"A structurally simple fault produced one of the most complex earthquakes on record, rewriting the rules of seismic hazard."
An Earthquake That Defied Expectations
In March 2025, a devastating magnitude 7.7 earthquake struck near Mandalay, Myanmar, claiming over 3,600 lives and causing widespread economic destruction. The event has since emerged as a pivotal moment for earthquake science, challenging long-held beliefs about how and where major quakes begin.
A Simple Fault, A Complex Rupture
The earthquake occurred on the Sagaing Fault, a geological feature considered remarkably simple—long, straight, and devoid of sharp bends. Despite this simplicity, the rupture traveled an astonishing 450 kilometers, tearing through a region that scientists had previously considered less dangerous.
Using satellite radar data to measure ground displacement and combining it with computer models simulating centuries of stress accumulation, an international team of researchers has uncovered why.
The Key Finding: Small Differences, Big Consequences
The study, published in Science, reveals that long-term, minor variations in motion rates along different fault segments—as little as 10–20%—can build uneven stress over time. This uneven stress, not the fault's shape, controls where a rupture starts, how it spreads, and how large it ultimately becomes.
"The rupture started outside a known seismic gap, then propagated through it—directly contradicting the seismic gap hypothesis."
This finding strikes at the heart of the seismic gap hypothesis, which posits that fault segments which have remained quiet for a long time are the most likely to rupture. The Sagaing earthquake directly disproved this for a major event, moving through a "safe" zone with ease.
A New Framework for Global Hazard Assessment
The implications extend far beyond Myanmar. The researchers state that similar processes are likely at work on other major fault systems, including:
- The San Andreas Fault in California
- The Alpine Fault in New Zealand
The team argues that combining satellite data, geological records, and advanced simulations can dramatically improve earthquake hazard assessments worldwide.
Study Limitations
The authors acknowledge that their models rely on simplifying assumptions and cannot directly measure certain properties of the deep fault. However, the models successfully reproduced the main features of the 2025 rupture, providing a robust framework for future research.
Authorship & Funding
- Corresponding Author: Mingqi Liu (postdoc at USC Dornsife, now at ENS Paris)
- Senior Author: Sylvain Barbot (USC Dornsife)
- Collaborators: Peking University and China Earthquake Administration
- Funding: U.S. National Science Foundation (EAR-1848192), Swiss National Science Foundation Postdoc Mobility Fellowship (P500PN_214251), National Natural Science Foundation of China (42374019 & 42474013)