Sediment-modulated supershear rupture of the 2025 Mw 7.7 Myanmar earthquake

The 2025 Myanmar earthquake caused heavy casualties and economic losses in Myanmar and surrounding regions. The mechanism of the unexpectedly long rupture and the effect of sediments on its rupture dynamics remain unclear. Here we integrate seismic and geodetic observations with kinematic inversions and dynamic rupture simulations, revealing that the rupture extended ~450 km with a maximum slip of 6.9 m concentrated within the top 10 km of the upper crust. The rupture propagated ~70 km northward (subshear to supershear) and ~380 km southward (subshear to supershear and back to subshear). The long southward-propagating supershear rupture created a highly energetic front that resulted in an unexpectedly long surface rupture. Moreover, we find the coexistence of shallow subshear and deep supershear around station NPW due to the influence of sediments. Our results highlight the importance of combining data-driven inversions and physics-based modeling to decipher the rupture dynamics of large earthquakes. Integrating geodetic and seismic data with kinematic and dynamic modeling suggests that the 2025 Mw 7.7 Myanmar rupture transitioned between subshear and supershear speeds in both directions and was strongly influenced by thick sediments.