Intermittent lab earthquakes in dynamically weakening fault gouge

Vito Rubino, Ares J. Rosakis, & Nadia Lapusta

Accepted May 11, 2022, SCEC Contribution #11854

Large and destructive earthquakes on mature faults in the Earth’s crust occur as slip in a layer of a fine granular material – fault gouge - produced by comminution during sliding. A range of insights into frictional resistance of faults - one of the main factors controlling earthquake nucleation, dynamic propagation, and arrest, and hence the destructive ground shaking of earthquakes - has been obtained in experiments with spatially uniform slip imposed in small samples. However, how various features of gouge friction combine to determine spontaneous progression of earthquakes is difficult to study in the lab due to significant challenges with sample sizes and adequate imaging. Here we show, using novel lab experiments, that spontaneously propagating dynamic ruptures navigate a fault region with fine rock gouge through complex, intermittent slip processes with dramatic friction evolution. These include repeated arrest of rupture propagation caused by friction strengthening at lower slip rates and dynamic earthquake re-nucleation enabled by pronounced rapid friction weakening at higher slip rates consistent with flash heating. The spontaneous repeated weakening and strengthening of friction in fine rock gouge highlights fundamental dependence of friction on slip rate and associated processes, such as shear heating, localization/delocalization of shear, and dilation/compaction of the shear layer. Our findings expand experimental support of the concept that co-seismic weakening may enable earthquake rupture to break through stable fault regions, with significant implications for seismic hazard.

Citation
Rubino, V., Rosakis, A. J., & Lapusta, N. (2022). Intermittent lab earthquakes in dynamically weakening fault gouge. Nature, (accepted).


Related Projects & Working Groups
Fault and Rupture Mechanics (FARM)