Coseismic Slip Model and Interseismic Strain Accumulation of the 2025 Mw 7.7 Mandalay, Myanmar, Earthquake Revealed by Geodetic Observations

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Abstract
On 28 March 2025, a devastating Mw 7.7 earthquake struck the central and southern segments of the Sagaing fault in Myanmar and led to the largest surface rupture length of over 500 km ever documented for a strike-slip event. Here, the Synthetic Aperture Radar images from Sentinel-1A/B satellites were processed using the pixel offset tracking (POT) method to retrieve high-resolution coseismic displacements of the 2025 Mw 7.7 Mandalay earthquake. By integrating Differential Interferometric Synthetic Aperture Radar, aperture interferometry, and POT observations, we quantified the near-field on-fault and off-fault deformation patterns and constrained fault geometry and slip distribution of the Mandalay earthquake. The results show that the rupture of the Mandalay earthquake is dominated by right-lateral strike-slip motions with the maximum slip of ∼6 m located in the shallowest part. The shallow slip deficit of the Mandalay earthquake is small (<15%), consistent with the generally small diffuse deformation on the off-fault damage zones. We also inverted the interseismic coupling distribution on the Sagaing fault constrained by updated Global Navigation Satellite Systems velocities. The result indicates that the coseismic slip of the Mandalay earthquake did not penetrate deeper than the regional seismogenic layer, exhibiting high spatial correlation with interseismic strongly coupled patches on the Sagaing fault. The rupture of the Mandalay earthquake nucleated in a transitional area with heterogeneous stress distribution caused by a rapid change of fault coupling depth on the fault plane. Coulomb stress analysis indicates increased loading on the southern Nay Pyi Taw and northern Sagaing fault segments, implying elevated seismic hazard in these areas. Considering the strong coupling of adjacent segments and the dense population in central Myanmar, heightened attention to future earthquake potential is warranted.

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