Slide-hold-slide tests of infilled granite fractures affected by normal stress oscillations during the relaxation stage

Abstract

Slide-hold-slide (SHS) test is commonly used to investigate the frictional sliding stability of tectonic faults/fractures in laboratory. However, almost SHS tests are performed under constant normal stress, which cannot truly reflect the dynamic disturbance around fault zones. In this study, we conducted a series of ‘dynamic SHS tests’ which included oscillatory normal stress during the relaxation (hold) stage characterized by different amplitudes and frequencies. The granite fractures filled with synthetic quartz gouge were sheared using a double direct shear apparatus. We found that, normal load oscillation amplitude has an evident impact on the relaxation and healing characteristics of the fractures. Larger oscillation amplitude induces higher magnitude of frictional relaxation and frictional healing, and the rate of frictional healing increased uniformly when improving the oscillation amplitude under different stress levels. However, oscillation frequencies have little influence on the relaxation and healing characteristics. Finally, we used the rate and state friction (RSF) law to simulate the shear stress evolution in the hold stage, and it cannot appropriately reflect the dynamic frictional response. These results provide a deeper understanding of interseismic friction evolution of natural faults under stress disturbances.