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

[SCG45-43] Fault gouge evolution during sequences of high-velocity slip pulses

★Invited Papers

*John D Bedford¹, Daniel R Faulkner¹, Takehiro Hirose² (1.University of Liverpool, 2.JAMSTEC)

Keywords:Fault, Friction, Earthquake, High-velocity experiments, Fault gouge

During their lifetime, seismogenic faults will experience numerous earthquakes, with each event imparting damage onto the rocks that comprise the fault core and the surrounding country rock. The evolution of fault core properties (e.g., gouge grain size, surface area) during sequences of multiple earthquakes will have important implications for the rupture breakdown energetics in subsequent events, and also the fluid flow properties of the fault (i.e., by altering fault permeability). Here, to investigate the evolution of fault rock properties during multiple seismic slip events, we perform a series of high-velocity slip-pulse experiments on simulated quartz gouge. The quartz gouge layers are repeatedly sheared (up to 25 slip pulses) in a high-velocity rotary shear apparatus at sliding velocities of up to 1 m/s for a total displacement of 0.8 m during each slip pulse. The pore fluid pressure is controlled at a constant value of 5 MPa during each experiment, while the effective normal stress is varied between 2.5 to 6.25 MPa. Permeability measurements are performed between each seismic slip event to investigate the evolution of fluid flow after each pulse. We find a systematic evolution in the breakdown down energy as the number of slip pulses increases during the experiment, which we relate to an evolution of the gouge grain size (increasing number of submicron particles) and surface area caused by the accumulation of fracture damage after each event. We also find that the large shear strains achieved during the multiple events leads to a dramatic reduction in permeability, with the permeability reduction being more strongly controlled by the effective normal stress (i.e., higher effective normal stress produces lower permeability gouge) than the maximum sliding velocity during the slip pulses. Our results provide new insights on the evolution of fault gouge properties during multiple earthquake sequences and the implications this has for the partitioning of the rupture energy budget during future earthquake events.