New rupture theory challenges classical earthquake propagation model, allowing continuous propagation through previously 'forbidden' speed range
Researchers have developed a revised rupture theory showing that earthquakes can propagate continuously through a speed range previously considered physically impossible. Classical two-dimensional rupture theory held that earthquakes must abruptly jump from sub-Rayleigh to super-shear speeds, skipping the intermediate 'super-Rayleigh' range entirely. The findings suggest that frictional rate dependence — a property routinely observed in laboratory experiments — fundamentally alters how fast earthquakes accelerate, with potential implications for seismic hazard modeling.
A new theoretical study posted to arXiv challenges a foundational assumption in earthquake physics: that ruptures propagating faster than shear wave-speed must undergo a discontinuous 'super-shear transition,' skipping over the intermediate super-Rayleigh speed range. The classical two-dimensional rupture theory treats this range — between the Rayleigh and shear wave-speeds — as 'forbidden,' predicting an abrupt jump rather than smooth acceleration. The new framework incorporates the dependence of fault frictional resistance on slip rate, a property widely documented in experimental settings but neglected in classical models. The revised theory shows strong quantitative agreement with numerical simulations across most of the sub-Rayleigh regime, but near the Rayleigh wave-speed, frictional rate nonlinearity causes rupture solutions to change character, allowing continuous propagation through the previously forbidden zone into the super-shear regime. This means the sharp super-shear transition predicted by classical theory may not occur in real faults where rate-dependent friction is present. The work was submitted by Eran Bouchbinder and colleagues and spans geophysics, materials science, and soft condensed matter physics.
What's missing
The study is a preprint and has not yet undergone peer review. The authors acknowledge that the theory is two-dimensional, leaving open whether the results hold in three-dimensional fault geometries more representative of real earthquakes.
What different sources said
- arXiv physicsCenter
Breakdown of the classical rupture theory and earthquake propagation in the "forbidden" super-Rayleigh range
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