Seismic study sheds light on factors that led to 2025 Myanmar supershear rupture

Recently, Science put out an article detailing new research on the Myanmar earthquake that occurred on March 28, 2025. In one of these studies, Shengji Wei and colleagues analyze data on the event and provide insight on multiple factors that lead to these rare and devastating supershear ruptures. Their research was published this week.

Widespread destruction in Myanmar

The Myanmar earthquake was one of the longest and fastest-moving ruptures ever recorded on land, causing widespread destruction along the Sagaing Fault. The moment magnitude is reported to have been 7.7 to 7.8, resulting in at least 5,352 fatalities and extensive structural damage. Its effects were felt as far as Bangkok, Thailand, 1,000 km away.

The earthquake produced a surface rupture over 450 kilometers in length, stretching north to south through major cities, like Mandalay and Naypyidaw. The surface rupture broke supershear speeds—meaning the rupture traveled faster than the local shear wave speed. This is similar to what happens when a supersonic aircraft travels faster than the speed of sound.

Better understanding for better future outcomes

While studies on these kinds of massive earthquakes can’t prevent them from occurring, they can help at-risk communities understand their level of risk and prepare accordingly. Findings from these studies can inform hazard analysis for other major strike-slip faults with similar characteristics, like the San Andreas Fault or the North Anatolian Fault.

The Myanmar event provided a unique opportunity for researchers to study how fault zones influence rupture dynamics for a deeper understanding of how these events occur. Wei and his team took this opportunity to analyze rupture dynamics through a multifaceted lens, consisting of satellite-based and seismic techniques, including 3D surface deformation mapping, strong-motion records, and receiver function analysis. They also used remote sensing, teleseismic data, and local seismic arrays to resolve rupture dynamics and fault structure.

Unveiling supershear dynamics

Faults that experience supershear events, such as the San Andreas, North Anatolian, and Sagaing faults, have some common features. For example, they are all simple, straight faults, which tend to allow energy to concentrate instead of disperse. This leads to weakening crust along the fault and more damage during earthquakes.

The study researchers say that the rupture started at subshear velocities and rapidly shifted to supershear. Their results show velocities up to 5.3 km/s.

“The rupture initiated as bilateral subshear and transitioned to supershear (~5.3 km/s) about 100 km south of the epicenter, sustaining this velocity for more than 200 km. The supershear segment aligns with a ~2-km–thick low-velocity fault zone exhibiting ~45% shear wave speed reduction. We suggest that the thick fault zone, aided by fault geometry and basin structure, enabled prolonged supershear propagation,” the study authors explain.

They note that simple fault geometry and wide fault zone most likely provided the most essential conditions behind the prolonged distance of the supershear and subshear-to-supershear transition, due to the fault stress perturbations that lead to the supershear rupture front developing.

“As the rupture propagated onto the west dipping fault, the smooth fault geometry provided the ‘superhighway’ to help sustain the supershear rupture, similar to what may have happened for other supershear events. The relatively thick (~2 to 3 km) sedimentary basin along the southern fault segment serves as another favorable condition to sustain supershear rupture, as the waves reflected from the bottom of the basin could have increased shear stress on the fault and promoted rupture propagation,” the study authors say.

Insights into features that lead to a higher probability of supershear rupture speeds can help improve the earthquake hazard models for regions with known thick fault zones and simple fault geometries, particularly for cities near major strike-slip faults. However, there is still work to be done. More comprehensive models that incorporate detailed fault zone structures would be helpful for more detailed earthquake hazard assessment.

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