Surface rupture process of the Sagaing Fault during the 2025 M_(W)7.7 Myanmar earthquake revealed by videobased optical flow analysisOA

On March 28,2025,a M_(W)7.7 earthquake ruptured the Sagaing Fault in Myanmar,producing a more than 400 km of surface rupture.A surveillance camera at the Great Success Energy site,located approximately 124.5 km south of the epicenter,captured the complete rupture process.Using this footage,we extracted displacement time histories and permanent displacements at eight reference points across the fault deformation zone.After video stabilization using StabNet,displacement trajectories were obtained via optical flow tracking,and a geometric transformation model was developed to convert image coordinates into three-dimensional spatial coordinates.The derived displacements were validated against post-earthquake measurements of offset at the plant’s outer drainage fence,confirming their reliability.The earthquake produced a maximum coseismic displacement of up to 2.2 m across the nearby north-south right-lateral strike-slip Sagaing Fault,highlighting the distributed nature of deformation.Surface deformation was spatially concentrated within approximately 20 m,reflecting localized energy release.Time-series analyses showed that the maximum transient displacement was modestly greater than the permanent displacement.Velocity and acceleration time histories derived from the displacement records were used to characterize near-fault strong ground motion and to determine the arrival of seismic waves,the onset of strong shaking,and the onset of the velocity pulse.Comparison of ground motions indicates that the western fault block experienced much stronger shaking than the eastern block,with a peak ground acceleration exceeding 1.41 g and a peak velocity pulse of 3.80 m/s.Slip between the two blocks initiated at the onset of the pulse,resulting in a relative displacement of 2.84 m.