Myanmar fault had ideal geometry to produce 2025 supershear earthquake
UCLA-led research reveals how fault structure and rock contrasts enabled one of the fastest continental ruptures ever observed
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, published 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 five 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. Coauthors include researchers from Nanjing University, Central South University, the Chinese Academy of Sciences, and UC Santa Barbara.
Journal
Science
Supershear rupture sustained in thick fault zone during 2025 Mandalay earthquake, study in research package shows
Summary author: Walter Beckwith
American Association for the Advancement of Science (AAAS)
A massive March 2025 earthquake in Myanmar tore through nearly 500 kilometers of the Sagaing Fault at extremely high speeds. In a new study – part of a package of four research articles on seismic activity in Myanmar – researchers show that an unusually thick, low-velocity fault zone acted like a high-speed corridor, driving one of the fastest and longest continental ruptures ever recorded. The largest earthquakes that occur within continental crusts can rupture faults extending for hundreds of kilometers and pose significant seismic threats. Many of these powerful events evolve into supershear ruptures – earthquakes in which the rupture front moves faster than the speed at which shear waves travel through the crust, making them especially powerful. This behavior often occurs on simple, straight faults like the San Andreas, North Anatolian, and Sagaing faults, which let energy concentrate instead of dispersing. During such quakes, parts of the crust around the fault weaken, forming damage zones that can affect how future earthquakes unfold. However, the relationship between fault zones and major strike-slip ruptures, and their influence on long-lasting supershear events, remains poorly understood.
According to Shengji Wei and colleagues, the March 28, 2025, magnitude 7.8 Mandalay earthquake in Myanmar offers new insight into these seismic dynamics. The Mandalay quake struck along the Sagaing Fault, breaking a 250-kilometer section that hadn’t ruptured in over a century, and produced a surface rupture exceeding 450 kilometers that reached supershear speeds. Using an interdisciplinary approach that combined satellite geodesy, broadband seismic data, receiver function imaging, and numerical simulations, Wei et al. reconstructed the earthquake’s 3D surface deformation, slip distribution, and rupture dynamics. They discovered that the rupture started in both directions from the epicenter and transitioned to supershear speeds (~5.3 km/s) about 100 kilometers to the south. This transition occurred along a roughly 2-kilometer-thick low-velocity fault zone, where shear-wave speeds were reduced by about 45%, coinciding with a shift in fault shape and structure. Wei et al. argue that it is these factors likely enabled the initiation and continuation of the supershear rupture and suggest that these events are more likely to occur along wide, simple strike-slip faults that have evolved through repeated seismic activity. Such insights could improve hazard assessments for major continental faults, such as California’s San Andreas and Türkiye’s North Anatolian faults, where similar conditions exist.
Journal
Science
Article Title
Supershear rupture sustained through a thick fault zone in the 2025 Mw 7.8 Mandalay earthquake
Article Publication Date
30-Oct-2025
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