The 28 March 2025 Mw 7.7 earthquake in Myanmar occurred along the N–S striking Sagaing Fault near Mandalay and ruptured a previously identified ‘seismic gap’. This shallow, bilateral rupture spanned \(\sim\) 400 km and lasted about 80 s. The rupture initially propagated northward at sub-shear speed and then transitioned to a super-shear southward rupture, which likely sustained the rupture on such a long fault. The mainshock was followed by a significant Mw 6.7 aftershock just 11 minutes later. Teleseismic-waveform-data analysis of the mainshock revealed three distinct sub-events, with the central one (10–40 s) contributing the most energy and dominating the radiation pattern. A frequency-dependent radiation is observed for the super-shear southern rupture, which ended in oblique–slip. The mainshock seismic moment is \(\sim 6.26\times 10^{20}\) N.m, and moment magnitude is 7.79. The average slip on the fault is \(\sim\) 2 m, with stress-drop of \(\sim 15 \pm 5\) bars. Source directivity analysis indicated stronger ground motion to the south, consistent with the super-shear rupture. The mainshock not only released the strain, accumulated over decades, on the Sagaing Fault, but potentially increased stress on the adjacent, fully-locked Rakhine-Bangladesh megathrust. This has major implications for seismic hazard in Bangladesh and northeast India.
