UCLA

Supershear earthquakes, whose rupture speeds are faster than that of the seismic shear waves, can be highly destructive owing to the associated strong ground shaking. These events are rare, and understanding why they occur may provide insights into fault mechanics. However, identified samples of supershear earthquakes are rare, which hinders systematic analysis of their mechanism. In this work, I optimized observational methods and applied them to find more supershear earthquakes. Eventually, a global survey of earthquake rupture speeds reveals that supershear earthquakes occur much more frequently than previously thought. Our findings provide a much greater basis for evaluating the conditions favourable for driving supershear rupture. We observe that supershear rupture is more common along faults that separate oceanic and continental plates. These oceanic–continental supershear events also generate rupture in the same relative direction as the stiffer fault block moves. We find that fault zone width is thicker in regions where supershear earthquakes occur, and that supershear ruptures occur relatively frequently in mature oceanic transform faults. Our works confirm observations made from laboratory and numerical experiments and will be able to guide future research into these destructive earthquakes.