Scientists studying the devastating March 28, 2025, Myanmar earthquake have determined the primary seismic energy wave moved through the southern portion of its rupture at ‘supershear’ velocity of 5 to 6 kilometers per second.
With more than 5,000 confirmed casualties across Myanmar and neighboring countries like Thailand, the 7.7 magnitude earthquake ruptured roughly 480 kilometers of the Sagaing Fault, which extends north-south through the central part of the country. The scientists behind the findings said that the extraordinary length of this level of strike-slip rupture, particularly given its supershear velocity, makes it roughly equivalent to the over 400 km long rupture caused by the 1906 San Francisco earthquake known as the “Big One.”
Date Reveals Supershear Velocity of Earthquake Rupture
Previously in a 2005 study, Stanford University scientists offered new data that the infamous 1906 San Francisco earthquake, known as the “Big One,” also reached supershear velocity. At the time, Stanford said Professor Gregory C. Beroza explained that supershear is when “the slipping part of the fault moves faster than the shear-wave velocity.”
“It’s analogous to supersonic,” Beroza explained. “You get a sonic boom.”
More recently, in a statement announcing the current study, seismologists Lingling Ye, Thorne Lay, and Hiroo Kanamori note some initial reporting had already suggested the Myanmar earthquake reached supershear velocity. Still, determining the rupture’s actual speed required analyzing satellite and seismic data recorded during the event.
The team explained that seismic data revealed measurements of “strong ground motion” recorded about five kilometers west of the Sagaing fault near Nay Pyi Taw. Ye indicated this data collection station is “one of the closest seismic stations to record the rupture passage for a great earthquake.”
“Earthquake seismologists have long desired to have near-fault records like this,” the seismologist added.
Lay said this data was “immediately convincing” of a supershear speed earthquake rupture, given the time between the weak, dilational P wave first arrival and the arrival of a “large shear offset of the fault” at the station.
“That was unusually clear and convincing evidence for supershear rupture relative to other long strike-slip events that I have worked on,” Lay said.
In their published study, the team stated that the initial P waves, indicating a rupture, arrived at the Nay Pyi Taw station roughly 36 seconds after the event began. 12 seconds later, the equipment detected much stronger motions. The team said that the “strong directivity” of the rupture toward the south, combined with the event’s supershear velocity, may account for the impacts felt as far away as Bangkok.
Event Was Exceptionally Long and Straight
Further analysis also revealed that the earthquake was exceptionally long and straight, especially given its overall magnitude. According to the team’s statement, satellite data captured during and after the event revealed evidence of a large slip “up to seven meters” extending around 85 kilometers north and 395 kilometers south of the earthquake’s epicenter near the city of Mandalay. Although the southern portion of the rupture was described as “more patchy” than the northern portion with depths varying between 1 and 6 meters, the overall length still made it a rare event.
“The length of the rupture is on the high end relative to the seismic moment,” said Lay.
The seismologist believes the relative straightness of the southern two-thirds of the recorded rupture combined with the fact that it has been almost seventy years since the fault’s last rupture likely aided the rupture’s expansion.
The last earthquake of magnitude seven or larger along the Sagaing Fault occurred in 1956, with another major event preceding it in 1930. However, the team said the recent event appeared to rupture a segment of the fault that had been “seismically quiet” since events in 1912 and 1839
“The 2025 event appears to have ruptured a bit further north and further south than might be expected from the locations of prior events in 1956 in the north and 1930 in the south, but the precise locations and slip distributions for those events are not known,” Lay explained.
Better Understanding Could Aid Efforts to Predict Major Seismic Events
Although improved data available for the more recent event was able to establish that the earthquake’s rupture moved at supershear velocity, Lay believes that overlap with the 1930 and 1956 events may “represent our lack of knowledge of precise strain release patterns” for those two previous events, or an “incomplete strain release in those earlier events.”
The seismologist also suggests that “longer histories and better understanding of fault segmentation and geometry” will be needed to predict future events. However, Lay said he would not expect another failure of the fault’s central area before it goes through a long period of “rebuilding strain energy.”
The study “The 28 March 2025 7.8 Myanmar Earthquake: Preliminary Analysis of an ∼480 km Long Intermittent Supershear Rupture” was published in The Seismic Record.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.