Fig. 1

Hydrothermal shear tests on layers of simulated calcite fault gouge at 550 °C. a Experiments performed at a constant effective normal stress (σ _n ^eff) of 50 MPa, using a sliding velocity (v) of 0.1 and 100 μm s⁻¹. b Effective normal stress-stepping experiments. c Steady-state shear stress plotted against effective normal stress, taken from experiments performed using v = 0.1 μm s⁻¹ (NS-slow_A and NS-slow_B) and ≥1 μm s⁻¹ (NS-fast_A and NS-fast_C). d Velocity-stepping experiments. Supplementary Tables 1–3 list all experiments and strength data