On predictability of slip, rupture geometry, and rupture speed of the Mw7.8 2025 Mandalay (Myanmar) Earthquake

Abstract The 2025 Mw7.8 Mandalay earthquake ruptured ~480 km of the Sagaing fault, producing one of the longest strike-slip events ever documented and impacting a vulnerable region with limited instrumental coverage. We combine remote sensing observations and numerical modeling to demonstrate that key earthquake characteristics, such as subsurface fault geometry, slip distribution, and supershear rupture speed could be anticipated from observations made before the event. Along-strike variations in coseismic and interseismic deformation jointly reveal a helix-shaped geometry of the Sagaing fault. The average coseismic slip is equal to, or greater than the accumulated interseismic slip deficit, consistent with a loosely slip-predictable model. We use the best-fit static slip model to derive an ensemble of 3-D dynamic rupture simulations that can reproduce multi-scale space geodetic, seismic, and near-field video observations. The preferred rupture scenario begins with a bilateral phase that transitions rapidly to unilateral southward supershear propagation at depth, while shallow rupture remains subshear. These complex dynamics are shaped by localized stress heterogeneity and low fracture energy, characteristic of a structurally mature fault zone. We show that for mature strike-slip faults with well-constrained geometries and slip histories, physically consistent dynamic rupture models can be derived from static constraints, bridging the gap between interseismic monitoring and physics-based seismic hazard assessment.