Interplay between slow slip and seismic ruptures: an experimental study

Seismic faults release the stress accumulated during tectonic movement through a spectrum of events ranging from rapid ruptures to slow slip events. Slow slip plays a crucial role in the seismic cycle impacting the occurrence of earthquakes. However, the interplay mechanisms between a slow-slip region and seismogenic zones are not well understood. In addition, the conditions required for a fault to experience slow slip have not yet been established, and the question of whether the same fault can experience different slip behavior is still under debate.

In this experimental study, we highlight a system where a slow slip region acts as a nucleation center for seismic ruptures, increasing the frequency of earthquakes (Faure and Bayart, 2024). Furthermore, we observe that along the same interface, zones can rupture seismically or experience slow slip depending on the loading conditions.

In our experiments, we emulate slow slip regions by introducing a granular material inclusion along part of a laboratory fault. By measuring the response of the fault to shear and performing interfacial slip measurements, we show that the slow-slip region acts as an initial rupture that destabilizes into a dynamic rupture, leading to a seismic event. By varying the loading conditions of the granular inclusion, we show that the earthquake frequency is related to the initial rupture characteristics, i.e., length and loading at the tip, as predicted by initiation criteria for rupture destabilization. We also find that the region of slow slip extends beyond the compositional heterogeneity, along regions that otherwise rupture seismically, demonstrating that fault composition is not the only requirement for slow slip. Our results pave the way for the construction of novel models that account for the evolution of the slow slip region under varying loading conditions, in order to improve fault monitoring and seismic hazard mitigation.

Faure, Y., Bayart, E. Experimental evidence of seismic ruptures initiated by aseismic slip. Nat Commun 15, 8217 (2024). doi:10.1038/s41467-024-52492-2.