Similar scaling laws for earthquakes and Cascadia slow-slip events.

Faults can slip not only episodically during earthquakes but also during transient aseismic slip events1-5, often called slow-slip events. Previous studies based on observations compiled from various tectonic settings6-8 have suggested that the moment of slow-slip events is proportional to their duration, instead of following the duration-cubed scaling found for earthquakes9. This finding has spurred efforts to unravel the cause of the difference in scaling6,10-14. Thanks to a new catalogue of slow-slip events on the Cascadia megathrust based on the inversion of surface deformation measurements between 2007 and 201715, we find that a cubic moment-duration scaling law is more likely. Like regular earthquakes, slow-slip events also have a moment that is proportional to A3/2, where A is the rupture area, and obey the Gutenberg-Richter relationship between frequency and magnitude. Finally, these slow-slip events show pulse-like ruptures similar to seismic ruptures. The scaling properties of slow-slip events are thus strikingly similar to those of regular earthquakes, suggesting that they are governed by similar dynamic properties.