The next major earthquake on the San Andreas Fault could be significantly larger than long-held expectations for “the Big One.” This warning comes from scientists who studied the devastating magnitude 7.7 earthquake that struck Myanmar on 28 March 2025, killing more than 5,000 people. Researchers found that the Sagaing Fault behaved in ways many geologists had not anticipated. Instead of rupturing only within the section where stress had accumulated for decades, the earthquake propagated across more than 310 miles (approximately 500 km) of the fault — extending well beyond the zones previously considered most likely to break. This discovery challenges a core assumption in earthquake science: that faults tend to repeat similar rupture patterns over time, with earthquakes largely confined to segments where stress has built up since the previous event. The Myanmar quake demonstrated that ruptures can cascade across much larger sections of a fault than expected, releasing more slip and involving longer distances than earlier models predicted. These insights are especially relevant for California because the Sagaing Fault shares important similarities with the San Andreas Fault. Both are long, relatively straight strike-slip faults where the two sides slide horizontally past one another. The San Andreas stretches about 746 miles (1,200 km) through California and has produced some of the largest earthquakes in U.S. history, including the catastrophic 1906 San Francisco earthquake. The 2025 Myanmar event serves as a powerful reminder that faults do not always follow historical patterns. In some cases, future earthquakes may rupture longer distances, involve larger fault sections, and generate more energy than previously anticipated. Scientists stress that this does not mean a giant earthquake is imminent. Precise prediction of earthquakes remains impossible. Nevertheless, the study shows that relying solely on past earthquake behavior may underestimate the true potential size and impact of major events on long strike-slip faults. [Li, B., et al. Seismic gap breached by the 2025 Mw 7.7 Mandalay (Myanmar) earthquake. Nature Geoscience. 2025. DOI: 10.1038/s41561-025-01861-7]