Fig. 2
From: Can clay minerals account for the behavior of non-asperity on the subducting plate interface?
An example of slide-hold-slide test showing friction coefficient as a function of time for illite under wet condition. Friction coefficient decays from the steady-state level during holding period. When the piston was advanced again (sliding), a peak friction appears, and then friction decays to the steady-state level. The frictional healing (∆μ) is difference between the peak and steady-state frictions