The 28 March 2025 Mw 7.8 Myanmar Earthquake: Preliminary Analysis of an ~480 km Long Intermittent Supershear Rupture

Abstract

On 28 March 2025, an Mw 7.8 shallow strike-slip earthquake ruptured ∼480 km of the 1200 km long Sagaing fault extending north–south across central Myanmar. This active right-lateral fault hosted six major earthquakes in the twentieth century and locates along the two largest cities of Myanmar, constituting a major seismic hazard. The rupture, con-strained by finite-fault inversion of teleseismic body waves, backprojections of short-period P waves, and informed by initial Interferometric Synthetic Aperture Radar imagery of surface deformation has large slip of up to 7 m extending ∼85 km north of the epicenter near Mandalay, with patchy slip of 1–6 m distributed along ∼395 km to the south, with about 2 m near the capital Nay Pyi Taw. Rupture expanded at a supershear velocity of 5–6 km/s south-ward, during the ∼80 s rupture duration. Long-period point-source moment tensors indi-cate eastward dip of 48.5°–60°, and such dip is required to match the teleseismic P-wave first motions for the early large slip in the northern part of the rupture. Dip likely steepens along strike to the south, although resolving that will require detailed analysis of surface defor-mation. Southward directivity associated with the finiteness and supershear rupture velocity contributed to remote distant shaking damage in Thailand.