Kyoto, Japan -- During the midday Friday prayer hours on 28 March 2025, a magnitude 7.7 earthquake struck central Myanmar along the Sagaing Fault. With an epicenter close to Mandalay, the country's second-largest city, it was the most powerful earthquake to strike Myanmar in more than a century and the second deadliest in its modern history.
The cause was a strike-slip fault, in which two masses of earth "slip" past each other horizontally along a vertical fault plane. To an observer, it would look like the ground were split in two along a defined line, with both sides being wrenched past each other in opposite directions.
Previous seismological studies have inferred pulse-like rupture behavior and curved slip paths from the analysis of seismic data. However, because the recording instruments were at a considerable distance from the fault itself, these findings were indirect.
This time, however, a CCTV camera caught this slip in action, presenting a unique opportunity for a team researchers at Kyoto University to study the fault motion in real time.
The team applied a technique known as pixel cross-correlation to the CCTV footage to analyze the fault's movement frame-by-frame. Their analysis reveals that the fault slipped sideways 2.5 meters in just 1.3 seconds, with a maximum speed of 3.2 meters per second. The total sideways movement recorded during this earthquake is typical of strike-slip ruptures, but the short duration of the fault slip is a major discovery.
"The brief duration of motion confirms a pulse-like rupture, characterized by a concentrated burst of slip propagating along the fault, much like a ripple traveling down a rug when flicked from one end," says corresponding author Jesse Kearse.
The team's analysis also proves that the slip path was subtly curved, a finding which aligns with previous geological observations from faults around the world. This may suggest that such slips are typically curved, as opposed to being completely linear.
The study demonstrates that video-based monitoring of faults is a powerful tool for seismology, enabling unprecedented insights into earthquake behavior. Capturing this level of detail is fundamental to improving our understanding of earthquake processes and enhancing our ability to anticipate the ground shaking expected in future large events.
"We did not anticipate that this video record would provide such a rich variety of detailed observations. Such kinematic data is critical for advancing our understanding of earthquake source physics," says Kearse.
The next phase of their research will utilize physics-based models to investigate the factors that control fault behavior as revealed by this analysis.
