Multiscale fault-zone structures governed by earthquake rupture dynamics

Damage zones exist along faults, and a comprehensive understanding of fault-zone structures is essential for seismic hazard assessment. Despite extensive geological and geophysical observations, the fundamental process controlling the formation of fault-zone structures remains unclear. Here, we integrate geophysical and geological observations with analytical and numerical models, providing new evidence that earthquake rupture dynamics govern the formation of fault-zone structures. By analyzing the scaling with distance from the fault via strain, fracture, and aftershock datasets, we observe multiscale fault-zone widths from the scaling breaks in the 2021 Maduo earthquake, in stark contrast to the 2019 Ridgecrest earthquake, which shows no resolvable breaks in the damage scaling. We use dynamic modeling to reconcile these two end-member damage zones, characterized by contrasting scaling breaks, which we find are controlled by rupture speed and rock yield strength. Dynamic ruptures with nearly supershear speeds and low rock yield strengths can explain the multiscale fault-zone structures in the Maduo earthquake. Particularly, we find that high rock yield strength is a necessary condition to reproduce the extremely narrow fault-zone structures in the Ridgecrest earthquake, as supported by the geological evidence. Our analysis provides new physical insights into the mechanisms of fault-zone structures.