John Bedford, Takehiro Hirose, Yohei Hamada

Fault strength recovery (healing) following an earthquake is a key process in controlling the recurrence of future events; however, the rates and mechanisms of fault healing are poorly constrained. Here, by performing high-velocity friction experiments at seismic slip rates (0.57 m/s), we show that granite and gabbro fault gouges recover their strength rapidly after experiencing dynamic weakening. The healing rates are one to two orders of magnitude faster than those observed in typical frictional healing experiments performed at slow slip velocities (micrometers to millimeters per second). Analysis of the sheared gouges using Raman spectroscopy suggests that enhanced healing after seismic slip is associated with thermally activated chemical bonding at frictional contacts in the gouge. Our results indicate that seismogenic faults can potentially regain their strength early during interseismic periods, which would imply that healing may not be the dominant control on earthquake recurrence, with other processes, such as far-field tectonic loading or frictional stability transitions, possibly dictating the occurrence of future events.