Co-seismic and Post-seismic Seismic Velocity Changes Along the Sagaing Fault Following the 28 March 2025 Mw 7.7 Myanmar Earthquake: Insights from Ambient Noise Interferometry and Volumetric Strain Modelling
Abstract
Abstract The Sagaing Fault, a major right-lateral strike-slip structure accommodating relative motion between the Indian and Sunda plates, ruptured over ~480 km on 28 March 2025 in a shallow Mw 7.7 earthquake near Mandalay, central Myanmar. Despite the region's high seismicity, upper-crustal velocity changes associated with large earthquakes here remain poorly documented. We applied ambient noise-based seismic interferometry to continuous records from four broadband stations (NPW, NGU, TGI, and MHIT) to resolve co- and post-seismic relative velocity changes (dv/v) between March and April 2025. All stations show a co-seismic dv/v decline coincident with the mainshock, with the largest reduction (~1.9%) at NPW, the station closest to the fault, decreasing systematically to ~0.6%, ~0.5%, and ~0.05% at NGU, TGI, and MHIT, respectively. A gradual post-seismic recovery follows at all sites, interrupted by minor fluctuations tied to aftershock activity, though velocities remain below pre-earthquake levels through the end of the observation window, indicating only partial healing. Comparison with modelled co-seismic static volumetric strain shows that NPW alone lies within a zone of positive volumetric strain (dilation), consistent with its pronounced velocity drop, while the more distant stations fall within weak compressional zones that appear to partly offset dynamically induced damage. Together, these results indicate that transient dynamic shaking is the primary source of…
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