Sustained supershear rupture during the 2025 Mandalay, Myanmar earthquake

Abstract

The 2025 Mw 7.8 Myanmar earthquake ruptured the Sagaing fault, where sparse near-fault seismic observations limit source characterization. Here, we integrate optical imagery, InSAR, finite-fault slip inversion, back-projection (BP), and dynamic rupture simulations to investigate rupture kinematics and dynamics. Surface rupture extended for 472 km, with an average offset of 3.7 ± 0.4 m. Coseismic slip features no apparent shallow slip deficit. BP reveals southward supershear rupture ~30 s after nucleation. Calibrated with geodetic and seismic observations, dynamic rupture modeling indicates bilateral rupture initiation, with northward sub-shear propagation for 27 s at an average speed of 2.3 km/s. Southward rupture exhibits sub-shear (2.9 km/s) in 20 s, then transitions to sustained supershear (4.1‒5.9 km/s) over ~312 km in ~68 s, with its onset governed by the Burridge-Andrews mechanism and subsequently promoted by free-surface effects. These results reveal rupture complexity of this earthquake, emphasizing the need for improved near-fault observations in vulnerable regions. (Figure presented.).