At a Glance
- The 2025 Myanmar earthquake ruptured a surprisingly long 510-kilometer stretch of the Sagaing Fault, challenging conventional scientific models of how earthquakes behave on major fault lines.
- This event has significant implications for California, as the Sagaing Fault is geologically similar to the well-known San Andreas Fault, suggesting a future quake there could be unpredictable.
- Scientists were surprised that the rupture included fault sections that had broken in more recent history, not just the “seismic gap” that had been building stress for over a century.
- Computer simulations based on the event indicate that massive earthquakes on these faults do not follow a repeatable pattern, making it challenging to predict the characteristics of future events.
- Researchers now believe California could face a variety of scenarios, from smaller but more frequent quakes to a massive rupture exceeding magnitude 8 along the San Andreas Fault.
A recent study on a massive earthquake in Myanmar offers a cautionary tale for California, suggesting the next “Big One” on the San Andreas fault could be far more unpredictable than previously thought. Research published in the Proceedings of the National Academy of Sciences details the 2025 magnitude 7.7 Mandalay earthquake, which ruptured an unexpectedly long 510-kilometer section of the Sagaing Fault. This fault is often compared to California’s San Andreas due to its similar geological structure. The quake’s immense rupture challenges long-held scientific ideas about how and where stress builds up and is released along fault lines, a concept known as seismic gaps.
Scientists were surprised that the Mandalay earthquake tore through not only a section of the fault that had been quiet since 1839 but also segments that had ruptured more recently in the 20th century. This observation contradicts the simpler “slip-predictable” model, where scientists estimate future earthquake characteristics based on past events. The study, co-authored by Caltech researchers, highlights that faults do not necessarily break in neat, repeatable patterns. The extraordinary length of the rupture, the longest ever documented on a continent, may have been helped by the Sagaing Fault’s unusually smooth and straight geometry, allowing the quake to travel at “supershear” speeds—faster than the seismic waves it generates.
These findings have significant implications for seismic hazard assessment in regions such as California. “Earthquakes never come back exactly the same way,” said Solene L. Antoine, a Caltech postdoctoral fellow and the study’s lead author, in a statement to Phys.org. Instead of a simple repeat of the 1906 San Francisco or 1857 Fort Tejon earthquakes, the San Andreas could rupture in a variety of new and complex ways. This could mean a series of more minor, more frequent quakes or, more alarmingly, a single massive event larger than a magnitude 8 that ruptures the fault from Northern California to the Mexican border.
To better understand these possibilities, the research team used physics-based computer simulations to model thousands of years of earthquake activity along the Sagaing Fault. The simulations generated a diverse range of earthquake sequences, demonstrating that large, destructive events can occur irregularly, without a clear, predictable pattern. The team plans to apply this complex modeling to the San Andreas Fault, aiming to create a catalog of potential future earthquake scenarios. While this will not predict when the next quake will strike, it will provide a much clearer picture of what California should prepare for.
References
- Antoine, S. L., Shrestha, R., Milliner, C., Im, K., Rollins, C., Wang, K., Chen, K., & Avouac, J.-P. (2025). The 2025 Mw 7.7 Mandalay, Myanmar, earthquake reveals a complex earthquake cycle with clustering and variable segmentation on the Sagaing Fault. Proceedings of the National Academy of Sciences, 122(33), e2514378122. https://doi.org/10.1073/pnas.2514378122
- Lin, R.-G. I. (2025, August 12). The next ‘Big One’ on the San Andreas fault might not be the earthquake we expect, researchers say. Phys.Org; Phys.org. https://phys.org/news/2025-08-big-san-andreas-fault-earthquake.html
