Mechanical mechanism on the 2025 <italic>M</italic>_S7.9 Mandalay, Myanmar Earthquake

On March 28, 2025, an MS7.9 earthquake suddenly occurred in Mandalay, Myanmar. This earthquake occurred on the strike-slip Sagaing Fault zone (SF), which has experienced 9 strong earthquakes with magnitude MS≥7.0 since 1906, causing profound disasters to local residents. To study the dynamic mechanism of the earthquake, we at first merged the GNSS data observed in different regions and time periods published by different previous authors. Then, the update comprehensive results of GNSS data relative to the Eurasian reference frame were obtained. Based on the GNSS velocities, we found that an inverted U-shape-turn crustal motion (IUCM) is located in the southeastern Tibetan Plateau, with the Sagaing Fault as a pivotal axis. To the west of SF, crustal material moves along the NNE direction, but it goes from west to east to the north of SF. However, to the east of SF, crustal material is basically moving towards SSE direction. Meanwhile, the strain rate field was calculated based on the new merged GNSS data. The strain rates are in good agreement with the geological and geophysical investigations generally. Spatial distribution of strain rates displayed that high values are mainly concentrated on the eastern Himalayan syntaxis, along the Himalaya main boundary thrust, the SF, and the Xianshuihe Fault zone (XF). In particular, the loading rate of the SF is much higher than that of the XF, giving rise to that strong earthquakes occur more frequently along the SF than on the XF. The IUCM feature of crustal movement around the SF results in simultaneously loading to the SF in two opposite directions. In addition, the east-west compression of the SF increases the normal stresses on the fault surface, allowing the SF to accumulate higher elastic strain energy, resulting in more destructive earthquakes. It can be seen that this study has important scientific significance for a deeper understanding of dynamic mechanisms for the 2025 Myanmar earthquake and the formation and evolution of the Tibetan Plateau.