How the fault in the 2025 Myanmar earthquake ruptured

What is it about?

Researchers report characteristics of the rupture zone of the 2025 Myanmar Earthquake, showing how the rupture’s propagation speed was affected by variations in structure and stress level at different points along the Sagaing fault. The Sagaing fault is one of the longest and most active strike-slip faults, with multiple segments that have a history of producing earthquakes of Mw 7 or greater. Lingling Ye and colleagues reconstructed the detailed process of fault rupture during the earthquake using near-fault motion sensor data, geodetic measurements, and seismic data. During the earthquake, the authors found that the northward propagation of the rupture ended after about 100 km with a speed less than the shear wave speed. The southward rupture propagation, however, extended by about 380 km, fully traversing a predefined seismic gap that had remained unruptured since 1839. The authors write that the rupture experienced at least two intermittent supershear phases, during which the rupture propagation moved faster than the shear wave, with cycles of acceleration and deceleration before gradually stopping after traversing segments ruptured in 1930. According to the authors, the results show how the local fault structure can mediate the speed and extent of rupture propagation.

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Photo by Zoshua Colah on Unsplash

Photo by Zoshua Colah on Unsplash

Why is it important?

Intermittent supershear rupture (rupture propagating faster than the local shear-wave speed, enhancing ground shaking) has infrequently been documented for natural earthquakes, mainly due to the scarcity of dense near-fault observations. Using multiple complementary datasets, we resolve that the ~480-km-long 2025 Myanmar MW 7.7 earthquake exhibits north-south asymmetry with long-duration slip near the epicenter and at both ends, and short-duration slip with a higher slip rate in the center. We find that localized along-strike variations in fault geometry might strongly mediate the rupture dynamics, including north-south asymmetry, intermittent supershear rupture, and small-scale slip segmentation.

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