Supershear Rupture Along the Sagaing Fault Seismic Gap: The 2025 Myanmar Earthquake

Abstract

The 28 March 2025 Mw 7.7 Myanmar earthquake on the Sagaing fault caused widespread building collapses and over 3800 fatalities, as well as strong shaking in Bangkok. Highfrequency backprojection very early on revealed an 500 km rupture. Following a bilateral subshear propagation, the rupture accelerated southward to at least 5.3 km/s, reaching the stable supershear regime, as also confirmed by Mach-cone analysis with Love waves. Pixel tracking analysis from optical and radar imagery confirms the rupture length and indicates a peak surface offset of 5 m and average offsets of 3-4 m along the rupture zone. Pseudodynamic rupture inversion constrained by seismic waveforms and the radarinterferometric deformation field indicates 4 m slip over 15 km depth range. The earthquake yielded unusually few aftershocks; its supershear rupture likely released most of the accumulated stress. It appears that the rupture almost certainly broke the Sagaing gap and very likely overlapped completely with the 1956 M 7.0 event. It may also have partially overlapped with the 1946 M 7.8 rupture zone in the north and the 1930 M 7.5 event in the south. Acceleration to supershear only started in the gap area, and the rupture decelerated and arrested after moving into the previously broken segment.