Mechanics of supershear earthquakes: theory and modeling across scales

About This Grant

Supershear earthquakes are rare but extremely powerful. They occur when the rupture along a fault moves faster than the speed at which shear waves travel through the surrounding rock. Much like supersonic jets produce a sonic boom when they exceed the speed of sound, supershear earthquakes generate Mach cones—shear shock fronts that carry concentrated energy and radiate intense shaking. These waves can travel much farther than those produced by traditional (subshear) earthquakes, causing widespread destruction. A recent example is the 2023 Kahramanmaraş earthquake doublet, which caused severe damage across southern Turkey and northern Syria. Despite their devastating impact, the physical conditions that allow such fast ruptures to occur remain poorly understood. This project addresses that gap by investigating the mechanics that govern the onset and recurrence of supershear earthquakes, particularly on long, mature faults that often appear stable. The research will improve earthquake hazard models and support safer infrastructure design in earthquake-prone regions. It will also help scientists better understand how faults accumulate and release stress across multiple earthquake cycles. Broader impacts include the training of graduate and undergraduate students through mentoring, hands-on research, and collaborative group activities. A new graduate course on dynamic earthquake mechanics will bring together students from civil engineering and geophysics. Project results will be disseminated through conferences, peer-reviewed publications, and a dedicated website, with key concepts also shared with the public through interactive exhibits at the Chicago Museum of Science and Industry. The project combines theoretical modeling and state-of-the-art numerical simulations to advance the understanding of supershear earthquake dynamics. It has three main objectives. First, it will develop a new fracture-mechanics-based equation of motion for ruptures that propagate faster than the shear wave speed, accounting for energy partitioning and the variation of fracture energy with rupture velocity. Second, it will investigate how slip complexity and residual stress from partial ruptures influence the conditions for supershear transition across multiple spontaneous earthquake cycles. Third, it will examine the role of thermally activated weakening mechanisms, which may significantly increase the likelihood of supershear nucleation. To achieve these goals, the project will use an efficient spectral boundary integral method capable of capturing efficiently both fast dynamic rupture and long-term aseismic slip. This integrated framework will provide new insight into when and where supershear earthquakes occur—and how often. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.