The 2025 Mw7.7 Mandalay, Myanmar, earthquake: extremely long and uniform rupture part of a fault supercycle

Solène L. Antoine, Rajani Shrestha, Chris Milliner, Kyungjae Im, Chris Rollins, Kang Wang, Kejie Chen, & Jean-Philippe Avouac

Submitted September 7, 2025, SCEC Contribution #14265, 2025 SCEC Annual Meeting Poster #TBD

Large earthquakes often occur on faults that were known to have produced destructive events in the past. The 2025 Mw7.7 Mandalay earthquake is no exception as it ruptured a known seismicity gap along the Sagaing fault. Remote sensing observations of the co-seismic deformation reveal an extremely long (~510 km) and localized surface rupture that also encompasses sections that ruptured during more recent (1929 to 1956) events, some of them with high-slip. The seismic rupture involved the locked portion of the fault over its entire depth extent (0-13km) with a remarkably uniform slip distribution that averages 3.3 m, and no shallow-slip deficit. The amplitude and spatial distribution of fault slip in the 2025 event conform only approximatively to the slip-predictable model and the segmentation inferred from the fault geometry and past ruptures. Moment budget analysis shows that the 2025 event occurred as part of a period of enhanced seismicity, with earthquake clustering and variable segmentation likely favored by the smoothed but curved geometry of the Sagaing fault. We reproduce sequences of earthquakes with variable magnitude, segmentation, and return periods, including events similar to the 2025 earthquake in quasi-dynamic simulations using a simplified but non-planar fault geometry. Based on this simulation, Mw > 7.5 events return irregularly with an interevent time of ~141 years on average and a standard deviation of ~40 year. The simulation is consistent with the historical seismicity and with the maximum magnitude ~Mw 7.9 and return period (~250yr) derived from moment conservation. These observations challenge the usual approaches used in seismic hazard studies to evaluate how a fault is spatially divided and strain is built up and released over time, and show that data assimilation into such simulations could provide a way for time dependent hazard assessment in the future.

Key Words
Earthquake, strike-slip, supershear, mature fault, supercycle

Citation
Antoine, S. L., Shrestha, R., Milliner, C., Im, K., Rollins, C., Wang, K., Chen, K., & Avouac, J. (2025, 09). The 2025 Mw7.7 Mandalay, Myanmar, earthquake: extremely long and uniform rupture part of a fault supercycle. Poster Presentation at 2025 SCEC Annual Meeting.

Related Projects & Working Groups
Tectonic Geodesy