A new seismic analysis has identified a trio of geological factors that combined to produce the catastrophic 2025 Myanmar earthquake, an event that ruptured the Sagaing Fault at speeds faster than the seismic waves it generated. The research provides the most detailed reconstruction to date of the magnitude 7.7 supershear event, offering a crucial framework for understanding and potentially anticipating similar high-hazard earthquakes on major faults around the world.
The study, led by a team of geophysicists at the University of California, Los Angeles, explains why the quake was so destructive. An earthquake that ruptures at “supershear” speeds—outpacing the shear waves that shake the ground—creates a seismic shock front analogous to a sonic boom. This phenomenon can dramatically amplify ground shaking. The researchers found that a combination of a remarkably straight fault line, nearly two centuries of accumulated stress, and specific rock properties created an ideal runway for the rupture to accelerate and maintain its devastating velocity across more than 450 kilometers.
Anatomy of a High-Speed Rupture
A supershear earthquake occurs when the speed at which a fault breaks exceeds the velocity of the seismic shear waves, or S-waves, that travel through the surrounding rock. Normally, a rupture propagates at a speed below that of the S-waves. However, under certain conditions, the rupture can accelerate through this speed barrier. When this happens, the energy that would typically radiate away from the fault tip becomes trapped and focused into a powerful, coherent shock wave.
This effect is often compared to a fighter jet breaking the sound barrier. In the air, this creates a sonic boom; in the earth, it generates a seismic Mach cone. This shock front can carry intense energy far from the fault, leading to ground shaking that can be double the intensity of a conventional earthquake of the same magnitude. Scientists have identified several historical earthquakes as supershear events, including the 1906 San Francisco earthquake and the 2023 earthquakes in Turkey, but the 2025 Myanmar event stands out for its extreme length and speed.
Reconstructing the 2025 Event
To dissect the March 2025 quake, the scientific team integrated multiple streams of advanced observational data. They combined readings from the global seismic network with satellite radar (InSAR) and high-resolution optical imagery that showed the physical displacement of the ground. This multi-faceted approach allowed them to reconstruct the rupture’s evolution along the Sagaing Fault with unprecedented detail.
The model revealed that the earthquake ruptured a total length of approximately 530 kilometers. A southern segment, stretching 450 kilometers, sustained supershear speeds, at times reaching an incredible velocity of five kilometers per second. This was significantly faster than the shear wave velocity in the region’s crust. In contrast, the northern branch of the rupture propagated at more conventional, sub-shear speeds. The detailed reconstruction provided the raw data needed to identify the precise geological conditions responsible for the supershear behavior.
A Triad of Causal Factors
The study, published in the journal Science, pinpointed three primary conditions that worked in concert to prime the Sagaing Fault for a supershear rupture. While supershear events were once considered rare, they are now understood to be more common on mature, continent-spanning strike-slip faults, where two tectonic plates slide sideways against each other. The Myanmar quake serves as a textbook example of how specific fault characteristics can facilitate these extreme events.
A Remarkably Straight Fault
One of the most critical factors was the geometry of the Sagaing Fault itself. The segment that ruptured at supershear speeds is exceptionally straight and smooth. Many faults have bends, steps, or rough patches that act as barriers, slowing a rupture down or causing it to stop. The smooth, linear nature of this part of the Sagaing Fault provided a clear, uninterrupted path for the rupture to accelerate and maintain its high velocity without impediment.
Nearly Two Centuries of Stress
The region had been building toward a major release of energy. The last major earthquake to rupture this segment of the Sagaing Fault occurred in 1839. This allowed for more than 180 years of tectonic stress to accumulate along the fault line. The immense stored energy acted as a powerful fuel source for the rupture, enabling it to not only start but also to propagate with extreme speed once it overcame the initial friction holding the rock masses together.
Contrasting Geological Makeup
The third contributing factor involved the properties of the rock on either side of the fault. The research team’s analysis suggested that contrasting rock types across the fault interface created conditions that were highly conducive to a high-speed rupture. While the precise mechanisms are still being studied, these differences in rock rigidity and composition likely influenced the friction and stress dynamics at the point of the rupture, further enabling the acceleration to supershear speeds.
Implications for Global Hazard Assessment
The findings carry significant weight for seismic hazard planning worldwide. The 2025 Myanmar quake caused widespread destruction, including the collapse of numerous buildings and extensive soil liquefaction that was visible in satellite imagery. According to Lingsen Meng, a professor of geophysics at UCLA and the study’s senior author, the seismic shock fronts generated by the event could have doubled the shaking intensity, contributing to the severe damage observed hundreds of kilometers away.
This research underscores that many existing building codes and hazard assessments do not adequately account for the distinct damage patterns associated with supershear earthquakes. By identifying a clear set of pre-existing conditions—a straight fault, high accumulated stress, and favorable rock properties—the study provides a new diagnostic toolkit for seismologists. This could help scientists identify other major strike-slip faults around the globe, such as the San Andreas Fault in California, that may be primed to produce a devastating supershear rupture in the future.