Effect of Pore Pressure Rate on Rate and State Frictional Slip In Experiments

This project examines the effects of imposed rate of pore pressure change on the stability of rate and state frictional slip. The work is motivated by recent experiments that impose pressure at different rates. These find that the slip velocity and shear stress drops of accelerated slip events correlated with pore pressure rate rather than the magnitude of the pore pressure. Additional motivation comes from field observations suggesting that injection rate is an important factor in the occurrence of induced earthquakes in mid-continental US. Numerical simulations for a simple spring – slider model assuming sliding is governed by rate and state friction show that the pressure rate can control the frequency of rapid slip events. Refinement of the model indicates how the features of slip events observed in the laboratory depend on frictional parameters, rate of loading, rate and magnitude of pore pressure increase, and diffusivity. The work provides a fundamental basis for understanding the effects of pore pressure rate accompanying injection of fluids in laboratory test and at field sites.