Figure 3. (a) The relationship between the contact temperature of the contact surface and friction coefficient of the loess. (b) The relationship between the contact temperature of the contact surface and friction coefficient of the fault geomaterial. (c) The relationship between the ambient temperature and friction coefficient of the loess under different sliding velocities. (d) The relationship between the ambient temperature and friction coefficient of the fault geomaterial under different sliding velocities.
4.2 Strengthening and weakening effects of friction
Before the contact temperature reaches the phase transition temperature, the friction coefficient will show different trends with the increase of sliding velocity, i.e., gradually decreasing (weakening effect), basically unchanged, and progressively increasing (strengthening effect). This is since the difference between the creep activation energy in the normal and tangential directions of the geomaterial.
This difference indicates the relative ease with which creep occurs in the normal and tangential directions. When the difference between the activation energy of tangential and normal creep is small, the friction coefficient is a very slight change with the slow increase of the sliding velocity. This means that the tangential and normal creep processes are similar in difficulty, resulting in almost constant friction coefficient, as shown in Figure 4.