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A UCLA-led team of scientists has uncovered how the devastating magnitude 7.7 earthquake that struck Myanmar in March 2025 produced one of the longest and fastest-moving ruptures ever recorded on land.

The study, in Science, shows that the earthquake ruptured about 530 kilometers of the Sagaing Fault, with a 450-kilometer segment racing faster than the speed of seismic shear waves—a rare phenomenon known as a supershear rupture. These "Mach-like" ruptures generate shock waves that can greatly amplify ground shaking and damage.

"Supershear earthquakes are like breaking the sound barrier, but in rock," said Lingsen Meng, a professor of geophysics in UCLA's department of Earth, planetary, and space sciences and senior author of the study. "They create seismic shock fronts that can double the intensity of shaking, even hundreds of kilometers away."

Supershear quakes are caused when faults beneath the surface rupture faster than shear waves—the seismic waves that shake the ground back and forth—can move through rock. The effect corrals energy that is then released violently; the effect can be compared to a sonic boom. Supershear earthquakes can therefore produce more shaking, and are potentially more destructive, than other earthquakes of the same magnitude.

Using an integrated approach that combined global seismic data, satellite radar (InSAR), and optical imagery, the researchers reconstructed the Myanmar rupture in unprecedented detail. The results show that the southern branch of the Sagaing Fault experienced sustained supershear speeds of up to 5 kilometers per second, while the northern branch propagated more slowly.

The team attributes the extreme speed of the rupture to several key geological factors: a straight and smooth fault geometry, long-term stress accumulation since the last major earthquake in 1839, and contrasting rock properties across the fault interface. Together, these conditions created an ideal setting for the rupture to accelerate and maintain supershear velocities over hundreds of kilometers.

The earthquake caused widespread destruction across central Myanmar, including building collapses and soil liquefaction visible from space. Because field surveys were limited by ongoing civil conflict, the researchers used satellite-based "damage proxy maps" to remotely assess the extent of the devastation.

"This event reminds us that even well-studied continental faults can behave in unexpected and dangerous ways," Meng said. "Understanding the physical conditions that allow a rupture to reach these speeds will help us better estimate future earthquake hazards—especially in fault systems near major cities."

The research highlights the need to re-evaluate seismic risks in other continental regions with similar fault geometries, such as parts of Asia and California, where long linear faults and contrasting rock layers coexist.

UCLA doctoral student Liuwei Xu led the seismic imaging analysis. Co-authors include researchers from Nanjing University, Central South University, the Chinese Academy of Sciences, and UC Santa Barbara.