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Sustained supershear earthquake ruptures produce distinct ground-motion characteristics compared with subshear earthquakes, according to a study published in the Bulletin of the Seismological Society of America, with potential implications for current building codes and ground-motion models.
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Supershear earthquakes occur when the fault rupture itself moves faster than the earthquake's shear waves, creating a Mach cone—an intense shock front similar to the sonic boom of a supersonic jet. The phenomenon creates intense shaking close to the fault.
While seismologists used to think supershear earthquakes were rare, recent devastating earthquakes in Türkiye in 2023 and Myanmar in 2025 contained supershear ruptures. In fact, researchers have identified supershear ruptures in nearly 36% of strike-slip earthquakes of magnitude 7 or greater in the past 15 years.
Observations near the fault remain scarce
Observations of ground shaking near the fault in supershear earthquakes remain rare, however. This leaves seismologists with a fundamental question, said Mohamed Abdelmeguid, the study's lead author.
"Do supershear ruptures produce ground motions that are distinctly different from subshear ruptures, and potentially more damaging to the built environment? Given what we're learning about how common supershear may be, answering that question has become urgent," he said.
Existing building codes and ground-motion models "do not explicitly separate rupture speed or sustained supershear propagation as design-relevant parameters," he added.
Idealized simulations show stronger shaking
Abdelmeguid and his colleagues at Caltech studied the features of simulated supershear earthquakes to learn how they might differ from subshear earthquakes.
The simulated earthquakes in the BSSA study don't include features such as different types of rock or ground structures that could potentially scatter and weaken seismic waves. Under these idealized conditions, "prolonged and sustained ruptures consistently produce stronger ground-motion amplitudes than their subshear counterparts," the authors write.
The researchers found that peak ground velocity, or PGV (the maximum speed the ground moves during an earthquake), for supershear ruptures remained high even up to 20 kilometers (12 miles) away from the fault. What's more, the PGV calculated for these simulated supershear ruptures was higher than predicted by ground-motion models.
A double punch near the fault
Nearer to the fault—within 7 kilometers (4 miles)—supershear ruptures caused shaking to last longer than during subshear ruptures. The longer duration is likely due to the "double punch" effect, where shaking arrives first with a "pulse" of energy at the supershear rupture's leading edge, trailed by a secondary subshear pulse.
"What stood out to us was how strongly the effects depended on the length of sustained supershear propagation," Abdelmeguid explained. "Short or episodic supershear bursts produce ground-motion characteristics that look quite similar to subshear cases, while longer sustained supershear propagation leads to ground-motion features that are … distinct from subshear events."
Stronger stress on mid-rise buildings
Abdelmeguid and colleagues concluded that supershear ruptures produce larger spectral accelerations, or the maximum acceleration buildings experience during an earthquake. Supershear earthquakes generate larger spectral accelerations, especially in the frequency range that affects 3- to 5-story buildings, their study shows.
Abdelmeguid and his BSSA co-authors also published an editorial in Seismological Research Letters in 2025 that discussed the importance of supershear earthquakes for seismic hazard and design standards.
More information: Mohamed Abdelmeguid et al, Ground-Motion Characteristics of Idealized Supershear Ruptures: Do They Matter for Engineering Applications?, Bulletin of the Seismological Society of America (2026). DOI: 10.1785/0120250186
Provided by Seismological Society of America
This story was originally published on Phys.org.
