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On March 28, 2025, a major earthquake with a moment magnitude (Mw) of 7.7 struck Mandalay, central Myanmar (referred to as the 2025 Myanmar earthquake). This event caused severe shaking and substantial damage in Myanmar and neighboring countries. Aftershock distribution extended southward from the epicenter, indicating predominant southward rupture propagation.

In such cases, a Doppler-like directivity effect usually results in sharp, high-amplitude pulse waveforms recorded in the rupture propagation direction (south of the epicenter in this instance). However, seismic observations showed large amplitudes and sharp pulses at stations north of the epicenter, while stations to the south recorded smaller amplitudes and prolonged, multi-peaked waveforms.

This anomalous pattern suggests that the Myanmar earthquake exhibited an unconventional rupture behavior.

To investigate this, researchers applied the potency density tensor inversion method to flexibly analyze the seismic waveform data without predefining the rupture direction or fault geometry. The analysis revealed that the source process consisted of multiple rupture episodes with complex characteristics.

Notably, asymmetric ruptures propagated in both north and south directions, while each episode generally extended southward from the hypocenter. In particular, during the initial rupture episode, the rupture propagated southward before reversing direction and propagating northward in a boomerang-like manner at a shear velocity exceeding the S-wave velocity, indicating supershear rupture.

These findings, now in Seismica, underscore the potential of using high-quality seismic waveform data and flexible analytical methods to robustly and rapidly estimate complex source processes immediately after an earthquake.

The intricate rupture propagation patterns identified in this study are crucial for improving our understanding of earthquake generation mechanisms and assessing the development of strong ground motions capable of causing severe damage. Moreover, these insights are essential for comprehending the long-period seismic motions that caused structural damage in distant locations such as Bangkok, far from the earthquake's epicenter.