behavior expected from the theory’s separation between rapid propagation and slower pulse evolution.
What the test can and cannot say
The experiments also showed an example of a decaying-to-growing transition. The pulse first decayed and then grew after a small prestress change, while the nucleation voltage remained fixed. Because the document presents an example rather than a frequency estimate, the observation describes what can happen in the tested setup, not how often it happens.
The comparison has a built-in theoretical limit. The exact constitutive law—the mathematical rule describing how the fault interface responds as it slips—was unknown for the experiment. The researchers therefore could not compute in advance the exact fixed-prestress steady-state relation against which the pulses might be judged. The measured L̃(t) was also a proxy for the theory’s idealized pulse size L(t).
The experiments described here used the controlled PMMA laboratory system. The authors interpret the results as confirming essentially all predictions of the theory and as demonstrating generality across the prestress conditions and fault constitutive laws tested. They suggest the framework could eventually help estimate earthquake source parameters and analyze complexity in fault slip.
The manuscript is an arXiv version-1 preprint dated 26 August 2026.
Paper data and sources
Original title: Lab earthquakes confirm the theory of frictional slip pulses
Authors: Alina Shafir, Tom Gabrieli, Yuval Tal, Eran Bouchbinder
Journal/Repository: arXiv
Status: Preprint, not yet peer-reviewed
First online: 2026-08-26
DOI: Not available
Original paper · Full text