Fig. 1

Friction curves obtained in the experiments on anorthite. The friction coefficient μ, as defined in Eq. (1), is plotted as a function of the displacement of the loading piston. a Dry samples at 20 and 600 °C. The boxes show the portions of the curves enlarged in b. The part of the friction curve around the velocity steps: b dry samples at 20, 200, 375, 500, and 600 °C; c wet samples at 200 and 400 °C. The arrows in a and c indicate the timing of the fast step in sliding velocity