[S-CG45] Science of slow-to-fast earthquakes

[SCG45-01] Slow Earthquake Scaling Revisited

*Satoshi Ide¹, Gregory C Beroza² (1.Department of Earth an Planetary Science, University of Tokyo, 2.Stanford University)

Keywords:Slow earthquake, Scaling, Moment rate, Diffusional process

The scaling law for slow earthquakes, which is a linear relationship between seismic moment and duration, was proposed 15 years ago and initiated a debate on the difference in physical processes governing slow vs. fast (ordinary) earthquakes. Based on new observations across a wide period range, we show that linear scaling of slow earthquakes remains valid, but as a well-defined upper bound on moment rate of ~ 10¹³ Nm/s. The large gap in moment-rate between the scaling of slow and fast earthquakes remains unfilled. Slow earthquakes occur near the detectability threshold, such that we are unable to detect deformation events with lower moment rates. Observed trends within slow earthquake categories support the idea that this unobservable field is populated with events of lower moment rate. This suggests a change in perspective that the proposed scaling should be considered a bound, or speed limit, on slow earthquakes. We propose that slow earthquakes represent diffusional propagation, and that the bound on moment rate reflects an upper limit on the speed of diffusional process. Ordinary earthquakes, in contrast, occur as a coupled process between seismic wave propagation and fracture. Thus, even though both phenomena occur as shear slip the difference of scaling reflects a difference in the physical process controlling propagation.