Supershear-subshear-supershear rupture sequence during the 2025 Mandalay Earthquake in Myanmar

Abstract: We investigate the rupture dynamics of the Mw 7.7 Mandalay earthquake in Myanmar on March 28, 2025. The earthquake involved a near-vertical strike-slip rupture exceeding 400 km, with shallow slip up to 6 m. A previous inversion result revealed that the rupture initially propagated at supershear velocities ($\sim$6 km/s) near the hypocenter. A unique video recording of surface rupture, captured 124 km south of the epicenter, indicates a deceleration to subshear speeds ($\sim$3 km/s) before reaching the camera location. This deceleration is supported by observed fault-normal acceleration patterns. Satellite imagery also indicated a local minimum in slip (2--3 m) around 50 km south of the epicenter, suggesting a region of reduced stress drop, which likely caused the temporary deceleration. Beyond this point, the rupture appears to have re-established supershear propagation.