Breaching a seismic gap: the 2025 magnitude 7.7 Myanmar earthquake

Seismic gaps are fault sections that have not experienced large earthquakes for a long time compared to neighboring segments, making them likely sites for future large events. Historical information, earthquake catalogs, and field geology help define their dimensions, which inform estimates of potential earthquake size. The 2025 M _w 7.7 Myanmar earthquake ruptured a known seismic gap and extended far beyond it, producing an unusually ~460 km long fault rupture. Integrating SAR-image observations, back-projection analysis, kinematic Bayesian finite-fault estimation, and dynamic rupture simulations, we investigated the earthquake’s rupture process and factors that enabled the rupture to breach the seismic gap. Our results reveal a two-stage earthquake rupture: initial subshear bilateral propagation (~20 s), followed by unilateral supershear rupture (~70 s). Simulation-based sensitivity tests show the seismic gap boundary is not a strong mechanical barrier. Instead, rupture nucleation far away from the gap's boundary played a key role, rather than supershear rupture speed, in allowing the rupture to outgrow the gap and propagate ~160 km beyond it. This indicates that the dimensions of seismic gaps may not reflect the size of future earthquakes. Instead, ruptures may cascade through additional fault sections to generate larger and potentially more damaging earthquakes.